New research finds 3D printed artificial microcilia exhibit the speed, coordination, and motion of their biological counterparts - using just 1.5 volts and responding in milliseconds.
Study: 3D-printed low-voltage-driven ciliary hydrogel microactuators. Image Credit: Rui Serra Maia/Shutterstock.com
The work, published in Nature, identifies a previously unrecognized microscale actuation mechanism in hydrogels and offers a new platform for electrically programmable fluid control at the micrometre scale.
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Microscale Biomimetics
In living systems, dense carpets of cilia drive fluid transport, locomotion, and developmental processes through rapid, non-reciprocal three-dimensional beating. Replicating these motions artificially has proved difficult.
Existing approaches - magnetic, optical, electrostatic, or electrochemical - often rely on external fields, slow actuation, limited durability, or motion confined to just two dimensions, unlike the cilia's three.
By focusing on scale rather than these other factors, the new study overcomes many previous limitations.
Shrinking soft hydrogel actuators to micrometer dimensions and engineering their internal structure at the nanometer level has unlocked a fundamentally faster actuation regime.
3D Printing Soft Actuators
The team constructed hydrogel microcilia using two-photon polymerization, a high-resolution 3D printing technique. Each filament measures 2 to 10 µm in diameter and up to 90 µm in height.
Careful control of printing parameters produced a hydrogel network with nanometre-scale pores.
This porous architecture dramatically increases the effective surface area inside the gel and enhances overlap of electric double layers.
As a result, ions can migrate rapidly through the material under low applied voltages of only up to 1.5 volts, below the threshold for electrolysis.
Microelectrode arrays patterned around individual cilia or ciliary bundles generate localized electric fields with programmable timing and polarity, allowing each actuator to be controlled independently or in coordinated groups.
Ion Migration Leads to Fast, Directional Motion
Unlike bulk hydrogels, which respond slowly through interfacial swelling or pH gradients, these microcilia are actuated by internal ion migration. The direction of bending depends on the surrounding electrolyte.
In deionized water, highly mobile protons migrate within the gel and collapse the polymer network locally, causing the cilia to bend toward the cathode.
In physiological saline, sodium ions dominate, drawing water into the network and producing bending toward the anode.
At intermediate salt concentrations, the competition between these mechanisms produces transient bending reversals.
Because ions only need to travel micrometre distances, redistribution occurs within milliseconds. This enables rotational and oscillatory beating at frequencies up to about 40 hertz - comparable to natural cilia and roughly 100 times faster than millimeter-scale hydrogel actuators.
Testing Demonstrates Speed, Durability, and Control
Systematic testing shows that thinner filaments and lower acrylic acid content yield faster responses and larger bending amplitudes at high frequencies.
Long-term cycling experiments demonstrate stable operation beyond 330,000 actuation cycles, with around 70 % of the original bending amplitude retained.
But the hydrogel itself shows little fatigue. The primary durability limitation arises instead from the thin-film microelectrodes, which can delaminate after prolonged operation. This distinction points to clear engineering targets for future improvements.
By integrating individually addressable electrodes, the researchers programmed collective dynamics ranging from synchronized oscillations and counter-rotating pairs to phase-shifted metachronal waves and large-area spatial patterns.
These coordinated motions generate well-defined vortices and directional flows in surrounding fluids. Particle-tracking experiments and particle-image velocimetry measurements closely match numerical simulations, confirming precise control over microscale fluid transport.
The 3D-printed microcilia could be adapted for more complex demonstrations.
Arrays inspired by starfish larvae reproduce biologically relevant vortex patterns, while hybrid micromachines convert hydrogel bending into flapping or rotary motion, mechanically coupling soft ionic actuation to rigid structures.
Performance in Physiological Fluids
Actuation strength depends strongly on ionic composition. The largest bending amplitudes occur in deionized water and simple proton-dominated fluids.
Performance decreases in physiological saline and is further attenuated in buffered solutions and biological fluids containing multiple competing ion species.
These trends, reported systematically across different environments, reflect the sensitivity of ion-migration-driven actuation to ion mobility and competition.
While the microcilia remain functional in physiological fluids, the results highlight key design constraints for future biomedical or lab-on-chip applications.
While not presenting a finished device, the study establishes a general actuation principle: at the microscale, ion transport through nanoporous hydrogels can drive fast, low-voltage, durable motion in aqueous environments.
By combining high-resolution 3D printing, flexible microelectrodes, and predictive electro-chemo-mechanical modelling, the work lays a foundation for programmable ciliary surfaces capable of controlled fluid manipulation, particle transport, and mechanobiological studies.
Translating these capabilities into long-term biomedical or in vivo systems remains an open challenge, but the physical framework is now in place.
Journal Reference
Liu, Z., et al. (2026). 3D-printed low-voltage-driven ciliary hydrogel micro actuators. Nature. 1-9. DOI: 10.1038/s41586-025-09944-6
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