text: Micromachines http://www.mdpi.com/journal/micromachines Latest open access articles published in Micromachines at http://www.mdpi.com/journal/micromachines http://www.mdpi.com/2072-666X/6/3/396 This paper presents a transdermal power transfer device for the application of implantable devices or systems. The device mainly consists of plug and socket. The power transfer process can be started after inserting the plug into the socket with an applied potential on the plug. In order to improve the maneuverability and reliability of device during power transfer process, the metal net with mesh structure were added as a part of the socket to serve as intermediate electrical connection layer. The socket was encapsulated by polydimethylsiloxane (PDMS) with good biocompatibility and flexibility. Two stainless steel hollow needles placed in the same plane acted as the insertion part of the needle plug, and Parylene C thin films were deposited on needles to serve as insulation layers. At last, the properties of the transdermal power transfer device were tested. The average contact resistance between needle and metal mesh was 0.454 Ω after 50 random insertions, which showed good electrical connection. After NiMH (nickel-metal hydride) batteries were recharged for 10 min with current up to 200 mA, the caused resistive heat was less than 0.6 °C, which also demonstrated the low charging temperature and was suitable for charging implantable devices. Micromachines 2015-03-23 6 3 Article 10.3390/mi6030396 396 408 2072-666X 2015-03-23 doi: 10.3390/mi6030396 Jing-Quan Liu Yue-Feng Rui Xiao-Yang Kang Bin Yang Xiang Chen Chun-Sheng Yang http://www.mdpi.com/2072-666X/6/3/390 This paper presents a reflection-type phase shifter (RTPS) at W-band in a 0.13 µm complementary metal oxide semiconductor (CMOS) process. The RTPS is composed of a 90° hybrid coupler and two identical reflection loads. Lumped-distributed element transmission line is introduced in the 90° hybrid coupler to reduce the chip size. Series inductor-capacitor (LC) resonators are used as the reflective loads and parallel inductors are deployed to reduce insertion loss variation. By cascading two-stage RTPS, 90° phase shifting range and 10.5 dB insertion loss with 1 dB variations from 80 GHz to 90 GHz are achieved. An impressive 0.1 dB variation is obtained at 86 GHz. Micromachines 2015-03-23 6 3 Article 10.3390/mi6030390 390 395 2072-666X 2015-03-23 doi: 10.3390/mi6030390 Xiao-Dong Deng Yihu Li Wen Wu Yong-Zhong Xiong http://www.mdpi.com/2072-666X/6/3/375 This paper proposes the design of a weighted-rotor energy harvester (WREH) in which the oscillation is caused by the periodic change of the tangential component of gravity, to harvest kinetic energy from a rotating wheel. When a WREH is designed with a suitable characteristic length, the rotor's natural frequency changes according to the wheel rotation speed and the rotor oscillates at a wide angle and high angular velocity to generate a large amount of power. The magnetic disk is designed according to an optimized circular Halbach array. The optimized circular Halbach array magnetic disk provides the largest induced EMF for different sector-angle ratios for the same magnetic disk volume. This study examined the output voltage and power by considering the constant and accelerating plate-rotation speeds, respectively. This paper discusses the effects of the angular acceleration speed of a rotating wheel corresponding to the dynamic behaviors of a weighted rotor. The average output power is 399 to 535 microwatts at plate-rotation speeds from 300 to 500 rpm, enabling the WREH to be a suitable power source for a tire-pressure monitoring system. Micromachines 2015-03-23 6 3 Article 10.3390/mi6030375 375 389 2072-666X 2015-03-23 doi: 10.3390/mi6030375 Yu-Jen Wang Yu-Ti Hao Hao-Yu Lin http://www.mdpi.com/2072-666X/6/3/364 We developed a confined microfluidic cell culture system with a bottom plate made of a microscopic slide with planar platinum sensors for the measurement of acidification, oxygen consumption, and cell adhesion. The slides were commercial slides with indium tin oxide (ITO) plating or were prepared from platinum sputtering (100 nm) onto a 10-nm titanium adhesion layer. Direct processing of the sensor structures (approximately three minutes per chip) by an ultrashort pulse laser facilitated the production of the prototypes. pH-sensitive areas were produced by the sputtering of 60-nm Si3N4 through a simple mask made from a circuit board material. The system body and polydimethylsiloxane (PDMS) molding forms for the microfluidic structures were manufactured by micromilling using a printed circuit board (PCB) milling machine for circuit boards. The microfluidic structure was finally imprinted in PDMS. Our approach avoided the use of photolithographic techniques and enabled fast and cost-efficient prototyping of the systems. Alternatively, the direct production of metallic, ceramic or polymeric molding tools was tested. The use of ultrashort pulse lasers improved the precision of the structures and avoided any contact of the final structures with toxic chemicals and possible adverse effects for the cell culture in lab-on-a-chip systems. Micromachines 2015-03-23 6 3 Article 10.3390/mi6030364 364 374 2072-666X 2015-03-23 doi: 10.3390/mi6030364 Sebastian Bonk Paul Oldorf Rigo Peters Werner Baumann Jan Gimsa http://www.mdpi.com/2072-666X/6/3/347 Indoor positioning in a multi-floor environment by using a smartphone is considered in this paper. The positioning accuracy and robustness of WiFi fingerprinting-based positioning are limited due to the unexpected variation of WiFi measurements between floors. On this basis, we propose a novel smartphone-based integrated WiFi/MEMS positioning algorithm based on the robust extended Kalman filter (EKF). The proposed algorithm first relies on the gait detection approach and quaternion algorithm to estimate the velocity and heading angles of the target. Second, the velocity and heading angles, together with the results of WiFi fingerprinting-based positioning, are considered as the input of the robust EKF for the sake of conducting two-dimensional (2D) positioning. Third, the proposed algorithm calculates the height of the target by using the real-time recorded barometer and geographic data. Finally, the experimental results show that the proposed algorithm achieves the positioning accuracy with root mean square errors (RMSEs) less than 1 m in an actual multi-floor environment. Micromachines 2015-03-03 6 3 Article 10.3390/mi6030347 347 363 2072-666X 2015-03-03 doi: 10.3390/mi6030347 Zengshan Tian Xin Fang Mu Zhou Lingxia Li http://www.mdpi.com/2072-666X/6/3/330 Tissue engineering is viewed as a promising option for long-term repair of cartilage lesions, but current engineered cartilage constructs fail to match the mechanical properties of native tissue. The extracellular matrix of adult human articular cartilage contains highly organized collagen fibrils that enhance the mechanical properties of the tissue. Unlike articular cartilage, mesenchymal stem cell (MSC) based tissue engineered cartilage constructs lack this oriented microstructure and therefore display much lower mechanical strength. The goal of this study was to investigate the effect of biomolecular gradients and shear stress on MSCs undergoing chondrogenesis within a microfluidic device. Via poly(dimethyl siloxane) soft-lithography, microfluidic devices containing a gradient generator were created. Human MSCs were seeded within these chambers and exposed to flow-based transforming growth factor β1 (TGF-β1) gradients. When the MSCs were both confluent and exposed to shear stress, the cells aligned along the flow direction. Exposure to TGF-β1 gradients led to chondrogenesis of MSCs, indicated by positive type II collagen staining. These results, together with a previous study that showed that aligned MSCs produce aligned collagen, suggest that oriented cartilage tissue structures with superior mechanical properties can be obtained by aligning MSCs along the flow direction and exposing MSCs to chondrogenic gradients. Micromachines 2015-03-02 6 3 Article 10.3390/mi6030330 330 346 2072-666X 2015-03-02 doi: 10.3390/mi6030330 Alexander Rivera Harihara Baskaran http://www.mdpi.com/2072-666X/6/3/328 We have found three errors in our paper [1], and thus would like to make the following corrections to this paper:[...] Micromachines 2015-03-02 6 3 Correction 10.3390/mi6030328 328 329 2072-666X 2015-03-02 doi: 10.3390/mi6030328 Su Xu Yan Li Yifan Liu Jie Sun Hongwen Ren Shin-Tson Wu http://www.mdpi.com/2072-666X/6/3/312 The objective of this study is to develop and analyze a nonlinear suspended energy harvester (NSEH) that can be mounted on a rotating wheel. The device comprises a permanent magnet as a mass in the kinetic system, two springs, and two coil sets. The mass vibrates along the transverse direction because of the variations in gravitational force. This research establishes nonlinear vibration equations based on the resonance frequency variation of the energy harvester; these equations are used for analyzing the power generation and vibration of the harvester. The kinetic behaviors can be determined according to the stiffness in the two directions of the two suspended springs. Electromagnetic damping is examined to estimate the power output and effect of the kinematic behaviors on NSEH. The power output of the NSEH with a 52 Ω resistor connected in series ranged from approximately 30 to 4200 μW at wheel speeds that ranged from nearly 200 to 900 rpm. Micromachines 2015-02-27 6 3 Article 10.3390/mi6030312 312 327 2072-666X 2015-02-27 doi: 10.3390/mi6030312 Yu-Jen Wang Chung-De Chen Chung-Chih Lin Jui-Hsin Yu http://www.mdpi.com/2072-666X/6/3/291 Severely disabled people, like completely paralyzed persons either with tetraplegia or similar disabilities who cannot use their arms and hands, are often considered as a user group of Brain Computer Interfaces (BCI). In order to achieve high acceptance of the BCI by this user group and their supporters, the BCI system has to be integrated into their support infrastructure. Critical disadvantages of a BCI are the time consuming preparation of the user for the electroencephalography (EEG) measurements and the low information transfer rate of EEG based BCI. These disadvantages become apparent if a BCI is used to control complex devices. In this paper, a hybrid BCI is described that enables research for a Human Machine Interface (HMI) that is optimally adapted to requirements of the user and the tasks to be carried out. The solution is based on the integration of a Steady-state visual evoked potential (SSVEP)-BCI, an Event-related (de)-synchronization (ERD/ERS)-BCI, an eye tracker, an environmental observation camera, and a new EEG head cap for wearing comfort and easy preparation. The design of the new fast multimodal BCI (called sBCI) system is described and first test results, obtained in experiments with six healthy subjects, are presented. The sBCI concept may also become useful for healthy people in cases where a "hands-free" handling of devices is necessary. Micromachines 2015-02-27 6 3 Article 10.3390/mi6030291 291 311 2072-666X 2015-02-27 doi: 10.3390/mi6030291 Tatsiana Malechka Tobias Tetzel Ulrich Krebs Diana Feuser Axel Graeser http://www.mdpi.com/2072-666X/6/2/281 We investigated the aluminum nitride etching process for MEMS resonators. The process is based on Cl2/BCl3/Ar gas chemistry in inductively coupled plasma system. The hard mask of SiO2 is used. The etching rate, selectivity, sidewall angle, bottom surface roughness and microtrench are studied as a function of the gas flow rate, bias power and chamber pressure. The relations among those parameters are reported and theoretical analyses are given. By optimizing the etching parameters, the bottom surface roughness of 1.98 nm and the sidewall angle of 83° were achieved. This etching process can meet the manufacturing requirements of aluminum nitride MEMS resonator. Micromachines 2015-02-16 6 2 Article 10.3390/mi6020281 281 290 2072-666X 2015-02-16 doi: 10.3390/mi6020281 Jian Yang Chaowei Si Guowei Han Meng Zhang Liuhong Ma Yongmei Zhao Jin Ning http://www.mdpi.com/2072-666X/6/2/266 In this paper, a novel approach for processing the outputs signal of the microelectromechanical systems (MEMS) gyroscopes was presented to reduce the bias drift and noise. The principle for the noise reduction was presented, and an optimal Kalman filter (KF) was designed by a steady-state filter gain obtained from the analysis of KF observability. In particular, the true angular rate signal was directly modeled to obtain an optimal estimate and make a self-compensation for the gyroscope without needing other sensor's information, whether in static or dynamic condition. A linear fit equation that describes the relationship between the KF bandwidth and modeling parameter of true angular rate was derived from the analysis of KF frequency response. The test results indicated that the MEMS gyroscope having an ARW noise of 4.87°/h0.5 and a bias instability of 44.41°/h were reduced to 0.4°/h0.5 and 4.13°/h by the KF under a given bandwidth (10 Hz), respectively. The 1σ estimated error was reduced from 1.9°/s to 0.14°/s and 1.7°/s to 0.5°/s in the constant rate test and swing rate test, respectively. It also showed that the filtered angular rate signal could well reflect the dynamic characteristic of the input rate signal in dynamic conditions. The presented algorithm is proved to be effective at improving the measurement precision of the MEMS gyroscope. Micromachines 2015-02-16 6 2 Article 10.3390/mi6020266 266 280 2072-666X 2015-02-16 doi: 10.3390/mi6020266 Liang Xue Chengyu Jiang Lixin Wang Jieyu Liu Weizheng Yuan http://www.mdpi.com/2072-666X/6/2/252 In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask. Micromachines 2015-02-09 6 2 Article 10.3390/mi6020252 252 265 2072-666X 2015-02-09 doi: 10.3390/mi6020252 Harutaka Mekaru http://www.mdpi.com/2072-666X/6/2/239 In the past decade a large amount of analysis techniques have been scaled down to the microfluidic level. However, in many cases the necessary sample preparation, such as separation, mixing and concentration, remains to be performed off-chip. This represents a major hurdle for the introduction of miniaturized sample-in/answer-out systems, preventing the exploitation of microfluidic's potential for small, rapid and accurate diagnostic products. New flow engineering methods are required to address this hitherto insufficiently studied aspect. One microfluidic tool that can be used to miniaturize and integrate sample preparation procedures are microvortices. They have been successfully applied as microcentrifuges, mixers, particle separators, to name but a few. In this work, we utilize a novel corner structure at a sudden channel expansion of a microfluidic chip to enhance the formation of a microvortex. For a maximum area of the microvortex, both chip geometry and corner structure were optimized with a computational fluid dynamic (CFD) model. Fluorescent particle trace measurements with the optimized design prove that the corner structure increases the size of the vortex. Furthermore, vortices are induced by the corner structure at low flow rates while no recirculation is observed without a corner structure. Finally, successful separation of plasma from human blood was accomplished, demonstrating a potential application for clinical sample preparation. The extracted plasma was characterized by a flow