After an unexpected discovery, a team of scientists from Rice University, the University of Cambridge, and Stanford University have streamlined the production of a material widely used in computing applications and medical research. The study was published in the journal Advanced Materials.
Implantable electrocorticography device (left) made using the heat treatment method; Rice University logo (right) patterned into PEDOT: PSS using a femtosecond laser. Image Credit: Margaux Forner; Siddharth Doshi
Scientists have used a chemical crosslinker to stabilize the conductive polymer in water for over 20 years when working with a composite material called PEDOT: PSS. Siddharth Doshi, a Stanford PhD candidate working with Rice Materials Scientist Scott Keene, forewent the addition of the crosslinker and prepared the material at a higher temperature to precisely pattern the material for use in biomedical optics applications.
He was surprised to learn that the final sample was stable without a crosslinker.
It was more of a serendipitous discovery because Siddharth was trying out processes very different to the standard recipe, but the samples still turned out fine. We were like, ‘Wait! Really?’ This prompted us to look into why and how this worked.
Scott Keene, Materials Scientist, Rice University
Keene and his colleagues discovered that heating PEDOT:PSS above the typical threshold produces higher-quality devices and makes them stable without the need for a crosslinker.
This technique may simplify and increase the manufacturing reliability of bioelectronic devices, which may be used in neural implants, biosensors, and next-generation computer systems.
PEDOT:PSS is a composite of two polymers: one that conducts electronic charge and is water-insoluble, and another that conducts ionic charge and is water-soluble. PEDOT: PSS connects living tissue and technology because it conducts both kinds of charges.
“It allows you to essentially talk the language of the brain,” said Keene.
Keene researches cutting-edge materials for more compact, high-resolution electrodes that precisely record and stimulate neural activity.
While electronic devices use electrons to transmit signals, the human nervous system uses ions, which are charged particles like sodium and potassium. For neural implants and other bioelectronic devices that must convert biological activity into readable data and transmit signals without harming delicate tissue, a material that can handle both is essential.
The research findings simplify the PEDOT: PSS fabrication process and enhance its performance by removing the crosslinker. The new process yields a material that is three times more electrically conductive and more stable across batches, which are important benefits for medical applications.
The crosslinker chemically bonded the two types of polymer strands in PEDOT: PSS to create an interconnected mesh. However, it left some of the water-soluble strands exposed, which is probably what caused the stability problems. The crosslinker added unpredictability and possible toxicity to the substance.
The increased heat, on the other hand, stabilizes PEDOT: PSS by altering the material's phase. When the water-insoluble polymer is heated above a particular point, the internal reorganization forces the water-soluble components to the surface, where they can be removed. A thinner, purer, and more stable conducting film is left.
Keene said, “This method pretty much simplifies a lot of these problems that people have working with PEDOT: PSS. It also essentially eliminates a potentially toxic chemical.”
Heat-treated bioelectronic devices, including transistors, spinal cord stimulators, and electrocorticography arrays implanted grids or strips of neuro electrodes used to record brain activity were easier to fabricate, more reliable, and equally high-performing than those fabricated using the crosslinker, according to Margaux Forner, a Doctoral Student at Cambridge who co-authored the study with Doshi.
The devices made from heat-treated PEDOT: PSS proved to be robust in chronic in vivo experiments, maintaining stability for over 20 days postimplantation. Notably, the film maintained excellent electrical performance when stretched, highlighting its potential for resilient bioelectronic devices both inside and outside the body.
Margaux Forner, Doctoral Student, Study Co-author, University of Cambridge
The discovery could help explain why stability problems plagued earlier attempts to employ PEDOT: PSS in long-term neural implants, such as those made by Neuralink.
This finding could contribute to neurotechnology development by improving the reliability of PEDOT: PSS, which could be used in interfaces that connect the brain to external devices and implants that restore movement following spinal cord injuries.
The team discovered a method to pattern PEDOT: PSS into microscopic 3D structures, which goes beyond making fabrication simpler and could lead to further advancements in bioelectronic devices.
By heating specific sections of the material with a high-precision femtosecond laser, the researchers can create unique textures that improve the way cells interact with the devices.
We are really excited about the ability to 3D-print the polymers at the microscale. This has been a major goal for the community as writing this functional material in 3D could let you interface with the 3D world of biology. Typically, this is done by combining PEDOT:PSS with different photosensitive binders or resins; however, these additions affect the properties of the material or are challenging to scale down to micron-length scales.
Siddharth Doshi, PhD Candidate, Stanford University
According to Keene's previous research on patterning grooves onto electrodes, cells preferentially adhere to grooves in the same order as their length scale. In other words, “a 20-micron cell likes to grab on to 20-micron-sized textures,” he said.
This method could create neural interfaces that promote greater integration with the surrounding tissue, enhancing the longevity and quality of signals.
Keene previously studied PEDOT: PSS about neuromorphic memory devices that speed up AI algorithms. Neuromorphic memory, an artificial memory type, imitates the way the brain remembers information.
Keene said, “It basically emulates the synaptic plasticity of your brain. We can modify the connection between two terminals by controlling how conductive this material is; this is very similar to how your brain learns by strengthening or weakening synaptic connections between individual neurons.”
The research disproved a long-held belief, making PEDOT: PSS more powerful and easier to work with. This change could hasten the creation of safer, more efficient neural implants and bioelectronic systems.
Stanford, Meta, the Wu Tsai Human Performance Alliance at Stanford, the Joe and Clara Tsai Foundation, the Wellcome Trust, the National Science Foundation, the Henry Royce Institute, the United Kingdom Engineering and Physical Sciences Research Council, and the European Union funded the study.
Journal Reference:
Doshi, S., et al. (2025) Thermal Processing Creates Water‐Stable PEDOT: PSS Films for Bioelectronics. Advanced Materials. doi.org/10.1002/adma.202415827.