text: Materials http://www.mdpi.com/journal/materials Latest open access articles published in Materials at http://www.mdpi.com/journal/materials http://www.mdpi.com/1996-1944/8/4/1499 The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (<0.08 at%) in air atmosphere, in the temperature range of 1000 to 1200 °C, was studied. The investigation was carried out on the thin-walled (<1 mm) elements prepared by Laser Engineered Net Shaping (LENS) from alloy powder of a given composition. Characterization of the specimens, after the oxidation, was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM, with back-scatter detector (BSE) and energy-dispersive X-ray spectroscopy (EDS) attachments). The investigation has shown, that the oxidized samples were covered with a thin, homogeneous α-Al2O3 oxide layers. The intensity of their growth indicates that the material lost its resistance to oxidation at 1200 °C. Structural analysis of the thin-walled components' has not shown intensification of the oxidation process at the joints of additive layers. Materials 2015-03-30 8 4 Article 10.3390/ma8041499 1499 1512 1996-1944 2015-03-30 doi: 10.3390/ma8041499 Radosław Łyszkowski http://www.mdpi.com/1996-1944/8/4/1482 The generation of tribo-electric charge during pharmaceutical powder processing can cause a range of complications, including segregation of components leading to content uniformity and particle surface adhesion. This phenomenon becomes problematical when excipients are introduced to a powder mixture alongside the highly charging active pharmaceutical ingredient(s) (APIs). The aim of this study was to investigate the tribo-electric charging and adhesion properties of a model drug, theophylline. Moreover, binary powder mixtures of theophylline with methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), having different polymer to drug ratios, were formed in order to study the impact of polymer concentration, particle size, substitution ratio and molecular size on the tribo-electric charging and surface adhesion properties of the drug. Furthermore, the relationship between tribo-electric charging and surface adhesion was also studied. The diversity in physicochemical properties of MC/HPMC has shown a significant impact on the tribo-electric charging and adhesion behaviour of theophylline. It was found that the magnitude of electrostatic charge and the level of surface adhesion of the API were significantly reduced with an increase in MC and HPMC concentration, substitution ratios and molecular size. In addition, the tribo-electric charge showed a linear relationship with particle surface adhesion, but the involvement of other forces cannot be neglected. Materials 2015-03-30 8 4 Article 10.3390/ma8041482 1482 1498 1996-1944 2015-03-30 doi: 10.3390/ma8041482 Muhammad Ghori Enes Šupuk Barbara Conway http://www.mdpi.com/1996-1944/8/4/1459 Self-compacting concrete (SCC) demands more studies of durability at higher temperatures when subjected to more aggressive environments in comparison to the conventional vibrated concrete (CC). This work aims at presenting results of durability indicators of SCC and CC, having the same water/binder relations and constituents. The applied methodologies were electrical resistivity, diffusion of chloride ions and accelerated carbonation experiments, among others, such as microstructure study, scanning electron microscope and microtomography experiments. The tests were performed in a research laboratory and at a construction site of the Pernambuco Arena. The obtained results shows that the SCC presents an average electrical resistivity 11.4% higher than CC; the average chloride ions diffusion was 63.3% of the CC; the average accelerated carbonation penetration was 45.8% of the CC; and the average open porosity was 55.6% of the CC. As the results demonstrated, the SCC can be more durable than CC, which contributes to elucidate the aspects related to its durability and consequent prolonged life cycle. Materials 2015-03-27 8 4 Article 10.3390/ma8041459 1459 1481 1996-1944 2015-03-27 doi: 10.3390/ma8041459 Carlos Calado Aires Camões Eliana Monteiro Paulo Helene Béda Barkokébas http://www.mdpi.com/1996-1944/8/4/1442 In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize the effect of specimen size on fiber distribution, 48 cylinder specimens 150 mm in diameter and 300 mm in height were prepared and then subjected to uniaxial compression. From the test results, it was shown that steel fiber-reinforced concrete (SFRC) specimens exhibited ductile behavior after reaching their compressive strength. It was also shown that the strain at the compressive strength generally increased along with an increase in the fiber volumetric ratio and fiber aspect ratio, while the elastic modulus decreased. With consideration for the effect of steel fibers, a model for the stress–strain relationship of SFRC under compression is proposed here. Simple formulae to predict the strain at the compressive strength and the elastic modulus of SFRC were developed as well. The proposed model and formulae will be useful for realistic predictions of the structural behavior of SFRC members or structures. Materials 2015-03-27 8 4 Article 10.3390/ma8041442 1442 1458 1996-1944 2015-03-27 doi: 10.3390/ma8041442 Seong-Cheol Lee Joung-Hwan Oh Jae-Yeol Cho http://www.mdpi.com/1996-1944/8/4/1428 Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation. Materials 2015-03-27 8 4 Article 10.3390/ma8041428 1428 1441 1996-1944 2015-03-27 doi: 10.3390/ma8041428 Qinglong An Weiwei Ming Ming Chen http://www.mdpi.com/1996-1944/8/4/1413 The rise in pellet consumption has resulted in a wider variety of materials for pellet manufacture. Thus, pellet industry has started looking for alternative products, such as wastes from agricultural activities, forestry and related industries, along with the combination thereof, obtaining a broad range of these products. In addition, the entry into force of EN ISO 17225 standard makes wood pellet market (among other types) possible for industry and household purposes. Therefore, wastes that are suitable for biomass use have recently increased. In this study, the main characteristics of ten kinds of laboratory-made pellets from different raw materials were analyzed. Thus, we have focused on the most limiting factors of quality standards that determine the suitability for biomass market, depending on the kind of pellet. The results showed considerable differences among the analyzed pellets, exceeding the limits established by the standard in almost all cases, especially concerning ash content and N and S composition. The requirements of the studied standard, very demanding for certain factors, disable the entry of these densified wastes in greater added value markets. Materials 2015-03-27 8 4 Article 10.3390/ma8041413 1413 1427 1996-1944 2015-03-27 doi: 10.3390/ma8041413 Teresa Miranda Irene Montero Francisco Sepúlveda José Arranz Carmen Rojas Sergio Nogales http://www.mdpi.com/1996-1944/8/4/1398 The article presents an investigation on the effectiveness of nanostructured titanium-10 wt% 45S5 Bioglass-1 wt% Ag composite foams as a novel class of antibacterial materials for medical applications. The Ti-based composite foams were prepared by the combination of mechanical alloying and a "space-holder" sintering process. In the first step, the Ti-10 wt% 45S5 Bioglass-1 wt% Ag powder synthesized by mechanical alloying and annealing mixed with 1.0 mm diameter of saccharose crystals was finally compacted in the form of pellets. In the next step, the saccharose crystals were dissolved in water, leaving open spaces surrounded by metallic-bioceramic scaffold. The sintering of the scaffold leads to foam formation. It was found that 1:1 Ti-10 wt% 45S5 Bioglass-1 wt% Ag/sugar ratio leads to porosities of about 70% with pore diameter of about 0.3–1.1 mm. The microstructure, corrosion resistance in Ringer's solution of the produced foams were investigated. The value of the compression strength for the Ti-10 wt% 45S5 Bioglass-1 wt% Ag foam with 70% porosity was 1.5 MPa and the Young's modulus was 34 MPa. Silver modified Ti-10 wt% 45S5 Bioglass composites possess excellent antibacterial activities against Staphylococcus aureus. Porous Ti-10 wt% 45S5 Bioglass-1 wt% foam could be a possible candidate for medical implants applications. Materials 2015-03-25 8 4 Article 10.3390/ma8041398 1398 1412 1996-1944 2015-03-25 doi: 10.3390/ma8041398 Karolina Jurczyk Grzegorz Adamek Marcelina Kubicka Jaroslaw Jakubowicz Mieczyslaw Jurczyk http://www.mdpi.com/1996-1944/8/4/1384 The type of lightweight aggregate and its volume fraction in a mix determine the density of lightweight concrete. Minimizing the density obviously requires a higher volume fraction, but this usually causes aggregates segregation in a conventional mixing process. This paper proposes a two-stage casting process to produce a lightweight concrete. This process involves placing lightweight aggregates in a frame and then filling in the remaining interstitial voids with cementitious grout. The casting process results in the lowest density of lightweight concrete, which consequently has low compressive strength. The irregularly shaped aggregates compensate for the weak point in terms of strength while the round-shape aggregates provide a strength of 20 MPa. Therefore, the proposed casting process can be applied for manufacturing non-structural elements and structural composites requiring a very low density and a strength of at most 20 MPa. Materials 2015-03-25 8 4 Article 10.3390/ma8041384 1384 1397 1996-1944 2015-03-25 doi: 10.3390/ma8041384 Jin Yoon Jae Kim Yoon Hwang Dong Shin http://www.mdpi.com/1996-1944/8/4/1369 Mesoporous polyaniline-silica nanocomposites with a full interpenetrating structure for pseudocapacitors were synthesized via the vapor phase approach. The morphology and structure of the nanocomposites were deeply investigated by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis and nitrogen adsorption-desorption tests. The results present that the mesoporous nanocomposites possess a uniform particle morphology and full interpenetrating structure, leading to a continuous conductive polyaniline network with a large specific surface area. The electrochemical performances of the nanocomposites were tested in a mixed solution of sulfuric acid and potassium iodide. With the merits of a large specific surface area and suitable pore size distribution, the nanocomposite showed a large specific capacitance (1702.68 farad (F)/g) due to its higher utilization of the active material. This amazing value is almost three-times larger than that of bulk polyaniline when the same mass of active material was used. Materials 2015-03-25 8 4 Article 10.3390/ma8041369 1369 1383 1996-1944 2015-03-25 doi: 10.3390/ma8041369 Lei Zu Xiuguo Cui Yanhua Jiang Zhongkai Hu Huiqin Lian Yang Liu Yushun Jin Yan Li Xiaodong Wang http://www.mdpi.com/1996-1944/8/3/1350 Nanoporous and single phase α-alumina membranes with pore diameters tunable over a wide range of approximately 60–350 nm were successfully fabricated by optimizing the conditions for anodizing, subsequent detachment, and heat treatment. The pore diameter increased and the cell diameter shrunk upon crystallization to α-alumina by approximately 20% and 3%, respectively, in accordance with the 23% volume shrinkage resulting from the change in density associated with the transformation from the amorphous state to α-alumina. Nevertheless, flat α-alumina membranes, each with a diameter of 25 mm and a thickness of 50 μm, were obtained without thermal deformation. The α-alumina membranes exhibited high chemical resistance in various concentrated acidic and alkaline solutions as well as when exposed to high temperature steam under pressure. The Young's modulus and hardness of the single phase α-alumina membranes formed by heat treatment at 1250 °C were notably decreased compared to the corresponding amorphous membranes, presumably because of the nodular crystallite structure of the cell walls and the substantial increase in porosity. Furthermore, when used for filtration, the α-alumina membrane exhibited a level of flux higher than that of the commercial ceramic membrane. Materials 2015-03-20 8 3 Article 10.3390/ma8031350 1350 1368 1996-1944 2015-03-20 doi: 10.3390/ma8031350 Tatsuya Masuda Hidetaka Asoh Satoshi Haraguchi Sachiko Ono http://www.mdpi.com/1996-1944/8/3/1341 We have designed a sugar-responsive pseudopolyrotaxane (PPRX) by combining phenylboronic acid-modified polyethylene glycol (PBA–PEG) and γ-cyclodextrin. Phenylboronic acid (PBA) was used as a sugar-recognition motif in the PPRX because PBA reacts with a diol portion of the sugar molecule and forms a cyclic ester. When D-fructose or D-glucose was added to a suspension of PPRX, PPRX disintegrated, depending on the concentration of the sugars. Interestingly, catechol does not show a response although catechol has a high affinity for PBA. We analyzed the response mechanism of PPRX by considering equilibria. Materials 2015-03-20 8 3 Communication 10.3390/ma8031341 1341 1349 1996-1944 2015-03-20 doi: 10.3390/ma8031341 Tomohiro Seki Misato Namiki Yuya Egawa Ryotaro Miki Kazuhiko Juni Toshinobu Seki http://www.mdpi.com/1996-1944/8/3/1325 In order to reduce the harmful constituents in cigarette smoke, two hierarchical composites were synthesized. Based on, zeolites HZSM-5 or NaY fragments were introduced into the synthetic system of mesoporous silica SBA-15 or MCM-41 and assembled with the mesoporous materials. These porous composites combine the advantages of micro- and mesoporous materials, and exhibit higher effects than activated carbon on reducing tobacco specific nitrosamines (TSNA) and some vapor phase compounds in smoke. Materials 2015-03-20 8 3 Article 10.3390/ma8031325 1325 1340 1996-1944 2015-03-20 doi: 10.3390/ma8031325 Yan Li Yi Cao Ming Yue Jing Yang Jian Zhu http://www.mdpi.com/1996-1944/8/3/1283 Researchers have long been searching for the materials to enhance thermoelectric performance in terms of nano scale approach in order to realize phonon-glass-electron-crystal and quantum confinement effects. Peierls distortion can be a pathway to enhance thermoelectric figure-of-merit ZT by employing natural nano-wire-like electronic and thermal transport. The phonon-softening known as Kohn anomaly, and Peierls lattice distortion decrease phonon energy and increase phonon scattering, respectively, and, as a result, they lower thermal conductivity. The quasi-one-dimensional electrical transport from anisotropic band structure ensures high Seebeck coefficient in Indium Selenide. The routes for high ZT materials development of In4Se3−δ are discussed from quasi-one-dimensional property and electronic band structure calculation to materials synthesis, crystal growth, and their thermoelectric properties investigations. The thermoelectric properties of In4Se3−δ can be enhanced by electron doping, as suggested from the Boltzmann transport calculation. Regarding the enhancement of chemical potential, the chlorine doped In4Se3−δCl0.03 compound exhibits high ZT over a wide temperature range and shows state-of-the-art thermoelectric performance of ZT = 1.53 at 450 °C as an n-type material. It was proven that multiple elements doping can enhance chemical potential further. Here, we discuss the recent progress on the enhancement of thermoelectric properties in Indium Selenides by increasing chemical potential. Materials 2015-03-20 8 3 Review 10.3390/ma8031283 1283 1324 1996-1944 2015-03-20 doi: 10.3390/ma8031283 Jong-Soo Rhyee Jin Kim http://www.mdpi.com/1996-1944/8/3/1264 A full-scale experimental test was conducted to analyze the composite behavior of insulated concrete sandwich wall panels (ICSWPs) subjected to wind pressure and suction. The experimental program was composed of three groups of ICSWP specimens, each with a different type of insulation and number of glass-fiber-reinforced polymer (GFRP) shear grids. The degree