Characterization of skin penetration efficacy by Au-coated Si microneedle array electrode

• Si microneedle array fabricated for sensing skin penetration efficacy.
• Robust Au coated microneedle array proved mechanically stable and reusable.
• Significant reduction of skin impedance compared to flat electrode (>50%).
• Incremental increase of penetration force resulting in impedance change <10%).
• Impact assisted penetration of MNA confirming penetration of stratum corneum (skin-electrode impedance change >90%).

Investigation of skin penetration efficacy by a silicon microneedle array is presented. Experiments were performed on porcine and chicken skin samples in vitro and on human skin in vivo. Solid microneedle arrays (13 × 13 mm2), each consisting of 100 microneedles, were designed and fabricated by deep reactive ion etching process. To evaluate the penetration efficacy through the mechanically and electrically resistant upper skin layer of stratum corneum, the electrical skin impedance change with applied force was measured by using Au-coated Si microneedle array as working electrode in 2 and 3 electrode configurations. Skin impedance changes between 2 and 8% were measured when applying incremental force, increased from 1 to 10 N on a Au metalized microneedle array electrode. When impact assisted penetration of microneedle array was applied instead of incremental increase of applied force, a significant impedance reduction of up to 50% on animal skin and 95% on human skin was obtained, which is a strong evidence of successful skin penetration. Furthermore, the microneedle array electrode showed consistently lower interface impedance compared to the flat electrode for the samples involved. Analyses of Si microneedle mechanical properties revealed that by proper use a satisfactory safety margin (>60) can be achieved.