Will Kyle

Water-responsive (WR) materials respond mechanically to changes in ambient humidity. WR materials, due to their exceptional strength, can be used for a variety of applications ranging from sustainable energy generation to soft robotics. My project involves testing a combination of two well-studied WR materials. The first material is the dormant form, also known as the endospore, of the Bacillus subtilis bacterium, and the second material is silk from the common silkworm, Bombyx mori. Both materials possess characteristics that we hypothesize will make them mutually beneficial. The goal of this research is to determine whether a combination of these two materials is more energy dense, possessing more energy per volume, than either material on its own. In order to meet this goal, we created and tested bilayers. Bilayers are two extremely thin layers of materials stacked on top of each other. In our testing, one layer is plastic and the other is a WR material. When humidity changes, the WR bilayer will curl or uncurl depending on the thickness of the WR layer and the WR material’s energy density. Our results show that the combination of B. subtilis endospores and B. mori silk is significantly water-responsive, but to date we are unable to precisely measure the energy density of the combination. We found that the spores clump together within the liquid silk during the drying process, leading to inconsistent and unpredictable performance. Recently, the main focus has been trying several methods to reduce the clumping, but none of them have been consistently successful. The next step for this project after the clumping issue is resolved is to determine the performance of the combo material through the bilayer method.