Using Oscillation to Improve the Insertion Depth and Consistency of Hollow Microneedles for Transdermal Insulin Delivery with Mechanistic Insights

Microneedles (MNs) offer the potential for discrete and painless transdermal drug delivery, yet poor insertion and dosing consistency have hindered their clinical translation. Specifically, hollow MNs are appropriate for the administration of liquid modalities, including insulin, which could prove to be beneficial for patients with type 1 diabetes mellitus. This work aimed to design and manufacture a hollow MN with an improved insertion and delivery profile suitable for insulin administration. <i>Ex vivo</i> insertion studies demonstrated that oscillation of MNs upon insertion into skin produced a favorable insertion profile, with reduced variation, compared to static MN insertion. Histological staining showed that this could be due to the repeated motion of the oscillating MN disrupting elastic fibers in the dermis. Additionally, permeation studies demonstrated that increased quantities of insulin were able to permeate the skin when oscillation was employed compared to static MN insertion. This study has shown that oscillation is a valuable tool in improving the transdermal delivery of insulin via a single hollow MN <i>in vitro</i>. Moving forward, <i>in vivo</i> studies should be completed to gain a fuller understanding of the benefits of the oscillation of MNs on transdermal drug delivery.