Shape‐Dependent Cytotoxicity and Proinflammatory Response of Poly(3,4‐ethylenedioxythiophene) Nanomaterials

Poly(3,4‐ethylenedioxythiophene) (PEDT) is recognized as one of the most promising conducting polymers for future applications in the fields of electronics, optics, energy storage/conversion, and biomedical science. The toxicity of PEDT could be considered to affect the potential for its widespread application. Herein, the cytotoxicity and proinflammatory response of PEDT nanomaterials of three different shapes toward human lung fibroblast (IMR90) and mouse alveolar macrophage (J774A.1) cells are investigated. The shape‐dependent toxicity of the PEDT nanomaterials is evaluated by examining cell morphological change, cytotoxicity, apoptosis/necrosis, oxidative stress, and immune response. The cytotoxicity and apoptosis of the nanomaterials increase with their decreasing aspect ratio in both cell lines. The formation of reactive oxygen species in cells treated with PEDT nanomaterials is dependent on the shape and concentration of the nanomaterial. Proinflammatory cytokines, such as interleukin‐1, interleukin‐6, and tumor necrosis factor α from macrophages, are induced by PEDT nanomaterial‐treated cells.     

Poly(3,4‐alkylenedioxypyrroles): The PXDOPs as Versatile Yet Underutilized Electroactive and Conducting Polymers

The poly(3,4‐dioxypyrrole) (PXDOP) family of conducting and electroactive polymers has now been developed to the point that multiple synthetic routes allow many functionalized polymers with controllable optoelectronic and redox properties. These properties, which include high conductivity, multicolor cathodic and anodic electrochromism, and rapid redox switching, allow these materials to be used in a variety of applications that potentially include conducting coatings, electrochromic windows and displays, chemical sensors, bioactive materials, and mechanical actuators. Surprisingly, the scientific literature published on the PXDOP derivatives has been isolated and sparse compared to that of other conducting polymers. This report will highlight the synthesis and materials properties of PXDOPs and show how these powerful materials fit into the frontier of conducting polymers research.     

Influence of Biodopants on PEDOT Biomaterial Polymers: Using QCM‐D to Characterize Polymer Interactions with Proteins and Living Cells

Organic conducting polymers (OCPs) are currently the subject of intense research in the area of biomaterials and bioelectronics. Of the OCPs, poly(3,4‐ethylenedioxythiophene) (PEDOT) has attracted significant interest, however there has been little work on investigating the incorporation of biological compounds as the dopant species in the polymer which are aimed at enhancing the biocompatibility and biofunctionality of the material. Here, we incorporate the biological dopants dextran sulphate, chondroitin sulphate, and alginate, into PEDOT polymers and investigate their influence on a suite of physicochemical and electrochemical properties. We employ QCM‐D to study the mass of adsorption and the viscoelastic properties of the important extracellular matrix proteins fibronectin and collagen. Furthermore, we use QCM‐D to study the adhesion of PC12 neural cells to the PEDOT‐biodopant polymers with and without an adsorbed protein conditioning layer. QCM‐D was found to be an excellent tool with which to study conducting polymer–biological interactions, with this report the first time that QCM‐D has been used to study cell interactions with conducting polymer biomaterials.     

Conducting Polymers with Confined Dimensions: Track‐Etch Membranes for Amperometric Biosensor Applications

Organic conducting polymers can be synthesized inside the pores of a track‐etch membrane, and the resulting hollow tubules are shown to have enhanced electrical properties compared to their corresponding bulk materials. The polymerization of monomers (e.g., pyrrole, thiophenes) inside the confined space of these pores, combined with electrostatic interaction, ensures the alignment of the organic polymers on the interior, leading to higher conductivity. The application of these conducting tubes in the development of amperometric glucose sensors is discussed. Due to the special properties of conducting polymers inside a track‐etch membrane, biosensors with a unique electron‐transfer mechanism have been developed.     

