Strontium/magnesium-doped coralline hydroxyapatite for bone regeneration

The biocompatibility, osteoconductivity and porous structure of coral make it a popular material for bone regeneration. However, coral mismatches host bone degradation rates and lacks osteoinductivity. No prior research has investigated the physicochemical properties of strontium-doped coralline hydroxyapatite (Sr-CHA), magnesium-doped (Mg-CHA) and strontium- and magnesium-co-doped (Sr-Mg-CHA), especially their osteogenic mechanisms. This study synthesized CHA doped with osteoinductive elements (Sr, Mg and Sr-Mg) via a hydrothermal reaction to preserve 26.5-33.5% of the unconverted inner core of calcium carbonate (CaCO₃). Under identical reaction circumstances, the Sr doping ratio in the Sr-CHA outperformed Mg in the Mg-CHA. In contrast, Sr and Mg mutually inhibit each other during co-doping in the Sr-Mg-CHA. The Sr-CHA nanorods on nanocluster spheres were the longest, while the Mg-CHA were the shortest, with the Sr-Mg-CHA occupying an intermediate length. The Sr-CHA, Mg-CHA and Sr-Mg-CHA exhibited 16 times the specific surface area and 14 times the pore volume of the coral and displayed better biocompatibility and expression levels of osteogenesis-related genes and proteins (e.g. ALP, Runx2, COL I, OCN and OPN) compared to coral in vitro, as well as improved osteogenesis than coral or Bio-Oss^®  in vivo. With its optional Sr²⁺ release concentration and degradation rates and large specific surface area and pore volume, the Sr-CHA performs the best. This study improved bone tissue engineering and regenerative medicine by enhancing the understanding of doped CHA and revealing new ways to overcome bone repair material problems.