Hydrogel polymer that acts like a muscle

A team from Japan has developed a polymer hydrogel that stretches and contracts in response to temperature

According to research published in Nature Materials, a team led by scientists from the RIKEN Centre for Emergent Matter Science, in Japan, has developed a hydrogel that works like an artificial muscle.

The team has also managed to use the polymer to build an L-shaped object that slowly walks forward as the temperature is repeatedly raised and lowered.

Hydrogels are polymers that can maintain large quantities of water within their networks. Because of this, they can swell and shrink in response to changes in the environment such as voltage, heat, and acidity.

However, most hydrogels do this very slowly and must absorb and excrete water to either expand or shrink in volume.

The unique property of the hydrogel developed by the RIKEN team is that it acts like an artificial muscle, which does not contract equally in all directions. Rather, they [it] contracts? in one dimension while expanding in another, meaning that it? can change shape repeatedly without absorbing or excreting water.

The secret to the new hydrogel's property is electrostatic charge.

Using a method that it published earlier this year, the team arranged metal-oxide nanosheets into a single plane within a material by using a magnetic field and then fixed them in place using a procedure called light-triggered in-situ vinyl polymerisation, which essentially uses light to congeal a substance into a hydrogel.

The nanosheets ended up stuck within the polymer, aligned in a single plane. Due to electrostatic forces, the sheets create electrostatic resistance in one direction but not in the other.

Yasuhiro Ishida, a member of the research team, said: "We originally designed this material to be stretchable in one direction, but we also found that at 32 degrees Celsius, the polymer rapidly changed shape, stretching in length. Intriguingly, the gel did not change in volume. “

The group now plans to conduct further studies to create substances that can be used in practical applications.

Ishida said: "We are now planning further work to improve the properties of the substance. One idea we have is to use a hydrogel like this to make artificial muscles."