A synthetic chemical strategy aimed at altering the cross-linking density of the electropolymerized conjugated polymer polypyrrole has been devised and implemented. The actuation performance of the synthesized material was assessed using a new type of apparatus capable of making rapid, non-contact dynamic measurements. The affect of cross-linking on the actuation performance of polypyrroles, was investigated.

Stem cell function is regulated by intrinsic as well as microenvironmental factors, including chemical and mechanical signals. Conducting polymer-based cell culture substrates provide a powerful tool to control both chemical and physical stimuli sensed by stem cells. Here we show that polypyrrole (PPy), a commonly used conducting polymer, can be tailored to modulate survival and maintenance of rat fetal neural stem cells (NSCs). NSCs cultured on PPy substrates containing different counter ions, dodecylbenzenesulfonate (DBS), tosylate (TsO), perchlorate (ClO4) and chloride (Cl), showed a distinct correlation between PPy counter ion and cell viability. Specifically, NSC viability was high on PPy(DBS) but low on PPy containing TsO, ClO4 and Cl. On PPy(DBS), NSC proliferation and differentiation was comparable to standard NSC culture on tissue culture polystyrene. Electrical reduction of PPy(DBS) created a switch for neural stem cell viability, with widespread cell death upon polymer reduction. Coating the PPy(DBS) films with a gel layer composed of a basement membrane matrix efficiently prevented loss of cell viability upon polymer reduction. Here we have defined conditions for the biocompatibility of PPy substrates with NSC culture, critical for the development of devices based on conducting polymers interfacing with NSCs.

The dimensionality of charge transport in an organic electrochemical transistor depends on the degree of advancement of the electrochemical half-reaction at the organic semiconductor/electrolyte interface. A carbon nanotube (CNT) nanoporous gate electrode leads to bulk transport in the semiconductor, while a flat Au gate electrode allows for localizing of the electrochemical oxidation of the semiconducting polymer at the organic semiconductor/electrolyte interface.

Electrolyte-gated organic thin-film transistors (OTFTs) can offer a feasible platform for future flexible, large-area and low-cost electronic applications. These transistors can be divided into two groups on the basis of their operation mechanism: (i) field-effect transistors that switch fast but carry much less current than (ii) the electrochemical transistors which, on the contrary, switch slowly. An attractive approach would be to combine the benefits of the field-effect and the electrochemical transistors into one transistor that would both switch fast and carry high current densities. Here we report the development of a polyelectrolyte-gated OTFT based on conjugated polyelectrolytes, and we demonstrate that the OTFTs can be controllably operated either in the field-effect or the electrochemical regime. Moreover, we show that the extent of electrochemical doping can be restricted to a few monolayers of the conjugated polyelectrolyte film, which allows both high current densities and fast switching speeds at the same time. We propose an operation mechanism based on self-doping of the conjugated polyelectrolyte backbone by its ionic side groups.

Graphical Abstract

Let it grow: The conjugated polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was synthesized with heparin as the counterion to form a cell culture substrate. The surface of PEDOT:heparin in the neutral state associated biologically active growth factors (see picture). Electrochemical in situ oxidation of PEDOT during live cell culture decreased the bioavailability of the growth factor and created an exact onset of neural stem cell differentiation.

An electronic detachment technology based on thin films of a poly(3,4-ethylene-dioxythiophene) derivative is evaluated for controlled release of human epithelial cells. When applying a potential of 1 V, the redox-responsive polymer films detach and disintegrate and at the same time release cells cultured on top in the absence of any enzymatic treatment with excellent preservation of membrane proteins and cell viability.

