Among load-bearing implants, total hip arthroplasty (THA) is probably the most clinically successful intervention. CoCrMo alloy, a wear resistant material of choice, is typically used in femoral heads for THAs. In vivo life of THAs are often reduced due to debris generation, and Co and Cr metal ion release from modular junctions. Management of taper corrosion from trunnions of CoCrMo head and Ti6Al4V stems remain a serious challenge today. Taper corrosion happens primarily due to mechanically assisted crevice corrosion (MACC) along with fretting and galvanic corrosion, and leads to adverse local tissue reactions (ALTR), an immune- mediated biological reaction due to elevated Co and Cr ions. ALTR has profound influence on bone, leading to implant failure, which can result in early revision surgery. Co and Cr ions can also cause other symptoms such as deafness, blindness, and interstitial cell damage resulting in impaired renal functioning. Our application is focused on self-lubricating and self-healing calcium phosphate (CaP) reinforced Ti- or CoCrMo-alloys to minimize bio-tribocorrosion in applications such as trunnions in modular taper interlocks in THAs. CoCrMo-CaP composite will be designed to minimize Co and Cr ion release compared to pure CoCrMo alloy; while Ti alloy- CaP composites will be designed to completely eliminate the release of Co and Cr ions due to corrosion or wear degradation. The objective of this proposed research is to test our central hypothesis that CaP based solid lubricants in Ti or CoCrMo alloys will form an in situ film at the contact surface to minimize bio- tribo-corrosion and reduce metal ion release. The rationale is that once we understand the mechanisms of tribofilm formation and its influence on bio-tribo-corrosion, we can design implants with reduced metal ion release possibility in vivo. Our preliminary data show in situ tribofilm formation with CaP reinforcement in Ti6Al4V or CoCrMo alloys during in vitro bio-tribo- corrosion studies. Presence of tribofilm lowered wear induced damage and minimized metal ion release in vitro. We have three Specific Aims for the proposed program – (1) to understand tribocorrosion mechanism and tribofilm formation in CaP reinforced Ti-alloy matrix composites, and measure their in vitro biological response; (2) to understand tribocorrosion mechanism and tribofilm formation in CaP reinforced CoCrMo composites, and measure their in vitro biological response, and (3) to measure in vivo biological properties of CaP added Ti or CoCrMo alloys.

The objective of this proposed research is to test our central hypothesis that CaP based solid lubricants in Ti or CoCrMo alloys will form an in situ film at the contact surface to minimize bio-tribo-corrosion and reduce metal ion release. The clinical success of our program lies with manufacturing innovative femoral head with CaP added Ti or CoCrMo alloy composites via 3D Printing as an alternative to pure CoCrMo. These composites will minimize or eliminate Co and Cr ions leaching due to corrosion and wear degradation in vivo.