Self-healing, stretchable and recyclable polyurethane-PEDOT:PSS conductive blends.

Future electronics call for materials with mechanical toughness, flexibility, and stretchability. Moreover, self-healing and recyclability are highly desirable to mitigate the escalating environmental threat of electronic waste (e-waste). Herein, we report a stretchable, self-healing, and recyclable material based on a mixture of the conductive polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) with a custom-designed polyurethane (PU) and polyethylene glycol (PEG). This material showed excellent elongation at brake (∼350%), high toughness (∼24.6 MJ m-3), moderate electrical conductivity (∼10 S cm-1), and outstanding mechanical and electrical healing efficiencies. In addition, it demonstrated exceptional recyclability with no significant loss in the mechanical and electrical properties after being recycled 20 times. Based on these properties, as a proof of principle for sustainable electronic devices, we demonstrated that electrocardiogram (ECG) electrodes and pressure sensors based on this material could be recycled without significant performance loss. The development of multifunctional electronic materials that are self-healing and fully recyclable is a promising step toward sustainable electronics, offering a potential solution to the e-waste challenge.

Electroconductive cardiac patch based on bioactive PEDOT:PSS hydrogels.

Engineering cardiac implants for treating myocardial infarction (MI) has advanced, but challenges persist in mimicking the structural properties and variability of cardiac tissues using traditional bioconstructs and conventional engineering methods. This study introduces a synthetic patch with a bioactive surface designed to swiftly restore functionality to the damaged myocardium. The patch combines a composite, soft, and conductive hydrogel-based on (3,4-ethylenedioxythiophene):polystyrene-sulfonate (PEDOT:PSS) and polyvinyl alcohol (PVA). This cardiac patch exhibits a reasonably high electrical conductivity (40 S/cm) and a stretchability up to 50% of its original length. Our findings reveal its resilience to 10% cyclic stretching at 1 Hz with no loss of conductivity over time. To mediate a strong cell-scaffold adhesion, we biofunctionalize the hydrogel with a N-cadherin mimic peptide, providing the cardiac patch with a bioactive surface. This modification promote increased adherence and proliferation of cardiac fibroblasts (CFbs) while effectively mitigating the formation of bacterial biofilm, particularly against Staphylococcus aureus, a common pathogen responsible for surgical site infections (SSIs). Our study demonstrates the successful development of a structurally validated cardiac patch possessing the desired mechanical, electrical, and biofunctional attributes for effective cardiac recovery. Consequently, this research holds significant promise in alleviating the burden imposed by myocardial infarctions.

Effect of ionic conductivity of electrolyte on printed planar and vertical organic electrochemical transistors.

Conducting polymers with mixed electronic/ionic transport are attracting a great deal of interest for applications in organic electrochemical transistors (OECTs). Ions play a crucial role in OECT performance. The concentration and mobility of ions in the electrolyte influence the current flow in the OECT and its transconductance. This study examines the electrochemical properties and ionic conductivity of two semi-solid electrolytes, iongels, and organogels, with diverse ionic species and properties. Our results indicate that the organogels exhibited higher ionic conductivities than the iongels. Furthermore, the geometry of OECTs plays an important role in determining their transconductance. Thus, this study employs a novel approach for fabricating vertical-configuration OECTs with significantly shorter channel lengths planar devices. This is achieved through a printing method that offers advantages, such as design versatility, scalability, expedited production time, and reduced cost relative to traditional microfabrication methods. The transconductance values obtained for the vertical OECTs were significantly (approximately 50 times) higher than those of the planar devices because of their shorter channel lengths. Finally, the impact of different gating media on the performance of both planar and vertical OECTs was studied, and devices gated by organogels demonstrated improved transconductance and switching speed (almost two times higher) than those gated by iongels.

Advances in Electrode Materials for Scalp, Forehead, and Ear EEG: A Mini-Review.

Electroencephalogram (EEG) records the electrical activity of neurons in the cerebral cortex and is used extensively to diagnose, treat, and monitor psychiatric and neurological conditions. Reliable contact between the skin and the electrodes is essential for achieving consistency and for obtaining electroencephalographic information. There has been an increasing demand for effective equipment and electrodes to overcome the time-consuming and cumbersome application of traditional systems. Recently, ear-centered EEG has met with growing interest since it can provide good signal quality due to the proximity of the ear to the brain. In addition, it can facilitate mobile and unobtrusive usage due to its smaller size and ease of use, since it can be used without interfering with the patient's daily activities. The purpose of this mini-review is to first introduce the broad range of electrodes used in conventional (scalp) EEG and subsequently discuss the state-of-the-art literature about around- and in-the-ear EEG.

