AlGaN/GaN high electron mobility transistors (HEMTs) are promising candidates for the application as transducers in biosensors. The chemical stability and biocompatibility [1] of GaN surfaces as well as their high pH-sensitivity [2] serve as the basis for this application. By covalent immobilization of enzymes on the gate area of an AlGaN/GaN HEMT one obtains an enzyme-modified field-effect transistor with the type of enzyme defining the specificity of the biosensor. Essential to this concept is the formation of an acid or a base as a product of the enzymatic reaction. The pH-change is then detected by the AlGaN/GaN HEMT in terms of a change in the gate-source voltage ΔU_GS at constant channel current, giving rise to the sensor signal. The enzyme used in the experiments presented here is acetylcholinesterase (AChE) which produces acetic acid during its enzymatic reaction by decomposing the neurotransmitter acetylcholine (ACh). Thereby, the preparation of such an acetylcholinesterase-modified field-effect transistor (AcFET) is accomplished via a wet chemical process [3, 4].
Here, the characteristics of AcFETs were analyzed by measuring ΔU_GS in dependence of the concentration of administered acetylthiocholine iodide, an ACh analogue, and evaluated applying a kinetic model [5] that yields microscopic parameters representing both the enzymatic activity (by the Michaelis constant K_M) and the transistor/enzyme/electrolyte system (by the normalized exchange rate constants across the respective interfaces).
The utilization of AcFETs allows for monitoring of the release of the neurotransmitter ACh and, hence, the activity of neurons. This is shown here on the example of myenteric neurons from 5-8 days old Wistar rats, cultured on the gate area of the AcFETs, with the release of ACh induced by a potassium chloride stimulus. The recorded AcFET signal due to the chemical stimulus is related to the enzymatic activity of the covalently immobilized AChE.
Concluding, on the one hand our results show that AcFETs based on AlGaN/GaN HEMT structures provide a suitable platform not only for the realization of a specific biosensor but also for the analysis of the functionality of immobilized AChE. On the other hand we have been able to monitor the activity of myenteric neurons non-invasively and thus converting a biological into an electrical signal.
[1] G. Steinhoff et al., Adv Funct Mater 13 (2003), 841
[2] G. Steinhoff et al., Appl Phys Lett 83 (2003), 177
[3] B. Baur et al., Appl Phys Lett 87 (2005), 263901-1
[4] K. Gabrovska et al., Int J Biol Macromol 43 (2008), 339
[5] S. Glab et al., Analyst 116 (1991), 453

Combined systems of semiconducting polymers and aqueous electrolytes are emerging as the new frontier of organic electronics, with many promising applications in biology, neuroscience and medicine. A detailed characterization of polymer/water interfaces is thus urgently needed. In particular, the combined effect of contact with electrolytes and visible illumination should be taken into account, since many applications rely on exposure to light, or are meant to work in ambient room light conditions.
In this work, we first extensively characterize the chemical-physical processes occurring in thin films of poly(3-hexylthiophene) exposed to water saline solutions and visible light. Through combination of different spectroscopic techniques, we demonstrate that prolonged contact with saline solutions does not add further degree to photo-activated doping processes of the polymer; instead, it turns out that the reduced number of oxygen molecules present in water, compared to open air, acts as a limiting factor, thus fully validating the use of semiconducting polymers in contact with electrolytes.
In addition, we demonstrate that the recently demonstrated technique of cell stimulation by polymer photo-excitation (CSP) represent a versatile platform for full-optical control of cell excitation/inhibition. We report examples of functional interfaces between several combinations of conjugated polymers and different cell cultures (HeK cells, astrocytes, neuronal networks). A detailed model of the mechanisms occurring at the polymer/electrolyte interface and leading to cell photoexcitation, based on electrical and optical measurements, will be finally presented and critically discussed

A visible trend over the past few years involves the application of conducting polymer devices to the interface with biology, with applications both in sensing and in actuation. Examples include biosensors, artificial muscles, and neural interface devices. The latter are of particular interest, as conducting polymers offer several distinct advantages compared to incumbent technologies, including mechanical flexibility, enhanced biocompatibility, better signal-to-noise ratio and capability for drug delivery. As such, they promise to yield new tools for neuroscience and enhance our understanding on how the brain works. After a brief introduction, I will present a few examples of electrodes and transistors for applications ranging from recording brain activity inside the skull to cutaneous recordings of muscle movement. In vivo performance, electrical characteristics and properties such as mechanical flexibility and biocompatibility will be discussed.

The miniaturization of bioelectronic intracellular probes opens up opportunities to study functional structures inaccessible by existing methods and to interrogate biological systems with minimal invasiveness. Here, we report the design, fabrication and demonstration of the intracellular bioelectronic probes with size down to sub-10-nm regime based on a nanowire-nanotube heterostructure, in which nanowire FET detectors are synthetically-integrated with the nanotube cellular probes. Water-gate measurements together with numerical simulations show that devices with probes sizes as small as 5 nm, which approaches the size of a single ion channel, have sufficient time response to resolve fast electrical signals in live cells. The use of phospholipid modification enabled spontaneous penetration of the cell membrane by the nanotube probe, and allowed full-amplitude, stable recording of intracellular action potentials by these ultra-small bioelectronic probes. Furthermore, simultaneous multi-site recording from both single cells and cell networks, and the recording of low frequency transmembrane potential demonstrated the capability, robustness and reliability of these ultra-small bioelectronic probes for intracellular interrogation and their potential for neural and cardiac activity mapping.

Debilitating neurological disorders such as Parkinson&’s disease and essential tremor are often treated via electrical stimulation using implantable devices. However, such procedures are highly mechanically invasive as well as not specific to cell type. Conversion of alternating magnetic fields in the radiofrequency range into heat via hysteretic power loss in superparamagnetic nanoantennas has been used to remotely control gene transcription in vivo and action potential firing in vitro. This actuation of TRPV1, a heat-sensitive calcium ion channel, with magnetothermal conversion may lead to minimally-invasive deep brain stimulation therapies. However, the timescale required - tens of seconds - suggests that further optimization to this magnetothermal approach is needed to shorten the actuation time to biologically relevant timescales.
Recently, we have applied a dynamic hysteretic model to optimize the magnetic nanomaterials properties, which allowed us to achieve record heat dissipation rates in magnetic nanoparticles (MNPs) at physiologically safe driving conditions. We find that iron oxide nanoparticles ~22 nm in diameter can reach temperature changes needed to trigger TRPV1 an order of magnitude faster than what was previously achieved at field frequencies and amplitudes relevant to magnetic hyperthermia. By sensitizing neurons to heat using a viral delivery system for TRPV1 DNA, we demonstrate how the heat dissipative abilities of our MNPs can be harnessed for minimally invasive deep brain stimulation therapies in vivo. Such an approach has implications towards remote control of biological functions at a single-cell level.

Mechanical cues affect cell behavior. In vitro, neurons and supporting cells show distinct response to substrate stiffness and topography. In vivo, and in particular for long-term implantations, the physical properties of the implant are key to maintain a stable, non-damaging, connection between the nervous tissue and the electrodes. The mechanical mismatch at the soft neural tissue to hard implant material interface combined with local micromotions induces an inflammatory reaction by immune cells, the generation of fibrotic tissue and/or a scar capsule, withdrawal or death of the nearby neurons and progressive loss of electrode contact, and thus implant failure.
We hypothesize that microfabricated electrode implants mechanically matched to the surrounding tissue may be a robust technological route for chronic synthetic neural implants. To do so, soft electrode implants are prepared with silicone elastomers. With elastic moduli as low as 10skPa, elastomers are some of the softest materials still compatible with MEMS-like fabrication processing. Furthermore their surface can be engineered in the form of large-area matrix of elastic micron-sized pillars thereby producing an interface with even lower stiffness.
We will review the materials and fabrication process to produce soft neural electrodes then illustrate the potential of this “soft technology” in the context of peripheral nerve interfaces and spinal cord electrode implants.

The development of advanced biomedical devices capable of real-time stimulation and recording of neural cells bioelectrical activity is a demand to improve our understanding of the functional mechanisms of the Nervous System and the need for effective in vitro drug screening targeted to neuropathophysiologies.
Organic semiconductor materials which combine long-term biocompatibility and mechanical flexibility are suitable candidates for neural cell interfacing. Of particular relevance is the study of the effect of the material interface interaction with neural cells, namely neurons and astrocytes. In particular, the material interface should support the cells adherence and promote their growth and differentiation on the device structure. The cell bioelectrical activity should be preserved, avoiding alteration of the electrophysiological properties due to the interaction with the organic semiconductor. Here, we show that primary neurons and astroglial cells can adhere, grow and differentiate on a suitably engineered perylene-based field-effect transistor platform, while maintaining their firing properties even after a prolonged time of cell-culturing. The development of transparent Organic Cell Stimulating and Sensing Transistors (O-CSTs) that provide bidirectional stimulation and recording of primary neurons is also reported. We demonstrate that O-CST enables depolarization and hyperpolarization of primary neurons membrane potential. The transparency of the device also allows the optical imaging of the modulation of the neural cell signalling. The O-CST device enable extracellular recording from neurons with maximal amplitude-to-noise ratio 16 times better than a micro electrode array (MEA) system on the same neuronal preparation. Our organic cell stimulating and sensing device paves the way to a new generation of devices for stimulation, manipulation and recording of neural cell bioelectrical activity in vitro and in vivo.
Supported by EU-FP7-ITN Olimpia, Firb-Futuro in Ricerca, SILK.IT

The goal of this project is to develop a nanoprobe device for intracellular electrical signal recording and stimulation of neuronal cells. This paper presents a platform that integrates “Fin” shaped nanoelectrodes and cell microprinting technology. The “Fin” shaped nanoeletrodes were designed to increase the electrode area and conductance so as to reduce the signal loss seen in the case of traditional circular nanopillar designs. The microprinting technology, in turn enables controlled number and volume of cells to be printed on top of the nanoeletrodes in order to realize ease in cell penetration.
The overarching goal of neuroscience is to target and discover the relationships between the functional connectivity-map of neuronal circuits and their physiological or pathological functions. In the past, extracellular microelectrode arrays (MEAs) have been used to record and stimulate a population of excitable cells for months in-vivo (Kipke et al.). The recorded spikes (signal) by extracellular electrodes, though informative, do not provide the source mechanism for neuron firing; because the extracellular recordings do not record synaptic signals (subthreshold). On the other hand, intracellular recording can help study the functions of “silent” neurons and neuroplasticity (Spira et al.). In this respect, the current intracellular recording technologies include a sharp or patch electrode to measure only a few neurons. For recording a record large number of neurons, technologies such as gold mushroom-shaped microelectrodes (Hai et al.), vertical nanowire electrode arrays (Robinson et al.) and nanoFET technology (Tian et al.) are currently under development. The gold mushroom-shaped electrodes in order of microns are invasive for smaller cells with no successful recording on rat hippocampal neurons and primary rat cardiomyocytes. The vertical nanowire electrode arrays show high electrode impedance which causes large signal loss. The nanoFET show higher noise levels and the manipulation of a single nanotube to penetrate a single cell are very challenging. In this work, we present the design and fabrication of “Fin” shaped nanoelectrode which seeks to overcome the restrictions between electrode impedance and electrode size. Compared to the 3x3 array of 150 nm diameter nanowire electrodes, the “Fin” electrodes reduces impedance by factor of ten. 150 nm thick fins are seen to be less damaging compared to mushroom-shaped electrodes. We demonstrate the ability of microprinting technology to print viable neuronal PC12 cells onto pre-defined areas such as within the reservoir with nanoelectrodes. The relationship between the electrode geometry and neuronal cell viability is studied. Finally, the intracellular neuronal activity (action potential) with and without sub-threshold (10-40mV) electrical stimulus, along the effect of electrode surface coating on signal coupling is presented.

Due to their structural kinship to proteins, carbohydrates and nuclei acids, the use of organic conducting polymers in biomedical research and medical applications is highly intuitive from a biological and chemical perspective. The availability of organic chemistry toolkits to functionalize and adapt these molecules, convenient processing techniques like soft lithography, electrodeposition or vapor phase polymerization as well as the possibility to reversibly modify their chemical and electrical properties by switching between the redox states of the conducting polymer backbone qualifies them as interesting materials for the development of functional tissue-device interfaces.
Using organic electronic devices with different designs and polymer bases, one can achieve control of cell growth and attachment on different levels. On a surface switch based on the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with tosylate (PEDOT:tosylate) we show modulation of epithelia formation by presenting electrochemically oxidized versus reduced surfaces as substrates for cell attachment. By further modification of the device, adding a channel and gate electrode, an organic electrochemical transistor (OECT) is developed, which allows for active control of epithelial cell-density gradients along the channel. Electronic control of cell release was demonstrated in a similar devices using the self-doping compound PEDOT-S:H.
Organic electronic devices can also be designed to facilitate modulation of cell signaling in a biomimetic fashion. Electrical actuation of neuronal cells in a three dimensional nano-fiber scaffold is achieved on an electrospun scaffold coated with PEDOT:tosylate. The unique property of organic electronics to utilize both electrons and ions as charge carriers is used in the organic electronic ion pump (OEIP). When addressed electronically, the OEIP translates electronic signals into electrophoretic migration of ions or neurotransmitters. The precise, spatiotemporally controlled delivery of signaling substances in absence of liquid flow was demonstrated as a novel interface to modulate mammalian senses.
This presentation will highlight the potential of communication interfaces based on conjugated polymers in generating complex substrate signaling to control cell and tissue physiology. Organic electronic devices will have widespread applications across basic medical research fields as well as future applicability in medical devices in multiple therapeutic areas.

The study of interconnectivity within neural networks is limited by the existing experimental techniques for massively parallel electrical recordings. Multielectrode arrays and patch clamps are the current standards for recording neuronal membrane potentials; however, neither offers the combination of sensitive, long-duration recordings. Developing solid-state devices via scalable fabrication techniques requires thoughtful design informed by the conditions at cell surfaces. To achieve sensitive, long-term recordings, we target biomimetic integration of probes with the plasma membrane, using a layered structure we describe as “stealth probes.” Stealth probes are solid-state nanostructures that can span cell membranes, forming electrically tight seals against the phospholipid bilayer structure. The junction between probe and cell is both mechanically stable and offers high resistance against ion exchange between cytoplasm and media. Gigaohm-level leak resistance is the critical need for non-invasive intracellular measurements with the scalability of a multielectrode array. Through cell-probe interface modeling, we have identified the parameters required for sensitive cellular electrical recordings, and are employing fabrication techniques to target devices accordingly. We have developed a hybrid on-wire lithographic approach to fabricate biologically compatible, individually addressable solid-state nanoelectrode arrays. Here, we describe device fabrication and the necessary parameters for sensitive electrophysiological recordings. We focus on the electrical characteristics of the probes, the relationship between device impedance and signal-to-noise ratio, and the requirements necessary for immediate deployment of the technology for experiments in neuroscience.

