Hydrobots: Robots Powered by Humidity

Batteries, which are finite, are a thing of the past. These robots need no artificial source of power and, instead, use naturally occurring moisture to “inch” forward.

The inspiration for these hydrobots comes from plants. Plants can absorb humidity from the ground or air to change shape (known as hydro expansion). The pine cone, for example, opens when dry and closes when wet. While the robots aren’t composed of plants, they certainly draw inspiration from them.

The applications of these robots in the medicinal field are revolutionary. The robots require no batteries, which are toxic if introduced inside a body. As an example, a hydrobot was drenched in antibiotics and set on a bacteria filled culture plate. The hydrobot crossed the culture plate, using only moisture. As it did, a sterilized trail was left in its wake. In the future, these robots can be used to deliver drugs into the human body.

As to how these hydrobots work on a technical level, ScienceMag reports:

“The actuator uses a hygroscopically responsive film consisting of aligned nanofibers produced by directional electrospinning, which quickly swells and shrinks in lengthwise direction in response to the change of humidity. The ratchets based on asymmetric friction coefficients rectify oscillatory bending motion in a directional locomotion.”

In layman terms, the hydrobot has two layers (composed of nanofibers), one of which absorbs moisture and one that does not. When placed near moisture, the humidity absorbing layers swell. This shoots the bot up and away from the surface. When the layer dries the bot comes back down, where the cycle is repeated. This creates motion.

The report goes on to say that the robots were studied until, mathematically, its movements were able to be predicted and optomized. These bots can be modified to react to different vapors. It is predicted they can one day be used to deliver chemotherapy directly to tumors and affected areas.

Image: Shin et al., Sci. Robot. 3, eaar2629 (2018)