Study of curved microwire glass electrodes for use with a high resolution retinal stimulation array.

Abstract

Abstract: : Purpose: Microwire glass electrodes are unique in their ability to carry signals from a flat microelectronic stimulator chip to the curved surface of the retina. The purpose of this preliminary study was to examine the effects of using microwire glass electrodes. We screened different types of matrix glass for short term biocompatibility, examined a method of sealing the glass to reduce any possible cell mortality and evaluated the effect of curved electrodes on the implant procedures. Methods: We screened four types of glass; Silica, Corning^(TM) 8161, Corning 8260/borosilicate and R–6/soda lime. Primary cortical cultures from 18–day embryonic rats were plated onto 3 samples of each glass type. For glass sealing experiments we used Corning 8161 microchannel glass with nickel microwires electroplated throughout. We imaged the effect of sealing the electrode surface with Epotek^(TM) ND353 biocompatible epoxy upon HEK–293T cells. We also performed mechanical and electrical model procedures to evaluate the benefit of the curved electrodes. Results: Silica, Borosilicate and R–6 glasses exhibited minimal cell death as determined by cell morphology. 8161 glass had a strong negative effect upon the cells, causing significant cell death after only 4 days. We attempted to seal the 8161 glass electrodes with biocompatible epoxy. Without sealing the HEK–293T cells died as indicated by Ethidium Bromide uptake into the nucleus. With epoxy sealing the cells survived as indicated by Calcein–AM uptake and cleavage. Our mechanical model surgeries indicated that the device would benefit from the curved electrode structure. Conclusions: The standard glass used to make microchannel glass electrodes with microwires is Corning 8161 leaded glass. Switching to Borosilicate or Soda lime glasses can eliminate the potentially deleterious effects of this glass. One alternative to changing glass types is to seal the glass surface of the electrode.

Keywords: electrophysiology: non–clinical • retinal culture • retinal degenerations: cell biology