An Implantable MEMS Drug-Delivery Device

A novel drug-delivery system based on MEMS technology is being developed. This implantable microchip is capable of delivering vasopressin, a known vasoconstrictor that can prevent or delay death by hemorrhagic shock. The device is specially tailored to treat hemorrhagic shock in ambulatory settings and is intended for in vivo use as a micro-implant in the peritoneum for people in high-risk situations.

The device has a modular design and is composed of three layers: a large reservoir layer, where the drug solution is stored; a membrane layer from where the drug is ejected; and a bubble-generating layer, where bubbles are formed. The reservoir layer is defined by drilling through a Pyrex 7740 wafer with a diamond bit. Wafer thickness and hole diameter can be modified to change reservoir capacity. The membrane layer is composed of silicon nitride membranes covering through-holes etched by DRIE into a silicon substrate. Thin gold fuses can be patterned on the membranes to detect ruptures, which then shows as an open circuit. The bubble-generating layer is defined by micro-resistors, which can quickly and locally heat the contained fluid to generate bubbles. The pressure exerted by these bubbles causes rupture of the silicon nitride membranes and forces the contained solution out of the device.

In vitro operation of the device has been demonstrated. Further developments of this device include reduction of power consumption during activation, wireless activation, and adaptation of the device for a pen-size, transdermal delivery system. We believe that the ramifications of this MEMS-based drug delivery system can be useful for a vast number of medical applications.