A Multidrug Delivery System Using a Piezoelectrically Actuated Silicon Valve Manifold With Embedded Sensors

This paper describes a drug delivery system for chronic pain that can accommodate multidrug protocols. An element that is important to the function of the system is a customized silicon micromachined valve manifold. Each valve is piezoelectrically actuated and operates by pressing an elongated valve seat against a shared glass substrate. The dual-valve substrate has two inlets and one outlet; a piezoresistive pressure sensor is embedded in the Si structure near each of these three ports. The sensors, which permit closed-loop control and error monitoring of the flow rate, have a typical sensitivity of 698 ppm/kPa. The 1 × 1.5 × 3 cm³ manifold provides modulation and mixing capabilities. The manifold is integrated into a stainless steel housing with a total volume of 130 cm³ and a reservoir volume of 40 cm³. Two spring-loaded polyethylene reservoirs feed the valve manifold at pressures up to 0.52 kPa/mL. Benchtop tests of bolus and continuous flow delivery demonstrate flow rates ranging from 2.30 to 0.51 mL/h. (Both larger and smaller rates can be achieved by adjusting the parameters of the manifold valves or reservoir springs.) Additional tests suggest that the system can compensate for changes in spinal fluid pressure and that pressure profiles can be used to detect catheter occlusions and disconnects.