In vitro feasibility testing of floating light-activated minroelectrical stimulators

One of the major challenges of neural stimulation is the mechanical stress and resulting trauma induced on the implanted electrodes by the constant movement of the interconnects. A potential way of eliminating interconnects is to use floating micro-stimulators that can be activated through optical means. As a method of energy transfer to the micro-stimulator, we propose to use a laser beam at near infrared (NIR) wavelengths. There are two main objectives in this project to test the feasibility of the main approach; investigate the charge injection capacity of titanium nitride (TiN) and iridium oxide (IrOx) as potential contact materials, and measure the transmitted light power through the neural tissue for various implantation depths. The charge injection capacity of TiN electrodes for an extended range of cathodic voltages was also investigated. Because the microstimulator will be implanted into the neural tissue, the laser beam must penetrate a few millimeters before reaching the device. The transmitted light power was measured for various types of neural tissue. The transmitted light power through rat brain gray matter was much higher than that of the white matter and the sciatic nerve. Penetration depth and reflectance were calculated according to Lambert-Beer’s law from measurements of transmission for various tissue thicknesses. The results suggest that FLAMES approach is feasible for implantation depths of a few millimeters in the peripheral and central nervous system. Both IrOx and TiN allow sufficient charge injection for this application. TiN is preferred for future experimentation since TiN does not require a bias voltage to achieve useful charge injection rates, and thus is a good choice as an electrode material in this application