A Parylene MEMS Electrothermal Valve

Abstract

The first microelectromechanical-system normally closed electrothermal valve constructed using Parylene C is described, which enables both low power (in milliwatts) and rapid operation (in milliseconds). This low-power valve is well suited for applications in wirelessly controlled implantable drug-delivery systems. The simple design was analyzed using both theory and modeling and then characterized in benchtop experiments. Operation in air (constant current) and water (current ramping) was demonstrated. Valve-opening powers of 22 mW in air and 33 mW in water were obtained. Following integration of the valve with catheters, our valve was applied in a wirelessly operated microbolus infusion pump, and the in vivo functionality for the appropriateness of use of this pump for future brain mapping applications in small animals was demonstrated.

MEMS-enabled implantable drug infusion pumps for laboratory animal research, preclinical, and clinical applications

“…An electrothermal principle was selected to open the normally-closed valve placed inline with the drug reservoir. A short current pulse applied to the metallic resistor element induced Joule heating which rapidly melted the polymer membrane and opened the flow path (7.5 mA over 66 msec for flap design [24]; typically >15 mA with current ramping over 150 sec for serpentine design [23]). Drug housed within the inline pressurized reservoir escaped through the opened catheter and into the systemic circulation.…”

“…The pressure-responsive one-way valve opened only under dosing conditions (elevated reservoir pressure) and prevented back flow of fluids into the device [94-96, 100, 101]. Low power operation allows wireless activation of drug delivery (shown in vitro) [23]. Drug delivery and refill were first demonstrated in enucleated porcine eyes prior to acute drug pumping performed in rabbits [94, 95].…”

“…The bottom row shows the opened valve following the application of current. The left column optical micrographs originally appeared in [23] © 2009 IEEE. Reprinted, with permission, from IEEE/ASME Journal of Microelectromechanical Systems.…”

“…Photograph of the microbolus infusion pump with integrated MEMS electrothermal valve [23] © 2009 IEEE. Reprinted, with permission, from IEEE/ASME Journal of Microelectromechanical Systems.…”

Micro- and nano-fabricated Implantable drug-delivery Systems

“…Temporary valves formed from polymer membranes with metallic resistor structures were robust enough to securely contain reservoir contents. A short current pulse applied to the metallic resistor was used to thermally degrade the polymer membrane and allow release of reservoir contents [27,28]. …”