Decoupling Conductivity, Heterogeneous Electron Transfer Rate, and Diffusion in Organic Molecular Electrocatalysis: Oxygen Reduction Reaction on Poly(3,4-ethylenedioxythiophene).

The electrified production of hydrogen peroxide (HO) by oxygen reduction reaction (ORR) is attractive to increase the sustainability of chemical industry. Here the same chains of intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) are utilized, as ORR electrocatalyst, while varying polymeric primary dopants (PSS and Nafion) and the level of secondary doping with DMSO. These changes modulate various properties of the film, such as its microscale organization and electronic conductivity.

Exploring the Elastomer Influence on the Electromechanical Performance of Stretchable Conductors.

Stretchable electronics has received major attention in recent years due to the prospects of integrating electronics onto and into the human body. While many studies investigate how different conductive fillers perform in stretchable composites, the effect of different elastomers on composite performance, and the related fundamental understanding of what is causing the performance differences, is poorly understood. Here, we perform a systematic investigation of the elastomer influence on the electromechanical performance of gold nanowire-based stretchable conductors based on five chemically different elastomers of similar Young's modulus.

Stretchable and biodegradable plant-based redox-diffusion batteries.

The redox-diffusion (RD) battery concept introduces an environmentally friendly solution for stretchable batteries in autonomous wearable electronics. By utilising plant-based redox-active biomolecules and cellulose fibers for the electrode scaffold, separator membrane, and current collector, along with a biodegradable elastomer encapsulation, the battery design overcomes the reliance on unsustainable transition metal-based active materials and non-biodegradable elastomers used in existing stretchable batteries. Importantly, it addresses the drawback of limited attainable battery capacity, where increasing the active material loading often leads to thicker and stiffer electrodes with poor mechanical properties.

Stretchable Tissue-Like Gold Nanowire Composites with Long-Term Stability for Neural Interfaces.

Soft and stretchable nanocomposites can match the mechanical properties of neural tissue, thereby minimizing foreign body reactions to provide optimal stimulation and recording specificity. Soft materials for neural interfaces should simultaneously fulfill a wide range of requirements, including low Young's modulus (<<1 MPa), stretchability (≥30%), high conductivity (>> 1000 S cm), biocompatibility, and chronic stability (>> 1 year). Current nanocomposites do not fulfill the above requirements, in particular not the combination of softness and high conductivity.

Tuneable Anisotropic Plasmonics with Shape-Symmetric Conducting Polymer Nanoantennas.

A wide range of nanophotonic applications rely on polarization-dependent plasmonic resonances, which usually requires metallic nanostructures that have anisotropic shape. This work demonstrates polarization-dependent plasmonic resonances instead by breaking symmetry via material permittivity. The study shows that molecular alignment of a conducting polymer can lead to a material with polarization-dependent plasma frequency and corresponding in-plane hyperbolic permittivity region.

Soft Electromagnetic Vibrotactile Actuators with Integrated Vibration Amplitude Sensing.

Soft vibrotactile devices have the potential to expand the functionality of emerging electronic skin technologies. However, those devices often lack the necessary overall performance, sensing-actuation feedback and control, and mechanical compliance for seamless integration on the skin. Here, we present soft haptic electromagnetic actuators that consist of intrinsically stretchable conductors, pressure-sensitive conductive foams, and soft magnetic composites.

Flexible Organic Electronic Ion Pump Fabricated Using Inkjet Printing and Microfabrication for Precision In Vitro Delivery of Bupivacaine.

The organic electronic ion pump (OEIP) is an on-demand electrophoretic drug delivery device, that via electronic to ionic signal conversion enables drug delivery without additional pressure or volume changes. The fundamental component of OEIPs is their polyelectrolyte membranes which are shaped into ionic channels that conduct and deliver ionic drugs, with high spatiotemporal resolution. The patterning of these membranes is essential in OEIP devices and is typically achieved using laborious microprocessing techniques.

Flexible Organic Electronic Ion Pump for Flow-Free Phytohormone Delivery into Vasculature of Intact Plants.

