Hygrobot is the name that has now been given to tiny robot-like entities that are capable of creeping, crawling, and slithering-like movements powered by moisture alone. The term, as well as the research on this was conducted by a group of researchers at the Seoul National University in South Korea, and is a shortened reference to hygroscopically powered robots.
The paper which has since been published in Science Robotics explains the idea for a moisture-powered robot stems from plants, as these are another entity that are capable of responding with movement when exposed to external stimuli, such as water or moisture. In comparison to animals (and machines for that matter) which typically adopt more of a muscle-based approach to movement. While the level of movement referred to in the plant world (and detailed in this paper) is minimal to say the least, this sort of self-powering technology is not designed with the likes of smartphones or other more power-demanding devices in mind. Instead, the researchers explain how the technology behind hygrobots could have real-world usage benefit in industries such as the military and medicine.
For example, one of the benefits highlighted from this natural form of power generation is its purity – lack of toxins – which makes it more ideal for microrobot use in general. Something which has recently become a front-running contender for the next wave of medicine-related technology. With usage during medical operation and/or as a means to distribute drugs within the body as two of the most commonly touted benefits offered with microbots. Both are also examples that highlight a need for microbots to be able to move and fulfill their duties without using more conventional (and possible hazardous to the body) means of power. The image below (provided by the researchers) demonstrates this point as the blue color seen in the image represents "a trail of antibiotics" left by a hygrobot (which was powered by the environment) when moving through a plate of bacteria. As a means of discussing further research and practical applications, the researchers suggest hygrobots could be tweaked in the future to also respond (through the inclusion of sensors) in a similar fashion to specific gas molecules.