Osteogenic Properties of OCP/β-TCP Mixture as a Bone Graft Material

Objectives: Octacalcium phosphate (OCP) possesses biological properties to promote the osteogenic differentiation and regeneration of new bone tissue. OCP shows progressive conversion to hydroxyapatite (HAp) under physiological conditions with absorbing the calcium ion and releasing the phosphate ion. On the other hand, β-tricalcium phosphate (β-TCP) has been reported to exhibit releases of calcium ions and adsorbs phosphate ions in the physiological environment. The aim of this study was to improve the osteogenic properties of OCP through ion-regulation by mixing with β-TCP and to investigate the characterization of OCP/β-TCP mixture as a bone graft material.
Methods: The mixing ratio of OCP and β-TCP differed that depends on the experimental group, including 100:0, 75:25, 50:50, 25:75, 0:100. The characteristics of synthetic OCP were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, ion concentration in the simulated body fluid (SBF) immersed with calcium phosphate powder mixture (CaPs) was detected by inductively coupled plasma mass spectrometry (ICP-OES), and the crystal phase change of CaPs after immersion was analyzed using XRD. To confirm osteogenic differentiation, alkaline phosphatase (ALP) activity and quantitative real-time PCR (qPCR) were carried out.
Results: The OCP was found to be successfully synthesized through XRD and SEM. After immersion in SBF, the characteristic diffraction of OCP disappeared in the pattern of CaPs containing OCP over time. Ion release analysis indicated that calcium ions tended to increase until day 3, and after day 3, they decreased depending on OCP content, whereas phosphate ions gradually increased in all groups. ALP activity and qPCR indicated that OCP50TCP50 induced higher levels of osteogenic gene markers compared to other groups.
Conclusions: These results showed that the OCP/β-TCP mixture can control the rate of conversion of OCP to HAp by regulating the concentration of ions around the bone graft material through dissolution and conversion under physiological conditions. In addition, it was effective in the differentiation of osteoblast cells into bone gene expression. Therefore, the OCP/β-TCP mixture could be used as a novel bone graft material for the regeneration of bone in the field of dentistry and orthopedics.