Inspired by electric eels, which use modified muscle cells known as electrocytes to generate electric shocks, the Cambridge team created these batteries with a similar layered structure. This design enables them to deliver an electric current effectively.
The new jelly batteries can stretch over ten times their original length without losing conductivity, marking the first successful combination of such high stretchability and conductivity in a single material. The findings have been published in the journal Science Advances.
These batteries are made from hydrogels, which are 3D polymer networks containing more than 60% water. The polymers are interconnected by reversible interactions that control the material's mechanical properties.
Stephen O'Neill, the first author from Cambridge's Yusuf Hamied Department of Chemistry, highlighted the challenge in creating a material that is both stretchable and conductive. "It's difficult to design a material that is both highly stretchable and highly conductive, since those two properties are normally at odds with one another," he said. "Typically, conductivity decreases when a material is stretched."
Co-author Dr Jade McCune from the Department of Chemistry explained, "Normally, hydrogels are made of polymers that have a neutral charge, but if we charge them, they can become conductive. And by changing the salt component of each gel, we can make them sticky and squish them together in multiple layers, so we can build up a larger energy potential."
Unlike conventional electronics, which rely on rigid materials and electron charge carriers, these jelly batteries use ions to carry the charge, similar to electric eels.
The hydrogels' strong adhesion is due to reversible bonds formed between layers using barrel-shaped molecules called cucurbiturils, which act like molecular handcuffs. This strong adhesion ensures that the jelly batteries can stretch without the layers separating and without losing conductivity.
Professor Oren Scherman, Director of the Melville Laboratory for Polymer Synthesis, who led the research with Professor George Malliaras from the Department of Engineering, emphasized the biomedical potential of these hydrogels. "We can customise the mechanical properties of the hydrogels so they match human tissue," he said. "Since they contain no rigid components such as metal, a hydrogel implant would be much less likely to be rejected by the body or cause the build-up of scar tissue."
In addition to their flexibility, the hydrogels are tough and can withstand squashing without permanent deformation. They also possess self-healing properties.
Future research will focus on testing these hydrogels in living organisms to evaluate their medical application potential.
Research Report:Highly Stretchable Dynamic Hydrogels for Soft Multilayer Electronics
