Age-Dependent Finite Element Analysis of Microneedle Penetration into Human Skin: Influence of Insertion Velocity, and Microneedle's Geometry and Material

Abstract

Microneedles offer a minimally invasive alternative to hypodermic needles for drug delivery and point-of-care diagnostics. Previous studies on microneedle insertion force often used human skin with constant mechanical properties. However, this study, for the first time, investigates the combined effect of human age (29–68 years) and other variables such as insertion velocity (3 and 4.5 m/s), material (poly(glycolic acid) (PGA), Vectra MT-1300, and Zeonor 1060R) and geometry (cone-shaped and tapered cone-shaped) on insertion force using finite element analysis (FEA). The results show that insertion force increases significantly with age due to higher stratum corneum (SC) stiffness and failure criteria. For example, for a PGA cone-shaped microneedle at 4.5 m/s, the insertion force is 111.56%, 64.09%, 36.46%, and 10.52% higher for individuals aged 68, 53, 41, and 33 years, respectively, compared to 29 years. Microneedle material also significantly affects insertion force, with stiffer materials requiring less force to penetrate the SC. Cone-shaped microneedles exhibit lower insertion forces than tapered cone-shaped designs due to their smaller tip angle. Increasing insertion velocity substantially reduces the insertion force, with higher velocity having a more evident effect than changes in microneedle geometry. Finally, stress distribution within the microneedle and skin deformation are evaluated.