PSS Hydrogel Research Articles

Tissue‐Like Optoelectronic Neural Interface Enabled by PEDOT:PSS Hydrogel for Cardiac and Neural Stimulation

Optoelectronic biointerfaces have made a significant impact on modern science and technology from understanding the mechanisms of the neurotransmission to the recovery of the vision for blinds. They are based on the cell interfaces made of organic or inorganic materials such as silicon, graphene, oxides, quantum dots, and π-conjugated polymers, which are dry and stiff unlike a cell/tissue environment. On the other side, wet and soft hydrogels have recently been started to attract significant attention for bioelectronics because of its high-level tissue-matching biomechanics and biocompatibility. However, it is challenging to obtain optimal opto-bioelectronic devices by using hydrogels requiring device, heterojunction, and hydrogel engineering. Here, an optoelectronic biointerface integrated with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, hydrogel that simultaneously achieves efficient, flexible, stable, biocompatible, and safe photostimulation of cells is demonstrated. Besides their interfacial tissue-like biomechanics, ≈34kPa, and high-level biocompatibility, hydrogel-integration facilitates increase in charge injection amounts sevenfolds with an improved responsivity of 156mA W-1 , stability under mechanical bending , and functional lifetime over three years. Finally, these devices enable stimulation of individual hippocampal neurons and photocontrol of beating frequency of cardiac myocytes via safe charge-balanced capacitive currents. Therefore, hydrogel-enabled optoelectronic biointerfaces hold great promise for next-generation wireless neural and cardiac implants.

PEDOT:PSS hydrogel gate electrodes for OTFT sensors

PEDOT:PSS hydrogel is used as soft, conductive gate electrodes for low-voltage hygroscopic insulator field effect transistors (HIFETs). HIFETs are sensitive to aqueous solutions of KCl, NaCl and H2O2, introduced through the hydrogel gate electrode.

A conducting polymer PEDOT:PSS hydrogel based wearable sensor for accurate uric acid detection in human sweat

Noninvasive wearable sensors present key information about targeting epidermally retrievable biofluids in human health monitoring. Tracking circulating uric acid (UA) in human sweat performs a simple and prompt way for reducing risk of gout and hyperuricemia. Herein, we propose a wearable microfluidic-based electrochemical sensor via incorporating conducting polymer PEDOT:PSS hydrogel towards accurate and sensitive detection of UA in sweat. The microfluidic device validly realizes the capture for sweat in real-time, and the conducting PEDOT:PSS hydrogel with large surface area plays multiple roles in this wearable sensor for UA detecting, electrolyte storing, and flexibility enhancing. The prepared flexible sensor shows an ultrahigh sensitivity of 0.875 µA µM−1 cm−2 and a low limit of detection (LOD) down to 1.2 μM (S/N = 3). Furthermore, it can detect UA levels in real human sweat samples collected from volunteers before and after purine-rich diets, and the results are highly correlated with those measured by the standard enzyme linked immunosorbent assay (ELISA). This PEDOT:PSS hydrogel based flexible sensor, together with the sweat-collecting microfluidic device, is believed to be promising for the construction of high performance wearable sensors to monitor biomarkers, metabolites and nutrients.

Synthesis and Characterization of Porous, Electro-Conductive Chitosan-Gelatin-Agar-Based PEDOT: PSS Scaffolds for Potential Use in Tissue Engineering.

