Optimization of impedance spectroscopy techniques for measuring cutaneous micropore formation after microneedle...

The objective of this study was to optimize a reproducible impedance spectroscopy method in elderly subjects as a means to evaluate the effects of microneedles on aging skin.

Human volunteers were treated with microneedles at six sites on the upper arm. Repeated impedance measurements were taken pre- and post-microneedle insertion. Two electrode types were evaluated (dry vs. gel), using either light or direct pressure to maintain contact between the electrode and skin surface. Transepidermal water loss (TEWL) was measured as a complementary technique.

Five control subjects and nine elderly subjects completed the study. Microneedle insertion produced a significant decrease in impedance from baseline in all subjects (p < 0.05, regardless of electrode type or pressure application), confirming micropore formation. This was supported by a complementary significant increase in TEWL (p < 0.05). The gel*direct condition produced the lowest variability between measurements, as demonstrated by a coefficient of variation of 3.8% and 3.5% (control and elderly subjects, respectively). This was lower than variation between TEWL measurements at the same sites: 19.8% and 21.6% (control and elderly subjects, respectively).

Impedance spectroscopy reproducibly measures micropore formation in elderly subjects, which will be essential for future studies describing microneedle-assisted transdermal delivery in aging populations.