Calcium phosphate scaffolds with different macro-pores constructed vascularized natural bone-like grafts at non-osseous sites in vivo for bone defect repairing

摘要

Introduction: The architectural characteristics (e.g., geometry, size, and interconnectivity etc.) of scaffolds were suggested to a critical factor to ectopic bone formation. Calcium phosphate ceramics with the special architecture can induce bone formation in soft tissue. Our previous studies have shown that the porous bioceramic scaffolds with complementary porous structures are vascularized with new bone formation in canine dorsal muscle and abdominal cavity. In the present study, the influence of macro-pore structure on osteoinduction and vascularisation and the effect of pre-vascularised scaffolds with different pre-vascularised time to reconstruct the femur defects were explored. Materials and Methods: The hydroxyapatite (HA) scaffolds with different macro-pore sizes were respectively fabricated via spherulite-accumulating and porogen-preparing methods. The porous characteristics of scaffolds were investigated by micro-computed tomography (uCT). Next they were implanted into dorsal muscle and abdominal cavity of dogs for 1 month, 3 months and 6 months to observe their osteoinduction and angiogenesis at the non-osseous sites. The vascularised scaffolds were harvested at different implantation periods and applied to reconstruct femur defects in dogs. Histological examination and bio-mechanical evaluation were performed to characterize the properties of porous scaffolds, their ectopic bone formation ability and repair effect. Results and Discussion: Morphological observation showed that the scaffolds sizes of macro-pores are in range of 500-650μm (scaffold A), 750-900μm (scaffold B) and 1050-1200μm (scaffold C), which all have good interconnectivity. Image analyses of μCT revealed that all the scaffolds featured relatively regular porosity distributions. Histological observation showed that scaffold B had more new bone formation and angiogensis than other scaffolds from 1 to 6 months implantation. After 6 months implantation, the percent of new bone formation area of scaffolds A, B, C reached 19.3 %±4.3%, 37.1%±6.9% and 26.2%±3.7% in the dorsal muscle and 9.2%±2.1%, 14.3% ±1.8% and 11.1%±1.9% in the abdominal cavity, respectively. The results suggested that porous scaffolds exhibit an appropriate range of macro-pore size to osteogenesis and vascularisation in scaffold. The compressive strength of scaffolds fabricated via spherulite-accumulating approached to natural cancellous bone at 6 months implantation. The bending strength of repaired bone showed that the femur defects which were repaired with pre-vascularized scaffolds at 6 months reached 94.7MPa, with mechanical level near to the natural femur, after 3 months repair period. The repair period of defect femur decreased following the increased pre-vascularized time in vivo. Conclusion: The differences of ectopic bone formation induced by different macro-pore structures revealed the significant effect of scaffold macro-pore structure on osteoinduction and vascularisation. The pre-vascularised scaffolds at 6 months were successfully applied to reconstruct the femur defects in dogs.