Influence of electron beam irradiation doses on bone regeneration by octacalcium phosphate collagen composites

An octacalcium phosphate and collagen composite (OCP/Col) achieved efficient bone regeneration with excellent resorbability. After the confirmation of its safety and efficacy in preclinical animal studies, the present study investigated the influence of electron beam irradiation doses on bone regeneration by OCP/Col in order to secure its commercialization. OCP/Col was prepared as previously described and the packed OCP/Col was sterilized using different doses of electron beam irradiation. A standardized defect, 9 mm in diameter, was made in the rat calvarium. A disk of OCP/Col (diameter 9 mm, thickness 1.5 mm) sterilized using different doses of electron beam irradiation was then implanted into the defect. Five defects in each group were treated and fixed 4, 12 and 24 weeks after implantation. Specimens were decalcified and stained with haematoxylin and eosin. In a histomorphometrical analysis, the percentage of newly formed bone in the defect (n-Bone%) was calculated. In OCP/Col 15 kGy, newly formed bone was enhanced and present throughout the defect with the resorption of OCP/Col. Furthermore, vigorous bone remodelling and bone maturation were observed. In OCP/Col 40 kGy, newly formed bone was not as prominent as that with OCP/Col 15 kGy. A histomorphometrical analysis using Student's t-test at 24 weeks revealed that the n-Bone% of OCP/Col 15 kGy (65.9 ± 7.14%) was significantly higher than that of OCP/Col 40 kGy (38.0 ± 10.2%). These results suggest that different electron beam irradiation doses influence bone regeneration by OCP/Col.