| Avascular necrosis of the femoral head (ANFH) is a refractory disease that may progress to collapse of the subchondral and articular cartilage of the joint. Despite best efforts, there still have not an effective method to fully prevent collapse of the femoral head in many patients. With the development of tissue engineering and biomechanics, we have a chance to treat the disease with these techniques. A primary and exploratory experiment of femoral head's bone defect in dogs reconstructed with tissue engineering technique was performed in our study. At first, we fabricated biomimetic scaffolds and constructed tissue engineering bones in vitro according to the results of biomechanical research. Then, they were implanted into the bone defect of the dog's femoral head. The treatment effect were evaluated by related methods.OBJECTIVE1. Observe the biomechanical influence of the proximal femur after the defect of principal load-bearing region in human femoral head being planted by different trabecular bone.2. Reconstruct and evaluate the three-dimensional structure of the trabecular bone in dog's femoral head and ANFH.3. Fabricate biomimetic biphasic calcium phosphate(BCP) ceramic scaffolds using three-dimensional(3D) gel-lamination technique and evaluate their structure with 3D parameters and related method.4. Select seed cells and fabricate tissue engineering bones in vitro. Observe their treatment effect in vivo by animal experiment.MATERIAL AND METHODS1. Three different size of bone defects(14mm diameter x 20mm depth, 20mm diameter x 20mm depth, 20mm diameter x 30mm depth) within human femoral heads' principal load-bearing region were drilled and the biomechanical properties of the proximal femora were tested in vitro by simulating single-leg stance phase. Rigidity of the whole proximal femora and the strain value at the juncture of femoral head and neck were evaluated after the loading being exerted on the femoral head with different size of bone defects. And then, the bone defects (20mm diameter x 30mm depth) were implanted with different structural trabecular bone or packed with bone chips. The rigidity and the strain value were recorded same as above. In order to illustrate the inner stress distribution in the femoral head, finite-element analysis(FEA) was done by repeating above-mentioned process in computer.2. According to the series two-dimensional images obtained by microtome section and Micro-CT, three-dimensional figures of trabecular structure from dog's femoral head and human ANFH bone specimens were reconstructed by computer. And then, the structure of these specimens was evaluated by three-dimensional parameters. These parameters included Bone Volume Fraction (BVF, BV/TV), Bone surface/bone volume (BS/BV), Trabecular thickness (Tb.Th), Trabecular number (Tb.N), Trabecular spacing (Tb.Sp), Structure Model Index (SMI) and Trabecular Pattern Factor (Tb.Pf).3. Porous biomimetic biphasic calcium phosphate(BCP) ceramic scaffolds with oriented trabecular structure were fabricated with three-dimensional (3D) gel-lamination technique according to the two-dimensional images of dog's trabecular specimen. Then, the three-dimensional structure of the scaffolds were reconstructed by computer according to the series Micro-CT images of these scaffolds and evaluated by three-dimensional parameters same as above. The biomechanical properties and cell biocompatibility of these scaffolds were also evaluated in our study.4. After choosing MSCs as seed cells in our study, biomimetic BCP tissue engineering bones were constructed in vitro and implanted into the bone defects of dog's femoral head for thirty weeks.Result1. According to the size of the bone defects, the stress distribution of the femoral head changed greatly and the rigidity of the whole proximal femora decreased 5.56%, 21.80% and 26.30% respectively. Unlike the packing of bone chips, after the bone defect were implanted with structural bone from femoral head, the stress distribution of the femoral head improved greatly in FEA result and the rigidity increased 10.82% in vitro biomechanical test.2. There was significant difference between the lower and super part of the dogs' femoral head specimens in BV/TV, BS/BV, Tb.Th, Tb.N, Tb.Sp, SMI and Tb.Pf. The super part of the specimen had higher value in BV/TV and lower value in Tb.Sp. The parameter SMI of this part represented the plate-rod characteristic of trabecular structure. The value of three-dimensional parameters in osteonecrosis specimen, which was different from that of normal trabecular structure, represented difference in sclerosis region and collapse region.3. There was no significant difference between trabecular samples and BCP scaffolds in BV/TV, Tb.Th, Tb.N, and Tb.Pf. The trabecular system of the scaffold, which had some orientation, represented plate-like model. With a macro-porous porosity of 62%, the average compressive modulus and ultimate strength along the axis of the scaffolds reached 464±36.03MPa and 5.62 ± 0.78MPa respectively. The results of cell biocompatibility test indicated MSCs survival and cell attachment on the surface of the BCP trabecular was good.4. Thirty weeks after operation, the basic contour of the femoral head in experimental group kept integrity. Trabecula of the BCP scaffolds were covered by a layer of new bone and the strength of defect region reached normal. On the country, the femoral heads in contrast group collapsed and lost their strength in...
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