Advancing metallic implant: A review of magnesium alloys as bio-absorbable alternatives to orthopedic devices

Permanent biomedical devices have been used as the backbone of orthopedic medical devices for decades due to their mechanical behavior, durability, and biocompatibility. However, these permanent devices showed limitations due to their stress-shielding effect, long-term inflammatory response, and require secondary surgery for removal of the implant after healing is completed. Consequently, the transformation is shifted from a permanent implant to a temporary implant, which is a bioabsorbable metallic implant used during bone tissue healing as a mechanical support for a temporary period and subsequently degrades and eliminates the need for secondary surgery. Magnesium alloy implants have shown as a promising bioabsorbable metallic implant due to their biodegradability, biocompatibility, and mechanical behavior related to bone. However, the abiding problem of Mg-based orthopedic implants is their fast degradation rate, release of Mg²⁺ and hydrogen (which causes bubbles and delayed healing) in the human body, and mechanical failure before completion of healing, thus hindering their clinical applicability. In order to improve the above problems, several researchers have explored and applied different techniques such as alloy composition, surface modification techniques as effective and efficient ways. Therefore, this review comprehensively examines the highlights of permanent and temporary implants, the degradation mechanism of magnesium in vivo, factors affecting the performance of magnesium alloys orthopedic implants, and performance optimization of magnesium-based orthopedic implants in orthopedic applications.