Progress and perspectives of metal-ion-substituted hydroxyapatite for bone tissue engineering: comparison with hydroxyapatite

Hydroxyapatite (HA) is one of the most common bioceramics and is abundant in human bones. HA is composed of calcium phosphate, which is prevalent in biomedical processes, particularly bone formation, osteogenesis, and angiogenesis. As HA is one of the core materials that makes up the human body, there has been considerable research on methods of synthesizing HA while changing its properties by substituting various types of metal ions. In particular, previous studies have intensively investigated the size, crystallinities, and morphologies generated using various synthesis methods to change the characteristics of HA by substituting different metal ions. This review summarizes the findings of these studies on HA, including findings on the characteristics of HA in natural bone, methods of synthesizing HA, and findings on metal-ion-substituted HA. Furthermore, the characteristics and applications of HA that were investigated in previous studies are summarized, and the latest trends and perspectives on the future of the field are also presented.