Conducting polymers (CPs) are easy to process and have tunable physical and chamical properties including conductivity, volume, color, and hydrophobicity. Therefore, these organic polymers are attractive in a broad spectrum of biomedical applications ranging from implentable electornics, and biosensing to tissue engineering and drug delivery. Among CPs, polypyrrole (PPy) is particularly appleaing for biomedical applications due to its biocompatibility and excellent stability. PPy can be electropolymerized into thin films and serve as substrates for in vitro cell cultures. Patterned films of conductive polymers, particularly with various surface chemistries, provide an excellent platform to study cellular behavior. We recently introduced a unique and verstaile method for direct patterning of PPy films on gold substrates. In this method, we employed an agarose hydrogel stamp as a carrier of polymer precursor solution including pyrrole and dopants. Upon placement of the stamp on an electrode and subsequent application of a current, the polymerization of pyrrole only occurred in the contact areas between the topographically-patterned hydrogel and the gold substrate. We demonstrated the capability of this method to generate positive patterns of PPy films with different sizes and geometries in a single-step and solution-free process. More importantly, we demonstrated that the posts on a hydrogel stamp can deliver different monomer/dopant combinations to create a patterned PPy film with different and addressable surface chemistries in a parallel fashion.
Here, we aim to apply this innovative and multifaceted technique to cage bioactive molecules within the CP network by simply adding the desired biomolecules to the polymer precursor solution that is applied for inking the hydrogel stamp. We hypothesize that the biocompatible agarose gel stamps can safely deliver the bioactive molecules during the electropolymerization process, leading to the entrapment of these molecules within the CP film. We tested this hypothesis by incorporation of D-biotin molecules into PPy network and confirmed the presence of D-biotin in these films by fluorescence immunohistochemistry and ATR-FTIR. Most importantly, we demonstrated that this hydrogel-mediated electrodeposition technique can create spatially addressable patterned films of PPy decorated with multiple different proteins and biomolecules in one-step process. Currently, we are employing these bio-functionalized PPy films to control and study neuronal cell adhesion and differentiation. The goal of this study is to apply these biofunctionalized PPy films to control stem cell fates for applications in neural tissue engineering.

Ever since the pioneer titanium alloy (Ti6Al4V) has been used as biomaterial, lack of biocompatibility has been extensively reported and propelled research on improved materials with appropriate mechanical behavior and adequate biocompatibility. Studies have indicated that vanadium produces oxides harmful to the human body; in order to replace vanadium containing Ti alloys, Ti-6Al-7Nb was developed. Today this alloy is the preferred choice for cementless total joint replacements. It is very important to produce a nanostructured bioactive metal implant with appropriate mechanical properties and we applied a chemical and thermal treatment that converts the surface of titanium alloy into bioactive surface. Therefore, bioactive Ti6Al7Nb might represent an alternative for advanced orthopedic implants under load-bearing conditions.
Eleven mini-pigs weighting around 50 kg, with free access to food pellets and water, were the experimental animals for this study. Ten of these pigs (one is the control) were anesthetized and after shaving, disinfection and draping, a straight 3 cm incision was made and the implants (plate and pin) were implanted into the epiphyses of the tibiae. Surgical procedures were performed bilaterally. At 6 months after implantation, the mini-pigs were sacrificed.
After sacrifice, the segments of the proximal tibia epiphyses containing the implanted plates and pins were cut off, fixed in phosphate-buffered formalin and dehydrated in serial concentrations of ethanol after which they were embedded in polyester resin and then cutted and grounded to a thickness of 75-100 µm. With these samples SEM-EDX examinations were made. The aluminium content was measured by electrothermal atomic absorption spectrometry in different organs: brain, fat, kidney, spleen and liver.
All the results revealed that the plates and pins are in direct contact with newly formed bone without any intervening soft tissue layer. No aluminium accumulation occurs during the experiment and we regard it as one of the advantages of this implant in consideration for clinical applications.

Conducting polymers (CPs) have been the subject of significant research in recent years for their optical and electronic properties, as well as their potential use in biomedical applications. Medical procedures requiring electrical stimuli have traditionally used metallic compounds, which have severe issues with tissue compatibility. CPs are a promising replacement to metals in these applications due to their biocompatibility, electrical conductivity, and range of chemical and physical properties. However, standard CPs are typically brittle and difficult to process into 3D structures which has limited their use. We aim to develop new CPs that incorporate a peptide motif based on an amino acid sequence found in silk fibroin that is capable of self-assembly and is responsible for the characteristic strength of silk. We hypothesize that hydrogen bonding between chains of the peptide functionalized conducting polymers will influence the 3D organization and improve mechanical strength while retaining biocompatibility. To make such materials we are investigating two complimentary approaches: 1) assembling and polymerizing peptides containing a thiophene-based monomer or 2) functionalizing a pre-made polymer with silk peptides. Here, we present the synthesis of silk-inspired peptides coupled to 3,4-ethylenedioxythiophene (EDOT) monomers, the characterization their electrochemical properties, and their capability to self-assemble. We also demonstrate the ability to incorporate these thiophene-peptide conjugates into copolymers with EDOT.

Implantable biomedical devices such as emerging MEMS-based neural prostheses require long-term stability in the human body. Since these devices cannot be protected with conventional metal or ceramic enclosures, a conformal encapsulation that provides chronic protection against water and ion ingress is necessary to achieve this goal. Commonly used materials include some urethanes, silicones, ceramics and metals. Amorphous silicon carbide (a-SiC) was proposed as a protective coating due to its biocompatibility and low dissolution rate in saline compared to other commonly used dielectric materials for IC passivation, such as silicon nitride (SiNx) and silicon dioxide. In addition, the deposition, patterning and etching of SiC are compatible with standard CMOS processing. These factors provide a strong incentive to investigate the potential of a-SiC as a protective coating for implantable devices.
In this study, we examined the properties of a-SiC deposited at 325°C by plasma enhanced chemical vapor-phase deposition (PECVD). We focused on three properties of a-SiC that are critical to its success as a protective coating: dissolution rates in accelerated saline tests, pinholes, trench coverage and barrier properties. The existence of any pinhole in the SiC layer will expose the underlying materials to the physiological medium causing them to dissolve, adversely affecting functionality of electrical devices, and inducing biological response in the human body. We performed a fast pinhole test by immersing the device in selective SiO2 and Si etchants and found that SiC films as thin as 200nm protected the front surface of MEMS devices completely with no evidence of pinholes. We demonstrated that SiC is able to cover most of the regions inside deep trenches (with an aspect ratio of 6:1), while a small number of pinholes were identified on the sidewalls. Further research is needed to eliminate these pinholes.
To test stability of the silicon device with polysilicon-filled trenches protected by a-SiC in the biological medium, we soaked both protected and unprotected devices in saline at 87°C for 12 days, which is equivalent to ~ 1 year at the human body temperature. SEM images showed that devices without a-SiC coating degraded significantly, while devices with a SiC coating stayed mostly intact. We also examined the forward and reverse I-V characteristics of pn junctions underneath the SiC coating before and after soaking, and observed no significant difference. These results indicate that a-SiC provided an effective barrier for our MEMS-based retinal prosthetic implants.

Biocompatible materials capable of conducting electricity have numerous biomedical applications including use as electrodes for neurological stimulation and recording, artificial muscles, and stimuli-responsive sensors. Conducting polymers (CPs) such as poly(pyrrole) and poly(thiophene) are advantageous for these applications as they are biocompatible, and their chemical and physical properties can be easily tuned. A major hurdle in the development of practical biomedical devices utilizing conducting polymers is dealing with the poor mechanical properties of the bulk polymers. The conjugated π-system of CPs that allows electron flow also results in the bulk material being stiff and brittle, complicating the fabrication of three-dimensional electrodes. In order to improve the mechanical properties of CP networks, we have established methodology for the fabrication of composites materials made of (poly)pyrrole interpenetrating into a flexible silk fibroin scaffold. Silk fibroin is a well-studied biomaterial capable of being processed into a variety of forms, such as films, hydrogels, and 3D scaffolds. Here we present new electropolymerization strategies to increase the conductivity and versatility of these silk-CP composites, and methods to tailor their surface morphology to maximize performance.

Optical analysis of deep brain structures has remained an elusive challenge, due to the presence of highly scattering, randomly distributed, dense lipid bilayers surrounding neurons. Though laser scanning coherent anti-Stokes Raman scattering (CARS) microscopy has been successful in rendering three-dimensional (3D) spatial resolution in live cells and tissues, light dispersion still reduces laser intensity and signal quality, and prohibits imaging of deeper targets without first making incisions to access the tissue. This problem may be addressed by using a newly developed technology, known as CLARITY, which enables unprecedented resolution of detailed structural and molecular information of intact biological systems. During CLARITY sample preparation, intact tissue (such as whole brains) can be transformed into nanoporous tissue-polymer hybrids, which are then made transparent using electrophoretic lipid removal. The final product of CLARITY is tissue that has been stabilized through effective replacement of structure-maintaining lipids with a hydrogel covalently bonded to proteins. The resulting transparency of the tissue-polymer hybrid permits true high resolution, 3D analysis of neural networks and biomolecular architecture by much simpler, less damaging, and cost-effective imaging techniques. In this study, we investigated polymer formation and hybridization within tissue using confocal Raman scattering, complemented by two-photon fluorescence microscopy. This work represents the first demonstration of three-dimensional Raman spectral mapping of brain tissue, providing a new perspective on the distribution and identity of protein and polymer bonds. Information from these maps can be correlated with biological features identified using appropriate staining techniques and two-photon microscopy, and can be employed to quantitatively explore the influence of key reactants on CLARITY tissue-polymer hybrid properties. These results will be significant in helping to tune the CLARITY platform for various applications, and provide a deeper understanding of how polymers form and crosslink within tissues.

Natural-origin hydrogen-bonded molecular solids such as the indigo and its derivatives are very promising semiconducting materials because of remarkable physical and chemical properties as well as biocompatibility and biodegradability. With mobility in the range of 1 cm2/Vs and stable operation in air, they are competitive with many synthetic materials. In recent years, we have demonstrated that it is possible to produce green electronic devices using the indigo compounds. In this report, we bring our recent works into practical implementations of electronic circuits, such as complementary-like voltage inverters and ring oscillators, where indigo and its derivatives are remarkable for their air stability.

As an artificial cell membrane on solid wafer surface, supported-lipid bilayer (SLB) is one of most promising biological platform in biophysics research because it opens possibilities to study the fundamental properties of cell membrane by modern surface-based characterization techniques and advanced nanotechnology. In the meantime, carbon nanotubes (CNTs), as a typical one-dimensional molecular system, have been attracted enormous attentions for their remarkable electrical properties and CNT-based field effect transistors (FETs) have shown high sensitivity in bio- or chemical sensors. However, a challenge is how to engineer graphene&’s sensitivity to a specific analyte of interest.
Here, we incorporate ion channel membrane proteins gA and α-HL in an SLB on a functionalized all-semiconducting nanotube network, where SLB forms an insulating barrier on FET surface. The nanotube transistor as a charge sensor only detects the ions or biomoleculars through ion channels. Nonetheless, due to the nature hydrophobic surface of carbon nanotube, lipid bilayer doesn&’t form a continuous film on high-density nanotube network surface. At the same time, the main drawback of solid supported lipid bilayer is the very limited distance between solid substrate and lipid bilayer, usually only up to 1nm. Therefore, it is crucile to utilize surface functionalization for fabricating a robust lipid bilayer on surface and spacing the membrane up from the substrate. Our functionalization strategy is using silane molecular as a linker to covalently bind with substrate and lipid monolayer. The space distance can be delicately tuned by changing the length of silane molecular. The second layer lipid layer can be easily formed on the tethered lipid surface by vesicle fusion or directly dropping lipid ethanol solution. The quality of lipid membrane is estimated by fluorescence recovery after photobleaching (FRAP), atomic force microscopy (AFM) and impedance spectroscopy. Moreover, combining with microfluidic channel, we are able to detect single ion channel activity. Dynamic opening and closing of the pores is observed through measurement of the current from the nanotube network, through the nanopores, and into solution. The all-semiconducting nanotube network devices are compatible with microfabrication process, opening a window for massively parallel manufacturing of nanotechnology for a variety of applications in electrophysiology and biosensors.

We have recently demonstrated how we can use charge trapping/detrapping in an array of gold nanoparticules (NPs) at the SiO2/pentacene interface to design a SYNAPSTOR (synapse transistor) mimicking the dynamic plasticity of a biological synapse. This device (memristor-like) mimics short-term plasticity (STP) [1] and temporal correlation plasticity (STDP, spike-timing dependent plasticity) [2], two "functions" at the basis of learning processes. A compact model was developed [3], and we demonstrated an associative memory, which can be trained to present a pavlovian response [4].
Here we develop an electrolyte-gated version of this device for biocompatible applications. We report on a detailed understanding of the electrical behavior of these synapstors in physiologically relevant conditions. We compare synapstors operated by the traditional bottom gate structure in air and by a water-electrolyte gate geometry. We show that the increased capacitance of the pentacene/water interface leads to a large improvement of the synapse-like behavior of these devices. STP of comparable amplitude (about 50% of the total output current) is observed at a reduced working voltage (i.e. spike voltage of 0.4V in water, instead of 10 V in air). Moreover, the typical dynamic time response of the synapstor is also decreased by about a factor 10 (ca. 0.2s instead of ca. 2-5s). These last results represent major improvements towards the use of these organic/NPs synapstor in biocompatible application e.g. as synapse prosthesis.
This work has been financially supported by the EU 7th framework programme [FP7/2007-2013] under grant agreement n° 280772, project "I ONE”.
References
[1] F. Alibart et al., Adv. Func. Mater. 20, 330 (2010).
[2] F. Alibart et al., Adv. Func. Mater. 22, 609-16 (2012).
[3] O. Bichler et al., IEEE Trans. Electron. Dev. 57(11), 3115-3122 (2010).
[4] O. Bichler et al., Neural Computation 25(2), 549-566 (2013).

Materials capable of controlled movements that can also interface with biological environments are highly sought after for biomedical devices such as valves, blood vessel sutures, cochlear implants and controlled drug release devices. Here we report the synthesis of films composed of a conductive interpenetrating network of the biopolymer silk fibroin and poly(pyrrole). These silk-PPy composites function as bilayer electromechanical actuators in a biologically-relevant environment, can be actuated repeatedly, and are able to generate forces comparable with natural muscle (>0.1 MPa), making them an ideal candidate for interfacing with biological tissues. We will discuss the mechanical properties and actuation performance of these promising devices under biologically relevant conditions.

Currently there is enormous interest in organic electronics devices.Such organic devices may aid the development of new technologies such as OFETs, OLEDs and OPVs that were active in clean energy production. Melanin that is an organic biopolymer, has great potential, as an active component in these devices. Recently soluble melanin derivatives have been obtained by a synthetic procedure carried out in DMSO (D-melanin).[1] In this work a comparative study of the structural characteristics of synthetic melanin derivatives obtained by oxidation of L-DOPA in H2O and DMSO is presented. To this end, Fourier-transform infrared spectroscopy as well as, proton and carbon nuclear magnetic resonance techniques have been employed. In addition, aging effects have been investigated for D-melanin. The results suggest that there is incorporation of sulfonate groups (-SO2CH3), from the oxidation of DMSO, into melanin, which confers protection to the phenolic hydroxyl group present in its structure. The solubility of D-melanin in DMSO is attributed to the presence of these groups. When the obtained melanin is left in air for long time periods, the sulfonate groups leave the structure, and an insoluble compound is obtained. NaOH and water have been used, in order to accelerate the release of the sulfonate groups attached to D-melanin, thereby corroborating the proposed structure and the mechanism suggested for the synthetic procedure. In this work we study also the influence of temperature on D-Melanin synthesis and properties. To this end, UV-Vis and Fourier-transform infrared (FTIR) spectroscopy techniques have been employed to analyze D-Melanin synthesized in the range of 25 C to 100 C. Through UV-Vis spectroscopy, it was possible to follow the process of polymerization and the optical properties of D-Melanin under different syntheses conditions. The increase in synthesis temperature enhances the reaction kinetics and also influences the elimination of carbonyls present in the monomers, thus facilitating the polymerization of D-Melanin. Another consequence of synthesizing at higher temperatures is an easier control of the reaction product.
[1] S.N. Dezidério, C.A. Brunello, M.I.N.da Silva, M.A. Cotta, C.F.O.Graeff,
Journal of Non-Crystaline Solids, Vol.63 (2004) 338-340.

