Fig. 3: Micromotor impellers.

Frames from Supplementary Movie 5 of a micro-gear rotating at 360°/s in a suspension of a 1-μm-diameter and b 15-μm-diameter polystyrene microbeads. Red arrows indicate the direction of rotation of the micro-gear and revolution of the particles. c Schematic of a rotating micro-gear (with angular velocity ω) and its influence on a nearby particle (with linear velocity v), and distance D between the two. Microscope images of a 7-μm-diameter polystyrene microbead and a micro-gear with d D = 50 μm and e D = 95 μm. f Linear velocities of 7-μm-diameter beads revolving around rotating micro-gears as a function of D for micro-gears rotated at 200°/s (blue triangles), 300°/s (red circles), and 360°/s (black squares). Error bars represent ±1 SD from three measurements for each condition. 3D (g), 2D (h), 1D (i), and 2D (j) plots of numerical simulation of the velocity of flow (in μm/s) around a micro-gear rotating at 360°/s after 2 s of rotation. Velocities in (g, h, and j) are shown as a heat map from 0 μm/s (blue) to over 600 μm/s (red), and arrows in (h) are velocity vectors. h is an XY slice from (g) at Z = 11 μm, i is an X slice of (h) [denoted by the red line in (h)], and j is an XZ slice from (g) at Y = 0 μm (the white boxes denote the position of the micro-gear).