When we think of robots, we normally think of motors and batteries and electronics, but engineers at Caltech and ETH Zurich have created a swimming robot that's powered by material deformation. That means it's made using materials that change shape in response to temperature swings, and that deformation pushes the device through water.
A whole range of robots made from responsive materials have been shown off over the years, including light-activated worms, caterpillars, an origami-inspired robot that unfurls when warmed up along with a self-healing, shape-shifting smart material that responds to both heat and light in different ways.
The new creation is also powered by heat, thanks to a temperature-sensitive polymer. When cool this material is naturally curled, but once it warms up it straightens. The team harnessed these abilities by making switches out of polymer strips, building them into the robot body and connecting them to oars. When warmed up, the polymer expands and in turn flicks the oar to propel the robot forwards.
That makes for a robot that can move without needing any kind of motor or battery. And since thicker strips of the polymer take longer to heat up, it can be fine-tuned to perform a set of movements in a specific order, using different thicknesses.
So, for example, picture a swimming robot with two paddles and a little claw on the front. With the polymer switches of different thicknesses made to fire at different times, the robot can be made to swim forwards, open the claw to release a payload, then paddle back to where it started. The team managed to demonstrate just this scenario.
"Combining simple motions together, we were able to embed programming into the material to carry out a sequence of complex behaviors," says Osama Bilal, co-first author of the study.
At the moment, the robot's usefulness is limited because each of the switches can only be flicked once before needing to be manually reset. But the researchers are working on ways to make them flip back the other way as the temperature changes again, paving the way for robots that can keep swimming for as long as the water temperature fluctuates.
In future, the researchers say that the robots could be made with polymers that respond to other environmental influences, such as pH or salinity levels. While it's hard to imagine the current clunky prototype that is good for one thrust only being put to much practical use, the team says the concept could one day be adapted to clean up chemical spills or, if shrunk down, deliver drugs inside the body.
The research was published in the journal Proceedings of the National Academy of Sciences. The robot can be seen in action in the video below.
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