How well a protein conducts electrons depends on how well the protein is coupled to the contacts via which currents are measured and voltage applied and the electronic coupling across the protein. Assessing the importance of each of these couplings will help understanding electron flow across proteins. Using monolayers of Cyt C we find that chemical protein-contact binding improves room temperature conduction twofold and halves the activation energy for steady-state hopping. At low (< ~ 150K) temperatures, where transport is by tunneling via super-exchange, covalent binding increases conduction up to 10-fold. The importance of coupling across the protein is shown by changing the protein&’s orientation, relative to the electrodes, using seven different mutants. Remarkably, currents do not depend on the distance between electrodes, defined by the orientation of each electrode-bound mutant, of either room temperature or 30K currents. Rather, the distance between the heme group and the top or bottom electrode affects the ETp process. In general, mutants with proximal heme have lower thermal activations at higher temperatures, and higher conductance at low temperatures (temperature-independent regime), than those with a distal heme. Thus, while illustrating and emphasizing the importance of covalent binding, we find that factors beyond simple geometrical ones need to be considered, to describe ETp across proteins, a finding that warrants further study.

Graphene nanoribbon-nanopore (GNR-NP) sensors offer the potential, because of their thickness, for ultimate spatial resolution at high measurement bandwidth for single-molecule DNA analysis and sequencing. We developed graphene nanoribbons (GNRs) (width: down to 20 nm, length: 600 nm, on 40 nm thick silicon nitride (SiNx) membranes) that can sustain micro ampere currents at low voltages (sim; 50 mV) in buffered electrolyte solution and exhibit a sensitivity to local potential of ~ 1% / mV, enabling high bandwidth sensing (>1MHz). GNR conductance measurements, conducted in situ inside a TEM operating at 200 kV, show that during nanopore formation and imaging, GNR resistance increases linearly with electron dose and that GNR sensitivity decreases by a factor of ten or more upon exposure at high magnification. We present a methodology for forming a nanopore at the edge or in the center of a nanoribbon in scanning TEM (STEM) mode, in which the position of the converged electron beam can be controlled with high spatial precision via automated feedback, that minimizes the exposure of the GNRs to the beam before and during nanopore formation and preserves the high conductivity and sensitivity of the GNR-NP sensors.

Charge transfer across the biotic-abiotic interface remains to be a significant obstacle for the integration of biological and electronic systems in high-performance bioelectronic devices. In our approach to modify the biotic-abiotic interface, easily accessible synthetic constructs of tunable properties, namely, conjugated oligoelectrolytes (COEs) are utilized to improve charge extraction in microbial fuel cells (MFCs). COEs are small organic molecules characterized by an electronically delocalized, hydrophobic backbone-bearing pendant charged, hydrophilic functional groups. Arising from these molecular features, COEs are water-soluble and amphiphilic in nature, which allow them to spontaneously intercalate into lipid bilayers and cell membranes. COEs have demonstrated the ability to facilitate electron transfer across a supported lipid bilayer, which lead to their introduction into biological systems for the improvement of transmembrane charge transport. In pure culture systems such as yeast and E. coli biofuel cells, enhanced current generation is observed with the addition of COEs, such as (4,4&’-bis(6”-(N,N,N-trimethylammonium)hexyl)amino)-styryl)-stilbene tetraiodide (DSSN+). The increase in performance is also observed in mixed consortia systems such as wastewater MFCs, along with a corresponding increase in organic contaminant removal. Recent results indicate that COEs are not only increasing the current generation but also decreasing the internal resistance of the fuel cell, contributing to the overall increase in power density. To fully understand the participation of COEs in the overall improvement of MFC performance, electrochemical impedance spectroscopy (EIS) and polarization techniques are used to characterize the limiting factors that are decreased by COE addition in both mixed consortia and E. coli fuel cells. The ability of these nontoxic, synthetic COEs to mediate transmembrane charge transfer without acting as conventional redox shuttles suggests the potential for future applications in the field of bioelectronics.

Hybrid organic/inorganic nanostructures are engineered to function as two terminal devices with enhanced functionality. The devices are the building blocks for designing hybrid organic/inorganic circuits in the nanoscale. In our work, we have demonstrated the sensing capabilities of electrospun conducting polyaniline nanofibers for designing nanoweb devices towards detection of biomolecules.
In electrospinning, the nanofibers formed by the evaporation of the solvent from the electrified polymer jet are randomly aligned. Deposition of electrospun nanofibers in desired alignment can be achieved through the careful selection of the collector geometry. In this work the polyaniline nanofibers of diameter in the range 50-300 nm was obtained by controlling flow rate and the applied voltage. Nanofibers of defined morphology were deposited in an ordered pattern on a non-conducting collector substrate patterned with metal microelectrode array. Concentration below the critical entanglement concentration of the polymer solution resulted in the formation of beaded fiber matrix. The device designed in this research comprises of a glass substrate with a metal microelectrode array of a crossbar array configuration and was used for electrical characterization of polymer cross bar junction. With the described technique the polyaniline nanofibers were directly patterned at the crossbar junction. The electrically active area comprises of gold nanoparticles embedded in the nanofiber matrix.
Biomolecules with surface charge such as nucleic acids were detected on this device by interfacing the biomolecules with the polymer/metal composites. The change in electrical properties due to modulation in charge transport at the crossbar junction is used to obtain switching behavior was identified as the measured electrical signal for designing sensors. Nanotextured surface offers strong charge carrier transport and hence enhances the strength of the detected signal. This device is used to quantify the hybridization event of DNA molecules. The hybridization event at the crossbar junction effectively modulates the charge transfer kinetics and modifies the junction characteristics due to the surface potential associated with the organic molecules. The net change in surface charge can be measured either as changes in the diode current in the two terminal configuration or as changes in the source- drain current in the three terminal configuration. Smaller the fiber diameter, larger is the surface area for immobilization of DNA molecules and higher the sensitivity of the device. Detection sensitivity in the order of fg/mL was targeted by measuring the voltammetric current response (in microamperes). This was measured between -3V and 3V. The switching behavior is observed when the change in the measured current is higher than three orders of magnitude.

Cortisol “a steroid hormone” is known as a potential biomarker for psychological stress estimation and abnormality is indicative of many disorders. A simple, low-cost, label free sensor is required to detect Cortisol. Electrochemical immunosensors due to increased range, rapid detection, and sensitivity have been developed to detect Cortisol. The sensing performance is dependent on the functionality and electrical behavior of immobilizing matrix for high electron transport for signal amplification and loading of higher biomolecule.
In recent studies, nonmaterials have been deposited usually on Au or Au-coated silicon or glass or other hard substrate, which was then used as a sensing device for biosensing. Nanomaterials grown on flexible and wearable plastic substrates are suitable to biomedical instrumentation as they reduce the weight and cost of the device.
In this work, nanostructured ZnO due to bio compatibility, chemical stability, high iso electric point, electrochemical activity, high electron mobility, ease of synthesis and high surface-to- volume ratio has been explored for electrochemical Cortisol immunosensing. ZnO nanostructures synthesized by Sonochemical method are used to immobilize Ant-Cortisol antibody (Anti-Cab). ZnO nanorods and nanoflakes are directly synthesized on ITO/PET as flexible substrates at ambient conditions by reacting Zinc acetate dehydrate (Zn (O2CCH3)2 .2H2O), zinc nitrate hexahydrate (Zn (NO3)2. 6H2O) and hexamethylenetetramine (HMT, (CH2). 6N4) in aqueous solutions. The selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) studies on the nanostructures showed that the nanostructures grown are single crystalline with orientation along [0001]. Electro chemical detection is utilized for detection of Cortisol using anti- Cortisol antibodies (Anti-Cab) immobilized on ZnO nanostructures. The electrodes are characterized by using Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and cyclic voltammetry (CV).
Electrochemical response studies of Anti-Cab/ZnO/ITO/PET immunoelectrode shows a linear relationship between the obtained current response and Cortisol concentration. The sensor exhibits a linearity from 1 pg/mL to 100 ng/mL, with a detection limit of 1 pg/mL and a sensitivity of 4µA/ (pg/mL) with a regression coefficient of 0.98. The obtained sensing performance is in physiological range. This developed sensor can be integrate with fluidic system for the automated sensing at point-of-care application

Over the past few years, a considerable effort has been spent on the development and optimization of organic polymers based memory elements. In this work we introduce an interesting approach consisting in the employment of a double gate dielectric - Organic Thin Film Transistor for the fabrication of high retention time, non volatile memory elements. The device structure consists in an aluminum gate electrode on which an ultrathin oxide layer, nominal thickness of 5 nm, is grown by means of UV-Ozone treatment. At the top of this structure, a second ultrathin insulating layer (thickness of 25 nm), made out of Parylene C, is deposited from vapor phase, and on top of it, metal source and drain electrodes have been patterned by means of photolithography or by inkjet printing. In all cases, TIPS-penatcene was employed as organic semiconductor. Thanks to the high capacitance coupling induced by the ultrathin double-layer insulating film, such devices can be operated at ultralow voltages, as low as 1V, showing mobility up to 0.4 cm2/Vs, Ion/Ioff up to 10^5 and remarkably low leakage currents (100 pA), with a typical breakdown field higher that 5MV/cm. Interestingly, we have found that by applying a pulsed gate voltage, possibly slightly higher than the nominal breakdown voltage, it is possible to induce a pronounced threshold voltage shift in the transistor behavior. In particular, we observed that the charges injected into the device channel are trapped into the Parylene C low-k dielectric (called electret), whereas, the Al2O3 high-k blocking dielectric avoid trapped charges to move all the way through the gate electrode.
It was found that, by applying a gate voltage pulse of -20V for 10 ms, usually gives rise to a threshold voltage shift higher than 1.5V in the same verse of the applied field. In other words, the device is strongly driven to its off state. We have observed a remarkably high Ion/Ioff ratio, usually in the range of 103, measured at -1V, and retention times higher than 105 s are typically obtained. We will demonstrate that by properly tuning the thicknesses of the two insulating layers and the program parameters (amplitude, duration and number of pulses) it is possible to dramatically increase the retention time up to 10^7 s.
Moreover, being all devices fabricated on a highly flexible (13 um thick) Kapton substrate, we will demonstrate that the final devices are characterized by a remarkable robustness to mechanical deformation. In particular we will show that the electrical performances of the fabricated OTFTs are not affected by a continuous mechanical deformation, and that the fabricated memory elements are able to retain the data even after more than 500 cycles at bending radii as small as 150 um.
The flexibility of the proposed structure and the simplicity of the employed fabrication procedure make this approach very interesting for practical applications.

Metal-reducing bacteria Geobacter sulfurreducens have been found to be able to transfer electrons to external electron acceptors (EEA) such as insoluble Fe(III) oxides, or anode electrodes in bioelectrochemical systems for electricity production, by either direct cell-EEA contact or the production of type IV pili as biological nanowires. The biological nanowires in G. sulfurreducens have been reported to be electrically conductive with and without bacteria cells and enable electron transfer from distant G. sulfurreducens cells in biofilm to electrodes.
However, up to now, the conducting mechanism of nanowires in G. sulfurreducens is still not clear. Previous scanning tunneling microscopy results did not find the evidence of cytochrome heme groups contributing to nanowires&’ conductivity. Denaturing cytochromes did not affect nanowire conductivity of G. sulfurreducens either. Although the protein sequence suggested less than 9% aromatic amino acids content in nanowire&’s protein pilin, PilA, X-ray diffraction patterns of purified nanowires surprisingly indicated tightly packed crystalline regions against amorphous background, leading to the guess of π-π interchain stacking between aromatic amino acids present in nanowires. In this presentation, we will show the characterization of the material properties of nanowires in G. sulfurreducens regarding their electric conductivity and elasticity under different conditions. Further exploration of their conducting features and the feasibility of using biological nanowires as conductive material will also be covered.

We have investigated M-DNA hydrogel gate graphene transistors utilizing water and hydrogel composition based on six M-DNA (M = Na, Mg, Ca, Fe and Zn). The capacitances for the water and M-DNA based hydrogels are almost same values at 20 Hz (~1.6mu;F/cm2), however, begin to change different value by increasing frequency. These results have shown that the smaller valence number lead to faster capacitive response with M-DNA hydrogel. Furthermore, capacitance behavior was observed by controlling concentration of Na-DNA. We have discovered three regimes in the capacitance vs. concentration of Na-DNA, and the each regime has different predominance, which rely on correlation between viscosity and capacitive response. Finally, the dynamic response for graphene transistors and inverter based on these M-DNA based materials is determined primarily by the change in the ON and OFF state, which in turn reflects the conductivity-frequency characteristic of the hydrogel dielectric and the device footprint. Future efforts to improve the switching frequency must focus on shrinking the device dimensions and on improving the capacitance-frequency and conductivity-frequency responses of the hydrogel materials.

Within the family of π-conjugated polyelectrolytes, there is great promise in cationic polythiophenes for the development of biosensors for genomic and proteomic applications, as for the detection of the amyloid fibrils formation or for the detection of Single-Nucleotide Polymorphism.[1] Recently, a series of DNA hybridization biosensors have been described, for which the cationic polythiophenes act as optical transducers through fluorescence properties.[2] However, is has been shown that the fluorescence signal of DNA hybridization biosensors is strongly dependent on DNA sequence, which affect the detection sensitivity and the homogeneity of the assays. So far, the lack of understanding in the DNA-CPT supramolecular assembly and hybridization processes constitute a strong limitation for applications in biosensors and bioelectronics.
Recently, we reported on the design of a series of cationic polythiophenes that assemble with DNA in hybrid chiral supramolecular complexes, for which the CPT helical assembly depend on the DNA sequence and topology.[3] In this work, we exploit these remarkable properties to probe the effects of DNA hybridization in DNA-CPT biosensor experiments in solution. Several important processes for the functioning of hybridization biosensors are examined, such as the formation of single-stranded DNA - CPT complexes, the hybridization of complementary DNA sequences, and the double-stranded DNA melting. By studying a series of complementary DNA probes, we reveal how the self-assembly is influenced by the DNA sequence, topology, and stability. Moreover, by means of a joint experimental/theoretical approach, we give important clues on the conformational changes and DNA-CPT binding mechanisms, which are important for achieving a rational design of biosensors.
[1] Hammarström, P.; Simon, R.; Nystrom, S.; Konradsson, P.; Aslund, A.; Nilsson, K. P. Biochemistry 2010, 49, 6838 ; Gaylord, B. S.; Massie, M. R.; Feinstein, S. C.; Bazan, G. C. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 34.
[2] Ho, H.-A., A. Najari, M. Leclerc, Acc. Chem. Res. 2008, 41, 168. Charlebois, I.; Gravel, C.; Arrad, N.; Boissinot, M.; Bergeron, M. G.; Leclerc, M. Macromol. Biosci. 2013, 13, 717.
[3] Rubio-Magnieto, J.; Thomas, A.; Richeter, S.; Mehdi, A. ; Dubois, P.; Lazzaroni, R.; Clément, S.; Surin, M. Chem. Commun. 2013, 49, 5483.

Bioelectronics field demands the development of new materials that have a tendency to combine the features of organic with that of inorganic materials. One of outlook candidates for that purpose is glycine - the simplest amino acid and one of the basic and important elements in biology as it serves as building block for proteins. It is known that glycine has three polymorphic forms with different physical properties, but more perspectives are polar γ- and β- phases with hexagonal (P3₂) and monoclinic (P2₁) non-centrosymmetric space groups respectively. The minor differences in space group and angle between COO_ and NH3₊ functional group cause γ- phase are more stable and attractive for applications than β- phases. But the situation is changed when recently the interest in β- phase glycine has arisen from its useful functional properties such high value of the nonlinear optical susceptibility and ferroelectricity including possibility to ferroelectric switching domains.
In this work we present the growth of stable β phase glycine microcrystals with clear crystallographic habitus grown on Pt/SiO₂/Si substrates. The influence of various parameters (e.g. concentration of solution, solvent, volume of microdroplets, temperature, humidity) on the formation of polymorph phases was evaluated using X-ray diffraction analysis and Raman spectroscopy. We have established that β- polymorph has strong interaction with a light beam. The high value of the optical susceptibility (greater than that in γ-phase glycine with reference to the z-cut quartz) was confirmed by means of nonlinear optical second harmonic generation method (SHG). Additionally, the evidence of ferroelectric properties was confirmed by means of Piezoresponse Force Microscopy (PFM) where the piezoelectric response and ferroelectric switching domains of the β- glycine have been investigated. The value of electromechanical coupling in bio-organic β- glycine has been revisited and this property was found to be sufficient for micromechanical applications.
The major part of this work was supported by the Marie-Curie ITN project “Nanomotion” (grant agreement no. 290158).

