Design, Fabrication and Characterization of Ultrananocrystalline Diamond (UNCD) Membranes for Drug Delivery Devices

P. GURMAN; M. ZALAZAR; J. PARK; O. AUCIELLO

Simposio; Symposium EE: Diamond Electronics and Biotechnology?Fundamentals to Applications VI; 2012

Ultrananocrystalline Diamond (UNCD) is a promising material for biomedical applications, due to its extraordinary mulifunctionality, including tunable electrical conductivity, extremely low wear, very low coefficient of friction, high smoothness, bio-inertness and biocompatibility. UNCD is exceptional for implantable medical devices requiring stringent biological performance. Drug delivery systems are important medical devices providing significant medical (improve pharmacokinetics decreasing drug dose and toxicity) and commercial (increasing product portfolio by adding new products and decreasing drug discovery costs by recycling old drugs) advantages. This presentation will focus on the design, fabrication and characterization of UNCD membranes for passive and active drug delivery devices. UNCD membranes were fabricated in a clean room facility using thin film deposition and microfabrication techniques, including: 1) UNCD thin film growth by microwave plasma chemical vapor deposition (MPCVD) on a Si substrate after a nanodiamond seeding process on the silicon surface, 2) photolithography using a specially designed mask to define a window on the backside of the wafer, 3) reactive ion etching (RIE) to pattern the Si3N4 mask for the cavity sustaining the UNCD membrane on the backside of the wafer, and 4) wet chemical etching to create the cavity sustaining the UNCD membrane. Square membranes of 200-1000 µm in size with a thickness ranging between 100-500 nm were fabricated and characterized by Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM) and reflectometry. Fabrication of passive drug delivery devices was done using the focused ion beam (FIB) technique to produce holes with micron size dimensions in the UNCD membranes to enable controlled drug diffusion through the latter. For the active drug delivery device, based on a piezoelectrically actuated valve, a Pt/piezoelectric AlN/Pt layer heterostructure was grown and patterned on the UNCD membrane with a Ti adhesion layer, followed by FIB etching to define the valve aperture. By applying voltages between the top and bottom Pt electrodes layers the piezoelectric AlN layer is actuated allowing opening and closing the valve. Work in progress will be described, showing the optimization of AlN film growth and integration with UNCD membranes and development of fabrication processes to produce piezoelectrically actuated valves. PDMS was used to seal the bottom face of the Si substrate, where the integrated UNCD membrane/cavity structure was fabricated, to create the reservoirs. Work in progress to optimize and test active and passive drug delivery devices based on UNCD membranes will be discussed in the presentation.