Fluid flow past an aperture in a microfluidic channel.

Electroosmotically driven flow in neurotransmitter-based retinal prostheses offers a novel approach to interfacing the nervous system. Here, we show that electroosmotically driven flow in a microfluidic channel can be used either to eject or to withdraw fluid through a small aperture in the channel wall. We study this fluid movement numerically using a finite-element method and experimentally using microfabricated channels and apertures. Two devices are used to test the concept of fluid ejection and withdrawal: (1) a single, large channel with four apertures and (2) a prototype neural interface with four individually addressable apertures. We compared experimental and numerical results in microchannels using the observed pH dependence of the fluorescent dye fluorescein, finding good agreement between the results. Because of the simplicity and rapid response of electroosmotic flow, this technique may be useful for neurotransmitter-based neural interfaces.