Figure 4. Bubble-based actuator for patterning of suspended 15 µm particles under a flow rate of 2 μL/min withdrawn from the outlet of the main channel: (a) The layout of microfluidic system.

The response of 15 μm particles when the bubble is enlarged enough to touch the opposite sidewall of the main channel: (b) The disordered passage of particles through the two gaps formed at the bottom and top corners of the main channel when the bubble tip has just touched the opposite sidewall of the main channel, (c-d) Partial patterning of the particles by further pushing of the bubble, (e) Ordered patterning of the particles along a straight line by further pushing of the bubble. Inset is the schematic cross sectional view of the main channel along AA′ line. The length of the intimate contact between the bubble and the opposite sidewall (shown with red arrow) increases from 0 μm at (b) to 240 μm at (c), to 340 μm at (d) and eventually to 390 μm in (e). Scale bar is 500 μm.