Fig. 6: Micromachine 3: the micro-rack-and-pinion.

a Schematic of a micro-rack-and-pinion system. b, c Frames from Supplementary Movie 15 illustrating a micro-rack-and-pinion system in operation, in which rotating the pinion counterclockwise or clockwise can make the rack translate to the left or the right, respectively (with the direction indicated by yellow dashed arrows). d Schematic of a permanent microchannel structure designed to interface with micro-rack-and-pinion systems. e Microscope images of a microfluidic valve formed from two micro-rack-and-pinion systems that can be individually controlled. f–i Frames from Supplementary Movie 15 illustrating how two rack and pinion structures can work together to choke and isolate flow in the microchannels. j, k Frames from Supplementary Movie 16 illustrating the use of micro-rack-and-pinion structures as valves to control the movement of 10-μm-diameter microbeads in microfluidic channels. In (b, c, e, f), red and yellow dashed lines with arrowheads represent the motion of the (active) pinions and the (passive) racks, respectively. In (j), red lines with arrowheads represent the moving direction of the microbeads.