2025 Volume 14 Pages 196-204
Microneedle arrays (MNAs) consisting of numerous tiny needles have attracted considerable attention for selective intradermal and subcutaneous delivery of pharmaceutical agents. Since reliable skin puncture and insertion are essential for dose control, applicators that push MNAs into the skin using springs or other mechanisms have been extensively researched. The puncture and insertion capabilities of an MNA depend on the compressive load generated when it is pressed against the skin. The compressive load is considered to be influenced not only by the MNA per se and the application method, but also by the structures and mechanical properties of the biological tissues at the application site. Nevertheless, most previous studies on evaluating the puncture and insertion abilities of MNAs did not consider the impact of subcutaneous soft tissues. In this study, the compressive loads generated by an applicator were measured at various sites of the body in 15 healthy adults. We used a proprietary test applicator that employed a spring to impact the skin at high speed, and a system that can measure the short-term load generated during impact. Furthermore, the structures and mechanical properties of the skin and subcutaneous soft tissues at the same body locations among the 15 individuals were evaluated and correlated with the measured compressive loads. The compressive load induced by the impact varied significantly with location, and correlated highly with the distance to the bone. There was no correlation with age, sex, or body mass index, or with the structure or mechanical properties of the skin. These results indicate that the structure of the subcutaneous tissue has a strong influence on the compression load and the ability to puncture and insert the MNA. The findings of this study can be useful for developing MNAs and applicators, determining their essential physical characteristics, selecting the appropriate administration locations, and developing non-clinical methods for evaluation.
