Anthony King
Researchers have developed a flexible hydrogel material intended to replace metal electrodes in medical devices.
Whatever their form and function, nearly all implants include electrodes, which are small conductive elements that attach to, and electrically stimulate, muscles and nerves.
Researchers have developed a flexible hydrogel material intended to replace metal electrodes in medical devices. The jelly-like material could conduct electricity similar to metals and electrically stimulate cardiac muscle or even neurons in the brain.
The new material comprises gels that are similar in water content to body tissue. It is made by weaving together a conducting polymer and hydrogel to create a bendable and biocompatible gel that can conduct current.
It could replace electrodes made from silicon that are great for conducting electricity, but stiff and inflexible. The challenge in developing the material was to combine polyurethane and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).
‘Both hydrophilic polyurethane and PEDOT:PSS are moderately phase-separated without substantial aggregation and precipitation in the mixed solvent, with 70v/v% ethanol and 30v/v% water,’ notes Tao Zhou at Massachusetts Institute of Technology, Cambridge, US, first author of the report (Nature Materials, doi: 10.1038/s41563-023-01569-2). The ink produced showed a unique phase-separation of mechanical phase and electrical phase.
Other conducting hydrogels usually have a conductivity of below 0.3Scm-1, notes Zhou, whereas the conductivity of this new material is around two orders of magnitude higher. ‘This material is the first hydrogel material that is highly conductive, tough and stretchable,’ according to Zhou. ‘Its toughness is higher than skeletal muscles.’
It can stretch over 400%, with 80% water content and tissue-like softness. The researchers demonstrated 3D printing of the hydrogel for bioelectronic interfaces for long-term electrophysiological recording and stimulation of various organs in rodents.
Bioelectronics made of hydrogels are less likely to trigger an immune response and tissue damage when implanted in the body, compared with those based on silicon. They could be widely used to replace existing bioelectronics in cardiac pacemakers, for example, the researchers note.
A flexible and stretchable material would make it far easier for electrodes to interact with tissue, especially in the brain, says Peter Janssen, a neuroscientist at the University of Leuven in Belgium. With future advances, patients could be implanted for many decades to restore mobility or vision, he adds.
Silicon electrodes can cause scarring and other problems due to their inflexibility. ‘The brain can move around 2mm inside the skull, so electrodes inserted in the brain must follow this movement. Otherwise you will get tissue damage and scar tissue,’ says Janssen. ‘A big advantage of these hydrogels is that they are very flexible and stretchable.’
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