Figure 1
Figure 1. Chemotherapy-induced cell death increases the stiffness of leukemia cell populations measured by AFM and microfluidic channels. (A) An illustration of the AFM setup (not to scale). A single cell sitting within a microwell is immobilized for force microscopy with an AFM cantilever. A polydimethylsiloxane (PDMS) collar is pressed on the glass to create an open-air chamber. Tubes entering and exiting the chamber continually pass media through, keeping the media fresh over the long time scale of the experiments. The piezoelectric stage moves vertically, causing the cantilever to deflect against the cell. The stage is maintained at 37°C throughout the experiment. (B) An epifluorescence/brightfield overlay of a typical experiment. Seen here are an AFM cantilever tip and 2 dead K562 cells (PI positive, fluorescent), with the left cell immobilized in a microwell. An empty microwell is at the top. Scale bar is 20 μm. (C) Two typical cell indentation acquisitions. As the piezoelectric platform moves the cells up against the cantilever (in the direction of the arrow), the cantilever deflects. When the curves are fit to an elastic Hertzian model, the stiffness of the cells can be determined. The stiffness of a pre-B-ALL cell exposed to 1 μM dexamethasone (red) was 4.3 kPa whereas the stiffness of a control (not exposed to chemotherapy) pre-B-ALL cell (green) from the same patient was 0.2 kPa. (D) Dead (red) lymphoid leukemic cells exposed to 1 μM dexamethasone are significantly stiffer than untreated (green) cells. (E) Dead (red) myeloid leukemic cells exposed to 1 μM daunorubicin are significantly stiffer than untreated (green) cells. Error bars represent standard error. (n > 15, P < .05 for all comparisons of dead/untreated populations). (F) Dual brightfield/epifluorescence microscopy of dexamethasone-exposed pre-B-ALL cells that were passed, from left to right, through PDMS microfluidic channels modeling a branching microvasculature network. Dead (PI+) cells (red arrows) were more likely than live (unstained) cells (green arrows) to initiate obstruction and cause cell aggregation in the 5-μm wide by 12-μm tall, capillary-sized channels. Frame from panel G was taken 15 seconds after that seen in panel F, illustrating the relative mobility of 2 live cells, one of which has left the field of view, compared with dead cells that remain fixed in place. Scale bar is 10 μm.

Chemotherapy-induced cell death increases the stiffness of leukemia cell populations measured by AFM and microfluidic channels. (A) An illustration of the AFM setup (not to scale). A single cell sitting within a microwell is immobilized for force microscopy with an AFM cantilever. A polydimethylsiloxane (PDMS) collar is pressed on the glass to create an open-air chamber. Tubes entering and exiting the chamber continually pass media through, keeping the media fresh over the long time scale of the experiments. The piezoelectric stage moves vertically, causing the cantilever to deflect against the cell. The stage is maintained at 37°C throughout the experiment. (B) An epifluorescence/brightfield overlay of a typical experiment. Seen here are an AFM cantilever tip and 2 dead K562 cells (PI positive, fluorescent), with the left cell immobilized in a microwell. An empty microwell is at the top. Scale bar is 20 μm. (C) Two typical cell indentation acquisitions. As the piezoelectric platform moves the cells up against the cantilever (in the direction of the arrow), the cantilever deflects. When the curves are fit to an elastic Hertzian model, the stiffness of the cells can be determined. The stiffness of a pre-B-ALL cell exposed to 1 μM dexamethasone (red) was 4.3 kPa whereas the stiffness of a control (not exposed to chemotherapy) pre-B-ALL cell (green) from the same patient was 0.2 kPa. (D) Dead (red) lymphoid leukemic cells exposed to 1 μM dexamethasone are significantly stiffer than untreated (green) cells. (E) Dead (red) myeloid leukemic cells exposed to 1 μM daunorubicin are significantly stiffer than untreated (green) cells. Error bars represent standard error. (n > 15, P < .05 for all comparisons of dead/untreated populations). (F) Dual brightfield/epifluorescence microscopy of dexamethasone-exposed pre-B-ALL cells that were passed, from left to right, through PDMS microfluidic channels modeling a branching microvasculature network. Dead (PI+) cells (red arrows) were more likely than live (unstained) cells (green arrows) to initiate obstruction and cause cell aggregation in the 5-μm wide by 12-μm tall, capillary-sized channels. Frame from panel G was taken 15 seconds after that seen in panel F, illustrating the relative mobility of 2 live cells, one of which has left the field of view, compared with dead cells that remain fixed in place. Scale bar is 10 μm.

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