| Growth plate injury in a child caused by injures, infection and tumour is the most typical and common disease. Growth plate injury may lead to the physeal defect resulting in growth arrest and angular deformity and seriously influencing the life of the children. Nowdays, excising the bony bridge and inserting fat, bone cement, bone wax as interposition material have been used to treat the physeal injury clinically. Over the years, with the rapid progress of tissue-engineering, varying degrees of success have been achieved by tissue-engineered epiphyseal plate. However, the antigenicity of xeno-chondrocytes limited the clinical application. In this study, we made use of APA microencapsulated epiphyseal chondrocytes to reduce the immunological rejection, and to release TGF-βinducing MSCs into chondrocytes in order to repair the growth plate injures.Objective:established the experiment method of chondrocytes segregation, cultivate and freeze conservation in vitro; prepared the APA microencapsulated growth plate chondrocytes, and observed the differentiation of APA microencapsuled epiphyseal chondrocytes to bone marrow mesenchymal stem cells; and then implanted the APA-chondrocytes into the epiphyseal defects of growth plate and evaluate whether it may prevent the formation of the bone bridge,extend the period during growth plate fusion and recovery the ability of longitudinal growth.Method:(1) Cultured growth plate chondrocytes in vitro which have been harvested from growth plate of the distal femur and proximal tibia, and determined the phenotype of chondrocytes by staining with Safranin "O",Toluddine blue and immunehistochemistry of conllagen typeⅡ,detected the TGF-β1 which is secreted by physeal chondrocytes by way of the ELISA.(2) Constructed the APA microencapsulated epiphyseal chondrocytes, and detected the TGF-p1 which was secreted by APA-chondroyctes, and appraised whether the biology phenotype was expressed by the BMSCs which is co-culture with the APA microencapsulated epiphyseal chondrocytes.(3) Constructed the growth plate injures of distal femur in the rabbits.The animals were then randomly divided into 4 groups. The defects of physeal plate were filled with APA microencapsulated chondrocytes, APA microencapsule and chondrocytes, and the control group is left empry. Radiographs were taken of both legs after the operation to appraise the energy of growth and angle of the operated-on and unoperated-on femur. The speciments in every groups were obtained at 4,8,12, and 16 weeks. Many histologic staining were made in order to appraisal the treatment of the epiphyseal plate injury.Results:(1)The physeal chondrocytes with well biologic activity were obtained from the physeal chondrocytes, growth curve by the CCK-8 proved the condition of culture invitro was well. The chondrocytes were considered as the phenotype characteristic by the positive of the many histologic staining.(2) The chondrocytes could proliferated and synthesized the extracellular matrix,such as type-Ⅱcollagen and proteoglycans with the good histocompatibility. TGF-β1 excreted by chondrocytes passed through the microencapsule to induce MSCs into chondrocytes. The freeze conservation could been used to conserve the microencapsulated epiphyseal chondrocytes.(3) In the APA-chondrocytes group, the columnar arrangement of chondrocytes and the chondrocytes lacune in the region surrounding them were visible after surgery. The angular deformity and length discrepancy were less in the APA-chondrocytes group than in the other groups from 4 weeks until the last examination (16 weeks) after surgery, although it gradually increased during this period. There were lots of microencapsuled chondrocytes, which was kept integrity and spherical in the physeal defect, a few of living chondrocytes were seen in the APA. In APA gronps, microcapsule and ossification were found in the marginal area.In chondrocytes groups, residual chondroyctes and lymphocytes were diffused distribution in the defect. In the Defect group, the residual space had filled with connective tissue and blood vessels,the cavity had completely collapsed and filled with the bone bridge.Conclusion:We found that transplantation of APA-chondrocytes transplated into the model of the physeal injury could released TGF-β1 which induced the BMSCs into the chondrocytes and repair the physela injury to correct the angular deformity and length discrepancy of the leg with the injured physis. The APA microencapsulation could processed the isolatation of immunity and reduced the immunological rejection from recipients.
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