Spatiotemporal Control of Active Materials

Faculty Coordinators: A. Dinner, B. Tian

This IRG concerns the study, design, and synthesis of ‘active’ materials that contain distributed molecular elements that are out of equilibrium and convert energy input from diverse sources (e.g., chemical, optical, thermal, etc.) into mechanical work. Naturally occurring materials comprising such elements underlie the spatiotemporally regulated shape changes that occur autonomously in migrating cells and developing tissues; in these systems, mechanochemical feedbacks enable sensing of environmental stimuli to modify internal materials architecture and mechanical response to guide diverse physiological functions such as cell division, migration and tissue formation.

By harnessing behaviors found in living tissue in novel molecular contexts, active materials could provide smart actuation beyond materials that can be made now, with chemical functionalities/reactivities, environmental compatibilities (e.g., temperatures, pH, etc.), and durabilities beyond biological systems. For example, a sheet of such material could dynamically sculpt its shape, size, and rigidity in response to external forces and self-heal to enable repeated dramatic deformation. Overcoming the design and fabrication challenges for such a material would be a step toward realizing self-propelled mesoscale robotics with diverse applications.

Progress in active materials is currently limited by the lack of knowledge of their underlying physical principles. The issues are exemplified by the actin cytoskeleton, a class of active polymer networks that controls cell morphogenic processes. These materials use chemical energy in the form of ATP/GTP hydrolysis, and the mechanochemical feedbacks that dynamically control their structure and response are not well understood.  We seek to achieve control of active materials and ultimately to create novel molecular assemblies with robust tunable functionalities.

Achieving these goals requires an interdisciplinary effort on three fronts: (1) dynamically controlling material structure, (2) engineering assemblies consisting of natural and synthetic components (and hybrids of the two) that can transform shape, and (3) establishing environments that elicit competing materials behaviors. All three focus areas are important for fully realizing the potential of active materials, but progress on any one would have immediate rewards for fundamental materials science. 

The ability to control network assembly dynamically and spatially modulate contractility could enable the design and implementation of a primitive ‘artificial cell’ that is capable of recapitulating the physical behaviors of living systems.  Such a material should be able to respond to a varied external chemical/physical environment to change its shape, self-propel or divide, for instance.  Success would be defined by identifying minimal combinations of elements capable of programmable shape changes, autonomous movement and collective behavior, and such a material could be tailored to environments and situations beyond the reach of biological systems.