ABSTRACT Two‐photon polymerization (2PP) 3D printing is an additive manufacturing process to fabricate micro and nanostructures such as microneedles. These can be used as a noninvasive drug delivery tool, wherefore mechanical stability is crucial for effective and safe drug delivery. This study investigates the fabrication and stability of varying 1 mm tall needle geometries with different internal structures (solid, tunnel, and hollow) in an experimental uniaxial compression test setup. The force applied to one single needle was gradually increased to 3 N. The results demonstrate that solid needle designs with a plateau making up 50% of its total height exhibit superior mechanical stability with reduced buckling at higher forces compared to other geometries. Tunnel and hollow designs display comparable mechanical behaviors. With finite element analysis (FEM) the critical load, at which the needle tip becomes unstable and could collapse, is simulated in a nonlinear buckling analysis. Therefore, the viscoelastic needle polymer is characterized in a prior Storåkers material model parameter estimation. The simulation implies that the proposed needle designs can handle 0.6–1.0 N before the tip could collapse. Lastly, the buckling behavior of an optimized needle is simulated to improve the efficiency of drug delivery.
Wittemann et al. (2026) studied this question.