Laser additive manufacturing of biodegradable Mg-based alloys for biomedical applications: A review

Metallic implants are widely used in internal fixation of bone fracture in surgical treatment. They are mainly used for providing mechanical support and stability during bone reunion, which usually takes a few months to complete. Conventional implants made of stainless steels, Ti-based alloys and CoCrMo alloys have been widely used for orthopedic reconstruction due to their high strength and high corrosion resistance. Such metallic implants will remain permanently inside the body after implantation, and a second surgery after bone healing is needed because the long-term presence of implant will lead to various problems. An implant removal surgery not only incurs expenditure, but also risk and psychological burden. As a consequence, studies on the development of biodegradable implants, which would degrade and disappear in vivo after bone reunion is completed, have drawn researchers' attention. In this connection, Mg-based alloys have shown great potentials as promising implant materials mainly due to their low density, inherent biocompatibility, biodegradability and mechanical properties close to those of bone. However, the high degradation rate of Mg-based implants in vivo is the biggest hurdle to overcome. Apart from materials selection, a fixation implant is ideally tailor-made in size and shape for an individual case, for best surgical outcomes. Therefore, laser additive manufacturing (LAM), with the advent of sophisticated laser systems and software, is an ideal process to solve these problems. In this paper, we reviewed the progress in LAM of biodegradable Mg-based alloys for biomedical applications. The effect of powder properties and laser processing parameter on the formability and quality was thoroughly discussed. The microstructure, phase constituents and metallurgical defects formed in the LAMed samples were delineated. The mechanical properties, corrosion resistance, biocompatibility and antibacterial properties of the LAMed samples were summarized and compared with samples fabricated by traditional processes. In addition, we have made some suggestions for advancing the knowledge in the LAM of Mg-based alloys for biomedical implants.