Figure 3

Differentiated HL-60 cell thermotaxis in response to temperature gradients. (a) Schematic representation of the microfluidic temperature gradient chamber with cross sections in X and Y directions. Copper reservoirs were used as a heat source and a heat sink, with their temperatures held constant at 65 °C and 5 °C, respectively. (b) 3D Volume temperature gradient distribution computed by COMSOL Multiphysics. A 27–43 °C temperature gradient is generated along the 2 mm wide microchannel. (c) Temperature gradient effects on cell adhesion and migration. After application of the gradient, ~ 40% of cells remained attached. 72% of the attached cells were non-mobile. Of the mobile cells, approximately 50% migrated towards the heat sink (negative thermotaxis) and 40% migrated towards the heat source (positive thermotaxis). (d) Differentiated HL-60 cell speed in the presence of the temperature gradient. 25 cells in each direction were tracked. No significant differences in cell speed were found between those moving towards the heat source and those toward the heat sink, but both were approximately 50% slower than those in a constant 37 °C environment. (e) Migration tracks of 50 cells migrating both towards and away from the heat source. Cells that migrated at an angle of 60˚ or less with respect to temperature gradient direction (in this case the Y axis) are considered to have directed migration towards either the heat source or sink (red and blue triangles). 10% of cells showed non-directed migration. (f) Polar histogram of the relative angles from cell step to cell step calculated for 50 cells tracked under temperature gradient. Small steps less than 2 µm were disregarded. For all: 2 independent experiments were performed. Error bars represent 95% CIs of the data. ****P < 0.0001, N.S. not significant.