Advancements in electrode design and laser techniques for fabricating micro-electrode arrays as part of a retinal prosthesis

Bioelectronics-on-a-chip for cardio myoblast proliferation enhancement using electric field stimulation

Background

Cardio myoblast generation from conventional approaches is laborious and time-consuming. We present a bioelectronics on-a-chip for stimulating cells cardio myoblast proliferation during culture.

Method

The bioelectronics chip fabrication methodology involves two different process. In the first step, an aluminum layer of 200 nm is deposited over a soda-lime glass substrate using physical vapor deposition and selectively removed using a Q-switched Nd:YVO₄ laser to create the electric tracks. To perform the experiments, we developed a biochip composed of a cell culture chamber fabricated with polydimethylsiloxane (PDMS) with a glass coverslip or a cell culture dish placed over the electric circuit tracks. By using such a glass cover slip or cell culture dish we avoid any toxic reactions caused by electrodes in the culture or may be degraded by electrochemical reactions with the cell medium, which is crucial to determine the effective cell-device coupling.

Results

The chip was used to study the effect of electric field stimulation of Rat ventricular cardiomyoblasts cells (H9c2). Results shows a remarkable increase in the number of H9c2 cells for the stimulated samples, where after 72 h the cell density double the cell density of control samples.

Conclusions

Cell proliferation of Rat ventricular cardiomyoblasts cells (H9c2) using the bioelectronics-on-a-chip was enhanced upon the electrical stimulation. The dependence on the geometrical characteristics of the electric circuit on the peak value and homogeneity of the electric field generated are analyzed and proper parameters to ensure a homogeneous electric field at the cell culture chamber are obtained. It can also be observed a high dependence of the electric field on the geometry of the electrostimulator circuit tracks and envisage the potential applications on electrophysiology studies, monitoring and modulate cellular behavior through the application of electric fields.

Microchannel neural interface manufacture by stacking silicone and metal foil laminae

OBJECTIVE

Microchannel neural interfaces (MNIs) overcome problems with recording from peripheral nerves by amplifying signals independent of node of Ranvier position. Selective recording and stimulation using an MNI requires good insulation between microchannels and a high electrode density. We propose that stacking microchannel laminae will improve selectivity over single layer MNI designs due to the increase in electrode number and an improvement in microchannel sealing.

APPROACH

This paper describes a manufacturing method for creating MNIs which overcomes limitations on electrode connectivity and microchannel sealing. Laser cut silicone-metal foil laminae were stacked using plasma bonding to create an array of microchannels containing tripolar electrodes. Electrodes were DC etched and electrode impedance and cyclic voltammetry were tested.

MAIN RESULTS

MNIs with 100 μm and 200 μm diameter microchannels were manufactured. High electrode density MNIs are achievable with electrodes present in every microchannel. Electrode impedances of 27.2 ± 19.8 kΩ at 1 kHz were achieved. Following two months of implantation in Lewis rat sciatic nerve, micro-fascicles were observed regenerating through the MNI microchannels.

SIGNIFICANCE

Selective MNIs with the peripheral nervous system may allow upper limb amputees to control prostheses intuitively.

A cortical integrate-and-fire neural network model for blind decoding of visual prosthetic stimulation

We present a computational model of the optic pathway which has been adapted to simulate cortical responses to visual-prosthetic stimulation. This model reproduces the statistically observed distributions of spikes for cortical recordings of sham and maximum-intensity stimuli, while simultaneously generating cellular receptive fields consistent with those observed using traditional visual neuroscience methods. By inverting this model to generate candidate phosphenes which could generate the responses observed to novel stimulation strategies, we hope to aid the development of said strategies in-vivo before being deployed in clinical settings.

Activation and inhibition of retinal ganglion cells in response to epiretinal electrical stimulation: a computational modelling study

OBJECTIVE

Retinal prosthetic devices aim to restore sight in visually impaired people by means of electrical stimulation of surviving retinal ganglion cells (RGCs). This modelling study aims to demonstrate that RGC inhibition caused by high-intensity cathodic pulses greatly influences their responses to epiretinal electrical stimulation and to investigate the impact of this inhibition on spatial activation profiles as well as their implications for retinal prosthetic device design. Another aim is to take advantage of this inhibition to reduce axonal activation in the nerve fibre layer.

APPROACH

A three-dimensional finite-element model of epiretinal electrical stimulation was utilized to obtain RGC activation and inhibition threshold profiles for a range of parameters.

MAIN RESULTS

RGC activation and inhibition thresholds were highly dependent on cell and stimulus parameters. Activation thresholds were 1.5, 3.4 and 11.3 μA for monopolar electrodes with 5, 20 and 50 μm radii, respectively. Inhibition to activation threshold ratios were mostly within the range 2-10. Inhibition significantly altered spatial patterns of RGC activation. With concentric electrodes and appropriately high levels of stimulus amplitudes, activation of passing axons was greatly reduced.

SIGNIFICANCE

RGC inhibition significantly impacts their spatial activation profiles, and therefore it most likely influences patterns of perceived phosphenes induced by retinal prosthetic devices. Thus this inhibition should be taken into account in future studies concerning retinal prosthesis development. It might be possible to utilize this inhibitory effect to bypass activation of passing axons and selectively stimulate RGCs near their somas and dendrites to achieve more localized phosphenes.

Parylene-coated metal tracks for neural electrode arrays - fabrication approaches and improvements utilizing different laser systems

In the past we developed a method for the fabrication of neural electrodes based on laser-structuring metal foil to form tracks and electrode sites within a silicone rubber substrate. Here, this process was refined by an additional coating of the laser-patterned metal tracks to improve their mechanical properties. Parylene C has been found to be the coating material of choice due to excellent electrical and mechanical characteristics and its well known biocompatibility. An almost ten times increased tensile strength compared to uncoated tracks could be achieved. Investigating the electrical properties of parylene C and silicone rubber attested both materials excellent insulating capabilities by withstanding voltages of more than 400 V(DC) for layer thicknesses as intended to be used in electrode array fabrication (some 10 µm). This paper outlines the feasibility of the manufacturing process using a 1064 nm Nd:YAG laser in the nanosecond pulse regime. However, an improvement of the whole processing was demonstrated when a 355 nm Nd:YVO(4) laser in the picosecond regime is used. Benefits of this short pulse duration range from ablating materials independent of their optical properties to increased manufacturing speed and superior processing quality.