Drug resistance heterogeneity in MM. The human MM cell lines H929 and H929/60, resistant to HYD-1 were suspended in matrigel and loaded in a microfluidic chamber, across which a stable drug (HYD-1) gradient (from 0 to 50uM) was established. The media contained a fluorescent dye to mark the nuclei of dead cells (A). The fluorescent channel was converted to a black and white mask (B), which was superimposed to the brightfield channel (C), removing the dead cells (D). The number of live cells for each region of interest (ROI), or drug concentration, was quantified (E). After 24h of drug exposure the number of live cells is significantly reduced (F). Through non-linear regression (G), we determined the parameters of dose response of each population (H).