thermoplastic polyurethane ( tpu ) and polydimethylsiloxane rubber ( pdms ) are two well known biomaterials with excellent biocompatibility and biostability . a large volume of literature resources are available describing the biomedical applications of these two materials [ 16 ] . if tpu and pdms are blended together , the mechanical strength and biocompatibility of tpu can be added to the inertness and biocompatibility of pdms . one of the main advantages is the formation of a thermoplastic elastomer material , which has the properties of an elastomer at room temperature and allows processing in conventional plastic processing equipments like injection moulding machine or an extruder . furthermore , it allows tailoring of the end use property requirements by adjusting the ratio of the blend components . being a thermoplastic elastomer material , the need for crosslinking the pdms component can be avoided , which is a major gain . this is because crosslinking involves the use of various curing chemicals and there is a chance for migration of these chemicals to the surrounding tissues during the long term implantation period of the material , which will result in toxicity for the surrounding tissues and results in the rejection of the implant from the body . the main obstacle in blending tpu with pdms is the formation of an immiscible blend which will lead to phase separation . this can be addressed by adopting the reactive blending or in situ compatibilization technique using a copolymer capable of making specific interactions with the blend components . the authors have reported the in situ compatibilization of an 80  :  20 blend of tpu and pdms compatibilized with a copolymer of ethylene and methyl acrylate ( ema ) . a compatibilized blend of tpu and pdms could be used for a variety of biomedical applications where the biocompatibility , strength , and toughness of tpu and the inertness , biocompatibility , and flexibility of pdms are required . such applications include artificial organs , scaffolds for tissue engineering , membranes for guided tissue regeneration , soft tissue replacements , cartilage replacements , and so forth . the theory behind the microporous implant is that a controlled network of porosity will improve the invasion and proliferation of cells on to the biomaterial surface [ 1012 ] . miyamoto et al .   described a technique to create microporosity in small - caliber vascular prostheses in which calcium carbonate ( mean particle size , 8  m ) was incorporated with polyurethane during the fabrication of the prosthesis , followed by placing the tube in hydrochloric acid to remove the calcium carbonate and thereby created microporosity on the device . in the present study , microporous structures of compatibilized blends of tpu and pdms were formed by a crazing mechanism proposed by chandavasu et al . the minor phase that is well dispersed in the matrix , acts as a stress concentrator . the porosity is introduced by drawing the samples . when the sample is deformed by drawing , the minor phase , domains are debonded due to the weak adhesion between phases . microcracks are initiated at points of high stress concentration which are at interface between the two phases . subsequent growth occurs by a process in which crazes propagate into the major phase of blends . one of the major problems associated with synthetic membranes for biomedical applications is the cutting or tearing of the membrane through the suture hole . suture holding strength or suture tearing strength is a measure of the mechanical resistance to cutting with a suture . this measurement is important for membranes intended to be tightly sutured with host tissues or organs . the objectives of present study include the preparation of a compatibilized blend of tpu and pdms and generation of microporosity on the blend surface , study the suture holding strength of the membranes , and carry out detailed evaluation of in vitro cytotoxicity of the blend . thermoplastic polyurethane ( desmopan ku 2 - 8600e , an ether type tpu , with melting point 190c and specific gravity 1.11 ) was supplied by bayer , india . pdms ( ke 151  u , with