Bioelectrical Applications Research Articles

Preparation and Characterization of Highly Conductive and Biorepulsive Polypyrrole/Polyglycerol Surface Films

Highly conductive and biorepulsive polymer films can be deposited onto gold by electrochemical polymerization of a polyglycerol-modified pyrrole derivative in aqueous solution. The growth of the polymer film is linearly determined by current density and time. Thicknesses of up to 400 nm can be obtained, where the polymerization is self-terminated due to the growth mechanism. Cyclic voltammetry and electrochemical impedance measurements were employed to characterize the film formation dynamics and the conductivity of the films at different thicknesses. Furthermore, the films and their growth were characterized by reflection/absorption infrared spectroscopy, quartz crystal microbalance, atomic force microscopy, as well as contact angle measurements. The films are highly biorepulsive even at thicknesses as low as 10 nm, which could be demonstrated using protein and bacterial adhesion assays, thus opening the opportunity for their use in bioelectrical applications.

Perovskite nickelate ionotronics for AI and brain-machine interfaces

Human brain is the ultimate computing machine in nature. Creating brain-like devices that emulate how the brain works and can communicate with the brain is crucial for fabricating highly efficient computing circuits, monitoring the onset of diseases at early stages, and transferring information across brain-machine interfaces. Simultaneous transduction of ionic-electronic signals would be of particular interest in this context since ionic transmitters are the means of information transfer in human brain while traditional electronics utilize electrons or holes. In this perspective, we propose strongly correlated oxides (mainly focused on perovskite nickelates) as potential candidates for this purpose. The capability of reversibly accepting small ions and converting ionic signal to electrical signals renders perovskite nickelates strong candidates for neuromorphic computing and bioelectrical applications. We will discuss the mechanism behind the interplay between ionic doping and the resistivity modulation in perovskite nickelates. We will also present case studies of using the perovskite nickelates in neuromorphic computing and brain-machine interface applications. We then conclude by pointing out the challenges in this field and provide our perspectives. We hope the utilization of strong electron correlation in the perovskite nickelates will provide exciting new opportunities for future computation devices and brain-machine interfaces.

Layered graphene composite for flexible bioelectrical sensor applications

A layered graphene (G) composite was prepared onto an ITO/PEN substrate to develop a novel low-cost, transparent, and flexible biosensor. This layered structure comprises of graphene oxide (GO) on the top layer acting as a sensing surface, and G on the bottom layer featuring a high conductivity for transmission. The O2/H2 low damage plasma treatment (O/H-LDPT) was utilized for atomic layer oxidation of bilayer G to form layered composite GO/G. After immobilization, the resistance variation was measured at different concentrations (10 pM–100 nM) of micro ribonucleic acid-21 (miRNA-21). A high sensitivity and detection accuracy was confirmed with a linearity of 0.9825 and detection limit as low as 16.1 pM. In addition, different sequences of target were detected to ensure the selectivity. While detecting the 4-base mismatched target, the rate of resistance variation decreased from 16.4% to 4.49%, indicating a certain specificity for target miRNA-21. Additionally, in the bending test for devices, after a 24 h continuous bending with a bending radius of 12.3 mm, the device maintained its original high sensitivity to detect the target miRNA-21.

SPARC: Chronic Simultaneous Recording of Gastric Motility and Ad Libitum Feeding Behavior in Awake, Freely Moving Rats with Vagal Nerve Simulation

