基于全营养元素的可降解镁合金界面螺钉的制备及其对腱骨结合部组织细胞的影响机理

Tendon-bone healing in bone tunnel has been regarded as the most critical issue of treatment for periarticular ligament and tendon injuries. The fixation of grafting tendon in bone tunnel is one of principle elements on healing. Interference screw is an effective extruding material, but screws based on titanium alloy or polylactic acid also have obvious deficiency in clinic. Although attracting much more attention as a new type of biodegradable material in recent years, magnesium alloy has some defects such as fast degradation and containing harmful elements, which impedes its clinical application. Our prophase development of biodegradable magnesium alloy based on whole nutrient element has removed harmful effects of aluminum and stannum. We has also improved strength, biocompatibility and degradation of magnesium alloy, which is superior to polylactic acid and titanium alloy. Hence magnesium alloy is presumed as an ideal biomaterial to prepare interfere screw due to its favorable histiocytic compatibility. Based on preliminary work, this study will continue research and development of interfere screw in magnesium alloy of high purity; observation of its mechanical property and corrosion in vitro; study of histiocytic effects of different magnesium concentrations on bone-tendon junction and PI3K signaling pathway; regulation of the rate of magnesium release and degradation and optimizing the devise of screws; observation of its effect on tendon-bone healing in bone tunnel in the animal model of ligament restoration. We will further optimize the screw property to lay a foundation for its clinical application of the new biodegradable interfere screws.

腱骨隧道内愈合是关节周围韧带肌腱损伤治疗中最为关键的问题。移植肌腱骨隧道内的固定是影响愈合的重要因素之一。界面螺钉是挤压式固定的有效材料，但目前使用的钛合金螺钉和聚乳酸螺钉各有明显的不足，临床缺陷较大。镁合金作为新型可降解材料近年备受关注，但降解过快、含有有害元素等缺点使其在骨科临床应用受阻。我们前期开发的全营养元素可降解镁合金，去除了工业镁合金中铝和稀有元素的有害影响，强度和生物相容性优于聚乳酸，降解性能优于钛合金，有良好的组织细胞相容性，是理想的制备界面螺钉的生物材料。本研究在前期工作基础上，研发高纯度镁锌合金界面螺钉，观察其体外力学性能及腐蚀性能变化；研究不同浓度镁离子对腱骨结合部组织细胞的生物活性及PI3K信号传导通路的影响，调控螺钉降解释放速率，据此优化螺钉设计；同时观察其对动物韧带修复模型的腱骨隧道愈合的影响，进一步验证优化后螺钉性能，为该新型界面螺钉的临床应用奠定理论基础。

界面螺钉是关节运动损伤后韧带重建以及肌腱转位常用的骨科器械。目前界面钉材料包括传统金属以及可吸收高分子聚合物，但都存在着各自的缺陷。本课题组通过优化高纯镁材料的加工工艺，制备出高纯镁界面螺钉，对金相结构以及力学性能进行检测；之后提取高纯镁界面螺钉浸提液，分析浸提液对人骨髓间充质干细胞分化成纤维软骨组织的影响；同时，在自体半腱肌重建新西兰白兔膝关节前交叉的模型中，用高纯镁界面螺钉和相同规格的纯钛螺钉固定移植物，并在术后第3,6,9和12周，观察膝关节X线表现、膝关节活动度、膝关节大体外观、腱骨复合体力学性能、股骨MicroCT影像、腱骨结合界面组化和免疫组化特征以及移植物止点组织中纤维软骨标志基因，纤维软骨基质以及相关细胞因子BMP-2，VEGF的表达量改变。加工后的高纯镁材料金相结构致密而均匀，力学性能明显提高。高纯镁界面螺钉在浸提液降解缓慢，其降解浸提液可以提高人骨髓间间充质干细胞的活性，同时促进了BMP-2、VEGF表达，上调了纤维软骨标志基因（Aggrecan，COL2A1，SOX9）表达和纤维软骨基质（GAG）的生成。在前交叉韧带重建术后，高纯镁界面螺钉植入后X线未表现出植入物宿主排异反应，膝关节功能恢复良好，关节面大体形态正常。在生物力学性能方面，高纯镁界面螺钉固定腱骨复合体的力学强度和纯钛界面螺钉固定下的力学强度在术后12周无明显差异。组化结果显示，高纯镁界面螺钉组在术后12周可观察到高分化的纤维软骨过渡层连接着腱骨界面，而纯钛界面螺钉组纤维软骨组织分化程度低、面积小。同时，免疫组化，RT-PCR，western blot结果证实纤维软骨分化相关细胞因子BMP-2，VEGF和BMP-2特异受体BMPR1A在高纯镁界面螺钉组分布更为广泛。高纯镁界面螺钉具有良好的降解特性，生物活性以及力学性能，表现出致密的微观结构和坚强的力学性能，可促进骨髓间充质干细胞向纤维软骨组织方向分化。在前交叉韧带重建的过程中，镁金属界面螺钉力学性能和降解速率能满足腱骨愈合的要求，在降解的同时可以促进腱骨结合处纤维软骨再生，使腱骨愈合达到生物学固定，同时参与了BMP-2和VEGF相关的纤维软骨止点再生机制，有望成为新的肌腱韧带内固定材料。