Effect of nitrogen ion irradiation on the nano-tribological and surface mechanical properties of ultra-high molecular weight polyethylene

Generation of wear debris is the principal obstacle limiting the durability of ultra-high molecular weight polyethylene (UHMWPE) in biomedical applications. Aiming to enhance UHMWPE wear resistance, surface modification with swift heavy ion irradiation (SHI) appears as a potential and attractive methodology. Contrary to ion implantation techniques, the swift heavy ions range can reach tens to hundreds microns and its extremely high linear energy is able to induce effective chemical modifications using low fluence values. Nano-wear performance and surface mechanical properties of samples of pristine and SHI irradiated (using N₂⁺ ions at 33 MeV and a fluence of 1 × 10¹² ions/cm²) were characterized by depth sensing indentation (DSI) and scanning probe microscopy (SPM). It turned out that modifications induced by irradiation at the surface layers were successful to reduce nano-wear volume and creep deformation. These improvements were related to beneficial changes in hardness, elastic modulus, hardness to elastic modulus ratio and friction coefficient.