Development of hollow out-of-plane polymer microneedles using solvent casting

Abstract

In recent years, extensive research has been done to find innovative ways of drug delivery to replace traditional injection using hypodermic needles. Although microneedles are proposed to provide one of the most effective and convenient transdermal drug delivery methods, their expensive fabrication techniques have created a barrier for their mass fabrication and as a result, their entry to the commercial market. A novel method, based on solvent casting, is presented for inexpensive fabrication of hollow out-of-plane polymer microneedles. Microneedles are formed during a solvent evaporation process which leaves a thick polymer layer around pillars in a pre-fabricated mold. This process is fast and allows fabrication of microneedles in variety of shapes and dimensions. The effectiveness of the microneedle arrays fabricated using this process has been demonstrated through in vivo and in vitro experiments. In order to further optimize the microneedle design, a novel experimental method based on confocal microscopy and particle image velocimetry (PIV) is presented for characterizing the flow in a thin film during solvent casting. Using this method, the impact of temperature on polymer film formation, on a vertical profile in a mold, is investigated and discussed. This method also allowed observing some important phenomena during solvent casting such as a surface counter flow. The PIV measurements show significant differences in the flow velocity fields at different temperatures that correlate with different final polymer thicknesses on the vertical wall of the mold.