Temperature-controlled hydrogel can walk
Scientists have developed a new hydrogel that stretches and contracts just like an artificial muscle. The team created an L-shaped object made out of the hydrogel and immersed it in a water bath. When the water’s temperature was varied, it slowly "walked" forward.
The researchers at theRiken Center for Emergent Matter Science in Japan got the hydrogel to move bytweaking its properties. Polymers like hydrogels carry large amounts of waterwithin their structure which gives them the capacity to respond to variationsin environmental factors such as acidity, voltage and temperature. Typically,this response time is quite slow, as the hydrogel must excrete or absorb waterto correspondingly shrink or expand.
The Japanesescientists altered the new hydrogel to enable it to contract only in onedimension while expanding in another. Since the hydrogel doesn’tcontract equally in every direction, it’s able to alter its shape withoutabsorbing or excreting any water. To test the hydrogel's properties, the team created an L-shapedpolymer and changed the temperature repeatedly to observe itsresponse.
Metal-oxide nanosheets were arranged on a single plane using a magnetic field. The nanosheets were then fixed in place using a process called light-triggered in-situ vinyl polymerization, where the light helped to stick them together within the polymer. The nanosheets create electrostatic resistance in one direction, but not the other.
The polymer’s "legs" not only lengthened and contracted at pace, allowingit to move forward, but its overall volume also remained the same. Thisbreakthrough, the researchers claim, allows them to create fast-reacting hydrogelsthat can function in other environments.
"In principle, thishydrogel can walk not only in water, but also in various non-aqueous media includingan open-air environment," Yasuhiro Ishida, one of the paper’s authors, tellsGizmag. The L-shaped polymer can walk indefinitely, Ishida says, as long as the heating and cooling cycle isrepeated.
The resulting hydrogel is reported to change shape in around one second, with a deformation rate of about 70 percent per second.
Possible applicationsfor the hydrogel include creating artificial muscles that can automaticallyopen and close systems in response to temperature changes, to prevent them fromoverheating, for instance. Biological applications are also possible.
"Such water-rich, softactuators would also find applications as components of artificial internalorgans and artificial muscles," says Ishida.
The team is now planning tocreate hydrogel actuators that respond to stimuli other than temperature.
A paper on the research wasrecently published in the journal Nature.