Methods of poly(3,4)-ethylenedioxithiophene (PEDOT) electrodeposition on metal electrodes for neural stimulation and recording

Synthesis and Polymerization of Thiophene-Bearing 2-Oxazolines and 2-Oxazines

Intrinsically conductive polymers have garnered a great deal of attention for use in medical and bioelectronic applications. Despite this, challenges associated with the mechanical stability, processability, and fabrication of conducting polymers have limited their utility. To circumvent these limitations, thiophene substituted 2-oxazolines (2Ox) and 2-oxazines (2Ozi) are introduced, which can be polymerized to form a thermally stable and potentially melt-processable polymers as precursors for conductive polymers. A series of such monomers are synthesized and yields above 50% are obtained for gram scale reactions. The monomers can subsequently be polymerized using standard cationic ring-opening methods to yield thiophene-bearing poly(2-oxazoline)s (POx) and poly(2-oxazine)s (POzi) with narrow to moderate dispersity. The polymers exhibit glass transition temperatures between 50 °C and 100 °C and thermal stability beyond 250 °C. Moreover, random copolymers can be produced by introducing aliphatic 2-oxazolines during polymer synthesis, which facilitates tailoring of the polymer properties and may enable new applications in melt extrusion printing or electrospinning of precursors for conducting polymer systems. Overall, a facile approach is described for the synthesis of thiophene-functionalized monomers and polymers, providing covalent integration of thiophenes that opens new avenues toward the generation of functional and stimuli-responsive biomaterials.

Wearable Systems of Reconfigurable Microneedle Electrode Array for Subcutaneous Multiplexed Recording of Myoelectric and Electrochemical Signals

The real-time monitoring of in vivo electrophysiological and biochemical signals provides critical insights into the activities of tissues and organs. As the activity and metabolic state of different sites in the muscle vary, multichannel detection is necessary to capture the functional state of the whole muscle, yet the access to the bio-information in subcutaneous space remained challenging. This work reports the development of a reconfigurable microneedle electrode array integrated system designed to achieve painless and minimally invasive monitoring of subcutaneous electromyogram (EMG), oxygen species, and pH through an array of thumbtack-shaped microneedle (TSMN) electrode. By assembling discrete TSMNs into an array, the system enables multi-parameter detection with single microneedle resolution. The PEDOT: PSS layer is electrochemically deposited on the TSMNs, enhancing their signal-sensing capabilities and electrochemical properties. Additionally, the design of the pogo pin interface ensures reliable signal transmission and stable device performance, while allowing flexible replacement of the TSMNs, which enhances system maintainability and longevity. Validation experiments conducted on in vivo animal models demonstrate the system's capability in real-time monitoring of muscle fatigue and indicators related to sciatic nerve injury. These results advance the development of wearable technologies for monitoring subcutaneous physiological and biochemical information for diagnosing neuromuscular disorders.

Active Neural Interface Circuits and Systems for Selective Control of Peripheral Nerves: A Review

Interfaces with peripheral nerves have been widely developed to enable bioelectronic control of neural activity. Peripheral nerve neuromodulation shows great potential in addressing motor dysfunctions, neurological disorders, and psychiatric conditions. The integration of high-density neural electrodes with stimulation and recording circuits poses a challenge in the design of neural interfaces. Recent advances in active electrode strategies have achieved improved reliability and performance by implementing in-situ control, stimulation, and recording of neural fibers. This paper presents an overview of state-of-the-art neural interface systems that comprise a range of neural electrodes, neurostimulators, and bio-amplifier circuits, with a special focus on interfaces for the peripheral nerves. A discussion on the efficacy of active electrode systems and recommendations for future directions conclude this paper.

Array-wide uniform PEDOT:PSS electroplating from potentiostatic deposition

Electroplating of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is important in many neuroelectronic applications but is challenging to achieve uniformity on large-scale microelectrode arrays (MEA) using conventional galvanostatic methods. In this study, we address this challenge through a potentiostatic method and demonstrate highly uniform electroplating of PEDOT:PSS on MEA with more than one hundred electrodes, all at cellular sizes. The validation of this approach involves comparisons with galvanostatic deposition methods, showcasing unparalleled deposition yield and uniformity. Systematic electrochemical characterizations reveal similarities in structure and stability from potentiostatic deposited coatings. The advances developed here establish the potentiostatic method and detailed process to achieve a uniform coating of PEDOT:PSS on large-scale MEA, with broad utility in neuroelectronics.

Influences of solvents and monomer concentrations on the electrochemical performance and structural properties of electrodeposited PEDOT films: a comparative study in water and acetonitrile

Poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as a promising coating for neural electrodes especially through convenient electrodeposition methods. To investigate the influences of solvents and EDOT monomer concentrations on the electrochemical performance and structural characteristics of PEDOT, both aqueous and acetonitrile solutions were employed with varying monomer concentrations during deposition. The prepared PEDOT films were examined for the surface morphology, electrochemical performance, and chemical structures. The results showed that an increase in EDOT concentration in either solvent led to PEDOT films with improved charge storage capacity and reduced impedance magnitude. At equivalent monomer concentrations, PEDOT films generated in acetonitrile exhibited a rougher surface texture and better electrochemical performance. Notably, the growth rate of charge storage capacity of PEDOT prepared in acetonitrile relative to the deposited charge density was 2.5 times that of PEDOT prepared in water. These findings could help to the optimization of PEDOT coating preparation to enhance electrode performance.

