Evaluation of the effect of polymeric microneedle arrays of varying geometries in combination with a high-velocity applicator on skin permeability and irritation.

Polymeric microneedles offer the advantages of being both mass-producible and inexpensive. However, their weakness lies in the fact that they are not adequate for sharp fabrication of a needle tip, which is an important factor for effective penetration. We hypothesized that effective penetration can be achieved using a high-velocity application system. Therefore, in the present study, we investigated the influence of various polymeric microneedle array geometries on skin permeability and irritation using such a system. Volar forearms of 16 healthy volunteers were treated using the microneedle system with four different parameters: applicator velocity (4.3, 6, and 8.5 m/s), tip radius (10, 15, and 20 μm), length (100, 200, and 300 μm), and number of needles (189 and 305 on a 50-mm(2) area). A higher velocity of piercing clearly enhanced skin permeability and damage. A larger tip radius resulted in lower skin permeability and irritation at an applicator velocity of 4.3 m/s but did not have an effect at 6 m/s. Skin permeability was positively variable, ranging from 100 to 200 μm of needle length, and needle number showed no influence in the range investigated. In conclusion, a faster application speed could significantly enhance skin permeability and damage and compensate for insufficient penetration of the larger tip radius and shorter needles, which are also important factors for effective insertion.