“…However, biological apatite (as occurs in natural bone) is a nonstoichiometric form of HA and is susceptible to ionic substitutions. Consequently, it contains 4–8 wt % of carbonate ions in addition to trace elements of ions such as Mg 2+ , Fe 2+ , Na + , K + , F − , Cl − , and HPO 1, 6, 10, 13–19. Synthetically, carbonate ions can be substituted at two different sites in the crystal lattice of the HA, either at hydroxyl ion site (referred to as A‐type CHA) or at the phosphate site (referred to as B‐type CHA) 10, 14, 16, 20.…”