Photoelectric Dye-Coupled Polyethylene Film: Photoresponsive Properties Evaluated by Kelvin Probe and In Vitro Biological Response Detected in Dystrophic Retinal Tissue of Rats

Electrodes that output electric current as conduction current are widely used to stimulate nerves and cardiac cells in human body. We designed a photoelectric dye-coupled polyethylene film for use as a thin film device to stimulate nerve cells by electric potential changes. The aim of this study was to measure its photo-responsive properties and to record in vitro biological response. When measured using a Kelvin probe system, the photoelectric dye-coupled film showed rapid rise and fall of surface electric potential in response to light-on-and-off. Light-evoked surface electric potential of the dye-coupled film increased in response to increasing light intensity. In vitro biological response to the dye-coupled film was assessed in isolated rat retinal tissues using a multielectrode array recording system. As positive control, electroretinogram-like waves were recorded in response to light from normal rat retinal tissue placed with the inner retinal surface at the bottom of the multielectrode array dish. In contrast, no light-elicited wave was recorded from degenerative retinal tissue isolated from retinal dystrophic Royal College of Surgeons (RCS) rats. When the dye-coupled film was simply overlaid on the degenerative retinal tissue with the inner retinal surface placed at the bottom of the multielectrode array dish, electroretinogram-like waves were elicited in response to light projected from the bottom. Plain polyethylene film without photoelectric dye coupling was used as negative control, and did not yield light-elicited response when placed on the degenerative retinal tissue. For detailed recordings of action potential spikes high-passed at 100 Hz, a nylon mesh anchor was placed on top of the preparation to ensure close contact between the multielectrode array and the retinal tissue with or without the dye-coupled film. In this experimental setting, the degenerative retinal tissue alone showed spontaneous action potential spikes as numerous small trivial amplitudes in the background noise, while the degenerative retinal tissue overlain with the dye-coupled film showed action potential spikes with increased amplitude in response to light against the background of spontaneous spikes. This study confirmed that the photoelectric dye-coupled polyethylene film is able to stimulate degenerative retinal tissue that has lost photoreceptor cells, and may function as a novel type of retinal prosthesis. Electric potential changes, probably as displacement current or capacitive current, may be an alternative approach to stimulate nerves in human body.