Finite element analysis of polymeric microneedle insertion into skin

• Deformable FE models reveal polymeric microneedle failure modes not captured by rigid body assumptions. • Just 5° misalignment causes stresses exceeding polystyrene yield strength, leading to microneedle fracture. • Skin curvature induces non-uniform tip contact and higher bending forces on outer array microneedles. • Tip diameter linearly affects insertion force while aspect ratio impacts penetration depth. • Not all polymers overcome skin resistance—HA fails while PS, PC, and PLA successfully penetrate. Polymer-based microneedles have the potential to improve transdermal drug and vaccine delivery. However, their mechanical strength remains a critical challenge. In this study, we developed a 2D finite element model to investigate the polystyrene (PS) microneedle insertion into a hyperelastic bilayer representing skin. The model treated the microneedles as deformable bodies, enabling observation of microneedle-skin interactions and potential microneedle failure modes, particularly under applicator misalignment and skin curvature conditions. The effects of microneedle geometry, array interspacing, and material properties were also examined. We found that misalignment insertion at an angle of just 5 degrees can cause the stresses at the microneedle base to exceed the yield strength of PS, indicating high sensitivity to off-axis loading. The curvature of the skin plays a vital role in non-uniform contact between the microneedle tips and the skin surface, resulting in a higher bending force acting on the outer microneedles. Microneedle shape and tip angle significantly influenced penetration force, while tip diameter notably affected insertion force. Furthermore, the model showed that not all polymers can overcome skin resistance forces, even when made into the same microneedle geometry. These findings provide important insights for optimizing polymeric microneedle designs to enhance strength and skin penetration reliability.