Biodegradable Humidity Actuators for Sustainable Soft Robotics using Deliquescent Hydrogels

Intelligent materials offer new avenues when designing sustainable robotics as they allow for the creation of dynamic constructs which react autonomously to changes in the environment, such as humidity. Here we present a novel humidity actuator which exploits the unique property of deliquescent salts to allow for the spontaneous rehydration of hydrogels in ambient environments. By soaking a 2% w/v alginate, 3% w/v Agar composite in 1M calcium chloride, an intelligent humidity-driven actuator was developed. The hydrogel was able to gain 73.8±7.1% of its weight from a dehydrated state in just 6 hours through water absorption from ambient air. Using this novel formulation, linear and bilayer bending actuators were constructed. In addition to this, a biodegradable deliquescence-actuated artificial flower was demonstrated, highlighting this material's potential to act as an intelligent humidity actuator for the construction of environmentally-reactive biomimetic sustainable robotics.