Herein we report the synthesis and characterization of electro-conductive chitosan–gelatin–agar (Cs-Gel-Agar) based PEDOT: PSS hydrogels for tissue engineering. Cs-Gel-Agar porous hydrogels with 0–2.0% (v/v) PEDOT: PSS were fabricated using a thermal reverse casting method where low melting agarose served as the pore template. Sample characterizations were performed by means of scanning electron microscopy (SEM), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR), X-ray diffraction analysis (XRD) and electrochemical impedance spectroscopy (EIS). Our results showed enhanced electrical conductivity of the cs-gel-agar hydrogels when mixed with DMSO-doped PEDOT: PSS wherein the optimum mixing ratio was observed at 1% (v/v) with a conductivity value of 3.35 × 10−4 S cm−1. However, increasing the PEDOT: PSS content up to 1.5 % (v/v) resulted in reduced conductivity to 3.28 × 10−4 S cm−1. We conducted in vitro stability tests on the porous hydrogels using phosphate-buffered saline (PBS) solution and investigated the hydrogels’ performances through physical observations and ATR–FTIR characterization. The present study provides promising preliminary data on the potential use of Cs-Gel-Agar-based PEDOT: PSS hydrogel for tissue engineering, and these, hence, warrant further investigation to assess their capability as biocompatible scaffolds.

Tissue-adhesive, stretchable, and self-healable hydrogels based on carboxymethyl cellulose-dopamine/PEDOT:PSS via mussel-inspired chemistry for bioelectronic applications

A new generation of wearable devices using hydrogel-based sensors has attracted attention for human motion monitoring detection. On the other hand, integrating multiple properties, such as self-adhesiveness, repeatable adhesion, stretchability, high conductivity, good mechanical performance, and good electrical stability within a single hydrogel, which remains a challenge. In this study, hydrogels composed of borate crosslinked pendant catechol groups of carboxymethyl cellulose-dopamine conjugate (CMC-DA) in a polyacrylamide (PAM) crosslinked network (CDB-PAM) were developed. The stretchability (2763%) and tensile strength (36.9 ± 2.3 KPa) of the CDB-PAM hydrogel were improved when 4 wt% of CMC-DA was used for hydrogel preparation. The incorporation of 2.0 wt% PEDOT:PSS greatly improved the tensile stress (44.9 ± 2.6 KPa), low elastic modulus (3.1 ± 0.15 KPa), and stretchability (2873%). The CDB-PAM-PEDOT:PSS hydrogel had self-healing and recoverable properties. The hydrogel demonstrated self-adhesive properties (e.g., skin adhesion to porcine skin 65.1 ± 2.2) with long-term reusability by maintaining redox-active catechol groups in the hydrogel. The in vitro biocompatibility test using skin fibroblasts and keratinocytes cells confirmed the good biocompatibility of the hydrogels. The PEDOT:PSS-incorporated CDB-PAM hydrogel showed good conductivity (41.6 S/m) because of the charge transfer between PEDOT and catechol/quinone groups of CMC-DA in the hydrogel, forming a well-connected electric path. Furthermore, the developed hydrogel-based strain sensor was sensitive to human flexible wearable devices in bioelectronic applications. Overall, the hydrogel with multiple properties, such as high stretchability, self-healing, and high conductivity, demonstrated promising for flexible wearable devices in bioelectronic applications.

Chemical stability and reversibility of PEDOT:PSS electrodes in view of low-cost biocompatible cellulose-assisted biosensors

The increasing necessity for small electronics and wireless technologies in energetic devices, such as batteries or supercapacitors and in medical devices, such as sensors, drug delivery systems, calls for new materials, devices and preparation methods. In this work, the possibility of using a PEDOT:PSS hydrogel film as a cathode for a biocompatible cellulose-assisted biosensing device has been explored. The effect of film formulation and preparation method on the electrical conductivity is investigated, i.e. adding a cross-linker and different solvent additives on one side and adding an ionic liquid with and without a metal salt on the other side, for two film thicknesses. The chemical composition of the electrode is studied as a function of the used formulation as well as after being used as cathode in the biosensing device. It appeared that the electrode based on the cross-linker was mechanically robust, but suffered in electrical conductivity, despite the enhancement provided by the solvent additives. The electrode based on the ionic liquid showed a considerable increase in electrical performance, although the mechanical stability was not easy to maintain. The thin film showed a higher electrical conductivity. Although the metal salt enhanced somewhat further the electrical performance, the mechanical one suffered considerably. An application of the PEDOT:PSS electrode as cathode in a biosensing device showed promising results. Concentrations of the order of μl were measured without difficulty and the cathode seemed to be chemically stable and therefore reutilisable, opening future applications in reutilisable low-cost wearable biosensors and corresponding wearable batteries.

