Surface functionalization of additively manufactured titanium alloy for orthopaedic implant applications

The evolution and progress of 3D printing and additive manufacturing (AM) processes have revolutionized the defence, aviation, automobile and health care domain. In fact, this decade old technology have tremendous potential to fabricate freeform objects from scratch with highest sustainability. The AM technology have capability to fabricate biomedical instruments of complex geometries specifically for individual patients which is infeasible with the conventional manufacturing processes. Although, the overall performance of metallic implants produced using AM method is limited due to its geometrical distortion, surface morphology, roughness and other physical defects. Titanium and its alloys is determined as signature candidate for implant fabrication due to extraordinary combination of properties such as high strength to weight ratio, superior corrosion resistance property and low elastic modulus that goes excellent with the natural bone elastic modulus. However, recent research is inclined towards post-fabrication surface engineering technology that have potential to functionalize and develop component in accordance with the end-user's need. This review presents ongoing research and developments in the fields of surface engineering technology to functionalize laser and electron beam melted metal implants. Current progress in functionalizing implants by incorporating anti-microbial features with a higher stability have been discussed. To highlight the benefits to the clinicians a benchmark safety and performance of orthopaedic metal implants have been presented. In all cases, a special focus have been provided on clinical challenges such as osseointegration, anti-microbial activity, stress-shielding and fatigue life. Applying surface coatings to as built AM processed Ti implants and MOA electrochemical surface treatment process for porous Ti implants are recommendable methods for maximising clinical outcomes. The influence of different post-processing measures are described in relation to physio-mechanical attributes, tribological properties and biological responses. Production of lattice structured orthopaedic implants via AM routine could be the future generative approach to treat infectious medical conditions. Challenges in industrializing AM process for freeform fabrication of metal implants are openly raised and possible solutions with viability is discussed.