ObjectiveIn spite of its apparent promise, bioelectric modulation of the vagal innervation of the stomach has had limited success modifying ingestive behavior. But, importantly, stimulation parameters in previous bioelectrical applications were arbitrarily employed without information as to their stimulus‐response relationships or optimal locations. With this in mind, we established a model of chronic vagal nerve stimulation (VNS) where we record GI motility continuously in unanesthetized, freely moving rats while their intake is monitored as they consume chow and water ad libitum (automated food and liquid intake monitors; BioDAQ, Research Diets Inc.).MethodsA patch electrode (MicroProbes) was attached to the muscle wall of the proximal forestomach of healthy adult male Sprague‐Dawley rats at a site known to contain the highest density of vagal mechanoreceptors. A strain gauge was similarly attached to the muscle wall of the antrum. Rats were maintained in their home cages equipped with BioDAQ feeders, while continuously tethered to overhead commutators. Following recovery, the feeding and drinking behavior as well as antral motility of individual rats was continuously monitored and recorded with and without concomitant VNS (pulse parameters, derived from acute studies: 0.3mA/0.2ms/10Hz; 20s On:40s Off). Subjects were exposed to each of the following four conditions on different days at the onset of lights off: a 2 h fast, a 2 h fast while being stimulated, 2 h ad lib access to chow, and 2 h ad lib access to chow while being stimulated. In a separate study, 2 days of strain gauge activity was continuously recorded: 24 h without stimulation followed by 24 h with stimulation.ResultsRats recovered quickly following surgery. Compared to the 2 h fasted condition, there was a 17% increase in antral peristalsis (change in amplitude and frequency expressed as area under the curve) when subjects were fasted while being stimulated; similarly, there was an 18% increase in antral peristalsis when subjects were stimulated while consuming chow compared to 2 h intake of chow without stimulation. The same pattern was observed in the 2 d study with a 23% increase in antral activity during 24 h of stimulation compared to 24 h pre‐stimulation. Interestingly, a 12% increase in total chow intake occurred when stimulated for 24 h while no difference was noted in water intake between the two conditions.ConclusionsInitial exposure to VNS results in a modest increase in antral activity with and without the presence of food in the stomach. Analyses are underway to tease apart the effect of stimulation on motility in relation to meal size. Finally, these findings confirm that our chronic VNS model has considerable potential for determining optimal stimulation parameters necessary for making meaningful changes in gut motility.Support or Funding InformationSPARC/NIH Office of the Director OT2 OD023847NIDDK/NIH R01 DK027627

A novel active AC coupled input stage of instrumentation amplifier for bioelectrical applications

For recording bioelectrical signals using Instrumentation Amplifiers (INA), capacitive AC coupling of the differential inputs is necessary for two major reasons, providing DC electrical isolation of the subject to avoid hazards of tissue burn, and to block DC or very low frequency skin-electrode contact potentials. The latter, when met, allows high admissible differential gain of the INA, which in turn, is expected to give a desirable high Common Mode Rejection Ratio (CMRR). However, the use of conventional passive RC high pass filters at the input greatly reduces CMRR. This work intends to design an improved AC coupled input circuitry for INA giving high CMRR and high input impedance. A differential RC high-pass input circuit has been developed using an active element. It creates an effective high resistance for the common mode current but provides a low resistance path to input bias currents for normal operation of the INA. Between 1 Hz and 100 Hz, CMRR of the DC coupled INA (LT1167) was 115 dB, using a well matched traditional RC coupling, 55 to 95 dB, while it was 110 dB using the improved active AC coupled circuit. This improvement was practically demonstrated through Electrocardiogram measurements from a human subject. A novel active AC coupling circuitry has been proposed and developed giving high CMRR, very close to the maximum of an INA, which is non-varying within the frequency band of interest of Bioelectrical amplifiers. The developed input circuit will improve all bioelectrical measurements in the future.

An eco-friendly, low-power charge storage device from bio-tolerable nano cerium oxide electrodes for bioelectrical and biomedical applications

Objective. A growing demand exists for eco-friendly, low-power charge storage devices for both biomedical and neuro-electrical applications, with a push towards the use of biocompatible and bio-tolerable electrodes and eco-friendly electrolytes that could be easily integrated with wearable electronics. Approach. One of the promising bio-tolerable, biomedical materials is nano cerium oxide, which finds wide applications in biology and medicine, namely spinal cord injury, radiotherapy, cardio-protection, etc. Here, nano cerium oxide was used as an electrode material to test whether such a bio-tolerable material could be used in bioelectrical and neuro-electrical applications. Main results. We developed a symmetric charge storage device using nano-ceria electrodes coated with fructose (a fruit sugar that is neutral to diabetes patients). This device attains a potential window of +0.8 V to −0.8 V in the presence of an aqueous electrolyte, Na2SO4, which is an eco-friendly electrolyte. The device retains 85% of the specific capacitance (∼350 F g−1) and peak current density of 12 mA cm−2 after completion of 10 000 cycles, thus highlighting the stability of the newly developed device. Further, the device could be used to operate DC fans and other solid state electronic devices. The CeO2 electrode was tested in biologically relevant fluids, namely phosphate buffered saline and Leibovitz (L-15) medium, and found to be functioning and stable. Significance. Bio-tolerable nano cerium oxide electrodes could find new and innovative applications in bio-electronics, electro-therapy, neuro-electronics, charge storage and wearable electronics.

