Influence of macropore bone block on osteogenic activity and mechanical property in vivo

Abstract

Objective To observe and identify the osteogenic activity, biocompatibility and mechanical property of a type of macro-pore bone block bioactive glass in rabbits. Methods Establish the femoral condyle defect model with New Zealand white rabbit. Implant in the defect with macro-pore bone block bioglass, β-TCP and NOVABONE® respectively. According to the different materials implanted in the defect, three groups were divided as macro-pore bone block bioglass group, β-TCP group and NOVABONE group. After the surgery, X-ray examination was performed to confirm the location and fixation of the materials and to observe the femoral condyle fracture. The specimens were harvested at 4, 12 and 24 weeks after the surgery respectively. Micro-CT was performed to assess the new bone formation and degradation of the materials. Tetracycline-calcein double labeling was used to detect the mineral apposition rate of new bone. Van Gieson staining was used to assess the new bone formation percentage. Biomechanical markers including the compress strength and elasticity modulus were also measured. Results X-ray examination showed that each femoral defect was filled fully with materials and the materials were all in proper position. As indicated by Micro-CT results, at 24 weeks, the bone regeneration volume fraction of each group was 37.48% ± 0.70%, 25.29% ± 1.45%, 27.03% ± 1.25% respectively and the difference between macro-pore bone block group and β-TCP group or NOVABONE group was statistically significant. The residual material volume fraction of each group was 34.67%±3.52%,55.66%±2.05%,7.52% ±1.15% respectively and the difference between macro-pore bone block group and β-TCP group or NOVABONE group was statistically significant. The results of tetracycline-calcein double labeling showed that the mineral apposition rate in macro-pore bone block bioglass group, β-TCP group and NOVABONE group at 4 weeks was(1.577±0.045)um/d,(2.064±0.068)um/d,(1.19±0.09)um/d respectively and the difference between macro-pore bone block bioglass group and β-TCP group was statistically significant. As shown by the results of Van Gieson staining, the new bone area percentage of macro-pore bone block bioglass group, β-TCP group and NOVABONE group was 5.43% ± 1.25%, 2.77% ± 0.85%, 6.51% ± 1.21% at 4 weeks, 8.48% ± 0.84%, 2.94% ± 0.65%, 11.42% ± 2.66% at 12 weeks, 23.55%±1.13%, 12.92%±0.45%, 19.53%±0.91% at 24 weeks. The difference between macro-pore bone block bioglass group and β-TCP group or NOVABONE group at 24 weeks was statistically significant. By biomechanical test, the compress strength of specimens in macro-pore bone block bioglass group and β-TCP group increased as time prolonged, with no statistically significant between the two groups. The elasticity modulus of specimens in macro-pore bone block bioglass group and NOVABONE group was stable after surgery, closer to the rabbit bone, while elasticity modulus of the β-TCP group increased a lot, unsuit to the rabbit bone. Conclusion Macro-pore bone block bioglass presented good biological activity, biocompatibility and suitable biomechanical properties. This research loaded foundation for the application in weight-bearing sites of this new material Key words: Bone substitutes; Silicates; Materials testing; Osteogenesis; Biomechanics