of composite action of each specimen was analyzed according to the load direction, type of the insulation, and number of GFRP shear grids by comparing the theoretical and experimental values. The failure modes of the ICSWPs were compared to investigate the effect of bonds according to the load direction and type of insulation. Bonds based on insulation absorptiveness were effective to result in the composite behavior of ICSWP under positive loading tests only, while bonds based on insulation surface roughness were effective under both positive and negative loading tests. Therefore, the composite behavior based on surface roughness can be applied to the calculation of the design strength of ICSWPs with continuous GFRP shear connectors. Materials 2015-03-19 8 3 Article 10.3390/ma8031264 1264 1282 1996-1944 2015-03-19 doi: 10.3390/ma8031264 Insub Choi JunHee Kim Ho-Ryong Kim http://www.mdpi.com/1996-1944/8/3/1249 We have deposited aluminium oxide films by atomic layer deposition on titanium oxide nanoparticles in a fluidized bed reactor at 27 ± 3 °C and atmospheric pressure. Working at room temperature allows coating heat-sensitive materials, while working at atmospheric pressure would simplify the scale-up of this process. We performed 4, 7 and 15 cycles by dosing a predefined amount of precursors, i.e., trimethyl aluminium and water. We obtained a growth per cycle of 0.14–0.15 nm determined by transmission electron microscopy (TEM), similar to atomic layer deposition (ALD) experiments at a few millibars and ~180 °C. We also increased the amount of precursors dosed by a factor of 2, 4 and 6 compared to the base case, maintaining the same purging time. The growth per cycle (GPC) increased, although not linearly, with the dosing time. In addition, we performed an experiment at 170 °C and 1 bar using the dosing times increased by factor 6, and obtained a growth per cycle of 0.16 nm. These results were verified with elemental analysis, which showed a good agreement with the results from TEM pictures. Thermal gravimetric analysis (TGA) showed a negligible amount of unreacted molecules inside the alumina films. Overall, the dosage of the precursors is crucial to control precisely the growth of the alumina films at atmospheric pressure and room temperature. Dosing excess of precursor provokes a chemical vapour deposition type of growth due to the physisorption of molecules on the particles, but this can be avoided by working at high temperatures. Materials 2015-03-19 8 3 Article 10.3390/ma8031249 1249 1263 1996-1944 2015-03-19 doi: 10.3390/ma8031249 David Valdesueiro Gabrie Meesters Michiel Kreutzer J. van Ommen http://www.mdpi.com/1996-1944/8/3/1230 The effect of various dimethacrylates on the structure and properties of homo- and copolymer networks was studied. The 2,2-bis-[4-(2-hydroxy-3- methacryloyloxypropoxy)phenyl]-propane) (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA) and 1,6-bis-(methacryloyloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane (HEMA/TMDI), all popular in dentistry, as well as five urethane-dimethacrylate (UDMA) alternatives of HEMA/TMDI were used as monomers. UDMAs were obtained from mono-, di- and tri(ethylene glycol) monomethacrylates and various commercial diisocyanates. The chemical structure, degree of conversion (DC) and scanning electron microscopy (SEM) fracture morphology were related to the mechanical properties of the polymers: flexural strength and modulus, hardness, as well as impact strength. Impact resistance was widely discussed, being lower than expected in the case of poly(UDMA)s. It was caused by the heterogeneous morphology of these polymers and only moderate strength of hydrogen bonds between urethane groups, which was not high enough to withstand high impact energy. Bis-GMA, despite having the highest polymer morphological heterogeneity, ensured fair impact resistance, due to having the strongest hydrogen bonds between hydroxyl groups. The TEGDMA homopolymer, despite being heterogeneous, produced the smoothest morphology, which resulted in the lowest brittleness. The UDMA monomer, having diethylene glycol monomethacrylate wings and the isophorone core, could be the most suitable HEMA/TMDI alternative. Its copolymer with Bis-GMA and TEGDMA had improved DC as well as all the mechanical properties. Materials 2015-03-19 8 3 Article 10.3390/ma8031230 1230 1248 1996-1944 2015-03-19 doi: 10.3390/ma8031230 Izabela Barszczewska-Rybarek Sebastian Jurczyk http://www.mdpi.com/1996-1944/8/3/1213 Ground granulated blast furnace slag is widely used as a mineral admixture to replace partial Portland cement in the concrete industry. As the amount of slag increases, the late-age compressive strength of concrete mixtures increases. However, after an optimum point, any further increase in slag does not improve the late-age compressive strength. This optimum replacement ratio of slag is a crucial factor for its efficient use in the concrete industry. This paper proposes a numerical procedure to analyze the optimum usage of slag for the compressive strength of concrete. This numerical procedure starts with a blended hydration model that simulates cement hydration, slag reaction, and interactions between cement hydration and slag reaction. The amount of calcium silicate hydrate (CSH) is calculated considering the contributions from cement hydration and slag reaction. Then, by using the CSH contents, the compressive strength of the slag-blended concrete is evaluated. Finally, based on the parameter analysis of the compressive strength development of concrete with different slag inclusions, the optimum usage of slag in concrete mixtures is determined to be approximately 40% of the total binder content. The proposed model is verified through experimental results of the compressive strength of slag-blended concrete with different water-to-binder ratios and different slag inclusions. Materials 2015-03-18 8 3 Article 10.3390/ma8031213 1213 1229 1996-1944 2015-03-18 doi: 10.3390/ma8031213 Han-Seung Lee Xiao-Yong Wang Li-Na Zhang Kyung-Taek Koh http://www.mdpi.com/1996-1944/8/3/1204 This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO2) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient (d33) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF2) etch and therefore eliminating the need for backside lithography and etching. Materials 2015-03-17 8 3 Article 10.3390/ma8031204 1204 1212 1996-1944 2015-03-17 doi: 10.3390/ma8031204 Azadeh Ansari Che-Yu Liu Chien-Chung Lin Hao-Chung Kuo Pei-Cheng Ku Mina Rais-Zadeh http://www.mdpi.com/1996-1944/8/3/1187 This article reviews recent progress made in the development of electrochemical glycated hemoglobin (HbA1c) sensors for the diagnosis and management of diabetes mellitus. Electrochemical HbA1c sensors are divided into two categories based on the detection protocol of the sensors. The first type of sensor directly detects HbA1c by binding HbA1c on the surface of an electrode through bio-affinity of antibody and boronic acids, followed by an appropriate mode of signal transduction. In the second type of sensor, HbA1c is indirectly determined by detecting a digestion product of HbA1c, fructosyl valine (FV). Thus, the former sensors rely on the selective binding of HbA1c to the surface of the electrodes followed by electrochemical signaling in amperometric, voltammetric, impedometric, or potentiometric mode. Redox active markers, such as ferrocene derivatives and ferricyanide/ferrocyanide ions, are often used for electrochemical signaling. For the latter sensors, HbA1c must be digested in advance by proteolytic enzymes to produce the FV fragment. FV is electrochemically detected through catalytic oxidation by fructosyl amine oxidase or by selective binding to imprinted polymers. The performance characteristics of HbA1c sensors are discussed in relation to their use in the diagnosis and control of diabetic mellitus. Materials 2015-03-17 8 3 Review 10.3390/ma8031187 1187 1203 1996-1944 2015-03-17 doi: 10.3390/ma8031187 Baozhen Wang Jun-ichi Anzai http://www.mdpi.com/1996-1944/8/3/1176 La1−xSrxTiO3+δ (LST) has been studied in many fields, especially in the field of microelectronics due to its excellent electrical performance. Our previous theoretical simulated work has suggested that LST has good dielectric properties, but there are rare reports about this, especially experimental reports. In this paper, LST was prepared using a solid-state reaction method. The X-rays diffraction (XRD), scanning electron microscope (SEM), broadband dielectric spectroscopy, impedance spectroscopy and photoconductive measurement were used to characterize the sample. The results show that the values of dielectric parameters (the relative dielectric constant εr and dielectric loss tanδ), dependent on temperature, are stable under 350 °C and the value of the relative dielectric constant and dielectric loss are about 52–88 and 6.5 × 10−3, respectively. Its value of conductivity increases with rise in temperature, which suggests its negative temperature coefficient of the resistance. In addition, the band gap of LST is about 3.39 eV, so it belongs to a kind of wide-band-gap semiconductor materials. All these indicate that LST has anti-interference ability and good dielectric properties. It could have potential applications as an electronic material. Materials 2015-03-17 8 3 Article 10.3390/ma8031176 1176 1186 1996-1944 2015-03-17 doi: 10.3390/ma8031176 Wenzhi Li Zhuang Ma Lihong Gao Fuchi Wang http://www.mdpi.com/1996-1944/8/3/1162 CaO-Al2O3-SiO2 (CAS) as a liquid phase was introduced into hydroxyapatite (HAp) to prepare bone scaffolds. The effects of the CAS content (1, 2, 3, 4 and 5 wt%) on microstructure and mechanical properties of HAp ceramics were investigated. The optimal compression strength, fracture toughness and Vickers hardness reached 22.22 MPa, 1.68 MPa·m1/2 and 4.47 GPa when 3 wt% CAS was added, which were increased by 105%, 63% and 11% compared with those of HAp ceramics without CAS, respectively. The improvement of the mechanical properties was attributed to the improved densification, which was caused by the solid particle to rearrange during liquid phase sintering. Moreover, simulated body fluid (SBF) study indicated the HAp ceramics could maintain the mechanical properties and form a bone-like apatite layer when they were immersed in SBF. Cell culture was used to evaluate biocompatibility of the HAp ceramics. The results demonstrated MG-63 cells adhered and spread well. Materials 2015-03-17 8 3 Article 10.3390/ma8031162 1162 1175 1996-1944 2015-03-17 doi: 10.3390/ma8031162 Songlin Duan Pei Feng Chengde Gao Tao Xiao Kun Yu Cijun Shuai Shuping Peng http://www.mdpi.com/1996-1944/8/3/1150 In this study, type I collagen was coated onto unmodified and modified microporous biphasic calcium phosphate (BCP) scaffolds. Surface characterization using a scanning electron microscope (SEM) and a surface goniometer confirmed the modification of the BCP coating. The quantity of the collagen coating was investigated using Sirius Red staining, and quantitative assessment of the collagen coating showed no significant differences between the two groups. MG63 cells were used to evaluate cell proliferation and ALP activity on the modified BCP scaffolds. The modified microporous surfaces showed low contact angles and large surface areas, which enhanced cell spreading and proliferation. Coating of the BCP scaffolds with type I collagen led to enhanced cell-material interactions and improved MG63 functions, such as spreading, proliferation, and differentiation. The micropore/collagen-coated scaffold showed the highest rate of cell response. These results indicate that a combination of micropores and collagen enhances cellular function on bioengineered bone allograft tissue. Materials 2015-03-16 8 3 Article 10.3390/ma8031150 1150 1161 1996-1944 2015-03-16 doi: 10.3390/ma8031150 Mun-Hwan Lee Changkook You Kyo-Han Kim http://www.mdpi.com/1996-1944/8/3/1124 Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS2-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS2 sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor. Materials 2015-03-16 8 3 Review 10.3390/ma8031124 1124 1149 1996-1944 2015-03-16 doi: 10.3390/ma8031124 Priyanka Jood Michihiro Ohta http://www.mdpi.com/1996-1944/8/3/1108 The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al2O3 and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl− (NaCl) and pH ~4 (H2SO4) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones. Materials 2015-03-13 8 3 Article 10.3390/ma8031108 1108 1123 1996-1944 2015-03-13 doi: 10.3390/ma8031108 Cezary Senderowski Michal Chodala Zbigniew Bojar http://www.mdpi.com/1996-1944/8/3/1089 In order to model the effect of mixture parameters and material properties on the hardened properties of, prestressed self-compacting concrete (SCC), and also to investigate the extensions of the statistical models, a factorial design was employed to identify the relative significance of these primary parameters and their interactions in terms of the mechanical and visco-elastic properties of SCC. In addition to the 16 fractional factorial mixtures evaluated in the modeled region of −1 to +1, eight axial mixtures were prepared at extreme values of −2 and +2 with the other variables maintained at the central points. Four replicate central mixtures were also evaluated. The effects of five mixture parameters, including binder type, binder content, dosage of viscosity-modifying admixture (VMA), water-cementitious material ratio (w/cm), and sand-to-total aggregate ratio (S/A) on compressive strength, modulus of elasticity, as well as autogenous and drying shrinkage are discussed. The applications of the models to better understand trade-offs between mixture parameters and carry out comparisons among various responses are also highlighted. A logical design approach would be to use the existing model to predict the optimal design, and then run selected tests to quantify the influence of the new binder on the model. Materials 2015-03-13 8 3 Article 10.3390/ma8031089 1089 1107 1996-1944 2015-03-13 doi: 10.3390/ma8031089 Wu-Jian Long Kamal Khayat Guillaume Lemieux Feng Xing Wei-Lun Wang http://www.mdpi.com/1996-1944/8/3/1074 Foamed alumina was previously synthesised by direct foaming of sulphate salt blends varying ammonium mole fraction (AMF), foaming heating rate and sintering temperature. The optimal product was produced with 0.33AMF, foaming at 100 °C/h and sintering at 1600 °C. This product attained high porosity of 94.39%, large average pore size of 300 µm and the highest compressive strength of 384 kPa. To improve bioactivity, doping of porous alumina by soaking in dilute or saturated solutions of Ca, P, Mg, CaP or CaP + Mg was done. Saturated solutions of Ca, P, Mg, CaP and CaP + Mg were made with excess salt in distilled water and decanted. Dilute solutions were made by diluting the 100% solution to 10% concentration. Doping with Si was done using the sol gel method at 100% concentration only. Cell culture was carried out with MG63 osteosarcoma cells. Cellular response to the Si and P doped samples was positive with high cell populations and cell layer formation. The impact of doping with phosphate produced a result not previously reported. The cellular response showed that both Si and P doping improved the biocompatibility of the foamed alumina. Materials 2015-03-13 8 3 Article 10.3390/ma8031074 1074 1088 1996-1944 2015-03-13 doi: 10.3390/ma8031074 Edwin Soh Elizabeth Kolos Andrew Ruys http://www.mdpi.com/1996-1944/8/3/1059 TiO2-SiO2-based nanocomposites with highly porous structures are gaining ever increasing attention due to their specific properties and large variability of synthesis pathways together with wide information on the impact of the synthesis on the activity of the catalyst. This thereby offers an alternative approach to traditional/commercially available photocatalysts. In our work TiO2-SiO2 based aerogels were obtained