Rejuvenating silicon probes for acute neurophysiology

Neurophysiological recording with a new probe often yields better signal quality than with a used probe. Why does the signal quality degrade after only a few experiments? Here, we considered silicon probes in which the contacts are densely packed, and each contact is coated with a conductive polymer that increases its surface area. We tested 12 Cambridge Neurotech silicon probes during 61 recording sessions from the brain of three marmosets. Out of the box, each probe arrived with an electrodeposited polymer coating on 64 gold contacts and an impedance of around 50 kΩ. With repeated use, the impedance increased and there was a corresponding decrease in the number of well-isolated neurons. Imaging of the probes suggested that the reduction in signal quality was due to a gradual loss of the polymer coating. To rejuvenate the probes, we first stripped the contacts, completely removing their polymer coating, and then recoated them in a solution of 10 mM 3,4-Ethylenedioxythiophene (EDOT) monomer with 11 mM Poly(sodium 4-styrenesulfonate) (PSS) using a current density of about 3 mA/cm2 for 30 s. This recoating process not only returned probe impedance to around 50 kΩ but also yielded significantly improved signal quality during neurophysiological recordings. Thus, insertion into the brain promoted the loss of the polymer that coated the contacts of the silicon probes. This led to degradation of signal quality, but recoating rejuvenated the probes.NEW & NOTEWORTHY With repeated use, a silicon probe's ability to isolate neurons degrades. As a result, the probe is often discarded after only a handful of uses. Here, we demonstrate a major source of this problem and then produce a solution to rejuvenate the probes.

Pillar electrodes embedded in the skeletal muscle tissue for selective stimulation of biohybrid actuators with increased contractile distance

Electrodes are crucial for controlling the movements of biohybrid robots, but their external placement outside muscle tissue often leads to inefficient and non-selective stimulation of nearby biohybrid actuators. To address this, we propose embedding pillar electrodes within the skeletal muscle tissue, resulting in enhanced contraction of the target muscle without affecting the neighbor tissue with a 4 mm distance. We use finite element method simulations to establish a selectivity model, correlating the VIE(volume integration of electric field intensity within muscle tissue) with actual contractile distances under different amplitudes of electrical pulses. The simulated selective index closely aligns with experimental results, showing the potential of pillar electrodes for effective and selective biohybrid actuator stimulation. In experiments, we validated that the contractile distance and selectivity achieved with these pillar electrodes exceed conventional Au rod electrodes. This innovation has promising implications for building biohybrid robots with densely arranged muscle tissue, ultimately achieving more human-like movements. Additionally, our selectivity model offers valuable predictive tools for assessing electrical stimulation effects with different electrode designs.

Flexible high-density microelectrode arrays for closed-loop brain-machine interfaces: a review

Flexible high-density microelectrode arrays (HDMEAs) are emerging as a key component in closed-loop brain-machine interfaces (BMIs), providing high-resolution functionality for recording, stimulation, or both. The flexibility of these arrays provides advantages over rigid ones, such as reduced mismatch between interface and tissue, resilience to micromotion, and sustained long-term performance. This review summarizes the recent developments and applications of flexible HDMEAs in closed-loop BMI systems. It delves into the various challenges encountered in the development of ideal flexible HDMEAs for closed-loop BMI systems and highlights the latest methodologies and breakthroughs to address these challenges. These insights could be instrumental in guiding the creation of future generations of flexible HDMEAs, specifically tailored for use in closed-loop BMIs. The review thoroughly explores both the current state and prospects of these advanced arrays, emphasizing their potential in enhancing BMI technology.

Advances in Smart Photovoltaic Textiles

Energy harvesting textiles have emerged as a promising solution to sustainably power wearable electronics. Textile-based solar cells (SCs) interconnected with on-body electronics have emerged to meet such needs. These technologies are lightweight, flexible, and easy to transport while leveraging the abundant natural sunlight in an eco-friendly way. In this Review, we comprehensively explore the working mechanisms, diverse types, and advanced fabrication strategies of photovoltaic textiles. Furthermore, we provide a detailed analysis of the recent progress made in various types of photovoltaic textiles, emphasizing their electrochemical performance. The focal point of this review centers on smart photovoltaic textiles for wearable electronic applications. Finally, we offer insights and perspectives on potential solutions to overcome the existing limitations of textile-based photovoltaics to promote their industrial commercialization.

Integrated Three-Electrode Dual-Mode Detection Chip for Place Cell Analysis: Dopamine Facilitates the Role of Place Cells in Encoding Spatial Locations of Novel Environments and Rewards

The functioning of place cells requires the involvement of multiple neurotransmitters, with dopamine playing a critical role in hippocampal place cell activity. However, the exact mechanisms through which dopamine influences place cell activity remain largely unknown. Herein, we present the development of the integrated three-electrode dual-mode detection chip (ITDDC), which enables simultaneous recording of the place cell activity and dopamine concentration fluctuation. The working electrode, reference electrode, and counter electrode are all integrated within the ITDDC in electrochemical detection, enabling the real-time in situ monitoring of dopamine concentrations in animals in motion. The reference, working, and counter electrodes are surface-modified using PtNPs and polypyrrole, PtNPs and PEDOT:PSS, and PtNPs, respectively. This modification allows for the detection of dopamine concentrations as low as 20 nM. We conducted dual-mode testing on mice in a novel environment and an environment with food rewards. We found distinct dopamine concentration variations along different paths within a novel environment, implying that different dopamine levels may contribute to spatial memory. Moreover, environmental food rewards elevate dopamine significantly, followed by the intense firing of reward place cells, suggesting a crucial role of dopamine in facilitating the encoding of reward-associated locations in animals. The real-time and in situ recording capabilities of ITDDC offer new opportunities to investigate the interplay between electrophysiology and dopamine during animal exploration and reward-based memory and provide a novel glimpse into the correlation between dopamine levels and place cell activity.