cytometer and compared to plasma obtained from a standard benchtop centrifuge and from chips without a corner structure. Micromachines 2015-02-06 6 2 Article 10.3390/mi6020239 239 251 2072-666X 2015-02-06 doi: 10.3390/mi6020239 Anna Haller Andreas Spittler Lukas Brandhoff Helene Zirath Dietmar Puchberger-Enengl Franz Keplinger Michael Vellekoop http://www.mdpi.com/2072-666X/6/2/230 A dual-chamber anode structure is proposed in order to solve two performance problems of the conventional passive micro direct methanol fuel cell (μ-DMFC). One of the problems is the unstable performance during long time discharge. The second problem is the short operating time. In this structure, low concentration chamber is filled with methanol solution with appropriate concentration for the μ-DMFC. Pure methanol in high concentration chamber diffuses to the low concentration chamber to keep the concentration of methanol solution suitable for long-term discharge of μ-DMFC. In this study, a Nafion-Polytetrafluoroethylene (PTFE) composite membrane is inserted between the two chambers to conduct pure methanol. The experimental results during long-term discharge show that the stable operating time of passive μ-DMFC increases by nearly 2.3 times compared to a conventional one with the same volume. These results could be applied to real products. Micromachines 2015-02-04 6 2 Article 10.3390/mi6020230 230 238 2072-666X 2015-02-04 doi: 10.3390/mi6020230 Xiaowei Liu Shuo Fang Zezhong Ma Yufeng Zhang http://www.mdpi.com/2072-666X/6/2/216 This study presents a double-side diaphragm peristaltic pump for efficient medium transport without the unwanted backflow and the lagging effect of a diaphragm. A theoretical model was derived to predict the important parameter of the micropump, i.e., the motion of the valves at large deformations, for a variety of air pressures. Accordingly, we proposed an easy and robust design to fabricate a Polydimethylsiloxane (PDMS)-based micropump. The theoretical model agrees with a numerical model and experimental data for the deformations of the PDMS membrane. Furthermore, variations of the generated flow rate, including pneumatic frequencies, actuated air pressures, and operation modes were evaluated experimentally for the proposed micropumps. In future, the theoretical equation could provide the optimal parameters for the scientists working on the fabrication of the diaphragm peristaltic pump for applications of cell-culture. Micromachines 2015-01-29 6 2 Article 10.3390/mi6020216 216 229 2072-666X 2015-01-29 doi: 10.3390/mi6020216 Chi-Han Chiou Tai-Yen Yeh Jr-Lung Lin http://www.mdpi.com/2072-666X/6/2/196 The accurate estimation of measurements covariance is a fundamental problem in sensors fusion algorithms and is crucial for the proper operation of filtering algorithms. This paper provides an innovative solution for this problem and realizes the proposed solution on a 2D indoor navigation system for unmanned ground vehicles (UGVs) that fuses measurements from a MEMS-grade gyroscope, speed measurements and a light detection and ranging (LiDAR) sensor. A computationally efficient weighted line extraction method is introduced, where the LiDAR intensity measurements are used, such that the random range errors and systematic errors due to surface reflectivity in LiDAR measurements are considered. The vehicle pose change is obtained from LiDAR line feature matching, and the corresponding pose change covariance is also estimated by a weighted least squares-based technique. The estimated LiDAR-based pose changes are applied as periodic updates to the Inertial Navigation System (INS) in an innovative extended Kalman filter (EKF) design. Besides, the influences of the environment geometry layout and line estimation error are discussed. Real experiments in indoor environment are performed to evaluate the proposed algorithm. The results showed the great consistency between the LiDAR-estimated pose change covariance and the true accuracy. Therefore, this leads to a significant improvement in the vehicle's integrated navigation accuracy. Micromachines 2015-01-28 6 2 Article 10.3390/mi6020196 196 215 2072-666X 2015-01-28 doi: 10.3390/mi6020196 Shifei Liu Mohamed Atia Yanbin Gao Aboelmagd Noureldin http://www.mdpi.com/2072-666X/6/2/186 We report an infrared (IR) optical switch using a wedge-like cell. A glycerol droplet is placed in the cell and its surrounding is filled with silicone oil. The droplet has minimal surface area to volume (SA/V) ratio in the relaxing state. By applying a voltage, the generated dielectric force pulls the droplet to move toward the region with thinner cell gap. As a result, the droplet is deformed by the substrates, causing the SA/V of the droplet to increase. When the voltage is removed, the droplet can return to its original place in order to minimize the surface energy. Owing to the absorption of glycerol at 1.55 μm, the shifted droplet can be used to attenuate an IR beam with the advantage of polarization independent. Fluidic devices based on this operation mechanism have potential applications in optical fiber switches, IR shutter, and variable optical attenuations. Micromachines 2015-01-27 6 2 Article 10.3390/mi6020186 186 195 2072-666X 2015-01-27 doi: 10.3390/mi6020186 Miao Xu Xiahui Wang Boya Jin Hongwen Ren http://www.mdpi.com/2072-666X/6/2/172 In this work, we demonstrate continuous and discrete functions in a digital microfluidic platform in a programmed manner. Digital microfluidics is gaining popularity in biological and biomedical applications due to its ability to manipulate discrete droplet volumes (nL–pL), which significantly reduces the need for a costly and precious biological and physiological sample volume and, thus, diagnostic time. Despite the importance of discrete droplet volume handling, the ability of continuous microfluidics to process larger sample volumes at a higher throughput cannot be easily reproduced by merely using droplets. To bridge this gap, in this work, parallel channels are formed and programmed to split into multiple droplets, while droplets are programmed to be split from one channel, transferred and merged into another channel. This programmable handling of channels and droplets combines the continuous and digital paradigms of microfluidics, showing the potential for a wider range of microfluidic functions to enable applications ranging from clinical diagnostics in resource-limited environments, to rapid system prototyping, to high throughput pharmaceutical applications. Micromachines 2015-01-22 6 2 Article 10.3390/mi6020172 172 185 2072-666X 2015-01-22 doi: 10.3390/mi6020172 Ananda Banerjee Joo Noh Yuguang Liu Philip Rack Ian Papautsky http://www.mdpi.com/2072-666X/6/2/163 Single-cell electrical properties (e.g., specific membrane capacitance (Cspecific membrane) and cytoplasm conductivity (σcytoplasm)) have been regarded as potential label-free biophysical markers for the evaluation of cellular status. However, whether there exist correlations between these biophysical markers and cellular status (e.g., membrane-associate protein expression) is still unknown. To further validate the utility of single-cell electrical properties in cell type classification, Cspecific membrane and σcytoplasm of single PC-3 cells with membrane staining and/or fixation were analyzed and compared in this study. Four subtypes of PC-3 cells were prepared: untreated PC-3 cells, PC-3 cells with anti-EpCAM staining, PC-3 cells with fixation, and fixed PC-3 cells with anti-EpCAM staining. In experiments, suspended single cells were aspirated through microfluidic constriction channels with raw impedance data quantified and translated to Cspecific membrane and σcytoplasm. As to experimental results, significant differences in Cspecific membrane were observed for both live and fixed PC-3 cells with and without membrane staining, indicating that membrane staining proteins can contribute to electrical properties of cellular membranes. In addition, a significant decrease in σcytoplasm was located for PC-3 cells with and without fixation, suggesting that cytoplasm protein crosslinking during the fixation process can alter the cytoplasm conductivity. Overall, we have demonstrated how to classify single cells based on cellular electrical properties. Micromachines 2015-01-22 6 2 Article 10.3390/mi6020163 163 171 2072-666X 2015-01-22 doi: 10.3390/mi6020163 Song-Bin Huang Yang Zhao Deyong Chen Shing-Lun Liu Yana Luo Tzu-Keng Chiu Junbo Wang Jian Chen Min-Hsien Wu http://www.mdpi.com/2072-666X/6/1/160 The editors of Micromachines would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...] Micromachines 2015-01-07 6 1 Editorial 10.3390/mi6010160 160 162 2072-666X 2015-01-07 doi: 10.3390/mi6010160 Micromachines Editorial Office http://www.mdpi.com/2072-666X/6/1/151 Design optimization of the coupling region is conducted in order to solve the difficulty of achieving a higher quality factor (Q) for large size resonators based on silicon-on-insulator (SOI). Relations among coupling length, coupling ratio and quality factor of the optical cavities are theoretically analyzed. Resonators (R = 100 μm) with different coupling styles, concentric, straight, and butterfly, are prepared by the micro-electro-mechanical-systems (MEMS) process. Coupling experimental results show that micro-cavity of butterfly-coupled style obtains the narrowest (3 dB) bandwidth, and the quality factor has been greatly improved. The results provide the foundation for realization of a large size, high-Q resonator, and its development and application in the integrated optical gyroscopes, filters, sensors, and other related fields. Micromachines 2014-12-31 6 1 Article 10.3390/mi6010151 151 159 2072-666X 2014-12-31 doi: 10.3390/mi6010151 Shubin Yan Minghui Li Liang Luo Kezhen Ma Chenyang Xue Wendong Zhang http://www.mdpi.com/2072-666X/6/1/136 This paper presents and compares two different strategies in the numerical simulation of passive microfluidic mixers based on chaotic advection. In addition to flow velocity field calculations, concentration distributions of molecules and trajectories of microscale particles were determined and compared to evaluate the performance of the applied modeling approaches in the proposed geometries. A staggered herringbone type micromixer (SHM) was selected and studied in order to demonstrate finite element modeling issues. The selected microstructures were fabricated by a soft lithography technique, utilizing multilayer SU-8 epoxy-based photoresist as a molding replica for polydimethylsiloxane (PDMS) casting. The mixing processes in the microfluidic systems were characterized by applying molecular and particle (cell) solutions and adequate microscopic visualization techniques. We proved that modeling of the molecular concentration field is more costly, in regards to computational time, than the particle trajectory based method. However, both approaches showed adequate qualitative agreement with the experimental results. Micromachines 2014-12-30 6 1 Article 10.3390/mi6010136 136 150 2072-666X 2014-12-30 doi: 10.3390/mi6010136 Eszter Tóth Eszter Holczer Kristóf Iván Péter Fürjes http://www.mdpi.com/2072-666X/6/1/121 Microfluidic devices are electrical/mechanical systems that offer the ability to work with minimal sample volumes, short reactions times, and have the possibility to perform massive parallel operations. An important application of microfluidics is blood rheology in microdevices, which has played a key role in recent developments of lab-on-chip devices for blood sampling and analysis. The most popular and traditional method to fabricate these types of devices is the polydimethylsiloxane (PDMS) soft lithography technique, which requires molds, usually produced by photolithography. Although the research results are extremely encouraging, the high costs and time involved in the production of molds by photolithography is currently slowing down the development cycle of these types of devices. Here we present a simple, rapid, and low-cost nonlithographic technique to create microfluidic systems for biomedical applications. The results demonstrate the ability of the proposed method to perform cell free layer (CFL) measurements and the formation of microbubbles in continuous blood flow. Micromachines 2014-12-30 6 1 Article 10.3390/mi6010121 121 135 2072-666X 2014-12-30 doi: 10.3390/mi6010121 Elmano Pinto Vera Faustino Raquel Rodrigues Diana Pinho Valdemar Garcia João Miranda Rui Lima http://www.mdpi.com/2072-666X/6/1/110 This work describes an improvement in the layout of coplanar electrodes for electrical impedance spectroscopy. We have developed, fabricated, and tested an improved electrode layout, which improves the sensitivity of an impedance flow cytometry chip. The improved chip was experimentally tested and compared to a chip with a conventional electrode layout. The improved chip was able to discriminate 0.5 μm beads from 1 μm as opposed to the conventional chip. Furthermore, finite element modeling was used to simulate the improvements in electrical field density and uniformity between the electrodes of the new electrode layout. Good agreement was observed between the model and the obtained experimental results. Micromachines 2014-12-30 6 1 Article 10.3390/mi6010110 110 120 2072-666X 2014-12-30 doi: 10.3390/mi6010110 Casper Clausen Gustav Skands Christian Bertelsen Winnie Svendsen http://www.mdpi.com/2072-666X/6/1/96 Stereolithography that uses a femtosecond laser was employed as a method for multiphoton-sensitized polymerization. We studied the stereolithography method, which produces duplicate solid shapes corresponding to the trajectory of the laser focus point and can be used to build a three-dimensional (3D) structure using a conductive polymer. To achieve this, we first considered a suitable polymerization condition for line stereolithography. However, this introduced a problem of irregular polymerization. To overcome this, we constructed a support in the polymerized part using a protein material. This method can stabilize polymerization, but it is not suited for building 3D shapes. Therefore, we considered whether heat accumulation causes the irregular polymerization; consequently, the reduction method of the repetition rate of the femtosecond laser was used to reduce the heating process. This method enabled stabilization and building of a 3D shape using photo-polymerization of a conductive polymer. Micromachines 2014-12-29 6 1 Article 10.3390/mi6010096 96 109 2072-666X 2014-12-29 doi: 10.3390/mi6010096 Junji Sone Katsumi Yamada Akihisa Asami Jun Chen http://www.mdpi.com/2072-666X/6/1/80 This paper presents a novel dosing concept for drug delivery based on a peristaltic piezo-electrically actuated micro membrane pump. The design of the silicon micropump itself is straight-forward, using two piezoelectrically actuated membrane valves as inlet and outlet, and a pump chamber with a piezoelectrically actuated pump membrane in-between. To achieve a precise dosing, this micropump is used to fill a metering unit placed at its outlet. In the final design this metering unit will be made from a piezoelectrically actuated inlet valve, a storage chamber with an elastic cover membrane and a piezoelectrically actuated outlet valve, which are connected in series. During a dosing cycle the metering unit is used to adjust the drug volume to be dispensed before delivery and to control the actually dispensed volume. To simulate the new drug delivery concept, a lumped parameter model has been developed to find the decisive