Developing a molecular blueprint for mechanical response

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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.