Frictional behavior between bone and additively manufactured Ti6Al4V implants is affected by bone density and surface texture under varying loads

Friction at the bone-implant interface is a key factor in the initial stability of cementless orthopedic implants, largely affecting their long-term osseointegration behavior. Yet, there is limited data available for coefficients of friction (COFs) of different combinations of bone qualities and implant surface morphologies, particularly those produced by additive manufacturing techniques. This study measured the interfacial COFs of combinations of three levels of human cancellous bone qualities, characterized based on the BMD, and four Ti6Al4V micro and macro surface textures, produced using selective laser melting (SLM), under three levels of normal stress (0.5, 1.0, and 1.5 MPa), using a reciprocal friction test apparatus. Results indicated a wide range for the COF (0.37-0.95), significantly influenced by the individual effect of each of the metal surface roughness (strong positive: P-value < 0.05 and F-value = 19.12), bone density (moderate negative: P-value < 0.05 and F-value = 7.22) and normal stress (strong negative: P-value < 0.05 and F-value = 40.63), but not the interaction effects. A more variable frictional behavior was observed for both a lower density bone and a sharper-edged metallic texture, presumably due to the higher ploughing inconsistencies involved. The findings highlight the capability of SLM for developing COF-tailored patient-specific implants, based on personalized bone properties and biomechanical considerations.