All-printed and stretchable organic electrochemical transistors using a hydrogel electrolyte.

Stretchable electronic devices are expected to play an important role in wearable electronics. Solution-processable conducting materials are desirable because of their versatile processing. Herein, we report the fabrication of fully stretchable organic electrochemical transistors (OECTs) by printing all components of the device. To achieve the stretchability of the whole body of the devices, a printed planar gate electrode and polyvinyl alcohol (PVA) hydrogel electrolyte were employed. Stretchable silver paste provided a soft feature to drain/source, gate and interconnect, without any additional strategies needed to improve the stretchability of the metallic components. The resulting OECTs showed a performance comparable to inkjet or screen-printed OECTs. The maximum transconductance and on/off ratio were 1.04 ± 0.13 mS and 830, respectively. The device was stable for 50 days and stretched up to 110% tensile strain, which makes it suitable for withstanding the mechanical deformation expected in wearable electronics. This work paves the way for all-printed and stretchable transistors in wearable bioelectronics.

Fabrication of Curli Fiber-PEDOT:PSS Biomaterials with Tunable Self-Healing, Mechanical, and Electrical Properties.

Poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) is a highly conductive, easily processable, self-healing polymer. It has been shown to be useful in bioelectronic applications, for instance, as a biointerfacing layer for studying brain activity, in biosensitive transistors, and in wearable biosensors. A green and biofriendly method for improving the mechanical properties, biocompatibility, and stability of PEDOT:PSS involves mixing the polymer with a biopolymer. Via structural changes and interactions with PEDOT:PSS, biopolymers have the potential to improve the self-healing ability, flexibility, and electrical conductivity of the composite. In this work, we fabricated novel protein-polymer multifunctional composites by mixing PEDOT:PSS with genetically programmable amyloid curli fibers produced byEscherichia coli bacteria. Curli fibers are among the stiffest protein polymers and, once isolated from bacterial biofilms, can form plastic-like thin films that heal with the addition of water. Curli-PEDOT:PSS composites containing 60% curli fibers exhibited a conductivity 4.5-fold higher than that of pristine PEDOT:PSS. The curli fibers imbued the biocomposites with an immediate water-induced self-healing ability. Further, the addition of curli fibers lowered the Young's and shear moduli of the composites, improving their compatibility for tissue-interfacing applications. Lastly, we showed that genetically engineered fluorescent curli fibers retained their ability to fluoresce within curli-PEDOT:PSS composites. Curli fibers thus allow to modulate a range of properties in conductive PEDOT:PSS composites, broadening the applications of this polymer in biointerfaces and bioelectronics.

An intrinsically stretchable and bendable electrochromic device.

Stretchable electrochromic devices (ECDs) were fabricated from electrospun PEDOT:PSS (poly(3, 4-ethylenedioxythiophene):polystyrene sulfonate) fibers. Stretchable and transparent electrodes with a sheet resistance of 1200 Ω sq-1were prepared by depositing the conductive fibers on elastomeric substrates that were prepared from polydimethylsiloxane. The conductive substrates replaced the ITO coated glass electrodes that are typically used in ECDs. The functioning device was prepared from a flexible chitosan electrolytic gel and a 4, 7-bis(4-diphenylaminophenyl)-2, 1, 3-benzothiaziazole (TPA-BZT-TPA) electrochrome that were deposited on the streatchable transparent electrodes. The assembled device could be stretched to 150% its original length and bent to a curvature of 0.1. The device could be operated and switched between its yellow (off) and blue (on) states while being stretched and bent with a maximum contrast ΔT ≈ 30% at 805 nm and a coloration efficiency of 168 cm2C-1. The stretchable device had an electrochromic contrast that was 30% greater than its counterpart that was prepared from conventional ITO-glass electrodes. The critical composition required for making devices truly stretchable was possible by evaluating the performance of five types of devices consisting of different layers.

Recent Progress on Self-Healable Conducting Polymers.

Materials able to regenerate after damage have been the object of investigation since the ancient times. For instance, self-healing concretes, able to resist earthquakes, aging, weather, and seawater have been known since the times of ancient Rome and are still the object of research. During the last decade, there has been an increasing interest in self-healing electronic materials, for applications in electronic skin (E-skin) for health monitoring, wearable and stretchable sensors, actuators, transistors, energy harvesting, and storage devices. Self-healing materials based on conducting polymers are particularly attractive due to their tunable high conductivity, good stability, intrinsic flexibility, excellent processability and biocompatibility. Here recent developments are reviewed in the field of self-healing electronic materials based on conducting polymers, such as poly 3,4-ethylenedioxythiophene (PEDOT), polypyrrole (PPy), and polyaniline (PANI). The different types of healing, the strategies adopted to optimize electrical and mechanical properties, and the various possible healing mechanisms are introduced. Finally, the main challenges and perspectives in the field are discussed.