The importance of mechanotransduction for physiological systems is becoming increasingly recognized. The effect of mechanical stimulation is well studied in organs and tissues, for instance by using flexible tissue culture substrates that can be stretched by external means. However, on the cellular and subcellular level, dedicated technology to apply appropriate mechanical stimuli is limited. Here we report an organic electronic microactuator chip for mechanical stimulation of single cells. These chips are manufactured on silicon wafers using traditional microfabrication and photolithography techniques. The active unit of the chip consists of the electroactive polymer polypyrrole that expands upon the application of a low potential. The fact that polypyrrole can be activated in physiological electrolytes makes it well suited as the active material in a microactuator chip for biomedical applications. Renal epithelial cells, which are responsive to mechanical stimuli and relevant from a physiological perspective, are cultured on top of the microactuator chip. The cells exhibit good adhesion and spread along the surface of the chip. After culturing, individual cells are mechanically stimulated by electrical addressing of the microactuator chip and the response to this stimulation is monitored as an increase in intracellular Ca(2+). This Ca(2+) response is caused by an autocrine ATP signalling pathway associated with mechanical stimulation of the cells. In conclusion, the present work demonstrates a microactuator chip based on an organic conjugated polymer, for mechanical stimulation of biological systems at the cellular and sub-cellular level.

Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 degrees C, the best commercially available inorganic semiconductors are bismuth telluride (Bi2Te3)-based alloys, which possess a figure of merit ZT close to one(1). Most of the recently discovered thermoelectric materials with ZT andgt; 2 exhibit one common property, namely their low lattice thermal conductivities(2,3). Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (lambda = D 0.37W m(-1) K-1) yields a ZT = 0.25 at room temperature that approaches the values required for efficient devices.

Background: Nanomedicine is a research area with potential to shape, direct, and change future medical treatments in a revolutionary manner over the next decades. While the common goal with other fields of biomedicine is to solve medical problems, this area embraces an increasing number of technology platforms as they become miniaturized. Organic electronics has over the past two decades developed into an exciting and thriving area of research. Scope of review: Today, the organic electronics field stands at the interface with biology. As the area of organic bioelectronics advances, it holds promise to make major contributions to nanomedicine. The progress made in this direction is the topic of this review. Major conclusions: We describe the inherent features of conducting polymers, and explain the usefulness of these materials as active scaffolds in cell biology and tissue engineering. We also explain how the combined ionic and electronic conductive nature of the polymers is used to precisely control the delivery of signal substances. This unique feature is key in novel devices for chemical communication with cells and tissues. General significance: This review highlights the results from the creative melting pot of interdisciplinary research in organic bioelectronics. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

We present a methodology to extract parameters for an electrolyte-gated organic field effect transistor DC model. The model is based on charge drift/diffusion transport under electric field and covers all regimes. Voltage dependent capacitance, mobility, contact resistance and threshold voltage shift are taken into account in this model. The feature parameters in the model are simply extracted from the transfer or output characteristics of electrolyte-gated organic field effect transistors. The extracted parameters are verified by good agreements between experimental and simulated results.

Presently, we contemplate the merger of paper and electronics in different forms. There is a great desire to further explore this twinning of the information displaying features of printed papers and electronic inks. Here, we report a full-color paperboard display technology comprised of thermochromic and static inks combined with a patterned heater foil. Black and full-color thermochromic ink dots were screen-printed adjacent to, and on top of, static ink dots using a zero-angle mesh and template pattern orientation. As the heater is turned on and off, the display alter its content in between two predefined four-color pictures.

In this work, polyanionic and polycationic electrolytes are used as gate insulators in p- and n-channel thin-film transistors, respectively. These material combinations are motivated by that the mobile ions in the electrolytes will be attracted to the oppositely charged gate electrodes when the transistors are operated in the accumulation mode. The electronic charges in the semiconductor channels will thus be balanced by the polyions, which are effectively immobile and cannot penetrate into the semiconductor bulk and cause electrochemical doping.

Polypyrrole is electromechanically active and actuates due to ion and solvent movements during redox switching, causing both reversible and irreversible swelling. The swelling of polymers is known to be highly dependent on the degree of cross-linking. Despite this, little research has been undertaken to date on the affect that cross-linking has on the actuation of conjugated polymers. It is likely that there exists a level of cross-linking, that results in optimum actuation performance. An understanding of this relationship, would allow actuators to be designed that are capable of greater movement, operating speeds and force generation. We have implemented novel synthetic strategies aimed at altering the degree of cross-linking of electrosynthesised polypyrrole. The actuating performance of these materials has been assessed using new apparatus capable of making non-contact dynamic measurements. After highlighting a number of applications that use the anisotropic strain of PPy(DBS) e.g. the mechanostimulation of cells, we will describe our synthetic strategies, measurement setup and results.