We have demonstrated proton-conducting transistors using palladium hydride as a proton-injecting contact. Palladium absorbs hydrogen gas, forming palladium hydride (PdHx), with x varying from 0 to 0.7 depending on the concentration of hydrogen present. When a bias is applied, the PdHx contacts can inject protons into a proton-conducting material. Here, I present an in-depth characterization of the proton-injection characteristics of the PdHx contacts. Time-resolved electrical measurements and micro-scale four-point probe measurements are discussed. The effects of proton concentration in the contacts on the contact protochemical potential and diffusion coefficient are measured, along with the differences between the material&’s alpha (xasymp;0.1) and beta (xasymp;0.7) phases. The results of these measurements are compared with a finite-element simulation of the contacts, which considers the changes in both conductivity and charge carrier concentration.

Conducting polymers have the potential to be widely used in biomedical applications due to their biocompatibility and inherent conductivity. More specifically, conducting polymers are well suited to be used as artificial muscles because they can operate as electromechanical actuators in biological fluids under low applied voltages. However, the material properties limit their use as artificial muscles because the conjugated backbone of conducting polymers makes the bulk materials brittle, and ion mobility through the polymers is low. Here we present the synthesis and characterization of new copolymers containing flexible oligoether linker units of varying length in the polymer backbone aimed at improving both the mechanical properties and the ionic conductivity of thiophene-based conducting polymers. Furthermore, we have developed a method to crosslink PEDOT-OH to make the material more robust. The copolymers were characterized using FTIR, CV, 4-point probe resistivity measurements, film morphology was evaluated with SEM, and mechanical properties were evaluated using a dynamic mechanical analyzer. Preliminary actuation experiments will also be presented.

Dopant-functionalized anilines with improved electrocatalytic properties are promising building blocks for the construction of bioelectronic devices [1]. The present study is devoted to the use of polyanillines possessing different substitution patterns in the interaction with the enzyme PQQ-GDH, which is advantageous in biosensor engineering [2] as well as in the construction of biofuel cells [3]. The aim is to obtain an electron transfer from the substrate reduced enzyme to the polymer without additional shuttle molecules. This has been first studied in solution and then transferred to a surface in order to build a reagentless enzyme electrode. 6 polymers have been prepared from different mixtures of sulfoxy-, methoxy- and carboxy-substituted aniline by chemical synthesis and characterized by UV/VIS, IR and NMR spectroscopy. It is shown that 4 polymers containing carboxy-modifications at the aniline ring are in the pernigraniline state after synthesis, whereas polymers substituted only by sulfoxy- and methoxy- groups appear in the emeraldine state. The different redox state clearly influences the reaction with the enzyme in solution: only the latter polymers can be reduced by the enzymatic reaction. pH dependence of the reduction indicates that the behaviour is dominated by the enzyme activity. The reaction can also be verified electrochemically with two polymers (sulfoxy- and methoxy-modifications only) showing that electrons can not only be transferred from the enzyme to the polymer, but further towards an electrode surface. In a next step the polymers have been immobilized as thin films on the electrode and the enzyme has been coupled to these films. Under these conditions it can be shown that the electrode potential can appear as a valuable driving force for direct electron transfer even for polymers which are not reacting in solution [4]. Thus, these results can be considered as a further step towards the better understanding of the roles played by the structure and interface of polymers in their interaction with biomolecules.
[1] Wallace GG, Kane-Maguire LAP. Manipulating and monitoring biomolecular interactions with conducting electroactive polymers. Adv Mater 511 2002;14:953-60
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[2] Durand F, Stines-Chaumeil C, Flexer V, Andre I, Mano N. Designing a highly active soluble PQQ-glucose dehydrogenase for efficient glucose biosensors and biofuel cells. Biochem Biophys Res Commun. 2010;402: 750-4.
[3] Schubart IW, Göbel G, Lisdat F. A pyrroloquinolinequinone-dependent glucose dehydrogenase (PQQ-GDH)-electrode with direct electron transfer based on polyaniline modified carbon nanotubes for biofuel cell application. Electrochim Acta 2012;82:224-32.
[4] Sarauli D et al. Differently substituted sulfonated polyanilines: The role of polymer compositions
in electron transfer with pyrroloquinoline quinone-dependent glucose dehydrogenase Acta Biomater 2013; 9: 8290-8298

Charge transport in double stranded DNA (dsDNA) molecules has been intensively investigated over the past two decades. Various experimental techniques and theoretical approaches have been used to understand charge transport in dsDNA. However, little is known about charge transport though mixed oligomers such as DNA:RNA duplexes. DNA:RNA hybrids are important biological components and are integral to the processes of DNA replication, transcription and reverse transcription. However, these hybrid oligonucleotide pairs have significant changes in structure compared to dsDNA. As such, the charge transport properties of DNA:RNA hybrids are expected to be substantially different than dsDNA. In this work, the conductance of individual DNA:RNA hybrids is measured, and we systematically study the transport properties of these systems by changing both the length and sequence of the hybrid pair and comparing these results to the equivalent dsDNA duplexes to obtain fundamental insight into the conductance properties of these important biological systems.
In this work, the conductance of the oligonucleotide duplexes is directly measured using the Scanning Tunneling Microscope (STM)—break junction technique in aqueous solution. This approach, which has previously been used to obtain reproducible conductance values for dsDNA has been adopted to directly measure individual DNA:RNA hybrid duplexes by linking them in between the tip and substrate in an STM. With this setup, thousands of individual conductance measurements can be obtained rapidly for statistical analysis, thus allowing the most probable conductance of a single molecule to be determined. In this work, measurements of various number of G:C or A:T/U base pairs provide us a better understanding of the fundamental charge transport mechanisms in DNA:RNA hybrids.

Combinations of an ISFET with a reference field-effect transistor (REFET) have been reported in the past by many researchers. In conventional ISFET/REFET pairs, the ISFET is sensitive to pH and by covering the gate oxide with a polymeric layer an REFET with zero sensitivity to pH is achieved . This work is dedicated to integration of the same concept to a silicon nanowire (SiNW) FET sensor. The new nanowire/microfluidic channel combination is covered with an alkoxysilane monolayer which offers minimized pH and ion sensitivity conditions as required previously for the REFETs.
The SiNW FET in our work consists of both sensor (SENW) and reference nanowire (RENW) sets with identical electrical properties. The purpose of the first integrated reference set is to eliminate disturbances in the signal caused by the nanowire/background electrolyte interface and the second set enables us to differentiate the specific binding of target molecules from nonspecific interactions. In order to verify the feasibility of such reference sets, their oxide surface should be modified such that they are chemically inert to the molecular species under detection. As a result, the oxide surface of all the silicon nanowires in the sensor chip was first covered with 3-aminopropyltriethoxysilane (APTES) film through microwave-assisted silanization in anhydrous toluene at 75°C for various silanization times. The APTES films were characterized using ellipsometry, Atomic force microscopy (AFM) and attenuated total reflection (ATR) mode of Fourier transform infrared (FTIR) spectroscopy. Surface characterization results suggest that microwave-assisted silanization for 10 minutes produces a continuous and uniform monolayer of APTES on the nanowire surface. Electrical measurements on the silanized SiNW FET in buffer solution reveal that the produced APTES monolayer successfully passivates the surface silanol groups and compared to bare silicon oxide surface, the response to ion or change in concentration is minimized.
Furthermore, single-stranded DNA probes were attached to the silanized surface of the nanowires and the adopted functionalization strategy was investigated through hybridization with a fluorophore-tagged complementary DNA strand (also referred to as target DNA). The results show that the APTES monolayer can be chemically modified if desired for biosensing.
The results of these investigations have led to the design of a SENW/RENW FET which is optimized for sensing target biomolecules or change in pH of a solution measured as a differential current referenced to silanized and/or bio-functionalized nanowire sets integrated on the chip.

This project demonstrates the development of a zinc oxide (ZnO) based microelectrode sensor for the ultra-sensitive detection of protein biomarkers. Biomarkers are unique biological macromolecules that may indicate the presence or risk of certain developing ailments. Point-of-care, rapid quantification of these molecules is essential to disease identification, monitoring, and analysis. Currently employed technologies for quantitative detection of protein biomarkers suffer from problems such as a lack of sensitivity/selectivity, dominance of signal noise, adaptability of detection to a wide range of biomolecules, and are not geared for rapid detection. Our research focuses on utilizing a materials-based approach to overcome these problems often associated with the detection of biomarkers by utilizing ZnO as part of our biosensor for (1) improved binding surface area for enhancing sensitivity and (2) creating nanostructures for biomolecule confinement that can enhance output signal response. This study integrated nanotextured ZnO thin films onto printed circuit boards using RF magnetron sputter deposition at room temperature. By manipulating ZnO deposition conditions, certain properties of the material can be tuned to increase the efficacy of signal transduction. These fabrication conditions not only dictate the number of oxygen vacancies within the film but also regulate the amount of zinc and oxygen terminated ends occurring on the material surface.
This study focuses on the correlation between the effect of physical confinement and surface termination of nanotextured ZnO to its performance as a biosensor. ZnO films sputtered with and without the presence of oxygen were examined for possible differences in biosensor efficacy. Two cross-linker molecules, dithiobis succinimidyl propionate and (3-aminopropyl)triethoxysilane, were evaluated for their ability to bind to these two different surfaces using fluorescent studies. Qualitative and quantitative assessment of cross-linker binding was accomplished using microscopy and fluorescent intensity measurements. Impedance spectroscopy (EIS) was used as the electrical transduction mechanism for detection of the well-established cardiac biomarker, troponin-T, whose presence in trace quantities is indicative of multiple cardiovascular ailments. Utilizing EIS with a functionalized immunoassay on the ZnO surface, troponin-T was detected as low as 10 fg/mL in purified buffer media as well as in human serum. The enhanced detection of the cardiac biomarker using ZnO films sputtered without oxygen can be directly attributed to 1) oxygen vacancies within the metal oxide film, 2) the nanotexturing of the sensing site surface, and 3) the ability to bind a significant amount of cross-linker molecules for immobilizing capture antibodies. This platform demonstrates applicability as a sensitive, low-cost, rapid and easy to use tool that can be integrated as a point-of-care diagnostic device.

Iontophoresis is a one of methods to enhance the drug penetration across the skin via ion movement under electrical potential known as transdermal drug delivery system (TDDS). In this work, calcium-alginate (Ca-Alg) hydrogel was used as a matrix, which was prepared by solution casting using CaCl2 as a crosslinker. Benzoic acid (BA) is an anionic drug which was used to study the release mechanism and the diffusion coefficient. The diffusion coefficients increase with decreasing crosslinking ratio due to larger mesh size of hydrogel. The diffusion coefficient is shown to be controlled by applied electric field strength and electrode polarity. The release behavior is further developed by using poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticle as the conductive polymer as the drug substrate and blended with a Ca-alg hydrogel. The PEDOT nanoparticle was synthesized via the chemical oxidation polymerization at various oxidant and surfactant concentrations. Variously distinct particle shapes were obtained: irregular, raspberry agglomerate, coralliform, orange-peel, globular, and plum shape. The particle sizes and the electrical conductivity values were in the range of 60 nm to 900 nm and < 1 S/cm to 153 S/cm, respectively, depending on the polymerization condition. Due to the various and distinct PEDOT nanoparticle sizes and morphologies, they are expected to extend the operation window of TDDS.

Biosensors have been developed widely in the medical and the human healthcare sectors for many years since the biosensors provide attractive options such like the cost-effectiveness, the good sensitivity and the rapid response times. Especially portable biosensor systems based on Si based transistor for the rapid detection of specific biomolecules are crucial for anti-bioterrorism, disease diagnostics, and food safety. However, the rigid and the opaque characteristics of the Si wafer induce some difficulties to apply it to flexible skin or to detect anti-body reaction by microscope in transmittance mode.
Here, we demonstrated high sensitive and high transparent amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) employing indium-gallium-zinc oxide (IZO) as the source and the drain electrodes for biosensor applications. The device performance shows a high field effect mobility of ~ 6 cm²/Vs, a subthreshold slope of 650 mV/decade, drain current on-off ratio of ~ 10⁶ with high transparency over 80%. To store the culturing media, we also achieved 2-step reservoir structure with SU-8 polymer on TFTs. The bio-sensing effect of the IGZO TFT design has been studied using bacteria of thermococcus gammatolerans and olfactory receptor neurons. The thermococcus gammatolerans and the olfactory receptor neurons from rat nerve cells are well cultured on the IGZO junction layer or the insulator surface for passivation. The reaction of the bacteria or the specific odorant molecules with a-IGZO TFTs can be detected in real time with high signal ratio. The characteristics of oxide TFTs-based sensors can be optimized by simple surface engineering. Furthermore, IGZO-based TFTs can operate in aqueous electrolytes that are essential for real-time chemical and biological sensing applications. The low process temperature of IGZO TFTs can give an important merit to use flexible substrate. Therefore, the IGZO TFT-based biosensor satisfies important requirements, such as high sensitivity, transparency, disposability, high throughput sensing and application as flexible biosensor.

Microtubules are a subset of cytoskeletal eukaryotic proteins. Their role has been proposed by different groups in memory retentions with feasible ionotropic or metabotropic mecahnisms, pertaining to electrical charge transfer process. Tuszynski and group have proposed that microtubules behave as ferroelectric materials and have given a detailed theoretical justification for the same. We've used microtubules together with microtubule-associated proteins, that are meant to give them structural stability, further known as MAPs-rich microtubules.
Following up, we did two separate studies for the electrical characterization, namely, electrostatic force microscopy (EFM) and polarization-voltage (P-V) measurements. The samples were prepared on n+ Silicon (resistivity- 0.05 ohm-cm) and PET sheets with two planar Cr-Au (50 nm: 5 nm Cr + 45 nm Au) electrodes deposited by metal evaporation process, for EFM and P-V measurements respectively. Liquid MAPs-rich microtubules (~0.1 mg/ml) was drop-casted on the substrate and further spinning was done for uniform coverage of the protein sample on Si and between the electrodes.
There was no colour reversal (from light-to-dark and vice versa) upon reversing the applied voltage bias in EFM; a loop with no saturation plateau (likening to that of a banana) in P-V measurement was observed. Hence, we observed a chargeable dielectric behaviour in both the characterizations.

Bottom-up assembly, which enables construction of complex architectures from molecular building blocks, is a promising alternative for the fabrication of future electronic devices. DNA and, in particular, DNA origami have made possible the fabrication of complex, self-assembled, molecularly addressable, nanostructured templates. This paper describes the results of our efforts to selectively deposit two different metals on the same DNA origami template as a step towards the fabrication of complete nanoelectronic circuits. The deposition of copper and gold onto pre-designated locations on the template, as verified by both compositional and morphological data, was accomplished to form a heterogeneous Cu-Au junction. Seeding and deposition were performed in sequential steps. An enabling aspect of this work was the use of an organic layer or “chemical mask” to prevent unwanted deposition during deposition of the second metal. The approach demonstrated in this work can be used for site-specific deposition of a much broader set of materials like semiconductors, which are required for circuit fabrication on DNA templates. Continuing efforts seek to optimize the yield, morphology, and electronic properties of multiple metals deposited on DNA origami templates.

