One-touch embeddable microneedles for hair loss treatment.

With increasing clinical demands for painless and easy administration of medications, such as for hair loss, microneedles (MNs) have been widely exploited for facilitating drug permeation in a minimally invasive manner. However, precise dose control and long-term drug delivery without the infection risk through punctured holes have remained unresolved. Herein, we developed swellable microneedles (MNs) with an air-pocket structure, enabling shear-induced implantation inside the skin. The air-pocket MNs (AP-MNs) were prepared by one-step molding process with genipin-crosslinked gelatin solutions. This MN design induced mechanical difference following insertion due to selective hydration at the inserted MN tips, causing them to break at the interface between the swollen tip and the non-inserted column. The AP-MNs (80-90 %) were embedded into the skin and played a barrier function by tightly sealing punctured holes. Minoxidil (MXD) for hair loss treatment were quantitatively loaded in the AP-MNs depending on swellable tip heights, with 90 % of loaded MXD in the AP-MN tips released over 48 h. In animal studies, the MXD-loaded AP-MNs exhibited higher efficiency than topical application for hair loss treatment. These results indicate that the design of shear-induced embeddable MNs could provide a high-efficiency, convenient, safe, and potentially self-administered method for drug delivery.