Hydrogels are very curious objects for scientists these days. They have properties that science is trying to put to good use. Hydrogels can maintain large quantities of water within their networks, which enables them to expand and contract in response to voltage, heat, and acidity, although very slowly. Now team of researchers at RIKEN Center for Emergent Matter Science in Japan has created a new hydrogel, which can stretch and contract very quickly in response to changing temperature. In other words, it works as an artificial muscle.
Most hydrogels work a little bit like cells of plants – they absorb and excrete water to either expand or shrink in volume. Plant cells similarly are able to change shape as the amount of water within them changes in response to environmental conditions. However, this new hydrogel does not act like this. Instead, it works a bit like artificial muscle, which does not contract equally in all directions. Instead, muscles (as well as this hydrogel) contract in one dimension while expanding in another. This allows hydrogel to change shape repeatedly without absorbing or excreting water.
This hydrogel works because of electrostatic charge. In order to achieve this, team of researchers stuck nanosheets within the hydrogel. They 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 polymerization, which essentially uses light to congeal a substance into a hydrogel. Since all these nanosheets are situated in one plane, they create electrostatic resistance in one direction but not in the other.
Originally, scientists designed this hydrogel to be stretchable only in one direction. But during testing they found that at certain temperature of 32 degrees Celsius, which they called the lower critical solution temperature, the hydrogel rapidly changed shape, stretching in length, but not changing in volume.
Walking hydrogel – scientists chose such shape in order to demonstrate how quick hydrogel can change shape and how it could be applied practically.
Furthermore, this change could be observed in air as well as in a liquid environment. This allowed scientists to determine that the hydrogel does not require the uptake of water for the change of shape, which means it will work even in a normal air environment. Furthermore, this change in shape is so sudden, taking only one second, with the rate of deformation, at about 70% per second, it makes this hydrogel much faster in changing shape than other hydrogels.
In order to demonstrate how this hydrogel can be used practically, team of researchers designed an L-shaped piece of this polymer. By changing the temperature of the water environment in which the hydrogel is placed into, scientists were able to make the L-shaped piece of this polymer walk as the legs lengthen and contract in response to changing temperature. Although scientists proudly say that this hydrogel is a lot like artificial muscle, it is unlikely that it will actually be used like one in robotics or medicine.
Scientists say that a lot of work remains to be done till this hydrogel can reach a practical application. Yasuhiro Ishida, one of the authors of the study, 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 that could automatically open and close radiator systems as temperatures rise and fall. This could be used, for example, to prevent a device from overheating.” So now we have to wait and see how this idea develops and in what devices will we be able to see this technology.