Conductive Polymer Waving in Liquid Nitrogen

A Nanofibrous Polypyrrole Membrane with an Ultrahigh Areal Specific Capacitance and Improved Energy and Power Densities

For conductive polymers to be competitive with carbon-based electrode materials, it is critical to increase their surface area and electroactivity. In this work, a thick nanofibrous polypyrrole (PPy) membrane with communicating interfiber spaces was prepared through one-pot interfacial polymerization for the first time. The electrochemical properties and conductivity of the membrane were studied with cyclic voltammetry, electrochemical impedance spectroscopy, and a four-point probe. Its morphology, chemistry, and thermostability were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The areal specific capacitances measured between 0.0 and 0.8 V at 1 mA/cm2 were 19179, 13264, 7238, and 4458 mF/cm2 for the membranes doped with docusate sodium (AOT), camphor-10-sulfonic acid (β) (CSA), Cl-, and poly(sodium 4-styrenesulfonate) (PSS), respectively. The capacity retentions after 1000 cycles were 83, 74, 67, and 61% for the AOT-, CSA-, PSS-, and Cl--doped membranes, respectively. The Coulombic efficiency was above 99% for all of the membranes. They showed energy densities of 1.7, 1.2, 0.7, and 0.4 mWh/cm2 and power densities of 0.61, 0.75, 0.66, and 0.62 mW/cm2 for the AOT-, CSA-, Cl--, and PSS-doped membranes, respectively. The ultrahigh areal specific capacitance of PPy-AOT is due to its nanofibrous structure. A mechanism has been proposed to explain how this structure is formed based on the role of AOT as the surfactant. This nanofibrous PPy membrane is easy to prepare and metal-free and offers a very high areal specific capacitance, making it an excellent candidate to construct electrodes in pseudosupercapacitors.

Beyond nothingness in the formation and functional relevance of voids in polymer films

Voids-the nothingness-broadly exist within nanomaterials and impact properties ranging from catalysis to mechanical response. However, understanding nanovoids is challenging due to lack of imaging methods with the needed penetration depth and spatial resolution. Here, we integrate electron tomography, morphometry, graph theory and coarse-grained molecular dynamics simulation to study the formation of interconnected nanovoids in polymer films and their impacts on permeance and nanomechanical behaviour. Using polyamide membranes for molecular separation as a representative system, three-dimensional electron tomography at nanometre resolution reveals nanovoid formation from coalescence of oligomers, supported by coarse-grained molecular dynamics simulations. Void analysis provides otherwise inaccessible inputs for accurate fittings of methanol permeance for polyamide membranes. Three-dimensional structural graphs accounting for the tortuous nanovoids within, measure higher apparent moduli with polyamide membranes of higher graph rigidity. Our study elucidates the significance of nanovoids beyond the nothingness, impacting the synthesis‒morphology‒function relationships of complex nanomaterials.

Bioinspired Asymmetric Polypyrrole Membranes with Enhanced Photothermal Conversion for Highly Efficient Solar Evaporation

Solar-driven interfacial evaporation (SDIE) has attracted great attention by offering a zero-carbon-emission solution for clean water production. The manipulation of the surface structure of the evaporator markedly promotes the enhancement of light capture and the improvement of evaporation performance. Herein, inspired by seedless lotus pod, a flexible pristine polypyrrole (PPy) membrane with macro/micro-bubble and nanotube asymmetric structure is fabricated through template-assisted interfacial polymerization. The macro- and micro-hierarchical structure of the open bubbles enable multiple reflections inner and among the bubble cavities for enhanced light trapping and omnidirectional photothermal conversion. In addition, the multilevel structure (macro/micro/nano) of the asymmetric PPy (PPy-A) membrane induces water evaporation in the form of clusters, leading to a reduction of water evaporation enthalpy. The PPy-A membranes achieve a full-spectrum light absorption of 96.3% and high evaporation rate of 2.03 kg m-2  h-1 under 1 sun. Long-term stable desalination is also verified with PPy-A membranes by applying one-way water channel. This study demonstrates the feasibility of pristine PPy membranes in SDIE applications, providing guidelines for modulation of the evaporator topologies toward high-efficient solar evaporation.

