Designing Living-Synthetic, Shape-Morphing Composites Non-technical abstract This award by the Biomaterials Program in the Division of Materials Research, to the University of Texas at Dallas, seeks to design and characterize shape-changing composites comprised of both living cells and non-living materials. Single-celled organisms sense and respond to very small changes in their surroundings, but it is difficult to use these organisms as materials in engineering applications. By comparison, most synthetic materials do not respond to their environment or only respond to very large changes, but the properties of these materials can be readily controlled. This research effort will focus on the synthesis, 3D printing, and characterization of hybrid materials that combine the advantages of both living and non-living components. Specifically, Baker's yeast will be embedded in a hydrogel, a soft material largely comprised of water. The growth of these cells causes the entire material to change in shape. By controlling the genes of the yeast, materials can be built to change shape and produce specific biomolecules after detecting specific, small changes in the environment. These materials may be used for simple sensors capable of detecting and reporting changes in bodily fluids or in the environment. The behavior of these new materials could also enable drug-delivery devices that sense disease states in the gut and respond by delivering treatment to the area. This research will also create opportunities for K-12 students to learn about topics in both biology and materials science. Technical abstract The objective of the proposed work is to harness the controlled proliferation of microorganisms to create synthetic-living hydrogels capable of programmable shape change. Specifically, Saccharomyces cerevisiae will be embedded in acrylamide hydrogels, and the proliferation of these cells will induce shape change in the composite. The primary advantage of this approach, as compared to engineering purely synthetic, responsive materials, is that genetic engineering and material formulation can be used to program the macroscopic composite response to predetermined and incredibly specific stimuli. This work consists of four research tasks: 1) Quantify local and global mechanical deformation during proliferation-induced shape change of the composite and measure the effects of hydrogel mechanical properties on growth, 2) 3D print synthetic-living composites and measure the effects of geometry and porosity on composite growth, 3) Elucidate the fundamental relationship between dose and response and elucidate the specificity of living composites to metabolites, proteins, and light as stimuli that evoke shape change, and 4) Design hydrogel matrices that respond controllably to enzymes produced by the yeast, enabling feedback control of shape change. The effect of metabolites, stimuli, and proteins produced by the yeast on growth throughout the composite will be measured, thus providing understanding of the fundamental relationships that govern living materials. This work will address a critical need for materials that sense highly specific biochemical or weak physical cues and then respond in a controlled manner. These materials will impact areas of critical national need, including drug-delivery strategies that could be used in the gut and simple biochemical sensors. Research activities will be coupled to outreach efforts for K-12 students on topics including genetics, hydrogels, and yeast. These efforts will be aimed at both increasing participation of underrepresented groups in science careers and dissemination of research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
