Compositionally graded doped hydroxyapatite coating on titanium using laser and plasma spray deposition for bone implants.

Plasma sprayed hydroxyapatite (HA) coating is known to improve the osteoconductivity of metallic implants. However, the adhesive bond strength of the coating is affected due to a mismatch in coefficients of thermal expansion (CTE) between the metal and HA ceramic. In this study, a gradient HA coating was prepared on Ti6Al4V by laser engineered net shaping (LENS™) followed by plasma spray deposition. In addition, 1 wt% MgO and 2 wt% Ag2O were mixed with HA to improve the biological and antibacterial properties of the coated implant. Results showed that the presence of an interfacial layer by LENS™ enhanced adhesive bond strength from 26 ± 2 MPa for just plasma spray coating to 39 ± 4 MPa for LENS™ and plasma spray coatings. Presence of MgO and Ag2O did not influence the adhesive bond strength. Also, Ag+ ions release dropped by 70% less with a gradient HA LENS™ layer due to enhanced crystallization of the HA layer. In vitro human osteoblast cell culture revealed presence of Ag2O had no deleterious effect on proliferation and differentiation when compared to pure HA as control and provided antibacterial properties against E. coli and S. aureus bacterial strands. This study presents an innovative way to improve interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic as well as dental implants. STATEMENT OF SIGNIFICANCE: Implants are commonly composed of metals that lack osteoconductivity. Osteoconductivity is a property where bone grows on the surface meaning the material is compatible with the surrounding bone tissue. Plasma sprayed hydroxyapatite (HA) coating improves the osteoconductivity of metallic implants, however, the adhesive bond strength can be weak. This study incorporates a gradient HA coating by using an additive manufacturing technique, laser engineered net shaping (LENS™), followed by plasma spray deposition to enhance the adhesive bond strength by incorporating a thermal barrier. The proposed system has not been well studied in the current literature and the results presented bring forth an innovative way to improve the interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic implants.