Calcium Phosphate and Ion-substituted Coatings for Resorbable Magnesium-Based Bone Implants: A Review

Magnesium (Mg) and its alloys are promising alternatives to conventionally used bioinert metals for bone repair due to their favorable biocompatibility and mechanical properties that closely mimic that of natural bone. However, Mg-based implants are limited by rapid corrosion in physiological environments, posing significant challenges such as premature implant failure, hydrogen gas accumulation and potential cytotoxicity. Calcium phosphate and ion-substituted coatings can not only enhance corrosion resistance of Mg-based implants by providing a barrier layer but also promote osseointegration and offer therapeutic functionality. These ceramic coatings, including hydroxyapatite and other substituted variations with strontium, zinc, silicon and silver offer further advantageous properties that can improve bone-implant integration and enhance antibacterial efficiency, leading to better patient outcomes. Advanced deposition techniques, including RF Magnetron sputtering and biomimetic immersion, enable precise control over coating properties and composition resulting in highly functionalized and tailored thin film coatings. This review discusses and evaluates various coating technologies and deposition techniques applicable to bone defect repair and implantation devices, with a focus on ceramic calcium phosphates and ion-substituted apatites, for the optimization of Mg-based implants towards clinic translation.