Development of Micro-Valves actuated by polypyrrole/gold bilayers
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Many American women suffer from urinary incontinence that decreases their quality of life. To treat urinary incontinence without surgery, we are developing micro-valves that can be used in the bladder to open and close the flow of urine. A process was developed to microfabricate the valves on a Kapton substrate. The micro-valves are actuated by polypyrrole(PPy)/gold bilayers, and the open and closed states of the valve are controlled by application of a small voltage (< 1V).
In order to show the feasibility of operating the micro-valves in the human bladder, the valves were tested under various pH (4 9), body temperature (30 42 oC), and pressure (10 110 cm of water) ranges. The power consumption of the valve was determined; a small silver oxide battery that provides 110 mA-hr of power can be used to power the valve for 30 days. Also, the lifetime of the valves, which was initially tens of cycles due to delamination of gold and polypyrrole from the substrate, was increased to 1,000 cycles. An adhesion layer of Cr between the Kapton and Au, as well as an electroplated layer of Au between the evaporated Au and electrochemically deposited PPy, were used to prevent the early delamination.
Lastly, in order to optimize the performance of the bilayer, we wanted to determine the relationships among PPy thickness and bilayer hinge length, force, and bending angle. A new actuator was designed to collect bending angle and force. Larger bending angles were observed with longer hinges, and smaller bending angles with thicker PPy. Preliminary force measurements were made by stacking weights on the actuators. The thicker the PPy was, the heavier the weight it could lift.