DNA is one of the most fascinating materials used in nanoscience today. First, it is a promising molecule for applications in molecular electronics. It was noticed early that the structure of double-stranded DNA (dsDNA) provides a pi-stacking structure that could potentially lead to efficient conduction along the chain. Secondly, DNA has self-assembly properties, and recent advances in DNA origami have demonstrated its utility for creating nanostructured. These properties suggest that it may be possible to design hybrid DNA-based materials with tunable electrical properties. Moreover, DNA is currently used in the diagnosis of many diseases. A clear picture of the electrical conductivity of this molecule could open the doors for the design of diagnostic tools that could be read electronically; improving the sensitivity and reducing costs.
Although results of DNA conductance reported in the literature span a huge range and differ by orders of magnitude, some consensus has been achieved in the charge transport mechanism, being found to be tunneling in short molecules (less than 4bp) and hopping in longer DNA molecules. Besides length, other factors influence DNA conductance. Sequence can modulate conductance, as some bases participate in the charge transport process. The presence of single nucleotide polymorphisms (SNP) has been reported to modulate conductance as well. But, to date, conductance modulation by structure in different DNA forms has not been studied. The B-form typical for dsDNA is a right-handed double helix with an average distance of 0.33 nm per base pair and it has been extensively studied. The A-form is the prototypical structure for dsRNA, but can be induced in dsDNA by dehydration. It is a right-handed helix with a shorter rise per base pair than the B-form (0.23nm/bp).
Herein we report conductance measurements of amino-functionalized short dsDNA molecules using the STM-break junction method. Briefly, a gold STM tip is brought into contact with a gold electrode and then retracted with the molecule present in solution while the current between the electrodes is recorded. This process is repeated thousands of times and results can be used to obtain conductance histograms. We study dsDNA conductance as function of length, sequence and structure. The structure is changed from B-form to A-form by adding ethanol during the experiment.
Results demonstrate that A-form dsDNA is ~10 times more conductive than B-form in GC rich sequences. These results help to rationalize the divergence in conductance results reported in the literature and pave the way for the design of nanodevices based on DNA with tunable structural and electrical properties and sensors that could take profit of this conductance-structure modulation

Emulation of human touch sense via electronic means is of pivotal importance for developing intelligently accessible and natural interfaces between human/environment and machine, which necessitates the development of large-scale pressure sensors array with high spatial-resolution, high-sensitivity and fast response. Using the piezoelectric polarization charges created at metal-semiconductor interface under strain to modulate transport of local charge carriers, piezotronic effect has been applied to design 3D array of independently addressable strain-gated vertical piezotronic transistors (SGVPT) based on vertically aligned ZnO nanowires (NWs), which convert mechanical stimuli applied on the devices into local electronic controlling signals. By combining the patterned in-place bottom-up synthesis of vertically aligned ZnO NWs with state-of-the-art microfabrication, macro-scale integration of SGVPT array with taxel density of 92 × 92 in 1 cm2 has been achieved and parallel manufacturing of SGVPT arrays on 4-inch PET flexible substrates has been presented. The taxel area density of SGVPT array is 8464/cm2, not only enabling a 15-to-25-fold increase in number of taxels and 300-to-1000-fold increase in taxel area density compared to recent reports (~ 6-27/cm2), but also much larger than the number of mechanoreceptors embedded in the human fingertip skins (~ 240/cm2). The fabricated sensors are capable of mapping spatial profiles of small pressure changes (< 10 kPa).
The reliability and stability of device operations have been probed, exhibiting a good stability of SGVPT array operation for future applications like in vivo physiological sensing in complex environments for certain designed time of period. The feasibility of SGVPT array for applications such as self-powered active and adaptive artificial skin has been presented by converting mechanical stimulations into electrical signals without external bias, which emulates the physiological operations of mechanoreceptors in biological entities. This enables real time detection of the device shape change and feeding-back the sensed changes in shape for calibration of other functionalities as well as corresponding control/response performed by the system, which is a desirable feature for sensors embedded in an artificial tissue or prosthetic device. The scalability of this technology in integrating in-place synthesized single-crystalline NWs in controllable manners together with its demonstrated compatibility with state-of-the-art microfabrication techniques enables future implementation of nanomaterials for practical applications in smart skin, prosthetics and novel surgical instruments.
Ref: Wu W. Z.*, Wen X. N.*, Wang Z. L. Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging. Science 340, 952-957, 2013. *Authors with equal contributions

Human pulse, an essential indicator of health conditions, can be found at any point on the body where an artery's pulsation is transmitted to the surface. Here we introduce a cost-effective and highly sensitive flexible accelerometer, which can sense human pulse by detecting the pulsation. Conventionally, accelerometers are fabricated by expensive micro fabrication techniques with rigid substrates like silicon or silicon nitride. In contrast, this work employed a facile fabrication method to generate flexible light-weight accelerometers by direct-printing of silver nano-inks on pre-patterned flexible paper substrates. The accelerometer employs capacitive sensing with a structure of two parallel plate electrodes with the optimally designed top electrode pattern in order to achieve high sensitivity. A double-bridged membrane type top electrode and a simple bottom electrode are defined in pre-patterned paper via spraying of silver nano-inks, followed by thermal annealing at 160 degree celsius. Finally, a readout circuit is designed and integrated with the accelerometers by thin wires to convert capacitance changes to a voltage change signal. When the accelerometer is attached to the body surfaces: neck, inner elbow, or any other pulsation point, a continuous pulse wave is obtained which shows accurate pulse rate and amplitude by reading out the voltage output signal.
Reference
Y. Zhang, T. Lei, and W.S. Kim*, “Design-optimized Membrane-based Flexible Paper Accelerometer with Silver Nano Ink” Applied Physics Letters 103, pp.073304 (2013).

Recording neural electrodes capture the electrical activity generated by neurons. To obtain long-term reliable signals, the electrode must be biocompatible, and have stable electrical properties; micro-size electrodes are needed in order to have higher spatial selectivity. As the electrode size goes down, initial electrode impedance increases and therefore, sensitivity and quality of signal decreases. Hence, several strategies have been conducted to modulate a tradeoff between the size (spatial selectivity) and quality of signal recordings (sensitivity) in neural electrodes. However still having devices with sufficient electrical properties is a challenge. Bioelectric signals in physiological environments are in the form of ionic currents. In order to process these biological signals, neural electrode transduces them to the electronic from. Conducting polymers (CPs) have been extensively used for biomedical applications; in particular, for neural interfaces due to their unique characteristics, such as biocompatibility, both ionic and electrical conductivity and response to electrical stimulation.
Here we report a novel method for fabrication of conducting polymer microspherical cups (CPMSCs) for improvement of electrical properties and on-demand drug release. The fabrication process involves electrospraying of biodegradable poly (lactic-co-glycolic acid) (PLGA) microspheres on a gold substrate, followed by electrochemical polymerization of conductive polymers poly (3,4-ethylenedioxythiophene) (PEDOT) on the gold substrate and around the PLGA microspheres. We can control the diameter of the PLGA microspheres by controlling the electrospraying parameters such as polymer concentration, flow rate and voltage. The diameters of the microspheres range from 3±2mu;m, and wall thickness of the PEDOT spherical cups varies from 50-100nm. By changing the polymerization time, we can reproducibly control the opening size of the CPMSCs and create either fully coated PEDOT (sphere) or partially coated PEDOT (spherical cup). Fabrication of CPMSCs on the surface of electrodes will provide an extremely low impedance and high charge transfer capacity recording electrode due to extremely high effective surface area of CPs. These results demonstrate superiority of CPMSCs for neural recordings and stimulations whereas the low-impedance electrode tissue interface is essential.
As future study we envision the extension of the CPMSC system reported here as a controlled drug delivery system by incorporation anti-neoplastic agents during electrospraying process. We anticipate that drug can be released from CPMSCs in a controlled fashion by actuation of CP during electrical stimulation (~1V). This system holds considerable promise for simultaneously detection and targeted and controlled release systems. By employing a targeted release method, drug release rate can be tailored to the need of a specific application, while reducing side effects and improving patient compliance.

An increasing number of visceral organs and associated disease conditions have been demonstrated to be under neural control. Precision electrical modulation of neural signalling patterns has the potential to provide therapeutic benefit in a host of chronic diseases such as diabetes, asthma, hypertension, arthritis and even cancer. The bioengineering demands of creating “bioelectronics medicines” centred on neural interfaces are considerable. Such devices require advanced geometries and materials, which will enable miniaturized electrodes to interface with peripheral nerves anywhere in the viscera. The interfaces must be compliant and malleable to conform to visceral nerve anatomies including plexi, and have high-density geometries able to target specific fibre subsets including fascicles. Ideally, they would be able to perform controlled nerve re-configuration, re-shaping, or opening to limit the long-term penetration damage and must have a high signal to noise ratio which should experience minimal change over a period of several months. Spatial resolution should target single axon level interrogation and may require conductive materials and coatings to improve charge injection density. Implantable device electronics should be able to read and write the full complexity of the signalling pattern within the nerve; and smart enough to operate in a closed loop fashion, regulating organ function in response to therapeutic signatures. This presentation will outline research efforts and several funding opportunities being provided by GSK for the development of such neural interfaces.

In electronic circuits as well as in the cell systems of mammalians signals are processed, amplified and distributed utilising complex pathways and various discrete components. In electronics, those are represented by electrically conducting networks, resistors, diodes and transistors. In biology, nerves and the vascular network together with the axons, glands, the synaptic terminals etc represent the circuit system. Here, we report ionic conductors, resistors, diodes and transistors that together represent a chemical circuit technology that enable translation of electronic addressing signals into delivery of complex chemical signals and gradients. The chemical circuit technology is built up from solid-state anionic and cationic polyelectrolytes combined with conjugated polymers. We report the characteristics of ionic resistors and conductors together with the principle of operation of ion bipolar junction transistors and diodes. Further, an array of different chemical circuit systems has been built, aiming for complex regulation of biology, at high chemical and spatiotemporal resolution. The performance and application of those circuits in cell biology and therapy experiments are reported, as well.

Bioelectronic medicine has numerous promising applications for the treatment of diseases and disorders of the nervous system, but also many challenges. Two of the key limiting factors to the development of next-generation neural interfaces are the low charge transfer area and poor neural tissue integration of conventional metallic electrodes [1, 2]. The “synaptic electrode" concept draws upon knowledge from both implantable neurostimulator and bioelectrode research, and combines it with the principles of tissue engineering. The basis of this technology is a conductive hydrogel (CH) which provides a new approach to tailoring the neural interface by decreasing the strain mismatch while providing a conductive path within a soft, deformable hydrogel matrix [3]. A typical CH consists of a biosynthetic hydrogel integrated with a CP, such as poly(ethylene dioxythiophene) (PEDOT). The hydrogel is a co-polymer of poly(vinyl alcohol) (PVA) and a modified biological molecule. Varying the type of biomolecule has allowed the properties of the CH to be tailored such that specific cells will interact with the electrode coating. CH efficacy and safety has been demonstrated in vivo, with reduced scar tissue compared to conventional platinum interfaces. The “synaptic electrode” construct is produced by the addition of a degradable PVA layer overlying the CH, in which cells can be encapsulated. This hydrogel layer provides both the ability to encapsulate cells within the electrode and simultaneously deliver therapeutic agents to promote regeneration or directed growth of neurons. Specifically, co-cultures of neurons and supporting glia have been embedded in the electrode coating, and found to survive and differentiate to produce active neural processes. The neural networks grown within the hydrogel matrix are excitable at lower thresholds than typical neural tissue at the implant interface. It is expected that integration of this bioelectrode into neural tissue will create a “synaptic electrode” to directly interact with excitable target tissue. These studies provide evidence that next-generation electrode arrays can be developed to safely deliver stimulus and accurately record from high density electrode arrays using natural synaptic processes. These bioactive neural interfaces create a technology platform which can be tailored for bioelectronic applications such as functional electrical stimulation (FES), nerve guides, bionic ear and eye devices and deep brain stimulators.
References
1. Ludwig, K.A., et al., Chronic neural recordings using silicon microelectrode arrays electrochemically deposited with poly(3,4-ethylenedioxythiophene) (PEDOT) film. J Neural Eng, 2006. 3: p. 59-70.
2. Green, R.A., et al., Conducting polymers for neural interfaces: Challenges in developing an effective long-term implant. Biomaterials, 2008. 29: p. 3393-9.
3. Green, R.A., et al., Conductive hydrogels: Mechanically robust hybrids for use as biomaterials. Macromol Biosci, 2012. 12.

Biocompatible materials capable of conducting electricity have numerous biomedical applications including use as electrodes for neurological stimulation and recording, tissue engineering, artificial muscles, and stimuli-responsive actuators or sensors. Therefore, we are developing new ‘soft&’, flexible, polymer-based electrode materials that can be integrated into biological tissues with minimal damage to the host. To this end, we have synthesized composite materials composed of the polypeptide silk fibroin (for mechanical strength, flexibility, biocompatibility) and poly(pyrrole) or poly(3,4-ethylenedioxythiophene) (conducting polymers for electrical interfacing). Covalent attachment of negatively charged, hydrophilic sulfonic acid groups to the silk protein can selectively promote pyrrole absorption and polymerization within the modified films to form a conductive, interpenetrating network of polypyrrole and silk that is incapable of delamination. Using this strategy, we are able to produce silk-based ‘electrodes&’ with various architectures including fibers, 2D films, 3D porous sponges and hydrogels. In addition, we have found that specially designed silk-polypyrrole composites can function as electromechanical bending actuators, which show immense promise for the development of implantable valves or drug delivery devices.

Nanostructured forms of carbon have extraordinary mechanical and electrical properties.
The fact that carbon is considered inherently biocompatible means that these more recently discovered forms have attracted the attention of those of us interested in the development of more effective electromaterials for medical bionics.
A number of different carbon nanotube based electromaterial platforms have been shown to provide effective electrical communication with both nerve and muscle cells. These advances will be presented here.
More recently a structure consisting of graphene layers deposited on a biopolymer substrate has proven to be effective in nerve cell communication. A striking feature of this electrode structure is that the very thein layer of (bilayer) graphene used has minimal effective on the mechanical properties of the underlying biopolymer yet provides sufficient electronic conductivity for electrical stimulation of nerve cells.

Nerve defect in both central and peripheral nervous system is a major health problem. Spontaneous axonal regeneration is only applicable to small lesions within the injured peripheral nervous system and is suppressed within the central nervous system. Axons can be guided along specific pathways by gradients of attractive and repulsive chemical and physical cues. However, the molecular mechanism of action of such gradients is poorly understood. To understand the effect of gradients of guidance cues individually or in combination on growth cone turning and growth rate modulation, the development of platforms that are capable of producing precisely controlled shape gradients of different guidance cues is essential. Conducting polymers have been widely reported in biomedical field especially for drug delivery systems and neural interfaces. Conducting polymers have the ability to response to electrochemical redox reaction by changing their color, conductivity, wettability, and volume. Previously we developed a novel method for fabrication of randomly oriented conducting polymer nanotubes for controlled release of an anti-inflammatory drug. We hypothesize that the aligned conducting polymer nanotubes will provide both physical and chemical guidance cues for axonal regeneration.
Here we report a novel method for fabrication of multifunctional aligned conducting polymer nanotubes for axonal regeneration. We successfully incorporated nerve growth factor (NGF) into poly (3, 4-ethylenedioxythiophene) (PEDOT) nanotubes using a templaing method. Electrochemical deposition of PEDOT was carried out by an applied current density of 0.5 mA/cm2. We characterized surface morphology and electrical properties of the NGF-loaded PEDOT nanotubes by using scanning electron microscopy and impedance spectroscopy, respectively. The diameter and wall thickness of PEDOT nanotubes were 100 ± 23 nm and 30 ± 5 nm, respectively. The impedance of substrates decreased about two orders of magnitudes after electrodeposition of PEDOT nanotubes. In order to release the NGF from PEDOT nanotubes in a controlled fashion, we actuated PEDOT nanotubes by applying a bias voltage 1 V for 5 times at three specific time points of 170, 360, and 600 hr. Preliminary results showed that NGF was precisely release (~65ng/ml) from PEDOT nanotubes after electrical actuation. To evaluate the biocompatibility of aligned PEDOT nanotubes, primary dorsal root ganglion (DRG) explants and PC12 cells from rats were cultured on the substrates. PEDOT nanotubes supported neurite outgrowth from the ganglia in the direction of the nanotubes In Future, we will design a multifunctional conduit using aligned PEDOT-NGF nanotubes and we will examine the rate of axonal regeneration nerve gap in rats.

