Optimal Microneedle Design for Drug Delivery Based on Insertion Force Experiments with Variable Geometry

Microneedles, which prick micro holes in the stratum corneum (SC), are promising minimally invasive drug delivery devices alternating pills, conventional needles, or transdermal patches. However, the microneedle fabrication based on the optimal design has been studied rarely. In this paper, the forces required to insert microneedles into a skin model were measured over the various geometries in order to optimize the microneedle design. To measure the insertion force, the microneedles were fabricated with inclined UV lithography and hot embossing processes. The insertion force was measured with a custom-made dynamic displacement device which can measure and record the force of mN range loads. The insertion force is strongly related with tip angle and radius of tip's curvature. The insertion forces increase with increasing width of shaft, but the relation is very week and the radius of fillet in the experimental range has no influence on the insertion force. This result can be used as an optimal design guide on the geometries of microneedle.