Revised preparation procedure of calcium hydroxyapatite with sol consisting of sodium alginate and sodium diphosphate

Calcium hydroxyapatite (Ca10(PO4)6(OH)2; CaHAp) was prepared from the cation-exchange of Na+ in the gel consisting of sodium alginate and Na4P2O7 with Ca2+ from the mixture of Ca(CH3COO)2 and Ca(NO3)2 in an aqueous solution at pH 10 although it had been already reported that CaHAp could be prepared with the employment of CaCl2 at pH 6.5, which rather afforded calcium chlorapatite (Ca10(PO4)6Cl2).