Magnesium (Mg) and its alloys posse’s great potential for the application of biodegradable medical implants. It is due to their unique properties like low density and elastic modulus, good biocompatibility, etc. But still there are many challenges for Mg alloy based implants. Due to rapid degradation of Mg and its alloys in biological fluid, it loses its mechanical integrity and fails to perform before the complete healing of bone fracture (in orthopedics application) or removal of plaque in arteries (in case of vascular implants). Using suitable alloying elements mechanical strength and corrosion resistance of Mg-alloys can be enhanced but cytotoxicity and long term inflammatory consequences of these elements are the major concern. Further modifying the surface characteristics of Mg-alloy through various surface coating, machining, mechanical working, etc., corrosion behaviour can be manipulated. In this field of biodegradable implants, the various opportunities are yet to be explored in detail to improve the clinical performance of Mg alloy implants for orthopedics and vascular applications. This review paper summarises the various challenges and opportunities in design and development of biodegradable Mg alloy implants.

Mg and its alloys evince strong candidature for biodegradable bone implants, cardiovascular stents, and wound closing devices. However, their rapid degradation rate causes premature implant failure, constraining clinical applications. Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements, besides yielding effective corrosion resistance. This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years, aiming to build up a comprehensive knowledge framework of coating techniques, processing parameters, performance measures in terms of corrosion resistance, adhesion strength, and biocompatibility. Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis, angiogenesis, cytocompatibility, hemocompatibility, anti-bacterial, and controlled drug release towards in-vitro and in-vivo study models. The challenges associated with metallic, ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated. The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.

NiTi is a shape memory alloy, mostly employed in cardiovascular stents, orthopedic implants, orthodontic wires, micro-electromechanical systems and so on. The effective and net shape machining of NiTi is very critical for excellent response of this material in medical and other applications. The present experimental work on wire electrical discharge machining process identifies the influence of process parameters that affect the cutting rate, dimensional shift and surface roughness while machining of porous nickel–titanium (Ni₄₀Ti₆₀) alloy. Porous Ni₄₀Ti₆₀ alloy was produced in-house using powder metallurgy technique. Response surface methodology–based central composite rotatable design has been used for the planning of experiments on wire electrical discharge machining. Empirical relations have been developed between the process parameters (pulse on-time, pulse off-time, servo voltage and peak current) and response variables. Desirability approach has been used for optimizing the three response variables simultaneously. Confirmation experiments were also performed at the optimized settings and reflect a close agreement between the predicted and experimental values (percentage error varies from −6.13% to +6.85%). Using wire electrical discharge machining, NiTi alloy can be machined easily and successfully in single-cutting operation, but after the first cut in wire electrical discharge machining, a surface projection appears on work surface which is the unmachined material on work surface.