Many biomolecules are charged and may therefore be transported with ionic currents. As a step toward addressable ionic delivery circuits, we report on the development of a npn ion bipolar junction transistor (npn-IBJT) as an active control element of anionic currents in general, and specifically, demonstrate actively modulated delivery of the neurotransmitter glutamic acid. The functional materials of this transistor are ion exchange layers and conjugated polymers. The npn-IBJT shows stable transistor characteristics over extensive time of operation and ion current switch times below 10 s. Our results promise complementary chemical circuits similar to the electronic equivalence, which has proven invaluable in conventional electronic applications.

Complementary circuits, processing digital signals, are a cornerstone of modern electronics. Such circuits require both p-and n-type transistors. Polyelectrolytes are used as gate insulators in organic thin film transistors (OTFTs) to establish an electric double layer capacitor upon gate bias that allows low operational voltages (andlt;1 V). However, stable and low-voltage operating n-channel organic transistors have proven difficult to construct. Here, we report ultra-low voltage n-channel organic polymer-based transistors that are stable in ambient atmosphere. Our n-type OTFTs exhibit on/off ratios around 10(3) for an applied drain potential as low as 0.1 V. Since small ions are known to promote electrochemical reactions within the semiconductors channel bulk and typically slow down the transistor, we use a solid polycationic gate insulator that suppresses penetration of anions into the n-channel semiconductor. As a result, our n-channel OTFTs switch on in under 5 ms and off in less than 1 ms.

High-dielectric-constant insulators, organic monolayers, and electrolytes have been successfully used to generate organic field-effect transistors operating at low voltages. Here, we report on a device gated with pure water. By replacing the gate dielectric by a simple water droplet, we produce a transistor that entirely operates in the field-effect mode of operation at voltages lower than 1V. This result creates opportunities for sensor applications using water-gated devices as transducing medium.

In the emerging technology field of printed electronics, circuits are envisioned to be powered with printed energy sources, such as printed batteries and printed supercapacitors (SCs). For manufacturing and reliability issues, solid electrolytes are preferred instead of liquid electrolytes. Here, a solid-state, polyanionic proton conducting electrolyte, poly(styrenesulfonic acid) (PSS:H), is demonstrated for the first time as an effective ion conducting electrolyte medium in SCs with electrodes based on carbon nanotube (CNT) networks. The effect of the ionic conductivity in the PSS:H film of those SCs is studied at different levels of relative humidity (RH) with impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. High capacitance values (85 F g(-1) at 80% RH) are obtained for these SCs due to the extremely high effective electrode area of the CNTs and the enhanced ionic conductivity of the PSS: H film at increasing RH level. The charging dynamics are primarily limited by the ionic conductivity of the electrolyte rather than a poor contact between the electrolyte and the CNT electrodes. The use of polyelectrolytes in SCs provides high mechanical strength and flexibility, while maintaining a high capacitance value, enabling a new generation of printable solid-state charge storage devices.

The field of organic electronics promises exciting new technologies based on inexpensive and mechanically flexible electronic devices. It has progressed over the past three decades to the point of commercial viability and is projected to grow to a 30 billion dollar market by the year 2015. Exploring new applications and device architectures, this book sets the tone for that exploration, gathering a community of experts in this area who are focused on the use of ionic functions to define the principle of operation in polymer devices. The contributors detail relevant technologies based on organic electronics, including polymer electrochromic devices and light-emitting electrochemical cells.

While polymer light-emitting diodes are currently finding commercial applications in displays and lighting, the development of low bandgap polymers emitting in the infrared has received much less attention in spite of potential applications for instance in the field of communication technologies. We report here a light emission at 1 eV from a low bandgap polymer made of an alternation of dialkoxy-phenylene units and a low bandgap monomer composed of an electron accepting 2-thia-1,3,5,8-tetraaza-cyclopenta[b]naphthalene group fenced with electron donating thiophene units. The electronic structure of the polymer chains has been characterized at a quantum-chemical level to shed light into the experimental results.

