| The repairing of bone defect is one of the problems in orthopeadics, which has not been solved satisfactorily today. Traditional methods such as autograft and allograft have some disadvantages to deal with, so people have been searching for the ideal substitutes as alternatives to autograft and allograft. Of all materials available, calcium phosphate cement (CPC) is an important biomaterial for hard tissue repair because of its chemical and crystallographic similarity to the carbonated apatite in bones and has received considerable attention. CPC consists of a mixture of fine particles of calcium phosphate salts, the CPC powder can be mixed with water to form a thick paste that can conform to osseous defects to form degradable hydroxyapatite (HA), therefore, CPC's moldability, together with its excellent biocompatibility and osteoconductivity, make it a highly desirable material for orthopaedic repair. However, due to its poor macropores, low strength and absorbable rate, the clinical usage of CPC was limited. A major difficulty of the large en bloc scaffolds presently lies in the conflicting relationship between porous microstructure and strength. Moreover, there is still scholastic controversy about the influence of porous microstructure on biological and mechanical properties of CPC.In this study, it is hypothesized that the formation of porous microstructure would be sped up by coating a kind of biomaterial with higher biodegradation on the fibers of the artificial bone, and the rationale for the microstructural design was that large-diameter absorbable fibers would initially strengthen and toughen the graft, then dissolve to form long macropores to facilitate cell infiltration, tissue ingrowth. Through the study on the distribution pattern of human bone's internal microstructure, two kinds of bionic microstructure artificial bone cylinders with perpendicular structure and concentric structure, consisting of self-harden calcium phosphate cement, Chitosan fiber (CF), type-I collagen, and recombinant human bone morphogenetic protein 2(rhBMP-2) were designed and fabricated by a new manufacturing process based on computer-aided design and rapid tooling techniques in this research.By the mechanical study, the bionic microstructure artificial bone scaffold reached a macroporosity of 64% after fiber dissolution, and the compressive strength of microstructure bones is 30MPa, 4 times higher than 6MPa of CPC control. It is concluded that the bionic structures have better mechanical properties. By in vitro and in vivo experiments (repairing canine cancellous bone defects), it was found that the bionic microstructure artificial bone formulation supported canine bone marrow stromal cells (BMSCs) adhesion, proliferation and viability, and the bone penetration ratio was in the following decreasing order: concentric structure groups, perpendicular structure groups, and CPC control groups (P<0.01) (Two-way ANOVA). The bioactivity of bionic artificial bone is closely related to the rule of pore formation and its fiber structure, the difference in fiber structure leads to the formation of different osteogeneses and biodegradation in a long period of implantation. The experiments show that the novel artificial bone grafts with bionic microstructures can facilitate new bone ingrowth, biomaterials regenenration and enhance the defect healing in big animal models; the bionic concentric fiber microstructure is a relatively ideal fiber structure, which proves the validity of this bionic structure design and the positive influence of three-constituent fiber-reinforced composite artificial bone with bionic structure on biomechanics and osteogeneses. |
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