A PARYLENE BELLOWS ELECTROCHEMICAL ACTUATOR FOR INTRAOCULAR DRUG DELIVERY P.-Y. Li 1* , R. Sheybani 2 , J.T.W. Kuo 2 , and E. Meng 1,2 1 Department of Electrical Engineering, University of Southern California, Los Angeles, California, USA 2 Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA ABSTRACT The first electrochemical actuator with a Parylene bellows for intraocular drug delivery is presented in which the bellows separates the electrolysis actuation chamber from the drug reservoir. The Parylene bellows was fabricated using a novel polyethylene glycol (PEG)- molding process and mechanically characterized. Optimization of the gas generation efficiency of the actuators was performed. We achieved an efficiency approaching 80% and over 1.5 mm deflection with our actuator. Wireless operation was also demonstrated. KEYWORDS Drug Delivery Device, Electrolysis Pump, Bellows, Intraocular Implant INTRODUCTION Water electrolysis using coplanar microelectrodes offers a promising pumping actuation mechanism for many bioMEMS applications [1, 2]. Electrolysis actuators possess a simple structure for ease of fabrication, low power consumption, low heat generation, and large driving force. Previously, we reported the first MEMS electrochemically-driven drug delivery device capable of targeted delivery to intraocular tissues [3]. The system consisted of a drug reservoir integrated with an electrolysis pump and Parylene cannula. The application of current initiated electrolysis of the drug solution which produced the necessary driving pressure to pump drug through the cannula and into the eye (Figure 1). Figure 1: Conceptual depiction of an intraocular drug delivery device. While the drug delivery concept was successfully demonstrated, several challenges related to the micropump design were identified during preliminary in vitro and in vivo experiments. First, drug was oxidized by the electrolysis reaction. Power was supplied through wires from an external source and thus, severely limited the ability to conduct chronic in vivo experiments. Electrode dimensions were arbitrarily selected; therefore, power consumption of the pump was not optimized. These issues are addressed in our new actuator described here. DESIGN, THEORY, AND MODELING The key features of our new, optimized pump actuator include (1) separation of the electrochemical reaction and drug with (2) a robust, high deflection Parylene bellows to prevent unwanted pH changes or drug degradation, (3) an efficiency-optimized electrochemical actuator electrode design, and (4) lower power consumption for long term wireless operation. The main body of the drug delivery system is implanted within the layers of the eye wall and the attached cannula is inserted through an incision and directed to the intraocular space. The actuator is contained within the main body and is in contact with the contents of the drug reservoir. Electrolysis-induced gas generation (phase change of water into hydrogen and oxygen gas) results in deflection of the bellows and thus pumping of the drug into the eye. Drug is carried directly to the targeted intraocular tissues through the cannula. Figure 2: An exploded view of the major system components. The pump actuator consists of interdigitated Pt electrodes and Parylene bellows that are fabricated separately. The chamber formed by the bellows and electrode base is filled with deionized (DI) water and then joined together (Figure 2). Electrolysis pumping is selected over other actuation methods for its low power consumption (~μW-mW) which makes it suitable for wireless operation and integration with other chronically implantable devices (Figure 3). In addition, current control of electrolysis provides a facile means of adjusting the flow rate. 978-1-4244-4193-8/09/$25.00 ©2009 IEEE Transducers 2009, Denver, CO, USA, June 21-25, 2009 1461 T4B.004