Electrically Conductive and 3D-Printable Oxidized Alginate-Gelatin Polypyrrole:PSS Hydrogels for Tissue Engineering.

Electroactive hydrogels can be used to influence cell response and maturation by electrical stimulation. However, hydrogel formulations which are 3D printable, electroactive, cytocompatible, and allow cell adhesion, remain a challenge in the design of such stimuli-responsive biomaterials for tissue engineering. Here, a combination of pyrrole with a high gelatin-content oxidized alginate-gelatin (ADA-GEL) hydrogel is reported, offering 3D-printability of hydrogel precursors to prepare cytocompatible and electrically conductive hydrogel scaffolds. By oxidation of pyrrole, electroactive polypyrrole:polystyrenesulfonate (PPy:PSS) is synthesized inside the ADA-GEL matrix. The hydrogels are assessed regarding their electrical/mechanical properties, 3D-printability, and cytocompatibility. It is possible to prepare open-porous scaffolds via bioplotting which are electrically conductive and have a higher cell seeding efficiency in scaffold depth in comparison to flat 2D hydrogels, which is confirmed via multiphoton fluorescence microscopy. The formation of an interpenetrating polypyrrole matrix in the hydrogel matrix increases the conductivity and stiffness of the hydrogels, maintaining the capacity of the gels to promote cell adhesion and proliferation. The results demonstrate that a 3D-printable ADA-GEL can be rendered conductive (ADA-GEL-PPy:PSS), and that such hydrogel formulations have promise for cell therapies, in vitro cell culture, and electrical-stimulation assisted tissue engineering.

One-Pot Hydrothermal Synthesis of Solution-Processable MoS2/PEDOT:PSS Composites for High-Performance Supercapacitors.

It is challenging to hydrothermally synthesize solution-processable MoS2, as the strong van der Waals force between MoS2 nanosheets induces self-assembly of agglomerates. Here, we introduce poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) into the precursor to impede aggregate formation in the hydrothermal process. A hybrid MoS2/PEDOT:PSS (MP) hydrogel is formed due to the electrostatic interactions between the negatively charged MoS2 and positively charged PEDOT chains. This hydrogel can be easily dispersed in water for subsequent solution processing such as vacuum filtration to form free-standing flexible films or extrusion 3D printing to create novel patterns. The MP film with a fracture strength of 18.59 MPa displays excellent electrochemical performance in both aqueous Na2SO4 electrolyte (474 mF cm-2) and solid-state PVA-H3PO4 electrolyte (360 mF cm-2). Flexibility and robustness can be evidenced by high capacitance retention rates of 94 and 89% after being repeatedly bent to 180° for 5000 cycles in aqueous and solid-state electrolytes, respectively.

The conducting fibrillar networks of a PEDOT:PSS hydrogel and an organogel prepared by the gel-film formation process

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a practical conducting polymer. The gel-film formation process produces a PEDOT:PSS organogel with a structure between a PEDOT:PSS water dispersion and a dried film. We found that this film has a high water-swelling ratio and thickens by a hitherto unreported factor of approximately 6600% as its swells to form a hydrogel. In this study, we investigated the drying behaviour of a hydrogel and an organogel with electrical properties to elucidate the internal structures of the gel responsible for the swelling and shrinkage behaviour with high expansion and contraction ratios. SEM revealed that the gel is composed of a 3D fibrillar network consisting of fibrils that are 4.6 ± 1.6 μm long and 0.63 ± 0.29 μm in diameter. This network plays a pivotal role in the conduction of electricity and swelling behaviour with high expansion ratios. The thickness of the gel decreased to 1/66 of its original value after drying on a substrate, while the total electrical resistance decreased by only 20%. The organogel exhibited the same drying behaviour as the hydrogel, which indicates that the network forms first in the organogel and is maintained in the subsequent swelling and drying processes. The electrical conductivity of the hydrogel increased from 9.0 ± 0.1 to 346.4 ± 1.2 S cm−1 under anisotropic shrinking from 3.1 ± 0.2 mm to 77.4 ± 3.3 μm. The network plays an important role as an enhanced swelling framework by providing effective pathways for the conduction of electricity.