design parameters. With the knowledge taken from the model a drug delivery system is designed that includes a silicon micro pump and, in a first step, a silicon chip with the storage chamber and two commercial microvalves as a metering unit. The lumped parameter model is capable to simulate the maximum flow, the frequency response created by the micropump, and also the delivered volume of the drug delivery system. Micromachines 2014-12-24 6 1 Article 10.3390/mi6010080 80 95 2072-666X 2014-12-24 doi: 10.3390/mi6010080 Florian Thoma Frank Goldschmidtböing Peter Woias http://www.mdpi.com/2072-666X/6/1/63 Quantitative, reverse transcription, polymerase chain reaction (qRT-PCR) is facilitated by leveraging droplet microfluidic (DMF) system, which due to its precision dispensing and sample handling capabilities at microliter and lower volumes has emerged as a popular method for miniaturization of the PCR platform. This work substantially improves and extends the functional capabilities of our previously demonstrated single qRT-PCR micro-chip, which utilized a combination of electrostatic and electrowetting droplet actuation. In the reported work we illustrate a spatially multiplexed micro-device that is capable of conducting up to eight parallel, real-time PCR reactions per usage, with adjustable control on the PCR thermal cycling parameters (both process time and temperature set-points). This micro-device has been utilized to detect and quantify the presence of two clinically relevant respiratory viruses, Influenza A and Influenza B, in human samples (nasopharyngeal swabs, throat swabs). The device performed accurate detection and quantification of the two respiratory viruses, over several orders of RNA copy counts, in unknown (blind) panels of extracted patient samples with acceptably high PCR efficiency (>94%). The multi-stage qRT-PCR assays on eight panel patient samples were accomplished within 35–40 min, with a detection limit for the target Influenza virus RNAs estimated to be less than 10 RNA copies per reaction. Micromachines 2014-12-23 6 1 Article 10.3390/mi6010063 63 79 2072-666X 2014-12-23 doi: 10.3390/mi6010063 Ravi Prakash Kanti Pabbaraju Sallene Wong Anita Wong Raymond Tellier Karan Kaler http://www.mdpi.com/2072-666X/6/1/42 This study designed and developed a bionic mimosa robot with delicate leaf swing behaviors. For different swing behaviors, this study developed a variety of situations, in which the bionic mimosa robot would display different postures. The core technologies used were Shape Memory Alloys (SMAs), plastic material, and an intelligent control device. The technology particularly focused on the SMAs memory processing bend mode, directional guidance, and the position of SMAs installed inside the plastic material. Performance analysis and evaluation were conducted using two SMAs for mimosa opening/closing behaviors. Finally, by controlling the mimosa behavior with a micro-controller, the optimal strain swing behavior was realized through fuzzy logic control in order to display the different postures of mimosa under different situations. The proposed method is applicable to micro-bionic robot systems, entertainment robots, biomedical engineering, and architectural aesthetics-related fields in the future. Micromachines 2014-12-23 6 1 Article 10.3390/mi6010042 42 62 2072-666X 2014-12-23 doi: 10.3390/mi6010042 Chung-Liang Chang Jin-Long Shie http://www.mdpi.com/2072-666X/6/1/32 In this work, electrophoretic deposition (EPD) is reported to form gallium thin film with high deposition rate and low cost while avoiding the highly toxic chemicals typically used in electroplating. A maximum deposition rate of ~0.6 μm/min, almost one order of magnitude higher than the typical value reported for electroplating, is obtained when employing a set of proper deposition parameters. The thickness of the film is shown to increase with deposition time when sequential deposition is employed. The concentration of Mg(NO3)2, the charging salt, is also found to be a critical factor to control the deposition rate. Various gallium micropatterns are obtained by masking the substrate during the process, demonstrating process compatibility with microfabrication. The reported novel approach can potentially be employed in a broad range of applications with Ga as a raw material, including microelectronics, photovoltaic cells, and flexible liquid metal microelectrodes. Micromachines 2014-12-23 6 1 Communication 10.3390/mi6010032 32 41 2072-666X 2014-12-23 doi: 10.3390/mi6010032 Hanfei Zhang Yiping Feng Sunand Santhanagopalan Dennis Meng http://www.mdpi.com/2072-666X/6/1/19 Ten picoseconds (200 kHz) ultrafast laser micro-structuring of piezoelectric substrates including AT-cut quartz, Lithium Niobate and Lithium Tantalate have been studied for the purpose of piezoelectric devices application ranging from surface acoustic wave devices, e.g., bandpass filters, to photonic devices such as optical waveguides and holograms. The study examines the impact of changing several laser parameters on the resulting microstructural shapes and morphology. The micromachining rate has been observed to be strongly dependent on the operating parameters, such as the pulse fluence, the scan speed and the scan number. The results specifically indicate that ablation at low fluence and low speed scan tends to form a U-shaped cross-section, while a V-shaped profile can be obtained by using a high fluence and a high scan speed. The evolution of surface morphology revealed that laser pulses overlap in a range around 93% for both Lithium Niobate (LiNbO3) and Lithium Tantalate (LiTaO3) and 98% for AT-cut quartz can help to achieve optimal residual surface roughness. Micromachines 2014-12-23 6 1 Article 10.3390/mi6010019 19 31 2072-666X 2014-12-23 doi: 10.3390/mi6010019 Lamia EL Fissi Victor Xhurdebise Laurent Francis http://www.mdpi.com/2072-666X/6/1/1 SU-8 has been widely used in a variety of applications for creating structures in micro-scale as well as sub-micron scales for more than 15 years. One of the most common structures made of SU-8 is tall (up to millimeters) high-aspect-ratio (up to 100:1) 3D microstructure, which is far better than that made of any other photoresists. There has been a great deal of efforts in developing innovative unconventional lithography techniques to fully utilize the thick high aspect ratio nature of the SU-8 photoresist. Those unconventional lithography techniques include inclined ultraviolet (UV) exposure, back-side UV exposure, drawing lithography, and moving-mask UV lithography. In addition, since SU-8 is a negative-tone photoresist, it has been a popular choice of material for multiple-photon interference lithography for the periodic structure in scales down to deep sub-microns such as photonic crystals. These innovative lithography techniques for SU-8 have led to a lot of unprecedented capabilities for creating unique micro- and nano-structures. This paper reviews such innovative lithography techniques developed in the past 15 years or so. Micromachines 2014-12-23 6 1 Review 10.3390/mi6010001 1 18 2072-666X 2014-12-23 doi: 10.3390/mi6010001 Jeong Lee Kyung-Hak Choi Koangki Yoo http://www.mdpi.com/2072-666X/5/4/1469 We present a comprehensive experimental investigation of a micromachined inductive suspension (MIS) based on 3D wire-bonded microcoils. A theoretical model has been developed to predict the levitation height of the disc-shaped proof mass (PM), which has good agreement with the experimental results. The 3D MIS consists of two coaxial wire-bonded coils, the inner coil being used for levitation, while the outer coil for the stabilization of the PM. The levitation behavior is mapped with respect to the input parameters of the excitation currents applied to the levitation and stabilization coil, respectively: amplitude and frequency. At the same time, the levitation is investigated with respect to various thickness values (12.5 to 50 μm) and two materials (Al and Cu) of the proof mass. An important characteristic of an MIS, which determines its suitability for various applications, such as, e.g., micro-motors, is the dynamics in the lateral direction. We experimentally study the lateral stabilization force acting on the PM as a function of the linear displacement. The analysis of this dependency allows us to define a transition between stable and unstable levitation behavior. From an energetic point of view, this transition corresponds to the local maximum of the MIS potential energy. 2D simulations of the potential energy help us predict the location of this maximum, which is proven to be in good agreement with the experiment. Additionally, we map the temperature distribution for the coils, as well as for the PM levitated at 120 μm, which confirms the significant reduction of the heat dissipation in the MIS based on 3D microcoils compared to the planar topology. Micromachines 2014-12-12 5 4 Article 10.3390/mi5041469 1469 1484 2072-666X 2014-12-12 doi: 10.3390/mi5041469 Zhiqiu Lu Kirill Poletkin Ulrike Wallrabe Vlad Badilita http://www.mdpi.com/2072-666X/5/4/1445 This paper illustrates an application of a technique for predicting the thermal characteristics of a bidirectional thermocycling device for polymerase chain reaction (PCR). The micromilling chamber is oscillated by a servo motor and contacted with different isothermal heating blocks to successfully amplify the DNA templates. Because a comprehensive database of contact resistance factors does not exist, it causes researchers to not take thermal contact resistance into consideration at all. We are motivated to accurately determine the thermal characteristics of the reaction chamber with thermal contact effects existing between the heater surface and the chamber surface. Numerical results show that the thermal contact effects between the heating blocks and the reaction chamber dominate the temperature variations and the ramping rates inside the PCR chamber. However, the influences of various temperatures of the ambient conditions on the sample temperature during three PCR steps can be negligible. The experimental temperature profiles are compared well with the numerical simulations by considering the thermal contact conductance coefficient which is empirical by the experimental fitting. To take thermal contact conductance coefficients into consideration in the thermal simulation is recommended to predict a reasonable temperature profile of the reaction chamber during various thermal cycling processes. Finally, the PCR experiments present that Hygromycin B DNA templates are amplified successfully. Furthermore, our group is the first group to introduce the thermal contact effect into theoretical study that has been applied to the design of a PCR device, and to perform the PCR process in a bidirectional thermocycler. Micromachines 2014-12-12 5 4 Article 10.3390/mi5041445 1445 1468 2072-666X 2014-12-12 doi: 10.3390/mi5041445 Jyh Chen Kun Li Wei Chen Yao Yang http://www.mdpi.com/2072-666X/5/4/1429 This paper presents a systematic numerical investigation of the transient transport phenomenon during the pileup of molten metal droplets on the substrate. The physical mechanisms of the pileup process, including the bulk liquid, capillarity effects at the liquid-solid interface, heat transfer, and solidification, are identified and quantified numerically. The droplet diameter is 100 μm, and the impact velocities are 1–3 m/s. These conditions correspond to Re = O(100), We = O(1). The initial substrate temperature is 350 K. The initial droplet temperature of aluminum alloy molten droplets is 960 K. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of impacting velocity and relative distances between two successive molten droplets on the end-shapes of impact regime are examined. This investigation is essential to implement effective process control in metal microdroplet deposition manufacture. Micromachines 2014-12-10 5 4 Article 10.3390/mi5041429 1429 1444 2072-666X 2014-12-10 doi: 10.3390/mi5041429 Jun Du Zhengying Wei Zhen Chen Suli Li Yiping Tang http://www.mdpi.com/2072-666X/5/4/1416 In this paper, we proposed a novel bonding technology to fabricate a microfluidic device based on Poly(methyl methacrylate) (PMMA). The method, which used chloroform and ethanol as miscible bonding solvent, can complete complex structures rapid assembly (10 min) at 40°C. A bonding strength of 267.5 N/cm2 can be achieved, while the micro channel deformation was less than 7.26%. Then we utilized this method to produce a three layers micro mixer, which included a T-shaped inlet channel and six H-shaped mixing units. Numerical simulation indicated that, the well mixing length of the mixer was only about 6 mm when Re = 10. Finally, fluorescence microscopy was used to verify mixer performance. The method provided the potential for mass production of multilayer rigid polymer microfluidic devices. Micromachines 2014-12-10 5 4 Article 10.3390/mi5041416 1416 1428 2072-666X 2014-12-10 doi: 10.3390/mi5041416 He Zhang Xiaowei Liu Tian Li Xiaowei Han http://www.mdpi.com/2072-666X/5/4/1373 In this paper, the advances of the silicon-based millimeter-wave (MMW) monolithic integrated circuits (MMICs) are reported. The silicon-based technologies for MMW MMICs are briefly introduced. In addition, the current status of the MMW MMICs is surveyed and novel circuit topologies are summarized. Some representative MMW MMICs are illustrated as design examples in the categories of their functions in a MMW system. Finally, there is a conclusion and description of the future trend of the development of the MMW ICs. Micromachines 2014-12-10 5 4 Review 10.3390/mi5041373 1373 1415 2072-666X 2014-12-10 doi: 10.3390/mi5041373 Han-Chih Yeh Ching-Chau Chiong Ming-Tang Chen Huei Wang http://www.mdpi.com/2072-666X/5/4/1344 In spite of the fact that more than five decades have passed since the invention of laser, some topics of laser-matter interaction still remain incompletely studied. One of such topics is plasma impact on the overall phenomenon of the interaction and its particular features, including influence of the laser-excited plasma re-radiation, back flux of energetic plasma species, and massive material redeposition, on the surface quality and processing efficiency. In this paper, we analyze different plasma aspects, which go beyond a simple consideration of the well-known effect of plasma shielding of laser radiation. The following effects are considered: ambient gas ionization above the target on material processing with formation of a "plasma pipe"; back heating of the target by both laser-driven ambient and ablation plasmas through conductive and radiative heat transfer; plasma chemical effects on surface processing including microstructure growth on liquid metals; complicated dynamics of the ablation plasma flow interacting with an ambient gas that can result in substantial redeposition of material around the ablation spot. Together with a review summarizing our main to-date achievements and outlining research directions, we present new results underlining importance of laser plasma dynamics and photoionization of the gas environment upon laser processing of materials. Micromachines 2014-12-09 5 4 Article 10.3390/mi5041344 1344 1372 2072-666X 2014-12-09 doi: 10.3390/mi5041344 Nadezhda Bulgakova Alexei Panchenko Vladimir Zhukov Sergey Kudryashov Antonio Pereira Wladimir Marine Tomas Mocek Alexander Bulgakov http://www.mdpi.com/2072-666X/5/4/1342 The study and application of microscale lenses and lens arrays have been actively