Electrical impedance spectroscopy on biological barriers

  • Elektrische Impedanzspektroskopie an biologischen Barrieren

Linz, Georg Franz; Wessling, Matthias (Thesis advisor); De Laporte, Laura (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik Series AVT.CVT - Chemical Process Engineering 26
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The ability to regulate the transport of ions and molecules is essential in supplying issues with nutrients, removing toxic compounds, or preventing the invasion of pathogens into deeper tissues. Barrier-forming epithelial and endothelial tissues possess a unique ability to form tight cell-to-cell connections that create compartmentalization in multicellular organisms and prevent unhindered diffusion across cellular barriers. Therefore, understanding the pathophysiology of various cellular barriers is crucial for fundamental and pharmaceutical research. Recently, in vitro models for various cell barriers have been introduced, allowing researchers to study transport phenomena across barriers in depth. However, cell culture experiments often suffer from limited commercial availability of laboratory-scale bioreactors, which allow experiments to be conducted under physiologically relevant conditions. Cultivation conditions with increased chemical, and physical complexities, close to the natural environment, are expected to bridge the gap between laboratory experiments and in vivo tissues. The development of barrier models is accompanied by the continuous barrier monitoring of the state and health during experiments. Cell layer observations commonly conducted by measuring the electrical resistance of the barrier by applying a direct current or a low-frequency alternating current. The drawback of this measurement is that the contribution of the cell layer resistance cannot be distinguished from the medium resistance without a comparative measurement of a blank sample. In this thesis, electrical impedance spectroscopy (EIS) was utilized in static and dynamic cultivations to overcome the disadvantages of single-frequency resistance measurements typically applied in cell barrier research. Contrary to the standard approach, the electric circuit modeling of EIS data allows for the separation of the barrier from the medium resistance and reveals the capacitive properties of the cell barrier. In the first part, the cell line Caco-2 as a model barrier was cultivated in transwell inserts, and EIS was measured by connecting a modified chopstick-like electrode to a potentiostat. Cell layer resistance and capacitance were employed to evaluate the influence of various substrate surface functionalization sand barrier disruption mechanisms on Caco-2 cell barriers. The second part of the work focused on the design of bioreactors to create a more physiological environment for the cell barrier. Furthermore, a 3D-printed bioreactor and a silicon-based microfluidic bioreactor were developed for cell cultivation under continuous medium flow. Both reactor systems were equipped with a four electrode setup for EIS measurements to allow in situ cell barrier monitoring. The functionality of the device was demonstrated by cultivating a Caco-2 cell barrier, while fluidic and electric field simulations supplemented the experimental results. The results validate that EIS on cell barriers cultivated in transwell inserts and bioreactors reveal the capacitance and resistance, which allow conclusions about the shape and tightness of the cell layer.

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