Impedance-based monitoring for tissue engineering applications

Impedance is a promising technique for sensing the overall process of tissue engineering. Different electrode configurations can be used to characterize the scaffold that supports cell organization in terms of hydrogel polymerization and degree of porosity, monitoring cell loading, cell proliferation as well as the spatial distribution of cell aggregates in 3D. We have previously shown that impedance measurements allow accurate determination of conductivity in physiological solutions independent of validation and analysis of a specific equivalent circuit. Similarly to a physiological solution, cell culture medium conductivity, and hence the measured impedance, can respond to proliferating or dying cells populating the scaffold. Impedance may therefore be a key parameter for monitoring the biochemical dynamics that modulate 3D mammalian cell cultures over time. Furthermore, the conductivity of the medium filling the pores of the scaffold can serve as the basis for porosity determination using Archie’s law. Different networks of structured or random channels and degree of porosity can be detected. In addition, by combining a number of two-, three- and four-terminal (2T, 3T, 4T) configurations, it is possible to obtain complementary information on spatial distribution of cells in a 3D scaffold. 2T- and 3T configurations also reflect the impedance at the interface between an electrode and cell-loaded scaffold (polarization impedance, Z_p), which may convey a further degree of information about the biochemical phenomena taking place in that sub-volume.