researched in recent years; new approaches in the fabrication of microlenses and microlens arrays have emerged. Also, novel applications of these microlenses and microlens arrays have been demonstrated. In an effort to disseminate the current advances in this specialized field of microlenses and microlens arrays, and to encourage discussion on the future research directions while stimulating research interests in this area, a Special Issue of Micromachines has been dedicated to "Microlenses". [...] Micromachines 2014-12-08 5 4 Editorial 10.3390/mi5041342 1342 1343 2072-666X 2014-12-08 doi: 10.3390/mi5041342 Hongrui Jiang http://www.mdpi.com/2072-666X/5/4/1323 This paper presents the design and simulation of an improved electro-thermal micromachined pump for drug delivery applications. Thermal actuators, which are a type of Micro Electro Mechanical system (MEMS) device, are highly useful because of their ability to deliver with great force and displacement. Thus, our structure is based on a thermal actuator that exploits the Joule heating effect and has been improved using the springy length properties of MEMS chevron beams. The Joule heating effect results in a difference in temperature and therefore displacement in the beams (actuators). Simulation results show that a maximum force of 4.4 mN and a maximum flow rate of 16 μL/min can be obtained by applying an AC voltage as low as 8 V at different frequencies ranging from 1 to 32 Hz. The maximum temperature was a problem at the chevron beams and the center shaft. Thus, to locally increase the temperature of the chevron beams alone and not that of the pumping diaphragm: (1) The air gaps 2 μm underneath and above the device layer were optimized for heat transfer. (2) Release holes and providing fins were created at the center shaft and actuator, respectively, to decrease the temperature by approximately 10 °C. (3) We inserted and used a polymer tube to serve as an insulator and eliminate leakage problems in the fluidic channel. Micromachines 2014-12-04 5 4 Article 10.3390/mi5041323 1323 1341 2072-666X 2014-12-04 doi: 10.3390/mi5041323 Ghader Yosefi Sattar Mirzakuchaki Farshid Raissi Saeid Afrang http://www.mdpi.com/2072-666X/5/4/1310 In this paper we examine the suitability of SU-8 2000 as a construction material for electrothermal actuators and the actuator stability for long-term operation. The fabrication of SU-8 was optimized for mechanical and thermal stability. Samples with different softbake duration, exposure dose and postbake temperature were evaluated using Fourier-Transform IR-spectroscopy and dynamic-mechanical analysis. The exposure dose and postbake temperature proved to have a strong influence on the cross-linking and the glass transition temperature. A final hardbake levels the effects of the process history. A high degree of crosslinking, a low drop of the dynamic modulus over temperature (30%) up to the glass transition temperature 100–140 °C were achieved for SU-8 with an exposure dose of 1500 mJ/cm², a postbake temperature of 95 °C and hardbake of 240 °C. Electrothermal actuators proved to be stable until the end of the experiment after 2400 duty cycles. Actuator deflections up to 55 μm were measured (actuator length: 4 mm) for input powers up to 160 mW and a maximum operating temperature of 120 °C. Higher temperatures led to permanent deformations and failure. An offset drift of up to 20% occurs during actuation, but converges after a burn-in phase of about two hours. Micromachines 2014-12-02 5 4 Article 10.3390/mi5041310 1310 1322 2072-666X 2014-12-02 doi: 10.3390/mi5041310 Thomas Winterstein Matthias Staab Christian Nakic Hans-Jürgen Feige Jürgen Vogel Helmut Schlaak http://www.mdpi.com/2072-666X/5/4/1296 Nanostructured gold and silver thin films were grown by pulsed laser deposition.Performing the process in an ambient gas (Ar) leads to the nucleation and growth ofnanoparticles in the ablation plasma and their self-organization on the substrate. Thedependence of surface nanostructuring of the films on the deposition parameters is discussedconsidering in particular the number of laser pulses and the ambient gas nature and pressure.The performance of the deposited thin films as substrates for surface-enhanced Ramanspectroscopy (SERS) was tested against the detection of molecules at a low concentration.Taking Raman maps on micrometer-sized areas, the spatial homogeneity of the substrateswith respect to the SERS signal was tested. Micromachines 2014-12-01 5 4 Article 10.3390/mi5041296 1296 1309 2072-666X 2014-12-01 doi: 10.3390/mi5041296 Enza Fazio Fortunato Neri Rosina Ponterio Sebastiano Trusso Matteo Tommasini Paolo Ossi http://www.mdpi.com/2072-666X/5/4/1287 Certain bacteria have motility and can be made non-toxic, and using them for drug delivery has been proposed. For example, using bacteria with flagella motion in multiple spin actuators in drug delivery microrobots has been suggested. This paper investigates various adhesion enhancement methods for attaching bacteria on preferred surfaces of cubic polymeric microstructures to achieve the directional control of motion. Serratia marcescens which has an excellent swimming behavior and 50-μm sized cubic structures made of biodegradable poly-capro-lactone (PCL) are used. Three treatment methods are investigated and compared to the untreated control case. The first method is retarding bacterial attachments by coating certain surfaces with bovine serum albumin (BSA) which makes those surfaces anti-adherent to bacteria. The second and third methods are roughening the surfaces with X-ray irradiation and plasma respectively to purposely increase bacterial attachments on the roughened surfaces. The measured motilities of bacteria-tethered PCL microactuators are 1.40 μm/s for the BSA coating method, 0.82 μm/s for the X-ray irradiation, and 3.89 μm/s for the plasma treatment method. Therefore, among the methods investigated in the paper the plasma treatment method achieves the highest directionality control of bacteria motility. Micromachines 2014-11-28 5 4 Article 10.3390/mi5041287 1287 1295 2072-666X 2014-11-28 doi: 10.3390/mi5041287 Hyung Yoo Sangmin Lee Dong-il Cho http://www.mdpi.com/2072-666X/5/4/1270 As an extension of our previous study, the flow and mixing characteristics of a serpentine mixer in non-creeping flow conditions are investigated numerically. A periodic velocity field is obtained for each spatially periodic channel with the Reynolds number (Re) ranging from 0.1 to 70 and the channel aspect ratio from 0.25 to one. The flow kinematics is visualized by plotting the manifold of the deforming interface between two fluids. The progress of mixing affected by the Reynolds number and the channel geometry is characterized by a measure of mixing, the intensity of segregation, calculated using the concentration distribution. A mixer with a lower aspect ratio, which is a poor mixer in the creeping flow regime, turns out to be an efficient one above a threshold value of the Reynolds number, Re = 50. This is due to the combined effect of the enhanced rotational motion of fluid particles and back flows near the bends of the channel driven by inertia. As for a mixer with a higher aspect ratio, the intensity of segregation has its maximum around Re = 30, implying that inertia does not always have a positive influence on mixing in this mixer. Micromachines 2014-11-27 5 4 Article 10.3390/mi5041270 1270 1286 2072-666X 2014-11-27 doi: 10.3390/mi5041270 Tae Kang Patrick Anderson http://www.mdpi.com/2072-666X/5/4/1254 The ability to elicit distinct duty cycles from the same self-regulating microfluidic oscillator device would greatly enhance the versatility of this micro-machine as a tool, capable of recapitulating in vitro the diverse oscillatory processes that occur within natural systems. We report a novel approach to realize this using the coordinated modulation of input volumetric flow rate ratio and fluidic capacitance ratio. The demonstration uses a straightforward experimental system where fluid inflow to the oscillator is provided by two syringes (of symmetric or asymmetric cross-sectional area) mounted upon a single syringe pump applying pressure across both syringes at a constant linear velocity. This produces distinct volumetric outflow rates from each syringe that are proportional to the ratio between their cross-sectional areas. The difference in syringe cross-sectional area also leads to differences in fluidic capacitance; this underappreciated capacitive difference allows us to present a simplified expression to determine the microfluidic oscillators duty cycle as a function of cross-sectional area. Examination of multiple total volumetric inflows under asymmetric inflow rates yielded predictable and robust duty cycles ranging from 50% to 90%. A method for estimating the outflow duration for each inflow under applied flow rate ratios is provided to better facilitate the utilization of this system in experimental protocols requiring specific stimulation and rest intervals. Micromachines 2014-11-27 5 4 Article 10.3390/mi5041254 1254 1269 2072-666X 2014-11-27 doi: 10.3390/mi5041254 Sasha Lesher-Perez Priyan Weerappuli Sung-Jin Kim Chao Zhang Shuichi Takayama http://www.mdpi.com/2072-666X/5/4/1219 Femtosecond laser micromachining has emerged in recent years as a new technique for micro/nano structure fabrication because of its applicability to virtually all kinds of materials in an easy one-step process that is scalable. In the past, much research on femtosecond laser micromachining was carried out to understand the complex ablation mechanism, whereas recent works are mostly concerned with the fabrication of surface structures because of their numerous possible applications. The state-of-the-art knowledge on the fabrication of these structures on metals with direct femtosecond laser micromachining is reviewed in this article. The effect of various parameters, such as fluence, number of pulses, laser beam polarization, wavelength, incident angle, scan velocity, number of scans, and environment, on the formation of different structures is discussed in detail wherever possible. Furthermore, a guideline for surface structures optimization is provided. The authors' experimental work on laser-inscribed regular pattern fabrication is presented to give a complete picture of micromachining processes. Finally, possible applications of laser-machined surface structures in different fields are briefly reviewed. Micromachines 2014-11-20 5 4 Review 10.3390/mi5041219 1219 1253 2072-666X 2014-11-20 doi: 10.3390/mi5041219 K. Ahmmed Colin Grambow Anne-Marie Kietzig http://www.mdpi.com/2072-666X/5/4/1202 We analyze the opportunities provided by the plasmonic nanoparticles inserted into the bulk of a transparent medium to modify the material by laser light irradiation. This study is provoked by the advent of photo-induced nano-composites consisting of a typical polymer matrix and metal nanoparticles located in the light-irradiated domains of the initially homogeneous material. The subsequent irradiation of these domains by femtosecond laser pulses promotes a further alteration of the material properties. We separately consider two different mechanisms of material alteration. First, we analyze a photochemical reaction initiated by the two-photon absorption of light near the plasmonic nanoparticle within the matrix. We show that the spatial distribution of the products of such a reaction changes the symmetry of the material, resulting in the appearance of anisotropy in the initially isotropic material or even in the loss of the center of symmetry. Second, we analyze the efficiency of a thermally-activated chemical reaction at the surface of a plasmonic particle and the distribution of the product of such a reaction just near the metal nanoparticle irradiated by an ultrashort laser pulse. Micromachines 2014-11-19 5 4 Article 10.3390/mi5041202 1202 1218 2072-666X 2014-11-19 doi: 10.3390/mi5041202 Anton Smirnov Alexander Pikulin Natalia Sapogova Nikita Bityurin http://www.mdpi.com/2072-666X/5/4/1188 The dispersion of cell deformability mapping is affected not only by the resolution of the sensing system, but also by cell deformability itself. In order to extract the pure deformability characteristics of cells, it is necessary to improve the resolution of cell actuation in the sensing system, particularly in the case of active sensing, where an actuator is essential. This paper proposes a novel concept, a "flow reduction mechanism", where a flow is generated by a macroactuator placed outside of a microfluidic chip. The flow can be drastically reduced at the cell manipulation point in a microchannel due to the elasticity embedded into the fluid circuit of the microfluidic system. The great advantage of this approach is that we can easily construct a high resolution cell manipulation system by combining a macro-scale actuator and a macro-scale position sensor, even though the resolution of the actuator is larger than the desired resolution for cell manipulation. Focusing on this characteristic, we successfully achieved the cell positioning based on a visual feedback control with a resolution of 240 nm, corresponding to one pixel of the vision system. We show that the utilization of this positioning system contributes to reducing the dispersion coming from the positioning resolution in the cell deformability mapping. Micromachines 2014-11-18 5 4 Article 10.3390/mi5041188 1188 1201 2072-666X 2014-11-18 doi: 10.3390/mi5041188 Shinya Sakuma Keisuke Kuroda Fumihito Arai Tatsunori Taniguchi Tomohito Ohtani Yasushi Sakata Makoto Kaneko http://www.mdpi.com/2072-666X/5/4/1173 This paper describes a light-addressable electrolytic system used to perform an electrodeposition of magnetically-guided cells encapsulated in alginate hydrogels using a digital micromirror device (DMD) for three-dimensional cell patterning. In this system, the magnetically-labeled cells were first manipulated into a specific arrangement by changing the orientation of the magnetic field, and then a patterned light illumination was projected onto a photoconductive substrate serving as a photo-anode to cause gelation of calcium alginate through sol-gel transition. By controlling the illumination pattern on the DMD, we first successfully produced cell-encapsulated multilayer alginate hydrogels with different shapes and sizes in each layer via performing multiplexed micropatterning. By combining the magnetically-labeled cells, light-addressable electrodeposition, and orientation of the magnetic fields, we have successfully demonstrated to fabricate two layers of the cell-encapsulated alginate hydrogels, where cells in each layer can be manipulated into cross-directional arrangements that mimic natural tissue. Our proposed method provides a programmable method for the spatiotemporally controllable assembly of cell populations into three-dimensional cell patterning and could have a wide range of biological applications in tissue engineering, toxicology, and drug discovery. Micromachines 2014-11-18 5 4 Article 10.3390/mi5041173 1173 1187 2072-666X 2014-11-18 doi: 10.3390/mi5041173 Shih-Hao Huang Hsiao-Tzu Chu Yan-Min Liou Kuo-Sheng Huang http://www.mdpi.com/2072-666X/5/4/1161 Improved glycemic control with insulin pump therapy in patients with type 1 diabetes mellitus has shown gradual reductions in nephropathy and retinopathy. More recently, the emerging concept of the artificial pancreas, comprising an insulin pump coupled to a continuous glucose meter and a control algorithm, would become