The Capillary number effect on the capture efficiency of cancer cells on composite microfluidic filtration chips

We present a systematic study of the Capillary number (Ca) effect on the capture efficiency of cancer cells on a composite microfluidic filtration chip. By altering the Ca in microchip experiments, the balance between the viscous force and the cell cortical tension affecting the capture efficiency has been investigated experimentally and analyzed theoretically. A `Phase Diagram´ for the capture efficiency of microfiltration chips is presented, for the first time, as a function of the normalized cell diameter and Ca. A critical value of Ca, around 0.03~0.04, has been identified for enhancing the capture efficiency of cancer cells. The phase diagram is found to be consistent with the results of cancer-cell capture in microfiltration systems reported previously by others. The diagram can be a useful tool for designing the next generation microfiltration devices for isolating circulating tumor cells.