PDMS based multielectrode arrays for superior in-vitro retinal stimulation and recording

Abstract

Understanding of the neural response to electrical stimulation requires simultaneous recording from the various neurons of retina. Electrodes form the physical interface with the neural or retinal tissue. Successful retinal stimulation and recording demands conformal integration of these electrodes with the soft tissue to ensure establishment of proper electrical connection with the excitable tissue. Mechanical impedance of polydimethylsiloxane (PDMS) being compliant with that of retinal tissue, offers excellent potential as a substrate for metal electrodes. In this paper, Cr/Au micro electrodes with 200 μm diameter were fabricated on rigid and flexible PDMS substrates under crack free condition. Spontaneous buckling of thin films over PDMS substrates improved electrode performance circumventing the fabrication issues faced over a buckled surface. Individual electrodes from the multielectrode arrays (MEAs) were examined with electrochemical impedance spectroscopy and cyclic voltammetry. Controlled fabrication process as described here generates buckles in the metal films leading to increased electrode surface area that increases the charge storage capacity and decreases the interface impedance of the metal electrodes. At 1 kHz, impedance was reduced from 490 ± 27 kΩ to 246 ± 19 kΩ and charge storage capacity was increased from 0.40 ± 0.87 mC/cm to 2.1 ± 0.87 mC/cm. Neural spikes recorded with PDMS based electrodes from isolated retina also contained less noise as indicated by signal to noise ratio analysis. The present study established that the use of PDMS as a substrate for MEAs can enhance the performance of any thin film metal electrodes without incorporation of any coating layers or nanomaterials.

Capacitive-like photovoltaic epiretinal stimulation enhances and narrows the network-mediated activity of retinal ganglion cells by recruiting the lateral inhibitory network

“…Although the axon initial segment is the cellular compartment with the lowest activation threshold [22], in practice, its activation threshold is barely distinguishable from those of more distal axonal segments [20], making the selective stimulation of a single axon a challenge. Various complementary approaches have been proposed to improve the stimulation resolution of epiretinal prostheses: minimizing the spread of the electric field generated by single electrodes to avoid stimulation crosstalk [25], using penetrating electrode arrays to reduce the stimulation distance [26][27][28], increasing the charge injection capacity of microelectrodes with coatings to reduce their size [29][30][31], tuning the stimulation parameters to selectively activate only those cells close to the electrode [32,33], or selecting the optimal cluster of electrodes curtailing the activation of distal axon segments [20,21].…”

Development of in vitro 2D and 3D microelectrode arrays and their role in advancing biomedical research

“…The conformal nature of PDMS also allowed Biswas et al [108] to demonstrate PDMS-based 200 µm diameter chrome/gold microelectrodes, which conformed to complex neural and retinal tissue geometries. Both a flexible and rigid design were implemented for comparison.…”

Bioinspired Artificial Eyes: Optic Components, Digital Cameras, and Visual Prostheses

“…This mechanical mismatch restricts the wide FoV, because a large‐size rigid and flat device can easily damage retinal tissue . Bioinspired strategies such as a hemispherically curved device design and soft‐form devices can provide biocompatible interfaces between soft retinal tissues and the retinal implants . One strategy is to apply a polyimide device with an origami structure that achieves a hemispherical configuration similar to the shape of the human eye to cover a large area of ​​the retina (Figure d) .…”