Dynamic control of chemical microenvironments is essential for continued development in numerous fields of life sciences. Such control could be achieved with active chemical circuits for delivery of ions and biomolecules. As the basis for such circuitry, we report a solid-state ion bipolar junction transistor (IBJT) based on conducting polymers and thin films of anion- and cation-selective membranes. The IBJT is the ionic analogue to the conventional semiconductor BJT and is manufactured using standard microfabrication techniques. Transistor characteristics along with a model describing the principle of operation, in which an anionic base current amplifies a cationic collector current, are presented. By employing the IBJT as a bioelectronic circuit element for delivery of the neurotransmitter acetylcholine, its efficacy in modulating neuronal cell signaling is demonstrated.

A polyanionic electrolyte is used as gate insulator in top-gate p-channel polymer thin-film transistors. The high capacitance of the polyelectrolyte film allows the transistors and integrated circuits to operate below 1.5 V. Seven-stage ring oscillators that operate at supply voltages down to 0.9 V and exhibit signal propagation delays as low as 300 µs per stage are reported.

The effect of mechanical forces on cells is a relatively unexplored area of cell biology. However, mechanical forces play an important role in cell proliferation and function. For instance in muscle contraction, bone growth, and morphogenesis. There is only a limited selection of tools to study this on a single cell level and/or follow the events in real time. Here, we present a new tool in order to mechanically stimulate cells both on a single cell level as well as parts of functional monolayers. The device is designed so that it can be used together with different imaging techniques used in cell biology. The device comprises polypyrrole microactuators. These microactuators can be operated in salt solutions including cell culture media, which makes them well suited for cell biology applications. In addition, polypyrrole is known to be biocompatible, making them a good choice for this device. We will present a device with which we can stretch cells and show the cellular response to this mechanical stimulation. Since the dawn of eukaryotic cells many parallel molecular mechanisms that respond to mechanical stimuli have evolved. This technology allows us to begin the investigation of these mechanisms on a single cell level.

The field of organic electronics promises exciting new technologies based on inexpensive and mechanically flexible electronic devices. It has progressed over the past three decades to the point of commercial viability and is projected to grow to a 30 billion dollar market by the year 2015. Exploring new applications and device architectures, this book sets the tone for that exploration, gathering a community of experts in this area who are focused on the use of ionic functions to define the principle of operation in polymer devices. The contributors detail relevant technologies based on organic electronics, including polymer electrochromic devices and light-emitting electrochemical cells.

Attempts to interface human-made systems with neural systems are commonly based on direct electrical stimulation or exogenous drug delivery. Few techniques have attempted to mimic neurons' own combination of electronic and chemical signaling with endogenous substances. We demonstrate below the organic electronic ion pump (OEIP), a technology which aims to accomplish just that: electronically controlled delivery of ions, neurotransmitters and other bio-substances. Based on electrophoretic migration through an organic electronic system, delivery is diffusive and non-convective, that is, without fluid flow. Various experiments involving OEIP technology are reviewed, culminating in its use, in an encapsulated form, to modulate sensory function in a living animal. As a first step towards an “artificial neuron”, this technology has significant potential for both neural system interfacing and in the treatment of various neurological disorders.

An electrochemical circuit to record time-temperature history has been realized by using the propagation of over-oxidation fronts in stripes of poly(3,4-ethylenedioxythiopehene) blended with poly(styrenesulfonate) (PEDOT:PSS). The over-oxidation front propagation has been characterized and related to the phase change of polyethylene glycol (PEG) electrolytes. The electrolytes were chosen to have a phase transition in the temperature interval to be monitored, resulting in large conductivity variations and thereby an easily interpreted output. A demonstrator has been fabricated and shown to detect a temperature increase and a following temperature decrease. This very simple device is cheap to produce and could be used to monitor the temperature of packages.

Low-cost passive wireless electronic sensor labels glued onto packages are highly desirable since they enable monitoring of the status of the packages for instance along the logistic chain or while stored at a shelf. Such additional sensing feature would be of great value for many producers and vendors, active in e.g. the food or construction industries. Here, we explore a novel concept for wireless sensing and readout, in which the humidity sensitive ionic motion in a polyelectrolyte membrane is directly translated into a shift of the resonance frequency of a resonance circuit. Thanks to its simplicity, the wireless sensor device itself can be manufactured entirely using common printing techniques and can be integrated into a low-cost passive electronic sensor label.