specific gravity 1.15 ) was obtained from shin - etsu , japan . ema ( melting point 81c and specific gravity 0.94 ) was supplied by exxon , india . blends of tpu and pdms with the various dosage of compatibilizer ( 0 to 10  wt% ) were prepared using haake polylab system rheomix 600p with cam rotors . the temperature for mixing was 190c and rotor speed of 80  rpm was employed . mixing time of 10 and 14 minutes were given for virgin tpu and the blends , respectively . the material after mixing was quickly transferred to a laboratory two roll mill ( 150  mm    300  mm ) and sheeted out at room temperature . from the blends , sheets of dimension 120  mm    120  mm    2  mm were obtained by compression molding in a heated press equipped with a water cooling system . samples for various physical property tests were cut from these sheets using a specimen punching machine . thin films were prepared by compression molding the blend samples between two parallel plates in the compression molding press . the treatments used for the preparation of microporous structure include the following interrelated steps : blend samples in the form of rectangular strips were uniaxially drawn ( 100600% ) with respect to the original dimension to induce debonded interphase crazing . the growth of crazes is controlled by the degree of applied stress.samples were then held for 10 minutes at various temperatures ( 2060c ) in the stretched condition to stabilize the microporous structure . blend samples in the form of rectangular strips were uniaxially drawn ( 100600% ) with respect to the original dimension to induce debonded interphase crazing . samples were then held for 10 minutes at various temperatures ( 2060c ) in the stretched condition to stabilize the microporous structure . universal testing machine ( utm ) fitted with an environmental chamber ( hounsfield h10ks ) was used to carry out the stretching experiments . the microporous structure was then observed through scanning electron microscope ( sem , s-2400 hitachi , japan ) . the suture holding strength was measured using the one - point suspension method described by matsumoto et al . ,   using a universal testing machine . the sample was fixed with a stitch , made up of nylon suture placed 5  mm from one edge , and then the opposite edge was fastened to the grip of the utm . a metallic hook was fixed on the other grip of the utm and the suture was carefully held with the hook . the maximum stretching strength was measured and expressed as tensile force per 1  mm width of the membrane . 
 in vitro cytotoxicity study button shaped samples were cleaned in an ultrasonic bath and subjected to -ray irradiation ( 2.5  mrad ) and used for the study . the in vitro cytotoxicity was assessed as per iso-10993 - 5 ( 2002 ) using l929 mouse fibroblast subcutaneous connective tissue cell line procured from national centre for cell sciences , pune , india . the cells were maintained in rpmi 1640 medium ( himedia , pune , india ) supplemented with 10% foetal bovine serum ( sigma , usa ) and 100  iu / ml penicillin and 100  g / ml streptomycin ( medical grade ) . the culture was incubated at 37    2c in a humidified atmosphere containing 5% carbon dioxide with a medium change at an interval of 3 days . cytotoxicity of compatibilized blend samples by direct contact method was evaluated as per iso-10993 - 5 :  8.3 ( 2002 ) . the control samples and the blend sample were placed in contact with the cells and incubated at 37    2c for 24 hours . high density polyethylene ( hdpe ) was taken as the negative control and organotin stabilized polyvinyl chloride ( o - pvc ) was taken as the positive control . cytotoxicity of compatibilized blend samples was also evaluated by testing on an extract as per iso-10993 - 5 8.2 ( 2002 ) . material extract was prepared by incubating 0.1  g of the blend sample in the culture medium at 37    2c for 24  h. phenol and tissue culture grade polystyrene ( tcps ) were used as the positive and negative controls , respectively . to analyse cytotoxicity , culture medium from confluent cells were replaced with material extracts and cytotoxicity was assessed qualitatively after 24  h. 
