New technique lets robots walk on water using heat-powered motions

A team of researchers from the University of Virginia's School of Engineering and Applied Science have developed a new fabrication technique called HydroSpread which allows them to pattern ultrathin flexible robots directly on a water surface. The new method — detailed in the journal Science Advances — eliminates a difficult manufacturing step and could enable the mass production of tiny robots for environmental monitoring and search and rescue.

The main challenge in creating water-walking soft robots is that their extremely thin bodies are often damaged in the process of transferring them from the rigid surface where they are made to a water surface. The new technique — HydroSpread — solves this problem by making the film directly on the water surface. The process starts with depositing a liquid polymer ink onto a water surface.

For the demonstrations, the researchers deposited polydimethylsiloxane (PDMS) onto a water surface, where it spread into perfectly uniform, bi-layered films. A laser is then used to precisely pattern the films into the desired shapes.

The researchers say this method offers better precision than fabricating on a solid surface. This is because the liquid substrate (water) quickly dissipates heat from the laser, preventing overheating, which can cause defects in the patterns.

The created two prototype devices using this technique: HydroFlexor which paddles with fin-like motions, and HydroBuckler which “walks” with a buckling motion that mimics water-strider insects. The robots are propelled by heat from an external infrared source, which makes the two layers of the film expand at different rates, creating motion.

The researchers say this technique could also see application in ultrathin films for wearable medical devices and flexible components for next-generation electronics.