Hybrid inorganic-organic semiconductor heterojunctions are nowadays scrutinized for optoelectronic devices, such as solar cells and light emitting diodes. Here, ZnO nanowires/polyfluorene heterojunctions have been entirely fabricated from solution by wet chemistry and low temperature processes. The transparent plastic electrode PEDOT injects holes in the polyfluorene, while the electrons are injected via the ZnO-Au contact, thus avoiding the use of air sensitive low work function metals. The hybrid inorganic-organic light emitting diode emits almost white light. Because of its solution processability, stable cathode, low cost and low temperature process, the ZnO/polymer heterojunction devices are promising for large area lightening applications.

Abnormal protein aggregates, so called amyloid fibrils, are mainly known as pathological hallmarks of a wide range of diseases, but in addition these robust well-ordered self-assembled natural nanostructures can also be utilized for creating distinct nanomaterials for bioelectronic devices. However, current methods for producing amyloid fibrils in vitro offer no spatial control. Herein, we demonstrate a new way to produce and spatially control the assembly of amyloid-like structures using an organic electronic ion pump (OEIP) to pump distinct cations to a reservoir containing a negatively charged polypeptide. The morphology and kinetics of the created proteinaceous nanomaterials depends on the ion and current used, which we leveraged to create layers incorporating different conjugated thiophene derivatives, one fluorescent (p-FTAA) and one conducting (PEDOT-S). We anticipate that this new application for the OEIP will be useful for both biological studies of amyloid assembly and fibrillogenesis as well as for creating new bioelectronic nanomaterials and devices.

Short-channel, vertically structured organic transistors with a polyelectrolyte as gate insulator are demonstrated. The devices are fabricated using low-resolution, self-aligned, and mask-free photolithography. Owing to the use of a polyelectrolyte, our vertical electrolyte-gated organic field-effect transistors (VEGOFETs), with channel lengths of 2.2 and 0.7 μm, operate at voltages below one volt. The VEGOFETs show clear saturation and switch on and off in 200 μs. A vertical geometry to achieve short-transistor channels and the use of an electrolyte makes these transistors promising candidates for printed logics and drivers with low operating voltage.

Complex patterning of the extracellular matrix, cells, and tissues under in situ electronic control is the aim of the technique presented here. The distribution of epithelial cells along the channel of an organic electrochemical transistor is shown to be actively controlled by the gate and drain voltages, as electrochemical gradients are formed along the transistor channel when the device is biased.

Current technologies for cell stimulation suffer from a variety of drawbacks. Indeed, precise, localized, and minimally disruptive machine-to-cell interfacing is difficult to achieve. Here we present the organic electronic ion pump (OEIP), a polymer-based delivery system exhibiting high spatial, temporal, and dosage precision. Based on electrophoretic transport of positively charged species, the OEIP can deliver - with high precision - an array of biologically relevant substances without fluid flow, thus eliminating convective disturbance of the target system's environment. We discuss our results to date, including oscillatory delivery profiles and stimulation of neuronal cells in vitro, as well as our ongoing work.

We report on a variety of electroactive surfaces for the control of in vitro cell adhesion, proliferation, and stimulation. Planar cell culture substrates have been coated with the conducting polymer PEDOT and by switching the redox state, adhesion and proliferation of MDCK epithelial cells was controlled as well as stem cell seeding density. Electronically active 3D-scaffolds based on electrospun PET nano-fibers coated with PEDOT have been used as a substrate to culture SH-SY5Y neuroblastoma cells and to induce Ca²⁺ signaling. Finally, we report on micromechanical stimulation of cells using an electroactive topography surface based on micropattened polypyrrole.

