Collaborative Research: Microfabrication and Self-Assembly of Shape-Changing Hydrogels with Chromonic Liquid Crystalline Order

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Shape-changing liquid crystal hydrogels are soft, rubbery materials that can perform mechanical work as "artificial" muscles, without motors, joints, or control systems. They move spontaneously in response to slight temperature changes, and can be designed to flex in different geometries. This collaborative research effort focuses on developing techniques to engineer these materials to produce novel devices such as self-cleaning surfaces. Like the cilia that sweep contaminants from human lungs, surfaces will be coated with micro-scale hydrogel structures that move as temperature fluctuates. These novel active coatings will address a critical need for self-cleaning devices in healthcare applications, and could prevent bacterial contamination that leads to frequent infections and thousands of deaths annually in the United States. In addition, community outreach efforts will be designed that engage young students and will help to broaden the diversity of the technical workforce, and research internships will help prepare high school students for advanced studies in science and engineering. Smart, programmable materials that respond mechanically to environmental stimuli are needed for smart biomedical devices. Hydrogels with chromonic liquid crystalline order are of interest for such applications because they morph anisotropically in response to biologically-benign temperature changes, and because their actuation trajectory can be programmed by patterning the material's molecular alignment. A key challenge is to fabricate such complex actuators at length scales too small to access via 3D printing and in shape profiles that are not flat films. This award supports development of novel techniques for design and microfabrication of shape-morphing hydrogels, using hierarchical patterning of molecular orientation achieved by combining soft lithography and liquid crystal self-assembly. This fundamental research will test the hypothesis that the shape of soft lithography molds can be used to pattern molecular alignment in micro-scale structures made of chromonic liquid crystal hydrogels, and that these aligned hydrogels can undergo programmable actuation in response to biologically-benign temperature changes. This processing approach will be used to create artificial cilia-like structures. Experimental efforts will be closely coupled to theory/simulation at two levels. First, the molecular order (nematic director) arising from surface anchoring from the soft lithography mold and liquid crystal chirality will be modeled. Second, nonlinear finite element elastodynamics simulations will be used to model shape evolution of active hydrogel micro-devices with a given director field as they transform under stimulus. This collaborative project brings together a multidisciplinary team with complementary expertise in responsive materials chemistry, materials modeling, and mechanical design.