Study of Chemical Polymerization of Polypyrrole with SDS Soft Template: Physical, Chemical, and Electrical Properties

Polypyrrole (PPy) is a conductive polymer known for its biocompatibility and ease of synthesis. Chemically polymerized PPy was synthesized in the presence of sodium dodecyl sulfate (SDS), showing correlations among chemical properties, physical morphology, and electrical properties. Focused synthesis parameters included the pyrrole (Py) concentration, SDS concentration, and ammonium persulfate (APS)/Py ratio. The addition of SDS during chemical polymerization influenced the physical morphology of PPy by altering the self-assembling process via micelle formation, yielding sheet-like morphologies. However, the phenomenon also relied heavily on other synthesis parameters. Varying SDS concentrations within the 0.01 to 0.30 M window produced PPy sheets with no significant difference in optical band gap or physical size. While using 0.10 M SDS, an increase in Py concentration from 0.10 to 0.30 M yielded a larger size of PPy as the morphology changed from sheet-like to irregular shape. The band gap dropped from 2.35 to 1.10 eV, and the conductivity rose from 6.80 × 10-1 to 9.40 × 10-1 S/m. With an increase in the APS/Py ratio, the PPy product changed from a random to a sheet-like form. The product provided a larger average size, a decreased band gap, and increased electrical conductivity. Py polymerization in the absence of SDS revealed no significant change in shape or size as the Py concentration increased from 0.10 to 0.30 M; only a sphere-like form was observed, with a large band gap and small conductivity. Results from Raman spectral analysis indicated a correlation between optical band gap, physical morphology, and bipolaron/polaron ratio, mainly at the wavelengths associated with C-C stretching and C-H deformation. The increase in average size was associated with a decrease in band gap and resistance as well as an increase in the bipolaron/polaron ratio. This work indicates a strong correlation between size, morphology, electrical properties, and the bipolaron/polaron ratio of PPy in the presence of SDS.

Polypyrrole Nanomaterials: Structure, Preparation and Application

In the past decade, nanostructured polypyrrole (PPy) has been widely studied because of its many specific properties, which have obvious advantages over bulk-structured PPy. This review outlines the main structures, preparation methods, physicochemical properties, potential applications, and future prospects of PPy nanomaterials. The preparation approaches include the soft micellar template method, hard physical template method and templateless method. Due to their excellent electrical conductivity, biocompatibility, environmental stability and reversible redox properties, PPy nanomaterials have potential applications in the fields of energy storage, biomedicine, sensors, adsorption and impurity removal, electromagnetic shielding, and corrosion resistant. Finally, the current difficulties and future opportunities in this research area are discussed.

A Simple Trick to Increase the Areal Specific Capacity of Polypyrrole Membrane: The Superposition Effect of Methyl Orange and Acid Treatment

Polypyrrole (PPy) is one of the attractive conducting polymers that have been investigated as energy storage materials in devices like supercapacitors. Previously, we have reported a free-standing soft PPy membrane synthesized through interfacial polymerization in which methyl orange (MO) and ferric chloride were used as nano template and oxidant. In this work, we report that the presence of MO and the treatment of the PPy-MO membrane with sulfuric acid can dramatically increase the specific capacitance of the membrane. The properties of the membranes were evaluated using scanning electron microscope (SEM) for morphology, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) for chemistry, thermogravimetric analysis (TGA) for thermal stability, and cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) for electrochemical activity. It was found that the areal specific capacitance of the PPy membrane increased from 2226 mF/cm2 to 6417 mF/cm2 and the charge transfer resistivity decreased from about 17 Ω to 3 Ω between 10,000 and 0.1 Hz due to the presence of MO and the acid treatment. It is likely that the superposition effect of MO and acid treatment helped the charge transfer process and consequently enhanced the charge storage performance and specific capacitance of the PPy membrane.

