Construction Of Strontium-doped Calcium Sulfate Hemihydrate-based Composite And Its Promotion Of Bone Defect Repair In Osteoporosis

With the increase of human life and the increasing proportion of aging in China,bone defect caused by osteoporosis has become a common disease in orthopaedics clinic.The use of artificial bone materials to repair osteoporotic bone defect is the main technical methods at present.Calcium sulfate hemihydrate?a-CSH?is the most widely used bone repair material in clinic filed due to its injectable and self-curing properties,non-immunogenicity,excellent biocompatibility,bone conductivity and complete absorption in vivo.In this study,aiming at the shortcomings of activity-lack and excessive degradation of?-CSH in the treatment of osteoporosis,a controllable and degradable osteoporotic bone repair material based on calcium sulfate was designed and constructed.The difference of material degradation and the effect of repairing osteoporotic bone defect were studied.This study includes the following three parts:?1?The common artificial bone repair material in clinic filed can only be used for the repair of common bone defects,and there is a problem of poor activity for repairing osteoporotic bone defects.How to design an artificial bone repairing material which has the effect of treating osteoporosis and bone repairing and has strong maneuverability as the key issue in the repair of osteoporotic bone defect.In this study,strontium-doped calcium sulfate hemihydrate?Sr CSH?was prepared by high-pressure hydrothermal salt solution method.The results showed that the doping of Sr²⁺does not change the phase structure of?-CSH,but the partial substitution of Ca²⁺by Sr²⁺leads to the lattice expansion of?-CSH.Sr CSH with different Sr²⁺doping amount has a long rod structure and uniform size,and the size of Sr CSH crystal decreases with the increase of Sr²⁺content.Bone cement prepared by CSH and Sr CSH has a three-dimensional porous structure,which is beneficial to nutrient transport and bone tissue growth.The results of cytocompatibility study showed that Sr CSH has better cell affinity than?-CSH,which is beneficial to cell adhesion and spreading,significantly promoted the proliferation activity of osteoblasts,and significantly up-regulated the expression of osteogenic proteins and genes.Osteoporotic skull defect experiments show that Sr²⁺doping can promote the growth of blood vessels in the defect area,the deposition of minerals and the maturation and calcification of osteoblasts.In addition,Sr²⁺can also inhibited the activity of osteoclasts and delayed the rate of bone metabolism,which is conducive to the repair of osteoporotic bone defects.?2?Based on the previous part,in order to broaden the application of Sr CSH in osteoporotic bone defect,CS-Sr CSH microspheres were prepared by electrostatic interaction between chitosan?CS?and Sr CSH in order to delay the degradation time of Sr CSH and improve the utilization efficiency of Sr²⁺.The results show that the phase structure of CS-Sr CSH microspheres is consistent with Sr CSH,and the microspheres were uniform in size and distributed in the range of 50-100 um.In vitro degradation data showed that compared with Sr CSH,the release rate of Sr²⁺in CS-Sr CSH microspheres was stable and reached the goal of sustained release.In vivo degradation experiments showed that the degradation time of CS-Sr CSH microspheres was 16 weeks,double that of Sr CSH.Cytotoxicity,systemic acute toxicity,systemic subacute toxicity,implant safety and genotoxicity experiments confirmed that CS-Sr CSH meets the standards of implanted materials and has good biosafety.The repair performance of Sr CSH/CS-Sr CSH composite and CS-Sr CSH for osteoporotic femoral defect was studied.The results showed that CS-Sr CSH with longer degradation time had better effect on repairing osteoporotic bone defect.It could provide Ca²⁺and Sr²⁺-rich environment for the defect area,promote vascular growth and mineral deposition,inhibit bone metabolism,and significantly improve the repairing effect of osteoporotic bone defect.?3?Due to the strong individual differences of osteoporotic bone defect patients,the demand for artificial bone repair materials is also different.In previous studies,Sr CSH-based osteoporotic bone repair materials with short-term and medium-term?<16weeks?degradation time were prepared.In this study,the strontium-doped calcium phosphate microspheres?Sr TCP?with different crystal structures??/??and porosity were prepared by high-voltage electrostatic droplet method from the perspective of long-term osteoporotic bone defect repair,and the Sr CSH/Sr TCP composite scaffolds with adjustable degradation time were obtained by compounding with Sr CSH.In this part,Sr CSH/Sr TCP with controlled degradation time by adjusting the crystal structure??/??and porosity of porous calcium-containing calcium phosphate microspheres?Sr TCP?composite scaffolds were prepared from the perspective of the application of complex osteoporotic bone defect repair.The results showed that the particle size of Sr TCP microspheres is inversely proportional to the voltage,and the porosity of the microspheres is proportional to the amount of porogens.As the results of in vivo degradation showed that the degradation rate of Sr CSH/?-Sr TCP was faster than Sr CSH/?-Sr TCP when the porosity was the same.On the other hand,the degradation time of microsphere scaffolds with small porosity was prolonged when the crystalline form was the same.Animal experiments showed that the degradation rate of Sr CSH/?-Sr TCP matched the new bone growth rate of osteoporotic bone defects,and the repair effect of the scaffolds was better;while Sr CSH/?-Sr TCP hindered the growth of new bone due to the slow degradation rate.The results of immunohistochemistry showed that the Sr CSH/?-Sr TCP group was more favorable for vascular ingrowth and new bone formation because of the higher expression of the internal angiogenesis marker CD31 and the new bone formation marker OCN.