Creation of dense hydroxyapatite (synthetic bone) by hydrothermal conversion of seashells

Strombus gigas (conch) shells and Tridacna gigas (Giant clam) shells have dense, tailored structures that impart excellent mechanical properties to these shells. In this study, conch and clam seashells were converted to hydroxyapatite (HAP) by a hydrothermal method at different temperatures and for different conversion durations. Dense HAP structures were created from these shells throughout the majority of the samples. High temperatures were found to accelerate the conversion process, however, cracks were found on the surface of the samples converted at high temperature or for very long conversion times. The conversion at 180 °C, refreshing the diammonium hydrogen phosphate [(NH4)2HPO4] solution every 2 days, produced samples of good quality. Different morphologies of HAP were found in different regions of the converted shells, which may be caused by different structural morphologies and in different amounts of porosity in the original shells. Partially converted shell samples with dense HAP layers on the surface growing inward and original shell structures inside have an average fracture stress about 137–218 MPa, which is close to the mechanical strength of compact human bone.