Natively stretchable micro-supercapacitors based on a PEDOT:PSS hydrogel

Highly stretchable (>200%) microsupercapacitors (with 93% retention of the capacitance) are prepared by a facile laser-patterning and injection method with a highly conductive PEDOT:PSS hydrogel.

Electrode Surface Rebuilding for Electrochemical Assembling of Conductive PEDOT:PSS Hydrogel Towards Biosensing

Electrode Surface Rebuilding for Electrochemical Assembling of Conductive PEDOT:PSS Hydrogel Towards Biosensing

Performance evaluation of all-solid-state flexible supercapacitors based on PVA & PEDOT:PSS hydrogel composite electrode

Performance evaluation of all-solid-state flexible supercapacitors based on PVA & PEDOT:PSS hydrogel composite electrode

High‐Performance PVA/PEDOT:PSS Hydrogel Electrode for All‐Gel‐State Flexible Supercapacitors

AbstractFlexible supercapacitors are widely favored because they can provide a stable energy supply under different deformations. However, how to avoid the delamination of flexible matrix and electroactive materials under high deformation and balance mechanical durability and electrochemical performance is still an urgent problem to be overcome. Here, a hybrid polyvinyl alcohol/poly(3,4‐ethylenedioxythiophene): polystyrene sulfonate (PVA/PEDOT:PSS) hydrogel electrode with 3D interpenetrated network structure is prepared by the freeze–thaw crosslinking and solution immersion method. Due to the strong intermolecular force between PVA and PEDOT:PSS, coupling with the use of liquid phase mixing, this hybrid hydrogel electrode shows uniform interconnectivity and robust mechanical properties. The all‐gel‐state flexible supercapacitor based on the PVA/PEDOT:PSS hydrogel is fabricated to demonstrate its excellent mechanical durability of which capacitance retention retains 98.1% after 1000 bending cycles as well as excellent electrochemical performance whose areal specific capacitance is 128.9 mF cm−2 and energy density is up to 11.46 μWh cm−2. Moreover, it can continuously power the liquid‐crystal display (LCD) watch in bending, compression, and low‐temperature environments. The outstanding comprehensive performance of this supercapacitor indicates that it has the potential to be used in a new generation of flexible energy storage devices.

Antifreezing and stretchable all-gel-state supercapacitor with enhanced capacitances established by graphene/PEDOT-polyvinyl alcohol hydrogel fibers with dual networks

Although aqueous fibrous supercapacitor is one of the most advantageous energy storage devices for powering wearable electronics due to its excellent flexibility, outstanding cycling stability and high safety, it is still a challenge for its electroactive components to be cold-tolerant and stretchable for adapting fluctuating climate environments. Herein, a graphene/PEDOT:PSS hydrogel fiber with a continuous rose flower-like network is firstly constructed, and an antifreezing polyvinyl alcohol (PVA) network is subsequently taken into the hydrogel fiber via solvent replacement to generate an antifreezing and stretchable graphene/PEDOT-PVA hydrogel fiber with dual networks. Benefiting from superior interface compatibility of the hydrogel fiber with a PVA electrolyte, the assembled all-gel-state supercapacitor delivers a high capacitance of 281.2 F g−1 (0.1 A g−1) at 25 °C, more than twice higher than that of an aerogel fiber-based supercapacitor. Furthermore, this supercapacitor exhibits stable subzero-temperature electrochemical performances due to the smooth ion-transport channels and good conductivity of the antifreezing hydrogel fiber electrode, evidenced by the high specific capacitance of 212.6 F g−1 and the excellent capacitance retention of 91% after 5000 charge/discharge cycles at −20 °C. Finally, a highly stretchable spring-like supercapacitor exhibits an excellent capacitance retention of 92% after 5000 stretching cycles at a strain of 500%.

