Mechanical characteristics of biodegradable magnesium matrix composites: A review

In recent years, a new generation of biodegradable metallic materials, magnesium alloys, has been called a revolutionary material for biomedical applications (i.e. in orthopedics applications as a bone-implant material), thanks to the reasonable strength (similar to bone tissue, compared to available metallic alloys) and high biocompatibility of magnesium and its alloys. However, pure magnesium can corrode too quickly in the physiological pH (7.4-7.6) and high chloride environment of the physiological system and therefore lose their mechanical integrity before tissues have sufficiently. Engineering approach to this challenge (high corrosion rate of Mg) can be (i) alloying of element additions, (ii) surface treatment and (iii) development of metal (magnesium) matrix composites (MMCs). Magnesium-based composites, as bio-materials, can provide a combination of unique characteristics including adjustable mechanical properties (i.e. tensile strength, elastic modulus, ductility) and corrosion resistance. This is the main advantage of magnesium-based composites as compared with alloying and surface treatment approaches. Here, the matrix materials are biomedical magnesium alloys based on Mg-Zn, Mg-Ca and Mg-REE alloy systems (REE stands for rare earth elements including yttrium, Y, cerium, Ce, lanthanum, La). The reinforcement phases are mainly based on hydroxyapatite (HAP), calcium polyphosphate (CPP), and β-tricalcium phosphate (β-TCP) particles, and hybrid HAP + β-TCP particles. In this paper a comprehensive review is provided on different grades of biodegradable magnesium matrix composites, with focus on their mechanical properties.