Scientists have developed innovative, stretchable 'gelatin batteries' with potential applications in wearable devices, soft robotics, and even as brain implants for drug delivery or treatment of diseases like epilepsy.

Researchers from the University of Cambridge found inspiration in electric eels, which stun their prey using electrocytes, specialized muscle cells.

The gelatinous materials developed by Cambridge researchers have a layered structure similar to Lego bricks, allowing the transmission of electrical current.

These self-adhesive gelatin batteries can stretch more than ten times their original length without losing conductivity, marking the first time these two characteristics have been combined in one material. The research results were published in the journal Science Advances.

Gelatin batteries are made from hydrogel, a three-dimensional network of polymers containing more than 60% water. The polymers are linked by reversible bonds that control the mechanical properties of the gel.

The ability to precisely control mechanical properties and mimic the characteristics of human tissue makes hydrogels ideal candidates for use in soft robotics and bioelectronics; however, for such applications, materials must be both conductive and stretchable.

"It is difficult to design a material that is both highly stretchable and highly conductive, as these two properties are usually at odds with each other," said Stephen O'Neill, lead author of the study and a member of the Yusuf Hamied Department of Chemistry at Cambridge. "Typically, conductivity decreases when the material is stretched."

"Usually, hydrogels are made from polymers with a neutral charge, but if we charge them, they can become conductive," said Dr. Jade McCune, co-author of the study from the Department of Chemistry. "By changing the salt composition in each gel, we can make them sticky and stack them in multiple layers, thereby increasing the energy potential."

Conventional electronics use rigid metallic materials with electrons as charge carriers, while gelatin batteries use ions to transfer charge, similar to electric eels.

Hydrogels bond firmly to each other thanks to reversible bonds that can form between different layers, using barrel-shaped molecules called cucurbiturils, which act like molecular handcuffs. The strong adhesion between layers enabled by molecular handcuffs allows the gelatin batteries to stretch without losing conductivity.

The properties of gelatin batteries make them promising for future use in biomedical implants, as they are soft and conform to human tissue. "We can tailor the mechanical properties of the hydrogels to match human tissue," said Professor Oren Scherman, director of the Melville Laboratory for Polymer Synthesis, who led the research in collaboration with Professor George Malliaras from the Department of Engineering. "Because they do not contain rigid components like metals, a hydrogel implant would be less likely to be rejected by the body or cause scar tissue formation."

In addition to their softness, hydrogels are surprisingly durable. They can withstand pressure without permanent loss of original shape and self-regenerate when damaged.

Researchers plan future experiments to test hydrogels in living organisms and assess their suitability for various medical applications.

The research was funded by the European Research Council and the Engineering and Physical Sciences Research Council (EPSRC), part of UKRI. Oren Scherman is a fellow of Jesus College, Cambridge.

Source: University of Cambridge