The electro-osmotic actuation of implantable insulin micropumps.

A study using an electro-osmotic cell suitable for actuating an implantable insulin micropump showed that controlled variable flow rates in the order of 0.2 mL/day are possible. The cell functioned continuously with low energy and power requirements and long service life. The principle of operation is compatible with achieving the very low flow rates necessary if highly concentrated insulin is to be used to avoid frequent insulin reservoir refilling. An electro-osmotic cell, Ag/AgCl/NaCl(aq)/cation exchange membrane/NaCl(aq)/AgCl/Ag, was connected to a constant current power supply which reversed the direction of the current every 10 mins causing a to-and-fro transport of fluid through the membrane. Flow rates of 0.15-0.60 microL/min were achieved with currents of 2.5-10 mA. At the low flow rate, energy consumption was 6.4 X 10(-2) J/microL and peak power requirement was less than 2.0 X 10(-4) W. Fluid was transported against a pressure gradient of 52 cm Hg. The cell contained a total electrolyte volume of less than 0.25 mL. The membrane showed no change in properties after 10,000 current reversals (69 days). To function as an actuator for an implantable insulin micropump, the electro-osmotic cell requires a switching and valving assembly; a suitable design for this is briefly considered.