Cell deformation by dielectrophoretic fields

The stiffness of cells is strongly influenced by specifics in their cytoskeleton. Their mechanical properties, therefore, are an easily accessible parameter for distinguishing between cells. Monitoring the cell deformation under the influence of external forces provides all the advantages of a label-free characterization, e.g. avoiding interference with the physiological state and obviating time-consuming labeling steps that also increase the intricacy of microsystems. In this way, individual cells can be identified in on-chip microfluidic applications before they are transferred to further manipulation steps, like fusion, sorting, exposure to chemicals or others. We use an electrically induced stretching of intact cells. This gives a distinct elongation of different cell lines. As an example system, we present results obtained from two well-established cancerous and non-cancerous cell lines. They differ in the extent of stretching displayed at the same electric forces and in the remanence strain after electric field removal. This deformation reflects differences in the internal cell structure: separate perturbation of cytoskeleton components indicated that the mechanical response in the chosen regime is defined primarily by the microtubule system. The advantage of electric fields for this purpose is that the integration of only two microelectrodes into the microfluidic chips is sufficient. This solution, therefore, is cheap since the respective manufacturing techniques are well established. The electric fields can be controlled finely by appropriate software programs. Overall, these benefits facilitate the transition to an automated and parallelized cell identification module.