Design and simulation of an implantable medical drug delivery system using microelectromechanical systems technology

A unique design of an implantable micropump for medical drug delivery systems was proposed. The peristaltic pumping principle was selected. Three pump chambers are individually actuated by each bulk PZT (lead zirconate titanate) disk in a peristaltic motion. It is this peristaltic motion that propels the fluid. The design of the micropump includes inlet, three pump chambers, three silicon membranes, three normally closed active valves, three bulk PZT actuators, three actuation reservoirs, flow microchannels, and outlet. To prohibit flow when no power is applied, the micropump was designed to be normally closed. The pump features an integral valve/membrane design such that the pump chambers not only pump the liquid, but also function as the inlet and outlet valves. To determine the dimensions of the proposed micropump, analytical modelling of the micropump chamber was conducted. The design tradeoffs between maximizing the pumped volume and reducing the overall size of the proposed micropump were analyzed. An electromechanical coupled field simulation using the FEA method was employed. Based upon the simulation results, 6 and 12 mm diameter silicon membranes with different thickness of 40 and 80 μm were fabricated using microelectromechanical systems (MEMS) technology. The deflection of these silicon membranes was tested. The PZT actuator was manually glued onto the micropump chamber. The testing data agreed well with the FEA simulation of the deflection. The conductive adhesive layer dramatically reduces the deflection. A 12 mm in diameter and 40 μm thick silicon membrane in each pump chamber is needed to meet the micropump design requirements. The fabrication and experiments of these silicon membranes reported in this paper determine the dimensions and fabrication processes for the complete micropump. A 70 mm × 35 mm × 1.0 mm micropump will be fabricated using MEMS fabrication technology. The complete micropump will be characterized to verify our design.