Electrochemistry of Poly(3,4‐alkylenedioxythiophene) Derivatives

An overview of the electrochemistry of poly(3,4‐alkylenedioxythiophene)s (PXDOTs) is presented. As a class of conducting and electroactive polymers that can exhibit high and quite stable conductivities, a high degree of optical transparency as a conductor, and the ability to be rapidly switched between conducting doped and insulating neutral states, PXDOTs have attracted attention across academia and industry. Numerous fundamental aspects are addressed here in detail, ranging from the electrochemical synthesis of PXDOTs, a variety of in‐situ characterization techniques, the broad array of properties accessible, and morphological aspects. Finally, two electrochemically‐driven applications, specifically electrochromism and chemical sensors of PXDOTs are discussed.     

Mechanically Flexible Conductors for Stretchable and Wearable E‐Skin and E‐Textile Devices

Considerable progress in materials development and device integration for mechanically bendable and stretchable optoelectronics will broaden the application of “Internet‐of‐Things” concepts to a myriad of new applications. When addressing the needs associated with the human body, such as the detection of mechanical functions, monitoring of health parameters, and integration with human tissues, optoelectronic devices, interconnects/circuits enabling their functions, and the core passive components from which the whole system is built must sustain different degrees of mechanical stresses. Herein, the basic characteristics and performance of several of these devices are reported, particularly focusing on the conducting element constituting them. Among these devices, strain sensors of different types, energy storage elements, and power/energy storage and generators are included. Specifically, the advances during the past 3 years are reported, wherein mechanically flexible conducting elements are fabricated from (0D, 1D, and 2D) conducting nanomaterials from metals (e.g., Au nanoparticles, Ag flakes, Cu nanowires), carbon nanotubes/nanofibers, 2D conductors (e.g., graphene, MoS₂), metal oxides (e.g., Zn nanorods), and conducting polymers (e.g., poly(3,4‐ethylenedioxythiophene):poly(4‐styrene sulfonate), polyaniline) in combination with passive fibrotic and elastomeric materials enabling, after integration, the so‐called electronic skins and electronic textiles.     

An All‐Plastic Field‐Effect Nanofluidic Diode Gated by a Conducting Polymer Layer

The design of an all‐plastic field‐effect nanofluidic diode is proposed, which allows precise nanofluidic operations to be performed. The fabrication process involves the chemical synthesis of a conductive poly(3,4‐ethylenedioxythiophene) (PEDOT) layer over a previously fabricated solid‐state nanopore. The conducting layer acts as gate electrode by changing its electrochemical state upon the application of different voltages, ultimately changing the surface charge of the nanopore. A PEDOT‐based nanopore is able to discriminate the ionic species passing through it in a quantitative and qualitative manner, as PEDOT nanopores display three well‐defined voltage‐controlled transport regimes: cation‐rectifying, non‐rectifying, and anion rectifying regimes. This work illustrates the potential and versatility of PEDOT as a key enabler to achieve electrochemically addressable solid‐state nanopores. The synergism arising from the combination of highly functional conducting polymers and the remarkable physical characteristics of asymmetric nanopores is believed to offer a promising framework to explore new design concepts in nanofluidic devices.     

Functionalized Conducting Polymer Nano‐Networks from Controlled Oxidation Polymerization toward Cell Engineering

In this work we present a general approach for bulk synthesis of various functionalized conducting polymer nano‐networks. 3,4‐ethylenedioxythiophene (EDOT) dimers are used to initiate the chemical polymerization of functionalized EDOT in the solvent system with high polarity, which leads to better control of the oxidation polymerization. Under these reaction conditions, various functionalized EDOT monomers form polymeric nano‐network structures. We also evaluate the cell growth and cell viability on these conducting polymer nano‐networks. The nano‐networks provide highly biocompatible materials for PC12 cells and they show nice attachment on the surface. These properties of functionalized conducting polymer nano‐networks indicate a promising platform for cell engineering.     

Inside Front Cover: Conducting‐Polymer Nanotubes for Controlled Drug Release (Adv. Mater. 4/2006)

Martin and co‐workers report on p. 405 that nanotubes formed from the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT), as shown on the inside cover, can be used for the controlled release of anti‐inflammatory drugs. The fabrication process includes electrospinning of a biodegradable polymer, either poly(L ‐lactide) or poly(lactide‐co‐glycolide), into which the required drug is incorporated, followed by electrochemical deposition of the conducting polymer around the drug‐loaded electrospun nanofibers. Drug release from the nanotubes is achieved by external electrical stimulation of the nanotubes.     

