HQ Team
September 30, 2024: Cambridge University researchers, taking inspiration from electric eels, have developed stretchable ‘jelly batteries’ that could be used to deliver drugs or treat conditions such as epilepsy.
These batteries can be used for wearable devices, soft robotics or implants in the brain to transport drugs for certain conditions and treatments, according to a university statement.
Like electrocytes — a modified muscle or nerve cell that generates electricity in certain fishes’ electric organs — the jelly-like materials have a layered structure that makes them deliver electric current.
The self-healing jelly batteries can stretch to over ten times their original length without affecting their conductivity – the first time that such stretchability and conductivity have been combined in a single material.
In addition to their softness, the hydrogels are also tough. They can withstand being squashed without permanently losing their original shape and can self-heal when damaged.
3D polymer network
The jelly batteries are made from hydrogels or a 3D polymer network containing over 60% water. The polymers are held together by reversible on-off interactions that control the jelly’s mechanical properties.
The ability to precisely control mechanical properties and mirror the characteristics of human tissue makes hydrogels ideal candidates for soft robotics and bioelectronics. However, they need to be both conductive and stretchy for such applications, according to the statement.
The hydrogels stick to each other because of reversible bonds that can form between the different layers, using barrel-shaped molecules called cucurbiturils that are like molecular handcuffs.
The strong adhesion between layers provided by the molecular handcuffs allows for the jelly batteries to be stretched, without the layers coming apart and crucially, without any loss of conductivity.
“It’s difficult to design a material that is highly stretchable, and highly conductive since those two properties are normally at odds with one another,” said first author Stephen O’Neill, from Cambridge’s Yusuf Hamied Department of Chemistry. “Typically, conductivity decreases when a material is stretched.”
‘Make them sticky’
Co-author Dr Jade McCune, 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 squish them together in multiple layers so that we can build up a larger energy potential,” she said.
Normal electronics use rigid metallic materials with electrons as charge carriers, while jelly batteries use ions to carry charge, like electric eels.
The properties of the jelly batteries make them promising for future use in biomedical implants since they are soft and moulded to human tissue. The researchers are planning future experiments to test the hydrogels in living organisms to assess their suitability for a range of medical applications.
“We can customise the mechanical properties of the hydrogels so they 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.
“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.”
