Fig. 3: Dynamic bending motions of gel microcilia arrays.

a, Reprogrammable motions of 2 gel microcilia (diameter 2 µm, height 18 µm; physiological saline; 5 Hz). (1) Synchronized unidirectional bending. (2) Unidirectional bending with 180° phase shift. (3) Synchronized clockwise 3D rotation. (4) Counter-rotating motion, left anticlockwise and right clockwise. b, Reprogrammable motions of an array of 5 × 5 gel microcilia (diameter 10 µm, height 90 µm; DI water). Yellow-shaded z-stack images show cilia motions. (1) Synchronized bending along the y-direction. (2) Synchronized bending along the x-direction. (3) Clockwise 3D rotation. (4) Anticlockwise 3D rotation. (5) 3 × 3 subarray (yellow dashed box) rotates clockwise, others anticlockwise. (6)–(10) Zoomed-in z-stack views corresponding to (1)–(5); cilia at identical time points share the same colour. (11) ‘HKUST’ displayed by an independently controlled 5 × 5 array; zoom-in shows opposite bending of adjacent cells in the ‘T’. Motion frequencies, 10 Hz ((1)–(4)); 20 Hz (5); 5 Hz (11). c, ‘MPIIS’ displayed by a 25 × 25 array (diameter 10 µm, height 90 µm; DI water; 5 Hz). Zoom-in shows the upper cilium bending upward, whereas the lower remains stationary. d, Applications of hydrogel actuators. Left, biomimetic artificial starfish larva. Right, flapping micromachine. (1) Photo of patterned electrodes before cilia integration. (2) SEM image with arrows indicating cilia rotation. (3) PIV flow field generated by cilia motion. (4) Schematic showing the flow generated by biological starfish larva. (5) Flapping mechanism with integrated hydrogel actuators. The first row is the SEM image, followed by video frames showing the flapping motion. The electrode polarity is indicated by + and − in a, b (11) and c. Because a uses physiological saline and b–d use DI water, the bending direction differs. Scale bars, 8 µm (a (4)); 150 µm (b (5)); 40 µm (b (10)); 150 µm (b (11)); 30 µm (b (11) zoom-in); 750 µm (c); 100 µm (c zoom-in); 400 µm (d (1)); 360 µm (d (2)); 100 µm (d (5)).