A Selectively Anodic Bonded Micropump for Implantable Medical Drug Delivery Systems

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Microelectromechanical Systems (MEMS) fabrication techniques offer a unique solution for implantable medical drug delivery systems. An implantable medical drug delivery system can relieve the pain associated with frequent injections and deliver a localized dosage. An implantable drug delivery system can also avoid contamination and infection better than conventional injection methods (such as intravenous injection). The major advantage of microfabricated drug delivery systems is the possibility of mass production at low cost. A silicon based peristaltically actuated implantable medical drug delivery system consisting of three pumping chambers was microfabricated and tested. The unique features of this microfabricated drug delivery system include the design of a selectively anodic bonded micropump. The selectively anodic bonded Pyrex glass wafer was used to seal the pump chambers and allow for a view of fluid movement. Chromium was used as a selective bonding material. A 20 nm thick chromium film deposited on the top surface of the silicon valves successfully prevented bonding between the valve and the glass wafer. The pump operates with a normally closed valve which consists of a silicon mesa located at the center of each chamber. This mesa makes intimate contact with the glass wafer. Three 180 μm deep and 12 mm diameter circular chambers were etched into the top surface of the silicon wafer using deep reactive ion etching (DRIE) and connected by two 1 mm wide channels. Directly opposite the chambers, three 12 mm diameter circular features were etched 320 μm deep using DRIE to create a 50 μm thick silicon membrane and provide an attachment point for piezoelectric actuating disks. The piezoelectric disks were applied using a conductive silver epoxy. A positive potential was applied to the gold layer that was e-beam deposited on the substrate, with the negative terminal applied to each individual actuator. The three pump chambers were actuated in a peristaltic motion with driving frequencies ranging from 0.5 to 4 Hz and actuation voltages ranging from 10–130 V. The design goal of 10 μL/min was met at driving frequencies of 2 and 4 Hz where the maximum flowrate was 10.1 and 11.4 μL/min for the 2 and 4 Hz actuation frequencies respectively at an actuation voltage of 130 V. The maximum pressure achieved by the pump was 35.8 mmH20 for the 2 and 4 Hz actuation frequencies at an actuation voltage of 130 V.