title: Impedance spectroscopy for the non-destructive evaluation of in vitro epidermal models.
abstract: OBJECTIVE
  Reconstructed human epidermis (RHE) is standardly used for the risk assessment of chemical compounds. However, analysis is dependent on invasive methods such as histological processing or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) staining.
  
  
  METHODS
  As an alternative, we have developed a non-destructive technology to analyze the integrity of epidermal equivalents based on impedance spectroscopy. RHEs were generated and impedance spectra were recorded. from these spectra, we extrapolated electrical characteristics such as the capacitance and the ohmic resistance. Furthermore, the measurable electrical parameters were used to quantify the effects of mechanical and chemical disruption of the epidermal integrity.
  
  
  RESULTS
  A fully matured RHE exhibits typical impedance spectra in a frequency ranging between 1 Hz and 100 kHz, which is comparable to the spectra of freshly isolated human epidermal biopsies. We could show that, during RHE maturation, these characteristics change significantly. Thus, capacitance and ohmic resistance can be employed as a criterion for the quality control of skin equivalents. Additionally, our application of impedance spectroscopy reveals sufficient sensitivity to detect a transient decreased ohmic resistance caused by 2-propanol, which is classified as a non-irritant by MTT assays.
  
  
  CONCLUSIONS
  These results indicate that impedance spectroscopy can be employed as a non-destructive complementary method to assess mild irritative effects, which is currently not possible.
authors.affiliation: Project Group Regenerative Technologies in Oncology, Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB), Roentgenring 11, Wuerzburg, 97070, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Groeber
authors.forename: L
authors.initials: L
authors.lastname: Engelhardt
authors.forename: S
authors.initials: S
authors.lastname: Egger
authors.forename: H
authors.initials: H
authors.lastname: Werthmann
authors.forename: M
authors.initials: M
authors.lastname: Monaghan
authors.forename: H
authors.initials: H
authors.lastname: Walles
authors.forename: J
authors.initials: J
authors.lastname: Hansmann
mesh_terms: D019840:2-Propanol / Q000494:pharmacology; D001696:Biomechanical Phenomena; D002478:Cells, Cultured; D058266:Dielectric Spectroscopy / Q000379:methods*; D017097:Electric Impedance; D004817:Epidermis / Q000737:chemistry* / Q000187:drug effects / Q000473:pathology; D006801:Humans; D013314:Stress, Mechanical
chemical_list: D019840:2-Propanol