Stretchable Microelectrode Array Research Articles

Stretchable microelectrode array using room-temperature liquid alloy interconnects

In this paper, we present a stretchable microelectrode array for studying cell behavior under mechanical strain. The electrode array consists of gold-plated nail-head pins (250 µm tip diameter) or tungsten micro-wires (25.4 µm in diameter) inserted into a polydimethylsiloxane (PDMS) platform (25.4 × 25.4 mm2). Stretchable interconnects to the outside were provided by fusible indium-alloy-filled microchannels. The alloy is liquid at room temperature, thus providing the necessary stretchability and electrical conductivity. The electrode platform can withstand strains of up to 40% and repeated (100 times) strains of up to 35% did not cause any failure in the electrodes or the PDMS substrate. We confirmed biocompatibility of short-term culture, and using the gold pin device, we demonstrated electric field pacing of adult murine heart cells. Further, using the tungsten microelectrode device, we successfully measured depolarizations of differentiated murine heart cells from embryoid body clusters.

Selective Stimulation of the Spinal Cord Surface Using a Stretchable Microelectrode Array

By electrically stimulating the spinal cord, it is possible to activate functional populations of neurons that modulate motor and sensory function. One method for accessing these neurons is via their associated axons, which project as functionally segregated longitudinal columns of white-matter funiculi (i.e., spinal tracts). To stimulate spinal tracts without penetrating the cord, we have recently developed technology that enables close-proximity, multi-electrode contact with the spinal cord surface. Our stretchable microelectrode arrays (sMEAs) are fabricated using an elastomer polydimethylsiloxane substrate and can be wrapped circumferentially around the spinal cord to optimize electrode contact. Here, sMEAs were used to stimulate the surfaces of rat spinal cords maintained in vitro, and their ability to selectively activate axonal surface tracts was compared to rigid bipolar tungsten microelectrodes pressed firmly onto the cord surface. Along dorsal column tracts, the axonal response to sMEA stimulation was compared to that evoked by rigid microelectrodes through measurement of their evoked axonal compound action potentials (CAPs). Paired t-tests failed to reveal significant differences between the sMEA’s and the rigid microelectrode’s stimulus resolution, or in their ranges of evoked CAP conduction velocities. Additionally, dual-site stimulation using sMEA electrodes recruited spatially distinct populations of spinal axons. Site-specific stimulation of the ventrolateral funiculus – a tract capable of evoking locomotor-like activity – recruited ventral root efferent activity that spanned several spinal segments. These findings indicate that the sMEA stimulates the spinal cord surface with selectivity similar to that of rigid microelectrodes, while possessing potential advantages concerning circumferential contact and mechanical compatibility with the cord surface.

Monitoring Hippocampus Electrical Activity In Vitro on an Elastically Deformable Microelectrode Array

Interfacing electronics and recording electrophysiological activity in mechanically active biological tissues is challenging. This challenge extends to recording neural function of brain tissue in the setting of traumatic brain injury (TBI), which is caused by rapid (within hundreds of milliseconds) and large (greater than 5% strain) brain deformation. Interfacing electrodes must be biocompatible on multiple levels and should deform with the tissue to prevent additional mechanical damage. We describe an elastically stretchable microelectrode array (SMEA) that is capable of undergoing large, biaxial, 2-D stretch while remaining functional. The new SMEA consists of elastically stretchable thin metal films on a silicone membrane. It can stimulate and detect electrical activity from cultured brain tissue (hippocampal slices), before, during, and after large biaxial deformation. We have incorporated the SMEA into a well-characterized in vitro TBI research platform, which reproduces the biomechanics of TBI by stretching the SMEA and the adherent brain slice culture. Mechanical injury parameters, such as strain and strain rate, can be precisely controlled to generate specific levels of damage. The SMEA allowed for quantification of neuronal function both before and after injury, without breaking culture sterility or repositioning the electrodes for the injury event, thus enabling serial and long-term measurements. We report tests of the SMEA and an initial application to study the effect of mechanical stimuli on neuron function, which could be employed as a high-content, drug-screening platform for TBI.

Characterization of an Elastically Stretchable Microelectrode Array and Its Application to Neural Field Potential Recordings

Elastically stretchable microelectrode arrays (SMEAs) were fabricated, and their functionality was tested by recording field potentials from neural tissue. The SMEA includes 11 microelectrodes, each with a recording area of and a reference electrode. The microelectrodes were fabricated by depositing and patterning thin-film gold conductors on the elastomeric substrate poly(dimethylsiloxane). A photopatternable silicone was used to encapsulate the microelectrodes and pattern vias for electrical contact. The recording sites of the microelectrodes were electroplated with platinum black to reduce the impedance of the electrode/electrolyte interface. Spontaneous and stimulus-evoked activity was recorded from hippocampal slices placed on an array that was biaxially stretched up to 13.3%. No appreciable difference in microelectrode properties was detected before and after stretching, demonstrating that the microelectrodes can be stretched reversibly.

Monitoring of Traumatically Injured Organotypic Hippocampal Cultures with Stretchable Microelectrode Arrays

ABSTRACTTraumatic brain injury (TBI) can be caused by motor vehicle accidents, falls and firearms. Approximately 2% of the US population lives with disabilities cause by TBI. To discover mechanisms of functional deficits underlying TBI, as well as to develop strategies to restore lost function with neural interfaces, we developed a stretchable microelectrode array (SMEA), which can be used for continuous recording of neuronal function, pre-, during, and post-stretch injury. The SMEAs were fabricated on elastomeric substrates, consisting of stretchable 100μm wide, 25nm thick gold electrodes patterned on a polydimethylsiloxane (PDMS) substrate, and encapsulated with a 10-20μm thick, photo-patternable silicone (WL-5150, Dow Corning) insulation layer. Finally, the SMEA was packaged between two printed circuit boards and mounted in a commercial Multi Channel Systems amplifier. Combining with our TBI model, which can generate precise and reproducible injury of hippocampal cultures, SMEAs were able to monitor the extracellular field potentials of neuronal populations within the cultures grown on SMEAs and injured by bi-axialy stretching the stretchable membranes. Previous biocompatibility tests showed no overt necrosis or cell death caused by the SMEAs after 2 weeks in culture [2]. The electrical performance of the SMEAs was tested in electrophysiological saline solution before, during and after biaxial stretching. The initial electrode impedance at 1kHz was ∼2kΩ. The SMEA was stretched to 8.5% biaxial strain. The microelectrode impedance increased with the strain to reach 800kΩ at 8.5% strain. Upon relaxation, the impedance recovered to 10kΩ. The working noise level of the sMEA remained below 20 ΩVpp during the whole process. New methodologies for improving the design of microelectrode arrays structure, the choice of materials and the new technology of fabrication were tested on gold microelectrode arrays supported on glass. By using the prototype arrays, population spikes were able to be recorded from organotypic hippocampal slice cultures of brain tissue. Our results demonstrate that the prototype arrays have good electrical performance compatible with existing multielectrode array systems. Moreover, the results indicate the ability of the prototype arrays to record neuronal activity from hippocampal slices. This novel technology of SMEAs will enable new studies to understand injury mechanisms leading to post-traumatic neuronal dysfunction.