Experimental Setup: The assembly of the PDMS substrate and cover glass containing the mixture was fixed to an XY piezo-drive stage (ML-20XYL, MESS-TEK, Japan) (Figure ) using small slips of double-sided tape. To generate circular vibrations, sinusoidal wave signals with a 90° phase offset were applied to the piezo stage using a waveform generator (AG 1022F, OWON, China) via an amplifier (M 2501-1, MESS-TEK, Japan). Bright-field images were taken using a digital microscope camera (Axiocam 503 mono, ZEISS, Germany) with an upright fluorescent microscope (Axio Scope A1, ZEISS, Germany) and objective lens (A-Plan 10x Objective Lens, ZEISS, Germany).