The effect of an octacalcium phosphate co-precipitated gelatin composite on the repair of critical-sized rat calvarial defects

This study was designed to investigate the extent to which an octacalcium phosphate/gelatin (OCP/Gel) composite can repair rat calvarial critical-sized defects (CSD). OCP crystals were grown with various concentrations of gelatin molecules and the OCP/Gel composites were characterized by chemical analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED) and mercury intrusion porosimetry. The OCP/Gel composite disks received vacuum dehydrothermal treatment, were implanted in Wistar rat calvarial CSD for 4, 8 and 16 weeks, and then subjected to radiologic, histologic, histomorphometric and histochemical assessment. The attachment of mouse bone marrow stromal ST-2 cells on the disks of the OCP/Gel composites was also examined after 1 day of incubation. OCP/Gel composites containing 24 wt.%, 31 wt.% and 40 wt.% of OCP and with approximate pore sizes of 10-500 μm were obtained. Plate-like crystals were observed closely associated with the Gel matrices. TEM, XRD, FTIR and SAED confirmed that the plate-like crystals were identical to those of the OCP phase, but contained a small amount of sphere-like amorphous material adjacent to the OCP crystals. The OCP (40 wt.%)/Gel composite repaired 71% of the CSD in conjunction with material degradation by osteoclastic cells, which reduced the percentage of the remaining implant to less than 3% within 16 weeks. Of the seeded ST-2 cells, 60-70% were able to migrate and attach to the OCP/Gel composites after 1 day of incubation, regardless of the OCP content. These results indicate that an OCP/Gel composite can repair rat calvarial CSD very efficiently and has favorable biodegradation characteristics. Therefore, it is hypothesized that host osteoblastic cells can easily migrate into an OCP/Gel composite.