Fabrication and Characterization of Polymer Hollow Microneedle Array Using UV Lithography Into Micromolds

Drug delivery through micromachined needles is an attractive alternative to intramuscular and subdermal injection by hypodermic needles, due to the potential for reduced pain caused by the micro-sized needles. In this paper, a polymer-based fabrication process using UV lithography into micromolds is developed, allowing the fabrication of microneedle (MN) shafts, tips, lumens, and substrate baseplate using lithography. Using UV lithography into micromolds allows complex three-dimensional structures to be defined, since both mask patterns and mold topography are available to define the structures. A hollow MN array and baseplate, in which the needle lumens extend through the thickness of the baseplate, are demonstrated. Fabricated SU-8 MNs are 825 μm in height and 400 μm in width, with a pyramidal tip; the needle lumen, 120 μm in diameter, intersects with one of the faces of the pyramidal tip. Mechanical characterization of the fabricated MNs shows that the fracture force of a single needle against a rigid surface is 12.0 N. The insertion force of a single needle into porcine skin is empirically determined to be 2.4 N. The fracture force of the needle against porcine skin is observed to be in excess of 90 N.

I. Introduction

Drug delivery through micromachined needles is of great interest to transport therapeutic agents, virus-like-particles, and other molecules into the body through the skin with minimal invasiveness and pain. Drug delivery with microneedles (MNs) has been shown to induce immune responses or biological effects that are comparable to those induced by a hypodermic needle (HN) injection in animal studies with influenza, Hepatitis B, Hepatitis C, and diabetes. [1]–[3] In addition, one human study with influenza reported that the influenza vaccines delivered with MNs produced immune responses similar to those from an HN vaccination. [4]