Organic electrochemical transistors (OECTs) have been targeted for a variety of in vitro and in vivo diagnostic applications owing largely to their efficient transduction of ionic to electronic signals. In these devices, the transistor drain current is modulated by de-doping of the PEDOT:PSS {poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate)} channel due to local variations of ion flux induced by, for example, neural activity. Owing to the efficient ion mobility and high capacitance in hydrated PEDOT:PSS, we are able to fabricate devices with high intrinsic amplification (transconductance), and when scaled to micron dimensions, broad-band response up to 10 kHz. Along with facile and robust/conformal fabrication schemes, these devices show great promise for a number of neuroscience applications. By studying film morphology and by systematically varying OECT device geometry, we develop a fundamental understanding of device operation and establish design rules for practical implementation of OECTs in vitro and in vivo, for both research and clinical applications. Considering the recording capabilities of common measurement techniques, and the nature (amplitude, frequency) of neural signals, we describe how a tradeoff between OECT device response time and transconductance can be navigated. With this scheme, we demonstrate the use of OECTs to record low amplitude, low frequency neural oscillations, high amplitude epileptiform activity, and show that measurements of individual action potentials are within reach. Thus, these devices can be tailored for various applications depending on the desired or required content of neural signals.

The long-term performance of introcortical neural probes is often complicated by a foreign body reaction that consists of accumulation of microglia, neuronal apoptosis and an insulating glial sheath around the implants. This extensive gliosis has been associated with the system impedance increase and signal deterioration and loss of the devices. Previously we have proposed that the in vivo polymerization of a conducting polymer, poly (3,4 ethylene dioxythiophene) (PEDOT), in living tissue may help to build a conducting pathway between the retreated neurons and the probe. The EDOT monomer can be infused into the tissue with a microcannula/electrode guide followed by electrochemical polymerization under the oxidative current through the electrodes. Here we examined the effects of this in vivo method by polymerizing PEDOT in living rat hippocampus at different time points post initial device implantation. We found that the system impedance was decreased for all the groups regardless of scarring stage. However, there seemed to be an optimal time window for sustained impedance improvement. The tissue responses to the polymer were examined with immunohistology. We also investigated the effects of polymerization on local neural function with a hippocampus-dependent behavior test, delayed alternation (DA). Compared to the control groups, in vivo polymerization did not cause significant deficit on the hippocampal function.

The material-tissue interface of a neuroprosthetic device determines its performance in chronic applications. Various pathways in the foreign body reaction might deteriorate both, the material and transducer properties of the implanted devices and the activity of the neuronal cells. Therefore, target specifications for implantable neuroprosthetic interfaces include not only electrical, chemical and mechanical stability and integrity of the material itself and the device but also an adequate reaction of the target tissue, i.e. little encapsulation by fibrotic or gliotic tissue and stable bidirectional transmission properties of sensors and actuators. Electrical nerve activity can be either recorded or stimulated by electrodes while optical interaction has been recently introduced by optogenetics, i.e. the optical activation of genetically modified nerve cells. Chemical monitoring and drug application is also feasible as diagnostic or therapeutic modality or as additional feature to modulate the foreign body reaction after implantation.
The essential requirements of materials are identical for many applications and implantation sites in neuroprosthetic interfaces but the design varies a lot. We present the performance of polyimide as relatively new substrate and insulation material for neural interfaces and discuss designs for applications in the peripheral and central nervous system. We assessed adhesion properties of polyimide-metal sandwiches in the devices as well as the electrical and electrochemical properties of the electrode-electrolyte interface in vitro and in vivo. Electrode coatings with valence change materials like iridium oxide or proton conductors like polyethylenedioxythiophene (PEDOT) increase the ability to reversely inject large amounts of charge and reduce the impedance during recoding. PEDOT also allows the incorporation, storage and release of drugs for chemical interaction with cells close to the electrodes. Electrode arrays for epi- and intracortical implantation for fundamental neuroscientific studies will be introduced as examples of central nervous system interfaces. Translational research has been done on peripheral nerve interfaces to treat phantom limb pain after amputation with an intrafascicular electrode array. We present the development of these devices from design studies to human implantation.
Silicone rubber (polydimethylsilosane: PDMS) is an established material in implant technology. Using precision mechanics as manufacturing technology limits the degree of miniaturization and integration density of neuroprosthetic implants. Micromachining by laser-structuring overcomes these limitations and allows electrode arrays with a high channel count for relatively fast transfer from bench to bedside in translational research. Design and development of electrode arrays for recordings from the brain surface (electrocorticograms: ECoG) are presented to discuss advantages and limitations of this approach.

Electronic devices that interface with living tissue have become medically important to improve diagnosis and treatments. On a more fundamental level, most breakthroughs in our understanding of the basic mechanisms of information processing in the brain have been obtained by means of recordings from implantable electrodes. There is a tremendous need for developing advanced materials solutions for the biotic/abiotic interface. Here, we demonstrate the use of a high-density conducting polymer based electrode arrays for acquiring neuronal activity at single neuron resolution from the surface of the brain in freely moving rats.

The surface probe consists of 4 mu;m thick Parylene C that contains 256 electrodes covered by the conducting polymer poly (3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) using a generic lithographic process. The electrodes are arranged on a hexagonal lattice, with individual electrodes having an area of 12 mu;m x 12 mu;m and a center-to-center distance of 20 mu;m. This particular design provides a fine surface map of the electrical activity in a brain region of interest, while also generating unprecedented single cell resolution without penetrating the brain.
Multi/single unit activities were successfully recorded from the surface of the somatosensory cortex. The surface spikes were clustered and isolated; the origin of the spikes was verified by simultaneously recording neurons with the movable tetrodes and silicon probes across all cortical layers. Numerous neurons, recorded from the superficial cortical layers, had a spatially unique distribution of action potential amplitude and morphology on the surface probe recording.
These findings establish a method of recording individual neuronal firing activity from the surface of the brain. This new class of biocompatible, highly conformable devices allows for non-invasive recording of brain activity with superior spatial and temporal resolution, holding great promise for various medical applications.

Long-term high fidelity performance for implanted neuroprosthetic devices remains an unmet challenge. Reduced electrode recording performance can be associated with brain cell responses to the implanted devices. We are (i) performing cell-resolution analysis of these responses in order to develop a critical knowledge base of the critical biological events associated with reduced electrode performance and (ii) using this new knowledge to develop necessary changes in device design, surface chemistry, and local drug delivery to mitigate the reactive cell responses. Critical criteria include the disruption of cell-to-cell interaction and communication by the presence of the device, modified surface chemistries to prevent protein and cell attachment, control of inflammatory responses by local delivery of anti-inflammatory agents or neurotrophic factors. Analysis of tissue responses around conventional silicon- and polymer-based devices have lead to the development of open-architecture devices that do disrupt cell-to-cell interactions. Improvement of biocompatibility is being tested using novel initiated chemical deposition of silicone on 4x4 “Utah” arrays. Local drug delivery is being tested using microfluidics and diffusion release. Independently, each of these procedures has an impact on brain cell responses that are being measured using 3D, multispectral imaging and FARSIGHT image analysis. Results from these studies are providing critical biological and engineering data to develop a generation of implantable neural prosthetics that will provide long-term high fidelity electrode recording performance.

Commercial retinal prostheses have 60 electrode contacts that can act as pixels to create an image. Blind patients with implants show improved vision, but there is a fundamental limit to the visual improvement due to the pixel count and electrode array size, which does not extend into the peripheral retina. Better materials are needed for a high resolution stimulator system with smaller electrode contacts covering a wider area of the retina. Below is a summary of recent materials research in our lab towards a high resolution retinal prosthesis.
Hermetic packaging for retinal prostheses should not increase implant size and must have hundreds of hermetic vias for a high resolution electrode array. Progress has been made on 3 key packaging technologies: 1) multilayer, multi-material films that have improved barrier properties to contaminants and can be deposited conformally on 3D structures, 2) integrated sensors capable of detecting contaminants, to serve both as tests of coating hermeticity and as an early warning system to predict implant failure, 3) a high-density hermetic feedthrough.
Electrodes must be modified to interface with more of the retina, in particular the peripheral regions. However, electrode size is limited by surgical considerations, which mandate eyewall incisions less than 5 mm. We have developed a hybrid silicone/polyimide electrode array with a 10 mm diameter. The inclusion of silicone around the implant edges enables better protection of the retina during the implant procedure and reduces mechanical mismatch between the implant and the surrounding retinal tissue after implantation. A 12.5 mm wide silicone substrate was molded into 3D contour with the same curvature of canine eyes measured by ultrasound imaging, which could precisely conform to the back of the eye. Attached to the silicon was the 10mm wide thermoformed flexible polyimide electrode array with 36 electrodes on central part and 24 electrodes on two peripheral arms, to allow rolling of the device for implantation through small incision. Devices were successfully tested in long-term implant experiments.
High resolution stimulation of the retina will require small electrode contacts, to create smaller pixels. The electrode material will need to safely apply a high charge density, while maintaining stable electrical properties. A platinum-iridium alloy can applied to electrodes using an electrodeposition process. The resulting material has a significantly higher charge density limit than platinum (6 mC/sq-cm vs. 0.35 mC/sq-cm for platinum). This material has shown stability during long-term stimulation, even on microfabricated electrodes, which often fail under continuous stimulation due to the poor quality of sputtered metal electrodes.
Significant progress has been made on advanced materials for high-resolution retinal prostheses. These materials and processes now must be integrated into systems for long-term testing.

Interfacing biological systems with electronic components augments the possibility of repairing and restoring various physiological processes. Conjugated polymers have been interfaced with biological sensory systems for modulation of cochlear function and recording of brain activity. In this study, we highlight the efficacy of polymer semiconductors as artificial receptors for interfacing with the visual systems.[1]
We demonstrate the use of optoelectronic properties of polymer semiconductor films to stimulate and evoke neuronal activity in a blind retina. We have utilized the photoinduced charge carrier generation in bulk heterojunction (BHJ) polymer films to drive neuronal activity in a chick retina at a light-insensitive stage of development. The method involves coating the photoactive BHJ layer, constituting a thiophene-based donor and naphthalene-based acceptor, on a multielectrode array for stimulating the retina epiretinally and recording its electrophysiological activity simultaneously. Our approach utilizes the polarity, dynamics and magnitude of the photoinduced surface potential of the BHJ layer in contact with the buffer medium for eliciting neuronal signals in the blind retina. We further show that the retinal activity (e.g. latency, spike rate and spike number) follows the optoelectronic response of the polymer film, and depends on incident light parameters such as intensity, pulse width, rate and spatial profile.[1]
The soft and biocompatible optoelectronic polymer interface presented here can provide visual intensity dependent encoded cues to a blind retina at moderate light levels. The BHJ based stimulating platform is solution processable, biocompatible, water-stable and does not require any external power sources or connection cables. An important outcome of our technique is that an optoelectronic epiretinal interface without any power sources simulates the natural retinal activity. Our system has striking advantages over the conventional methodologies of retinal stimulation reported earlier and can be used as a viable platform for future retinal implants. The ongoing studies involve dissociated retinal cell culture on certain BHJ polymer films under illumination and are directed towards studying the neuronal growth patterns on these platforms. Some of these recent results will also be discussed.
[1] A polymer optoelectronic interface provides visual cues to a blind retina.
Vini Gautam, David Rand, Yael Hanein, K.S. Narayan.
Advanced Materials (2013) Accepted.

We have developed novel process for micropatterning electrodes on hydrogel substrates to provide a flexible, stretchable and molecular permeable electrode for low-invasive stimulation and recording of cellular functions. Electropolymerized poly (3,4-ethylenedioxythiophene) (PEDOT) serves as the anchor for bonding the electrodes, including a highly stretchable conducting polyurethane, to the hydrogel substrates such as polyacrylamide, agarose, collagen etc. The prepared soft hydrogel-based electrode can be directly laminated to cells and tissues, and the continuous post-cultivation with the laminated electrode substrate was also possible owing to their molecular permeability.
The process starts with the micropatterning of electrodes on a glass plate. After forming or laminating hydrogels onto the microelectrode substrate, PEDOT was electropolymerized in order to bond the electrode patterns to the hydrogel matrix [1,2]. The Au microelectrodes bonded to the hydrogel by PEDOT were peeled from the glass substrate, and stored in water.
Such a moist, permeable and flexible electrode should have many unique applications such as an in-vivo lapping electrode and in-vitro cell cultivation. As an example, we can demonstrate the advantage of the present electrode for the electrical stimulation of myotubes that is required for research on type2 diabetes [3]. The other possible application is electroporation for molecular delivery by direct lamination of the gel-based electrodes to adherent cells and tissues. We succeeded in the electroporation-assisted uptakes of dye molecules and genes for normal human dermal fibroblast cells and human iPS cells.
Relating publications
[1] “Conducting Polymer Electrodes Printed on Hydrogel”
S. Sekine et al., J. Am. Chem. Soc., 2010, 132, 13174.
[2] “Conducting Polymer Microelectrodes Anchored to Hydrogel Films”
Y. Ido et al., ACS Macro Lett., 2010, 1, 400.
[3] “Spatiotemporally Controlled Contraction of Micropatterned Skeletal Muscle Cells on a Hydrogel Sheet”
K. Nagamine et al., Lab Chip, 2011, 11, 513.

Organic electroactive materials, currently used to produce devices such as
organic light-emitting diodes, transistors and photovoltaic cells, have
recently been introduced in bioelectronics, where electronic signals are
translated into biological signals. An example of an organic bioelectronic
device is the organic electrochemical transistor (OECT). OECTs have been
investigated in the last decade as sensors for hydrogen peroxide, glucose,
dopamine and cells as well as tools to investigate ionic transport in
conducting polymers. OECTs consist of an organic channel (a thin film of a
conducting polymer) in an ionic contact with a gate electrode accessed via
an electrolyte solution. Typically, a positive potential is applied at the
gate electrode, which causes cations from the electrolyte to enter the
conducting polymer film and dedope it, resulting in a switch from an
oxidized to a reduced state and a decrease of electrical conductivity.
Research objectives
The oxidation state of a conducting polymer changes gradually along the
channel of an OECT, thus permitting fine tuning of the reactivity of the
polymer surface with biological species such as proteins. This offers an
opportunity to create surfaces where protein immobilization can be
electrically controlled.
In order to chemically immobilize proteins (i.e. via chemical bonds) on the conducting polymer surface of an OECT channel we have found a strategy to introduce carboxylic groups in the bulk and at the surface of conducting polymers. Chemical immobilization of proteins ensures that fully bioactive proteins (e.g. growth factors) will be exposed in an
oriented fashion, which has been shown to drastically affect cell response
(proliferation, differentiation) compared to commonly employed random
grafting. Since the reactivity between the capture system and the conducting polymer depends on the polymer oxidation state, the density of immobilized proteins can be tuned
along the OECTs surface.
This work will have a major impact in the field of biomedical sciences since the proposed device may guide future development of protein-enhanced biomaterials interfaces such as those of corneal and vascular implants.

