In Situ Time-Resolved Studies of Octacalcium Phosphate and Dicalcium Phosphate Dihydrate in Simulated Body Fluid: Cooperative Interactions and Nanoapatite Crystal Growth

The present study is focused on the in vitro study of the biphasic octacalcium phosphate (OCP)-dicalcium phosphate dihydrate (DCPD) system transformations in simulated body fluid (SBF) for possible applications as bone substitute materials. The aim of this paper is to outline the role of the additional component DCPD during a transformation/crystallization processes. Energy dispersive X-ray diffraction and FTIR spectroscopy techniques were used for in situ monitoring of the processes taking place in the system in real time. Morphological investigations were performed applying the scanning electron microscopy technique. Several OCP-DCPD combinations were investigated: (1) 100% OCP; (2) 70% OCP-30% DCPD; (3) 100% DCPD. The obtained experimental results allowed us to conclude that when only OCP is present in SBF, the formation of carbonated hydroxyapatite takes place, whereas for the OCP-DCPD (30%) system in SBF, less kinetically favorable hydroxyapatite (HA) is formed. The additional component (DCPD) influences significantly the structural behavior of hydroxyapatite, acting as the HA crystallization inhibition agent. By means of this approach, allowing for the control of the HA crystallization, the calcium phosphate based biomaterials can be suitably modified for implant use in bone tissue engineering. The results obtained in this work provided some insights into the biomineralization mechanism.