Self-healing, stretchable, and highly adhesive hydrogels for epidermal patch electrodes.

Flexible, self-healing and adhesive conductive materials with Young's modulus matching biological tissues are highly desired for applications in bioelectronics. Here, we report self-healing, stretchable, highly adhesive and conductive hydrogels obtained by mixing polyvinyl alcohol, sodium tetraborate and a screen printing paste containing the conducting polymer Poly (3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) and diol additives. The as prepared hydrogels exhibited modelling ability, high adhesion on pig skin (1.96 N/cm2), high plastic stretchability (>10000%), a moderate conductivity, a low compressive modulus (0.3-3.7 KPa), a good strain sensitivity (gauge factor = 3.88 at 500% strain), and remarkable self-healing properties. Epidermal patch electrodes prepared using one of our hydrogels demonstrated high-quality recording of electrocardiography (ECG) and electromyography (EMG) signal. Because of their straightforward fabrication, outstanding mechanical properties and possibility to combine the electrode components in a single material, hydrogels based on PVA, borax and PEDOT:PSS are highly promising for applications in bioelectronics and wearable electronics. STATEMENT OF SIGNIFICANCE: Soft materials with electrical conductivity are investigated for healthcare applications, such as electrodes to measure vital signs that can easily adapt to the shape and the movements of human skin. Conductive hydrogels (i.e. gels containing water) are ideal materials for this purpose due softness and flexibility. In this this work, we report hydrogels obtained mixing an electrically conductive polymer, a water-soluble biocompatible polymer and a salt. These materials show high adhesion on skin, electrical conductivity and ability to self-repair after a mechanical damage. These hydrogels were successfully used to fabricate electrode to measure cardiac and muscular electrical signals.

Tailoring the Self-Healing Properties of Conducting Polymer Films.

The conducting polymer polyethylenedioxythiophene doped with polystyrene sulfonate (PEDOT:PSS) has received great attention in the field of wearable bioelectronics due to its tunable high electrical conductivity, air stability, ease of processability, biocompatibility, and recently discovered self-healing ability. It has been observed that blending additives with PEDOT:PSS or post-treatment permits the tailoring of intrinsic polymer properties, though their effects on the water-enabled self-healing property have not previously been established. Here, it is demonstrated that the water-enabled healing behavior of conducting polymers is decreased by crosslinkers or by acid post-treatment. Organic dopants of PEDOT have high water swelling ratios and lead to water-enabled healing, while inorganic dopants fail in the healing of PEDOT. The water-enabled healing of two isolated PEDOT:PSS squares with a 5 µm width gap and a thickness less than 1 µm is shown. This work will help pave the way for the further development of conducting polymer-based self-healable bioelectronics and flexible and stretchable electronics.

Electropolymerized Poly(3,4-ethylenedioxythiophene) (PEDOT) Coatings for Implantable Deep-Brain-Stimulating Microelectrodes.

Conducting polymers have been widely explored as coating materials for metal electrodes to improve neural signal recording and stimulation because of their mixed electronic-ionic conduction and biocompatibility. In particular, the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the best candidates for biomedical applications due to its high conductivity and good electrochemical stability. Coating metal electrodes with PEDOT has shown to enhance the electrode's performance by decreasing the impedance and increasing the charge storage capacity. However, PEDOT-coated metal electrodes often have issues with delamination and stability, resulting in decreased device performance and lifetime. In this work, we were able to electropolymerize PEDOT coatings on sharp platinum-iridium recording and stimulating neural electrodes and demonstrated its mechanical and electrochemical stability. Electropolymerization of PEDOT:tetrafluoroborate was carried out in three different solvents: propylene carbonate, acetonitrile, and water. The stability of the coatings was assessed via ultrasonication, phosphate buffer solution soaking test, autoclave sterilization, and electrical pulsing. Coatings prepared with propylene carbonate or acetonitrile possessed excellent electrochemical stability and survived autoclave sterilization, prolonged soaking, and electrical stimulation without major changes in electrochemical properties. Stimulating microelectrodes were implanted in rats and stimulated daily, for 7 and 15 days. The electrochemical properties monitored in vivo demonstrated that the stimulation procedure for both coated and uncoated electrodes decreased the impedance.

