Laure V. Kayser

This roadmap presents key advances and future directions in the field of the conducting polymer polyethylene dioxythiophene (PEDOT), with a focus on its role as multifunctional material in emerging electronic applications. It covers a broad spectrum of topics, including self-healing materials, plant bioelectronics, energy harvesting and storage, and neural interfaces. The roadmap also addresses recent progress in the synthesis and functionalization of PEDOT derivatives, as well as insights from molecular dynamics simulations and transport physics. Emphasis is placed on a range of processing techniques, such as electropolymerization, vapor phase polymerization, and 3D printing, and their implications for device performance. Specific applications explored include thermoelectrics, biosensors, organic electrochemical transistors, and advanced bioelectronic platforms for neuromodulation, stretchable electronics, and neuromorphic computing. This collective effort aims to serve as a comprehensive resource outlining the current state of PEDOT research and identifying challenges and opportunities for its integration across diverse electronic technologies.

Post-polymerization modification allows for the incorporation of functional groups that would otherwise be incompatible with polymerization conditions, enhancing synthetic efficiency and facilitating the creation of complex polymer architectures for specialized applications, such as biomedical devices, electronics, and advanced coatings. Herein, we report a method inspired by late-stage functionalization of small molecules for the post-polymerization modification of aromatic polymers, specifically polystyrene (PS), under mild reaction conditions. First, PS was converted to polystyrene sulfonamide (PSSNH₂) with an 85% yield using established procedures. PSSNH2 was subsequently transformed into a reactive sulfinate by deamination using an N-heterocyclic carbene (NHC) catalyst and benzaldehyde. The catalytic process was optimized by varying catalysts, solvents, bases, temperatures, and reaction times. The highest degree of deamination was 88% with a bicyclic NHC and K₂CO₃ base in DMSO for 18 hours at 120 °C. The reactive sulfinate was then treated with various functional reagents, resulting in a library of aromatic polymers with different substituents with high degrees of functionalization ranging from 74% to 98%. Similarly, we modified expanded PS waste with trifluorobutyl iodide with a degree of functionalization of 72%, highlighting a new avenue for plastic upgrading. This approach could be used to rapidly generate functionalized polymers from PS with potential applications, including antibacterial properties and flame retardancy.

Through shear-stiffening elastomers, human testing, and adhesion characterization, this study shows how to design the adhesive and viscoelastic properties of an object to achieve a desired level of perceptual stickiness in humans.

Electrically conductive hydrogels based on conducting polymers have found increased use in bioelectronics due to their low moduli that mimic biological tissues, their ability to transport both ionic and electronic charges, and their ease of processing in various form factors via printing or injection. Current approaches towards conductive hydrogels, however, rely on covalent and therefore irreversible crosslinking mechanisms. Here, we report a thermo-responsive conducting polymer (TR-CP) that undergoes a fully reversible non-covalent crosslinking at 35 °C within less than a minute to form conductive hydrogels. The TR-CP is based on a block polyelectrolyte complex, that self-assembles into well-defined colloidal particles in water which undergo an isovolumetric sol-gel transition just below physiological temperature. The hydrogels have tunable mechanical properties in the 20 to 200 Pa range, are stable at various pH and salt conditions, self-healing, injectable, and biocompatible in vitro and in vivo. We demonstrate that the TR-CPs can be used to fabricate sensitive, conformal and reusable electrodes for surface electromyography. This thermo-responsive material provides exciting opportunities for stimuli-responsive and adaptive bioelectronics.

During osteoarthritis (OA), negatively-charged proteoglycans are digested and lost from cartilage, which impairs tissue osmotic behavior and mechanical integrity, leading to further tissue degeneration. Existing strategies for introducing supplemental, soluble polyelectrolytes face barriers in compound performance in solid tissue: achieving sufficient tissue penetration by diffusion without losing the therapeutic in a short time by the same diffusive process. Here, we investigated thermo-responsive block copolymers, poly(styrene sulfonate)-block-poly(N-isopropylacrylamide) (PSS-b-PNIPAM) with a series of varying block ratios, as a strategy to improve polyelectrolyte delivery and improve retention due to thermal self-assembly into less-mobile aggregates within cartilage explants. Through histological staining, we found that block copolymers exhibited enhanced penetration into deeper zones of the tissue compared to PSS alone. Additionally, PSS-b-PNIPAM copolymers with a higher PNIPAM ratio improved solute retention compared to those with a lower PNIPAM ratio. Through diffusion modeling and polymer characterization by dynamic light scattering and small angle x-ray scattering, we showed that the design of thermo-responsive polyelectrolytes to penetrate and retain within solid porous tissue is an interplay between molecular weight, strength of the thermal response, and tissue microstructure.