Microfabricated and 3-D printed electroconductive hydrogels of PEDOT:PSS and their application in bioelectronics

Biofabrication techniques such as microlithography and 3-D bioprinting have emerged in recent years as technologies capable of rendering complex, biocompatible constructs for biosensors, tissue and regenerative engineering and bioelectronics. While instruments and processes have been the subject of immense advancement, multifunctional bioinks have received less attention. A novel photocrosslinkable, hybrid bioactive and inherently conductive bioink formed from poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) nanomaterials within poly(2-hydroxyethyl methacrylate-co-polyethyleneglycol methacrylate) p(HEMA-co-EGMA) was used to render complex hydrogel constructs through microlithographic fabrication and 3-D printing. Constructs were directly compared through established metrics of acuity and fidelity, using side-by-side comparison of microarray grids, triangles incorporating angles 15–90°, and a multi-ink hydrogel disk array. Compositional variation from 0.01 to 1.00 wt% PEDOT:PSS produced hydrogels of varying and tunable electrical and electrochemical properties, while maintaining similar rheological properties (up to 0.50 wt% PEDOT:PSS). Furthermore, hydrogel membrane resistances extracted from equivalent circuit modeling of electrical impedance spectroscopy data varied only according to the included wt% of PEDOT:PSS and were agnostic of fabrication method. An in-silico variable frequency active low-pass filter was developed using a microlithographically fabricated Individually Addressable Microband Electrode (IAME) as the filtering capacitor, wherein 3-D printed lines of varying wt% of PEDOT:PSS hydrogels were shown to alter the cutoff frequency of the analog filter, indicating a potential use as tunable 3-D printed organic electronic analog filtering elements for biosensors. Bioinks of different PEDOT:PSS (0.0, 0.1, and 0.5 wt%) manufactured into hydrogel disks using the two methods were shown to yield similarly cytocompatible substrates for attachment and differentiation of PC-12 neural progenitor cells.

PEDOT: PSS hydrogel film for supercapacitors via AlCl3-induced cross-linking and subsequent organic solvent treatments

An ionically crosslinked conducting polymer poly (3, 4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT: PSS) hydrogel was synthesized by fast gelation of PEDOT: PSS dispersion (PH1000) using a high concentration of Al3+ (2 M) with a high water content of 94.4 wt% and three-dimensional interconnected networks. The highly conductive PEDOT: PSS hydrogel film was achieved by soaking it in ethylene glycol (EG) for a certain time. It was found for the first time that the conductivity of the PEDOT: PSS hydrogel film can be further improved with the vapors of m-cresol. It delivers 158 F g−1 at a scan rate of 50 mV s−1 with an outstanding rate capability and good cycling stability with 84.9% capacitance retention after 2000 cycles.

Hierarchically interconnected conducting polymer hybrid fiber with high specific capacitance for flexible fiber-shaped supercapacitor

Polypyrrole (PPy) based fiber-shaped supercapacitor (FSSC) is attracting increasing attention as energy storage devices of flexible and wearable electronic products in recent years. However, its application is limited by the low specific capacitance and poor rate capability, mainly suffering from inferior conductivity and inhibited ions channels of fiber electrode. Here, a high-performance flexible FSSC is constructed based on hierarchically interconnected porous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/PPy composite fiber prepared by in situ chemical polymerization of pyrrole on a novel highly-conductive PEDOT:PSS hydrogel support. The good electronic and ionic conductor properties, hierarchically porous structure and π-π interaction of conducting polymer hybrid fiber ensure fast electrons transfer/ions diffusion and the efficient utilization of whole electrode. Benefiting from the well-designed hybrid architecture and synergistic effect, the PEDOT:PSS/PPy hybrid fiber in FSSC exhibits superb volumetric/areal/length specific capacitance (393.8 F cm−3, 770.6 mF cm−2 and 18.9 mF cm−1 at 2.0 A cm−3) and excellent rate performance (52.8% capacitance retention even at ultrahigh current density of 50 A cm−3). The FSSC device displays record-high energy density (8.3 mWh cm−3 or 16.2 μWh cm−2 at such a high power density of 389.1 mW cm−3 or 761.5 μW cm−2) compared to other previously-reported PPy based FSSCs, as well as long-term cycle stability and exceptional flexibility. The outstanding electrochemical and flexural performances of our PPy based FSSC are competent for portable and wearable electronics.