Biomolecule‐Doped PEDOT with Three‐Dimensional Nanostructures as Efficient Catalyst for Oxygen Reduction Reaction

Metal macro‐cyclic compounds have drawn considerable attention as alternative catalysts for oxygen reduction reaction. However, the continuous pyrolysis process usually needed for improving the performance of these compounds require an elevated temperature and complicated procedures, thus leading to an unpredictable transformation of the chemical structures and limiting their applications. Herein, we develop a new insight to fabricating hemin‐doped poly (3,4‐ethylenedioxythiophene) (PEDOT) with controllable three‐dimensional nanostructures via a one‐step, tri‐phase, self‐assembled polymerization routine. We demonstrate that the hemin‐induced synergistic effect results in a very high 4‐electron oxygen reduction activity, a better stability, and free from methanol crossover effects even in a neutral phosphate buffer solution (PBS).     

Flexible,Stretchable, and Transparent Planar Microsupercapacitors Based on 3D Porous Laser‐Induced Graphene

The graphene with 3D porous network structure is directly laser‐induced on polyimide sheets at room temperature in ambient environment by an inexpensive and one‐step method, then transferred to silicon rubber substrate to obtain highly stretchable, transparent, and flexible electrode of the all‐solid‐state planar microsupercapacitors. The electrochemical capacitance properties of the graphene electrodes are further enhanced by nitrogen doping and with conductive poly(3,4‐ethylenedioxythiophene) coating. With excellent flexibility, stretchability, and capacitance properties, the planar microsupercapacitors present a great potential in fashionable and comfortable designs for wearable electronics.     

Ultrahigh‐Conductivity Polymer Hydrogels with Arbitrary Structures

A poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) hydrogel is prepared by thermal treatment of a commercial PEDOT:PSS (PH1000) suspension in 0.1 mol L^?1 sulfuric acid followed by partially removing its PSS component with concentrated sulfuric acid. This hydrogel has a low solid content of 4% (by weight) and an extremely high conductivity of 880 S m^?1. It can be fabricated into different shapes such as films, fibers, and columns with arbitrary sizes for practical applications. A highly conductive and mechanically strong porous fiber is prepared by drying PEDOT:PSS hydrogel fiber to fabricate a current‐collector‐free solid‐state flexible supercapacitor. This fiber supercapacitor delivers a volumetric capacitance as high as 202 F cm^?3 at 0.54 A cm^?3 with an extraordinary high‐rate performance. It also shows excellent electrochemical stability and high flexibility, promising for the application as wearable energy‐storage devices.     

Layer‐by‐Layer Hydrogen‐Bonded Polymer Films: From Fundamentals to Applications

Recent years have seen increasing interest in the construction of nanoscopically layered materials involving aqueous‐based sequential assembly of polymers on solid substrates. In the booming research area of layer‐by‐layer (LbL) assembly of oppositely charged polymers, self‐assembly driven by hydrogen bond formation emerges as a powerful technique. Hydrogen‐bonded (HB) LbL materials open new opportunities for LbL films, which are more difficult to produce than their electrostatically assembled counterparts. Specifically, the new properties associated with HB assembly include: 1) the ease of producing films responsive to environmental pH at mild pH values, 2) numerous possibilities for converting HB films into single‐ or two‐component ultrathin hydrogel materials, and 3) the inclusion of polymers with low glass transition temperatures (e.g., poly(ethylene oxide)) within ultrathin films. These properties can lead to new applications for HB LbL films, such as pH‐ and/or temperature‐responsive drug delivery systems, materials with tunable mechanical properties, release films dissolvable under physiological conditions, and proton‐exchange membranes for fuel cells. In this report, we discuss the recent developments in the synthesis of LbL materials based on HB assembly, the study of their structure–property relationships, and the prospective applications of HB LbL constructs in biotechnology and biomedicine.     

