title: Optimization of impedance spectroscopy techniques for measuring cutaneous micropore formation after microneedle treatment in an elderly population.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  Impedance spectroscopy reproducibly measures micropore formation in elderly subjects, which will be essential for future studies describing microneedle-assisted transdermal delivery in aging populations.
authors.affiliation: Department of Pharmaceutical Sciences and Experimental Therapeutics, University of Iowa College of Pharmacy, Iowa City, Iowa, USA.
authors.forename: Megan N
authors.initials: MN
authors.lastname: Kelchen
authors.forename: Grant O
authors.initials: GO
authors.lastname: Holdren
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Farley
authors.forename: M Bridget
authors.initials: MB
authors.lastname: Zimmerman
authors.forename: Janet A
authors.initials: JA
authors.lastname: Fairley
authors.forename: Nicole K
authors.initials: NK
authors.lastname: Brogden
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D058266:Dielectric Spectroscopy; D016503:Drug Delivery Systems; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009339:Needles; D011312:Pressure; D012867:Skin / Q000648:ultrastructure*; D015595:Skin Aging; D014870:Water Loss, Insensible; D055815:Young Adult