Post-polymerization modification allows for the incorporation of functional groups that would otherwise be incompatible with polymerization conditions, enhancing synthetic efficiency and facilitating the creation of complex polymer architectures for specialized applications, such as biomedical devices, electronics, and advanced coatings. Herein, we report a method inspired by late-stage functionalization of small molecules for the post-polymerization modification of aromatic polymers, specifically polystyrene (PS), under mild reaction conditions. First, PS was converted to polystyrene sulfonamide (PSSNH2) with an 85% yield using established procedures. PSSNH2 was subsequently transformed into a reactive sulfinate by deamination using an N-heterocyclic carbene (NHC) catalyst and benzaldehyde. The catalytic process was optimized by varying catalysts, solvents, bases, temperatures, and reaction times. The highest degree of deamination was 88% with a bicyclic NHC and K2CO3 base in DMSO for 18 hours at 120 °C. The reactive sulfinate was then treated with various functional reagents, resulting in a library of aromatic polymers with different substituents with high degrees of functionalization. Similarly, we modified expanded PS waste with trifluorobutyl iodide with a degree of functionalization of 72%, highlighting a new avenue for plastic upgrading. This approach could be used to rapidly generate functionalized polymers from PS with potential applications, including antibacterial properties and flame retardancy.

Organic electrochemical transistors (OECTs) prepared from poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) have been widely investigated, typically with films prepared by spin-casting and drying from aqueous commercially available suspensions. Electrochemical deposition of PEDOT makes it possible to more precisely control film thickness and counterion composition. Here, we examined the influence of channel thickness and counterion composition on the properties of OECTs fabricated using electrochemically polymerized PEDOT with p-toluene sulfonate (pTS) and PSS on interdigitated gold electrodes. While PEDOT:PSS films deposited with a particular charge density were somewhat thicker (with more PSS in the film), PEDOT:pTS films showed higher volumetric capacitances consistent with their more rough, irregular surface morphologies. The maximum transconductance (gm,max) (∼70 mS) and on-current levels barely changed over the examined range of channel thicknesses (100–800 nm) with both counterions. The device stability (current retention in ON/OFF cycling) and transient response times (∼10 ms) were enhanced with larger counterions, thinner channel films (∼100 nm), and lower applied drain voltages (under −0.1 V). These design insights were used to create channel-functionalized OECT-based label-free glucose sensors with high stability. These results demonstrate the ability to optimize and enhance the performance and stability of electrochemically deposited PEDOT-based interdigitated OECT devices.

Electrically conductive hydrogels based on conducting polymers have found increased use in bioelectronics due to their low moduli that mimic biological tissues, their ability to transport both ionic and electronic charges, and their ease of processing in various form factors via printing or injection. Current approaches towards conductive hydrogels, however, rely on covalent and therefore irreversible crosslinking mechanisms. Here, we report a thermo-responsive conducting polymer (TR-CP) that undergoes a fully reversible non-covalent crosslinking at 35 °C within less than a minute to form conductive hydrogels. The TR-CP is based on a block polyelectrolyte complex, that self-assembles into well-defined colloidal particles in water which undergo an isovolumetric sol-gel transition just below physiological temperature. The hydrogels have tunable mechanical properties in the 20 to 200 Pa range, are stable at various pH and salt conditions, self-healing, injectable, and biocompatible in vitro and in vivo. We demonstrate that the TR-CPs can be used to fabricate sensitive, conformal and reusable electrodes for surface electromyography. This unique material provides exciting opportunities for stimuli-responsive and adaptive bioelectronics.