碱性环境对成骨细胞生长刺激作用及骨质疏松性骨再生材料微环境研究

Bone fractures caused by osteoporosis is a common clinical disorders. However, up to now, the development of biomaterials only stay in the concept of bone defect repair. Other than trauma, the treatment of osteoporosis must consider the unbalanced communication between osteoblasts and osteoclasts, in which pH plays the special role. Unfortunatley, no consideration of pH condition has been made in either resitrcting the activity of osteoclasts or enhancing the activity of osteoblasts...As we found, the effect of local pH on bone regeneration has never been properly studied or discussed. However, using a microelectrode, the pH on the surface of implant materials, rather than in the bulk, is measurable so that the biological response based on the local environment can be studied. It was found that the osteoblast viability was significantly enhanced with an increase of pH, to an optimum level at around pH 8-8.5; in contrast, the activity fell markedly below pH 6. The effect of strontium on osteoblast proliferation was further increased at pH ~8, suggesting a possible new approach for enhancing its activity in the treatment of osteoporosis. No stimulation of osteoblast proliferation was found for boron at normal physiological pH but, surprisingly, such an effect was found at pH 8.5. ..As a result, appropriately designed biomaterials, which create such an ideal ambient alkaline environment for bone regeneration, may be crucial aspects for bone substitutes. In this study, we will firstly verify the alkaline condition can be achived with the degradation of material, controlled by osteoblasts; secondly, the degradation rate of hydroxyapatite, borosilicate and calcium silicate can be controlled with the incorporation of strontium, in order to create an ambient alkaline microenviornment for bone regeneration; thirdly, in vivo study by osteoporotic animal model to monitor the degradation behaviour of the implant and track the bone formation ability.

由骨质疏松导致的骨折和骨缺损是临床中常见疾患。然而，迄今为止，骨再生材料的研发仍然停留在骨缺损修复的概念上。与单纯的创伤骨缺损不同，这种由疾病引起的骨缺损，在材料的设计中必须充分考虑到疾病的特点：即如何在抑制破骨细胞活力的同时，能有效提高成骨细胞活力。本项目组发现成骨细胞生存的最佳环境并非在pH 7.4的正常体液环境，而是略高于pH 8的碱性环境。进而发现随着硅酸钙的降解，可在材料表面营造出碱性的微环境。此微环境的存在将直接影响成骨细胞的活力。因此，本课题将首先对体外及体内成骨微环境进行研究，明确碱性微环境可由材料降解诱导成骨细胞调控；其次，以碱金属离子锶来调控羟基磷灰石、硼酸盐玻璃及硅酸盐的降解速率，以期营造出最适宜成骨细胞增殖的材料降解微环境；并在细胞/分子层次上对相关机理进行探讨；最后，通过骨质疏松性大鼠模型，追踪材料在动物体内降解所形成的微环境，为骨质疏松性骨再生机制研究提供新思路

骨质疏松骨缺损的再生过程缓慢，这是由于相对于正常骨再生过程，骨质疏松骨的微环境中成骨和破骨能力严重失衡。因此，与单纯的创伤骨缺损不同，为骨质疏松病人设计的材料必须考虑到疾病的特点进行设计：即通过调节干细胞及破骨细胞的活性，恢复骨折部位的正常骨再生能力，实现对骨折和骨质疏松的双重治疗。过去材料的设计与改性以局部改善细胞活力与分化能力为主，但恰恰忽略了这些细胞赖以生存的微环境pH值。本项目组发现成骨细胞生存的最佳环境并非在 pH 7.4 的正常体液环境，而是略高于 pH 8 的碱性环境。进而发现随着硅酸钙的降解，可在材料表面营造出碱性的微环境。此微环境的存在将直接影响成骨细胞的活力。本课题对由材料引起的体内微环境pH变化及其引起的生物学效应进行了详细讨论，取得相关研究成果如下：1.明确碱性微环境可由材料降解产生，发现骨质疏松大鼠骨髓基质干细胞在pH 7.4左右拥有最佳的增值效率，而在pH 7.8-8.0区间，成骨活性显著升高；同时，体外试验证明，材料表面微环境 pH 的微量改变对破骨细胞分化及活力产生显著的影响。2. 以碱金属离子锶来调控羟基磷灰石、硼酸盐玻璃及硅酸盐的降解速率，制备了一系列掺锶硅酸盐及硼酸盐玻璃/陶瓷材料，并完善了材料体外表面pH值及体内微环境pH值的测量方法。3. 建立了骨质疏松大鼠模型，证明不同的生物材料植入体内产生不同的微环境pH值，微环境pH高的生物材料在修复过程中有更多新骨生成；同时，较高的微环境pH值伴随TRAP阳性类破骨细胞的晚响应，并在修复过程中检测出有过渡矿化层的产生。本课题的顺利实施，为骨植入材料的研究提供了新的思路，证明了营造材料植入初期碱性微环境对局部骨组织再生的重要意义，并引发出对破骨细胞在骨再生过程中之重要意义的前瞻性的思考，为后续更深入的研究提供了保证。