Wooden robot arm is powered by plastic muscles

Technology 8 September 2021

By Chris Stokel-Walker

An artificial musculus made of a stretched shape-memory polymer contracts upon heating, bending a mannequin’s arm

Adapted from ACS Central Science 2021, DOI: 10.1021/acscentsci.1c00829

A polymer that changes signifier erstwhile heated tin assistance objects 5000 times its ain weight, with imaginable applications successful robotics.

Shape-memory polymers flip betwixt their mean state, wherever molecules are flexible and disordered, and their deformed state, wherever the molecules hindrance aft being stretched. Once successful the stretched, deformed state, the polymer tin beryllium unstretched – resuming its “normal” authorities – by applying vigor oregon light.

However, accepted shape-memory polymers don’t store important amounts of vigor portion being stretched – meaning they don’t merchandise overmuch vigor portion unstretching, which limits their usage successful tasks that impact lifting oregon moving objects.

Zhenan Bao astatine Stanford University successful California and her colleagues person present produced a shape-memory polymer that does store and merchandise appreciable amounts of energy. Their mentation has a polypropylene glycol backbone to which they added 4-,4’-methylene bisphenylurea units.

When stretched, the polymer chains go physically aligned, and intra- and intermolecular bonds – called hydrogen bonds – signifier betwixt the chains. These assistance the worldly support its highly stretched form. Then, erstwhile heated to 70°C, the hydrogen bonds interruption and the worldly tin revert to its archetypal unstretched form, releasing vigor from the bonds successful the process.

The polymer tin beryllium stretched to 5 times its archetypal magnitude and store up to 17.9 joules of vigor per gram successful its extended signifier – six times that of astir different shape-memory polymers. “It could beryllium utilized to assistance value oregon to assistance to assistance oregon supply further propulsion to idiosyncratic who possibly is having trouble walking,” says Bao.

To show its imaginable uses, the squad turned the worldly into an artificial musculus betwixt the precocious and little limb of a woody mannequin. When the mannequin’s elbow associated was straightened, the polymer stretched . Then, by applying vigor to the polymer, it contracted again, causing the mannequin’s elbow associated to bend.

“The reliable characteristics, and precocious spot of the worldly connection a caller method for designing joints that are susceptible of lifting aggregate times the worldly weight,” says Jonathan Aitken astatine the University of Sheffield, UK. However, Aitken questions the practicality of having to use vigor to the polymer.

Bao hopes to analyse the polymer’s properties to spot if determination is simply a molecular mechanics that tin automatically elongate and shrink erstwhile changing somesthesia naturally.

Journal reference: ACS Central Science, DOI: 10.1021/acscentsci.1c00829

More connected these topics:

• robotics