Developing artificial muscles to give weakened people their strength back

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Researchers have succeeded in making artificial muscle fibers from rubber thread, paving the way for sewing the muscles into a blouse and giving renewed strength to the wearer.

"I know it doesn't look like a lot, but it corresponds to what our own muscles can lift," says Anne Ladegaard Skov, Professor at DTU Chemical Engineering. She points to a small thin rubber wire with the letter D at the end, which bounces up and down.

The D is followed by a T and a U, and along with the rest of the line-up, the rocking university initials signal that a blouse with superpowers could be within reach.

"The rubber threads are made of silicone elastomers, and we have managed to make them in a shape resembling a sewing thread. The idea is to bundle them so we copy the body's own muscle structure. We can then weave the bundle into a piece of clothing," explains Skov.

Together with her research team, she has designed the silicone thread with a cavity which a conductive liquid can run through. Just like when the brain sends an electrical signal to the body's muscles to activate, the researchers can send current through the artificial muscle fibers via the conductive fluid and cause them to contract.

When this happens, they can lift 200 times their own weight. They thus have the potential to make life easier for millions of people with impaired muscle function.

"Our goal is to enable weakened people to carry five extra kilos, roughly equivalent to a half-filled carrier bag from the local supermarket. It's quite a lot, and there are still some things we need to solve before we have reached our goal," says Skov.

Gelatine and knitting patterns

One of the researchers' main tasks is to make their material stronger. Silicone itself is too fragile, which is why the researchers want to make muscle fibers where the synthetic silicone is combined with natural proteins.

"By adding proteins that, for example, twist around the silicone elastomer, the artificial muscles mimic an original muscle structure even more, and this is important for strength," says Skov.

Originally, the idea was that the added proteins would come from spider silk, but as the wait for the material was long, the researchers started experimenting with other materials. So why not gelatin, they asked themselves. And it was a good question, because gelatin turned out to be surprisingly effective.

"We found that we could make the gelatin behave differently depending on how we heat treat it. Now we actually expect to soon be able to 3D print muscle fibers with gelatin in them," says Skov, who calls the discovery a fortunate coincidence. Especially considering that gelatin is virtually cost-free. What can be a costly and long affair, however, is the development of the product design that will ultimately find its way into the consumers' wardrobes.

"Whether you weave or knit, what patterns you use, and what fabric you combine the muscle structures with—it all impacts how effective the artificial muscles become," explains Skov.

So books on weaving and knitting patterns have found their way onto her bookshelf, and together with the rest of her research group, combination patterns and sewing constructions are closely studied in the search for the optimal product design.

"Just like inside the body, the way muscle structures are bundled impacts how they move. We try to incorporate this knowledge into our solution design. It's important to give the artificial muscles optimal freedom of movement," explains Skov.

The big in the small

The ability to see the big in the small recently secured Skov's team first place at the Californian SPIE Smart Structures NDE conference—the largest of its kind in the elastomer industry. Part of the recognition is about the enormous societal value researchers predict their work can have.

"We see the final solution as a 'support suit,' first and foremost aimed at older people, who by getting the extra strength can cope better at home and require less home help. But we also see that the solution will be able to attract more women to workplaces where hard physical work is otherwise a barrier," says Skov.

She imagines that the final solution will be a blouse reminiscent of a wetsuit or a thick sports shirt. In the sleeves, the artificial muscles ensure that the arms go down when you turn on the power, for example via an iPhone, and that they go up again when you turn it off.

However, the researchers cannot say how long it will be before the blouse can be bought in stores. Trying out new ideas will probably take some time.

In Skov's office, for example, there is a bag from a health food store filled with collagen powder. While most people probably see a beauty product that can reduce wrinkles, Skov sees a protein that has the potential to give her research renewed strength.

Provided by Technical University of Denmark