the next major breakthrough in diabetes care. The patient safety and the efficiency of the therapy are directly derived from the delivery accuracy of rapid-acting insulin. For this purpose, a specific precision-oriented design of micropump has been built. The device, made of a stack of three silicon wafers, comprises two check valves and a pumping membrane that is actuated against stop limiters by a piezo actuator. Two membranes comprising piezoresistive strain gauges have been implemented to measure the pressure in the pumping chamber and at the outlet of the pump. Their high sensitivity makes possible the monitoring of the pumping accuracy with a tolerance of ±5% for each individual stroke of 200 nL. The capability of these sensors to monitor priming, reservoir overpressure, reservoir emptying, outlet occlusion and valve leakage has also been studied. Micromachines 2014-11-18 5 4 Article 10.3390/mi5041161 1161 1172 2072-666X 2014-11-18 doi: 10.3390/mi5041161 Dimitry Dumont-Fillon Hassen Tahriou Christophe Conan Eric Chappel http://www.mdpi.com/2072-666X/5/4/1135 By introducing smart materials in micro systems technologies, novel smart microactuators and sensors are currently being developed, e.g., for mobile, wearable, and implantable MEMS (Micro-electro-mechanical-system) devices. Magnetic shape memory alloys (MSMAs) are a promising material system as they show multiple coupling effects as well as large, abrupt changes in their physical properties, e.g., of strain and magnetization, due to a first order phase transformation. For the development of MSMA microactuators, considerable efforts are undertaken to fabricate MSMA foils and films showing similar and just as strong effects compared to their bulk counterparts. Novel MEMS-compatible technologies are being developed to enable their micromachining and integration. This review gives an overview of material properties, engineering issues and fabrication technologies. Selected demonstrators are presented illustrating the wide application potential. Micromachines 2014-11-18 5 4 Review 10.3390/mi5041135 1135 1160 2072-666X 2014-11-18 doi: 10.3390/mi5041135 Manfred Kohl Marcel Gueltig Viktor Pinneker Ruizhi Yin Frank Wendler Berthold Krevet http://www.mdpi.com/2072-666X/5/4/1106 The creation of complex three-dimensional (3D) fluidic systems composed of hollow micro- and nanostructures embedded in transparent substrates has attracted significant attention from both scientific and applied research communities. However, it is by now still a formidable challenge to build 3D micro- and nanofluidic structures with arbitrary configurations using conventional planar lithographic fabrication methods. As a direct and maskless fabrication technique, femtosecond laser micromachining provides a straightforward approach for high-precision, spatially-selective, modification inside transparent materials through nonlinear optical absorption. In this paper, we demonstrate rapid fabrication of high-aspect-ratio micro- and/or nanofluidic structures with various 3D configurations by femtosecond laser direct writing in porous glass substrates. Based on this approach, we demonstrate several functional micro- and nanofluidic devices including a 3D passive microfluidic mixer, a capillary electrophoresis (CE) analysis chip, and an integrated micro-nanofluidic system for single DNA analysis. The possible mechanisms behind the formation of high-aspect-ratio micro- and nanochannels are also discussed. This technology offers new opportunities to develop novel 3D micro-nanofluidic systems for a variety of lab-on-a-chip applications. Micromachines 2014-11-17 5 4 Review 10.3390/mi5041106 1106 1134 2072-666X 2014-11-17 doi: 10.3390/mi5041106 Yang Liao Ya Cheng http://www.mdpi.com/2072-666X/5/4/1082 Recent years have witnessed a rapid development of brain-computer interface (BCI) technology. An independent BCI is a communication system for controlling a device by human intension, e.g., a computer, a wheelchair or a neuroprosthes is, not depending on the brain's normal output pathways of peripheral nerves and muscles, but on detectable signals that represent responsive or intentional brain activities. This paper presents a comparative study of the usage of the linear discriminant analysis (LDA) and the naive Bayes (NB) classifiers on describing both right- and left-hand movement through electroencephalographic signal (EEG) acquisition. For the analysis, we considered the following input features: the energy of the segments of a band pass-filtered signal with the frequency band in sensorimotor rhythms and the components of the spectral energy obtained through the Welch method. We also used the common spatial pattern (CSP) filter, so as to increase the discriminatory activity among movement classes. By using the database generated by this experiment, we obtained hit rates up to 70%. The results are compatible with previous studies. Micromachines 2014-11-13 5 4 Article 10.3390/mi5041082 1082 1105 2072-666X 2014-11-13 doi: 10.3390/mi5041082 Juliano Machado Alexandre Balbinot http://www.mdpi.com/2072-666X/5/4/1069 In this work, we have modified the experimental setup for a vapor-solid (VS) process to synthesize Zinc oxide (ZnO) microtubes (MTs) with lengths up to 3 mm during a 90-min growth period. The critical idea behind this modification is to control the distribution of Zn vapor along the Si substrates. The morphology evolution of ZnO structures with the increasing reaction time was particularly explored. We found that, within the 90-min growth period, four different types of ZnO microstructures appeared in this synthesis process: microrods (MRs), short MTs, two-tier structures, and long MTs. Growth mechanisms were proposed to interpret the formation of these structures. Micromachines 2014-11-11 5 4 Article 10.3390/mi5041069 1069 1081 2072-666X 2014-11-11 doi: 10.3390/mi5041069 Zhihui Lu Xin Heng Anirban Chakraborty Cheng Luo http://www.mdpi.com/2072-666X/5/4/1061 The rapid growth of the micro-electro-mechanical systems (MEMS) is being driven by the rapid development of the micro manufacturing processes. Laser beam machining is one of the micro manufacturing processes which can shape almost all ranges of engineering materials. In this study, the effect of laser power on the quality of drilled micro holes using Cu50Zr50 amorphous alloys foils is experimentally investigated. It indicates that both entrance and exit circularities diameters increase with laser power. The circularities of the holes at the entry and the exit are in the range of 0.893 to 0.997. The taper of drilled holes increases quickly to a stable value with the increase of laser power from 60 to 110 W, then decreases quickly when the laser power becomes larger than 170 W. The micro holes with a diameter of 400 to 1200 μm are manufactured successfully by laser drilling processes. The formation mechanism of the quality of the laser drilled hole is analyzed based on the laser beam and the properties of amorphous alloys foils. Micromachines 2014-11-11 5 4 Article 10.3390/mi5041061 1061 1068 2072-666X 2014-11-11 doi: 10.3390/mi5041061 Chuan-Jie Wang Gang Chen Dong Luan Peng Zhang http://www.mdpi.com/2072-666X/5/4/1051 We report on high precision high speed micromachining of Al2O3 and AlN using pulsed near infrared fiber laser. Ablation thresholds are determined to be 30 J/cm2 for alumina and 18 J/cm2 for aluminum nitride. The factors influencing the efficiency and quality of 3D micromachining, namely the surface roughness, the material removal rate and the ablation depth accuracy are determined as a function of laser repetition rate and pulse overlap. Using a fluence of 64 J/cm², we achieve a material removal rate of up to 94 mm³/h in Al2O3 and 135 mm³/h in AlN for high pulse overlaps (89% and 84%). A minimum roughness of 1.5 μm for alumina and 1.65 μm for aluminum nitride can be accomplished for medium pulse overlaps (42% to 56%). In addition, ablation depth deviation of the micromachining process of smaller than 8% for alumina and 2% for aluminum nitride are achieved. Based on these results, by structuring exemplarily 3D structures we demonstrate the potential of high quality and efficient 3D micromachining using pulsed fiber laser. Micromachines 2014-11-10 5 4 Article 10.3390/mi5041051 1051 1060 2072-666X 2014-11-10 doi: 10.3390/mi5041051 Florian Preusch Benedikt Adelmann Ralf Hellmann http://www.mdpi.com/2072-666X/5/4/1034 In this paper, the dynamic performance of a Kalman filter (KF) was analyzed, which is used to combine multiple measurements of a gyroscopes array to reduce the noise and improve the accuracy of the individual sensors. A principle for accuracy improvement by the KF was briefly presented to obtain an optimal estimate of input rate signal. In particular, the influences of some crucial factors on the KF dynamic performance were analyzed by simulations such as the factors input signal frequency, signal sampling, and KF filtering rate. Finally, a system that was comprised of a six-gyroscope array was designed and implemented to test the dynamic performance. Experimental results indicated that the 1σ error for the combined rate signal was reduced to about 0.2°/s in the constant rate test, which was a reduction by a factor of more than eight compared to the single gyroscope. The 1σ error was also reduced from 1.6°/s to 0.48°/s in the swing test. It showed that the estimated angular rate signal could well reflect the dynamic characteristic of the input signal in dynamic conditions. Micromachines 2014-11-07 5 4 Article 10.3390/mi5041034 1034 1050 2072-666X 2014-11-07 doi: 10.3390/mi5041034 Liang Xue Lixin Wang Tao Xiong Chengyu Jiang Weizheng Yuan http://www.mdpi.com/2072-666X/5/4/1012 This paper considers the problem of indoor navigation by means of low-cost mobile devices. The required accuracy, the low reliability of low-cost sensor measurements and the typical unavailability of the GPS signal make indoor navigation a challenging problem. In this paper, a particle filtering approach is presented in order to obtain good navigation performance in an indoor environment: the proposed method is based on the integration of information provided by the inertial navigation system measurements, the radio signal strength of a standard wireless network and of the geometrical information of the building. In order to make the system as simple as possible from the user's point of view, sensors are assumed to be uncalibrated at the beginning of the navigation, and an auto-calibration procedure of the magnetic sensor is performed to improve the system performance: the proposed calibration procedure is performed during regular user's motion (no specific work is required). The navigation accuracy achievable with the proposed method and the results of the auto-calibration procedure are evaluated by means of a set of tests carried out in a university building. Micromachines 2014-11-05 5 4 Article 10.3390/mi5041012 1012 1033 2072-666X 2014-11-05 doi: 10.3390/mi5041012 Andrea Masiero Alberto Guarnieri Francesco Pirotti Antonio Vettore http://www.mdpi.com/2072-666X/5/4/1002 We describe a precision micropump for generation of precisely metered micro-aliquots of liquid at high rates. The use of custom designed piezoelectric valves positioned externally to the microfluidic chip allows for on-demand formation of micro-droplets with online control of their individual volumes from nLs to μLs at frequencies up to 400 Hz. The system offers precision of administering volumes of 1% and of time of emission of <0.5 ms. The use of a piezoelectric actuator provides two distinct vistas for controlling the volume of the droplets—either by digital control of the "open" interval or by analogue tuning of the lumen of the valve. Fast and precise generation of droplets make this system a perfect constituent module for microfluidic high-speed combinatorial screening schemes. Micromachines 2014-11-04 5 4 Article 10.3390/mi5041002 1002 1011 2072-666X 2014-11-04 doi: 10.3390/mi5041002 Slawomir Jakiela Pawel Debski Bogdan Dabrowski Piotr Garstecki http://www.mdpi.com/2072-666X/5/4/954 Advances in micro and nano fabrication technologies have enabled fabrication of smaller and more sensitive devices for applications not only in solid-state physics but also in medicine and biology. The demand for devices that can precisely transport material, specifically fluids are continuously increasing. Therefore, integration of various technologies with numerous functionalities in one single device is important. Scanning probe microscope (SPM) is one such device that has evolved from atomic force microscope for imaging to a variety of microscopes by integrating different physical and chemical mechanisms. In this article, we review a particular class of SPM devices that are suited for fluid dispensing. We review their fabrication methods, fluid-pumping mechanisms, real-time monitoring of dispensing, physics of dispensing, and droplet characterization. Some of the examples where these probes have already been applied are also described. Finally, we conclude with an outlook and future scope for these devices where femtolitre or smaller volumes of liquid handling are needed. Micromachines 2014-10-30 5 4 Review 10.3390/mi5040954 954 1001 2072-666X 2014-10-30 doi: 10.3390/mi5040954 Murali Ghatkesar Hector Garza Friedjof Heuck Urs Staufer http://www.mdpi.com/2072-666X/5/4/943 Thin film ablation with pulsed nanosecond lasers can benefit from the use of beam shaping optics to transform the Gaussian beam profile with a circular footprint into a Top-Hat beam profile with a rectangular footprint. In general, the quality of the transformed beam profile depends strongly on the beam alignment of the entire laser system. In particular, the adjustment of the beam shaping element is of upmost importance. For an appropriate alignment of the beam shaper, it is generally necessary to observe the intensity distribution near the focal position of the applied focusing optics. Systems with a low numerical aperture (NA) can commonly be qualified by means of laser beam profilers, such as a charge-coupled device (CCD) camera. However, laser systems for micromachining typically employ focus lenses with a high NA, which generate focal spot sizes of only several microns in diameter. This turns out to be a challenge for common beam profiling measurement systems and complicates the adjustment of the beam shaper strongly. In this contribution, we evaluate the quality of a Top-Hat beam profiling element and its alignment in the working area based on the ablated geometry of single pulse ablation of thin transparent conductive oxides. To determine the best achievable adjustment, we develop a quality index for rectangular laser ablation spots and investigate the influences of different alignment parameters, which can affect the intensity distribution of a Top-Hat laser beam profile. Micromachines 2014-10-27 5 4 Article 10.3390/mi5040943 943 953 2072-666X 2014-10-27 doi: 10.3390/mi5040943 Stefan Rung Johannes Barth Ralf Hellmann http://www.mdpi.com/2072-666X/5/4/929 Microactuators have become essential elements of microelectromechanical systems, for example, for positioning purposes and for fluid-handling tasks in microfluidic systems. UV depth lithography and other new micromachining technologies, which have been developed since the 1990s, have initiated extensive investigations of electromagnetic microactuators, which are characterized by high forces, large deflections, low driving voltages resulting from low input impedances and robustness under harsh environments. This paper reviews the comprehensive research on the design, fabrication and application of electromagnetic micromotors performed in our laboratory over the past years. Micromachines 2014-10-24 5 4 Review 10.3390/mi5040929 929 942 2072-666X 2014-10-24 doi: 10.3390/mi5040929 Stephanus Büttgenbach http://www.mdpi.com/2072-666X/5/4/913 A micromixer with unbalanced three-split rhombic sub-channels was proposed, and analyses of the mixing and flow characteristics of this micromixer were performed in this work. Three-dimensional Navier-Stokes equations in combination with an advection-diffusion model with two working fluids (water and ethanol) were solved for the analysis. The mixing index and pressure drop were evaluated and compared to those of a two-split micromixer for a range of Reynolds numbers from 0.1–120. The results indicate that the proposed three-split micromixer is efficient in mixing for a range of Reynolds numbers from 30–80. A parametric study was performed to determine the effects of the rhombic angle and sub-channel width ratio on mixing and pressure drop. Except at the lowest Reynolds number, a rhombic angle of 90° gave the best mixing performance. The three-split micromixer with minimum minor sub-channel widths provided the best mixing performance. Micromachines 2014-10-22 5 4 Article 10.3390/mi5040913 913 928 2072-666X 2014-10-22 doi: 10.3390/mi5040913 Shakhawat Hossain Kwang-Yong Kim http://www.mdpi.com/2072-666X/5/4/886 A trend in the global technological progress in the last few decades is the development of microsystem technology, microelectromechanical systems and corresponding technologies. Fluid mixing is an extremely important process widely used in various microfluidic devices (chemical microreactors, chemical and biological analyzers, drug delivery systems, etc.). To increase the mixing rate, it is necessary to use special devices: micromixers. This paper presents the results of a hydrodynamic simulation of Y-shaped micromixers. Flows are analyzed for both low and moderate Reynolds numbers. