Human muscles are an intertwined collection of muscle fibers. In a nutshell, when you want to lift something, your brain sends an electrical signal via the spinal cord to the muscle which needs to be activated, calcium is secreted, energy is obtained from ATP, and various layers of muscles get to work to cause the muscle to contract.

Inspired by this process, a team of researchers at the Linköping University in Sweden have combined traditional textile processes and electrochemistry to create a material that works as an artificial muscle in response to subtle electrical signals.

The team refers to this material as a textuator (a combination of textile and actuator). Like conventional actuators, they convert electrical energy to force.

Why would we need artificial muscles?

An application of this technology is the ability to create clothes that would help injured or disabled people get some assistance to move or even regain mobility.

Currently, people undergoing physiotherapy after an accident to restore the functioning of their limbs; or seniors with impaired movement; or even regular people who lift a lot of weight during their jobs can use battery powered mechanical exoskeletons to move. These exoskeletons respond quickly and are very powerful. But a better option would be small, soft, smooth and easy to mass produce textile actuators that can be worn inside normal clothing and work in harmony with the natural movements of the muscle.

“Our dream is suits you can wear under your clothing—hidden exoskeletons to help the elderly, help those recovering from injury, maybe one day make disabled people walk again,” said Edwin Jager, an associate professor of applied physics who led the research.

How were these artificial muscles made?

The team behind this study have created two types of actuators using different textile manufacturing processes. The woven version of the textile exerts more force whereas the knitted version is more flexible. They can combine these two and tweak them to obtain a proper balance of stretch and force.

To create these artificial muscles the team first fabricated cellulose yarn, which is renewable and biocompatible, into the two different forms stated above. The next step involved coating the fabrics with electroactive materials, using a process similar to the ones used in traditional textile fabrication. The primary electroactive material here, the one that would respond to the electrical stimuli, was a conductive polymer called polypyrrole (PPy).

Polypyrrole is an interesting material and has been widely for similar purposes because of the following main reason

It changes its size due to electrochemical reactions on the application of voltages. Expands when a negative voltage is applied. And contracts when a positive voltage is applied.

It does this due to the movement of ions and solvents through the polymer. This means that an electrolyte is required.

Let’s recall the working of the human muscle, an electrical trigger, followed by a chemical reaction in the presence of an electrolyte. Biomimicry!

The team then tested the effect of the electroactive coatings on the structure of the ‘artificial muscles’ using scanning electron microscopy (SEM) and found that the structure maintained its physical form.

After the various stress and strain tests, they were successful in lifting a LEGO lever arm weighing 2 grams.

When can I get a sweater made up of artificial muscles for myself?

Not soon. Note that this is in no way a finished product. There are many variations of textile fabrication, add to that the types of material that can be used. As a result, the number of tests that can be done to establish different possible outcomes becomes exhaustive. And this permutation is without even approaching the possibility to trying variations in the electroactive polymers’ section.

Polypyrrole (Ppy) has its limitations. It doesn’t react quickly to an electrical signal. It can take several seconds to expand or contract. Also, this experiment was carried out in a liquid electrolyte to activate the Ppy.

The team is currently working on ways to embed the electrolyte in a way that would make it feasible to work in the air. They are also working on reducing the diameter of the yarn to increase response times. The team also plans to use metallic embeds to improve conductivity and feedback loops to self-start the actuators.

Source: Knitting and weaving artificial muscle