Conducting polymers are soft, flexible materials, exhibiting material properties that can be reversibly changed by electrochemically altering the redox state. Surface chemistry is an important determinant for the molecular events of cell adhesion. Therefore, we analyzed whether the redox state of the conducting polymer PEDOT:Tosylate can be used to control epithelial cell adhesion and proliferation. A functionalized cell culture dish comprising two adjacent electrode surfaces was developed. Upon electronic addressing, reduced and oxidized surfaces are created within the same device. Simultaneous analysis of how a homogenous epithelial MDCK cell population responded to the electrodes revealed distinct surface-specific differences. Presentation of functional fibronectin on the reduced electrode promoted focal adhesion formation, involving α_vβ₃ integrin, cell proliferation, and ensuing formation of polarized monolayers. In contrast, the oxidized surface harbored only few cells with deranged morphology showing no indication of proliferation. This stems from the altered fibronectin conformation, induced by the different surface chemistry of the PEDOT:Tosylate electrode in the oxidized state. Our results demonstrate a novel use of PEDOT:Tosylate as a cell-hosting material in multiple-electrode systems, where cell adhesion and proliferation can be controlled by electrochemical modulation of surface properties.

The latest in organic electronics-based sensing and biotechnology Develop high-performance, field-deployable organic semiconductor-based biological, chemical, and physical sensor arrays using the comprehensive information contained in this definitive volume. Organic Electronics in Sensors and Biotechnology presents state-of-the-art technology alongside real-world applications and ongoing R & D. Learn about light, temperature, and pressure monitors, integrated flexible pyroelectric sensors, sensing of organic and inorganic compounds, and design of compact photoluminescent sensors. You will also get full details on organic lasers, organic electronics in memory elements, disease and pathogen detection, and conjugated polymers for advancing cellular biology. Monitor organic and inorganic compounds with OFETs Characterize organic materials using impedance spectroscopy Work with organic LEDs, photodetectors, and photovoltaic cells Form flexible pyroelectric sensors integrated with OFETs Build PL-based chemical and biological sensing modules and arrays Design organic semiconductor lasers and memory elements Use luminescent conjugated polymers as optical biosensors Deploy polymer-based switches and ion pumps at the microfluidic level

Monolithic integration of an electrolyte-gated organic field-effect transistor (OFET) and an organic electrochromic pixel is reported. Thanks to its versatility, the polyanionic proton conductor poly(styrenesulfonic acid) (PSSH) can serve both as the gate “insulator” in OFETs and as the electrolyte in electrochromic display pixels. Employing identical materials in both the display cells and in the driver transistors is a necessary prerequisite to achieve robust displays possible to manufacture on flexible carriers using printing tools. Smart pixels combining depletion mode electrochemical transistors and electrochromic displays have been reported in the past. Here, an enhancement mode OFET as the driver enables relatively shorter updating times and much simpler addressing and updating schemes.

Electrolyte-gate organic field-effect transistors embedded at the junction of textile microfibers are demonstrated. The fiber transistor operates below I V and delivers large current densities. The transience of the organic thin-film transistors current and the impedance spectroscopy measurements reveal that the channel is formed in two steps.

PEDOT:PSS-based electrochromic displays have been explored for manufacture on flexible paper substrates in roll-to-roll printing presses at high volumes and low costs. Here, we report the improvement of the optical contrast of such devices by adding an extra layer of a dihexyl-substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx2) to complement the optical absorption spectrum of PEDOT: PSS. The oxidized state of PProDOT-Hx2 is highly transparent and is an intense magenta color while in the reduced state. By adding a layer of PProDOT-Hx2 directly on top of PEDOT: PSS, we were able to improve the optical contrast by nearly a factor of two. In this report, we present optical and electrochemical data of PProDOT-Hx2/PEDOT: PSS-based electrochromic paper displays and compare their performance with PEDOT: PSS-only equivalents.

Electrolyte-gated organic field-effect transistors (OFETs) hold promise for robust printed electronics operating at low voltages. The polarization mechanism of thin solid electrolyte films, the gate insulator in such OFETs, is still unclear and appears to limit the transient current characteristics of the transistors. Here, the polarization response of a thin proton membrane, a poly(styrenesulfonic acid) film, is controlled by varying the relative humidity. The formation of the conducting transistor channel follows the polarization of the polyelectrolyte, such that the drain transient current characteristics versus the time are rationalized by three different polarization mechanisms: the dipolar relaxation at high frequencies, the ionic relaxation (migration) at intermediate frequencies, and the electric double-layer formation at the polyelectrolyte interfaces at low frequencies. The electric double layers of polyelectrolyte capacitors are formed in 1 µs at humid conditions and an effective capacitance per area of 10 µF cm^-2 is obtained at 1 MHz, thus suggesting that this class of OFETs might operate at up to 1 MHz at 1 V.

