Surface strengthening on UHMW polyethylene acetabular cup

To improve long-term biocompatibility of hip prosthetic products, much effort is employed to modify their wear resistance and to reduce the generation of wear debris at contact surfaces. Viewing from the mechanics of wear - the articulating surfaces, the role of their relative mechanical properties should be reconsidered. A part of our sequential studies: modification of UHMW polyethylene acetabular cup is performed by nitrogen ion implantation. With appropriate implantation doses, e.g. 10¹⁶ ions.cm^-2, onto the surface, followed by surface analyses and related simulations, an obvious modification has been found: such ion-implanted layer is estimated up to 500 nm of depth; it creates a diffused layer that is elastically hardened. The nano-hardness shows a distribution curve, with the increase of ca. 8 times for the dose of 10¹⁶ ions.cm^-2. It has significantly reduced the difference of mechanical properties with the abrasive part. The transformation of its mechanical resistance is correlated with the formation of cross-linked polymeric structures, which are likely 3-D networks localized at the outmost surface.