Development of integrated protection for a miniaturized drug delivery system

A bi-layer structure comprising a thin gold layer and a polypyrrole (PPy) film is developed as a valve. To create such structures, the thin metal layer is used as a working electrode, and the polypyrrole film is electrochemically deposited on the metal electrode. A layer of Cr deposited under a stationary part of the bi-layer flap adheres strongly to the gold layer and anchors the hinge of the flap, while the layer of polyimide deposited under a movable part of the flap adheres weakly to the gold layer of the flap. This bi-layer flap structure functions as an actuator valve for the opening and closing of an aperture. The actuation mechanism of the valve is based on a volume change in the PPy layer as cations move in and out of the polymer film during reduction and oxidation reactions. A bias of 1.2 V is used to actuate the flap. A method is proposed to increase the drug release system's functionality by placing the drug release flap within a protective enclosure that also serves as a drug reservoir. This integrated protection ensures reliable operation of the drug release flap unencumbered by surrounding tissues when used in vivo. A prototype system using a PDMS drug reservoir has been successfully tested in PBS buffer solution. The proposed integrated protection system holds promise for implantable biomedical devices.