Advances in tissue engineering, prosthetics, and regenerative medicine require the development of biomaterials that promote specific cellular responses. Current research is directed toward generating substrates and scaffolds that influence cell adhesion, growth, and organization. For example, cells may be recruited to an implanted material in order to improve its physical integration into a surgical site, to improve its biocompatibility, as for the patency of a vascular graft, or to attract and direct other cell types, as for nerve regeneration. Cells normally reside and interact in local environments with distinct and organized micro- and nano-topography, provided in part by the cells that surround them. Cells respond to topographical features, and these features can influence many important cellular functions. Studies suggest that material substrates with nanometer- and micron-scale surface features can increase cell adhesion, migration, and process extension, as compared to substrates with smooth surfaces.
In the case of the nervous system, successful nerve regeneration requires directed nerve growth. Axon guidance is elicited by a variety of cues in the neural environment and is critical to establish precise connections post-injury. After injury, sprouting axons navigate on top of Schwann cells, support cells in the peripheral nervous system, to extend across the lesion and find their final targets. When peripheral nerve regeneration is achieved in vivo, it is largely due to the endogenous growth-promoting environment provided by Schwann cells that includes a growth-promoting molecular milieu and the directional influence of the oriented Schwann cells themselves.
Until recently, the difficulty in reproducing the complex shapes of cells without including a mixture of molecular components has left the influence of cellular topography largely unexplored. We have developed biomimetic materials that replicate the micro- and nanoscale topography of Schwann cells. Further, we have developed Schwann cell-inspired geometric biomaterials via CAD design to analyze which topographical features encode critical guidance information to navigating neurites. Neurites have exhibited directed growth in response to both types of biomaterials, with distinct contributions from the topographical features of Schwann cell somas and cellular processes. This talk will discuss these materials, the contribution of cellular topography as an independent factor in cell growth, and in particular, the role of Schwann cell topography in axon guidance.

Motivation: Over the last thirty years proof of concept laboratory experiments have shown that neuroprosthetic devices could substantially reduce the burden of numerous neurological disorders. Unfortunately, relatively few neuroprosthetics have been taken beyond laboratory experiments, and even fewer have progressed beyond "first in human" feasibility studies to provide meaningful, long-term improvements in patient quality of life. Similarly, many biomaterials that have demonstrated great promise to improve the neural interface for prosthetics have yet to have substantial clinical impact.
Talk Overview: Dr. Kip Ludwig is the head of the Advanced Neural Prosthetics Program at the National Institute for Neurological Disorders and Stroke, has Industry experience developing manufacturing processes for biomaterial coatings to improve electrode performance in a market-approved implantable neuroprosthetic, and has conducted Good Laboratory Practice studies to enable successful clinical trials for these devices in both Europe and the United States. Drawing from these experiences he will provide a brief history of the clinical data supporting the efficacy of biomaterials to improve the electrode-tissue interface, and will discuss recent advances in the field in the context of steps necessary to achieve clinical impact. Finally, he will outline common reviewer concerns regarding grant applications in this area submitted to the National Institutes of Health.

The current technology used to probe neuronal network function relies on invasive brain penetrating devices that cause tissue damage and reduce the neural signaling quality. The use of soft, polymeric materials provides better matching of mechanical properties brain tissue. It is therefore necessary to develop new technologies that use biocompatible and multifunctional micropatterned arrays that are capable of high quality recordings of neural signals as well as stimulation, with minimal injury to the brain. We develop protocols for fabrication of devices from soft materials capable of micron scale electrical recording from inside of the brain. We demonstrate that these implants show a good biocompatibility and a high mechanical flexibility. Based on the immunological response in the brain the probes represent a promising avenue to increase the quality and duration of neuronal signaling in chronic experiments. The development of flexible probes represents a significant engineering advancement toward long term studies of in vivo physiological and pathological neural activity.

For biomedical devices, active areas are increasingly being coated or functionalized with biomolecules to improve biocompatibility and facilitate integration with living systems for both in vitro and in vivo applications. To achieve longer lifetime devices and controllable functionalization, covalent immobilization techniques are preferred over passive adhesion and electrostatic interactions. The rapidly emerging field of organic bioelectronics uses conducting polymers (or small molecules), as the active materials for transduction of the biological signal to an electronic one. The polythiophene PEDOT doped with the water dispersible polystyrene sulfonate (PSS) or with the tosylate anion (TOS) is currently the most commonly used conducting polymer in organic bioelectronic applications. This is due to a combination of factors including good thermal, and electrochemical stability, relatively high conductivity, and demonstrated biocompatibility, compared with other CPs. PEDOT based CPs have been widely used in neural prosthetic applications. In this talk I will focus on a number of different biofunctionalisation techniques used to attach biomolecules to these CPs with a view to improving the biotic/abiotic interface, for applications both in vivo and in vitro. The driving force of these studies is the being able to maintain not only the function of the biological molecule but also to ensure that the electronic/ionic properties of the CPs are unaltered. The use of biofunctionalised CP devices to generate a comprehensive in vitro model of communication between the blood brain barrier and underlying neurons will also be discussed.

Fibrous scar tissue and fluid encapsulation of chronically implanted Cochlear electrodes is often a result of insertion trauma and poor electrode/tissue integration, which adds a layer of electrical resistance between the device and the target neural tissue. Conductive polymer/hydrogel hybrids or conductive hydrogels (CHs) are an emerging technology that demonstrate great potential as coatings for chronically implanted neural electrodes [1]. In vitro studies performed by Green et al. on CH coated Pt substrates have shown CHs increased neural cell attachment and growth compared to bare Pt and homogenous PVA gel coatings similar to those reported in literature [1, 2]. CH coatings also improved interfacial electrical properties, increasing the charge storage capacity (CSC) of the Pt substrate by 37% [1]. To determine the feasibility of these materials as coatings for neural implants, CH coatings were applied to Nucleus® Contour Advance TM Cochlear electrode arrays. Electrical testing undertaken in this study demonstrated that CH coatings significantly improved the electrical performance of the array including up to 24 times increase in charge injection limit. Reduced impedance was also maintained for over 1 billion stimulations without evidence of delamination or degradation. Mechanical studies were performed to determine the effect of the coating on the pre-curl structure of the Contour Advance arrays. The CH coating did not hinder the curl of the electrode and model human scala tympani were used to confirm that adequate contact was maintained across the lateral wall. Additionally, CH coated platinum pins were implanted for up to 12 weeks in paravertebral muscles of the rabbit. Minimal fibrous encapsulation was observed in vivo at 12 weeks with no significant difference compared with platinum controls. The coating integrity was preserved with no delamination for the duration of the study. CH coatings are a viable, stable coating for improving electrical properties of the platinum arrays while imparting a softer material interface to reduce mechanical mismatch.
1. Green, R.A., et al., Conductive hydrogels: Mechanically robust hybrids for use as biomaterials. Macromol Biosci, 2012. 12(4): p. 494-501.
2. Green, R.A., et al., Conducting polymer-hydrogels for medical electrode applications. Science and Technology of Advanced Materials, 2010. 11: p. 014107.

Organic materials have significant potential for bio-functional neural interfacing given that their “soft” nature offers better mechanical compatibility with the nerve tissues than conventional semiconductors, and their flexibility allows realization of the non-planar forms typically required for biomedical implants. The integration of living cells into organic semiconductors is an important step towards the development of bio-organic electronic transducers of cellular activity from neurons. Moreover, an improved capacitive coupling between organic-functionalized interface and neurons is demonstrated in sensing devices, leading to a large transconductance and high device sensitivity at low voltages.
In this respect, we recently demonstrated an organic transistor structure (O-CST) based on the ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) n-type organic semiconductor provides bidirectional stimulation and recording of dorsal root ganglion primary neurons with a signal-to-noise ratio exceeding that of standard microelectrode array systems [1].
It is self-evident that a clear understanding at the micorscopic level of the functional and structural properties of device active-layer interfacing with the cell culture environment is crucial for the development of a device platform suitable for stimulation and recording of neural cells in vitro and for the therapeutic electrical stimulation in vivo.
Here, we report on a detailed physical-chemical characterization of n-type perylene-derivative implemented as active layer in the O-CST device in order to demonstrate its suitability as interface platform for organic neuroelectronic devices [2]. Notably, the morphological, structural and photophysical features of P13 thin-films do not change significantly upon exposure to the cell-culture media. It is noteworthy that the field-effect transistors preserve their electrical characteristics even after 10 days of incubation in cell culture media. Finally, we report on a impedance spectroscopy study performed onto O-CST device platform aimed at optimizing the device sensing performance by means of device architecture engineering (i.e. layer thickness, materials implemented electrode geometry). Indeed, it is generally known that the ability to record action potentials from individual neurons is dependent on a trade-off between the geometric area of the recording site and the site impedance, often referred to as the trade-off between selectivity and sensitivity.
Thus, the cross-correlation of different electrical, spectroscopic, and morphological investigation techniques coupled to cell-viability and electrophysiology tools allows us to validate n-type perylene derivatives as a suitable long-term interface platform for organic neuroelectronic devices.
[1] Benfenati V., et al. Nature Mat., 2013, 12, 672-680.
[2] Toffanin S., et al. J. Mater. Chem. B, 2013, 1, 3850-3859.

With its high conductivity, tunable surface morphology, relatively “soft” mechanical response, high chemical stability and excellent biocompatibility, poly(3,4-ethylenedioxythiophene) (PEDOT) has become a promising conjugated polymer coating material for biomedical device electrodes. However some applications are still challenged by its relatively poor adhesion between with conducting inorganic solid substrates. Here, we report the use of 2,3-dihydrothieno[3,4-b][1,4]dioxine-2-carboxylic acid (EDOT-acid) as an adhesion promoter to improve the adhesion between PEDOT thin films and oxidized metal electrodes. The adsorption of EDOT-acid onto electrode surfaces was characterized by Fourier Transform Infrared spectroscopy (FTIR), contact angle measurements, and X-ray photoelectron spectroscopy (XPS). PEDOT thin films were electrochemically deposited onto both EDOT-acid modified and unmodified electrodes. The electrical properties of these thin films were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Sonication tests confirmed the significantly improved adhesion and mechanical stability of the PEDOT films on electrodes with EDOT-acid treatment than those without treatment.

Conducting polymer coatings are of considerable interest for use in neural electrode applications because of their electronic and ionic conductivity, relatively “soft” mechanical properties, and large effective surface area (resulting in low impedances). However, the mechanical delamination and cracking of the polymer films after extended implantation in dynamic environments still pose challenges for chronic applications. Here we report the use of conjugated chemical crosslinkers, including 1,3,5-tris[2-(3,4-ethylenedioxythienyl)]-benzene (3-EDOT), as comonomers to improve the mechanical integrity of PEDOT-based films. The charge transport properties and stability of the copolymer films were examined with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The morphology of the films were studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The biocompatibility of the film was studied with in vitro cell cultures. The mechanical properties and the failure mechanisms were also investigated. This cross-linked PEDOT is expected to improve the stability and reliability of coatings for neural implants.

Neuronal and axonal guidance strategies are being pursued with the ultimate goal of creating biomimetic tissues in vitro. To this end, we have designed 3D hydrogel matrices of chitosan, agarose or crosslinked hyaluronan and then modified these with cell-adhesive peptides and growth factor concentration gradients. For example, axons have been guided on nerve growth factor concentration gradients immobilized on chitosan matrices, demonstrating that NGFdoes not have to be taken up by axons in order to signal axonal guidance. Growth factor concentration gradients have been immobilized in agarose hydrogels using Ti/sapphire, multiphoton laser patterning and photochemistry and shown to guide neural stem cell growth. Interestingly, gradients of immobilized vascular endothelial growth factor (VEGF) guide endothelial cells, which in turn guide retinal stem cell growth. Together, these studies demonstrate the importance of growth factor concentration gradients and other cells to neural cell guidance.

Many neurological disorders are characterized by inhibited/amplified neural activity in a particular region of the nervous system or lack of communication between the two regions. Current approaches to treatment of these disorders are often based on drugs with undesirable side effects and limited terms of effectiveness, or on mechanically invasive and bulky electronic devices. Consequently, there is a pressing need for biocompatible materials and devices allowing for precise minimally invasive manipulation and monitoring of neural activity.
In my presentation I will outline two complimentary materials approaches to neural stimulation and recording that we are pursuing: (1) Flexible polymer and hybrid optoelectronic devices for intimate neural interfaces; (2) Magnetic nanomaterials for minimally invasive manipulation of neural activity. I will illustrate how a fabrication process inspired by optical fiber production allows to create flexible multifunctional probes capable of optical, electronic and pharmacological interfaces with neural tissues in vivo. I will then demonstrate how these fiber-inspired neural probes (FINPs) can be tailored to applications within a specific part of nervous system such as the brain or spinal cord. Finally, my talk will cover materials synthesis and physics that enable minimally invasive neural stimulation via functional fusion of magnetic nanomaterials and ion channels on neuronal membranes.

Sensitive recordings of neuronal activity over long timescales (>24 hr) are necessary for probing the behavior of individual neurons and for mapping the network properties throughout the hierarchy of the brain. There is extraordinary demand for a device capable of intraneuronal recordings that combines the scalability and long-term viability of extracellular multi-electrode arrays with the sensitivity and stimulation capabilities of an intracellular patch clamp. An electrically tight junction between cell membrane and nanoscale probe is the chief technical challenge impeding electrical recordings with high signal-to-noise ratio. Such sensitivity is essential for probing subtle changes in cell polarization and low-frequency "sub-threshold" potentials. We have developed a highly configurable platform that enables rapid prototyping of fusogenic nanoelectrode architectures for individually addressing networked cells in vitro. We use a hybrid on-wire nanolithography approach that combines traditional semiconductor fabrication techniques with nanopore electrodeposition. Biomimetic probe arrays can be designed to favor envelopment by cells. Our modular design enables independent tuning of electrode size, aspect ratio, curvature, geometry, and surface functionalization to allow the optimization of the parameters critical for realizing functional solid-state intracellular recording arrays. Our platform enables us to test directly the fundamental assumptions regarding the interaction between cell and engineered architecture.

INTRODUCTION
Regenerative Peripheral Nerve Interface (RPNI) devices successfully transduce peripheral nerve action potentials to electrical signals suitable for prosthesis control. Voltage changes are the controlling mechanism and can be observed during electromyography (EMG). RPNI device signaling hasn&’t been extensively characterized during awake, voluntary movements. Our study: a) characterizes RPNI active to background signal EMG strength and b) defines the reliability and validity of RPNI EMG function during purposeful movements.
METHODS
Three groups were formed in rats: Control (n=3), RPNI (n=3), 100% Denervated (n=3). Bipolar electrodes were implanted onto the soleus muscles in each group. For RPNI devices, the soleus muscle was freely grafted to the ipsilateral femur and neurotized by the transected tibial nerve. In the 100% Denervated, the tibial nerve was transected. While walking on a treadmill, rats were video-graphed and raw EMG signals were simultaneously recorded. Video and EMG recordings were synchronized by time for stance, swing, and sit (nonactive) gait phases. Rectified EMG was integrated (iEMG) for each gait phase (Fig. 1). iEMG was normalized (NiEMG) to time for each phase. Data represent 16 gait cycles for each of 3 rats. Correlations were performed between iEMG and stance time to determine reliability. RPNI signaling was validated against Control group signal timing by step phases using Chi Square analysis.
RESULTS
We compared EMG signals to background signal strength in all groups during all gait phases (Table 1, Fig. 1). Fidelity of RPNI activity (stance) to background signaling (sit) was 5 to 1, higher than Control signal fidelity (Fig. 2). Significant differences between stance and swing NiEMG activity were confirmed for the Control and RPNI groups. As expected, stance and swing EMG signals were not different for the Denervated group. Correlations between iEMG and stance time for the Control (r=0.7) and RPNI (r=0.4) indicate “good” RPNI signal reliability (Fig. 3). NiEMG signals increased at the start of stance and fell to baseline at the start of swing in both Control and RPNI rat gait cycles (Fig. 1A).These data comparing step cycle to EMG activation accuracy between Control, RPNI, and Denervated groups validated RPNI signaling as purposeful peripheral nerve activity appropriate for meaningful control of prostheses movements (Chi Square; p<0.5).
CONCLUSION
RPNI signal fidelity, reliability and validity were examined during voluntary movement. With select filtering, signal fidelity was clear. RPNI signal reliability during the gait stance was “good”. RPNI signaling was successfully validated against normal peripheral nerve signaling during walking.

