Hydrogel set to find use in soft robotics

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Researchers at North Carolina State University are taking the development of soft robotic devices to a whole new level with electrically-charged hydrogels that can be patterned, folded and used to manipulate objects.

"This work brings us one step closer to developing new soft robotics technologies that mimic biological systems and can work in aqueous environments," said Dr Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State. The team's so-called 'ionoprinting' technique uses a copper electrode to inject positively-charged copper ions into a hydrogel material. The copper ions then bond with negatively charged ions in the hydrogel's polymer network, making the material stiffer and more resilient. "The bonds also pull the molecular strands closer together, causing the hydrogel to bend or flex," Dr Dickey noted. "And the more copper ions we inject into the hydrogel by flowing current through the electrodes, the further it bends." According to Dickey, the team was able to take advantage of the increased stiffness and bending behaviour in patterned sections to make the hydrogel manipulate objects. For example, the researchers created a V-shaped segment of hydrogel. When copper ions were injected into the bottom of the V, the hydrogel flexed – closing on an object as if the hydrogel were a pair of soft tweezers. By injecting ions into the back side of the hydrogel, the tweezers opened – releasing the object. The process is outlined in the video below.