Additive manufacturing of biodegradable magnesium implants and scaffolds: Review of the recent advances and research trends

Synthetic grafting needs improvements to eliminate secondary surgeries for the removal of implants after healing of the defected tissues. Tissue scaffolds are engineered to serve as temporary templates, which support the affected tissue and gradually degrade through the healing period. Beside mechanical function to withstand the anatomic loading conditions, scaffolds should also provide a decent biological function for the diffusion of nutrients and oxygen to the cells, and excretion of the wastes from the cells to promote the new tissue growth and vascularization. Moreover, the degradation byproducts of the scaffolds should be safe to the human body. Development of such multifunctional scaffolds requires selection of the right material, design, and manufacturing method. Mg has been recognized as the prominent biodegradable metal with regards to its mechanical properties matching to that of human bone, degradability in the body fluid, and its ability to stimulate new tissue growth. Scaffolds with intricate porous structures can be designed according to the patient-specific anatomic data using computer aided designs. Additive manufacturing (AM) is the right method to materialize these models rapidly with reasonably acceptable range of dimensional accuracy. Thus, the recent research trend is to develop ideal scaffolds using biodegradable Mg through AM methods. This review compiles and discusses the available literature on the AM of biodegradable Mg parts from the viewpoints of material compositions, process conditions, formation quality, dimensional accuracy, microstructure, biodegradation, and mechanical properties. The current achievements are summarized together, and future research directions are identified to promote clinical applications of biodegradable Mg through the advancement of AM.