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds and Péclet numbers, as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings is analyzed. Five different flow regimes were identified: (1) stationary vortex-free flow (Re < 5); (2) stationary symmetric vortex flow with two horseshoe vortices (5 < Re < 150); (3) stationary asymmetric vortex flow (150 < Re < 240); (4) non-stationary periodic flow (240 < Re < 400); and (5) stochastic flow (Re > 400). The maximum mixing efficiency was obtained for stationary asymmetric vortex flow. Micromachines 2014-10-20 5 4 Review 10.3390/mi5040886 886 912 2072-666X 2014-10-20 doi: 10.3390/mi5040886 Valery Rudyak Andrey Minakov http://www.mdpi.com/2072-666X/5/4/868 An available novel system for studying the cellular mechanobiology applies an equiaxial strain field to cells cultured on a PolyDiMethylSiloxane (PDMS) substrate membrane, which is stretched over the deformation of a cylindrical shell. In its application of in vitro cell culture, the in-plane strain of the substrate membrane provides mechanical stimulation to cells, and out-of-plane displacement plays an important role in monitoring the cells by a microscope. However, no analysis of the parameters has been reported yet. Therefore, in this paper, we employ analytical and computational models to investigate the mechanical behavior of the device, in terms of in-plane strain and out-of-plane displacement of the substrate membrane. As a result, mathematical descriptions are given, which are not only for quantitatively determining the applied load, but also provide the theoretical basis for the researchers to carry out structural modification, according to their needs in specific cell culture experiments. Furthermore, by computational study, the elastic modulus of PDMS is determined to allow the mechanical behavior analysis of a fabricated device. Finally, compared to the experimental results of characterizing a fabricated device, good agreement is obtained between the predicted and experimental results. Micromachines 2014-10-16 5 4 Article 10.3390/mi5040868 868 885 2072-666X 2014-10-16 doi: 10.3390/mi5040868 Feihu Zhao Joose Kreutzer Sami Pajunen Pasi Kallio http://www.mdpi.com/2072-666X/5/4/859 Polarization independent liquid crystal (LC) microlens arrays based on controlling the spatial distribution of the Kerr constants of blue phase LC are simulated. Each sub-lens with a parabolic distribution of Kerr constants results in a parabolic phase profile when a homogeneous electric field is applied. We evaluate the phase distribution under different applied voltages, and the focusing properties of the microlens arrays are simulated. We also calculate polarization dependency of the microlenses arrays at oblique incidence of light. The impact of this study is to provide polarizer-free, electrically tunable focusing microlens arrays with simple electrode design based on the Kerr effect. Micromachines 2014-10-03 5 4 Article 10.3390/mi5040859 859 867 2072-666X 2014-10-03 doi: 10.3390/mi5040859 Hung-Shan Chen Michael Chen Chia-Ming Chang Yu-Jen Wang Yi-Hsin Lin http://www.mdpi.com/2072-666X/5/4/839 A 3D printing fused filament fabrication (FFF) approach has been implemented for the creation of microstructures having an internal 3D microstructure geometry. These objects were produced without any sacrificial structures or additional support materials, just by precisely tuning the nozzle heating, fan cooling and translation velocity parameters. The manufactured microporous structures out of polylactic acid (PLA) had fully controllable porosity (20%–60%) and consisted of desired volume pores (~0.056 μm3). The prepared scaffolds showed biocompatibility and were suitable for the primary stem cell growth. In addition, direct laser writing (DLW) ablation was employed to modify the surfaces of the PLA structures, drill holes, as well as shape the outer geometries of the created objects. The proposed combination of FFF printing with DLW offers successful fabrication of 3D microporous structures with functionalization capabilities, such as the modification of surfaces, the generation of grooves and microholes and cutting out precisely shaped structures (micro-arrows, micro-gears). The produced structures could serve as biomedical templates for cell culturing, as well as biodegradable implants for tissue engineering. The additional micro-architecture is important in connection with the cell types used for the intention of cell growing. Moreover, we show that surface roughness can be modified at the nanoscale by immersion into an acetone bath, thus increasing the hydrophilicity. The approach is not limited to biomedical applications, it could be employed for the manufacturing of bioresorbable 3D microfluidic and micromechanic structures. Micromachines 2014-09-30 5 4 Article 10.3390/mi5040839 839 858 2072-666X 2014-09-30 doi: 10.3390/mi5040839 Mangirdas Malinauskas Sima Rekštytė Laurynas Lukoševičius Simas Butkus Evaldas Balčiūnas Milda Pečiukaitytė Daiva Baltriukienė Virginija Bukelskienė Arūnas Butkevičius Povilas Kucevičius Vygandas Rutkūnas Saulius Juodkazis http://www.mdpi.com/2072-666X/5/4/825 Recently, we showed that femtosecond laser induced "nanogratings" consist of thin regions with a low refractive index (Δn = −0.15), due to the formation of nanoporous silica surrounded by regions with a positive index change. In this paper, we investigate a wide range of laser parameters to achieve very high retardance within a single layer; as much as 350 nm at λ = 546 nm but also to minimize the competing losses. We show that the total retardance depends on the number of layers present and can be accumulated in the direction of laser propagation to values higher than 1600 nm. This opens the door to using these nanostructures as refined building blocks for novel optical elements based on strong retardance. Micromachines 2014-09-30 5 4 Article 10.3390/mi5040825 825 838 2072-666X 2014-09-30 doi: 10.3390/mi5040825 Matthieu Lancry Rudy Desmarchelier Kevin Cook Bertrand Poumellec John Canning http://www.mdpi.com/2072-666X/5/4/814 A high-temperature pressure sensor realized by the post-fire metallization on zirconia ceramic is presented. The pressure signal can be read out wirelessly through the magnetic coupling between the reader antenna and the sensor due to that the sensor is equivalent to an inductive-capacitive (LC) resonance circuit which has a pressure-sensitive resonance frequency. Considering the excellent mechanical properties in high-temperature environment, multilayered zirconia ceramic tapes were used to fabricate the pressure-sensitive structure. Owing to its low resistivity, sliver paste was chosen to form the electrical circuit via post-fire metallization, thereby enhancing the quality factor compared to sensors fabricated by cofiring with a high-melting-point metal such as platinum, tungsten or manganese. The design, fabrication, and experiments are demonstrated and discussed in detail. Experimental results showed that the sensor can operate at 600 °C with quite good coupling. Furthermore, the average sensitivity is as high as 790 kHz/bar within the measurement range between 0 and 1 Bar. Micromachines 2014-09-29 5 4 Article 10.3390/mi5040814 814 824 2072-666X 2014-09-29 doi: 10.3390/mi5040814 Tao Luo Qiulin Tan Liqiong Ding Tanyong Wei Chao Li Chenyang Xue Jijun Xiong http://www.mdpi.com/2072-666X/5/4/797 Microrobots have a number of potential applications for micromanipulation and assembly, but also offer challenges in power and control. This paper describes an uncalibrated vision-based control system for magnetically actuated microrobots operating untethered at the interface between two immiscible fluids. The microrobots are 20 μm thick and approximately 100–200 μm in lateral dimension. Several different robot shapes are investigated. The robots and fluid are in a 20 × 20 × 15 mm vial placed at the center of four electromagnets. Pulse width modulation of the electromagnet currents is used to control robot speed and direction. Given a desired position, a controller based on recursive least square estimation drives the microrobot to the goal without a priori knowledge of system parameters such as drag coefficients or intrinsic and extrinsic camera parameters. Results are verified experimentally using a variety of microrobot shapes and system configurations. Micromachines 2014-09-26 5 4 Article 10.3390/mi5040797 797 813 2072-666X 2014-09-26 doi: 10.3390/mi5040797 Jenelle Piepmeier Samara Firebaugh Caitlin Olsen http://www.mdpi.com/2072-666X/5/3/783 In this article, a novel Pyrex reflow bonding technology is introduced which bonds two functional units made of silicon via a Pyrex reflow bonding process. The practical application demonstrated here is a precision dosing system that uses a mechanically actuated membrane micropump which includes passive membranes for fluid metering. To enable proper functioning after full integration, a technique for device assembly must be established which does not introduce additional stress into the system, but fulfills all other requirements, like pressure tolerance and chemical stability. This is achieved with a stress-free thermal bonding principle to bond Pyrex to silicon in a five-layer stack: after alignment, the silicon-Pyrex-silicon stack is heated to 730 °C. Above the glass transition temperature of 525 °C Pyrex exhibits viscoelastic behavior. This allows the glass layer to come into close mechanical contact with the upper and lower silicon layers. The high temperature and the close contact promotes the formation of a stable and reliable Si-O-Si bond, without introducing mechanical stress into the system, and without deformation upon cooling due to thermal mismatch. Micromachines 2014-09-23 5 3 Article 10.3390/mi5030783 783 796 2072-666X 2014-09-23 doi: 10.3390/mi5030783 Florian Thoma Frank Goldschmidtböing Keith Cobry Peter Woias http://www.mdpi.com/2072-666X/5/3/766 The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its resolution and reproducibility. Here, a number of improvements to traditional photolithography are introduced to increase the versatility of the process. The shrinkage of SU-8 during carbonization is then detailed as one of the guidelines necessary to design carbon patterns. A couple of applications—(1) carbon-electrode dielectrophoresis for bioparticle manipulation; and (2) the use of carbon structures as micro-molds are also presented. Micromachines 2014-09-22 5 3 Article 10.3390/mi5030766 766 782 2072-666X 2014-09-22 doi: 10.3390/mi5030766 Rodrigo Martinez-Duarte http://www.mdpi.com/2072-666X/5/3/756 High-power electronics in the transportation and aerospace sectors need size and weight reduction. Multifunctional and multistructured materials are currently being developed to couple electromagnetic (EM) and thermal properties, i.e., shielding against electromagnetic impulsions, and thermal management across the thermal interface material (TIM). In this work, we investigate laser-machined patterned carbon nanotube (CNT) micro-brushes as an alternative to metallic structures for driving simultaneously EM and heat propagation. The thermal and electromagnetic response of the CNT array is expected to be sensitive to the micro-structured pattern etched in the CNT brush. Micromachines 2014-09-22 5 3 Article 10.3390/mi5030756 756 765 2072-666X 2014-09-22 doi: 10.3390/mi5030756 Aline Emplit Ester Tooten Victor Xhurdebise Isabelle Huynen http://www.mdpi.com/2072-666X/5/3/738 The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit Board (PCB) industry, can replace the more expensive and less available equipment, as the Mask Aligner that has been used in the last 15 years for SU-8 patterning. Moreover, high transparency masks, printed in a photomask, are used, instead of expensive chromium masks. The fabrication of well-defined SU-8 microstructures with aspect ratios more than 20 is successfully demonstrated with those facilities. The viability of using the gray-scale technology in the photomasks for the fabrication of 3D microstructures is also reported. Moreover, SU-8 microstructures for different applications are shown throughout the paper. Micromachines 2014-09-22 5 3 Article 10.3390/mi5030738 738 755 2072-666X 2014-09-22 doi: 10.3390/mi5030738 Vânia Pinto Paulo Sousa Vanessa Cardoso Graça Minas http://www.mdpi.com/2072-666X/5/3/722 This paper presents a chemical reaction-free sensor, based on the osmosis principle, fabricated to measure the change in glucose concentration levels. The sensor consists of a square cavity filled with a known concentration of glucose solution and sealed with a semi-permeable membrane. The volume inside the cavity changes in proportion to the glucose concentration outside the device and introduces the displacement in the silicon (Si) membrane on the top. The main considerations targeted for this sensor are better response time, chemical-free nature, improved lifetime and absence of any mechanical excitations. Moreover, as the size of a system plays a major role, efforts have been taken to reduce the dimension of the presented system. The designed glucose sensor is fabricated by employing a bulk micromachining technology on a SOI (silicon on insulator) substrate. This will allow batch fabrication, as well as the integration of the electronic circuit on the same substrate. The output voltage obtained is varied from Micromachines 2014-09-18 5 3 Article 10.3390/mi5030722 722 737 2072-666X 2014-09-18 doi: 10.3390/mi5030722 Nagesh Ch Roy