Improving the diversity of faculty in electrical and computer engineering (iredefine ece[point of view

As women faculty in electrical and computer engineering (ECE), we have been involved in several efforts targeted at increasing the participation of women in ECE departments. For example, at Rutgers University, we have organized presentations and workshops for first year students that highlighted the societal aspects of ECE, such as bioelectrical engineering applications. Such focus did bear fruit; between 2010 and 2016, the sophomore female enrollment in ECE at Rutgers rose from 11% to 19%. At the University of San Diego, we have conducted research on the demographics and outcomes of undergraduate students in ECE, facilitated workshops to help faculty teach in more inclusive ways, and are currently working on a National Science Foundation (NSF)-funded effort to revolutionize engineering education [1]. Also, as chairs, we have been considering ways to diversify our faculty carefully considering the overall hiring process including innovative approaches such as cluster hires [2], paying close attention to the language used when advertising faculty positions, the discussions during the review of the candidates, the candidate selection criteria, and the interview process [3]. However, the number of diverse graduate students is small to begin with, and in an era in which companies have realized the value of diversity, academia has to compete with companies such as Google and Microsoft for the best Ph.D. graduates. Without a diverse faculty, we cannot sustain a diverse student body.

A parametric framework for the development of bioelectrical applications: application to a bio-impedance signal simulator

A parametric framework for the development of bioelectrical applications: application to a bio-impedance signal simulator

Patterned Free-Standing Conductive Nanofilms for Ultraconformable Circuits and Smart Interfaces

A process is presented for the fabrication of patterned ultrathin free-standing conductive nanofilms based on an all-polymer bilayer structure composed of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) and poly(lactic acid) (PEDOT:PSS/PLA). Based on the strategy recently introduced by our group for producing large area free-standing nanofilms of conductive polymers with ultrahigh conformability, here an inkjet subtractive patterning technique was used, with localized overoxidation of PEDOT:PSS that caused the local irreversible loss of electrical conductivity. Different pattern geometries (e.g., interdigitated electrodes with various spacing, etc.) were tested for validating the proposed process. The fabrication of individually addressable microelectrodes and simple circuits on nanofilm having thickness ∼250 nm has been demonstrated. Using this strategy, mechanically robust, conformable ultrathin polymer films could be produced that can be released in water as free-standing nanofilms and/or collected on surfaces with arbitrary shapes, topography and compliance, including human skin. The patterned bilayer nanofilms were characterized as regards their morphology, thickness, topography, conductivity, and electrochemical behavior. In addition, the electrochemical switching of surface properties has been evaluated by means of contact angle measurements. These novel conductive materials can find use as ultrathin, conformable electronic devices and in many bioelectrical applications. Moreover, by exploiting the electrochemical properties of conducting polymers, they can act as responsive smart biointerfaces and in the field of conformable bioelectronics, for example, as electrodes on tissues or smart conductive substrates for cell culturing and stimulation.

A Blumlein-type, nanosecond pulse generator with interchangeable transmission lines for bioelectrical applications

The design and realization of a nanosecond, high-voltage electric pulse generator for bioelectrical applications is reported in this paper. A Blumlein type architecture was adopted, with some modifications, and realized in a microstrip line configuration with meander-shaped conducting strips, and with ultra-fast, high voltage solid state switches. Three microstrip-lines have been realized in such a way that, being interchangeable within the structure, they allow to match different load impedances. A fiber optic-based system was also realized to separate the high voltage side of the system from the switch-control circuit. The system is suitable for applying high voltage nanosecond electric pulses, with variable pulse duration, amplitude, repetition rate and polarity, to liquid media with different electromagnetic characteristics, hosted in electroporation cuvettes with different gap dimensions.