and modified with various amount of Ag nanoparticles, using different synthesis pathways. In the first instance their photocatalytic activity was examined in detail, by observing major differences toward salicylic acid and correlating them with their morphological and structural properties (investigating their mesoporous character, band-gap values, crystallinity grade etc.). Applying different techniques such as diffuse reflectance spectroscopy (DRS), X-ray diffraction measurements (XRD), transmission electron microscopy (TEM), Raman- and X-ray photoelectron spectroscopy (XPS) the nanoparticles and their composite morphological and structural details were successfully evaluated. Major differences were observed in the activity towards salicylic acid. Materials 2015-03-12 8 3 Article 10.3390/ma8031059 1059 1073 1996-1944 2015-03-12 doi: 10.3390/ma8031059 Gábor Kovács Zsolt Pap Cosmin Coteț Veronica Coșoveanu Lucian Baia Virginia Danciu http://www.mdpi.com/1996-1944/8/3/1043 In this paper, we report on the crystal structure and the electrical and thermal transport properties of the BiCuSe1−xSxO series. From the evolution of the structural parameters with the substitution rate, we can confidently conclude that a complete solid solution exists between the BiCuSeO and BiCuSO end members, without any miscibility gap. However, the decrease of the stability of the materials when increasing the sulfur fraction, with a simultaneous volatilization, makes it difficult to obtain S-rich samples in a single phase. The band gap of the materials linearly increases between 0.8 eV for BiCuSeO and 1.1 eV in BiCuSO, and the covalent character of the Cu-Ch (Ch = chalcogen element, namely S or Se here) bond slightly decreases when increasing the sulfur fraction. The thermal conductivity of the end members is nearly the same, but a significant decrease is observed for the samples belonging to the solid solution, which can be explained by point defect scattering due to atomic mass and radii fluctuations between Se and S. When increasing the sulfur fraction, the electrical resistivity of the samples strongly increases, which could be linked to an evolution of the energy of formation of copper vacancies, which act as acceptor dopants in these materials. Materials 2015-03-12 8 3 Article 10.3390/ma8031043 1043 1058 1996-1944 2015-03-12 doi: 10.3390/ma8031043 David Berardan Jing Li Emilie Amzallag Sunanda Mitra Jiehe Sui Wei Cai Nita Dragoe http://www.mdpi.com/1996-1944/8/3/1027 This article introduces a continuous, gas-phase method for depositing thin metallic coatings onto (nano)particles using a type of physical vapor deposition (PVD) at ambient pressure and temperature. An aerosol of core particles is mixed with a metal vapor cloud formed by spark ablation by passing the aerosol through the spark zone using a hollow electrode configuration. The mixing process rapidly quenches the vapor, which condenses onto the core particles at a timescale of several tens of milliseconds in a manner that can be modeled as bimodal coagulation. Gold was deposited onto core nanoparticles consisting of silver or polystyrene latex, and silver was deposited onto gold nanoparticles. The coating morphology depends on the relative surface energies of the core and coating materials, similar to the growth mechanisms known for thin films: a coating made of a substance having a high surface energy typically results in a patchy coverage, while a coating material with a low surface energy will normally "wet" the surface of a core particle. The coated particles remain gas-borne, allowing further processing. Materials 2015-03-11 8 3 Article 10.3390/ma8031027 1027 1042 1996-1944 2015-03-11 doi: 10.3390/ma8031027 Tobias Pfeiffer Puneet Kedia Maria Messing Mario Valvo Andreas Schmidt-Ott http://www.mdpi.com/1996-1944/8/3/1009 Surface coating is the simplest surface modification. However, bioactive molecules can not spread well on the commonly used polylactone-type skeletons; thus, the surface coatings of biomolecules are typically unstable due to the weak interaction between the polymer and the bioactive molecules. In this study, a special type of poly(lactide-co-glycolide) (PLGA)-based scaffold with a loosened skeleton was fabricated by phase separation, which allowed gelatin molecules to more readily diffuse throughout the structure. In this application, gelatin modified both the internal substrate and external surface. After cross-linking with glutaraldehyde, the surface layer gelatin was tightly bound to the diffused gelatin, thereby preventing the surface layer gelatin coating from falling off within 14 days. After gelatin modification, PLGA scaffold demonstrated enhanced hydrophilicity and improved mechanical properties (i.e., increased compression strength and elastic modulus) in dry and wet states. Furthermore, a sustained release profile of recombinant human bone morphogenetic protein-2 (rhBMP-2) was achieved in the coated scaffold. The coated scaffold also supported the in vitro attachment, proliferation, and osteogenesis of rabbit bone mesenchymal stem cells (BMSCs), indicating the bioactivity of rhBMP-2. These results collectively demonstrate that the cross-linked-gelatin-coated porous PLGA scaffold incorporating bioactive molecules is a promising candidate for bone tissue regeneration. Materials 2015-03-10 8 3 Article 10.3390/ma8031009 1009 1026 1996-1944 2015-03-10 doi: 10.3390/ma8031009 Juan Wang Dongsong Li Tianyi Li Jianxun Ding Jianguo Liu Baosheng Li Xuesi Chen http://www.mdpi.com/1996-1944/8/3/992 In this study, we develop binary polypropylene (PP) composites with hexagonal boron nitride (hBN) nanoplatelets and ternary hybrids reinforced with hBN and nanohydroxyapatite (nHA). Filler hybridization is a sound approach to make novel nanocomposites with useful biological and mechanical properties. Tensile test, osteoblastic cell culture and dimethyl thiazolyl diphenyl tetrazolium (MTT) assay were employed to investigate the mechanical performance, bioactivity and biocompatibility of binary PP/hBN and ternary PP/hBN-nHA composites. The purpose is to prepare biocomposite nanomaterials with good mechanical properties and biocompatibility for replacing conventional polymer composites reinforced with large hydroxyapatite microparticles at a high loading of 40 vol%. Tensile test reveals that the elastic modulus of PP composites increases, while tensile elongation decreases with increasing hBN content. Hybridization of hBN with nHA further enhances elastic modulus of PP. The cell culture and MTT assay show that osteoblastic cells attach and proliferate on binary PP/hBN and ternary PP/hBN-20%nHA nanocomposites. Materials 2015-03-10 8 3 Article 10.3390/ma8030992 992 1008 1996-1944 2015-03-10 doi: 10.3390/ma8030992 Kai Chan Hoi Wong Kelvin Yeung Sie Tjong http://www.mdpi.com/1996-1944/8/3/977 Current clinically used delivery methods for bone morphogenetic proteins (BMPs) are collagen based and require large concentrations that can lead to dangerous side effects. Fibrin hydrogels can serve as osteoinductive bone substitute materials in non-load bearing bone defects in combination with BMPs. Two strategies to even further optimize such a fibrin based system include employing more potent BMP heterodimers and engineering growth factors that can be covalently tethered to and slowly released from a fibrin matrix. Here we present an engineered BMP-2/BMP-7 heterodimer where an N-terminal transglutaminase substrate domain in the BMP-2 portion provides covalent attachment to fibrin together with a central plasmin substrate domain, a cleavage site for local release of the attached BMP-2/BMP-7 heterodimer under the influence of cell-activated plasmin. In vitro and in vivo results revealed that the engineered BMP-2/BMP-7 heterodimer induces significantly more alkaline phosphatase activity in pluripotent cells and bone formation in a rat calvarial model than the engineered BMP-2 homodimer. Therefore, the engineered BMP-2/BMP-7 heterodimer could be used to reduce the amount of BMP needed for clinical effect. Materials 2015-03-06 8 3 Article 10.3390/ma8030977 977 991 1996-1944 2015-03-06 doi: 10.3390/ma8030977 Lindsay Karfeld-Sulzer Barbara Siegenthaler Chafik Ghayor Franz Weber http://www.mdpi.com/1996-1944/8/3/966 Silica core-shell nanoparticles of about 60–120 nm with a closed outer layer of bismuth or molybdenum oxide of 1–10 nm were synthesized by an integrated chemical vapor synthesis/chemical vapor deposition process at atmospheric pressure. Film growth rates and activation energies were derived from transmission electron microscopy (TEM) images for a deposition process based on molybdenum hexacarbonyl and triphenyl bismuth as respective coating precursors. Respective activation energies of 123 ± 10 and 155 ± 10 kJ/mol are in good agreement with the literature and support a deposition mechanism based on surface-induced removal of the precursor ligands. Clean substrate surfaces are thus prerequisite for conformal coatings. Integrated aerosol processes are solvent-free and intrinsically clean. In contrast, commercial silica substrate particles were found to suffer from organic residues which hinder shell formation, and require an additional calcination step to clean the surface prior to coating. Dual layer core-shell structures with molybdenum oxide on bismuth oxide were synthesized with two coating reactors in series and showed similar film growth rates. Materials 2015-03-06 8 3 Article 10.3390/ma8030966 966 976 1996-1944 2015-03-06 doi: 10.3390/ma8030966 Frederik Weis Martin Seipenbusch Gerhard Kasper http://www.mdpi.com/1996-1944/8/3/959 The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects. Materials 2015-03-05 8 3 Article 10.3390/ma8030959 959 965 1996-1944 2015-03-05 doi: 10.3390/ma8030959 Hyeona Mun Kyu Lee Suk Kim Jong-Young Kim Jeong Lee Jae-Hong Lim Hee Park Jong Roh Sung Kim http://www.mdpi.com/1996-1944/8/3/932 The goal of the current publication is to provide a comprehensive literature review on the topic of dental implant materials. The following paper focuses on conventional titanium implants and more recently introduced and increasingly popular zirconia implants. Major subtopics include the material science and the clinical considerations involving both implant materials and the influence of their physical properties on the treatment outcome. Titanium remains the gold standard for the fabrication of oral implants, even though sensitivity does occur, though its clinical relevance is not yet clear. Zirconia implants may prove to be promising in the future; however, further in vitro and well-designed in vivo clinical studies are needed before such a recommendation can be made. Special considerations and technical experience are needed when dealing with zirconia implants to minimize the incidence of mechanical failure. Materials 2015-03-05 8 3 Review 10.3390/ma8030932 932 958 1996-1944 2015-03-05 doi: 10.3390/ma8030932 Reham Osman Michael Swain http://www.mdpi.com/1996-1944/8/3/914 Fe-Al intermetallic alloys with aluminum content over 60 at% are in the area of the phase equilibrium diagram that is considerably less investigated in comparison to the high-symmetry Fe3Al and FeAl phases. Ambiguous crystallographic information and incoherent data referring to the phase equilibrium diagrams placed in a high-aluminum range have caused confusions and misinformation. Nowadays unequivocal material properties description of FeAl2, Fe2Al5 and FeAl3 intermetallic alloys is still incomplete. In this paper, the influence of aluminum content and processing parameters on phase composition is presented. The occurrence of low-symmetry FeAl2, Fe2Al5 and FeAl3 structures determined by chemical composition and phase transformations was defined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) examinations. These results served to verify diffraction investigations (XRD) and to explain the mechanical properties of cast materials such as: hardness, Young's modulus and fracture toughness evaluated using the nano-indentation technique. Materials 2015-03-04 8 3 Article 10.3390/ma8030914 914 931 1996-1944 2015-03-04 doi: 10.3390/ma8030914 Piotr Matysik Stanisław Jóźwiak Tomasz Czujko http://www.mdpi.com/1996-1944/8/3/899 A full-scale experimental program was used in this study to investigate the structural behavior of novel insulated concrete sandwich wall panels (SWPs) reinforced with grid-type glass-fiber-reinforced polymer (GFRP) shear connectors. Two kinds of insulation-expanded polystyrene (EPS) and extruded polystyrene (XPS) with 100 mm thickness were incased between the two concrete wythes to meet the increasing demand for the insulation performance of building envelope. One to four GFRP shear grids were used to examine the degree of composite action of the two concrete wythes. Ten specimens of SWPs were tested under displacement control subjected to four-point concentrated loads. The test results showed that the SWPs reinforced with GFRP grids as shear connectors developed a high degree of composite action resulting in high flexural strength. The specimens with EPS foam exhibited an enhanced load-displacement behavior compared with the specimens with XPS because of the relatively stronger bond between insulation and concrete. In addition, the ultimate strength of the test results was compared to the analytical prediction with the mechanical properties of only GRFP grids. The specimens with EPS insulation presented higher strength-based composite action than the ones with XPS insulation. Materials 2015-03-03 8 3 Article 10.3390/ma8030899 899 913 1996-1944 2015-03-03 doi: 10.3390/ma8030899 JunHee Kim Young-Chan You http://www.mdpi.com/1996-1944/8/3/884 The effect of carbon black on the mechanical properties of elastomers is of great interest, because the filler is one of principal ingredients for the manufacturing of rubber products. While fillers can be used to enhance the properties of elastomers, including stress-free swelling resistance in solvent, it is widely known that the introduction of fillers yields significant inelastic responses of elastomers under cyclic mechanical loading, such as stress-softening, hysteresis and permanent set. When a filled elastomer is under mechanical deformation, the filler acts as a strain amplifier in the rubber matrix. Since the matrix local strain has a profound effect on the material's ability to absorb solvent, the study of the effect of carbon black content on the swelling characteristics of elastomeric components exposed to solvent in the presence of mechanical deformation is a prerequisite for durability analysis. The aim of this study is to investigate the effect of carbon black content on the swelling of elastomers in solvent in the presence of static mechanical strains: simple extension and simple torsion. Three different types of elastomers are considered: unfilled, filled with 33 phr (parts per hundred) and 66 phr of carbon black. The peculiar role of carbon black on the swelling characteristics of elastomers in solvent in the presence of mechanical strain is explored. Materials 2015-03-02 8 3 Article 10.3390/ma8030884 884 898 1996-1944 2015-03-02 doi: 10.3390/ma8030884 Shiau Ch'ng Andri Andriyana Yun Tee Erwan Verron http://www.mdpi.com/1996-1944/8/3/867 Titanium (Ti) and its alloys are amongst the most commonly-used biomaterials in orthopedic and dental applications. The Ti-aluminum-vanadium alloy (Ti6Al4V) is widely used as a biomaterial for these applications by virtue of its favorable properties, such as high tensile strength, good biocompatibility and excellent corrosion resistance. TiO2 nanotube (NTs) layers formed by anodization on Ti6Al4V alloy have been shown to improve osteoblast adhesion and function when compared to non-anodized material. In his study, NTs were grown on a Ti6Al4V alloy by anodic oxidation for 5 min using a super-oxidative aqueous solution, and their in vitro biocompatibility was investigated in pig periosteal osteoblasts and cartilage