Highly-conductive PEDOT:PSS hydrogel framework based hybrid fiber with high volumetric capacitance and excellent rate capability

Fiber supercapacitors (FSCs) are attractive energy storage devices for wearable and portable electronics. However, it still remains a great challenge to achieve high volumetric specific capacitance without sacrificing the rate capability of FSC. Here, we demonstrate a novel hierarchically nanostructured hybrid fiber with thin polyaniline (PANI) layer anchored on the highly-conductive poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) hydrogel framework as electrodes for FSCs. The hybrid fiber was prepared via hydrothermal assembly of a commercial PEDOT:PSS dispersion followed by acid treatment and in-situ chemical polymerization of aniline. The incorporation of highly-electroactive PANI boosts the whole capacitance of hybrid fiber; the robust PEDOT hydrogel framework provides abundant ions diffusion channels and rapid electron transfer pathways, improving the utilization efficiency and the kinetics of pseudocapacitance reaction of PANI. Attributed to the synergistic effect, the PEDOT/PANI hybrid fiber in FSC exhibits high volumetric/areal specific capacitance (554.1 F cm−3 or 740.0 mF cm−2 at 5 A cm−3), excellent rate performance and good electrochemical stability. The flexible FSC device delivers a high volumetric energy density of 11.9 mWh cm−3 at 981.4 mW cm−3 and areal energy density of 15.8 μWh cm−2 at 1310.5 μW cm−2, outperforming most of the reported counterparts. The well-designed PEDOT/PANI hybrid fiber based FSC hold a great potential for powering the next-generation wearable and portable electronics.

Room-Temperature-Formed PEDOT:PSS Hydrogels Enable Injectable, Soft, and Healable Organic Bioelectronics.

There is an increasing need to develop conducting hydrogels for bioelectronic applications. In particular, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hydrogels have become a research hotspot due to their excellent biocompatibility and stability. However, injectable PEDOT:PSS hydrogels have been rarely reported. Such syringe-injectable hydrogels are highly desirable for minimally invasive biomedical therapeutics. Here, an approach is demonstrated to develop injectable PEDOT:PSS hydrogels by taking advantage of the room-temperature gelation property of PEDOT:PSS. These PEDOT:PSS hydrogels form spontaneously after syringe injection of the PEDOT:PSS suspension into the desired location, without the need of any additional treatments. A facile strategy is also presented for large-scale production of injectable PEDOT:PSS hydrogel fibers at room temperature. Finally, it is demonstrated that these room-temperature-formed PEDOT:PSS hydrogels (RT-PEDOT:PSS hydrogel) and hydrogel fibers can be used for the development of soft and self-healable hydrogel bioelectronic devices.

An Electrochemical Gelation Method for Patterning Conductive PEDOT:PSS Hydrogels

Due to their high water content and macroscopic connectivity, hydrogels made from the conducting polymer PEDOT:PSS are a promising platform from which to fabricate a wide range of porous conductive materials that are increasingly of interest in applications as varied as bioelectronics, regenerative medicine, and energy storage. Despite the promising properties of PEDOT:PSS-based porous materials, the ability to pattern PEDOT:PSS hydrogels is still required to enable their integration with multifunctional and multichannel electronic devices. In this work, a novel electrochemical gelation ("electrogelation") method is presented for rapidly patterning PEDOT:PSS hydrogels on any conductive template, including curved and 3D surfaces. High spatial resolution is achieved through use of a sacrificial metal layer to generate the hydrogel pattern, thereby enabling high-performance conducting hydrogels and aerogels with desirable material properties to be introduced into increasingly complex device architectures.