In vitro evaluation of microneedle strength: a comparison of test configurations and experimental insights

To ensure the safe and effective application of microneedles for drug delivery to the skin, the mechanical properties the microneedles and their ability to penetrate the skin are critical quality control parameters. While ex vivo and in vivo evaluations may be valuable to demonstrate actual skin penetration, they can be costly and difficult to accomplish consistently due to the inherent biological variability of the skin. On the other hand, in vitro approaches provide a facile means of characterising the intrinsic mechanical properties of the microneedles, independent of such biological variability. Thus, they can be used to predict and screen for the in vivo and ex vivo performance of new microneedle formulations. A variety of experimental configurations has been reported in the literature focusing on mechanical evaluations including compression tests and in vitro microneedle insertion studies using a non-biological skin simulant, Parafilm® M. However, there has been a paucity of data that address the comparability of the various experimental configurations. Here, we evaluated several methods for assessing the mechanical properties of microneedles in vitro, including their ability to insert into a non-biological skin simulant under a defined axial force, and share some insights into the experimental design and data interpretation.