Paily http://www.mdpi.com/2072-666X/5/3/711 This paper presents the progress of monolithic technology for microwaveapplication, focusing on gallium nitride technology advances in the realization of integratedpower amplifiers. Three design examples, developed for microwave backhaul radios, areshown. The first design is a 7 GHz Doherty developed with a research foundry, while thesecond and the third are a 7 GHz Doherty and a 7–15 GHz dual-band combined poweramplifiers, both based on a commercial foundry process. The employed architectures, themain design steps and the pros and cons of using gallium nitride technology are highlighted.The measured performance demonstrates the potentialities of the employed technology, andthe progress in the accuracy, reliability and performance of the process. Micromachines 2014-09-12 5 3 Article 10.3390/mi5030711 711 721 2072-666X 2014-09-12 doi: 10.3390/mi5030711 Vittorio Camarchia Marco Pirola Roberto Quaglia http://www.mdpi.com/2072-666X/5/3/697 Flexures are components of micro-mechanisms efficiently replacing classical multi-part joints found at the macroscale. So far, flexures have been limited to two-dimensional planar designs due to the lack of a suitable three-dimensional micromanufacturing process. Here we demonstrate and characterize a high-strength transparent monolithic three-dimensional flexural component fabricated out of fused silica using non-ablative femtosecond laser processing combined with chemical etching. As an illustration of the potential use of this flexure, we propose a design of a Hoecken linkage entirely made with three-dimensional cross-spring pivot hinges. Micromachines 2014-09-11 5 3 Article 10.3390/mi5030697 697 710 2072-666X 2014-09-11 doi: 10.3390/mi5030697 Viktor Tielen Yves Bellouard http://www.mdpi.com/2072-666X/5/3/681 We propose a single cell extraction chip with an open structure, which utilizes vibration-induced whirling flow and a single cell catcher. By applying a circular vibration to a micropillar array spiral pattern, a whirling flow is induced around the micropillars, and target cells are transported towards the single cell catcher placed at the center of the spiral. The single cell catcher is composed of a single-cell-sized hole pattern of thermo-responsive gel. The gel swells at low temperatures (≲32 ◦C) and shrinks at high temperatures (≳32 ◦C), therefore, its volume expansion can be controlled by an integrated microheater. When the microheater is turned on, a single cell is trapped by the hole pattern of the single cell catcher. Then, when the microheater is turned off, the single cell catcher is cooled by the ambient temperature. The gel swells at this temperature, and the hole closes to catch the single cell. The caught cell can then be released into culture wells on a microtiter plate by heating the gel again. We conducted single cell extraction with the proposed chip and achieved a 60% success rate, of which 61% cells yielded live cells. Micromachines 2014-09-10 5 3 Article 10.3390/mi5030681 681 696 2072-666X 2014-09-10 doi: 10.3390/mi5030681 Takeshi Hayakawa Shinya Sakuma Takeshi Fukuhara Yoshiyuki Yokoyama Fumihito Arai http://www.mdpi.com/2072-666X/5/3/667 Stop-flow lithography (SFL) is a microfluidic-based particle synthesis method, in which photolithography with a two dimensional (2D) photomask is performed in situ within a microfluidic environment to fabricate multifunctional microstructures. Here, we modified the SFL technique by utilizing an adjustable electrostatic-force-modulated 3D (EFM-3D) mask to continuously fabricate microlens structures for high-throughput production. The adjustable EFM-3D mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses between two conductive glass substrates. An acrylate oligomer stream is photopolymerized via the microscope projection photolithography, where the EFM-3D mask was set at the field-stop plane of the microscope, thus forming the microlens structures. The produced microlens structures flow downstream without adhesion to the polydimethysiloxane (PDMS) microchannel surfaces due to the existence of an oxygen-aided inhibition layer. Microlens structures with variations in curvature and aperture can be produced by changing objective magnifications, controlling the morphology of the EFM-3D mask through electrostatic force, and varying the concentration of UV-light absorption dyes. We have successfully demonstrated to produce microlens structures with an aperture ranging from 50 μm to 2 mm and the smallest focus spot size of 0.59 μm. Our proposed method allows one to fabricate microlens structures in a fast, simple and high-throughput mode for application in micro-optical systems. Micromachines 2014-09-10 5 3 Article 10.3390/mi5030667 667 680 2072-666X 2014-09-10 doi: 10.3390/mi5030667 Shih-Hao Huang Chia-Kai Lin http://www.mdpi.com/2072-666X/5/3/654 This paper reports the numerical and experimental analysis of the acoustic streaming effect in a fluidic domain. The actuation of a piezoelectric transducer generates acoustic waves that propagate to the fluids, generating pressure gradients that induce the flow. The number and positioning of the transducers affect the pressure gradients and, consequently, the resultant flow profile. Two actuation conditions were considered: (1) acoustic streaming generated by a 28 μm thick β-poly(vinylidene fluoride) (β-PVDF) piezoelectric transducer placed asymmetrically relative to the fluidic domain and (2) acoustic streaming generated by two 28 μm thick β-PVDF piezoelectric transducers placed perpendicularly to each other. The transducers were fixed to the lower left corner of a poly(methyl methacrylate) (PMMA)cuvette and were actuated with a 24 Vpp and 34.2 MHz sinusoidal voltage. The results show that the number of transducers and their positioning affects the shape and number of recirculation areas in the acoustic streaming flows. The obtained global flows show great potential for mixing and pumping, being an alternative to the previous geometries studied by the authors, namely, a single transducer placed symmetrically under a fluidic domain. Micromachines 2014-09-01 5 3 Article 10.3390/mi5030654 654 666 2072-666X 2014-09-01 doi: 10.3390/mi5030654 Susana Catarino João Miranda Graça Minas http://www.mdpi.com/2072-666X/5/3/622 The development and application of magnetic technologies employing microfabricated magnetic structures for the production of switching components has generated enormous interest in the scientific and industrial communities over the last decade. Magnetic actuation offers many benefits when compared to other schemes for microelectromechanical systems (MEMS), including the generation of forces that have higher magnitude and longer range. Magnetic actuation can be achieved using different excitation sources, which create challenges related to the integration with other technologies, such as CMOS (Complementary Metal Oxide Semiconductor), and the requirement to reduce power consumption. Novel designs and technologies are therefore sought to enable the use of magnetic switching architectures in integrated MEMS devices, without incurring excessive energy consumption. This article reviews the status of magnetic MEMS technology and presents devices recently developed by various research groups, with key focuses on integrability and effective power management, in addition to the ability to integrate the technology with other microelectronic fabrication processes. Micromachines 2014-08-29 5 3 Review 10.3390/mi5030622 622 653 2072-666X 2014-08-29 doi: 10.3390/mi5030622 Giuseppe Schiavone Marc Desmulliez Anthony Walton http://www.mdpi.com/2072-666X/5/3/607 We report the development of an add-on, chip-based, optical module—termed the Microfluidic-based Oil-immersion Lenses (μOIL) chip—which transforms any stereo microscope into a high-resolution, large field of view imaging platform. The μOIL chip consists of an array of ball mini-lenses that are assembled onto a microfluidic silicon chip. The mini-lenses are made out of high refractive index material (sapphire) and they are half immersed in oil. Those two key features enable submicron resolution and a maximum numerical aperture of ~1.2. The μOIL chip is reusable and easy to operate as it can be placed directly on top of any biological sample. It improves the resolution of a stereo microscope by an order of magnitude without compromising the field of view; therefore, we believe it could become a versatile tool for use in various research studies and clinical applications. Micromachines 2014-08-28 5 3 Article 10.3390/mi5030607 607 621 2072-666X 2014-08-28 doi: 10.3390/mi5030607 Mayurachat Gulari Anurag Tripathi Mostafa Ghannad-Rezaie Nikos Chronis http://www.mdpi.com/2072-666X/5/3/594 Several recent detector technologies developed for particle physics applications are based on microfabricated structures. Detectors built with this approach generally exhibit the overall best performance in terms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for the manufacturing of microstructured particle detectors. This article aims to review some emerging detector technologies making use of SU-8 microstructuring, namely micropattern gaseous detectors and microfluidic scintillation detectors. The general working principle and main process steps for the fabrication of each device are reported, with a focus on the advantages brought to the device functionality by the use of SU-8. A novel process based on multiple bonding steps for the fabrication of thin multilayer microfluidic scintillation detectors developed by the authors is presented. Finally, a brief overview of the applications for the discussed devices is given. Micromachines 2014-08-26 5 3 Review 10.3390/mi5030594 594 606 2072-666X 2014-08-26 doi: 10.3390/mi5030594 Pietro Maoddi Alessandro Mapelli Sebastien Jiguet Philippe Renaud http://www.mdpi.com/2072-666X/5/3/583 Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing and thermal curing for the fabrication of much thicker hemispherical microstructures of SPMPC. The microstructures are fabricated by inkjet printing the nanoparticle-doped SU-8 onto flat substrates functionalized to reduce the surface energy and thus the wetting. The thickness and the aspect ratio of the printed structures are further increased by printing the composite onto substrates with confinement pedestals. Fully crosslinked microstructures with a thickness up to 88.8 μm and edge angle of 112° ± 4° are obtained. Manipulation of the microstructures by an external field is enabled by creating lines of densely aggregated nanoparticles inside the composite. To this end, the printed microstructures are placed within an external magnetic field directly before crosslinking inducing the aggregation of dense Fe3O4 nanoparticle lines with in-plane and out-of-plane directions. Micromachines 2014-08-25 5 3 Article 10.3390/mi5030583 583 593 2072-666X 2014-08-25 doi: 10.3390/mi5030583 Loïc Jacot-Descombes Maurizio Gullo Victor Cadarso Massimo Mastrangeli Olgaç Ergeneman Christian Peters Philipe Fatio Mouhamad Freidy Christofer Hierold Bradley Nelson Jürgen Brugger http://www.mdpi.com/2072-666X/5/3/570 Results obtained during the evaluation of radio frequency (RF) reliability carried out on several devices fabricated with different epi-structure and field-plate geometries will be presented and discussed. Devices without a field-plate structure experienced a more severe degradation when compared to their counterparts while no significant correlation has been observed with respect of the different epi-structure tested. RF stress induced two main changes in the device electrical characteristics, i.e., an increase in drain current dispersion and a reduction in gate-leakage currents. Both of these phenomena can be explained by assuming a density increase of an acceptor trap located beneath the gate contact and in the device barrier layer. Numerical simulations carried out with the aim of supporting the proposed mechanism will also be presented. Micromachines 2014-08-22 5 3 Article 10.3390/mi5030570 570 582 2072-666X 2014-08-22 doi: 10.3390/mi5030570 Alessandro Chini Gaudenzio Meneghesso Alessio Pantellini Claudio Lanzieri Enrico Zanoni http://www.mdpi.com/2072-666X/5/3/558 We present two simple methods, with parallel and serial gas flows, for the stacking of microfabricated silicon fuel cells with integrated current collectors, flow fields and gas diffusion layers. The gas diffusion layer is implemented using black silicon. In the two stacking methods proposed in this work, the fluidic apertures and gas flow topology are rotationally symmetric and enable us to stack fuel cells without an increase in the number of electrical or fluidic ports or interconnects. Thanks to this simplicity and the structural compactness of each cell, the obtained stacks are very thin (~1.6 mm for a two-cell stack). We have fabricated two-cell stacks with two different gas flow topologies and obtained an open-circuit voltage (OCV) of 1.6 V and a power density of 63 mW·cm−2, proving the viability of the design. Micromachines 2014-08-21 5 3 Article 10.3390/mi5030558 558 569 2072-666X 2014-08-21 doi: 10.3390/mi5030558 Gianmario Scotti Petri Kanninen Tanja Kallio Sami Franssila http://www.mdpi.com/2072-666X/5/3/547 A piezoelectric vibration feeder with a magnetic spring is discussed in this paper. The feeder can keep resonance frequency relatively stable under changing loading. Through the analysis on the working principle and magnetic spring stiffness characteristic of this feeder, the dynamic model was established and the relationship among system resonance frequency, loading and magnetic spring stiffness was obtained. The analysis showed that, as the loading changed, the magnetic spring stiffness changed accordingly, which maintained a trend of stability in the system resonance frequency. A prototype was made for the experiment, and the relationship among the loading, magnetic spring axial clearance and system resonance frequency was obtained. The result showed that, when the loading changes, the resonance frequency and feeding speed tended to be stable, which matched the theoretical analysis. Through comparison with a traditional vibration feeder, within nominal loading, this new feeder has more stable resonance frequency and feeding speed. Micromachines 2014-08-19 5 3 Article 10.3390/mi5030547 547 557 2072-666X 2014-08-19 doi: 10.3390/mi5030547 Xiaochao Tian Zhigang Yang Yong Liu Yanhu Shen Song Chen http://www.mdpi.com/2072-666X/5/3/528 We report a design concept for a deployable planar microdevice and the modeling and experimental validation of its mechanical behavior. The device consists of foldable membranes that are suspended between flexible stems and actuated by push-pull wires. Such a deployable device can be introduced into a region of interest in its compact "collapsed" state and then deployed to conformally cover a large two-dimensional surface area for minimally invasive biomedical operations and other engineering applications. We develop and experimentally validate theoretical models based on the energy minimization approach to examine the conformality and figures of merit of the device. The experimental results obtained using model contact surfaces agree well with the prediction and quantitatively highlight the importance of the membrane bending modulus in controlling surface conformality. The present study establishes an early foundation for the mechanical design of this and related deployable planar microdevice concepts. Micromachines 2014-08-11 5 3 Article 