CSEM Scientific and Technical Report 2008

On-chip Electrical Characterization of Cell Layers
M. Favre, N. Blondiaux, R. Ischer, M. Liley, A. Andar • , N. Gadegaard • , M. Riehle •
A microfabricated chip with a silicon nitride porous membrane and integrated platinum electrodes is being developed for cell culture and analysis.
The electrodes allow the measurement of the electrical resistance of epithelia cell layers that gives an evaluation of their tightness. This tool is
designed for in vitro screening in both toxicology and pharmacology.
In the body, epithelial cells are organized in sheets that make
up the epithelia. All epithelia have the function of providing a
barrier between body and the external world. In order to
achieve this, individual epithelial cells are joined via tight
intercellular junctions that make the epithelium impermeable.
Thus, transport across the epithelia occurs essentially through
the epithelial cells (trans-cellular transport) rather than
between or around the cells (para-cellular transport).
The study of epithelia and their transport properties is
important in both pharmacology and toxicology as it is
necessary for our understanding of where, when and how
toxins and drugs move through our bodies. These studies
have often relied on animal models, although in recent years,
in vitro models using epithelial cell layers have become
increasingly important.
In vitro models of epithelia must be tested for the presence of
tight junctions and the absence of gaps between the cells, to
ensure that transport across the in vitro model closely
resembles that of the epithelium in vivo. One of the most
widely used approaches to determine the tightness of a layer
of cells is the TransEpithelial Electrical Resistance (TEER)
measurement. A four-point method is usually used to minimize
the influence of the electrodes on the measured resistance of
the cell layer.
Figure 1: Left – Microfabricated chip with five culture wells and the
platinum electrodes around them; Right – Optical image of Calu-3
cells grown on the porous membrane in one of the wells.
At CSEM, a chip has been developed for the study of in vitro
model epithelia and their transport properties. The chip
contains five wells in which cells can be seeded and cultured.
Integrated platinum electrodes allow TEER measurements in
parallel across all five wells (Figure 1). The base of each well
consists of a porous membrane in order to allow the formation
of cell layers and the movement of toxins or drugs through the
membrane. The necessary liquids, such as culture medium or
buffers, are transported to and from the cells by a microfluidics
system. For each well, one pair of electrodes is used to inject
the current into the system, while a second pair of electrodes
measures the potential across the cell layer in order to
determine the resistance.
The porous membrane, with the epithelial cell layer on it,
divides the microfluidics circuit into a top and a bottom
compartment. A solution containing a drug or toxin is
transported to the cell layer in the top compartment that
represents the exterior of the body. Those substances that
cross the cell layer will move to the bottom compartment
where their presence can be detected.
Figure 2 shows the assembly of all components of the system.
The top (and bottom) part of the system is composed of:
• A microfabricated chip with the cell culture wells
• Polydimethylsiloxane (PDMS) microfluidics to deliver
culture medium and solutions to the cell layers
• A glass slide to apply pressure on the PDMS and seal all
the microfluidics elements
• Electrical contacts (10 on each side) that connect to the
on-chip platinum electrodes
Figure 2: Assembly of the chip, PDMS microfluidics, glass slide and
electrical contacts
Work to date has shown that cell growth in the wells can be
followed using electrical measurements and that cell layers’
are obtained with electrical properties comparable to those
described in literature. Future studies will focus on transport
across the cell layers.
This work was partly funded by the European Commission
(Contract number 515843-2). CSEM thanks them for their
support.
• Centre for Cell Engineering, University of Glasgow
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