Neural prosthetic devices (NPDs) have attracted considerable attention in the fields of fundamental and clinical neuroscience. NPDs are central technological components for advancing toward a functional brain computer interface. Current NPDs induce chronic inflammation due to the staggering discrepancies of mechanical properties with neural tissue, relatively large size of the implants, and traumas to the blood-brain barrier. Mitigation of these issues requires fabrication of a new generation of NPDs based on flexible and conductive materials. Layered nanocomposite materials from carbon nanotubes and gold nanoparticles can serve as a promising foundation for such materials. We systematically investigated the mechanical and electrochemical aspects of different nanocomposite materials. Our study determined the electrochemical performance of the nanocomposite for neural interface application. Furthermore, nanocomposite based NPDs with subcellular dimensions were fabricated by photolithography and implanted in vivo. In vivo functionality was demonstrated by successful registration of low frequency neural recording in live brains of anesthetized rats.

Technologies to interface neuronal tissue with implantable electrodes open up new possibilities for the exploration of basic neurological functions in vivo. The selective recording and stimulation of single neurons within the brain thereby is essential which in turn places high demands on the electrode and the interface itself. These include, amongst biocompatibility and flexibility, also the miniaturization of the actual electrode sites on the implant. Reduction of contacts down to tens of microns in diameter for matching high selectivity however results in a huge circumference-to-area ratio and high electrical impedance which might lead to unwanted side-effects (i.e. corrosion) under stimulation or low signal to noise ratio in recordings. Strategies to overcome this effect are based on increasing the effective area by introducing new materials or by modifying the present material to yield a roughened surface.
In this study we develop a process for the deposition of a thin platinum based layer with significant porosity (here referred to as Pt-grass) on top of conventional microelectrodes for reducing impedance and additionally provide a structured surface to serve as adhesion promoter for future bio-functionalization with conducting polymers. The platinum-grass deposition is performed as a passive wet-chemical reduction process from a platinic acid to be applicable as additional treatment to conventional implantable electrodes. Due to unspecific coverage of all surfaces by the Pt-grass in this approach, an active deposition process has been additionally established. Thereby the metallic electrodes serve as working electrode in an electrochemical setup so that the reduction of the Pt can be restricted to the desired areas of an implant. Both deposition routes proved to perform well on polyimide-based flexible electrodes whereas the passive approach initially covered also the polymer. Subsequent wiping however selectively removed the access Pt-grass resulting in a well adherent target layer only on the actual electrode sides. Active Pt-reduction on the electrodes restricts the grass formation to the metallic parts without the need for further cleaning steps and additionally increases the speed of the overall deposition process from a few days to some minutes. Electrochemical analysis of the deposited Pt-grass by means of electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV) revealed a significant reduction in impedance while the charge storage capacity (CSC) as well as the charge injection rate could be enhanced compared to bare Pt surfaces. This simple but efficient add-on process to already existing electrodes has the potential for improving the performance of geometrically small electrodes by introducing a high active surface area and thus adds a new tool for interfacing neuronal tissue.

Electrical stimulation is a primary route to repair or restore neurological functions. This requires that the electrical probe used for stimulation of neural cells is robust and exhibits low impedance, high charge injection capacity, and is biocompatible to facilitate cellular interactions. In this regard, we describe the underlying fundamental basis, chemical/structural design, and gifted attributes of a microelectrode comprising of organic (highly conducting polymer) - inorganic (carbon nanotubes) hybrid nanostructured electroactive coating on a metal electrode. Furthermore, the combination of in vitro experiments, fluorescence and electron microscopy of electrically stimulated cells (NB-39-Nu human neuroblastoma cells) at different applied electric field strength clearly demonstrated that electrochemically synthesized hybrid nanostructured coating is conducive to neurite growth. The study of the effects of electrical field strength on protein synthesis and mechanism implied cell-to-cell communication based on the change in the regulation of endogenous cytoskeletal proteins, actin, vinculin, and fibronection involving cell mobility and cell adhesion. The observations made here are not only promising for further exploration as new generation of advanced neural interfaces but are also relevant to functional neuronal circuits in cell translational therapy.

Cortically implanted microelectrode arrays (MEAs) allow researchers to stimulate neurons and obtain single unit extracellular recordings in the brain, but have a relatively short functional lifetime. One posited explanation for early device failure is the reactive tissue response. Activated microglia and reactive astrocytes attack foreign objects, and ultimately, electrically isolate implanted MEAs with an encapsulating glial sheath. A recent study utilized DC voltage pulses to alter the electrochemical properties of neural interfaces and improve signal to noise ratios of unit recordings in chronically implanted rats. The objective of this study is to expand upon this method of prolonging the lifetime of MEAs with the use of biphasic voltage pulses, which offer a safer charge balanced approach to the previous study. The AC voltage pulses are first optimized in phosphate buffered saline using silicon-substrate MEAs with iridium sites and bovine serum albumin as a model protein system. The impedance and charge carrying capacities of each electrode site are evaluated to determine the efficacy of this technique; and parametric studies are performed to identify the optimal frequency, waveform, and application time of the AC voltage pulses. Sprague-Dawley rats will be implanted with chronic MEAs to assess the viability of this technique in a living system. Electrochemical and electrophysiological recordings will be collected routinely, and AC pulses will be applied when the device appears to have failed. The effects of the AC pulses will be further explored using an equivalent circuit model of the electrode-tissue interface. Evaluation of the circuit model defines the electrical properties of the system and which aspects of the neural interface are being affected by the AC pulses. After the rats are sacrificed, immunohistochemistry will be performed to visualize the MEA and analyze the surrounding cell population.

Nanometer-scale structures represent a novel and intriguing field, where scientists and engineers manipulate materials at the atomic and molecular levels to produce innovative materials for composites, electronic, sensing, and biomedical applications. Carbon nanomaterials, such as carbon nanotubes, constitute a relatively new class of materials exhibiting exceptional mechanical and electronic properties, and are also promising candidates for gas storage and drug delivery.
Glassy surfaces, covered with carbon nanotubes are ideal substrates for neuronal growth. Nanotubes are compatible with neurons, but especially they play a very interesting role in interneuron communication, opening possibilities towards applications in spinal cord repair therapy.
During this talk we will describe our most recent results in the study of interactions of neurons and carbon nanotubes, extending the discussion to entire slices of spinal cord tissue, which appear to be sensitive to the presence of the carbon substrates.

Carbon nanotubes (CNT) have been demonstrated as a promising material in supporting neuron attachment, facilitating neuronal electrophysiology measurement as well as guiding neuronal network formation. Previous studies either coated CNTs on macroscopic substrates of millimeter sizes or patterned CNTS into micron-sized structures. There was, however, often an overlooked dimension mismatch between CNTs thin film and neuron cells. Cells are generally tens of microns in size, while CNTs are a thousand times smaller than cells and are only a few to tens of nanometers in diameter. The huge dimension gap between micron-sized neurons and nano-sized CNTs has rarely been explored. Here in this paper, we report the first method to create CNT thin films with mesoscale crinkly morphology in tens to hundreds nanometers. The crinkly CNT thin film is created by a solution-based expansion-and-shrinking approach, which can be easily applied to both 2D and 3D substrates. When culturing hippocampal neurons on a series of polyurethane (PU) sheets with different crinkly CNT coatings, higher cell density and greater cell polarization were observed with increasing crinkles. Our results indicated that the CNT thin film with mesoscale crinkly morphology has better support for neuron cells to attach, grow and differentiate. It opens up a new dimension for interacting neuron cells with CNTs.

Developing functional semiconductor-based devices for biomedical applications, including biosensors and implants for probing or controlling cellular growth and communication, relies on understanding the complex interactions taking place at the semiconductor surface. Gallium nitride has emerged as a highly promising material for these applications given its impressive chemical stability and electrical properties. By modifying the topography and chemistry of a GaN surface, the interface formed between probe and bio-environment can be influenced to promote or prevent certain interactions or characteristics. To demonstrate this effect, PC12 cells are cultured on as-grown flat, unidirectionally polished, nanoporous etched, and nanowire GaN surfaces with both unmodified and peptide-treated surface chemistries. The density of adherent cells increases with surface roughness, and the addition of the IKVAV peptide further increases cellular attachment. More compelling than this increase in adherent cells with roughness is the change in cellular morphology with surface topography. The polished and etched surfaces have comparable RMS roughness; however, the morphology of that roughness differs and drives significantly different behaviors in adherent cells, with the random texture driving greater cell spread across the surface and the unidirectional features promoting thin, stereotypic neurite extensions. This trend in morphology on the etched surfaces is reversed by the addition of the IKVAV peptide sequence, as the cell population shifts to predominant expression of the long, thin neurite phenotype. We thus present the dependence of cellular development on both substrate chemistry and topography, validating the importance of substrate modification for tuning semiconductor-biosystem interactions.

Electrospun nanofibers with a uniaxial alignment have recently gained its popularity in the field of neural tissue engineering. Many researchers have found that the anisotropic structure of the nanofibers can guide the neurites to extend along the direction of the alignment, resembling the native hierarchy of the nerve tissue. However, our observation indicated that the contact cues the nanofibers provided can be far more complicated than just guiding the neurites to extend along them. In recent studies, we used dorsal ganglia roots (DRG) as a model system to investigate the interaction between nanofibers and the neurites. We demonstrated, for the first time, that DRG neurites could not only project along the nanofibers, but also be guided to grow along a direction perpendicular to the aligned nanofibers, depending on a set of parameters. Our findings not only provide insights into the formation of well-defined neuronal network architecture (the so-called neural circuits) but also offer guidelines for the design of nanofiber-based scaffolds for nerve injury repair.

Traumatic injury to the Central Nervous System (CNS) is a significant health problem with injuries to the spinal cord and brain accounting for approximately 250,000 and 1.5 million new injuries each year in the United States, respectively. Currently, there are few effective treatments for CNS injuries because the CNS is refractory to neural circuit reconstruction and relatively inaccessible to many pharmacological treatments. Recently, unique nanocarriers are being designed that can be loaded with these therapeutic agents and can then release them gradually. However, design of slow-release carriers, for example, for releasing nerve growth factors (NGF) to treat various neurodegenerative disorders is a challenging issue. To overcome these challenges, researchers have designed a protein carrier-implant by taking advantage of an inverse thermoreversible gelation effect in an aqueous environment at body temperature. As the growth factor loaded dispersion is injected inside, the dispersion would gel to delay the diffusion and cause slow release of the imbibed drugs. In this work, we have evaluated the time dependent cellular uptake profile of these nanocarriers and the neurite outgrowth pattern from the Pheochromocytoma cell line 12 (PC12) cells at various dose levels.
A poly(ethylene glycol) methyl ether methacrylate-co-poly(ethylene glycol) ethyl ether methacrylate)-poly (acrylic acid) interpenetrating network (IPN) nanocarrier was synthesized. For neurite outgrowth evaluation, PC12 neuronal cells were routinely cultured for 72 hours, and then exposed to the IPN nanocarriers added (0 - 500 µg/mL) serum reduced culture media for 3 days in presence of beta NGF. Upon fixation, neurite growth was observed by performing optical and scanning electron microscopy. Time dependent (3-24 hr) uptake profile was assessed by performing confocal microscopy.
The designed nanospheres were externally tunable and internalized efficiently by PC12 cells. Particle agglomeration after sphere exposure was not observed. We found that nanospheres were readily incorporated into the cytosolic compartment within 3 hours and did not alter the morphology of cellular processes compared to cells not exposed to nanospheres. Live/Dead assays indicated that the toxicity was minimal, even at higher concentrations. Moreover, cells exposed to nanocarriers in presence of NGF for 72 hours revealed similar percentage of neurite bearing cells and enhanced neurite growth in culture similarly to the positive control conditions.
We interpret this data to indicate that the thermogel nanocarriers do not deleteriously affect neurite outgrowth from neuronal cells. Moreover, minimal toxicity and excellent intracellular uptake are extremely attractive features. Thus, it may lead to a new category of clinical solution that permits tailored release of pharmaceuticals to facilitate axon regeneration following traumatic brain or spinal cord injury.

Conducting polymers are highly promising platforms for electrical stimulation and regeneration of electroactive biological tissues, thanks to their potential for allowing the introduction of biocompatibility, flexibility and electronic features in one single structure [1]. To further enhance biological responses and electrical properties, these sophisticated materials can be supplemented with naturally charged biomolecules, most commonly via entrapment during electrochemical polymerisation [2]. In this study, we address the need for developing improved methods towards solution-processable, biofunctionalised conducting polymers. These systems, in contrast to electrochemically polymerised materials, are not restricted with regards to the techniques that can be used to process them into functional architectures as well as manipulate their electrical properties. We will present several functionalisation schemes based on covalent conjugation of bioactive adhesion peptides to conducting polymers via functional side groups. The use of covalent biofunctionalisation techniques are an attractive means to control the stability of biological cues, as opposed to non-covalently entrapped natural dopants that can easily be expelled from the systems by continuous redox cycling or simply through leaching out by diffusion; thereby reducing both electroactivity and bioactivity of the constructs with usage [3]. Additionally, the generated schemes are also easily transferable to new systems, as demonstrated by incorporation of different adhesion peptides.
[1] Berggren M, Richter Dahlfors A. Adv. mater. 19, pp. 3201-3213 (2007)
[2] Stauffer W, Cui X. Biomater. 27, pp. 2405-2413 (2006)
[3] Green RA et al., Acta Biomater. 6, pp. 63-71 (2010)

Implantable neural electrode arrays should be designed to minimally perturb the surrounding biological tissues. Ideally the implants should conform the curvilinear surface of the brain, spinal cord or nerves, and induce minimum, if any, inflammation. For stimulating electrodes, mechanical performance is also combined with high electrical charge injection over time. Addressing the soft-hard mismatch between the synthetic electrode and the biological tissue is even more urgent for chronic neural interfaces in behaving subjects where implant and nervous tissue are constantly in (relative) motion. We approach the challenge of a stretchable stimulating electrode by creating a Platinum - silicone composite that is compatible with stretch and the high current densities needed for stimulation.
We will report on the preparation and characterization of a Pt microspheres filled PDMS composite electrode and its patterning by screen printing. In electrochemical experiments under tensile strain we demonstrate that our electrode preserves its typical Pt signature at strains larger than 40%. Currently our composite electrodes are 300mu;m in diameter, have charge injection limits of 57±8mu;C/cm2 (in saline) and impedance of 4.2±0.6k#8486; at 1kHz. The Pt composite stimulating electrodes are integrated on a stretchable PDMS membrane. We will further demonstrate the chronic use (up to 4 weeks) of electrode arrays with 7 electrodes in stimulation of the surface of the spinal cord in rats.
Our surface electrode technology can be generalized to applications beyond the spinal cord such as for example ECoG recording of brain activity.

With the advancement of brain machine interface technologies, researchers have demonstrated that patients and animals with cortically implanted neuroprostheses have the ability to control prosthetic devices and interact with computer interfaces. However, a current limitation on the longevity of these devices is the decline of the signal to noise ratio over time, which leads to device failure. One explanation for these problems is the neural response to implantation: astrocytes and microglia becoming activated and surrounding implanted neural electrodes, pushing neurons away from the implant and creating a functionally isolating glial sheath. One method of alleviating these issues is with the use of systemically injected drugs and proteins, or potentially, implants with surface release capabilities. Thin film polymers allow for high loading efficiency of these mitigating factors and release from the entire device surface, while maintaining a small device footprint. Orthosilicates have the potential of forming thin film coatings capable of drug release while Tetramethyl Orthosilicate (TMOS) has demonstrated an ability to increase charge carrying capacities and decrease impedances when coated in a single layer upon silicon microelectrodes. Recently, our lab created a model system demonstrating that TMOS can also be used for protein release; tunable, short-term delivery of proteins was possible from a silicon substrate chip by altering protein concentrations within multiple layers of TMOS for up to six days. However, it was still unknown if multiple layers of TMOS will negatively impact electrical properties. This study aims to characterize and analyze the effect that multiple surface layers of TMOS have upon the impedance and charge carrying capacity of microelectrode arrays.