New kind of plastic lets the muscles flex

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Robots are becoming more and more human-like. So-called biomimetics transfers natural processes to machines. In the future, a partially humanoid automaton could be powered by a muscle-like substance instead of hydraulic means or countless electric motors. The technology could then flow into soft robotics systems, which could also be suitable for prostheses based on human biology.

Researchers at Stanford University in California are now pursuing such an idea. The team around Zhenan Bao from the Institute for Chemical Engineering created a plastic with fascinating properties. It is a shape memory polymer that can store and retrieve energy. After a deformation, which includes both pulling and bending, these materials return to their original position by applying certain parameters. This can be light, but also heat, as Bao and Co. demonstrate with a simple hair dryer.

More from MIT Technology Review

More from MIT Technology Review

More from MIT Technology Review

The problem: So far, such plastics have been rather weak in terms of their energy storage and re-release. The latest material from the Stanford team is now said to be can absorb almost six times more energy than previous, comparable variantsas they write in a paper in the American Chemical Society’s ACS Central Science.

Bao and her team achieved the new quality of energy storage by introducing certain methylene bisphenylurea units into an existing polypropylene glycol backbone. The storage effect is created by reshaping the contained polymer chains, which form hydrogen bonds between urea groups when they are deformed. The bonds are destroyed again by heat, which enables a return to the original state – with the said high energy effect (17.9 J / g). In the experiment, the polymer could be stretched to five times its length.

According to calculations by Bao & Co., the material could lift objects 5,000 times its weight when heated. In a demonstration, the polymer of a wooden dummy was used as “muscles” and demonstrated how it could bend the arm at the elbow. The material should also be inexpensive and easy to manufacture. Practical applications are currently being considered.


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