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Researchers at the University of Virginia have developed HydroSpread, a fabrication method that allows soft, ultrathin robots to be made directly on water — enabling leaf-sized machines that paddle or even "walk" across a pond's surface. This new technique could accelerate applications from environmental monitoring to medical wearables by simplifying how delicate films are produced and patterned.
A new way to build soft robots on liquid surfaces
Traditional soft-robot fabrication requires forming thin polymer films on rigid substrates like glass, then carefully transferring them to other surfaces — a delicate step that often tears or ruins the material. HydroSpread flips that workflow: the polymer is deposited as droplets that spread into uniform, nanometer-to-micrometer-thin sheets directly on the water, with the liquid itself serving as a self-leveling workbench. Researchers then use a focused laser to cut precise shapes — from simple strips and circles to intricate logos — without ever lifting the film off a solid surface.
Because the films are formed on water, they experience less mechanical stress during processing and retain their mechanical integrity. That makes it possible to produce buoyant, flexible devices at scales similar to water striders: small, light, and capable of exploiting surface tension for locomotion.
From lab prototypes to practical uses
Using HydroSpread, the UVA team created two prototypes: HydroFlexor, which uses fin-like paddles to propel itself, and HydroBuckler, which mimics walking through a controlled buckling of leg-like structures. In the lab, the devices were actuated with an infrared heater placed above the surface; heating caused asymmetric bending or buckling in the layered films, producing paddling or stepping motions. By switching the heat on and off, researchers could vary speed and direction — demonstrating controllable, repeatable movement.
Future iterations may rely on sunlight, embedded micro-heaters, or magnetic fields for actuation, enabling autonomous behavior without external heat lamps. Beyond small surface robots, HydroSpread could make it easier to manufacture fragile, flexible electronics and sensors for wearables, soft medical devices, or distributed environmental monitors that must be thin and conformable in wet or delicate settings.
Conclusion
HydroSpread represents a shift in how we think about building soft, thin devices: by using liquid surfaces as fabrication platforms, researchers reduce transfer damage and open new design possibilities. While current demonstrations are proof-of-concept, the method points to practical, low-cost routes for tiny water-walking robots and other flexible technologies that operate where rigid materials can’t. Continued work will focus on autonomous actuation, scalable manufacturing, and testing in real-world environments like polluted waterways or flood zones.
Source: scitechdaily
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