Light‐Emitting Polythiophenes

Polythiophenes are one of the most important classes of conjugated polymers, with a wide range of applications, such as conducting films, electrochromics, and field‐effect transistors, which have been the subject of a number of older and more recent reviews. Much less attention has been paid to the light‐emitting properties of this class of materials, although their unique properties present a number of opportunities unavailable from more popular polymeric light emitters such as polyfluorene or poly(p‐phenylene vinylene). This article reviews achievements to date in applications of thiophene‐based polymers and oligomers as electroluminescent materials. We demonstrate the basic principles of controlling the optical properties of polythiophenes through structural modifications and review the most important light‐emitting materials created from thiophene derivatives. Special attention is paid to consequences of structural variations on the performance of light‐emitting diodes fabricated with these materials.     

Stretchable Conductive Polymers and Composites Based on PEDOT and PEDOT:PSS

The conductive polymer poly(3,4‐ethylenedioxythiophene) (PEDOT), and especially its complex with poly(styrene sulfonate) (PEDOT:PSS), is perhaps the most well‐known example of an organic conductor. It is highly conductive, largely transmissive to light, processible in water, and highly flexible. Much recent work on this ubiquitous material has been devoted to increasing its deformability beyond flexibility—a characteristic possessed by any material that is sufficiently thin—toward stretchability, a characteristic that requires engineering of the structure at the molecular‐ or nanoscale. Stretchability is the enabling characteristic of a range of applications envisioned for PEDOT in energy and healthcare, such as wearable, implantable, and large‐area electronic devices. High degrees of mechanical deformability allow intimate contact with biological tissues and solution‐processable printing techniques (e.g., roll‐to‐roll printing). PEDOT:PSS, however, is only stretchable up to around 10%. Here, the strategies that have been reported to enhance the stretchability of conductive polymers and composites based on PEDOT and PEDOT:PSS are highlighted. These strategies include blending with plasticizers or polymers, deposition on elastomers, formation of fibers and gels, and the use of intrinsically stretchable scaffolds for the polymerization of PEDOT.     

Conjugated Polymer Actuators and Devices: Progress and Opportunities

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or “artificial muscles” for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.     

Highly Efficient (>10%) Flexible Organic Solar Cells on PEDOT‐Free and ITO‐Free Transparent Electrodes

A novel approach to fabricate flexible organic solar cells is proposed without indium tin oxide (ITO) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using junction‐free metal nanonetworks (NNs) as transparent electrodes. The metal NNs are monolithically etched using nanoscale shadow masks, and they exhibit excellent optoelectronic performance. Furthermore, the optoelectrical properties of the NNs can be controlled by both the initial metal layer thickness and NN density. Hence, with an extremely thin silver layer, the appropriate density control of the networks can lead to high transmittance and low sheet resistance. Such NNs can be utilized for thin‐film devices without planarization by conductive materials such as PEDOT:PSS. A highly efficient flexible organic solar cell with a power conversion efficiency (PCE) of 10.6% and high device yield (93.8%) is fabricated on PEDOT‐free and ITO‐free transparent electrodes. Furthermore, the flexible solar cell retains 94.3% of the initial PCE even after 3000 bending stress tests (strain: 3.13%).     

Optimal Reactivity and Improved Self‐Healing Capability of Structurally Dynamic Polymers Grafted on Janus Nanoparticles Governed by Chain Stiffness and Spatial Organization

Structurally dynamic polymers are recognized as a key potential to revolutionize technologies ranging from design of self‐healing materials to numerous biomedical applications. Despite intense research in this area, optimizing reactivity and thereby improving self‐healing ability at the most fundamental level pose urgent issue for wider applications of such emerging materials. Here, the authors report the first mechanistic investigation of the fundamental principle for the dependence of reactivity and self‐healing capabilities on the properties inherent to dynamic polymers by combining large‐scale computer simulation, theoretical analysis, and experimental discussion. The results allow to reveal how chain stiffness and spatial organization regulate reactivity of dynamic polymers grafted on Janus nanoparticles and mechanically mediated reaction in their reverse chemistry, and, particularly, identify that semiflexible dynamic polymers possess the optimal reactivity and self‐healing ability. The authors also develop an analytical model of blob theory of polymer chains to complement the simulation results and reveal essential scaling laws for optimal reactivity. The findings offer new insights into the physical mechanism in various systems involving reverse/dynamic chemistry. These studies highlight molecular engineering of polymer architecture and intrinsic property as a versatile strategy in control over the structural responses and functionalities of emerging materials with optimized self‐healing capabilities.