chondrocytes. Scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDX) and atomic force microscopy (AFM) were used to characterize the materials. Cell morphology was analyzed by SEM and AFM. Cell viability was examined by fluorescence microscopy. Cell adhesion was evaluated by nuclei staining and cell number quantification by fluorescence microscopy. The average diameter of the NTs was 80 nm. The results demonstrate improved cell adhesion and viability at Day 1 and Day 3 of cell growth on the nanostructured material as compared to the non-anodized alloy. In conclusion, this study evidences the suitability of NTs grown on Ti6Al4V alloy using a super-oxidative water and a short anodization process to enhance the adhesion and viability of osteoblasts and chondrocytes. The results warrant further investigation for its use as medical implant materials. Materials 2015-03-02 8 3 Article 10.3390/ma8030867 867 883 1996-1944 2015-03-02 doi: 10.3390/ma8030867 Ernesto Beltrán-Partida Aldo Moreno-Ulloa Benjamín Valdez-Salas Cristina Velasquillo Monica Carrillo Alan Escamilla Ernesto Valdez Francisco Villarreal http://www.mdpi.com/1996-1944/8/3/850 This in vitro study was conducted to evaluate the shear bond strength of "non-self-adhesive" resin to dental zirconia etched with hydrofluoric acid (HF) at room temperature and to compare it to that of air-abraded zirconia. Sintered zirconia plates were air-abraded (control) or etched with 10%, 20%, or 30% HF for either 5 or 30 min. After cleaning, the surfaces were characterized using various analytical techniques. Three resin cylinders (Duo-Link) were bonded to each treated plate. All bonded specimens were stored in water at 37 °C for 24 h, and then half of them were additionally thermocycled 5000 times prior to the shear bond-strength tests (n = 12). The formation of micro- and nano-porosities on the etched surfaces increased with increasing concentration and application time of the HF solution. The surface wettability of zirconia also increased with increasing surface roughness. Higher concentrations and longer application times of the HF solution produced higher bond-strength values. Infiltration of the resin into the micro- and nano-porosities was observed by scanning electron microscopy. This in vitro study suggests that HF slowly etches zirconia ceramic surfaces at room temperature, thereby improving the resin–zirconia bond strength by the formation of retentive sites. Materials 2015-03-02 8 3 Article 10.3390/ma8030850 850 866 1996-1944 2015-03-02 doi: 10.3390/ma8030850 Mun-Hwan Lee Jun Son Kyo-Han Kim Tae-Yub Kwon http://www.mdpi.com/1996-1944/8/3/832 In the present study, Eudragit S100 coated Citrus Pectin Nanoparticles (E-CPNs) were prepared for the colon targeting of 5-Fluorouracil (5-FU). Citrus pectin also acts as a ligand for galectin-3 receptors that are over expressed on colorectal cancer cells. Nanoparticles (CPNs and E-CPNs) were characterized for various physical parameters such as particle size, size distribution, and shape etc. In vitro drug release studies revealed selective drug release in the colonic region in the case of E-CPNs of more than 70% after 24 h. In vitro cytoxicity assay (Sulphorhodamine B assay) was performed against HT-29 cancer cells and exhibited 1.5 fold greater cytotoxicity potential of nanoparticles compared to 5-FU solution. In vivo data clearly depicted that Eudragit S100 successfully guarded nanoparticles to reach the colonic region wherein nanoparticles were taken up and showed drug release for an extended period of time. Therefore, a multifaceted strategy is introduced here in terms of receptor mediated uptake and pH-dependent release using E-CPNs for effective chemotherapy of colorectal cancer with uncompromised safety and efficacy. Materials 2015-02-27 8 3 Article 10.3390/ma8030832 832 849 1996-1944 2015-02-27 doi: 10.3390/ma8030832 M. Subudhi Ankit Jain Ashish Jain Pooja Hurkat Satish Shilpi Arvind Gulbake Sanjay Jain http://www.mdpi.com/1996-1944/8/2/829 Materials has established an annual award for the best article and for the best review published in Materials in order to acknowledge the outstanding contributions of our authors in the area of materials science and engineering.[...] Materials 2015-02-17 8 2 Editorial 10.3390/ma8020829 829 831 1996-1944 2015-02-17 doi: 10.3390/ma8020829 Maryam Tabrizian http://www.mdpi.com/1996-1944/8/2/815 The waves propagating within complex smart structures are hereby computed by employing a wave and finite element method. The structures can be of arbitrary layering and of complex geometric characteristics as long as they exhibit two-dimensional periodicity. The piezoelectric coupling phenomena are considered within the finite element formulation. The mass, stiffness and piezoelectric stiffness matrices of the modelled segment can be extracted using a conventional finite element code. The post-processing of these matrices involves the formulation of an eigenproblem whose solutions provide the phase velocities for each wave propagating within the structure and for any chosen direction of propagation. The model is then modified in order to account for a shunted piezoelectric patch connected to the composite structure. The impact of the energy dissipation induced by the shunted circuit on the total damping loss factor of the composite panel is then computed. The influence of the additional mass and stiffness provided by the attached piezoelectric devices on the wave propagation characteristics of the structure is also investigated. Materials 2015-02-17 8 2 Article 10.3390/ma8020815 815 828 1996-1944 2015-02-17 doi: 10.3390/ma8020815 Dimitrios Chronopoulos Manuel Collet Mohamed Ichchou http://www.mdpi.com/1996-1944/8/2/799 We report on the synthesis and the mechanical characterization of an alginate-collagen fibril composite hydrogel. Native type I collagen fibrils were used to synthesize the fibrous composite hydrogel. We characterized the mechanical properties of the fabricated fibrous hydrogel using tensile testing; rheometry and atomic force microscope (AFM)-based nanoindentation experiments. The results show that addition of type I collagen fibrils improves the rheological and indentation properties of the hydrogel. Materials 2015-02-16 8 2 Article 10.3390/ma8020799 799 814 1996-1944 2015-02-16 doi: 10.3390/ma8020799 Mahmoud Baniasadi Majid Minary-Jolandan http://www.mdpi.com/1996-1944/8/2/784 This study investigates the feasibility of co-firing fly ashes from different boilers, circulating fluidized beds (CFB) or stokers as a sustainable material in alkali activators for ground granulated blast-furnace slag (GGBS). The mixture ratio of GGBS and co-firing fly ashes is 1:1 by weight. The results indicate that only CF fly ash of CFB boilers can effectively stimulate the potential characteristics of GGBS and provide strength as an alkali activator. CF fly ash consists of CaO3 (48.5%), SiO2 (21.1%), Al2O3 (13.8%), SO3 (10.06%), Fe2O3 (2.25%) and others (4.29%). SA fly ash consists of Al2O3 (19.7%), SiO2 (36.3%), Fe2O3 (28.4%) and others (15.6%). SB fly ash consists of Al2O3 (15%), SiO2 (25.4%), Zn (20.6%), SO3 (10.9%), Fe2O3 (8.78%) and others (19.32%). The mixtures of SA fly ash and SB fly ash with GGBS, respectively, were damaged in the compressive strength test during seven days of curing. However, the built up strength of the CF fly ash and GGBS mixture can only be maintained for 7–14 days, and the compressive strength achieves 70% of that of a controlled group (cement in hardening cement paste). The strength of blended CF fly ash and GGBS started to decrease after 28 days, and the phenomenon of ettrigite was investigated due to the high levels of sulfur content. The CaO content in sustainable co-firing fly ashes must be higher than a certain percentage in reacting GGBS to ensure the strength of blended cements. Materials 2015-02-16 8 2 Article 10.3390/ma8020784 784 798 1996-1944 2015-02-16 doi: 10.3390/ma8020784 Yann-Hwang Wu Ran Huang Chia-Jung Tsai Wei-Ting Lin http://www.mdpi.com/1996-1944/8/2/751 Considerable research has been conducted over recent decades on the role of non‑metallic inclusions and their link to the machinability of different steels. The present work reviews the mechanisms of steel fractures during different mechanical machining operations and the behavior of various non-metallic inclusions in a cutting zone. More specifically, the effects of composition, size, number and morphology of inclusions on machinability factors (such as cutting tool wear, power consumption, etc.) are discussed and summarized. Finally, some methods for modification of non-metallic inclusions in the liquid steel are considered to obtain a desired balance between mechanical properties and machinability of various steel grades. Materials 2015-02-16 8 2 Review 10.3390/ma8020751 751 783 1996-1944 2015-02-16 doi: 10.3390/ma8020751 Niclas Ånmark Andrey Karasev Pär Jönsson http://www.mdpi.com/1996-1944/8/2/732 The thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials have attracted attention recently because of their remarkable electrical conductivity, power factor, and figure of merit. In this review, we summarize recent efforts toward improving the thermoelectric properties of PEDOT-based materials. We also discuss thermoelectric measurement techniques and several unsolved problems with the PEDOT system such as the effect of water absorption from the air and the anisotropic thermoelectric properties. In the last part, we describe our work on improving the power output of thermoelectric modules by using PEDOT, and we outline the potential applications of polymer thermoelectric generators. Materials 2015-02-16 8 2 Review 10.3390/ma8020732 732 750 1996-1944 2015-02-16 doi: 10.3390/ma8020732 Qingshuo Wei Masakazu Mukaida Kazuhiro Kirihara Yasuhisa Naitoh Takao Ishida http://www.mdpi.com/1996-1944/8/2/717 Rationalizing has become a new trend in the world of science and technology. Nanotechnology has ascended to become one of the most favorable technologies, and one which will change the application of materials in different fields. The quality of dental biomaterials has been improved by the emergence of nanotechnology. This technology manufactures materials with much better properties or by improving the properties of existing materials. The science of nanotechnology has become the most popular area of research, currently covering a broad range of applications in dentistry. This review describes the basic concept of nanomaterials, recent innovations in nanomaterials and their applications in restorative dentistry. Advances in nanotechnologies are paving the future of dentistry, and there are a plenty of hopes placed on nanomaterials in terms of improving the health care of dental patients. Materials 2015-02-16 8 2 Review 10.3390/ma8020717 717 731 1996-1944 2015-02-16 doi: 10.3390/ma8020717 Zohaib Khurshid Muhammad Zafar Saad Qasim Sana Shahab Mustafa Naseem Ammar AbuReqaiba http://www.mdpi.com/1996-1944/8/2/700 Recent interest in low and negative thermal expansion materials has led to significant research on compounds that exhibit this property, much of which has targeted the A2M3O12 family (A = trivalent cation, M = Mo, W). The expansion and phase transition behavior in this family can be tuned through the choice of the metals incorporated into the structure. An undesired phase transition to a monoclinic structure with large positive expansion can be suppressed in some solid solutions by substituting the A-site by a mixture of two cations. One such material, AlScMo3O12, was successfully synthesized using non-hydrolytic sol-gel chemistry. Depending on the reaction conditions, phase separation into Al2Mo3O12 and Sc2Mo3O12 or single-phase AlScMo3O12 could be obtained. Optimized conditions for the reproducible synthesis of stoichiometric, homogeneous AlScMo3O12 were established. High resolution synchrotron diffraction experiments were carried out to confirm whether samples were homogeneous and to estimate the Al:Sc ratio through Rietveld refinement and Vegard's law. Single-phase samples were found to adopt the orthorhombic Sc2W3O12 structure at 100 to 460 K. In contrast to all previously-reported A2M3O12 compositions, AlScMo3O12 exhibited positive thermal expansion along all unit cell axes instead of contraction along one or two axes, with expansion coefficients (200–460 K) of αa = 1.7 × 10−6 K−1, αb = 6.2 × 10−6 K−1, αc = 2.9 × 10−6 K−1 and αV = 10.8 × 10−6 K−1, respectively. Materials 2015-02-16 8 2 Article 10.3390/ma8020700 700 716 1996-1944 2015-02-16 doi: 10.3390/ma8020700 Rebecca Truitt Ilka Hermes Alyssa Main Anne Sendecki Cora Lind http://www.mdpi.com/1996-1944/8/2/684 Surface properties play a critical role in influencing cell responses to a biomaterial. The objectives of this study were (1) to characterize changes in surface properties of zirconia (ZrO2) ceramic after oxygen plasma treatment; and (2) to determine the effect of such changes on biological responses of human osteoblast-like cells (MG63). The results indicated that the surface morphology was not changed by oxygen plasma treatment. In contrast, oxygen plasma treatment to ZrO2 not only resulted in an increase in hydrophilicity, but also it retained surface hydrophilicity after 5-min treatment time. More importantly, surface properties of ZrO2 modified by oxygen plasma treatment were beneficial for cell growth, whereas the surface roughness of the materials did not have a significant efficacy. It is concluded that oxygen plasma treatment was certified to be effective in modifying the surface state of ZrO2 and has the potential in the creation and maintenance of hydrophilic surfaces and the enhancement of cell proliferation and differentiation. Materials 2015-02-16 8 2 Article 10.3390/ma8020684 684 699 1996-1944 2015-02-16 doi: 10.3390/ma8020684 Ching-Chou Wu Chung-Kai Wei Chia-Che Ho Shinn-Jyh Ding http://www.mdpi.com/1996-1944/8/2/652 This review article presents the recent advances in syntheses and applications of nanocomposites consisting of graphene derivatives with various polysaccharides. Graphene has recently attracted much interest in the materials field due to its unique 2D structure and outstanding properties. To follow, the physical and mechanical properties of graphene are then introduced. However it was observed that the synthesis of graphene-based nanocomposites had become one of the most important research frontiers in the application of graphene. Therefore, this review also summarizes the recent advances in the synthesis of graphene nanocomposites with polysaccharides, which are abundant in nature and are easily synthesized bio-based polymers. Polysaccharides can be classified in various ways such as cellulose, chitosan, starch, and alginates, each group with unique and different properties. Alginates are considered to be ideal for the preparation of nanocomposites with graphene derivatives due to their environmental-friendly potential. The characteristics of such nanocomposites are discussed here and are compared with regard to their mechanical properties and their various applications. Materials 2015-02-16 8 2 Review 10.3390/ma8020652 652 683 1996-1944 2015-02-16 doi: 10.3390/ma8020652 Zoi Terzopoulou George Kyzas Dimitrios Bikiaris http://www.mdpi.com/1996-1944/8/2/638 Calcium carbide residue (CCR) is a waste by-product from acetylene gas production. The main component of CCR is Ca(OH)2, which can react with siliceous materials through pozzolanic reactions, resulting in a product similar to those obtained from the cement hydration process. Thus, it is possible to use CCR as a substitute for Portland cement in concrete. In this research, we synthesized CCR and silica fume through a chemical combustion technique to produce a new reactive cementitious powder (RCP). The properties of paste and mortar in fresh and hardened states (setting time, shrinkage, and compressive strength) with 5% cement replacement by RCP were evaluated. The hydration of RCP and OPC (Ordinary