Skin-on-a-Chip: Transepithelial Electrical Resistance and Extracellular Acidification Measurements through an Automated Air-Liquid Interface

Abstract

Skin is a critical organ that plays a crucial role in defending the internal organs of the body. For this reason, extensive work has gone into creating artificial models of the epidermis for in vitro skin toxicity tests. These tissue models, called reconstructed human epidermis (RhE), are used by researchers in the pharmaceutical, cosmetic, and environmental arenas to evaluate skin toxicity upon exposure to xenobiotics. Here, we present a label-free solution that leverages the use of the intelligent mobile lab for in vitro diagnostics (IMOLA-IVD), a noninvasive, sensor-based platform, to monitor the transepithelial electrical resistance (TEER) of RhE models and adherent cells cultured on porous membrane inserts. Murine fibroblasts cultured on polycarbonate membranes were first used as a test model to optimize procedures using a custom BioChip encapsulation design, as well as dual fluidic configurations, for continuous and automated perfusion of membrane-bound cultures. Extracellular acidification rate (EAR) and TEER of membrane-bound L929 cells were monitored. The developed protocol was then used to monitor the TEER of MatTek EpiDerm^TM RhE models over a period of 48 hours. TEER and EAR measurements demonstrated that the designed system is capable of maintaining stable cultures on the chip, monitoring metabolic parameters, and revealing tissue breakdown over time.

Keywords: Organ-on-a-Chip; TEER; impedance; label-free monitoring; reconstructed human epidermis; skin models.

Figure 1

Schematic diagrams: (a) Standard BioChip with fluidic head, and (b) modified BioChip with transepithelial electrical resistance (TEER) fluidic head. The fluidic system with the medium is highlighted in red. IMOLA: Intelligent mobile lab.

Figure 2

The dual fluidic network consists of (a) a nutrient delivery module, capable of transporting cell culture medium to and from the BioChip, and (b), a TEER measurement module, which periodically perfuses the apical side of the membrane with phosphate buffered saline (PBS) to measure TEER. PMP: Pump; LBTM1: Low buffer treatment medium; SDS1: SDS Medium; TM: TEER medium, TS: Test substance

Figure 3

Recorded extracellular acidification (pH in mV vs. time) of L929 cells before and after addition of sodium dodecyl sulphate (SDS). mV: millivolts.

Figure 4

Calculated extracellular acidification rate (EAR) and TEER of L929 cells during 55-min stop intervals; Ω: Ohms.

Figure 5

(a) TEER values (real part) of the MatTek over time before and after exposure to SDS medium (at time = 37). (b) Green areas indicate time periods where fluidic pumping is occurring to either fill or remove PBS from the RhE model. Red spaces indicate places where fluidic pumping in the fluidic head is not occurring. Z: Impedance.