Plant vasculature transports molecules that play a crucial role in plant signaling including systemic responses and acclimation to diverse environmental conditions. Targeted controlled delivery of molecules to the vascular tissue can be a biomimetic way to induce long distance responses, providing a new tool for the fundamental studies and engineering of stress-tolerant plants. Here, a flexible organic electronic ion pump, an electrophoretic delivery device, for controlled delivery of phytohormones directly in plant vascular tissue is developed.

Screen-Printed Corrosion-Resistant and Long-Term Stable Stretchable Electronics Based on AgAu Microflake Conductors.

High-throughput production methods such as screen printing can bring stretchable electronics out of the lab into the market. Most stretchable conductor inks for screen printing are based on silver nanoparticles or flakes due to their favorable performance-to-cost ratio, but silver is prone to tarnishing and corrosion, thereby limiting the stability of such conductors. Here, we report on a cost-efficient and scalable approach to resolve this issue by developing screen printable inks based on silver flakes chemically coated by a thin layer of gold.

Exploiting mixed conducting polymers in organic and bioelectronic devices.

Efficient transport of both ionic and electronic charges in conjugated polymers (CPs) has enabled a wide range of novel electrochemical devices spanning applications from energy storage to bioelectronic devices. In this Perspective, we provide an overview of the fundamental physical processes which underlie the operation of mixed conducting polymer (MCP) devices. While charge injection and transport have been studied extensively in both ionic and electronic conductors, translating these principles to mixed conducting systems proves challenging due to the complex relationships among the individual materials properties.

Organic Bioelectronics for Neuromodulation.

The nervous system poses a grand challenge for integration with modern electronics and the subsequent advances in neurobiology, neuroprosthetics, and therapy which would become possible upon such integration. Due to its extreme complexity, multifaceted signaling pathways, and ∼1 kHz operating frequency, modern complementary metal oxide semiconductor (CMOS) based electronics appear to be the only technology platform at hand for such integration. However, conventional CMOS-based electronics rely exclusively on electronic signaling and therefore require an additional technology platform to translate electronic signals into the language of neurobiology.

Stretchable gold nanowire-based cuff electrodes for low-voltage peripheral nerve stimulation.

. Electrical stimulation of the peripheral nervous system (PNS) can treat various diseases and disorders, including the healing process after nerve injury. A major challenge when designing electrodes for PNS stimulation is the mechanical mismatch between the nerve and the device, which can lead to non-conformal contact, tissue damage and inefficient stimulation due to current leakage.

Soft Electronics Based on Stretchable and Conductive Nanocomposites for Biomedical Applications.

Research on the field of implantable electronic devices that can be directly applied in the body with various functionalities is increasingly intensifying due to its great potential for various therapeutic applications. While conventional implantable electronics generally include rigid and hard conductive materials, their surrounding biological objects are soft and dynamic. The mechanical mismatch between implanted devices and biological environments induces damages in the body especially for long-term applications.

Opto-E-Dura: A Soft, Stretchable ECoG Array for Multimodal, Multiscale Neuroscience.

Soft, stretchable materials hold great promise for the fabrication of biomedical devices due to their capacity to integrate gracefully with and conform to biological tissues. Conformal devices are of particular interest in the development of brain interfaces where rigid structures can lead to tissue damage and loss of signal quality over the lifetime of the implant. Interfaces to study brain function and dysfunction increasingly require multimodal access in order to facilitate measurement of diverse physiological signals that span the disparate temporal and spatial scales of brain dynamics.

Elastic conducting polymer composites in thermoelectric modules.

The rapid growth of wearables has created a demand for lightweight, elastic and conformal energy harvesting and storage devices. The conducting polymer poly(3,4-ethylenedioxythiophene) has shown great promise for thermoelectric generators, however, the thick layers of pristine poly(3,4-ethylenedioxythiophene) required for effective energy harvesting are too hard and brittle for seamless integration into wearables. Poly(3,4-ethylenedioxythiophene)-elastomer composites have been developed to improve its mechanical properties, although so far without simultaneously achieving softness, high electrical conductivity, and stretchability.

The intrinsic volumetric capacitance of conducting polymers: pseudo-capacitors or double-layer supercapacitors?

