In situ fabrication of hollow hydroxyapatite microspheres by phosphate solution immersion

► First study showing the as-prepared microspheres consisted of calcium deficient carbonated hydroxyapatite, which is biomimetic. ► Resulting apatite was B-type CO3HAP, and complete conversion to HAP microspheres is verified by Li content change in solution. ► Pore size distribution of the as-prepared HAP microspheres was mainly the mesopores with high pore volume and high total volume. ► Describe the transformation process and mechanism of hollow HAP microspheres accompanied with cross-sectional morphology status of the microspheres and open discussion.