Researchers have created soft, stretchable ‘jelly batteries’ that could have various applications such as in wearable devices, soft robotics, or even for medical purposes like delivering drugs or managing conditions like epilepsy.
Researchers have designed soft, stretchable ‘jelly batteries’ that could be utilized in wearable devices, soft robotics, or even implanted in the brain to deliver drugs or treat conditions such as epilepsy.
The team from the University of Cambridge found their inspiration in electric eels, which use modified muscle cells known as electrocytes to stun their prey.
Similar to electrocytes, the jelly-like materials developed by the Cambridge researchers feature a layered structure, reminiscent of sticky Lego bricks, enabling them to conduct electricity.
These self-healing jelly batteries can stretch to more than ten times their original length without losing their ability to conduct electricity – the first instance where both stretchability and conductivity have been integrated into a single material. The findings have been published in the journal Science Advances.
The jelly batteries are crafted from hydrogels: 3D networks of polymers containing over 60% water. The polymers are connected through reversible interactions that regulate the mechanical properties of the jelly.
The ability to precisely manage mechanical properties and imitate human tissue characteristics positions hydrogels as excellent candidates for applications in soft robotics and bioelectronics. However, for such utilities, they must exhibit both conductivity and stretchiness.
“It’s a challenge to create a material that is both highly stretchable and highly conductive, as these two properties typically conflict with each other,” remarked primary author Stephen O’Neill from Cambridge’s Yusuf Hamied Department of Chemistry. “Usually, conductivity decreases when a material is stretched.”
“Typically, hydrogels are composed of polymers with a neutral charge, but when charged, they can conduct electricity,” explained co-author Dr. Jade McCune from the Department of Chemistry. “By altering the salt component of each gel, we can make them sticky, stack them together in multiple layers, and thereby build up a larger energy capacity.”
Conventional electronics use rigid metallic materials with electrons as the charge carriers, whereas the jelly batteries rely on ions for charge transport, similar to electric eels.
The hydrogels strongly adhere to each other due to reversible bonds that can form between different layers, employing barrel-shaped molecules called cucurbiturils that act like molecular handcuffs. This robust adhesion facilitated by the handcuff-like molecules allows the jelly batteries to stretch without layers separating and crucially, without compromising conductivity.
The unique attributes of the jelly batteries make them promising for future use in biomedical implants since they are soft and can mold to human tissue. “We can tailor the mechanical properties of the hydrogels to match human tissue,” noted Professor Oren Scherman, Director of the Melville Laboratory for Polymer Synthesis, who spearheaded the research in collaboration with Professor George Malliaras from the Department of Engineering. “As they lack rigid components like metal, a hydrogel implant would be less likely to be rejected by the body or cause scar tissue build-up.”
Aside from their softness, the hydrogels exhibit surprising toughness. They can endure compression without permanently losing their original shape and can self-repair when damaged.
The researchers are set to conduct further experiments to evaluate the hydrogels in living organisms to gauge their suitability for a variety of medical uses.
The research received funding from the European Research Council and the Engineering and Physical Sciences Research Council (EPSRC), under UK Research and Innovation (UKRI). Oren Scherman is affiliated with Jesus College, Cambridge as a Fellow.
