Fabrication of monolithic SU-8 microneedle arrays having different needle geometries using a simplified process

Transdermal drug delivery using hollow microneedle enables creating small, wearable and minimally invasive closed-loop system. Polymer hollow microneedles are preferable because they are cost-effective and easy to manufacture. SU-8 is chosen for creating the hollow microneedles as it is a biocompatible photopolymer with robust mechanical properties. Previously reported SU-8 microneedles either use melt casting process for coating SU-8 which is laborious or do not have monolithic structures, thereby making these mechanically weak and difficult to integrate. To the best of our knowledge, for the first time, we report the use of a single-step spin coating process to achieve the desired thickness of SU-8 while using UV lithography to create a monolithic microneedle array. Three types of microneedles were fabricated with outer dimensions varying from 90 to 180 μm, and lumen dimensions ranging from 60 to 80 μm and needle height of 600 μm. These needles are fabricated in a 10×10 array with a platform thickness of 300 μm. Geometrical, mechanical and fluid flow characterisations are carried out for the fabricated arrays. We report the use of a non-destructive evaluation method to characterise the lumen of the fabricated microneedles. The fabricated needles are robust and offer low resistance to fluid flow. The triangular needles can withstand a bending load of 0.2 N and an axial load of 0.7 N. The needles with circular lumen offer least resistance to fluid flow of 0.2 Pa-min μL⁻¹.