Research Progress on Biomedical Functional Coatings for Titanium Alloys: A Review
Titanium alloys are widely used for implants, yet corrosion, bacterial colonization and incomplete osseointegration remain important causes of interfacial failure. This review critically analyzes major biomedical functional coating fabrication techniques employed to enhance the surface properties of titanium alloys, including micro-arc oxidation, anodic oxidation, magnetron sputtering, electrochemical deposition, electrophoretic deposition, plasma spraying, physical vapor deposition, plasma immersion ion implantation, laser surface treatment, and hybrid (composite) approaches. For each method, key operational principles, structural and functional characteristics, performance advantages and limitations, and representative application domains are critically analyzed. Across these routes, biological performance depends on coating continuity, pore or nanotube geometry, interfacial bonding, phase composition and ion release. Calcium- and phosphorus-rich oxides and hydroxyapatite deposits generally promote cell adhesion, proliferation, alkaline phosphatase activity, mineralization and osteogenic differentiation. Dense oxide, nitride, tantalum and carbon-based films strengthen corrosion barriers, whereas Mn, Zn, Cu and Ag containing surfaces can inhibit bacterial adhesion and biofilm formation. Excessive ion release, however, may compromise cytocompatibility. Reported outcomes also vary with test medium, exposure time, bacterial strain and cell model. Standardized quantitative endpoints and longer-term corrosion, biofilm and osseointegration studies are required to guide clinically reliable multifunctional coatings.