Engineered surfaces for biomedical implants: advances in coatings, materials, and techniques

The longevity and performance of biomedical implants depend strongly on surface properties, motivating coatings that enhance biocompatibility, mechanical resilience, and resistance to wear and infection. This review analyzes state-of-the-art coatings for orthopedic and dental implants, linking material choice, deposition method, and demonstrated in vitro performance. Bioinert systems (e.g., TiN, DLC), bioactive coatings such as hydroxyapatite and bioactive glass, and antibacterial approaches using silver-, zinc-oxide-, and graphene-based layers are compared for their effects on osseointegration, bacterial control, and durability. Deposition routes from plasma spraying to advanced methods including pulsed laser deposition, atomic layer deposition, and plasma-enhanced chemical vapor deposition are evaluated for adhesion, microstructure control, and clinical practicality. Across recent studies, nanostructured and multifunctional coatings consistently accelerate early osteogenic responses, ion- or carbon-modified hydroxyapatite improves interfacial bonding while adding antibacterial activity, conformal ultrathin films from atomic layer deposition enhance corrosion resistance on complex geometries without impairing cell viability, and multilayer or hybrid architectures reduce tribocorrosion under cyclic loading. Remaining challenges include maintaining long-term stability and uniform coverage on intricate implant designs and scaling fabrication economically. Emerging directions focus on stimuli-responsive surfaces and biodegradable, drug-eluting coatings aimed at reducing infection risk and speeding integration, with the overall trajectory pointing toward coatings that couple mechanical reliability with targeted biological function.