Portland Cement) pastes was also examined through SEM (scanning electron microscope). Test results showed that in comparison to control OPC mix, the hydration products for the RCP mix took longer to formulate. The initial and final setting times were prolonged, while the drying shrinkage was significantly reduced. The compressive strength at the age of 45 days for RCP mortar mix was found to be higher than that of OPC mortar and OPC mortar with silica fume mix by 10% and 8%, respectively. Therefore, the synthesized RCP was proved to be a sustainable active cementitious powder for the strength enhanced of building materials, which will result in the diversion of significant quantities of this by-product from landfills. Materials 2015-02-13 8 2 Article 10.3390/ma8020638 638 651 1996-1944 2015-02-13 doi: 10.3390/ma8020638 Hongfang Sun Zishanshan Li Jing Bai Shazim Memon Biqin Dong Yuan Fang Weiting Xu Feng Xing http://www.mdpi.com/1996-1944/8/2/625 This review work is an update of a previous work reporting the new cork based materials and new applications of cork based materials. Cork is a material which has been used for multiple applications. The most known uses of cork are in stoppers (natural and agglomerated cork) for alcoholic beverages, classic floor covering with composite cork tiles (made by the binding of cork particles with different binders), and thermal/acoustic/vibration insulation with expanded corkboard in buildings and some other industrial fields. Many recent developments have been made leading to new cork based materials. Most of these newly developed cork materials are not yet on the market, but they represent new possibilities for engineers, architects, designers and other professionals which must be known and considered, potentially leading to their industrialization. This paper is a review covering the last five years of innovative cork materials and applications also mentioning previous work not reported before. Materials 2015-02-10 8 2 Review 10.3390/ma8020625 625 637 1996-1944 2015-02-10 doi: 10.3390/ma8020625 Luís Gil http://www.mdpi.com/1996-1944/8/2/611 An Al2O3/5 vol%·ZrO2/5 vol%·Y3Al5O12 (YAG) tri-phase composite was manufactured by surface modification of an alumina powder with inorganic precursors of the second phases. The bulk materials were produced by die-pressing and pressureless sintering at 1500 °C, obtaining fully dense, homogenous samples, with ultra-fine ZrO2 and YAG grains dispersed in a sub-micronic alumina matrix. The high temperature mechanical properties were investigated by four-point bending tests up to 1500 °C, and the grain size stability was assessed by observing the microstructural evolution of the samples heat treated up to 1700 °C. Dynamic indentation measures were performed on as-sintered and heat-treated Al2O3/ZrO2/YAG samples in order to evaluate the micro-hardness and elastic modulus as a function of re-heating temperature. The high temperature bending tests highlighted a transition from brittle to plastic behavior comprised between 1350 and 1400 °C and a considerable flexural strength reduction at temperatures higher than 1400 °C; moreover, the microstructural investigations carried out on the re-heated samples showed a very limited grain growth up to 1650 °C. Materials 2015-02-10 8 2 Article 10.3390/ma8020611 611 624 1996-1944 2015-02-10 doi: 10.3390/ma8020611 Paola Palmero Giovanni Pulci Francesco Marra Teodoro Valente Laura Montanaro http://www.mdpi.com/1996-1944/8/2/600 Preparation of dense alumina (Al2O3) thin film through atomic layer deposition (ALD) provides a pathway to achieve the encapsulation of organic light emitting devices (OLED). Unlike traditional ALD which is usually executed at higher reaction n temperatures that may affect the performance of OLED, this application discusses the development on preparation of ALD thin film at a low temperature. One concern of ALD is the suppressing effect of ambient temperature on uniformity of thin film. To mitigate this issue, the pumping time in each reaction cycle was increased during the preparation process, which removed reaction byproducts and inhibited the formation of vacancies. As a result, the obtained thin film had both high uniformity and density properties, which provided an excellent encapsulation performance. The results from microstructure morphology analysis, water vapor transmission rate, and lifetime test showed that the difference in uniformity between thin films prepared at low temperatures, with increased pumping time, and high temperatures was small and there was no obvious influence of increased pumping time on light emitting performance. Meanwhile, the permeability for water vapor of the thin film prepared at a low temperature was found to reach as low as 1.5 × 10−4 g/(m2·day) under ambient conditions of 25 °C and 60% relative humidity, indicating a potential extension in the lifetime for the OLED. Materials 2015-02-10 8 2 Article 10.3390/ma8020600 600 610 1996-1944 2015-02-10 doi: 10.3390/ma8020600 Hui-Ying Li Yun-Fei Liu Yu Duan Yong-Qiang Yang Yi-Nan Lu http://www.mdpi.com/1996-1944/8/2/586 Lignin-based polyols were synthesized through microwave-assisted liquefaction under different microwave heating times (5–30 min). The liquefaction reactions were carried out using polyethylene glycol (PEG-400)/glycerol as liquefying solvents and 97 wt% sulfur acid as a catalyst at 140 °C. The polyols obtained were analyzed for their yield, composition and structural characteristics using gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectra. FT-IR and NMR spectra showed that the liquefying solvents reacted with the phenol hydroxyl groups of the lignin in the liquefied product. With increasing microwave heating time, the viscosity of polyols was slightly increased and their corresponding molecular weight (MW) was gradually reduced. The optimal condition at the microwave heating time (5 min) ensured a high liquefaction yield (97.47%) and polyol with a suitable hydroxyl number (8.628 mmol/g). Polyurethane (PU) foams were prepared by polyols and methylene diphenylene diisocyanate (MDI) using the one-shot method. With the isocyanate/hydroxyl group ([NCO]/[OH]) ratio increasing from 0.6 to 1.0, their mechanical properties were gradually increased. This study provided some insight into the microwave-assisted liquefied lignin polyols for the production of rigid PU foam. Materials 2015-02-10 8 2 Article 10.3390/ma8020586 586 599 1996-1944 2015-02-10 doi: 10.3390/ma8020586 Bai-Liang Xue Jia-Long Wen Run-Cang Sun http://www.mdpi.com/1996-1944/8/2/575 A two stage process including a sintering under a cyclic loading is proposed as an alternative fabrication method of dense FeAl intermetallics from elemental powder mixtures. The first stage (pre-sintering) is conducted at two temperature values (620 °C and 670 °C, respectively) under a static and a cyclic loading with a frequency of 20, 40 and 60 Hz. The second one includes a pressureless sintering at temperature of 1250 °C, under a protective argon atmosphere. A suitable selection of pre-sintering parameters (temperature, type and frequency of pressing) allows approximately five times grain size reduction of FeAl phase in comparison to particle size of raw Fe and Al powder material (40–60 µm), as well as induces an effective fragmentation of oxide layers. For the sinters obtained using 60 Hz loading frequency an oxide particle size of 4.0 or 4.5 µm (smaller for sintering with liquid phase) is observed. Material obtained after the full heat treatment are characterized by a fine-grained structure of chemically homogeneous FeAl phase with uniformly distributed Al2O3 spherical particles along grain boundaries. Moreover, it was found that temperature and frequency of loading during the presintering process also affect a consolidation level of the Fe-Al powder mixture, which increases with rising both temperature and frequency. Materials 2015-02-09 8 2 Article 10.3390/ma8020575 575 585 1996-1944 2015-02-09 doi: 10.3390/ma8020575 Tomasz Durejko Michał Ziętala Zbigniew Bojar http://www.mdpi.com/1996-1944/8/2/561 Hydrogen doped In2O3 thin films were prepared by room temperature sputter deposition with the addition of H2O to the sputter gas. By subsequent vacuum annealing, the films obtain high mobility up to 90 cm2/Vs. The films were analyzed in situ by X-ray photoelectron spectroscopy (XPS) and ex situ by X-ray diffraction (XRD), optical transmission and Hall effect measurements. Furthermore, we present results from in situ Hall effect measurements during vacuum annealing of In2O3:H films, revealing distinct dependence of carrier concentration and mobility with time at different annealing temperatures. We suggest hydrogen passivation of grain boundaries as the main reason for the high mobility obtained with In2O3:H films. Materials 2015-02-06 8 2 Article 10.3390/ma8020561 561 574 1996-1944 2015-02-06 doi: 10.3390/ma8020561 Hans Wardenga Mareike Frischbier Monica Morales-Masis Andreas Klein http://www.mdpi.com/1996-1944/8/2/551 The mechanical properties of type I collagen gel vary due to different polymerization parameters. In this work, the role of crosslinks in terms of density and stiffness on the macroscopic behavior of collagen gel were investigated through computational modeling. The collagen fiber network was developed in a representative volume element, which used the inter-fiber spacing to regulate the crosslink density. The obtained tensile behavior of collagen gel was validated against published experimental data. Results suggest that the cross-linked fiber alignment dominated the strain stiffening effect of the collagen gel. In addition, the gel stiffness was enhanced approximately 40 times as the crosslink density doubled. The non-affine deformation was reduced with the increased crosslink density. A positive bilinear correlation between the crosslink density and gel stiffness was obtained. On the other hand, the crosslink stiffness had much less impact on the gel stiffness. This work could enhance our understanding of collagen gel mechanics and shed lights on designing future clinical relevant biomaterials with better control of polymerization parameters. Materials 2015-02-06 8 2 Article 10.3390/ma8020551 551 560 1996-1944 2015-02-06 doi: 10.3390/ma8020551 Shengmao Lin Linxia Gu http://www.mdpi.com/1996-1944/8/2/535 A literature review points out a large discrepancy in the results of the mechanical tests on dentin that can be explained by stress and strain assessment during the tests. Errors in these assessments during mechanical tests can lead to inaccurate estimation of the mechanical properties of the tested material. On top of that, using the beam theory to analyze the bending test for thick specimens will increase these experimental errors. After summarizing the results of mechanical tests on dentin in the literature, we focus on bending tests and compare the stress assessment obtained by finite element analysis (FEA) and by beam theory application. We show that the difference between the two methods can be quite large in some cases, leading us to prefer the use of FEA to assess stresses. We then propose a new method based on coupling finite element analysis and digital image correlation (DIC) to more accurately evaluate stress distributions, strain distributions and elastic modulus in the case of a three-point bending test. To illustrate and prove the feasibility of the method, it is applied on a dentinal sample so that mean elastic modulus and maximum tensile stress are obtained (11.9 GPa and 143.9 MPa). Note that the main purpose of this study is to focus on the method itself, and not to provide new mechanical values for dentin. When used in standard mechanical testing of dentin, this kind of method should help to narrow the range of obtained mechanical properties values. Materials 2015-02-06 8 2 Article 10.3390/ma8020535 535 550 1996-1944 2015-02-06 doi: 10.3390/ma8020535 Wenlong Wang Nicolas Roubier Guillaume Puel Jean-Marc Allain Ingrid Infante Jean-Pierre Attal Elsa Vennat http://www.mdpi.com/1996-1944/8/2/519 An oral medication of a molecular targeted drug, lapatinib, is taken regularly to maintain the drug concentration within the desired therapeutic levels. To alleviate the need for such cumbersome administration schedules in several drugs, advanced drug delivery systems (DDSs), which can provide time-controlled and sustained drug release, have recently received significant attention. A biodegradable synthetic polymer, such as polycaprolactone (PCL), is usually used as a carrier material for DDSs. In this paper, lapatinib powder-entrapped, PCL microstructures were fabricated with a precise X-ray lithography-based method. In vitro experiments on HER2 positive-human gastric cancer derived NCI-N87 cells were performed to appraise the drug release characteristics of the fabricated DDSs. The in vitro results indicate that after the X-ray lithography process, the lapatinib powder is still working well and show time- and dose- dependent drug release efficiencies. The cell growth inhibition characteristics of one hundred 40-μm sized microstructures were similar to those of a 1 μM lapatinib solution for over 144 h. In conclusion, the developed lapatinib-entrapped PCL microstructures can be used in molecular targeted delivery and sustained release as effective cancer-targeted DDSs. Materials 2015-02-05 8 2 Article 10.3390/ma8020519 519 534 1996-1944 2015-02-05 doi: 10.3390/ma8020519 Eun-Goo Jeong Hyung Yoo Byeonghwa Song Hwang-Phill Kim Sae-Won Han Tae-You Kim Dong-Il Cho http://www.mdpi.com/1996-1944/8/2/499 In this research, we focused on the development of composite phase-change materials (CPCMs) by incorporation of a paraffin through vacuum impregnation in widely used building materials (Kaolin and ground granulated blast-furnace slag (GGBS)). The composite PCMs were characterized using environmental scanning electron microscopy (ESEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. Moreover, thermal performance of cement paste composite PCM panels was evaluated using a self-designed heating system. Test results showed that the maximum percentage of paraffin retained by Kaolin and GGBS was found to be 18% and 9%, respectively. FT-IR results show that CPCMs are chemically compatible. The phase-change temperatures of CPCMs were in the human comfort zone, and they possessed considerable latent-heat storage capacity. TGA results showed that CPCMs are thermally stable, and they did not show any sign of degradation below 150 °C. From thermal cycling tests, it was revealed that the CPCMs are thermally reliable. Thermal performance tests showed that in comparison to the control room model, the room models prepared with CPCMs reduced both the temperature fluctuations and maximum indoor center temperature. Therefore, the prepared CPCMs have some potential in reducing peak loads in buildings when applied to building facade. Materials 2015-02-05 8 2 Article 10.3390/ma8020499 499 518 1996-1944 2015-02-05 doi: 10.3390/ma8020499 Shazim Memon Wenyu Liao Shuqing Yang Hongzhi Cui Syed Shah http://www.mdpi.com/1996-1944/8/2/486 The objective of this study was to improve the solubility of albendazole and optimize the preparation of an oral nanoparticle formulation, using β-cyclodextrin (βCD) and chitosan-tripolyphosphate (TPP) nanoparticles. The solubility of albendazole in buffers, surfactants, and various concentrations of acetic acid solution was investigated. To determine drug loading, the cytotoxic effects of the albendazole concentration in human hepatocellular carcinoma cells (HepG2) were investigated. The formulations were prepared by mixing the drug solution in Tween 20 with the chitosan solution. TPP solution was added dropwise with sonication to produce a nanoparticle through ionic crosslinking. Then the particle size, polydispersity index, and zeta potential of the nanoparticles were investigated to obtain an optimal composition. The solubility of albendazole was greater in pH 