Characterisation of mechanical insertion of commercial microneedles

The protection provided by the human skin is mostly attributed to the stratum corneum. However, this barrier also limits the range of molecules that can be delivered into and across the skin. One of the methods to overcome this physiological barrier and improve the delivery of molecules into and across the skin is via the use of microneedles. This work evaluates the mechanical insertion of two different commercially available microneedle systems, Dermapen (R) and Dermastamp (TM). The influence of biaxial skin strain on the penetration of the two microneedle systems was evaluated ex vivo using a biaxial stretch rig. From the skin insertion study, it was apparent that for all levels of biaxial strain investigated, the Dermapen (R) required less force than the Dermastamp (TM) to puncture the skin. In addition, it was observed that the oscillating microneedle system, the Dermapen (R), resulted in deeper skin insertion ex vivo in comparison to the Dermastamp (TM). The use of this new biaxial stretch rig and the ex vivo skin insertion depth study highlights that the oscillating Dermapen (R) required less force to perforate the skin at varying biaxial strain whilst resulting in deeper skin penetration ex vivo in comparison to the Dermastamp (TM). Although the Dermapen (R) punctured the skin deeper than the Dermastamp (TM), such difference in penetration did not influence the permeation profile of the model drug, imiquimod across the skin as evidenced from a 24-h ex vivo permeation study.