Poly(3,4-ethylenedioxythiophene) (PEDOT) Coatings for High-Quality Electromyography Recording.

Conducting polymer coatings on metal electrodes are an efficient solution to improve neural signal recording and stimulation, due to their mixed electronic-ionic conduction and biocompatibility. To date, only a few studies have been reported on conducting polymer coatings on metallic wire electrodes for muscle signal recording. Chronic muscle signal recording of freely moving animals can be challenging to acquire with coated electrodes, due to muscle movement around the electrode that can increase instances of coating delamination and device failure. The poor adhesion of conducting polymers to some inorganic substrates and the possible degradation of their electrochemical properties after harsh treatments, such as sterilization, or during implantation limits their use for biomedical applications. Here, we demonstrate the mechanical and electrochemical stability of the conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with LiClO4, deposited on stainless steel multistranded wire electrodes for invasive muscle signal recording in mice. The mechanical and electrochemical stability was achieved by tuning the electropolymerization conditions. PEDOT-coated and bare stainless steel electrodes were implanted in the neck muscle of five mice for electromyographic (EMG) activity recording over a period of 6 weeks. The PEDOT coating improved the electrochemical properties of the stainless steel electrodes, lowering the impedance, resulting in an enhanced signal-to-noise ratio during in vivo EMG recording compared to bare electrodes.

Tin Dioxide Electrolyte-Gated Transistors Working in Depletion and Enhancement Modes.

Metal oxide semiconductors are interesting for next-generation flexible and transparent electronics because of their performance and reliability. Tin dioxide (SnO2) is a very promising material that has already found applications in sensing, photovoltaics, optoelectronics, and batteries. In this work, we report on electrolyte-gated, solution-processed polycrystalline SnO2 transistors on both rigid and flexible substrates. For the transistor channel, we used both unpatterned and patterned SnO2 films. Since decreasing the SnO2 area in contact with the electrolyte increases the charge-carrier density, patterned transistors operate in the depletion mode, whereas unpatterned ones operate in the enhancement mode. We also fabricated flexible SnO2 transistors that operate in the enhancement mode that can withstand moderate mechanical bending.

Water-Enabled Healing of Conducting Polymer Films.

The conducting polymer polyethylenedioxythiophene doped with polystyrene sulfonate (PEDOT:PSS) has become one of the most successful organic conductive materials due to its high air stability, high electrical conductivity, and biocompatibility. In recent years, a great deal of attention has been paid to its fundamental physicochemical properties, but its healability has not been explored in depth. This communication reports the first observation of mechanical and electrical healability of PEDOT:PSS thin films. Upon reaching a certain thickness (about 1 µm), PEDOT:PSS thin films damaged with a sharp blade can be electrically healed by simply wetting the damaged area with water. The process is rapid, with a response time on the order of 150 ms. Significantly, after being wetted the films are transformed into autonomic self-healing materials without the need of external stimulation. This work reveals a new property of PEDOT:PSS and enables its immediate use in flexible and biocompatible electronics, such as electronic skin and bioimplanted electronics, placing conducting polymers on the front line for healing applications in electronics.

Photolithographically Patterned TiO2 Films for Electrolyte-Gated Transistors.

Metal oxides constitute a class of materials whose properties cover the entire range from insulators to semiconductors to metals. Most metal oxides are abundant and accessible at moderate cost. Metal oxides are widely investigated as channel materials in transistors, including electrolyte-gated transistors, where the charge carrier density can be modulated by orders of magnitude upon application of relatively low electrical bias (2 V). Electrolyte gating offers the opportunity to envisage new applications in flexible and printed electronics as well as to improve our current understanding of fundamental processes in electronic materials, e.g. insulator/metal transitions. In this work, we employ photolithographically patterned TiO2 films as channels for electrolyte-gated transistors. TiO2 stands out for its biocompatibility and wide use in sensing, electrochromics, photovoltaics and photocatalysis. We fabricated TiO2 electrolyte-gated transistors using an original unconventional parylene-based patterning technique. By using a combination of electrochemical and charge carrier transport measurements we demonstrated that patterning improves the performance of electrolyte-gated TiO2 transistors with respect to their unpatterned counterparts. Patterned electrolyte-gated (EG) TiO2 transistors show threshold voltages of about 0.9 V, ON/OFF ratios as high as 1 × 10(5), and electron mobility above 1 cm(2)/(V s).