2 buffer, Tween 20, and βCD depending on the concentration of acetic acid. Drug loading was determined as 100 µg/mL based on the results of cell viability. The optimized ratio of Tween 20, chitosan/hydroxypropyl βCD, and TPP was 2:5:1, which resulted in smaller particle size and proper zeta positive values of the zeta potential. The chitosan-TPP nanoparticles increased the drug solubility and had a small particle size with homogeneity in formulating albendazole as a potential anticancer agent. Materials 2015-02-05 8 2 Article 10.3390/ma8020486 486 498 1996-1944 2015-02-05 doi: 10.3390/ma8020486 Bong-Seok Kang Sang-Eun Lee Choon Ng Jin-Ki Kim Jeong-Sook Park http://www.mdpi.com/1996-1944/8/2/474 We report a novel method to pattern the stiffness of an elastomeric nanocomposite by selectively impeding the cross-linking reactions at desired locations while curing. This is accomplished by using a magnetic field to enforce a desired concentration distribution of colloidal magnetite nanoparticles (MNPs) in the liquid precursor of polydimethysiloxane (PDMS) elastomer. MNPs impede the cross-linking of PDMS; when they are dispersed in liquid PDMS, the cured elastomer exhibits lower stiffness in portions containing a higher nanoparticle concentration. Consequently, a desired stiffness pattern is produced by selecting the required magnetic field distribution a priori. Up to 200% variation in the reduced modulus is observed over a 2 mm length, and gradients of up to 12.6 MPa·mm−1 are obtained. This is a significant improvement over conventional nanocomposite systems where only small unidirectional variations can be achieved by varying nanoparticle concentration. The method has promising prospects in additive manufacturing; it can be integrated with existing systems thereby adding the capability to produce microscale heterogeneities in mechanical properties. Materials 2015-01-30 8 2 Article 10.3390/ma8020474 474 485 1996-1944 2015-01-30 doi: 10.3390/ma8020474 Suvojit Ghosh Mehran Tehrani Marwan Al-Haik Ishwar Puri http://www.mdpi.com/1996-1944/8/2/462 Foamed mortar with a density of 1300 kg/m3 was prepared. In the initial laboratory trials, water-to-cement (w/c) ratios ranging from 0.54 to 0.64 were tested to determine the optimal value for foamed mortar corresponding to the highest compressive strength without compromising its fresh state properties. With the obtained optimal w/c ratio of 0.56, two types of foamed mortar were prepared, namely cement-foamed mortar (CFM) and slag-foamed mortar (SFM, 50% cement was replaced by slag weight). Four different curing conditions were adopted for both types of foamed mortar to assess their compressive strength, ultrasonic pulse velocity (UPV) and thermal insulation performance. The test results indicated that utilizing 50% of slag as cement replacement in the production of foamed mortar improved the compressive strength, UPV and thermal insulation properties. Additionally, the initial water curing of seven days gained higher compressive strength and increased UPV values as compared to the air cured and natural weather curing samples. However, this positive effect was more pronounced in the case of compressive strength than in the UPV and thermal conductivity of foamed mortar. Materials 2015-01-30 8 2 Article 10.3390/ma8020462 462 473 1996-1944 2015-01-30 doi: 10.3390/ma8020462 Xiao Zhao Siong-Kang Lim Cher-Siang Tan Bo Li Tung-Chai Ling Runqiu Huang Qingyuan Wang http://www.mdpi.com/1996-1944/8/2/451 In this work, the mechanical properties and microstructural features of an AISI 304L stainless steel in two presentations, bulk and fibers, were systematically studied in order to establish the relationship among microstructure, mechanical properties, manufacturing process and effect on sample size. The microstructure was analyzed by XRD, SEM and TEM techniques. The strength, Young's modulus and elongation of the samples were determined by tensile tests, while the hardness was measured by Vickers microhardness and nanoindentation tests. The materials have been observed to possess different mechanical and microstructural properties, which are compared and discussed. Materials 2015-01-29 8 2 Article 10.3390/ma8020451 451 461 1996-1944 2015-01-29 doi: 10.3390/ma8020451 Francisco Baldenebro-Lopez Cynthia Gomez-Esparza Ramon Corral-Higuera Susana Arredondo-Rea Manuel Pellegrini-Cervantes Jose Ledezma-Sillas Roberto Martinez-Sanchez Jose Herrera-Ramirez http://www.mdpi.com/1996-1944/8/2/435 This paper aims at presenting the effects of short-term sustained load and temperature on time-dependent deformation of carbon fiber-reinforced polymer (CFRP) bonded to concrete and pull-off strength at room temperature after the sustained loading period. The approach involves experimental and numerical analysis. Single-lap shear specimens were used to evaluate temperature and short-term sustained loading effects on time-dependent behavior under sustained loading and debonding behavior under pull-off loading after a sustained loading period. The numerical model was parameterized with experiments on the concrete, FRP, and epoxy. Good correlation was seen between the numerical results and single-lap shear experiments. Sensitivity studies shed light on the influence of temperature, epoxy modulus, and epoxy thickness on the redistribution of interfacial shear stress during sustained loading. This investigation confirms the hypothesis that interfacial stress redistribution can occur due to sustained load and elevated temperature and its effect can be significant. Materials 2015-01-29 8 2 Article 10.3390/ma8020435 435 450 1996-1944 2015-01-29 doi: 10.3390/ma8020435 Yoseok Jeong Jaeha Lee WooSeok Kim http://www.mdpi.com/1996-1944/8/2/424 The improvement of the surface qualities and surface hardening of precipitation hardened martensitic stainless steel 17-4PH was achieved by the plasma-transferred arc welding (PTAW) process deposited with Co-based alloy. The microstructure of the heat affected zone (HAZ) and base metal were characterized by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that there are obvious microstructural differences between the base metal and HAZ. For example, base material is transformed from lath martensite to austenite due to the heateffect of the welding process. On the other hand, the precipitate in the matrix (bar-like shape Cr7C3 phase with a width of about one hundred nanometres and a length of hundreds of nanometres) grows to a rectangular appearance with a width of about two hundred nanometres and a length of about one micron. Stacking fault could also be observed in the Cr7C3 after PTAW. The above means that welding can obviously improve the surface qualities. Materials 2015-01-29 8 2 Article 10.3390/ma8020424 424 434 1996-1944 2015-01-29 doi: 10.3390/ma8020424 Dewei Deng Rui Chen Qi Sun Xiaona Li http://www.mdpi.com/1996-1944/8/2/408 Synthetic and natural polymer association is a promising tool in tissue engineering. The aim of this study was to compare five methodologies for producing hybrid scaffolds for cell culture using poly-l-lactide (PLLA) and collagen: functionalization of PLLA electrospun by (1) dialkylamine and collagen immobilization with glutaraldehyde and by (2) hydrolysis and collagen immobilization with carbodiimide chemistry; (3) co-electrospinning of PLLA/chloroform and collagen/hexafluoropropanol (HFP) solutions; (4) co-electrospinning of PLLA/chloroform and collagen/acetic acid solutions and (5) electrospinning of a co-solution of PLLA and collagen using HFP. These materials were evaluated based on their morphology, mechanical properties, ability to induce cell proliferation and alkaline phosphatase activity upon submission of mesenchymal stem cells to basal or osteoblastic differentiation medium (ODM). Methods (1) and (2) resulted in a decrease in mechanical properties, whereas methods (3), (4) and (5) resulted in materials of higher tensile strength and osteogenic differentiation. Materials yielded by methods (2), (3) and (5) promoted osteoinduction even in the absence of ODM. The results indicate that the scaffold based on the PLLA/collagen blend exhibited optimal mechanical properties and the highest capacity for osteodifferentiation and was the best choice for collagen incorporation into PLLA in bone repair applications. Materials 2015-01-26 8 2 Article 10.3390/ma8020408 408 423 1996-1944 2015-01-26 doi: 10.3390/ma8020408 Flávia Gonçalves Ricardo Bentini Mariana Burrows Ana Carreira Patricia Kossugue Mari Sogayar Luiz Catalani http://www.mdpi.com/1996-1944/8/2/392 A miniaturized antenna employing a negative index metamaterial with modified split-ring resonator (SRR) and capacitance-loaded strip (CLS) unit cells is presented for Ultra wideband (UWB) microwave imaging applications. Four left-handed (LH) metamaterial (MTM) unit cells are located along one axis of the antenna as the radiating element. Each left-handed metamaterial unit cell combines a modified split-ring resonator (SRR) with a capacitance-loaded strip (CLS) to obtain a design architecture that simultaneously exhibits both negative permittivity and negative permeability, which ensures a stable negative refractive index to improve the antenna performance for microwave imaging. The antenna structure, with dimension of 16 × 21 × 1.6 mm3, is printed on a low dielectric FR4 material with a slotted ground plane and a microstrip feed. The measured reflection coefficient demonstrates that this antenna attains 114.5% bandwidth covering the frequency band of 3.4–12.5 GHz for a voltage standing wave ratio of less than 2 with a maximum gain of 5.16 dBi at 10.15 GHz. There is a stable harmony between the simulated and measured results that indicate improved nearly omni-directional radiation characteristics within the operational frequency band. The stable surface current distribution, negative refractive index characteristic, considerable gain and radiation properties make this proposed negative index metamaterial antenna optimal for UWB microwave imaging applications. Materials 2015-01-23 8 2 Article 10.3390/ma8020392 392 407 1996-1944 2015-01-23 doi: 10.3390/ma8020392 Md. Islam Mohammad Islam Md. Samsuzzaman Mohammad Faruque Norbahiah Misran Mohd Mansor http://www.mdpi.com/1996-1944/8/2/379 A novel polymer-drug conjugate was prepared by the chemical reaction between the copolymer Pluronic P123 and the docetaxel via a pH sensitive hydrazone bond. These pluronic P123-docetaxel (DTX) conjugates (P123-DTX) could form the stable drug-loaded materials that can self-assemble into the defined nano-micelles in aqueous solution because of their obvious amphiphilic property and low critical micelle concentration. The spherical morphology and particle size of the prepared nano-micelles were characterized by transmission electron microscopy and dynamic light scattering, respectively. Moreover, after the introduction of pH sensitive hydrazone bond, P123-DTX micelle showed a pH dependent drug release behavior. At pH 5.0 (in 48 h), the cumulative release amount of DTX were ~84.9%, which is about six times higher than that at pH 7.4. The prepared novel p123-DTX conjugates may offer a great benefit for drug delivery and controlling the drug release. Materials 2015-01-23 8 2 Article 10.3390/ma8020379 379 391 1996-1944 2015-01-23 doi: 10.3390/ma8020379 Yanchao Liang Zhihui Su Yao Yao Na Zhang http://www.mdpi.com/1996-1944/8/1/368 Temperature and relative humidity (RH) are two major external factors, which affect equilibrium moisture content (EMC) of wood-plastic composites (WPCs). In this study, the effect of different durability treatments on sorption and desorption isotherms of southern yellow pine (SYP)-high density polyethylene (HDPE) composites was investigated. All samples were equilibriumed at 20 °C and various RHs including 16%, 33%, 45%, 66%, 75%, 85%, 93%, and100%. EMCs obtained from desorption and absorption for different WPC samples were compared with Nelson's sorption isotherm model predictions using the same temperature and humidity conditions. The results indicated that the amount of moisture absorbed increased with the increases in RH at 20 °C. All samples showed sorption hysteresis at a fixed RH. Small difference between EMC data of WPC samples containing different amount of ultraviolet (UV) stabilizers were observed. Similar results were observed among the samples containing different amount of zinc borate (ZB). The experimental data of EMCs at various RHs fit to the Nelson's sorption isotherm model well. The Nelson's model can be used to predicate EMCs of WPCs under different RH environmental conditions. Materials 2015-01-20 8 1 Article 10.3390/ma8010368 368 378 1996-1944 2015-01-20 doi: 10.3390/ma8010368 Feihong Liu Guangping Han Wanli Cheng Qinglin Wu http://www.mdpi.com/1996-1944/8/1/355 Cadmium sulphide (CdS) quantum dot sensitized solar cells (QDSSCs) based on screen-printed TiO2 were assembled using a screen-printing technique. The CdS quantum dots (QDs) were grown by using the Successive Ionic Layer Adsorption and Reaction (SILAR) method. The optical properties were studied by UV-Vis absorbance spectroscopy. Photovoltaic characteristics and impedance spectroscopic measurements of CdS QDSSCs were carried out under air mass 1.5 illuminations. The experimental results of capacitance against voltage indicate a trend from positive to negative capacitance because of the injection of electrons from the Fluorine doped tin oxide (FTO) electrode into TiO2. Materials 2015-01-19 8 1 Article 10.3390/ma8010355 355 367 1996-1944 2015-01-19 doi: 10.3390/ma8010355 M. Atif W. Farooq Amanullah Fatehmulla M. Aslam Syed Ali http://www.mdpi.com/1996-1944/8/1/339 The performance of advance photocatalytic degradation of 4-chlorophenoxyacetic acid (4-CPA) strongly depends on photocatalyst dosage, initial concentration and initial pH. In the present study, a simple response surface methodology (RSM) was applied to investigate the interaction between these three independent factors. Thus, the photocatalytic degradation of 4-CPA in aqueous medium assisted by ultraviolet-active ZnO photocatalyst was systematically investigated. This study aims to determine the optimum processing parameters to maximize 4-CPA degradation. Based on the results obtained, it was found that a maximum of 91% of 4-CPA was successfully degraded under optimal conditions (0.02 g ZnO dosage, 20.00 mg/L of 4-CPA and pH 7.71). All the experimental data showed good agreement with the predicted results obtained from statistical analysis. Materials 2015-01-19 8 1 Article 10.3390/ma8010339 339 354 1996-1944 2015-01-19 doi: 10.3390/ma8010339 Kian Lee Sharifah Hamid http://www.mdpi.com/1996-1944/8/1/317 In the present study polyelectrolyte complexes (PECs) based on new sulfadiazine-chitosan conjugates with sodium hyaluronate have been developed with potential use in treatment of burn wounds. The PECs were chemically characterized using Fourier Transform—Infrared Spectroscopy, Scanning Electon Microscopy and Near Infrared Chemical Imaging Technique. The swelling behavior and in vitro sulfadiazine release were also investigated. The antimicrobial activity was evaluated towards three bacterial strains: Escherichia coli, Listeria monocytogenes and Salmonella thyphymurium. The developed PECs demonstrated their antimicrobial efficiency against tested bacterial strains, the PECs containing sulfadiazine-modified chitosan being more active than PECs containing unmodified chitosan. Materials 2015-01-16 8 1 Article 10.3390/ma8010317 317 338 1996-1944 2015-01-16 doi: 10.3390/ma8010317 Raluca Dumitriu Lenuta Profire Loredana Nita Oana Dragostin Nicolae Ghetu Dragoș Pieptu Cornelia Vasile http://www.mdpi.com/1996-1944/8/1/302 Evaluation of the mechanical properties of arterial wall components is necessary for establishing a precise mechanical model applicable in various physiological and pathological conditions, such as remodeling. In this contribution, a new approach for the evaluation of the mechanical properties of