In vitro quantification of optimal impact properties for microneedle penetration

Abstract

Microneedles provide a minimally invasive means of delivering drugs into the body via the skin. The challenge to effective microneedle penetration is to bypass the inherent elasticity of the stratum corneum, the skin’s uppermost layer. However, there are few studies in the literature which focus on optimising parameters for repeatable penetration into skin. Here, a dropped weight impact testing rig was developed to allow high-density polymethylmethacrylate (PMMA) microneedles to be applied on to neonatal porcine skin at various velocities and forces. Methylene blue and histological staining were used to determine penetration effectiveness. Whilst methylene blue staining confirmed successful penetration of the stratum corneum, subsequent histological imaging demonstrated how deeply the microneedles had breached the layers of skin. The optimal parameters of velocity and force for reproducible and predictable penetration of the skin were found to be 4.52-4.8 ms-1 (nominal velocity of 3 ms-1) and 3.35-4.17 N.