A piezoelectric driven controlled release micropump for insulin delivery

A piezoelectric disk bender was used to augment the rate of insulin transport across a membrane. Repeated displacement of the disk resulted in a pressure driven flow across the membrane, in addition to the basal delivery obtained because of the concentration difference between the insulin and downstream reservoirs. Augmentation increased nonlinearly with voltage, higher augmentation being achieved at voltages greater than 50 V DC (50% duty cycle). Augmentation was also much greater at frequencies near resonance (e.g., near 200 Hz for a 1.2 microns cellulose acetate membrane) and with smaller insulin reservoirs. Greater augmentations with reasonable basal rates were obtained with membranes that had high diffusive permeabilities and a high ratio of hydraulic to diffusive permeability. Theoretic calculations, using an equivalent circuit model of piezoelectric action, suggested that although the pressure increase in the insulin reservoir was approximately 0.19% of the maximum possible, this pressure increase was sufficient to account for approximately 95% of the augmented flow. Although further improvements are necessary, this device has the potential of delivering insulin to diabetics to better match supply and demand.