Droplet backside exposure for making slanted SU-8 microneedles

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.