Mechanical properties of polymeric biomaterials: Modified ePTFE using gamma irradiation

Evaluating the mechanical properties of expanded polytetrafluoroethylene (ePTFE) is essential to measure its resistance to permanent deformation from an applied force. These mechanical ePTFE properties must be comparable to the properties of real tissue. Various hydrophilic comono-mers 2-hydroxyethyl methacrylate (HEMA), N-isopropyla-crylamide (NIPAAM), and N-vinylcaprolactam were used individually for copolymerization with acrylic acid (AA) to be grafted onto ePTFE using the gamma irradiation-induced grafting method. After surface modification, the hydro-phobic and mechanical properties of ePTFE were altered. The water uptake and contact angle measurement showed that the modified ePTFE was less hydrophobic (similar to 500%, theta < 90 degrees) than the unmodified ePTFE (0%, theta = 140 degrees). Moreover, the mechanical properties of ePTFE changed after the modification process due to the polymer grafted onto the ePTFE surface. The data from mechanical tests, such as Young's modulus (74-121 MPa), ultimate tensile strength (5-9 MPa), and elongation at break (56-121%), obtained for the sample AA-co-HEMA and AA-co-NIPAAM remain within the ranges and are considered desirable for use as a biomaterial. The mechanical strength correlates well with the percentage of the grafting yield after the mod-ification process and is dependent on the parameters used, such as irradiation dose and type of comonomer.