Flexible polyimide-based hybrid opto-electric neural interface with 16 channels of micro-LEDs and electrodes

In this paper, a polyimide-based flexible device that integrates 16 micro-LEDs and 16 IrO(x)-modified microelectrodes for synchronous photostimulation and neural signal recording is presented. The 4 × 4 micro-LEDs (dimensions of 220 × 270 × 50 μm(3), 700 μm pitch) are fixed in the SU-8 fence structure on a polyimide substrate and connected to the leads via a wire-bonding method. The recording electrodes share a similar fabrication process on the polyimide with 16 microelectrode sites (200 μm in diameter and 700 μm in pitch) modified by iridium oxide (IrO(x)). These two subparts can be aligned with alignment holes and glued back-to-back by epoxy, which ensures that the light from the LEDs passes through the corresponding holes that are evenly distributed around the recording sites. The long-term electrical and optical stabilities of the device are verified using a soaking test for 3 months, and the thermal property is specifically studied with different duty cycles, voltages, and frequencies. Additionally, the electrochemical results prove the reliability of the IrO(x)-modified microelectrodes after repeated pressing or friction. To evaluate the tradeoff between flexibility and strength, two microelectrode arrays with thicknesses of 5 and 10 μm are evaluated through simulation and experiment. The proposed device can be a useful mapping optogenetics tool for neuroscience studies in small (rats and mice) and large animal subjects and ultimately in nonhuman primates.