Bone Regeneration using Silk Hydroxyapatite Hybrid Composite in a Rat Alveolar Defect Model

Background: To overcome the limited source of autogenous bone in bone grafting, many efforts have been made to find bone substitutes. The use of hybrid composites of silk and hydroxyapatite to simulate natural bone tissue can overcome the softness and brittleness of the individual components. Methods: Critical-sized, 7 x 4 x 1.5 mm alveolar defects were created surgically in 36 Sprague-Dawley rats. Three treatment groups were tested: an empty defect group (group I), a silk fibrin scaffold group (group II), and a hydroxyapatite-conjugated silk fibrin scaffold group (group III). New bone formation was assessed using computed tomography and histology at 4, 8, and 12 weeks, and semi-quantitative western blot analysis was done to confirm bone protein formation at 12weeks. Statistical analysis of new bone formation was done using the Kruskal-Wallis test. Results: Radiomorphometric volume analysis revealed that new bone formation was 64.5% in group I, 77.4% in group II, and 84.8% in group III (p=0.027) at 12 weeks. Histologically, the osteoid tissues were surrounded by osteoblasts not only at the border of the bone defect but in the center of the scaffold implanted area in group III from week 8 on. Semi-quantitative western blotting revealed that osteocalcin expression in group III was 1.8 times higher than group II and 2.6 times higher than group I. Conclusions: New bone formation was higher in hybrid scaffolds. Both osteoconduction at the defect margin and osteoinduction at the center of the defect were confirmed. There were no detected complications related to foreign body implantation.