Developing a molecular blueprint for mechanical response

松紧带为什么是松紧带？是什么使绳子变硬？当我们跑步时，我们的肌腱是如何吸收力的？这些问题与这些材料的弹性和粘度（“粘弹性”）有关，也就是说，当施加和释放应力时，它们变形的程度如何，然后又恢复到原来的形状。大自然利用蛋白质的能力来形成非常不同的机械结构。例如，我们身体中许多结构组织的分子构建块是胶原蛋白和弹性蛋白，它们组合（有时彼此或其他分子）形成肌腱、动脉、皮肤和许多其他组织。胶原蛋白为基础的组织往往相当僵硬，而弹性蛋白在数十亿次拉伸-放松循环中提供延展性。要用合理设计的蛋白质替代这些天然蛋白质，需要了解哪些力量负责这些生物材料的稳定性和粘弹性。我们建议通过减小材料的尺寸和复杂性来简化问题，而不是检查整个组织，我们首先拉伸这些蛋白质，一次拉伸一个，然后在它们组装成更复杂的结构时拉伸它们。通过观察这些不同的尺寸尺度（层次），我们希望我们对胶原蛋白和弹性蛋白的机械反应的研究将导致对粘弹性负责的因素有更深入的了解，并将有助于设计多功能替代品。

Why is an elastic band elastic? What makes a rope stiff? How do our tendons absorb forces when we run? These questions relate to the elasticity and viscosity ("viscoelasticity") of these materials, that is, how much they deform and then return to their original shape when stress is applied and released. Nature has exploited the ability of proteins to form very different mechanical structures. For example, the molecular building blocks for many of the structural tissues in our bodies are the proteins collagen and elastin, which assemble (sometimes with each other or other molecules) to form tendons, arteries, skin and many other tissues. Collagen-based tissues tend to be quite stiff, while elastin provides extensibility over billions of stretch-relax cycles. To replace these natural proteins with rationally engineered versions requires understanding what forces are responsible for the stability and viscoelasticity of these biomaterials. We propose to simplify the problem by reducing the size and complexity of the material - instead of examining whole tissues, we are first stretching these proteins, one at a time, and then stretching them as they undergo assembly into more complex structures. By looking at these different size scales (hierarchies), we hope our studies on the mechanical response of collagen and elastin will lead to a greater understanding of the factors responsible for viscoelasticity and will help in efforts to design versatile alternatives.