Abstract: All bonds in a periodic mechanical network are alike in their effect on mechanical response, but each bond in a disordered network affects response in its own way. This property of disordered networks makes them remarkably adaptable, so that mechanical properties such as the Poisson ratio can be tuned at will.  Mechanical networks can also be tuned to have functions reminiscent of biological functions. For example, allostery in a protein is the process by which a molecule binding locally to one site affects the ability of another molecule to bind at a second distant site. Inspired by the long-range coupled conformational changes that constitute allosteric function in proteins, we tune in “allostery” into disordered mechanical networks by modifying the network architecture to control the local strain at one point in such a network in response to a strain applied elsewhere in the system. The fact that allostery is a common means for regulation in biological molecules suggests that it is a relatively easy property to develop through evolution. In analogy, our 100% success rate in designing these responses by removing a very small fraction of bonds shows that it is similarly easy to create these types of elastic responses in disordered mechanical networks. We obtain similar results in flow networks, suggesting that adaptability to new functions may be general features of certain classes of networks.

Biography: Andrea Liu is a soft condensed matter physicist whose research combines theory and computation to study soft and living matter.  In living matter, her research focuses on the role of mechanics in biology, with the aim of understanding how new and general collective phenomena, often beyond those typically observed in inanimate soft matter, can emerge at the subcellular, cellular and tissue levels.  In soft matter, she and her collaborators have shown that jamming produces solids at an opposite pole from perfect crystals, providing a new way of thinking about the nature of rigidity in disordered solids. She received her A. B. degree in physics at the University of California, Berkeley, and her Ph. D. in the area of critical phenomena from Cornell University in 1989.  After postdoc positions at Exxon Research and Engineering Co. and in the Chemical Engineering, Materials Science and Physics departments at the University of California, Santa Barbara, she joined the Department of Chemistry and Biochemistry at the University of California, Los Angeles. She was a member of the physical chemistry faculty there for ten years before moving to the Department of Physics and Astronomy at the University of Pennsylvania in 2004, where she is now the Hepburn Professor of Physics.