The capacitance of conducting polymers represents one of the most important material parameters that in many cases determines the device and material performances. Despite a vast number of experimental studies, the theoretical understanding of the origin of the capacitance in conducting polymers remains unsatisfactory and appears even controversial. Here, we present a theoretical method, based on first principle capacitance calculations using density functional theory (DFT), and apply it to calculate the volumetric capacitance of two archetypical conducting polymers: poly(3,4-ethylene dioxythiophene) (PEDOT) and polypyrrole (PPy).

Implantable Organic Electronic Ion Pump Enables ABA Hormone Delivery for Control of Stomata in an Intact Tobacco Plant.

Electronic control of biological processes with bioelectronic devices holds promise for sophisticated regulation of physiology, for gaining fundamental understanding of biological systems, providing new therapeutic solutions, and digitally mediating adaptations of organisms to external factors. The organic electronic ion pump (OEIP) provides a unique means for electronically-controlled, flow-free delivery of ions, and biomolecules at cellular scale. Here, a miniaturized OEIP device based on glass capillary fibers (c-OEIP) is implanted in a biological organism.

Organic mixed ionic-electronic conductors.

Materials that efficiently transport and couple ionic and electronic charge are key to advancing a host of technological developments for next-generation bioelectronic, optoelectronic and energy storage devices. Here we highlight key progress in the design and study of organic mixed ionic-electronic conductors (OMIECs), a diverse family of soft synthetically tunable mixed conductors. Across applications, the same interrelated fundamental physical processes dictate OMIEC properties and determine device performance.

Layer-by-Layer Assembly of High-Performance Electroactive Composites Using a Multiple Charged Small Molecule.

Layer-by-layer (LbL) assembly is a versatile tool for fabricating multilayers with tailorable nanostructures. LbL, however, generally relies on polyelectrolytes, which are mostly insulating and induce large interlayer distances. We demonstrate a method in which we replace polyelectrolytes with the smallest unit capable of LbL self-assembly: a molecule with multiple positive charges, tris(3-aminopropyl)amine (TAPA), to fabricate LbL films with negatively charged single-walled carbon nanotubes (CNTs).

Thermoelectric materials and applications for energy harvesting power generation.

Thermoelectrics, in particular solid-state conversion of heat to electricity, is expected to be a key energy harvesting technology to power ubiquitous sensors and wearable devices in the future. A comprehensive review is given on the principles and advances in the development of thermoelectric materials suitable for energy harvesting power generation, ranging from organic and hybrid organic-inorganic to inorganic materials. Examples of design and applications are also presented.

Capillary-Fiber Based Electrophoretic Delivery Device.

Organic electronic ion pumps (OEIPs) are versatile tools for electrophoretic delivery of substances with high spatiotemporal resolution. To date, OEIPs and similar iontronic components have been fabricated using thin-film techniques and often rely on laborious, multistep photolithographic processes. OEIPs have been demonstrated in a variety of in vitro and in vivo settings for controlling biological systems, but the thin-film form factor and limited repertoire of polyelectrolyte materials and device fabrication techniques unnecessarily constrain the possibilities for miniaturization and extremely localized substance delivery, e.

Overcoming transport limitations in miniaturized electrophoretic delivery devices.

Organic electronic ion pumps (OEIPs) have been used for delivery of biological signaling compounds, at high spatiotemporal resolution, to a variety of biological targets. The miniaturization of this technology provides several advantages, ranging from better spatiotemporal control of delivery to reduced invasiveness for implanted OEIPs. One route to miniaturization is to develop OEIPs based on glass capillary fibers that are filled with a polyelectrolyte (cation exchange membrane, CEM).

Ion Electron-Coupled Functionality in Materials and Devices Based on Conjugated Polymers.

The coupling between charge accumulation in a conjugated polymer and the ionic charge compensation, provided from an electrolyte, defines the mode of operation in a vast array of different organic electrochemical devices. The most explored mixed organic ion-electron conductor, serving as the active electrode in these devices, is poly(3,4-ethyelenedioxythiophene) doped with polystyrelensulfonate (PEDOT:PSS). In this progress report, scientists of the Laboratory of Organic Electronics at Linköping University review some of the achievements derived over the last two decades in the field of organic electrochemical devices, in particular including PEDOT:PSS as the active material.