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The aim of this work is to provide optimization tools for cell and tissue engineering processes through continuous monitoring of cell cultures. Structural cell properties can be obtained from non-destructive electrical measurements by using electrical impedance spectroscopy (EIS). EIS measurements on monolayer animal cell cultures are usually performed using a two-electrode strategy. Because of this, the measurement is very sensitive to the electrode covering ratio and to the degree of adherence of cells. Of course, these parameters give useful information but can mask the behaviour of the cell layer above the electrodes. In a previous work, preliminary measurements with commercial microelectrode structures were performed with simulated grow processes using the settlement of cell suspensions with two and four microelectrode strategies to validate the technique. In this work, real cell growths of Vero cells are described and the resulting EIS biomass density estimators are compared to cell counts. The four-electrode impedance spectra are fitted to the Cole-Cole impedance model and the time course of their parameters are extracted and studied.

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BACKGROUND: Acquisition of electrical impedance spectroscopy (EIS) measurements enables one to obtain information about the features of cell cultures, which can be applied for real-time and on-linemonitoring purposes.\ud RESULTS: Impedance measurements were carried out in three different cell specimens with different sizes and shapes (Vero cells, hybridoma and Escherichia coli) at different stages of cell culture, as well as during a controlled detachment process of\ud an adherent animal cell line. The relaxation spectra obtained were fitted to a Cole impedance model and the corresponding\ud parameters analyzed. The use of a four-electrodes measurement system decreased the dependency on the electrode interface’s\ud impedance, and thus resulted in a systemmore sensitive to the cell features. The EISmonitoring of different cultures expansion\ud showed the expected inverse proportional relationship between the central relaxation frequency and the cell cross-sectional\ud area. The morphological changes of fibroblast cells during the detachment processes were also studied. Interestingly, EIS\ud displayed the proportional relationship between the ¿ parameter of the Cole impedance model and the cell shape dispersion\ud from sphericalmorphology (considering spherical shape ideality).\ud CONCLUSION: The results obtained reveal the potential for developing a real-time monitoring tool for cell morphology features\ud such as cell size and shape, which are involved inmany cellular processes like cell expansion, differentiation, cell attachment or\ud cell death.Peer ReviewedPostprint (author's final draft

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