New heat-powered microrobots built directly on water walk and paddle like insects
Drawing inspiration from water striders, engineers at the University of Virginia have unveiled a fabrication technique that forms ultrathin soft robots directly on a water surface—then sets them in motion using heat. The approach, called HydroSpread, could pave the way for mass production of water-walking microrobots for environmental monitoring, search-and-rescue on flooded terrain, and more.
Traditional soft microrobots are so delicate that moving them from a rigid manufacturing surface to water often damages them. HydroSpread sidesteps that problem by building the robot where it will operate. The process begins by depositing a liquid polymer ink onto the surface of water. In the team’s demonstrations, polydimethylsiloxane (PDMS) spreads into exceptionally uniform, bilayer films. A precisely controlled laser then patterns the films into functional shapes.
Patterning on water offers a surprising advantage: the liquid quickly dissipates heat from the laser, reducing the risk of overheating and defects. That thermal sink effect enables finer, cleaner features than comparable processes on solid substrates, boosting reliability and repeatability—key ingredients for scaling up production.
Using HydroSpread, the researchers built two tiny, bio-inspired machines. HydroFlexor paddles with fin-like strokes, while HydroBuckler “walks” via a rhythmic buckling motion reminiscent of water-strider legs. Both are activated by an external infrared source. When heated, the two layers of the film expand at different rates, creating controlled bending and thrust—much like a bimetal strip, but at the ultrathin, flexible scale required for soft robotics.
Beyond microrobots that skim across ponds or flooded streets, the same ultrathin bilayer films could be adapted for wearable medical devices and flexible components in next-generation electronics. By enabling direct-on-water fabrication with precise laser patterning, HydroSpread offers a versatile platform for soft robotic systems that are lightweight, low-cost, and ready for real-world conditions.
The research, published in Science Advances, highlights a practical path forward for water-walking robots powered by heat, marrying biomimicry with an elegant, scalable manufacturing method.
