In this work, we describe a novel tool for monitoring the quality of cell cultures in terms of contamination and genomic stability in real time. The proposed platform, the so-called heat-transfer method (HTM), enables to monitor the heat-transfer resistance at solid-liquid interfaces in real-time.1 Previously, it was shown that it is possible to detect cells in buffer solution in a fast, low-cost, highly selective and specific manner by combining HTM with surface imprinted polymers (SIPs).2 SIPs are synthetic cell receptors that can be made via various routes including the stamping method that was used here.3 To this extent, aluminum chips were coated with semi-cured polyurethane by spin coating. In parallel, a monolayer of target cells (the cell type one wishes to detect) was applied onto a PDMS stamp that was pressed onto the polyurethane-covered chip. The polymer layer was cured overnight, enabling the cross-linking polymer to interact with the template cells. After removal of the stamp and cells, microcavities were left behind on the stamp that are complementary to the template cells in size, shape and the distribution of functional groups.3 When cells are kept in culture for a prolonged period of time, the quality of these cell lines is often compromised.4 The lack of tools to effectively monitor cell culture quality in real time forces researchers to discard cell lines after a limited number of cell passages. Although the gold standard cell culture quality assay, STR DNA profiling allows researchers to uniquely identify cells and compare their cell cultures to the original cell line in a relatively straightforward manner,5 its use for routine screening of cell cultures is limited. The technique is typically slow, labor-intensive, the data interpretation requires some expertise and it needs to be used in a lab environment. In this work, we offer a label-free, fast, low-cost and user-friendly alternative that can be used on-site.
To assess the platform’s potential for cell culture quality screening, the breast cancer cell line ZR-75-1 was cultured for a prolonged period (25 passages). In parallel, a descendant, morphologically identical cell line that differs from the original cell line only in its growth pattern (steady adherent growth versus fast suspension growth) was cultured in the same lab. This cell line was acquired after the original cell line was cross-contaminated in a previous experiment, further stressing the need for a user-friendly tool to monitor cell culture quality in real time.
During the prolonged culturing phase of the ZR-75-1a cell line, a sample of the cell culture was analyzed with HTM at given time intervals. Initially the rise in thermal resistance (Rth) upon exposure to a cell culture sample remained constant. However, at higher passage numbers the signal started decaying, indicating that the cells had changed. Visually it could be seen that a number of cells started growing in suspension, possibly caused by a cross-contamination of the ZR-75-1 cell culture with the faster growing descendant cell line, which would explain the drop in Rth. These findings were confirmed by classical STR DNA profiling, indicating that our platform is indeed capable of monitoring the quality of cell cultures in real-time.
van Grinsven, B.; Eersels, K. et al. ACS Appl. Mater. Interfaces 2014, 6, 13309-13318.
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Acknowledgement: Funding by the Interreg Project “MicroBioMed” and the KU Leuven project “Smart Cellular Scaffolds” is greatly appreciated.