Markus J. Buehler
Department of Civil and Environmental Engineering,
Massachusetts Institute of Technology
Abstract:
After identifying the entire genetic code of several species, the next grand challenge
in the life sciences is the understanding of the multi-scale behavior of hierarchical
protein assemblies, that is, the elucidation of the interface between structure and material.
The advancement of this field is crucial for studies of biological systems, disease diagnosis
and treatment, as well as the design of novel materials. Proteins constitute critical
building blocks of life, forming materials such as hair, bone, skin, spider silk or cells,
which play a key role in providing important mechanical functions in biology.
The fundamental deformation and fracture mechanisms of biological protein materials, however,
remain largely unknown, partly due to a lack of understanding of how protein building blocks
respond to mechanical load and how they participate in the deformation and function of the
overall biological system. The mechanics of protein materials is vital for models of diseases,
the understanding of tissue injuries, for models of biological processes such as mechanotransduction, and the development of biomimetic and bioinspired materials.
Here we review atomistic molecular dynamics simulations implemented on supercomputing facilities,
combined with continuum mechanical and statistical theories, 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 predicting their unfolding behavior and thereby providing a structure-property
relationship. We review the development of a fracture theory and strength model for beta-sheets
and alpha-helices, two prominent protein motifs that form the basis of many protein materials,
including spider silk and intermediate filaments. Our studies elucidate intriguing material
concepts that facilitate to balance strength, dissipation and robustness via nanopatterned
hierarchical features. Our results suggest universal scaling laws that govern the ultimate
mechanical response of protein structures. We discuss these observations in light of a newly
proposed universality-diversity paradigm, which is based on the idea that the key to understand
the properties of protein materials is to consider the interplay of universal structural features
and a set of highly diverse features. It is found that this viewpoint can be applied to numerous
classes of protein materials, thereby providing a fundamental perspective to explain the
evolutionary footprint of structural protein materials. We discuss the implications of our work
for materials science, biology, the science of multi-scale interactions, and how this knowledge
can be exploited to develop new bioinspired materials and structures.
