Researchers from the University of Cambridge Researchers have created soft, elastic “gel batteries.” These batteries are used in wearable technology, soft robotics, or even as brain implants for drug delivery or treating diseases like epilepsy. The researchers were inspired by electric eels, which use modified muscle cells called electrolytes to stun their prey. The journal Scientific progress published this study.
The gelatinous materials created by the Cambridge researchers have a layered structure that allows them to deliver an electric current, just like electrocytes. Think of them as sticky Legos.
For the first time, stretchability and conductivity have been integrated into a single material, allowing self-healing batteries to expand to more than ten times their original length without losing any of their electrical properties.
Jelly batteries are made from hydrogels, three-dimensional networks of polymers containing more than 60% water. Reversible on/off interactions between the polymers hold the jelly together and regulate its mechanical properties.
Hydrogels are ideal for soft robotics and bioelectronics because they can precisely control mechanical qualities and replicate the characteristics of human tissues; however, they must be both conductive and flexible for such applications.
It is difficult to design a material that is both highly stretchable and highly conductive, because these two properties are usually incompatible. In general, conductivity decreases as a material is stretched..
Stephen O’Neill, first author of the study, Yusuf Hamied Department of Chemistry, University of Cambridge
Dr Jade McCune, co-author of the study from the Department of Chemistry, said: “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 crush them together into multiple layers, allowing us to create a greater energy potential..”
While gelatinous batteries use ions to transmit charge, much like electric eels, conventional electronics use rigid metallic materials with electrons as charge carriers.
Hydrogels exhibit significant interfacial adhesion due to the formation of reversible bonds between different layers through the use of barrel-shaped molecules called cucurbiturils, which resemble molecular handcuffs.
The molecular handcuffs create a strong adhesive between the layers, allowing the jelly batteries to be stretched without the layers separating and, more importantly, without losing any of their conductivity.
Gelatinous batteries are flexible and conform to human flesh; their qualities make them a promising option for biomedical implants of the future.
We can customize the mechanical properties of hydrogels to match human tissues. Because they do not contain any rigid components such as metal, a hydrogel implant would be much less likely to be rejected by the body or cause scar tissue to build up..
Oren Scherman, Professor and Director of the Melville Laboratory for Polymer Synthesis, University of Cambridge
Scherman led the research in collaboration with Professor George Malliaras of the Department of Engineering.
Hydrogels are surprisingly strong and flexible. They can repair themselves when damaged and can withstand being crushed without ever losing their original shape.
Future tests by the researchers will evaluate the hydrogels in living things to determine whether or not they are suitable for various medical uses.
The European Research Council and the Engineering and Physical Sciences Research Council, part of the UK Department for Research and Innovation, supported the study. Oren Scherman is a Fellow of Jesus College, Cambridge.
Journal reference:
Stephen, ON, et al. (2024) Highly stretchable dynamic hydrogels for flexible multilayer electronics. Scientific progress. is what i.org/10.1126/sciadv.adn5142.