Biodegradable Magnesium Composites for Orthopedic Applications

The new generation of biodegradable magnesium (Mg) implants has drawn substantial attention because of their similar physical properties (such as elastic modulus and relative density) to human bone. Due to this, Mg tends to overcome the stress shielding effect and secondary surgery in contrast to conventional metallic implants (stainless steel, titanium, and titanium alloys). However, the degradation rate of Mg is higher (standard electrode potential of -2.73 V) in the physiological environment, which ultimately produces a large amount of hydrogen gas. Hence, it exponentially induces a decrease in mechanical strength and failure of the implants with impaired bone healing. Several efforts have been taken, such as alloying, surface modifications, and nanocomposites, to control the onset degradation to address these concerns. Among them, Mg nanocomposites have gained much interest in controlling the biocorrosion of Mg. The appropriate shape, size, and reinforcement amount significantly alter nanocomposites’ functional properties. Various bioceramics such as metal oxides (MgO and ZnO), tricalcium phosphate (TCP), and hydroxyapatite (HA) have been used as bioceramics reinforcements in the Mg matrix for developing bioresorbable Mg-based composites. The synergy of load transfer from matrix to hard reinforcement and mismatch of elastic modulus between matrix and reinforcement can maintain the physical and mechanical properties in the biocorrosion environment and mechanical integrity. Further, apart from the reinforcements for proper composite design, the fabrication route is also an essential criterion as it directly influences the functional properties of the composites. In vitro and in vivo characteristics of Mg-based nanocomposites are highly based on the kind and quantity of reinforcements. Additionally, some of the techniques (additive manufacturing, friction stir processing, and spark plasma sintering) facilitate rapid fabrication, grain refinement, and the high performance of metal matrix composites. To illustrate the crucial updating of research and development on Mg-based nanocomposites for biomedical applications, attempts are made in this chapter.