Fabrication and evaluation of dissolving bird-bill microneedle arrays

Coated microneedles (MNs) have some disadvantages, such as low mechanical strength, the risk of clogging and infection due to repeated application, and denaturation at high temperatures. We aimed to fabricate a dissolving bird-bill MN (dBB MN) with a vertical groove between two thin plate-shaped needles and evaluated its ability of transdermally deliver a large-molecular-weight insulin drug into systemic circulation. Hydrogels with various concentrations of polyvinylpyrrolidone (PVP) or sodium hyaluronate (HA) were prepared, and dBB MN arrays were fabricated by micromolding under negative pressure for potential mass production. The needle height of the dBB MN was maximum when the hydrogel was 25 w/w% PVP, with a viscosity of 8–9 Pa∙s. Furthermore, the buckling force of dBB MNs made from 25 w/w% PVP was 130.6 ± 51.0 mN, which increased to 195.6 ± 65.3 mN when insulin was added at 1 w/w%. The blood glucose concentration in diabetic rats decreased slowly and significantly after a 3-h application of the insulin-loaded dBB MN array. Therefore, the dBB MN array demonstrated sufficient ability to puncture rat skin and transdermally deliver a large-molecular-weight drug into the systemic circulation. These findings suggest that the dBB MN array holds promise as a minimal invasive drug delivery platform, with potential applications in improving patient adherence and expanding access to essential therapies, particularly in resource-limited settings.