| With the aging of the population, the demand for biomaterials has been increasing, especially bone repair materials. Bone defect is commonly seen in clinics, mainly due to infection, trauma, tumor and congenital disorders. Currently, critical-size bone defects remain difficult to repair. Various approaches have been developed for the repair of large defects, including the use of autografts, allografts and synthetic materials. Autografts are currently the gold standard but are limited in availability. Allografts, on the other hand, involve the risks of immune reaction and inflammatory reaction. Synthetic materials have been regarded as important alternatives to allografts and autografts. However, metallic materials generally lack bioactivity and non-metallic materials do not meet the requirement of mechanical properties for load-bearing applications.Tissue engineering has been introduced as a promising approach to repair large bone defects. The scaffold materials for bone tissue engineering need to fulfill a few basic requirements, including biocompatibility, three-dimensional (3D) porous structure, biodegradability, favorable material/cell interface and mechanical properties. Furthermore, for in vivo bone tissue engineering, the surface properties of scaffolds (chemical composition, surface microstructure) also play critical roles.In this study, firstly, calcium titanate coatings were prepared on Ti6A14V substrates by a thermochemical surface transformation technique. This technique was simple and efficient. Secondly, HA spheres with controllable microstructure were prepared by a method combining sol-gel and water/oil emulsification techniques and then acculmulated in a porous tube as a porous scaffold. The effects of scaffold microstructure and the bio-functionalization were studied by in vitro cell culture, in vitro biomimetic mineralization and in vivo implantation in non-osseous sites. Then, ectopic hybrid scaffolds were implanted in experimentally created bone defects to evaluate their bone repair capability. The following conclusions were obtained:1. Reaction between the molten calcium nitrate and Ti6A14V formed a uniform layer of calcium nitrate. This technique was simple and efficient, and the coating was bioactive. This technique could be used as a way of surface modification for titanium and its alloys.2. HA spheres with controllable microstructure were successfully prepared by combining sol-gel and water/oil emulsification. Spheres with porous or dense surface could be prepared by adjusting the processing conditions. The surface microstructures of spheres could influence the bio-functionalization of scaffolds. The scaffolds constructed from spheres with a porous surface were found to have superior bioactivities, including a better osteoblasts adhesion, more active proliferation, and a faster deposition of calcium phosphate salts during in vitro biomimetic mineralization.3. Scaffolds constructed from spheres with porous or dense surfaces were implanted in the abdominal cavities of dogs, and the ectopic bone formation and the improvement of mechanical properties were evaluated. Results showed that:the mechanical properties of both scaffolds were improved. The scaffolds consisted of porous-surfaced spheres showed a better capability of inducing ectopic bone formation compared with those consisted of dense-surfaced spheres.. These findings suggest that the surface microstructure of spheres is an important factor for the in vivo functionalization of scaffolds.4. Repair of experimental bone defects with ectopically hybridized scaffolds showed that the hybrid scaffolds had a superior ability of bone repair. The histological analyses revealed that new bone tissues were formed when using hybrid scaffolds for bone repair. These results demonstrate the feasibility of in vivo construction of bone tissues. This approach may provide new possibilities of creating clinically viable bone grafts for the repair of large bone defects. |
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