Conversion of Borate Glass to Biocompatible Phosphates in Aqueous Phosphate Solution

Special compositions of CaO- containing borate glass have been shown to react with an aqueous phosphate solution at near room temperature to form hydroxypatite(HA),Ca10(PO4)6(OH)2, the main mineral constituent of bone. In the present work, the formation of other biocompatible phosphates was investigates by converting borate glass containing BaO or both BaO and CaO. The glass compositions were based on previously-studied CaO-containing borate glass by partially or fully replacing the CaO with BaO.The kinetics of the conversion reaction, as well as the composition and structure of the products formed from these BaO-containing glasses were investigated. Borate glass particles (150-300µm) with the required composition were prepared by conventional glass processing methods and placed in 0.25M K2HPO4 solution at 37oC and with a starting pH value of 9.0 or 12.0. At both pH values, the CaO containing glass particles were converted to HA, with fine needle-like crystals and high surface area (160-170 m2g). The BaO-containing glass converted to BaHPO4 at pH=9.0 and to Ba3(PO4)2 at pH =12.0, with both products having plate-like crystals and much lower surface areas (4-8 m2/g). The as-formed product from a glass containing both CaO and BaO was amorphous and , on calcinations for 8 hours at 7000C,yielded a mixture of two phosphates, a barium phosphate Ba3P4O13 and tricalcium phosphate Ca3(PO4)2