模仿天然肌肉钙离子应激收缩和被动延伸的生物材料的研究

Biomaterials capable of mimicking both contraction and extension behavior (both active elasticity and passive elasticity) of muscles are designed to overcome the world-wide shortage of sources for muscle tissues/heart repair and transplant. The loss and dysfunction of muscle tissues (including cardiac, skeletal and smooth muscles), such as heart failure and muscle injury, has become one of the most important causes of diseases and death. Many people are suffering from cardiac disease and heart failure has become a major cause of death all over the world. But heart repair and transplant sources are very limited. As a result, lots of patients with cardiac diseases are facing the problems of lacking heart transplant sources and have to be waiting for death. Therefore, materials that could be used for muscle tissue repair and replacement are in a great demand...To solve these problems, extensive researches have been conducted to explore synthetic muscle-mimetic materials for biomechanics and technical applications. Various polymer gels have been produced to mimic muscles, especially muscle contractions, in response to either physical or chemical stimuli, including chemical/pH/solvent, electric and magnetic change. The development of artificial muscles relies on that environmental stimuli can induce changes in conformation of polymer chains. These changes can manifest, leading to macroscopic shape/volume changes of the polymer gel and thus generating forces...However, there are still limits of these technologies. For instance, the power generated by the pH-sensitive artificial muscles is significantly lower than that of natural muscles. Besides, there is a same drawback of these technologies: most of the artificial muscle systems emphasize on mimicking the contraction (/active elasticity) of muscles lacking passive elasticity, not meeting a requirement to mimic muscles: material should mimic both the passive and active elasticity of muscles. There have been very few reports on muscle-mimetic materials that are able to mimic all the complex properties of natural muscles. ..In order to address this issue, it is necessary to obtain information from the sequence of biomechanical microscopic phenomena of natural muscles. Previous studies show that, in the active elasticity of muscles Ca2+-induced conformation change of myosin is the main cellular event, while in the passive elasticity of muscles titin is largely responsible. Inspired by natural muscles, we aimed to design biomaterials capable of force generation upon Ca2+-activated contraction and titin-mimetic passive extension. The resultant materials would represent a new type of muscle-mimetic biomaterials. We anticipate these materials could find various applications in both fundamental researches and biomedicine fields.

肌肉组织的丧失和功能障碍，如心脏衰竭和肌肉损伤，已成为世界各地疾病和死亡的重要原因之一。因为修复和移植替代物来源短缺，很多病人因缺乏移植物而死亡。因此，可用于肌肉组织修复和替换材料的研究存在着很大的需求。我们拟研究一种模仿肌肉的材料—模仿肌肉的收缩和延伸(主动弹性和被动弹性)。鉴于在肌肉的主动弹性中，钙离子诱导肌肉肌球蛋白构象发生变化是主要机制，而在被动弹性中，肌肉肌联蛋白起主要作用，我们拟研究设计能够同时响应钙离子激活主动收缩和仿肌联蛋白被动延伸产生力的材料。本项目拟使用一种钙离子结合蛋白和一种仿肌联蛋白的人造蛋白；通过分子生物学方法构建重组蛋白，将二者结合为一体；并通过一种光化学催化的方法，将蛋白交联合成水凝胶材料。本项目拟通过对模仿天然肌肉生物材料的研究，加深对天然肌肉生物力学的理解；所得新型仿肌肉材料，在解决肌肉修复和移植物来源短缺问题的研究中，也有潜在的应用前景。

大多数人造肌肉系统只单一强调模仿肌肉的收缩（主动弹性），或是延伸（被动弹性），而不能同时模仿肌肉的被动弹性和主动弹性，未能达到全面模仿肌肉的要求。目前为止，有关能够模拟天然肌肉的所有复杂机械性能的生物材料的报道很少。本项目提出研究设计能同时模仿肌肉的主动收缩和被动延伸的生物材料。本研究通过将钙离子响应型β-Roll蛋白质结构域（RTX）结合到人造弹性蛋白质（GB1）和节肢弹性蛋白序列多肽（Resilin）的融合蛋白中，可以构建出具有特殊宏观力学结构的新型生物材料，并在一定程度上达到可以同时模仿肌肉主动和被动弹性的目的。圆二色光谱检测结果证实了钙离子可诱导RTX蛋白质结构域发生构象变化。原子力显微镜和光镊单分子力谱实验结果表明，在分子层面上，钙离子诱导的RTX蛋白质结构域的折叠可导致力的增加。通过钌介导光化学催化法基于RTX蛋白质结构域的重组蛋白可被交联形成水凝胶，收缩测试结果显示钙离子可诱导基于RTX蛋白质结构域的重组蛋白制得的水凝胶体积发生变化。分别在恒定应变和恒定牵引速度下进行的机械力实验结果显示钙离子可诱导基于RTX蛋白质结构域的水凝胶产生力，与天然肌肉类似。本研究结果表明，基于RTX蛋白质结构域的水凝胶在宏观层面上独特的机械性能可以归因于RTX蛋白质结构域在单分子水平上具有的纳米机械性质。该材料是一种全新的模仿肌肉的材料体系，可以同时模仿其主动和被动弹性。这些材料在生物医学领域和基础研究领域具有广泛的应用前景，有望为肌肉组织移植资源短缺问题提供一种可能的解决方案。此外，本研究也为“自下而上”的设计方法提供了一个有力的证据，即首先在分子层面上设计性能而后转换至宏观层面上的材料性能。