Electronically conductive and electrochemically active 3D-scaffolds based on electrospun poly(ethylene terephthalate) (PET) nano-fibers are reported. Vapour phase polymerization was employed to achieve an uniform and conformal coating of poly(3,4-ethylenedioxythiophene) doped with tosylate (PEDOT:tosylate) on the nano-fibers. The PEDOT coatings had a large impact on the wettability, turning the hydrophobic PET fibers super-hydrophilic. SH-SY5Y neuroblastoma cells were grown on the PEDOT coated fibers. The SH-SY5Y cells adhered well and showed healthy morphology. These electrically active scaffolds were used to induce Ca2+ signalling in SH-SY5Y neuroblastoma cells. PEDOT:tosylate coated nano-fibers represent a class of 3D host environments that combines excellent adhesion and proliferation for neuronal cells with the possibility to regulate their signalling.

Significant advances have been made in the understanding of the pathophysiology, molecular targets and therapies for the treatment of a variety of nervous-system disorders. Particular therapies involve electrical sensing and stimulation of neural activity, and significant effort has therefore been devoted to the refinement of neural electrodes. However, direct electrical interfacing suffers from some inherent problems, such as the inability to discriminate amongst cell types. Thus, there is a need for novel devices to specifically interface nerve cells. Here, we demonstrate an organic electronic device capable of precisely delivering neurotransmitters in vitro and in vivo. In converting electronic addressing into delivery of neurotransmitters, the device mimics the nerve synapse. Using the peripheral auditory system, we show that out of a diverse population of cells, the device can selectively stimulate nerve cells responding to a specific neurotransmitter. This is achieved by precise electronic control of electrophoretic migration through a polymer film. This mechanism provides several sought-after features for regulation of cell signalling: exact dosage determination through electrochemical relationships, minimally disruptive delivery due to lack of fluid flow, and on-off switching. This technology has great potential as a therapeutic platform and could help accelerate the development of therapeutic strategies for nervous-system disorders.

When nerve cells are exposed to chemical stimuli, an electric potential is triggered. Migrating along the axon, the signal reaches the synapse, where it is converted into the release of neurotransmitters. This mode of cell-to-cell communication inspired us to develop an artificial nerve cell based on conducting polymers. Its use for precise stimulation of nerve cells in vivo illustrates its potential as an implantable device for automated correction of malfunctioning signaling pathways in pathophysiological conditions.

Organic semiconductor blends are commonly used in organic based (opto-)electronic devices. They are composed of two types of (macro-) molecules, referredto as the guest and host. To achieve optimum device operation, the chemicalnature, electronic structure, molecular order and the relative concentration of theguests and host are crucial. Here, we present simulation results of the currentdensity versus the voltage (J-V) behavior of a two-terminal device based on avariable-range hopping model in which the electronic states of the guest and hostare represented by two Gaussian distributions. The J-V behavior is investigatedfor various energetic mismatches between guest and host states, widths of thedistribution as well as the guest concentration. Finally, a simple tool enablingeasy prediction of the J-V behavior of organic host-guest diodes is derived.

A miniaturized organic electronic ion pump (OEIP) based on conjugated polymers is developed for delivery of positively charged biomolecules. Characterization shows that applied voltage can precisely modulate the delivery rate of the neurotransmitter acetylcholine. The capability of the device is demonstrated by convection-free, spatiotemporally resolved delivery of acetylcholine via a 10 mu m channel for dynamic stimulation of single neuronal cells.

