Study of in vitro bioactivity of biogenic hydroxyapatite synthesized from Black Sea Rapana venosa shells

The biogenic hydroxyapatite (BHA) used in this study was synthesized via solid-state reaction from Rapana venosa shells - a natural CaO source and monocalcium phosphate monohydrate Ca(H2PO4)2 ?H2O. The in vitro bioactivity of the synthesized BHA was evaluated in simulated body fluid (SBF) over 4, 7, 15 and 21 days (Kokubo protocol). After exposure to SBF, surface changes of the BHA samples and the ion exchange dynamics with the medium were analysed using different methods. Fourier-transform infrared spectroscopy analyses confirmed the stability of the phosphate structure of the BHA samples and the formation of apatitelike layers. The vibration modes of PO4 3 - tetrahedral are studied through Raman spectroscopy for all the analysed powders. Scanning electron microscopy images revealed increasing mineralization of the BHA samples in interaction with SBF in period of up to 15-21 days, evidenced by the formation and densification of the surface crystalline phase. Energy-dispersive X-ray spectroscopy analysis confirmed rising and stabilization of Ca/P content, corresponding to the secondary apatite formation. Inductively coupled plasma optical emission spectroscopy (ICP-OES) results indicated changes in Ca2+ and PO4 3 - concentrations in the SBF solution, confirming dissolution and precipitation dynamics. The results demonstrate a good bioactivity of the synthesized BHA and its potential for bone tissue engineering applications.