Conductive Hydrogel Electrodes Research Articles

Transparent stretchable capacitive touch sensor grid using ionic liquid electrodes

Low cost soft, flexible and stretchable sensors are being explored that can be applied to virtually any surface, and promise to enable tactile sensing on robots, prosthetics, skin and stretchable displays. Previous work has shown that capacitive sensors that are both stretchable and transparent can be created by using ionically conductive hydrogel electrodes. In this study, the electrodes are interpenetrating polymer networks swollen with ionic liquid, enabling high transparency and stretchability, without evaporation. The interpenetrating network is synthesized from poly(ethylene oxide) and nitrile butadiene rubber. Electrodes are patterned using femtosecond laser machining, creating stretchable electrodes. These were encapsulated in a polydimethylsiloxane substrate, producing a 95% transparent sensor (450 nm). A 4x4 tactile array shows the ability to sense proximity and multi-touch, as well as be robust to variations in environmental temperature (from 4°C to 72°C). Temperature change has a large effect on the resistance of the electrodes — an effect that could be used to measure device temperature. In addition, the sensor is able to detect proximity and touch while on skin, when covered by a layer of fabric or during stretch.

Elastic and conductive hydrogel electrodes.

Stretchable conductive hydrogels make microelectrode arrays that better interface with tissue.

The Potential of Conductive Hydrogel Electrodes at the Neural Interface: An Interview with Rylie Green

The Potential of Conductive Hydrogel Electrodes at the Neural Interface: An Interview with Rylie Green

Stimulation of peripheral nerves using conductive hydrogel electrodes.

Nerve block via electrical stimulation of nerves requires a device capable of transferring large amounts of charge across the neural interface on chronic time scales. Current metal electrode designs are limited in their ability to safely and effectively deliver this charge in a stable manner. Conductive hydrogel (CH) coatings are a promising alternative to metal electrodes for neural interfacing devices. This study assessed the performance of CH electrodes compared to platinum-iridium (PtIr) electrodes in commercial nerve cuff devices in both the in vitro and acute in vivo environments. CH electrodes were found to have higher charge storage capacities and lower impedances compared to bare PtIr electrodes. Application of CH coatings also resulted in a three-fold increase in in vivo charge injection limit. These significant improvements in electrochemical properties will allow for the design of smaller and safer stimulating devices for nerve block applications.

A Soft Stretchable Sensor: Towards Peripheral Nerve Signal Sensing

ABSTRACTWe propose a 3D-printable soft, stretchable, and transparent hydrogel-elastomer device that is able to detect simulated ‘nerve’ signals. The signal is passed to a conductive hydrogel electrode through a non-contact method of capacitive coupling through polydimethylsiloxane (PDMS). We demonstrate that the device is able to detect sinusoidal waveforms passed through a simulated ‘nerve’ made from conductive hydrogel over a range of frequencies (1 kHz – 1 MHz). Analysis of signal detection showed a correlation to the electrode contact area and a Vin/Vout of larger than 10%. This provides the framework for the future development of a soft, 3D-printable, capacitive coupling device that can be used as a cuff electrode for detecting peripheral nerve signals.

Conductive Hydrogel Electrodes for Delivery of Long-Term High Frequency Pulses

Nerve block waveforms require the passage of large amounts of electrical energy at the neural interface for extended periods of time. It is desirable that such waveforms be applied chronically, consistent with the treatment of protracted immune conditions, however current metal electrode technologies are limited in their capacity to safely deliver ongoing stable blocking waveforms. Conductive hydrogel (CH) electrode coatings have been shown to improve the performance of conventional bionic devices, which use considerably lower amounts of energy than conventional metal electrodes to replace or augment sensory neuron function. In this study the application of CH materials was explored, using both a commercially available platinum iridium (PtIr) cuff electrode array and a novel low-cost stainless steel (SS) electrode array. The CH was able to significantly increase the electrochemical performance of both array types. The SS electrode coated with the CH was shown to be stable under continuous delivery of 2 mA square pulse waveforms at 40,000 Hz for 42 days. CH coatings have been shown as a beneficial electrode material compatible with long-term delivery of high current, high energy waveforms.

Design of TENS electrodes using conductive yarn

Purpose – The purpose of this paper is to develop textile-based transcutaneous electrical nerve stimulation (TENS) electrodes using conductive yarn to bring a solution to uncomfortable feelings and hygiene problems of conventional conductive hydrogel electrodes. It proposes washing process, resistance measurements and subjective tests to evaluate the performance of the developed textile-based electrode. Design/methodology/approach – In this study, six different textile electrode pairs were designed and produced with different patterns. Designed electrodes were washed for ten times. In order to evaluate the effect of pattern differences and washing process on electrode performances, two different tests were realized before and after washing. The first of these tests is resistance measurement with a multimeter, and the second one is subjective test carried out on subjects. Findings – The results obtained from resistance measurements indicated that the pattern differences cause resistance values of electrodes to change. It is reported that subjects had electrical stimulation from all electrode samples in conducted trials and it is noticed that washing process does not cause any stimulation problems. Originality/value – In this study, textile-based TENS electrodes having different patterns were produced by machine stitching technique and their long-term usage behaviors were examined with repeated washing processes and trials on the subjects.

Fabrication of Self-Healable and Patternable Polypyrrole/Agarose Hybrid Hydrogels for Smart Bioelectrodes.

We present a new class of electrically conductive, mechanically moldable, and thermally self-healable hybrid hydrogels. The hybrid gels consist of polypyrrole and agarose as the conductive component and self-healable matrix, respectively. By using the appropriate oxidizing agent under conditions of mild temperature, the polymerization of pyrrole occurred along the three-dimensional network of the agarose hydrogel matrix. In contrast to most commercially available hydrogels, the physical crosslinking of agarose gel allows for reversible gelation in the case of our hybrid gel, which could be manipulated by temperature variation, which controls the electrical on/off behavior of the hybrid gel electrode. Exploiting this property, we fabricated a hybrid conductive hydrogel electrode which also self-heals thermally. The novel composite material we report here will be useful for many technological and biological applications, especially in reactive biomimetic functions and devices, artificial muscles, smart membranes, smart full organic batteries, and artificial chemical synapses.