Investigation of swelling mechanisms in self-adherent microneedles

Abstract Swellable microneedles (MNs) expand to mechanically interlock with wet biological tissue, offering improved adhesion and enhanced drug delivery over non-swellable counterparts. This study numerically evaluates how the material and geometric parameters of swellable MN arrays influence shape change. Using finite element simulation, MNs were subjected to unconstrained swelling, approximated via a thermal-strain analogy. Optimal MN design must support mechanical interlocking to prevent dislodgement. We observed that wet in vivo environments induce unwanted swelling-mediated curvature, hindering contact and interlocking. We quantified this bending and calibrated gel material swellability using experimental data. To counteract curling, we introduced a design approach to shift the direction of the unwanted curling and improve MN array conformability.