aortic media accounting for the lamellar structure is proposed. We assumed aortic media to be composed of two sets of concentric layers, namely sheets of elastin (Layer I) and interstitial layers composed of mostly collagen bundles, fine elastic fibers and smooth muscle cells (Layer II). Biaxial mechanical tests were carried out on human thoracic aortic samples, and histological staining was performed to distinguish wall lamellae for determining the dimensions of the layers. A neo-Hookean strain energy function (SEF) for Layer I and a four-parameter exponential SEF for Layer II were allocated. Nonlinear regression was used to find the material parameters of the proposed microstructural model based on experimental data. The non-linear behavior of media layers confirmed the higher contribution of elastic tissue in lower strains and the gradual engagement of collagen fibers. The resulting model determines the nonlinear anisotropic behavior of aortic media through the lamellar microstructure and can be assistive in the study of wall remodeling due to alterations in lamellar structure during pathological conditions and aging. Materials 2015-01-16 8 1 Article 10.3390/ma8010302 302 316 1996-1944 2015-01-16 doi: 10.3390/ma8010302 Hadi Taghizadeh Mohammad Tafazzoli-Shadpour Mohammad Shadmehr Nasser Fatouraee http://www.mdpi.com/1996-1944/8/1/285 In the current work, the evolutions of grain and dislocation microstructures are investigated on the basis of plane strain tension and simple shear tests for an interstitial free steel (DC06) and a 6000 series aluminum alloy (AA6016-T4). Both materials are commonly-used materials in the automobile industry. The focus of this contribution is on the characterization and comparison of the microstructure formation in DC06 and AA6016-T4. Our observations shed light on the active mechanisms at the micro scale governing the macroscopic response. This knowledge is of great importance to understand the physical deformation mechanisms, allowing the control and design of new, tailor-made materials with the desired material behavior. Materials 2015-01-15 8 1 Article 10.3390/ma8010285 285 301 1996-1944 2015-01-15 doi: 10.3390/ma8010285 Gregory Gerstein Benjamin Klusemann Swantje Bargmann Mirko Schaper http://www.mdpi.com/1996-1944/8/1/270 A series of esters of 2,3,6,7-tetrakis(hexyloxy)dibenzo[a,c]phenazine-11-carboxylic acid was prepared in order to probe the effects of the ester groups on the liquid crystalline behavior. These compounds exhibit columnar hexagonal phases over broad temperature ranges. Variations in chain length, branching, terminal groups, and the presence of cyclic groups were found to modify transition temperatures without substantially destabilizing the mesophase range. Materials 2015-01-14 8 1 Article 10.3390/ma8010270 270 284 1996-1944 2015-01-14 doi: 10.3390/ma8010270 Kevin Bozek Kuan Ho Tom Saint-Martin Panos Argyropoulos Vance Williams http://www.mdpi.com/1996-1944/8/1/251 In this study, the ability of lithium nitrite and amino alcohol inhibitors to provide corrosion protection to reinforcing steel was investigated. Two types of specimens—reinforcing steel and a reinforced concrete prism that were exposed to chloride ion levels resembling the chloride attack environment—were prepared. An autoclave accelerated corrosion test was then conducted. The variables tested included the chloride-ion concentration and molar ratios of anti-corrosion ingredients in a CaOH2-saturated aqueous solution that simulated a cement-pore solution. A concentration of 25% was used for the lithium nitrite inhibitor LiNO2, and an 80% solution of dimethyl ethanolamine ((CH3)2NCH2CH2OH, hereinafter DMEA) was used for the amino alcohol inhibitor. The test results indicated that the lithium nitrite inhibitor displayed anti-corrosion properties at a molar ratio of inhibitor of ≥0.6; the amino alcohol inhibitor also displayed anti-corrosion properties at molar ratios of inhibitor greater than approximately 0.3. Materials 2015-01-14 8 1 Article 10.3390/ma8010251 251 269 1996-1944 2015-01-14 doi: 10.3390/ma8010251 Han-Seung Lee Hwa-Sung Ryu Won-Jun Park Mohamed Ismail http://www.mdpi.com/1996-1944/8/1/231 Triton X-100 is one of the most widely-applied man-made non-ionic surfactants. This detergent can hardly be degraded by biological treatment. Hence, a more efficient degradation method is indispensable for the total mineralization of this pollutant. Application of heterogeneous photocatalysis based on a TiO2 suspension is a possible solution. Its efficiency may be improved by the addition of various reagents. We have thoroughly examined the photocatalytic degradation of Triton X-100 under various circumstances. For comparison, the efficiencies of ozonation and treatment with peroxydisulfate were also determined under the same conditions. Besides, the combination of these advanced oxidation procedures (AOPs) were also studied. The mineralization of this surfactant was monitored by following the TOC and pH values, as well as the absorption and emission spectra of the reaction mixture. An ultra-high-performance liquid chromatography (UHPLC) method was developed and optimized for monitoring the degradation of Triton X-100. Intermediates were also detected by GC-MS analysis and followed during the photocatalysis, contributing to the elucidation of the degradation mechanism. This non-ionic surfactant could be efficiently degraded by TiO2-mediated heterogeneous photocatalysis. However, surprisingly, its combination with the AOPs applied in this study did not enhance the rate of the mineralization. Moreover, the presence of persulfate hindered the photocatalytic degradation. Materials 2015-01-14 8 1 Article 10.3390/ma8010231 231 250 1996-1944 2015-01-14 doi: 10.3390/ma8010231 Péter Hegedűs Erzsébet Szabó-Bárdos Ottó Horváth Krisztián Horváth Péter Hajós http://www.mdpi.com/1996-1944/8/1/216 Nanoscale micelles as an effective drug delivery system have attracted increasing interest in malignancy therapy. The present study reported the construction of the cholesterol-enhanced doxorubicin (DOX)-loaded poly(D-lactide)-based micelle (CDM/DOX), poly(L-lactide)-based micelle (CLM/DOX), and stereocomplex micelle (CSCM/DOX) from the equimolar enantiomeric 4-armed poly(ethylene glycol)–polylactide copolymers in aqueous condition. Compared with CDM/DOX and CLM/DOX, CSCM/DOX showed the smallest hydrodynamic size of 96 ± 4.8 nm and the slowest DOX release. The DOX-loaded micelles exhibited a weaker DOX fluorescence inside mouse renal carcinoma cells (i.e., RenCa cells) compared to free DOX·HCl, probably because of a slower DOX release. More importantly, all the DOX-loaded micelles, especially CSCM/DOX, exhibited the excellent antiproliferative efficacy that was equal to or even better than free DOX·HCl toward RenCa cells attributed to their successful internalization. Furthermore, all of the DOX-loaded micelles exhibited the satisfactory hemocompatibility compared to free DOX·HCl, indicating the great potential for systemic chemotherapy through intravenous injection. Materials 2015-01-12 8 1 Article 10.3390/ma8010216 216 230 1996-1944 2015-01-12 doi: 10.3390/ma8010216 Jixue Wang Weiguo Xu Jianxun Ding Shengfan Lu Xiaoqing Wang Chunxi Wang Xuesi Chen http://www.mdpi.com/1996-1944/8/1/205 This work presents the nanoindentation and XPS results of a newly-developed biomaterial of titanium TNZ alloy after different surface treatments. The investigations were performed on the samples AR (as received), EP (after a standard electropolishing) and MEP (after magnetoelectropolishing). The electropolishing processes, both EP and MEP, were conducted in the same proprietary electrolyte based on concentrated sulfuric acid. The mechanical properties of the titanium TNZ alloy biomaterial demonstrated an evident dependence on the surface treatment method, with MEP samples revealing extremely different behavior and mechanical properties. The reason for that different behavior appeared to be influenced by the surface film composition, as revealed by XPS study results displayed in this work. The increase of niobium and zirconium in the surface film of the same titanium TNZ alloy after magnetoelectropolishing MEP treatment is meaningful and especially advantageous considering the application of this alloy as a biomaterial. Materials 2015-01-08 8 1 Article 10.3390/ma8010205 205 215 1996-1944 2015-01-08 doi: 10.3390/ma8010205 Tadeusz Hryniewicz Krzysztof Rokosz Ryszard Rokicki Frédéric Prima http://www.mdpi.com/1996-1944/8/1/193 The editors of Materials would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...] Materials 2015-01-07 8 1 Editorial 10.3390/ma8010193 193 204 1996-1944 2015-01-07 doi: 10.3390/ma8010193 Materials Editorial Office http://www.mdpi.com/1996-1944/8/1/181 Scrap tires continue to be a major source of waste due to the lack of valuable and effective disposal routes. A viable solution to this problem is to recycle crumb rubber (CR)—a granulated material derived from scrap tires—and use it to develop other valuable products. Herein we report the fabrication and characterization of CR-modified coatings with anticorrosive properties on metal substrates. By varying the particle size and concentration of CR, we have determined the coating composition that offers the highest level of erosion protection. Images from a scanning electron microscope (SEM) reveal that CR is homogenously dispersed in the coating, especially when fine particles are used. As the concentration of CR increases, the hardness of the coating decreases as a result of the elastic properties of CR. More importantly, the erosion rate of the coating decreases due to increased ductility. Following Potentiodynamic tests, the utilization of these coatings proved to be beneficial as they showed good protection against aqueous corrosion when tested in 0.5 M NaCl solution. Our newly developed coatings offer an incentive to recycling CR and open up a safe and sustainable route to the disposal of scrap tires. Materials 2015-01-06 8 1 Article 10.3390/ma8010181 181 192 1996-1944 2015-01-06 doi: 10.3390/ma8010181 Nasser Al-Aqeeli http://www.mdpi.com/1996-1944/8/1/162 In the present work, the influence of a gold nanoparticle's shape was investigated on the commercially available Evonik Aeroxide P25. By the variation of specific synthesis parameters, three differently shaped Au nanoparticles were synthetized and deposited on the surface of the chosen commercial titania. The nanoparticles and their composites' morphological and structural details were evaluated, applying different techniques such as Diffuse Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). The influence of the Au nanoparticles' shape was discussed by evaluating their photocatalytic efficiency on phenol and oxalic acid degradation and by investigating the H2 production efficacy of the selected composites. Major differences in their photocatalytic performance depending on the shape of the deposited noble metal were evidenced. Materials 2014-12-31 8 1 Article 10.3390/ma8010162 162 180 1996-1944 2014-12-31 doi: 10.3390/ma8010162 Zsolt Pap Zsejke Tóth Virginia Danciu Lucian Baia Gábor Kovács http://www.mdpi.com/1996-1944/8/1/149 The use of templates to assist and possess a control over the synthesis of nanomaterials has been an attractive option to achieve this goal. Here we have used sodium dodecyl sulfate (SDS) to act as a template for the low temperature synthesis of cobalt oxide (Co3O4) nanostructures. The use of SDS has led to tune the morphology, and the product was in the form of "cotton-like" nanostructures instead of connected nanowires. Moreover, the variation of the amount of the SDS used was found to affect the charge transfer process in the Co3O4. Using Co3O4 synthesized using the SDS for sensing of cholesterol was investigated. The use of the Co3O4 synthesized using the SDS was found to yield an improved cholesterol biosensor compared to Co3O4 synthesized without the SDS. The improvement of the cholesterol sensing properties upon using the SDS as a template was manifested in increasing the sensitivity and the dynamic range of detection. The results achieved in this study indicate the potential of using template assisted synthesis of nanomaterials in improving some properties, e.g., cholesterol sensing. Materials 2014-12-31 8 1 Article 10.3390/ma8010149 149 161 1996-1944 2014-12-31 doi: 10.3390/ma8010149 Sami Elhag Zafar Ibupoto Omer Nour Magnus Willander http://www.mdpi.com/1996-1944/8/1/137 The use of mixtures of synthetic and natural polymers is a potential option to reduce the pollution by plastic waste. In this work, the method for the chemical modification of chitosan with poly(lactic acid) was developed; then, the preparation of films of blends of polyethylene and chitosan-poly(lactic acid) produced by an extrusion method using polyethylene-graft maleic anhydride as a compatibilizer. It was possible to obtain films with a maximum content of 20 wt% and 30 wt%, chitosan, with and without compatibilizer, respectively. Scanning electron microscope (SEM) analysis showed a homogeneous surface on all films. The addition of the compatibilizer had a significant effect on the mechanical properties of the films, such as an increase in Young's modulus and a decrease in the elongation at break; additionally, the compatibilizer promotes thermal degradation in a single step and gives the film a slight increase in thermal resistance. These results are attributed to an improved interaction in the interface of polyethylene and chitosan-poly(lactic acid), promoted by the compatibilizer. Materials 2014-12-30 8 1 Article 10.3390/ma8010137 137 148 1996-1944 2014-12-30 doi: 10.3390/ma8010137 Jesús Quiroz-Castillo Dora Rodríguez-Félix Heriberto Grijalva-Monteverde Lauren Lizárraga-Laborín María Castillo-Ortega Teresa del Castillo-Castro Francisco Rodríguez-Félix Pedro Herrera-Franco http://www.mdpi.com/1996-1944/8/1/117 This paper creates a bi-directional prediction model to predict the performance of carbon fiber and the productive parameters based on a support vector machine (SVM) and improved particle swarm optimization (IPSO) algorithm (SVM-IPSO). In the SVM, it is crucial to select the parameters that have an important impact on the performance of prediction. The IPSO is proposed to optimize them, and then the SVM-IPSO model is applied to the bi-directional prediction of carbon fiber production. The predictive accuracy of SVM is mainly dependent on its parameters, and IPSO is thus exploited to seek the optimal parameters for SVM in order to improve its prediction capability. Inspired by a cell communication mechanism, we propose IPSO by incorporating information of the global best solution into the search strategy to improve exploitation, and we employ IPSO to establish the bi-directional prediction model: in the direction of the forward prediction, we consider productive parameters as input and property indexes as output; in the direction of the backward prediction, we consider property indexes as input and productive parameters as output, and in this case, the model becomes a scheme design for novel style carbon fibers. The results from a set of the experimental data show that the proposed model can outperform the radial basis function neural network (RNN), the basic particle swarm optimization (PSO) method and the hybrid approach of genetic algorithm and improved particle swarm optimization (GA-IPSO) method in most of the experiments. In other words, simulation results demonstrate the effectiveness and advantages of the SVM-IPSO model in dealing with the problem of forecasting. Materials 2014-12-30 8 1 Article 10.3390/ma8010117 117 136 1996-1944 2014-12-30 doi: 10.3390/ma8010117 Chuncai Xiao Kuangrong Hao Yongsheng Ding http://www.mdpi.com/1996-1944/8/1/96 C.I. Natural Red 4 dye, also known as carmine or cochineal, was adsorbed onto the surface of spongin-based fibrous skeleton of Hippospongia communis marine demosponge for the first time. The influence