Conductive biomaterials for cardiac repair: A review

Myocardial infarction (MI) is one of the fatal diseases in humans. Its incidence is constantly increasing annually all over the world. The problem is accompanied by the limited regenerative capacity of cardiomyocytes, yielding fibrous scar tissue formation. The propagation of electrical impulses in such tissue is severely hampered, negatively influencing the normal heart pumping function. Thus, reconstruction of the internal cardiac electrical connection is currently a major concern of myocardial repair. Conductive biomaterials with or without cell loading were extensively investigated to address this problem. This article introduces a detailed overview of the recent progress in conductive biomaterials and fabrication methods of conductive scaffolds for cardiac repair. After that, the advances in myocardial tissue construction in vitro by the restoration of intercellular communication and simulation of the dynamic electrophysiological environment are systematically reviewed. Furthermore, the latest trend in the study of cardiac repair in vivo using various conductive patches is summarized. Finally, we discuss the achievements and shortcomings of the existing conductive biomaterials and the properties of an ideal conductive patch for myocardial repair. We hope this review will help readers understand the importance and usefulness of conductive biomaterials in cardiac repair and inspire researchers to design and develop new conductive patches to meet the clinical requirements. STATEMENT OF SIGNIFICANCE: After myocardial infarction, the infarcted myocardial area is gradually replaced by heterogeneous fibrous tissue with inferior conduction properties, resulting in arrhythmia and heart remodeling. Conductive biomaterials have been extensively adopted to solve the problem. Summarizing the relevant literature, this review presents an overview of the types and fabrication methods of conductive biomaterials, and focally discusses the recent advances in myocardial tissue construction in vitro and myocardial repair in vivo, which is rarely covered in previous reviews. As well, the deficiencies of the existing conductive patches and their construction strategies for myocardial repair are discussed as well as the improving directions. Confidently, the readers of this review would appreciate advantages and current limitations of conductive biomaterials/patches in cardiac repair.

Electrical Stimulation and Cellular Behaviors in Electric Field in Biomedical Research

Research on the cellular response to electrical stimulation (ES) and its mechanisms focusing on potential clinic applications has been quietly intensified recently. However, the unconventional nature of this methodology has fertilized a great variety of techniques that make the interpretation and comparison of experimental outcomes complicated. This work reviews more than a hundred publications identified mostly from Medline, categorizes the techniques, and comments on their merits and weaknesses. Electrode-based ES, conductive substrate-mediated ES, and noninvasive stimulation are the three principal categories used in biomedical research and clinic. ES has been found to enhance cell proliferation, growth, migration, and stem cell differentiation, showing an important potential in manipulating cellular activities in both normal and pathological conditions. However, inappropriate parameters or setup can have negative effects. The complexity of the delivered electric signals depends on how they are generated and in what form. It is also difficult to equate one set of parameters with another. Mechanistic studies are rare and badly needed. Even so, ES in combination with advanced materials and nanotechnology is developing a strong footing in biomedical research and regenerative medicine.

Effects of electrical stimulation on human skin keratinocyte growth and the secretion of cytokines and growth factors

Electrical stimulation (ES) has been widely explored and found effective in promoting wound healing. However, the role of ES on keratinocytes, a major player in wound healing, has not been well established. The present work investigated the cellular and molecular behaviors of human skin keratinocytes being exposed to ES. HaCaT keratinocytes were seeded on a novel electrically conductive and soft PPy-PU/PLLA membrane and cultured under electrical intensities of 100 or 200 mV mm^-1for 6 and 24 h. The factors assessed after ES include cell proliferation, colony formation, cytokines, keratins, as well as phosphorylated ERK1/2 (pERK1/2) kinases. The results showed that the electrically stimulated cells exhibited a higher proliferative ability and secreted more IL-6, IL-1α, IL-8, GROα, FGF2, and VEGF-A. Interestingly, the 24 h ES induced a 'stimulus memory' by showing a significant rise in colony-forming efficiency in post-ES cells that were sub-cultured. Additionally, after stopping the 24 h ES, the productions of keratin 5 and keratin 14 were continuously increased for 3 d. The productions of keratin 10 and keratin 13 were significantly increased post the 6 h ES. Finally, the ES increased pERK1/2 kinases. The overall results demonstrated that the proliferation of keratinocytes and their secretion of cytokines and growth factors can be activated through appropriate ES to benefit skin wound healing.

