Advancements in coating technologies for additive manufactured biomedical implants: A critical review

Additive manufacturing (AM) has transformed biomedical implant fabrication by enabling patient-specific geometries, controlled porosity, and architected lattice structures that closely replicate the mechanical and anatomical requirements of native tissues. However, the surface quality, biological performance, and long-term durability of additively manufactured implants often remain inadequate for demanding clinical applications. Cold spray (CS), a solid-state deposition technology based on high-velocity particle impact, has emerged as a promising surface engineering strategy capable of overcoming these limitations while preserving the microstructural integrity of substrate and coating-materials. This review critically examines the integration of AM and CS for the development of next-generation biomedical implants. The fundamental principles of AM and CS are discussed alongside recent advances in feedstock design, bonding mechanisms, microstructural development, and coating–substrate interactions. Particular emphasis is placed on bioactive, antibacterial, and multifunctional coatings based on hydroxyapatite, calcium phosphates, bioactive glasses, titanium alloys, and composite systems. The influence of processing parameters on corrosion resistance, wear behavior, fatigue performance, osseointegration, and biological response is systematically evaluated. Recent developments in hybrid AM–CS manufacturing, functionally graded architectures, post-processing strategies, and intelligent process monitoring are also analyzed. Finally, current challenges associated with coating adhesion, process standardization, residual stress management, and clinical translation are identified, while future directions involving artificial intelligence, smart coatings, therapeutic surfaces, and patient-specific multifunctional implants are highlighted. The review demonstrates that the synergistic integration of AM and CS provides a promising pathway toward durable, bioactive, and personalized implant systems capable of addressing the evolving demands of regenerative and orthopedic medicine.