of the initial concentration of dye, the contact time, and the pH of the solution on the adsorption process was investigated. The results presented here confirm the effectiveness of the proposed method for developing a novel dye/biopolymer hybrid material. The kinetics of the adsorption of carmine onto a marine sponge were also determined. The experimental data correspond directly to a pseudo-second-order model for adsorption kinetics (r2 = 0.979–0.999). The hybrid product was subjected to various types of analysis (FT-IR, Raman, 13C CP/MAS NMR, XPS) to investigate the nature of the interactions between the spongin (adsorbent) and the dye (the adsorbate). The dominant interactions between the dye and spongin were found to be hydrogen bonds and electrostatic effects. Combining the dye with a spongin support resulted with a novel hybrid material that is potentially attractive for bioactive applications and drug delivery systems. Materials 2014-12-29 8 1 Article 10.3390/ma8010096 96 116 1996-1944 2014-12-29 doi: 10.3390/ma8010096 Małgorzata Norman Przemysław Bartczak Jakub Zdarta Włodzimierz Tylus Tomasz Szatkowski Allison Stelling Hermann Ehrlich Teofil Jesionowski http://www.mdpi.com/1996-1944/8/1/72 Water-assisted, or more generally liquid-mediated, melt compounding of nanocomposites is basically a combination of solution-assisted and traditional melt mixing methods. It is an emerging technique to overcome several disadvantages of the above two. Water or aqueous liquids with additives, do not work merely as temporary carrier materials of suitable nanofillers. During batchwise and continuous compounding, these liquids are fully or partly evaporated. In the latter case, the residual liquid is working as a plasticizer. This processing technique contributes to a better dispersion of the nanofillers and affects markedly the morphology and properties of the resulting nanocomposites. A survey is given below on the present praxis and possible future developments of water-assisted melt mixing techniques for the production of thermoplastic nanocomposites. Materials 2014-12-29 8 1 Review 10.3390/ma8010072 72 95 1996-1944 2014-12-29 doi: 10.3390/ma8010072 József Karger-Kocsis Ákos Kmetty László Lendvai Stavros Drakopoulos Tamás Bárány http://www.mdpi.com/1996-1944/8/1/57 A new design and analysis of a wide-band double-negative metamaterial, considering a frequency range of 0.5 to 7 GHz, is presented in this paper. Four different unit cells with varying design parameters are analyzed to evaluate the effects of the unit-cell size on the resonance frequencies of the metamaterial. Moreover, open and interconnected 2 × 2 array structures of unit cells are analyzed. The finite-difference time-domain (FDTD) method, based on the Computer Simulation Technology (CST) Microwave Studio, is utilized in the majority of this investigation. The experimental portion of the study was performed in a semi-anechoic chamber. Good agreement is observed between the simulated and measured S parameters of the developed unit cell and array. The designed unit cell exhibits negative permittivity and permeability simultaneously at S-band (2.95 GHz to 4.00 GHz) microwave frequencies. In addition, the designed unit cell can also operate as a double-negative medium throughout the C band (4.00 GHz to 4.95 GHz and 5.00 GHz to 5.57 GHz). At a number of other frequencies, it exhibits a single negative value. The two array configurations cause a slight shift in the resonance frequencies of the metamaterial and hence lead to a slight shift of the single- and double-negative frequency ranges of the metamaterial. Materials 2014-12-25 8 1 Article 10.3390/ma8010057 57 71 1996-1944 2014-12-25 doi: 10.3390/ma8010057 Md Hossain Mohammad Faruque Mohammad Islam Mohammad Ullah http://www.mdpi.com/1996-1944/8/1/42 The electronic structure and optical absorption spectra of polymer APFO3, [70]PCBM/APFO3 and [60]PCBM/APFO3, were studied with density functional theory (DFT), and the vertical excitation energies were calculated within the framework of the time-dependent DFT (TD-DFT). Visualized charge difference density analysis can be used to label the charge density redistribution for individual fullerene and fullerene/polymer complexes. The results of current work indicate that there is a difference between [60]PCBM and [70]PCBM, and a new charge transfer process is observed. Meanwhile, for the fullerene/polymer complex, all calculations of the twenty excited states were analyzed to reveal all possible charge transfer processes in depth. We also estimated the electronic coupling matrix, reorganization and Gibbs free energy to further calculate the rates of the charge transfer and the recombination. Our results give a clear picture of the structure, absorption spectra, charge transfer (CT) process and its influencing factors, and provide a theoretical guideline for designing further photoactive layers of solar cells. Materials 2014-12-25 8 1 Article 10.3390/ma8010042 42 56 1996-1944 2014-12-25 doi: 10.3390/ma8010042 Yuanzuo Li Dawei Qi Peng Song Fengcai Ma http://www.mdpi.com/1996-1944/8/1/31 N–F-co-embedded titania (N–F–TiO2) photocatalysts with varying N:F ratios were synthesized and tested for their ability to photocatalyze the degradation of pollutants present at indoor air levels using visible light. The synthesis was achieved using a solvothermal process with tetrabutyl titanate, urea and ammonium fluoride as sources of Ti, N and F, respectively. Three selected volatile organic compounds (toluene, ethyl benzene and o-xylene) were selected as the test pollutants. The prepared composites were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Ultra-violet (UV)-visible spectroscopy. The photocatalytic degradation efficiencies of N–F–TiO2 composites were higher than those obtained using pure TiO2 and N–TiO2. Moreover, these efficiencies increased as the N:F ratio decreased from sixteen to eight, then decreased as it dropped further to three, indicating the presence of an optimal N:F ratio. Meanwhile, as retention time decreased from 12.4 to 0.62 s, the average photocatalytic efficiencies decreased from 65.4% to 21.7%, 91.5% to 37.8% and 95.8% to 44.7% for toluene, ethyl benzene and o-xylene, respectively. In contrast, the photocatalytic reaction rates increased as retention time decreased. In consideration of all of these factors, under optimized operational conditions, the prepared N–F–TiO2 composites could be utilized for the degradation of target pollutants at indoor air levels using visible light. Materials 2014-12-24 8 1 Article 10.3390/ma8010031 31 41 1996-1944 2014-12-24 doi: 10.3390/ma8010031 Seung-Ho Shin Ho-Hwan Chun Wan-Kuen Jo http://www.mdpi.com/1996-1944/8/1/16 Novel photocatalysts Gd2FeSbO7, Gd2InSbO7 and Gd2YSbO7 were synthesized by the solid state reaction method for the first time. A comparative study about the structural and photocatalytic properties of Gd2MSbO7 (M = Fe, In, Y) was reported. The results showed that Gd2FeSbO7, Gd2InSbO7 and Gd2YSbO7 crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. The lattice parameter a for Gd2FeSbO7, Gd2InSbO7 or Gd2YSbO7 was 10.276026 Å, 10.449546 Å or 10.653651 Å. The band gap of Gd2FeSbO7, Gd2InSbO7 or Gd2YSbO7 was estimated to be 2.151 eV, 2.897 eV or 2.396 eV. For the photocatalytic water-splitting reaction, H2 or O2 evolution was observed from pure water with Gd2FeSbO7, Gd2InSbO7 or Gd2YSbO7 as catalyst under visible light irradiation (wavelength > 420 nm). Moreover, H2 or O2 also spilt by using Gd2FeSbO7, Gd2InSbO7 or Gd2YSbO7 as catalyst from CH3OH/H2O or AgNO3/H2O solutions under visible light irradiation (λ > 420 nm). Gd2FeSbO7 showed the highest activity compared with Gd2InSbO7 or Gd2YSbO7. At the same time, Gd2InSbO7 showed higher activity compared with Gd2YSbO7. The photocatalytic activities were further improved under visible light irradiation with Gd2FeSbO7, Gd2InSbO7 or Gd2YSbO7 being loaded by Pt, NiO or RuO2. The effect of Pt was better than that of NiO or RuO2 for improving the photocatalytic activity of Gd2FeSbO7, Gd2InSbO7 or Gd2YSbO7. Materials 2014-12-24 8 1 Article 10.3390/ma8010016 16 30 1996-1944 2014-12-24 doi: 10.3390/ma8010016 Jingfei Luan Yanyan Li http://www.mdpi.com/1996-1944/8/1/1 Rammed earth (RE) is attracting renewed interest throughout the world thanks to its "green" characteristics in the context of sustainable building. In this study, the ageing effects on RE material are studied on the walls which have been constructed and exposed for 22 years to natural weathering. First, mechanical characteristics of the "old" walls were determined by two approaches: in-situ dynamic measurements on the walls; laboratory tests on specimens which had been cut from the walls. Then, the walls' soil was recycled and reused for manufacturing of new specimens which represented the initial state. Comparison between the compressive strength, the Young modulus of the walls after 22 years on site and that of the initial state enables to assess the ageing of the studied walls. Materials 2014-12-23 8 1 Communication 10.3390/ma8010001 1 15 1996-1944 2014-12-23 doi: 10.3390/ma8010001 Quoc-Bao Bui Jean-Claude Morel http://www.mdpi.com/1996-1944/7/12/8197 Evidence is provided here that a class of materials with dielectric constants greater than 105 at low frequency (<10−2 Hz), herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials. Specifically it is demonstrated that high surface area alumina powders, loaded to the incipient wetness point with a solution of boric acid dissolved in water, have dielectric constants, near 0 Hz, greater than 4 × 108 in all cases, a remarkable increase over the best dielectric constants previously measured for energy storage capabilities, ca. 1 × 104. It is postulated that any porous, electrically insulating material (e.g., high surface area powders of silica, titania, etc.), filled with a liquid containing a high concentration of ionic species will potentially be an SDM. Capacitors created with the first generated SDM dielectrics (alumina with boric acid solution), herein called New Paradigm Super (NPS) capacitors display typical electrostatic capacitive behavior, such as increasing capacitance with decreasing thickness, and can be cycled, but are limited to a maximum effective operating voltage of about 0.8 V. A simple theory is presented: Water containing relatively high concentrations of dissolved ions saturates all, or virtually all, the pores (average diameter 500 Å) of the alumina. In an applied field the positive ionic species migrate to the cathode end, and the negative ions to the anode end of each drop. This creates giant dipoles with high charge, hence leading to high dielectric constant behavior. At about 0.8 V, water begins to break down, creating enough ionic species to "short" the individual water droplets. Potentially NPS capacitor stacks can surpass "supercapacitors" in volumetric energy density. Materials 2014-12-22 7 12 Article 10.3390/ma7128197 8197 8212 1996-1944 2014-12-22 doi: 10.3390/ma7128197 Samuel Fromille Jonathan Phillips http://www.mdpi.com/1996-1944/7/12/8189 We report on the efficiency improvement of organic solar cells (OPVs) based on the low energy gap polyfluorene derivative, APFO-3, and the soluble C60 fullerene PCBM, upon addition of a residual amount of poly (4-vinylpyridine) (PVP). We find that the addition of 1% by weight of PVP with respect to the APFO-3 content leads to an increase of efficiency from 2.4% to 2.9%. Modifications in the phase separation details of the active layer were investigated as a possible origin of the efficiency increase. At high concentrations of PVP, the blend morphology is radically altered as observed by Atomic Force Microscopy. Although the use of low molecular weight additives is a routine method to improve OPVs efficiency, this report shows that inert polymers, in terms of optical and charge transport properties, may also improve the performance of polymer-based solar cells. Materials 2014-12-22 7 12 Communication 10.3390/ma7128189 8189 8196 1996-1944 2014-12-22 doi: 10.3390/ma7128189 Rita Rodrigues Rui Meira Quirina Ferreira Ana Charas Jorge Morgado http://www.mdpi.com/1996-1944/7/12/8168 Titanium (Ti) and its alloys may be processed via advanced powder manufacturing routes such as additive layer manufacturing (or 3D printing) or metal injection moulding. This field is receiving increased attention from various manufacturing sectors including the medical devices sector. It is possible that advanced manufacturing techniques could replace the machining or casting of metal alloys in the manufacture of devices because of associated advantages that include design flexibility, reduced processing costs, reduced waste, and the opportunity to more easily manufacture complex or custom-shaped implants. The emerging advanced manufacturing approaches of metal injection moulding and additive layer manufacturing are receiving particular attention from the implant fabrication industry because they could overcome some of the difficulties associated with traditional implant fabrication techniques such as titanium casting. Using advanced manufacturing, it is also possible to produce more complex porous structures with improved mechanical performance, potentially matching the modulus of elasticity of local bone. While the economic and engineering potential of advanced manufacturing for the manufacture of musculo-skeletal implants is therefore clear, the impact on the biocompatibility of the materials has been less investigated. In this review, the capabilities of advanced powder manufacturing routes in producing components that are suitable for biomedical implant applications are assessed with emphasis placed on surface finishes and porous structures. Given that biocompatibility and host bone response are critical determinants of clinical performance, published studies of in vitro and in vivo research have been considered carefully. The review concludes with a future outlook on advanced Ti production for biomedical implants using powder metallurgy. Materials 2014-12-19 7 12 Review 10.3390/ma7128168 8168 8188 1996-1944 2014-12-19 doi: 10.3390/ma7128168 Alfred Sidambe http://www.mdpi.com/1996-1944/7/12/8151 Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film. Materials 2014-12-19 7 12 Article 10.3390/ma7128151 8151 8167 1996-1944 2014-12-19 doi: 10.3390/ma7128151 Sonia Ferreira Ana Conde María Arenas Luis Rocha Alexandre Velhinho http://www.mdpi.com/1996-1944/7/12/8131 The effect of chemical treatment of hemp hurds slices in three solutions (EDTA (Ethylenediaminetetraacetic acid), NaOH and Ca(OH)2) on the properties of natural material was discussed in this paper. Changes in the morphology, chemical composition and structure as well as thermal stability of hemp hurds before and after their modification were investigated by using FTIR (Fourier transform infrared spectroscopy), XRD (X-ray powder diffraction analysis) and TG (thermogravimetry)/DSC (differential scanning calorimetry). Size exclusion chromatography (SEC) measurements were used for determination of degree of cellulose polymerization of hemp hurd samples. Chemical modification is related to the partial removal of non-cellulosic components of lignin, hemicellulose and pectin as well as waxes from the surface of hemp hurd slices. Another effect of the chemical treatment applied is connected with increasing the crystallinity index of cellulose determined by FTIR and XRD methods. Decrease in degree of cellulose polymerization and polydispersity index in chemically modified hemp hurds compared to the original sample was observed. Increase in thermal stability of treated hemp hurd was found. The most significant changes were observed in alkaline treated hemp hurds by NaOH. Materials 2014-12-17 7 12 Article 10.3390/ma7128131 8131 8150 1996-1944 2014-12-17 doi: 10.3390/ma7128131 Nadezda Stevulova Julia Cigasova Adriana Estokova Eva Terpakova Anton Geffert Frantisek Kacik Eva Singovszka Marian Holub