Fracture mechanics of biological protein materials: Robustness, strength and adaptability

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• Markus J. Buehler, Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-272, Cambridge, Massachusetts 02139, USA
• Thursday 13 March 2008, 16:00-17:00
• Engineering Department - Room LR 6.

If you have a question about this talk, please contact Michelle L. Oyen.

Proteins constitute critical building blocks of life, forming biological materials such as hair, bone, skin, spider silk or cells, which play an important role in providing key mechanical functions in biological systems. The fundamental deformation and fracture mechanisms of biological protein materials remain largely unknown, partly due to a lack of understanding of how individual protein building blocks respond to mechanical load and how they participate in the function of the overall biological system. However, such understanding is vital to advance models of diseases, the understanding of biological processes such as mechanotransduction, or the development of biomimetic materials. Recent theoretical and computational progress provides us with the first insight into such mechanisms and clarifies how biology ‘works’ at the ultimate, molecular scale, and how this relates with macroscopic phenomena such as cell mechanics or tissue behavior, across multiple hierarchical scales. Here we review how molecular dynamics (MD) simulations implemented on ultra-large computing facilities, combined with statistical theories, is used to develop predictive models of the deformation and fracture behavior of protein materials. This approach explicitly considers the hierarchical architecture of proteins, including the details of their chemical bonding, capable of accurately predicting their unfolding behavior and thereby providing a rigorous structure-property relationship. We exemplify the approach in the analysis of the deformation mechanisms of beta-sheets and alpha-helices, two prominent protein motifs that form the basis of many protein materials, including spider silk and intermediate filaments. Spider silk is a protein material that can reach the strength of steel cables, despite the predominant weak hydrogen bonding. Intermediate filaments are an important class of structural proteins responsible for the mechanical integrity of eukaryotic cells, which, if flawed, can cause serious diseases such as the rapid aging disease progeria or muscle dystrophy. For both examples, our studies elucidate intriguing material concepts that enable them to balance strength, energy dissipation and robustness by selecting nanopatterned, hierarchical features. We present an analysis that reveals that the utilization of such hierarchical features in protein materials is vital to synthesize materials that combine seemingly incompatible material properties such as strength and robustness, self-adaptation and adaptability, by overcoming the physical limitations of conventional material design. We discuss the general implications of our work for the science of multi-scale interactions and how this knowledge can be utilized to develop de novo biomimetic materials based on a bottom-up structural design.

This talk is part of the Engineering for the Life Sciences Seminars series.

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