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Technische Universität München

3D tissue models: Upscaling in vitro tests

Electric Impedance Sensing as a Readout of Organoid Viability

Fig. 1: organoids derived from a pancreatic tumor cell line, growing as 3D entities in a dome of basement membrane extract (bme). The organoid cell mass may contribute up to 50% of the total volume of bme.

This collaborative project with Nanion Technologies and the Max Reichert group at Klinikum rechts der Isar is directed towards the investigation of Printed Circuit Board (PCB) technologies for their suitability to achieve a sensor-based readout of 3D cell models such as spheroids or organoids. There is a widespread use of both kinds of 3D cell models for preclinical and clinical research purposes. Fig. 1 shows a microscope image of an organoid culture.

One of the most beneficial features of a sensor-based, kinetic data readout is the ability to monitor the condition of 3D cell models individually and throughout the entire growth and drug incubation period. In contrast to endpoint measurements this allows additional longitudinal observations.

Fig.2: Photograph image of a 96 well test plate with a PCB bottom featuring gold electrodes

Multilayer PCB technology offers high-density integration of electrode structures for electric impedance recordings, industrial upscaling with low product costs and biocompatible assemblies (Fig. 2).

Fig. 3: Finite Element Modelling of spatial distributions of electric potentials and currents in heterogeneous 3D geometries is used to optimize PCB designs with respect to their sensitivity towards the detection of impedance alterations in specified objects under test.

The planning of PCB design usually starts with virtual prototyping, where different kinds of electrode setups and geometries are tested as finite element models (Fig. 3).

Fig. 4: With an altered electric field distribution due to an active “guardring electrode” adjacent to the working electrode, an increased share of working electrode current lines (in red) passes through the 3D object of interest to the counter electrode. Depending on the geometry of measurement, the sensitivity of detecting biological changes will be enhanced


One of the challenges of measuring the electric impedance of 3D culture objects is to guide electric currents through the 3D objects of interest and to avoid bypassing of high-impedance volumes. One of the approaches to achieve that is the use of guardring electrodes equipotential to the measuring working electrodes. Due to an altered electric field distribution with active guardring electrode, an increased share of working electrode current lines (in red) passes through the 3D object of interest. Depending on the geometry of measurement, the sensitivity of detecting biological changes will be enhanced (Fig. 4).

Fig. 5: While high frequency currents (blue arrows) cross the tissue without being disturbed by cellular structures, the electric impedance to lower frequency (<10 – 100 kHz) currents (red arrows) are sensitive to such changes.

Electric impedance measured in-vitro on 3D cellular structures in the 10 kHz frequency range will respond to changes of bulk electrical conductivity (e.g. due to cell metabolism) and structural changes that can be related to alterations or damages of cell-cell connections and cell membrane integrity (Fig. 5).

 

Contact: Dr. Martin Brischwein, brischwein@tum.de

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