Nano-carbonate hydroxyapatite synthesis through CO2 absorption and wet precipitation

Abstract

Calcium phosphate compounds are used as a bone implant material for the treatment of bond related disease or injury. Among many calcium phosphate compounds, hydroxyapatite (HAP, Ca10(PO4)6(OH)2) and β-tricalcium phosphate (β-TCP, Ca3(PO4)2) are the most widely used. Although the major components of natural bone are calcium and phosphate, there are many other ions in the bone such as carbonate, sodium, and kalium. Therefore, many studies about ion substitution in HAP were reported. Especially, the carbonate substituted hydroxyapatite is of great interest because of its composition similarity with natural bone and potential to enhance bioactivity of bone grafts. There are many carbonate hydroxyapatite synthesis methods, but most of them use carbon containing chemical for the source of substituted carbonate during the synthesis. In this research, nano-carbonate hydroxyapatite (CHA) was successfully synthesized through wet precipitation method in aqueous solution. By creating superoxide anion radical in the system, atmospheric CO2 was captured and used as a source of carbonate groups in CHA. CHA formation was confirmed using XRD and FT-IR analysis, and comparison study between synthesized CHA and HAP was carried out. The gas chromatography result showed that our CHA synthesis system absorbed large amount of CO2 in the air efficiently. After that, we observed phase transformation occurred during the CHA synthesis. The result showed that dicalcium phosphate dehydrate (DCPD) was intermediate phase of CHA. Lastly, we succeeded in controlling substituted CO3 amount in CHA by controlling used H2O2 amount. As a result, we successfully synthesized CHA with bone similar composition. This research has two major impacts. First of all, this synthesis method proposes a new way to mineralize large amount of atmospheric CO2 and use the mineralized form of CO2 as the carbon source of CHA. Second, synthesized CHA can be used as bone implant material because of its chemical composition similarity to natural bone. Consequently, our CHA synthesis system presents the innovative method for synthesizing bone implant material while capturing atmospheric CO2.