High-aspect-ratio tapered structures using an integrated lens technique

In this work, a fabrication approach for tapered column structures with high aspect ratio is presented, and its application to microneedle fabrication is discussed. Microlenses were fabricated on a glass substrate by chromium-masked isotropic wet etching. This substrate was subsequently coated with SU-8 negative epoxy resist and exposed from the back. The chromium acted in a self-aligned fashion to block light from the non-lens portion of the substrate, and the lenses acted to shape the beam through the epoxy to produce sharply-tapered structures. An extension of the technique allows for subsequent repetition of the structure through micromolding; solid biodegradable microneedles with a cone shape were fabricated in this manner. The microneedles have sharply tapered tips and are 1.5 mm in height. These needles were inserted into human skin and were demonstrated to be suitable for blood extraction.