Diarylethene molecules are photochromics (PCs) currently investigated for use in optical write/electrical read memory applications. The impact of the photoisomerization of PCs on the device behavior is analyzed with charge transport models. These results indicate that good electrical current switching can be achieved in a device when the PCs are combined with an organic semiconductor (in multilayered structures or blends). The frontier energy levels and dipole moment of a series of diarylethene compounds have been calculated using density functional theory. A good agreement is found between the calculated electronic structure and the measured ultraviolet photoelectron spectra. Shirts in the frontier energy levels and dipole moment are generated through two different approaches for chemical modification: (i) by changing the chemical nature of the aryl rings or (ii) by adding substituents on the ethylene, bridge. The frontier energy levels can be tuned by more than 2 eV via such chemical modifications. We find that, for this family of photochromic compounds, the photoinduced current switch effect in diodes is mainly due to the modulation in the frontier energy levels rather than the changes in the amplitude of the dipole moment.

Using organic electrochemical transistors as sensors, the sample-receptor reaction often induces moderate changes only in the drain current dynamics as the gate voltage level is switched. Here, we report an electrochemical sensor circuit including electrochemical transistors based on poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate that puts out a static sensor response signal. The circuit includes a sample and a reference transistor that are both driven in the resistive mode at 0.1 V. Measurements were performed on aqueous salt electrolytes ranging from 100 to 500 mM concentrations. The signal-ON sensor circuit provides a tenfold increase in the sensitivity as compared to single transistor sensors.

Adhesion is an essential parameter for stem cells. It regulates the overall cell density along the carrying surface, which further dictates the differentiation scheme of stem cells toward a more matured and specified population as well as tissue. Electronic control of the seeding density of neural stem cells (c17.2) is here reported. Thin electrode films of poly(3,4-ethylenedioxythiophene) (PEDOT):Tosylate were manufactured along the floor of cell growth dishes. As the oxidation state of the conjugated polymer electrodes was controlled, the seeding density could be varied by a factor of 2. Along the oxidized PEDOT:Tosylate-electrodes, a relatively lower density of, and less tightly bonded, human serum albumin (HSA) was observed as compared to reduced electrodes. We found that this favors adhesion of the specific stem cells studied. Surface analysis experiments, such as photoelectron spectroscopy, and water contact angle measurements, were carried out to investigate the mechanisms responsible for the electronic control of the seeding density of the c17.2 neural stem cells. Further, our findings may provide an opening for electronic control of stem cell differentiation.

A polyelectrolyte is used as gate insulator material in organic field-effect transistors with self-aligned inkjet printed sub–micrometer channels. The small separation of the charges in the electric double layer at the electrolyte-semiconductor interface, which builds up in tens of microseconds, provides a very high transverse electric field in the channel that effectively suppresses short-channel effects at low applied gate voltages.

 Microstructured polymer surfaces, including conducting and insulating polymers, have been prepared to achieve electrochemical control of the surface energy and topography. The reported surface switches include pillar- and mesh-like surface patterns of polypyrrole (PPy), poly(3,4-ethylene-dioxythiophene) (PEDOT), and photoresists. The structures have been evaluated by contact angle measurements and optical and scanning electron microscopy to determine the surfaces characteristics. These microstructured polymer surface switches can be electrochemically modified from dewetting to wetting conditions, with a maximum associated change of the water contact angle from 129° to 44°. This contact angle switching was observed for samples in which dynamic control of the surface topography and surface tension was coupled. Control of topography was achieved with a dynamic height-switching range of more than 3 ìm. In addition, dynamic control of anisotropic wetting is reported. Our experiments were carried out under conditions that are suitable for a biointerface, implying potential application in biotechnology and cell science. In particular, switching of the energy, chemistry, and topography of the surface, along with their associated orientation, are interesting features for dynamic (electronic) control of the seeding and proliferation for living cells. The technology reported promises for electronically controlled cell-growth within Petri dishes, well plates, and other cell-hosting tools. 

Polyelectrolytes are promising materials as gate dielectrics in organic field-effect transistors (OFETs). Upon gate bias, their polarization induces an ionic charging current, which generates a large double layer capacitor (10-500 µF cm^-2) at the semiconductor/electrolyte interface. The resulting transistor operates at low voltages (<1 V) and its conducting channel is formed in 50 µs. The effect of ionic currents on the performance of the OFETs is investigated by varying the relative humidity of the device ambience. Within defined humidity levels and potential values, the water electrolysis is negligible and the OFETs performances are optimum.