Figure 4.

Microfluidic applications for embedded microbubbles. (a) Controlled out-of-plane rotation of a single HeLa cell. The microstructure is excited at a constant frequency and voltage of 69.2 kHz and 5 V_PP, respectively. The white arrow denotes the direction of the specimen’s rotation, while the red arrow highlights a spot on the specimen’s surface. (b) Microfluidic mixing of two liquids in a 150 μm wide microchannel based on acoustically activated embedded microbubbles. The top image shows the laminar flow of the liquid where mixing is limited to diffusion. The red dots show the positions along the microchannel used for the evaluation of the mixing efficiency. The yellow rectangle indicates the area used for the calculation of the mixing index at position 2. The bottom image demonstrates the mixing procedure for an excitation voltage of 20 V_PP and a flow velocity of v_avg = 2.13 mm s^–1. (c) Experimental evaluation of the mixing index for different input voltages. The mixing index corresponds to the standard deviation of the normalized gray-scale image at the corresponding positions of the microchannel. The horizontal line at 10% denotes sufficient mixing. Scale bars: (a) = 10 μm; (b) = 150 μm.