Enhancing the Interface in Silk–Polypyrrole Composites through Chemical Modification of Silk Fibroin

To produce conductive, biocompatible, and mechanically robust materials for use in bioelectrical applications, we have developed a new strategy to selectively incorporate poly(pyrrole) (Ppy) into constructs made from silk fibroin. Here, we demonstrate that 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 Ppy and silk that is incapable of delamination. To further increase the conductivity and long-term stability of the Ppy network, a variety of small molecule sulfonic acid dopants were utilized and the properties of these silk-conducting polymer composites were monitored over time. The composites were evaluated using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), optical microscopy, energy-dispersive X-ray (EDX) spectroscopy, cyclic voltammetry, a 4-point resistivity probe and mechanical testing. In addition, the performance was evaluated following exposure to several biologically relevant enzymes. Using this strategy, we were able to produce mechanically robust polymer electrodes with stable electrochemical performance and sheet resistivities on the order of 1 × 10(2) Ω/sq (conductivity ∼1 S/cm).

The insulation performance of reactive parylene films in implantable electronic devices

Parylene-C (poly-chloro-p-xylylene) is an appropriate material for use in an implantable, microfabricated device. It is hydrophobic, conformally deposited, has a low dielectric constant, and superb biocompatibility. Yet for many bioelectrical applications, its poor wet adhesion may be an impassable shortcoming. This research contrasts parylene-C and poly(p-xylylene) functionalized with reactive group X (PPX-X) layers using long-term electrical soak and adhesion tests. The reactive parylene was made of complementary derivatives having aldehyde and aminomethyl side groups (PPX-CHO and PPX-CH 2NH 2 respectively). These functional groups have previously been shown to covalently react together after heating. Electrical testing was conducted in saline at 37 °C on interdigitated electrodes with either parylene-C or reactive parylene as the metal layer interface. Results showed that reactive parylene devices maintained the highest impedance. Heat-treated PPX-X device impedance was 800% greater at 10 kHz and 70% greater at 1 Hz relative to heated parylene-C controls after 60 days. Heat treatment proved to be critical for maintaining high impedance of both parylene-C and the reactive parylene. Adhesion measurements showed improved wet metal adhesion for PPX-X, which corresponds well with its excellent high frequency performance.

Heparin dopant increases the electrical stability, cell adhesion, and growth of conducting polypyrrole/poly(L,L‐lactide) composites

Polypyrrole (PPy) is a promising conductive polymer for tissue engineering and bioelectrical applications. However, its electrical conductivity deteriorates easily in aqueous conditions. Cell adhesion to PPy is also relatively poor. The goal of this study was to simultaneously improve the electrical stability of and cell adhesion to PPy by using heparin (HE) as dopant, for HE is both a polyanion and an important glycosaminoglycan in cell membranes and extracellular matrix. PPy particles doped with HE were synthesized through emulsion polymerization using Fenton's reagent as an oxidant. X-ray photoelectron spectroscopy (XPS), infrared and scanning electron microscopy (SEM) were used to investigate the PPy particles. Conductive biodegradable membranes of 10(2) to 10(3) Omega/square were prepared from 5% (w) PPy with various amounts of HE and 95% (w) poly(L,L-lactide) (PPy/PLLA). Azure A staining was employed to quantify the HE exposed on the surface of the PPy particles and PPy/PLLA membranes. The distribution of HE on membranes was demonstrated by DAPI staining. Results showed that HE was incorporated into the PPy particles as counterions and presented on particle surface. A unique "filament"-like morphology of the PPy preparation was observed at high-HE content. The electrical stability of the PPy/PLLA membranes was tested in saline at 37 degrees C for 500 h. Human skin fibroblasts were used to test the cell adhesion capacity. The conductive membranes containing HE-doped PPy particles recorded significantly increased electrical stability, cell adhesion, and growth. The electrically more stable and cell adhesive conductive biodegradable membrane may act as a platform for various biomedical applications.

Dc characteristics of a nanoscale water-based transistor

We demonstrate a nanoscale water-based transistor. The presented nanoscale water-based transistor relies on the controlled modification of the pH in deionized water through the base applied electric field. The dc characteristics are presented and studied with a focus on the influence of the base applied electric field, the base electrode design, and their proximity to the sensing emitter and collector nanoelectrodes. The demonstrated water-based nanoscale device is of interest for many bioelectrical applications due to the biocompatibility and the wide usage and presence of water in biological systems.