Lubrication Enhancement for UHMWPE Sliding Contacts through Surface Texturing

Considered a self-lubricating, abrasion-resistant biomaterial, ultra-high-molecular-weight polyethylene (UHMWPE) has become the most common acetabular cup material used in artificial hip joints. Artificial hip joints exist primarily in the boundary and mixed regimes, which can lead to premature failure due to surface wear, debris generation, and subsequent osteolysis. The tendency of failure due to the generation of wear debris has turned the hip problem into a complex tribological challenge with a focus on abrasion-resistant surfaces. Surface texturing in the form of microdimples has been shown in other applications to provide enhanced wear resistance through the trapping of wear debris and through the enhancement of fluid pressures to levels that promote mixed-to full-film lubrication even at low speeds. The objective of this investigation is to explore the potential for surface texturing of UHMWPE sliding contacts in enhancing the lubrication regimes present in total hip replacements. Surface textures were created using a mechanical micromachining process, and experiments were conducted on a pin-on-disk tribometer under lubricated conditions present in the hip for textured and untextured samples. Results show that the surface textures were able to reduce friction by up to 50% over that observed with untextured UHMWPE samples, with evidence that suggests a regime shift from boundary lubrication to mixed and full-film lubrication as the primary mechanism for friction reduction.