Spore-Based Water-Resistant Water-Responsive Actuators with High Power Density

Active materials and surfaces that are less intrusive and more compatible with humans and their environment are critical for robotic applications. Humidity- and water-responsive materials are emerging as versatile alternatives to commonly used actuators in robotic systems, due to ease of actuation with humidity gradients and pervasiveness of water in the environment. However, these materials exhibit relatively low work densities and slow responses, and they are degraded when placed in direct contact with water. Recent work has shown that as a humidity-responsive material, Bacillus spores exhibit high work density actuation. Here, spore-based actuators containing water-resistant UV-curable adhesives are reported. These adhesives improve the work and power density of spore-based actuators, allow patterning of actuators with lithographic approaches and, importantly, provide water resistance to the resulting actuators. As a result, it is possible to demonstrate spore-based actuators driven directly with liquid water, which increase the actuation speed and power by nearly 100-fold. These developments might facilitate broader use of humidity- and water-driven actuators in robotics and related applications.