Hydrogel cilia set new standard in microrobotics

Embargo details:

“3D-printed low-voltage-driven ciliary hydrogel microactuators” has been scheduled for publication in Nature on 14 January 2026 at 16:00 (London time), 14 January 2026 at 11:00 (US Eastern Time). The embargo will lift at this time.

Stuttgart – Cilia are micrometer-sized biological structures that occur frequently in nature. Their characteristic high-frequency, three-dimensional beating motions (5 – 40 Hz) play indispensable roles inside the body. In the human brain, ciliary motion is crucial for neuronal maturation; in the lungs, it is essential for clearing the respiratory tract; and in the reproductive system, cilia transport gametes. Conversely, impaired or damaged cilia can lead to neurodevelopmental disorders, respiratory dysfunction, infertility, or malformations of the embryo.

Scientists from the Physical Intelligence Department at the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart, from Hong Kong University of Science and Technology and Koç University in Istanbul created artificial cilia from hydrogel, which they can move individually or in groups applying an electric field. Their groundbreaking work will be published in Nature on January 14, 2026 bearing the title “3D-printed low-voltage-driven ciliary hydrogel microactuators”.

Each microactuator or microrobot is only 18 micrometers in length with a diameter of around 2 micrometers, nearly as small as real cilia. The scientists placed hundreds of their cilia on a flexible foil-like substrate that contains built-in electrodes. Around each cilium, they placed four small electrodes. When the electrodes are switched on, they create an electric field that causes ions inside the hydrogel to move. This controlled ion migration is what sets the cilia into motion.

Depending on how the scientists power the electrodes, the hydrogel cilia can bend or spin. Turning on the electrodes on one side pushes the ions in that direction, causing the cilium to bend toward that side. To make the cilium rotate, the four electrodes are turned on in sequence, which makes the ions move in a circular path. The cilium then follows this motion and rotates smoothly in 3D.

“At small scales, using electrical signals to drive ion movement for actuation has proven to be a highly effective and efficient method. For example, the human body relies on electrical muscle signals to control the distribution of ions in muscle tissue, which then generates motion,” says Zemin Liu, who is the first author of the study. “Inspired by this principle, we developed micrometer-scale ion-driven hydrogels. Just like human muscle, these hydrogels move when electrical signals stimulate the ions inside them. In our work, we use only 1.5 volts, which is below the electrolysis threshold in aqueous environments and is completely safe, for instance inside the human body.”

To build the tiny arrays, the scientists use a method called Two-Photon Polymerization, also known as 2PP.  The team printed the hydrogel cilia nanometer small layer by layer to optimize the hydrogel network structure and actuation performance.

“The fluid inside our hydrogel moves fast because we created tiny, nanometer-scale pores throughout the material. These pores act like miniature highways that let the fluid flow more quickly and in greater volume, which produces stronger and more effective motions,” says Wenqi Hu, who led the Bioinspired Autonomous Miniature Robot Group at MPI-IS and who is now an Assistant Professor at The Hong Kong University of Science and Technology. “With our fabrication technique, even a very low voltage is enough to create a strong electric field, which pushes the ions to move rapidly. Thanks to both the pore structure and the strong electric field, our artificial cilia can react extremely fast.”

The team tested their microrobotic cilia more than 330,000 times. The tiny structures showed almost no signs of wear. This number of cycles corresponds to about a full day of continuous beating at 5 Hz — roughly the natural working lifespan of real biological cilia. The researchers also demonstrated that their artificial cilia could operate in different types of fluids, including biologically relevant liquids, such as human serum and mouse plasma.

“In the past, researchers could only observe how natural cilia behave. Now we finally have a robotic platform that lets us study cilia in action: how they move, how they work together as a collective group, and what kinds of fluids they can transport or mix,” says Metin Sitti, who led the Physical Intelligence Department at MPI-IS and who is now President of Koç University in Istanbul. “These hydrogel cilia could one day be used in biomedical settings to help restore or replace damaged cilia. As an important step forward in microactuation technology, they also open up fresh opportunities for designing miniature robotic systems, such as the flapping micromachine we demonstrated in this work.”

What could this cilia-technology enable in the real world? The research paves the way for several promising future applications:

(1) A new platform for studying how biological cilia work: Researchers can now use these artificial cilia arrays to carefully test how natural cilia move, how they collectively work together, and how they help with important tasks, such as development, sensing the environment, and moving fluids.

(2) Potential medical applications: The soft, controllable hydrogel cilia may inspire future therapeutic devices designed to help replace or support damaged cilia in the human body, especially with diseases where natural cilia no longer function properly in our respiratory and reproductive systems and brain ventricles.

(3) A foundation for next-generation microrobots and microdevices: The fast, low-voltage actuation showcased in this work could be used to design new types of tiny robots, microfluidic tools, and advanced engineering systems at the small scale.

Reference:

Zemin Liu, Che Wang, Ziyu Ren, Chunxiang Wang, Wenkang Wang, Jongkuk Ko, Shanyuan Song, Chong Hong, Xi Chen, Hongguang Wang, Wenqi Hu, and Metin Sitti

DOI: 10.1038/s41586-025-09944-6

“3D-printed low-voltage-driven ciliary hydrogel microactuators”

Please find the images, the graphic and the captions here. 

Link to a video illustarting the work: https://www.youtube.com/watch?v=NalZmgF_u8o