 in vitro cell adhesion studies were performed using l929 cells for 48    1 hours on blend samples before and after creating microporosity on the surface . uniform number of cells were seeded on the samples and incubated at 37    1c under humidified atmosphere in presence of 5% co2 . after incubating for 2 days , the samples were washed with pbs and fixed with 2.5% glutaraldehyde in 0.1  m phosphate buffer for 30  min at 4c . after the fixation , the samples were washed twice with phosphate buffer and then dehydrated in ethanol solutions ( 50% to 100% ) . the samples were kept in 100% ethanol until being subjected to critical point drying ( cpd ) to avoid water contamination . the samples were then sputter coated by gold and examined by scanning electron microscope ( sem , s-2400 hitachi , japan ) . based on the results obtained from torque rheometry ( apparent viscosity values ) , mechanical property evaluation , infra red spectra , scanning electron microscopy ( sem ) , and atomic force microscopy ( afm ) , it was concluded that the optimum level of compatibilizer required to effectively compatibilize a polyblend system of 80  :  20 tpu and pdms was 2  wt% of ema . stretching experiments were carried out at various stretching speeds ( 200  mm / min500  mm / min ) , to various extension ( 100600% ) at different temperatures ( 2080c ) followed by holding the structure for 10  min in the stretched condition for stabilizing the morphology . series of experiments were carried out to optimize the conditions such as optimum stretching speed , optimum percentage extension , and optimum temperature leading to the development of a more uniform microporous structure . it was observed that the stretching speed of 500  mm / minute , extension of 300% , and temperature of 60c resulted in the optimum number of pores uniformly distributed over the blend surface . the scanning electron micrograph showing the microporosity in the compatibilized blend under these optimized conditions is shown in figure 3 . large numbers of pores with size in the range 15 microns are visible on the surface . also , the pores are distributed uniformly over the surface . the contact angle measurements of these membranes are expected to provide more information regarding the wettability of the surfaces and thereby help to assess the hydrophilicity / hydrophobicity of the material , which are important parameters in controlling the cell proliferation and growth over the membrane . the suture holding strength measurements were carried out on films of 80  :  20 blend of tpu  :  pdms containing compatibilizer varying from 0 to 5  pbw ( table 1 ) . the experiment was repeated after creating microporosity on the surface of the films under the optimum conditions . suture holding strength and tearing resistance are found to be higher for the blend containing 2  pbw of compatibilizer . 
 in vitro cytotoxicity studies carried out on compatibilized blend showed that the blend material is noncytotoxic to l929 cells in culture . l929 mouse fibroblast cells are well proven cell lines for cytotoxicity evaluation of biomaterials . in the direct contact study , the cells in contact with the blend material showed spindle morphology characteristic of mouse fibroblast cell line . similar results were obtained for the test performed on the extract of the material . in both cases , the morphology was similar to the negative control . figures 4(a)4(c ) and figures 5(a)6(c ) show the optical micrographs of direct contact test and test on extract respectively . figures 6 and 7 show the sem micrographs of cells proliferated on blend samples surfaces without and with surface microporosity . it can be observed that the fibroblast cells proliferated onto the surface of the membranes exhibited a flattened morphology that demonstrated a good adherence to the surface . in contrast , in blend samples without surface microporosity , the fibroblasts exhibited round morphology , showing low cell adherence and proliferation . it is well known that to mimic the topological and microstructure characteristics of the extracellular matrix , a biomaterial surface must have high degree of porosity , high surface - to - volume ratio , and high degree of pore interconnection , appropriate pore size , and geometry control . the increase in cell proliferation on samples with microporosity suggests that the porosity of the surface helped the cells to adhere closely to the samples . more information regarding the proliferation and growth of cell lines over the blend surface can be gathered by quantitative studies such as cell counting kit-8 ( cck-8 ) cell proliferation assay , which will be included in the future prospects of the present investigation . compatibilized blend of tpu and pdms was prepared by reactive blending technique and microporosity was created on the surface of this blend material . in vitro cytotoxicity studies indicate that the material is noncytotoxic towards l929 cell lines . the surface microporosity favoured the ingrowth and proliferation of the cells as evidenced from scanning electron micrographs . the blend material also possesses sufficient strength to prevent cutting and tearing through suture holes .
in the present investigation , a compatibilized blend of thermoplastic polyurethane ( tpu ) and polydimethylsiloxane ( pdms ) is prepared by using copolymer of ethylene and methyl acrylate ( ema ) as a reactive compatibilizer . 
 detailed in vitro biocompatibility studies were carried out for this compatibilized blend and the material was found noncytotoxic towards l929 mouse fibroblast subcutaneous connective tissue cell line . 
 microporosity was created on the surface of membranes prepared from the blend material by adopting the crazing mechanism . 
 cell proliferation and growth studies on the membranes surface showed that the microporous surface favoured ingrowth of the cells compared with a nonmicroporous surface . 
 suture holding strength studies indicate that the microporous membranes have enough strength to withstand the cutting and tearing forces through the suture hole . 
 this blend material could be evaluated further to find its suitability in various implant applications .