10.3390/mi5030528 528 546 2072-666X 2014-08-11 doi: 10.3390/mi5030528 Jinda Zhuang Y. Ju http://www.mdpi.com/2072-666X/5/3/515 Poly(dimethylsiloxane) (PDMS) surface modification via gradient-induced transport of embedded amphiphilic molecules is a novel, easy, flexible, and environmentally friendly approach for reducing protein adsorption on PDMS in microfluidic applications. To better understand the processing and the potential use in the viability-sensitive applications such as manipulation and culturing of primary neural cells, we systematically investigate how embedded molecules interact with a PDMS matrix and its surface in aqueous environments by studying the wetting angle over time under various processing conditions, including water exposure time, water exposure temperature, curing master materials, in addition to comparing different embedded amphiphilic molecules. The results indicate that the water exposure time clearly plays an important role in the surface properties. Our interpretation is that molecular rearrangement of the surface-embedded molecules improves surface coverage in the short term; while over a longer period, the transport of molecules embedded in the bulk enhance its coverage. However, this improvement finally terminates when molecules transported from the bulk to the surface are not sufficient to replace the molecules leaching into the water. Micromachines 2014-08-07 5 3 Article 10.3390/mi5030515 515 527 2072-666X 2014-08-07 doi: 10.3390/mi5030515 Wenjun Qiu Xiaojiao Sun Chaoqun Wu Klas Hjort Zhigang Wu http://www.mdpi.com/2072-666X/5/3/505 We report on the design, modeling and fabrication by multi-photon polymerization of a complex medical fluidic device. The physical dimensions of the built micro-valve prototype are compared to those of its computer-designed model. Important fabrication issues such as achieving high dimensional resolution and ability to control distortion due to shrinkage are presented and discussed. The operational performance of both multi-photon and CAD-created models under steady blood flow conditions was evaluated and compared through computational fluid dynamics analysis. Micromachines 2014-08-06 5 3 Article 10.3390/mi5030505 505 514 2072-666X 2014-08-06 doi: 10.3390/mi5030505 Stratos Galanopoulos Nikoleta Chatzidai Vasileia Melissinaki Alexandros Selimis Charalampos Schizas Maria Farsari Dimitris Karalekas http://www.mdpi.com/2072-666X/5/3/496 In this paper we report an adaptive liquid lens actuated by droplet movement. Four rectangular PMMA (Polymethyl Methacrylate) substrates are stacked to form the device structure. Two ITO (Indium Tin Oxide) sheets stick on the bottom substrate. One PMMA sheet with a light hole is inserted in the middle of the device. A conductive droplet is placed on the substrate and touches the PMMA sheet to form a small closed reservoir. The reservoir is filled with another immiscible non-conductive liquid. The non-conductive liquid can form a smooth concave interface with the light hole. When the device is applied with voltage, the droplet stretches towards the reservoir. The volume of the reservoir reduces, changing the curvature of the interface. The device can thus achieve the function of an adaptive lens. Our experiments show that the focal length can be varied from −10 to −159 mm as the applied voltage changes from 0 to 65 V. The response time of the liquid lens is ~75 ms. The proposed device has potential applications in many fields such as information displays, imaging systems, and laser scanning systems. Micromachines 2014-08-04 5 3 Article 10.3390/mi5030496 496 504 2072-666X 2014-08-04 doi: 10.3390/mi5030496 Chao Liu Qiong-Hua Wang Li-Xiao Yao Ming-Huan Wang http://www.mdpi.com/2072-666X/5/3/486 A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive synchrotron source needed to expose the photoresist layer in X-ray LIGA. SU-8 photoresist appeared to be well-suited for LIGA templates, but also as a permanent material. Based on UV-LIGA and SU-8, Mimotec SA has developed processes to manufacture mold inserts and metallic components for various market fields. From one to three-level parts, from Ni to other materials, from simple to complicated parts with integrated functionalities, UV-LIGA has established itself as a manufacturing technology of importance for prototyping, as well as for mass-fabrication. This paper reviews some of the developments that led to commercial success in this field. Micromachines 2014-07-23 5 3 Review 10.3390/mi5030486 486 495 2072-666X 2014-07-23 doi: 10.3390/mi5030486 Grégoire Genolet Hubert Lorenz http://www.mdpi.com/2072-666X/5/3/472 This work presents patterning of thick (10–50 µm) hybrid polymer structures of ORMOCER® by laser direct writing. ORMOCER® combine polymer-like fabrication processes with glass-like surface chemistry that is beneficial for many bio-microfluidic applications. ORMOCER® is liquid before exposure, so patterning is done by contact-free lithography, such as proximity exposure. With laser direct writing, we obtained higher resolution patterns, with smaller radius of curvature (~2–4 µm), compared to proximity exposure (~10–20 µm). Process parameters were studied to find the optimal dose for different exposure conditions and ORMOCER® layer thicknesses. Two fluidic devices were successfully fabricated: a directional wetting device (fluidic diode) and an electrophoresis chip. The fluidic diode chip operation depends on the sharp corner geometry and water contact angle, and both have been successfully tailored to obtain diodicity. Electrophoresis chips were used to separate of two fluorescent dyes, rhodamine 123 and fluorescein. The electrophoresis chip also made use of ORMOCER® to ORMOCER® bonding. Micromachines 2014-07-22 5 3 Article 10.3390/mi5030472 472 485 2072-666X 2014-07-22 doi: 10.3390/mi5030472 Akanksha Singh Gianmario Scotti Tiina Sikanen Ville Jokinen Sami Franssila http://www.mdpi.com/2072-666X/5/3/457 This article describes the manufacturing and characterisation of plano-convex miniaturised lenses using a CO2 laser engraving process in PMMA substrates. The technique allows for lenses to be fabricated rapidly and in a reproducible manner at depths of over 200 µm and for lens diameters of more than 3 mm. Experimental characterisation of the lens focal lengths shows good correlation with theory. The plano-convex lenses have been successfully embedded into capillary microfluidic systems alongside planar microlenses, allowing for a significant reduction of ancillary optics without a loss of detection sensitivity when performing fluorescence measurements. Such technology provides a significant step forward towards the portability of fluorescence- or luminescence-based systems for biological/chemical analysis. Micromachines 2014-07-21 5 3 Article 10.3390/mi5030457 457 471 2072-666X 2014-07-21 doi: 10.3390/mi5030457 Mazher-Iqbal Mohammed Marc Desmulliez http://www.mdpi.com/2072-666X/5/3/442 This paper introduces the synchronous micromotor concept and presents new investigations on its application as an integrated driving mechanism in microfluidic systems. A spiral channel viscous micropump and a microstirrer are considered and tested as examples to verify the concept. The fabrication technology of such integrated systems is based on UV depth lithography, electroplating and soft lithography. The synchronous micromotor consists of a stator including double layer coils, and a rotor disk containing alternate permanent magnets. The coils are distributed evenly around the stator and arranged in three phases. The phases are excited by sinusoidal currents with a corresponding phase shift resulting in a rotating magnetic field. Regarding the spiral channel viscous micropump, a spiral disk was fixed onto the rotor disk and run at different rotational speeds. Tests showed very promising results, with a flow rate up to 1023 µL·min−1 at a motor rotational speed of 4500 rpm. Furthermore, for the application of a microstirred-tank bioreactor, the rotor disk design was modified to work as a stirrer. The performance of the developed microbioreactor was tested over a time period of approximately 10 h under constant stirring. Tests demonstrated the successful cultivation of S. cerevisiae through the integration of the microstirrer in a microbioreactor system. These systems prove that synchronous micromotors are well suited to serve as integrated driving mechanisms of active microfluidic components. Micromachines 2014-07-18 5 3 Article 10.3390/mi5030442 442 456 2072-666X 2014-07-18 doi: 10.3390/mi5030442 Ala'aldeen Al-Halhouli Stefanie Demming Andreas Waldschik Stephanus Büttgenbach http://www.mdpi.com/2072-666X/5/3/432 We present a flexible variable-focus converging microlens actuated by electrowetting on dielectric (EWOD). The microlens is made of two immiscible liquids and a soft polymer, polydimethylsiloxane (PDMS). Parylene intermediate layer is used to produce robust flexible electrode on PDMS. A low-temperature PDMS-compatible fabrication process has been developed to reduce the stress on the lens structure. The lens has been demonstrated to be able to conform to curved surfaces smoothly. The focal length of the microlens is 29–38 mm on a flat surface, and 31–41 mm on a curved surface, varying with the voltage applied. The resolving power of the microlens is 25.39 line pairs per mm by a 1951 United States Air Force (USAF) resolution chart and the lens aberrations are measured by a Shack-Hartmann wavefront sensor. The focal length behavior on a curved surface is discussed and for the current lens demonstrated the focal length is slightly longer on the curved surface as a result of the effect of the curved PDMS substrate. Micromachines 2014-07-04 5 3 Article 10.3390/mi5030432 432 441 2072-666X 2014-07-04 doi: 10.3390/mi5030432 Chenhui Li Hongrui Jiang http://www.mdpi.com/2072-666X/5/3/420 An ultrasonic transducer is a key component to achieve ultrasonic imaging. This paper designs a new type of Microelectromechanical Systems (MEMS) based capacitive ultrasonic transducer and a linear array based on the transducer. Through directivity analysis, it can be found that its directivity is weak due to the small size of the designed transducer, but the directivity of the designed linear array is very strong. In order to further suppress the sidelobe interference and improve the resolution of the imaging system and imaging quality, the Dolph-Chebyshev weighting method and the Taylor weighting method are used to process −40dB sidelobe suppression, and satisfactory results are obtained, which can meet actual requirements. Micromachines 2014-07-03 5 3 Article 10.3390/mi5030420 420 431 2072-666X 2014-07-03 doi: 10.3390/mi5030420 Hongliang Wang Xiangjun Wang Changde He Chenyang Xue http://www.mdpi.com/2072-666X/5/3/408 In this paper, we present sequential atmospheric pressure plasma-assisted laser ablation of photovoltaic cover glass. First, glass samples were plasma pre-treated using a hydrogenous plasma process gas in order to accomplish a modification of the near-surface glass network by a chemical reduction and the implantation of hydrogen. As a result, the transmission at a wavelength of 355 nm was reduced by approximately 2% after plasma treatment duration of 60 min. Further, the surface polarity was increased by approximately 78%, indicating an increase of the near-surface index of refraction. Subsequently to the plasma pre-treatment, the samples were laser ablated applying the above-mentioned laser wavelength of a Nd:YAG nanosecond laser. Compared to untreated samples, a significant decrease of the form error by 45% without any mentionable change in the ablation rate was obtained in the case of pre-treated samples. For comparison, the results and findings are discussed with respect to previous work, where the presented plasma-assisted ablation procedure was applied to optical glasses. Micromachines 2014-07-02 5 3 Article 10.3390/mi5030408 408 419 2072-666X 2014-07-02 doi: 10.3390/mi5030408 Christoph Gerhard Maximilian Dammann Stephan Wieneke Wolfgang Viöl http://www.mdpi.com/2072-666X/5/2/396 In this paper, a novel capacitance pressure sensor based on Low-Temperature Co-Fired Ceramic (LTCC) technology is proposed for pressure measurement. This approach differs from the traditional fabrication process for a LTCC pressure sensor because a 4J33 iron-nickel-cobalt alloy is applied to avoid the collapse of the cavity and to improve the performance of the sensor. Unlike the traditional LTCC sensor, the sensitive membrane of the proposed sensor is very flat, and the deformation of the sensitivity membrane is smaller. The proposed sensor also demonstrates a greater responsivity, which reaches as high as 13 kHz/kPa in range of 0–100 kPa. During experiments, the newly fabricated sensor, which is only about 6.5 cm2, demonstrated very good performance: the repeatability error, hysteresis error, and nonlinearity of the sensor are about 4.25%, 2.13%, and 1.77%, respectively. Micromachines 2014-06-24 5 2 Article 10.3390/mi5020396 396 407 2072-666X 2014-06-24 doi: 10.3390/mi5020396 Chen Li Qiulin Tan Wendong Zhang Chenyang Xue Yunzhi Li Jijun Xiong http://www.mdpi.com/2072-666X/5/2/385 Two Si-based micro pulsating heat pipes (µPHPs) charged using HFE-7100 were either horizontally or vertically oriented and were tested using several heating powers. The width of each channel was 0.8 mm in one µPHP containing uniform channels, and the channel width was 1.0 mm or 0.6 mm in the other µPHP, which did not contain uniform channels. The depth of each channel was 0.25 mm. The overall size of each µPHP was 60 × 10 × 1.25 mm. Visual observation and temperature measurement of the µPHPs under various conditions were performed and the results were analyzed. The results indicated that when the µPHPs were operated horizontally at a heating power ranging from 1 to 7 W, the pulsating two-phase flow in the channels of the µPHPs could not begin, except when the µPHP containing nonuniform channels was tested at a heating power of 7 W. With a heating power less than 5 W, the frequency of the sine-like oscillating displacement of the vapor slug increased and the displacement of the vapor slug reduced in either vertically oriented μPHP, as the heating power increased With a heating power higher than 5 W, periodic "start-stop" behaviors were observed in the vertical μPHP containing nonuniform channels. Micromachines 2014-06-20 5 2 Article 10.3390/mi5020385 385 395 2072-666X 2014-06-20 doi: 10.3390/mi5020385 Kai-Shing Yang Yu-Chi Cheng Ming-Shan Jeng Kuo-Hsiang Chien Jin-Cherng Shyu http://www.mdpi.com/2072-666X/5/2/373 We present a wide-angle, broad-spectrum cylindrical lens based on reflections from an array of three-dimensional, high-aspect-ratio micro-mirrors fabricated on a cylindrical elastomeric substrate, functionally inspired by natural reflecting superposition compound eyes. Our device can perform one-dimensional focusing and beam-shaping comparable to conventional refraction-based cylindrical lenses, while avoiding chromatic aberration. The focal length of our cylindrical lens is 1.035 mm, suitable for micro-optical systems. Moreover, it demonstrates a wide field of view of 152° without distortion, as well as modest spherical aberrations. Our work could be applied to diverse applications including laser diode collimation, barcode scanning, holography, digital projection display, microlens arrays, and optical microscopy. Micromachines 2014-06-20 5 2 Article 10.3390/mi5020373 373 384 2072-666X 2014-06-20 doi: 10.3390/mi5020373 Chi-Chieh Huang Hongrui Jiang