Protein Materials Balance Strength, Energy Dissipation and Robustness by Selecting Nanopatterned, Hierarchical Features

Friday, July 27, 2007 - 3:40pm - 4:00pm
EE/CS 3-180
Markus Buehler (Massachusetts Institute of Technology)
Deformation and fracture are fundamental phenomena with major implications on the stability and reliability of machines, buildings and biological systems. All deformation processes begin with erratic motion of individual atoms around flaws or defects that quickly evolve into formation of macroscopic fractures as chemical bonds rupture rapidly, eventually compromising the integrity of the entire structure. However, most existing theories of fracture treat matter as a continuum, neglecting the existence of atoms or nanoscopic features. Clearly, such a description is questionable. Here we discuss an atomistic approach to describe such processes using ultra large-scale molecular dynamics (MD) simulation implemented supercomputers. MD provides unparalleled insight into the complex atomic-scale deformation processes, linking nano to macro, without relying on empirical input, since all atomic interaction parameters can be derived from fundamental quantum chemical theories. We demonstrate how MD can be used within a multi-scale simulation framework to predict the elastic and fracture properties of hierarchical protein materials, marvelous examples of structural designs that balance a multitude of tasks, representing some of the most sustainable material solutions that integrate structure and function across the scales. Breaking the material into its building blocks enables us to perform systematic studies of how microscopic design features influence the mechanical behavior at larger scales. We review studies of collagen – Nature’s super-glue, spider silk – a natural fiber that can reach the strength of a steel cable, as well as intermediate filaments – an important class of structural proteins responsible for the mechanical integrity of cells, which, if flawed, can cause serious diseases such as the rapid aging disease progeria. The common ground of these examples is the significance of the material properties at large deformation, its alteration under stress, presence of defects or the effect of variation of environmental conditions. Our studies elucidate intriguing material concepts that enable to balance strength, energy dissipation and robustness by selecting nanopatterned, hierarchical features.