Durable electromagnetic interference (EMI) shielding ramie fabric with excellent flame retardancy and Self-healing performance

Although more and more attention has been paid to electromagnetic interference (EMI) shielding fabric materials due to increasing electromagnetic waves pollution, little attention to their fire safety behavior and durability in practical use. Herein, durable EMI shielding ramie fabric with flame retardant and self-healing performance were fabricated by depositing ammonium polyphosphate (APP)/polyethyleneimine (PEI) layer, MXene sheets and polycaprolactone (PCL) layer. The resultant multifunctional fabric could self-extinguish and the peak heat release rate (pHRR) value reduced about 74.3% for the modified ramie fabric that contains about 12 wt% of PEI/APP bilayer compared with pure ramie fabric. Furthermore, the ramie fabric coated by a increasing amount of MXene sheets changed from insulating to conductive, thus gradually improving their EMI shielding performance, which exhibit a high electrical conductivity of 900.56 S/m with an outstanding SE value of 35 dB at a 1.2 mg/cm² content in the X-band. Besides, When the multifunctional fabric was cut off under external force, it could achieve self-healing and the EMI shielding performance can recover to 34 dB due to the low melting point and good fluidity of PCL. Thus, this multifunctional fabric holds great promise for wearable intelligent cloth, EMI shielding and other fields.

A biocompatible polypyrrole membrane for biomedical applications

Polypyrrole (PPy) is the most widely investigated electrically conductive biomaterial. However, because of its intrinsic rigidity, PPy has only been used either in the form of a composite or a thin coating. This work presents a pure and soft PPy membrane that is synergically reinforced with the electrospun polyurethane (PU) and poly-l-lactic acid (PLLA) fibers. This particular reinforcement not only renders the originally rather fragile PPy membrane easy to manipulate, it also prevents the membrane from deformation in an aqueous environment. Peel and mechanical tests confirmed the strong adhesion of the fibers and the significantly increased tensile strength of the reinforced membrane. Surface electrical conductivity and long-term electrical stability were tested, showing that these properties were not affected by the reinforcement. Surface morphology and chemistry were analyzed with scanning electron spectroscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Material thermal stability was investigated with thermogravimetric analysis (TGA). Finally, the adhesion and proliferation of human skin keratinocytes on the membrane were assessed by Hoechst staining and the methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay. In conclusion, this membrane proves to be the first PPy-based soft conductive biomaterial that can be practically used. Its electrical conductivity and cytocompatibility promise a wide range of biomedical applications.

A reinforced soft polypyrrole membrane.

Vapor/liquid polymerization of ultraporous transparent and capacitive polypyrrole nanonets

Freestanding, contiguous, and translucent polypyrrole nanonets are prepared within 90 minutes at room temperature in Petri dishes by exposing aqueous oxidant to static pyrrole vapor. The nanonets are 150 nm thick, with variable densities depending on polymerization time. The nanonets maintain a low sheet resistance of 29.1 Ω□^-1 at 30% optical transmission, and 423 Ω□^-1 at 50% transmission. A mechanism is proposed in which polypyrrole islands serve as nucleation sites for further surface-tension constrained polymerization. The nanonets exhibit a high degree of electrochemical dopability (over 24%). Nets are robust and processable, as evidenced by their ability to drape over 2D and 3D substrates. Large areas of films are manually twisted into highly porous sub-millimeter diameter conductive wires, able to recover their two-dimensional structure upon immersion in solvents. Moreover, nanonets exhibit a high specific capacitance of 518 F g^-1 for a 1.2 V potential window. Electrochemical capacitors fabricated with nanonet active electrodes show a high energy density of 9.86 W h kg^-1 at 1775 W kg^-1 when charged to 0.8 V.

