Hydroxyapatite-Reinforced, Infection-Resistant CoCrMo-3Cu for Load-Bearing Implants

CoCrMo (Cobalt-Chromium-Molybdenum, CCM) alloys offer excellent wear resistance for the articulating surfaces of load-bearing implants. However, cancer-causing cobalt ions may be released in vivo during articulation. Bacterial infection and biofilm formation on the implant surface are also contributing factors to the failure of these implants. Systemic or localized antibiotics are often not effective against such bacterial infections. Naturally, there is a need to design alloys that show inherent bacterial resistance with minimal release of cobalt ions. This study uses a potential biomedical alloy with copper (Cu) to provide inherent bacterial resistance and hydroxyapatite (HA) ceramic to enhance wear resistance by forming a solid lubricating tribofilm. CCM, CCM-3Cu, CCM-3Cu-1HA, and CCM-3Cu-2HA were processed using a laser-based directed energy deposition (L-DED) additive manufacturing (AM) technique. Antibacterial efficacy was evaluated using Pseudomonas aeruginosa, a Gram-negative bacterium, over 48 and 72 h. An extensive tribocorrosion study was conducted in physiologically relevant Dulbecco's Modified Eagle Medium (DMEM) at loads of 5 and 10 N, accompanied by microstructural analysis. Copper exhibits enhanced bacterial resistance, and the addition of HA improves wear resistance while also decreasing cobalt ion release. The wear resistance of CCM-3Cu-2HA showed a 6-fold improvement compared to CCM. These results indicate that HA-reinforced CCM-3Cu alloys are promising for the articulating surfaces of load-bearing implants.