Interpillar distance effect in a two-step microneedle DRIE process and its transfer to polymeric microneedles

This work presents the effect of interpillar distance in a two-step dry reactive ion etching DRIE process for microneedle fabrication. The two-step DRIE process consists of a pillar creation followed by the pillar etching till turning it into a needle. The effect was carried out in a dumbbell-well pattern. The employed dumbbell-well pattern was adjusted to produce 650-µm microneedle height. The microneedle density was fixed at 657/cm², and the interpillar distance was increased by reducing the pillar area. At a short interpillar distance, 25 µm, the etching rate is higher on the surface; for a wider distance, 75–100 µm, the etching produces triangular needles. At an interpillar distance of 200 µm or greater, the pillar etch rate becomes uniform along the microneedle height, producing a thin, sharp micropillar. The obtained silicon microneedles were employed to fabricate polymeric microneedles via micro-molding. The polymeric microneedles obtained by micro-molding showed the exact geometry of the original one. The obtained polymeric microneedles showed the capacity to penetrate the skin with a 0.5 N.