require low-impedance at the electrodetissue interface to maintain efficient charge injection during stimulation. [4] The impedance of the electrode sites of neural probes steadily increases with time during implantation due to the immune system's response to the insertion of the probes into tissue. [5] Conducting polymers have been widely explored as coatings for stimulating neural probes to reduce the impedance at the electrode-tissue interface. [6,7] Among conducting polymers, poly(3,4ethylenedioxythiophene) (PEDOT) has significantly contributed to improving the electrical stability of neural probes due to its high conductivity, electrochemical stability under chronic exposure to biological environments, and compliant mechanical properties which provide a softer interface between brain tissue and stiff probes. [8][9][10] The stability of PEDOT coatings on the electrode sites of neural probes is critical for ensuring the long-term functionality of the neural device. [11] One major mode of PEDOT coating failure is through coating delamination or cracking. [12][13][14][15] The coating must be able to survive mechanical stresses, swelling, and electrode corrosion in order to be considered for use in clinical applications. [16] Substantial improvements in PEDOT stability have been achieved through tuning the polymerization parameters, accurately selecting dopants and solvents used for polymerization, and incorporating additives into the PEDOT film. [10,[17][18][19][20] Chronic stability of PEDOT-based recording neural electrodes has been extensively studied and reviewed. [8,19,[21][22][23][24][25][26][27][28][29] Studies of PEDOT coating stability under stimulation have been recently reviewed. [7,16,17] In one study, electropolymerized PEDOT, containing carbon nanotubes, on Pt microelectrodes was monitored over 3 months of soaking in phosphate buffered saline (PBS) with and without stimulation, and were reported to have stable impedance. [30] An in vivo study stimulated the Au electrode sites of a neural probe coated with PEDOT and carbon nanotubes for 1 h a day for 10 days (20 mA, 200 Hz). PEDOT demonstrated similar impedance values to Au electrode sites at the end of the study. [31] On the other hand, PEDOT doped with tetrafluoroborate (PEDOT:BF 4 ) electropolymerized on platinum iridium (PtIr) neural probes was implanted for 15 days, stimulated daily for 90 min (20 mA, 130 Hz) while monitoring the impedance. At the end of the implantation period, Resulting from its many unique properties, such as mechanical compliancy, electrochemical stability, and high conductivity, the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a promising material for improving the stimulation efficiency of neural microelectrodes. The long-term electrochemical stability of penetrating PEDOT-coated electrodes undergoing high-frequency stimulation is not extensively studied in vivo and the inflammatory response of the brain to PEDOT-coated stimulating neural probes is not well understood. In this work, electropolymerized PE...

Highly stretchable and flexible bioelectronics should form close contact with skin and tissues while being able to withstand the stresses and strains endured by the body in order to reliably monitor physiological signals over time. Here, we report highly stretchable poly 3,4-ethylenedioxythiophene: polystyrene sulfonate (PEDOT:PSS) films printed on thermally resistant polyurethane (TPU) substrates. We established the stability of the conductivity of the devices under high strains up to 600%. The printed PEDOT:PSS film enabled the fabrication of printed organic electrochemical transistors (OECTs) with an ON/OFF ratio of 450 on a flexible substrate. We also acquired physiological signals from measuring the skin conductance arising from changes in sweat volume by directly interfacing a printed PEDOT:PSS-based sensor on TPU with human skin. Stretchable printed PEDOT:PSS films on TPU provide a facile method of producing highly stable stretchable sensors for bioelectronic applications, enabled with simple and direct printing fabrication.