A penetration efficiency model for the optimization of solid conical microneedles’ geometry

Microneedles (MNs) are promising alternatives to pills and traditional needles as drug delivery systems due to their fast, localized, and relatively less painful administration. Filling a knowledge gap, this study investigated and optimized the most influential geometrical factors determining the penetration efficiency of MNs. The effects of height, base diameter, and tip diameter were analyzed using the finite element method, with results showing that the most influencing factor was base diameter, followed by height. Moreover, the taper angle, which is dependent on all the geometrical factors, was found to directly affect the penetration efficiency at a fixed height. An additional model was developed to relate the height and taper angle to penetration efficiency, and the results were experimentally validated by compression testing of MN array prototypes printed using two-photon photolithography. The numerical model closely predicted the experimental results, with a root mean square error of 9.35. The results of our study have the potential to aid the design of high-penetration efficiency MNs for better functionality and applicability.