A shuttered neural probe with on-chip flowmeters for chronic in vivo drug delivery

This paper describes the development of shutters, fluidic ribbon cables, and flowmeters for use on bulk-micromachined neural probes. The resulting devices permit electrical recording, stimulation, and chemical drug delivery in the central nervous system at the cellular level. Dielectric shutters reduce unintended drug delivery by a factor of about 25 compared with an open orifice, while silicon fluidic cables are 1.5 times more flexible than the 70 mu m-ID polyimide tubing previously used. A pulsed thermal flowmeter integrated on the probe allows verification of drug delivery on a per-channel basis with a resolution of 150 pL/s. Thermal time constants are about 60 mu s, allowing multiple measurements within one delivery pulse while restricting any tissue heating to negligible levels. Finally, test structures have shown the process compatibility of on-chip thermopneumatic microvalves and micropumps. The fabrication of these fluidic structures (microchannels, shutters, cables, valves, and pumps) requires only two masks in addition to the eight normally used for passive probes, providing important new capabilities for use in neurophysiological research and neural prostheses.