Evaluation of Bioactive Glasses to Support New Bone Formation

Large bone defects resulting from trauma or resection of tumors represent a significant clinical problem. Bioactive glasses, synthetic graft materials used to repair bony defects, exchange ions with the environment, creating a hydroxyapatite-like layer which can bond strongly to bone. It has been shown that replacing the silica oxide of bioactive glasses with boron oxide results in higher neoformed bone tissue around glass particles. Based on these observations, borosilicate (13-93B1) and borate (13-93B3) bioactive glasses were created in scaffold form and implanted into a rat non-healing calvarial defect model. Objectives: The purpose of this study was to evaluate the effectiveness of borosilicate and borate bioactive glasses in bone regeneration, angiogenesis, and hydroxyapatite conversion. Methods: Critical-sized (4mm diameter) defects were created in rat parietal bone (2 defects/bone, n=28) and implanted with bioactive glasses: 45S5 silicate glass as packed particles (positive control), 13-93 silicate, 13-93B1 borosilicate, or 13-93B3 borate glasses as fiber scaffolds, or left empty (negative control). Calvarial samples were harvested, processed, and stained H&E to evaluate bone regeneration, PAS for blood vessel area, and von Kossa for mineralization. The samples were quantified using Osteomeasure histomorphometry software and statistics analyzed (ANOVA, Tukey's, p<0.05). Results: Amount of new bone was 12.4% for 45S5, 8.5% for 13-93, 9.7% for 13-93B1, and 14.9% for 13-93B3. Bone regeneration for B3 was significantly higher (p=0.04) than 13-93. Blood vessel area was significantly higher (p=0.009) with 45S5 (3.8%), with no differences in 13-93 (2.0%), B1 (2.4%), or B3 (2.2%). Percent von Kossa-positive area was 18.7% for 45S5, 25.4% for 13-93, 29.5% for 13-93B1, and 30.1% for 13-93B3, significantly higher (p=0.014) in B1 and B3 glasses than in 45S5. Conclusion: The 13-93B3 bioactive glass scaffolds could serve as an effective new substrate for bone repair. Funded by UMKC Summer Scholars Program and DOD/USA Med Research (W81XWH-08-1-0765).