Droplet backside exposure for making slanted SU-8 microneedles

Abstract

This paper presented a droplet backside exposure (DBE) method for making slanted microneedle structures on a flexible polymer substrate. To demonstrate the feasibility of the DBE approach, SU-8 microneedle arrays were fabricated on polydimethylsiloxane (PDMS) substrates. The length of the microneedles was controlled by tuning the volume of the SU-8 droplet, utilizing the wetting barrier phenomenon at a liquid-vapor-hydrophilic surface-hydrophobic surface interface. The experimental results showed excellent repeatability and controllability of the DBE method for microneedle fabrication. Analytical models were also studied to predict the dimensions of the microneedles, which agreed with the experimental data.

Design, fabrication, and packaging of an integrated, wirelessly-powered optrode array for optogenetics application

“…As described in Figure 2 , (1) a 3-inch glass wafer was cleaned and put through a dehydration bake, and a ~50 μm SU-8 (SU-8 3025, MicroChem Corp, MA, USA) layer was spun onto the wafer and patterned as the mock LEDs; (2) A thin layer of PDMS was spun onto the SU-8 master to create cavities matching the shape of the LED; (3) After the PDMS was cured for 40 min at 95°C, PR was patterned on the PDMS substrate to expose 7 mm-diameter circles, followed by oxygen plasma treatment to convert the exposed hydrophobic areas to hydrophilic ones; (4) After removal of the PR mask, ~45 μL SU-8 (SU-8 3005) was dispensed on top of the plasma treated PDMS surface using a micropipette; and (5) patterned with a backside droplet backside exposure (DBE) method that utilizes the height variance in a dome-shaped SU-8 structure to create out-of-plane microneedles of varying lengths (Kwon et al, 2013a , 2014b ); (6) After SU-8 development, the array was polished by O 2 plasma etching; (7) DC sputtering of a 0.1-μm-thick ITO layer was performed in a Kurt Lesker Axiss PVD System, followed by deposition of 5 μm Parylene-C. Then a 0.2-μm-thick Au layer was deposited in the thermal evaporator, and the tip of the waveguide was chemically etched for light delivery, followed by deposition of 5 μm Parylene-C as a protective layer. The Parylene-C film at the tip of the optrode was removed using reactive-ion etching (RIE); and (8) The optrode array then was released from the glass wafer, and the microneedles with the matched LED cavities were aligned onto the corresponding LEDs.…”