Modeling of Elastoplastic Deformation of Polymeric Microneedles using Finite Element Method

Polymeric microneedles have attracted attention as a minimally invasive medical device. To reduce pain during insertion, the needles should be as thin and small as possible. However, the relatively low mechanical strength of polymer materials imposes limitations on the needle shape. To establish the design principles for polymer microneedle geometries, we conducted elastoplastic analysis using the finite element method. Young's modulus, isotropic tangent modulus, and yield stress were obtained by bilinear fitting of the stress-strain curve. Prescribed displacements were applied to three-dimensional solid model of microneedles with varying tip diameters (45, 80, 110 μm) to achieve total reaction forces of 100, 200, and 300 mN at the tip surface, and the deformation and von Mises stress distributions were calculated. In the simulation, elastic deformation was calculated using Young's modulus in areas where the von Mises stress was below the yield stress, whereas plastic deformation was calculated using the isotropic tangent modulus in areas where the stress exceeded the yield stress. Microneedles with tip diameters of 45 μm and 80 μm undergo plastic deformation under a total reaction force of 200 mN or greater, whereas microneedles with a tip diameter of 110 μm deform only elastically, even at 300 mN. Because the simulation results align with the findings from previous insertion and compression tests, the simulation model developed in this study is expected to effectively predict the deformation during insertion in the design of microneedles.