Feb 5, 2009
Simplicity is crucial to design optimization at the nanoscale
MIT researchers investigating the structure of protein-based samples to determine the key to the material's lightweight and robust strength have found that the particular arrangement of proteins that produces the sturdiest product is not the arrangement with the most built-in redundancy or the most complicated pattern. Instead, the optimal arrangement appears to be a repeated pattern of two stacks of four-bundled alpha-helical proteins.
This composition of two repeated hierarchies (stacks and bundles) provides great strength – the ability to withstand mechanical pressure without giving way – and at the same time great robustness – the ability to perform mechanically, even if faults are present. Alpha-helices are a common protein building block of cellular filaments such as hair and hoof. Although their structure was already discovered in the 1940s, the properties of materials based on these proteins remain the subject of an intense scientific inquiry.
In a paper published in Nanotechnology, Markus Buehler and Theodor Ackbarow described a model of the protein's performance, based on molecular dynamics simulations. With their model they tested the strength and robustness of four different combinations of eight alpha-helical proteins: a single stack of eight proteins, two stacks of four-bundled proteins, four stacks of two-bundled proteins and double stacks of two-bundled proteins. Their molecular models replicate realistic molecular behavior, including hydrogen bond formation in the coiled spring-like alpha-helical proteins.
"The traditional way of designing materials is to consider properties at the macro level, but a more efficient way of material design is to play with the structural make-up at the nanoscale," said Buehler, the Esther and Harold E assistant professor in the Department of Civil and Environmental Engineering. "This provides a new paradigm in engineering that enables us to design a new class of materials."
More frequently, natural protein materials such as those based on alpha-helical proteins tested by Buehler and Ackbarow are being used as inspiration for synthetic material design based on nanowires and carbon nanotubes, which can be much stronger than biological materials. This work demonstrates that by rearranging the same number of nanoscale elements into hierarchies, the performance of a material can be radically changed simply by emphasizing re-use of building blocks and thus eliminating the need to invent new materials for each different application.
This work is funded by the Army Research Office, a National Science Foundation CAREER Award and the Air Force Office of Scientific Research. Ackbarow, a graduate student at the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany, was supported in this work by the German National Academic Foundation, the Hamburg Foundation for research studies abroad and the Dr Juergen Ulderup Foundation.
About the author
Markus Buehler currently holds the Esther and Harold E Edgerton Career Development Professorship in the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology. His research is focused on understanding the mechanics of deformation and failure of biological materials in the context of physiologically extreme conditions and disease. By utilizing a computational materials science approach based on molecular modeling, his goal is to understand the properties of biological materials from a fundamental level.