Conducting Polymers, Hydrogels and Their Composites: Preparation, Properties and Bioapplications

This review is focused on current state-of-the-art research on electroactive-based materials and their synthesis, as well as their physicochemical and biological properties. Special attention is paid to pristine intrinsically conducting polymers (ICPs) and their composites with other organic and inorganic components, well-defined micro- and nanostructures, and enhanced surface areas compared with those of conventionally prepared ICPs. Hydrogels, due to their defined porous structures and being filled with aqueous solution, offer the ability to increase the amount of immobilized chemical, biological or biochemical molecules. When other components are incorporated into ICPs, the materials form composites; in this particular case, they form conductive composites. The design and synthesis of conductive composites result in the inheritance of the advantages of each component and offer new features because of the synergistic effects between the components. The resulting structures of ICPs, conducting polymer hydrogels and their composites, as well as the unusual physicochemical properties, biocompatibility and multi-functionality of these materials, facilitate their bioapplications. The synergistic effects between constituents have made these materials particularly attractive as sensing elements for biological agents, and they also enable the immobilization of bioreceptors such as enzymes, antigen-antibodies, and nucleic acids onto their surfaces for the detection of an array of biological agents. Currently, these materials have unlimited applicability in biomedicine. In this review, we have limited discussion to three areas in which it seems that the use of ICPs and materials, including their different forms, are particularly interesting, namely, biosensors, delivery of drugs and tissue engineering.

Surface modification by assembling: a modular approach based on the match in nanostructures

A modular strategy is described to construct a multi-biofunctional and conductive membrane based on the assembling of a nanostructured substrate and functional nanoparticles.

Novel de novo synthesized phosphate carrier compound ABA-PEG20k-Pi20 suppresses collagenase production in Enterococcus faecalis and prevents colonic anastomotic leak in an experimental model

BACKGROUND

Previous work has demonstrated that anastomotic leak can be caused by collagenolytic bacteria such as Enterococcus faecalis via an effect on wound collagen. In humans, E. faecalis is the organism cultured most commonly from a leaking anastomosis, and is not routinely eliminated by standard oral or intravenous antibiotics. Novel strategies are needed to contain the virulence of this pathogen when present on anastomotic tissues.

METHODS

Polyphosphorylated polymer ABA-PEG20k-Pi20 was tested in mice for its ability to prevent anastomotic leak caused by collagenolytic E. faecalis. The study design included a distal colonic resection and anastomosis followed by introduction of E. faecalis to anastomotic tissues via enema. Mice were assigned randomly to receive either ABA-PEG20-Pi20 or its unphosphorylated precursor ABA-PEG20k in their drinking water. The development of anastomotic leak was determined after the animals had been killed.

RESULTS

Overnight incubation of two different E. faecalis collagenolytic strains with 2 mmol/l of ABA-PEG20k-Pi20 led to near complete inhibition of collagenase production (from 21 000 to 1000 and from 68 000 to 5000 units; P < 0·001; 6 samples per group) without suppressing bacterial growth. In mice drinking 1 per cent ABA-PEG20k-Pi20, the phosphate concentration in the distal colonic mucosa increased twofold and leak rates decreased from eight of 15 to three of 15 animals (P < 0·001). In mice drinking ABA-PEG20k-Pi20, the percentage of collagenolytic colonies among E. faecalis populations present at anastomotic tissue sites was decreased by 6-4800-fold (P = 0·008; 5 animals).

CONCLUSION

These data indicate that oral intake of ABA-PEG20k-Pi20 may be an effective agent to contain the virulence of E. faecalis and may prevent anastomotic leak caused by this organism. Clinical relevance Progress in understanding the pathogenesis of anastomotic leak continues to point to intestinal bacteria as key causative agents. The presence of pathogens such as Enterococcus faecalis that predominate on anastomotic tissues despite antibiotic use, coupled with their ability to produce collagenase, appears to alter the process of healing that leads to leakage. Further antibiotic administration may seem logical, but carries the unwanted risk of eliminating the normal microbiome, which functions competitively to exclude and suppress the virulence of pathogens such as E. faecalis. Therefore, non-antibiotic strategies that can suppress the production of collagenase by E. faecalis without affecting its growth, or potentially normal beneficial microbiota, may have unique advantages. The findings of this study demonstrate that drinking a phosphate-based polymer can achieve the goal of preventing anastomotic leak by suppressing collagenase production in E. faecalis without affecting its growth.