Fig. 2: Characterization of the gel microcilia actuator dynamics.

a, Step response of gel microcilia in experiments and corresponding bending simulations in DI water. (1) Time sequence of 30 wt% AAc gel microcilia bending in DI water with the left electrode as the anode and the right electrode as the cathode; dashed lines highlight cilia outlines. Under the field, cilia bend towards the cathode owing to H⁺ accumulation on the right side (region 1 in Fig. 1a (2)). (2)–(5) Experimental tip displacement at different AAc concentrations shows reduced bending with higher AAc content (mean ± s.d.; n = 6 samples). (6)–(9) Simulated bending for varying AAc content reproduces the same trend, with displacement decreasing from 21.5 µm to 15.1 µm. b, Step response and simulations in NaCl solutions. (1) In 0.00769 mol l⁻¹ NaCl, cilia first bend towards the cathode as fast H⁺ ions shrink the right side and then reverse towards the anode as slower Na⁺ ion swelling dominates on the right side. (2) In 0.15380 mol l⁻¹ NaCl, bending occurs only towards the anode. (3), (4) Simulations reproduce these bending behaviours in NaCl solutions. c, Influence of different factors on dynamic performance under a square-wave signal. (1) AAc concentration: lower AAc content enhances bending (mean ± s.d.; n = 6 samples). (2) Actuation cycle: the gel microcilia maintained a bending angle of 50° after 330,000 continuous actuation cycles, corresponding to 70% of the initial performance, and then stabilize (mean ± s.d.; n = 4 samples). (3) Cilium diameter: 2-µm actuators outperform 10-µm actuators at high frequencies (mean ± s.d.; n = 6 samples). (4) Solution type: gel microcilia tested in DI water, physiological saline, DPBS, human saliva, serum and mouse plasma (mean ± s.d.; n = 6 samples for DI and n = 5 samples for the others). Scale bars, 100 µm (a (1)); 100 µm (b (1), (2)). All of the characterization experiment details are provided in Supplementary Note 7.