Design and evaluation of Artemia-driven micro ratchet gears

• A micro ratchet gear driven by Artemia larva has been designed and fabricated．
• Gears are made by a 3D printer with the surface brightness control by painting for the better phototaxis.
• The dependence of rotation speed on the Artemia population is examined with a maximum rotation speed of 0.4 rpm.
• Long term duration is also examined with a longest period of 40 h.
• A simulation is performed to estimate rotation torque, resulting in 0.24 μNm.

This paper describes the design and evaluation of Artemia-driven micro ratchet gears and the results of performance evaluation. Larval-stage Artemia sallina (brine shrimp) were used in the experiments because they exhibit positive phototaxis and are more easily cultured within a shorter time than adults. The shrimp photactically migrated toward the gear surface, whose outskirts were partially illuminated by an aperture mask. Because the contour was asymmetric, the collision impacts on the ratchet surface generated a rotation torque. Gears were fabricated from an ultra-violet (UV) cured resin using a 3D printer. The appropriate gear radius (2.5 mm) and thickness (1.5 mm) were experimentally determined. Phototaxis was effectively enhanced by brightness control on the gear surface, achieved by painting the surface. The dependences of rotation speed on the Artemia population number and illumination wavelength were examined. A population density of 300 Artemia in 4 mL of culture medium under blue light illumination yielded the maximum speed (0.4 rpm). Long-term rotation without feeding and medium exchange was also evaluated and was maximized at 40 h. Because the small torque was difficult to be measured directly, it was simulated by a drag force model. The result (0.24 μNm) is reasonably consistent with previous measurements using adult Artemia.