Hydrogel robot inspired by earthworm locomotion.

Earthworm-Inspired Robot: How Hydrogels Could Revolutionize Soft Robotics

Jordan Keane in Tech & Innovation June 2025 • 3 min read.

"Scientists develop an innovative hydrogel actuator that mimics the earthworm's unique crawling motion, paving the way for adaptable and bio-compatible robots."

For years, scientists have looked to nature for inspiration in robotics. The earthworm, with its limbless, peristaltic motion, has proven a particularly intriguing model. Mimicking this unique form of movement could allow robots to navigate confined spaces and challenging terrains that are inaccessible to traditional machines.

Now, a team of researchers has developed a groundbreaking hydrogel actuator that achieves precisely that. This innovative material not only replicates the earthworm's crawling motion but also offers the potential for reversing direction, opening up exciting new possibilities for soft robotics.

This is not just another incremental step; it's a leap towards robots that are more adaptable, bio-compatible, and capable of performing complex tasks in diverse environments. The implications span from medical applications to environmental exploration.

The Science Behind the Crawl: Anisotropic Hydrogels

Hydrogel robot inspired by earthworm locomotion.

The key to this innovation lies in the creation of an anisotropic hydrogel. Unlike ordinary hydrogels, which expand uniformly, this material is designed to deform in a specific direction. This unique property is achieved through a clever combination of components:

Gold Nanoparticles: These tiny particles act as photothermal converters, absorbing light and generating heat. Think of them as miniature solar panels embedded within the gel.

Thermoresponsive Polymer Network: This network, made of poly(N-isopropylacrylamide) (PNIPA), controls the electrical permittivity of the gel. It essentially acts as a switch, changing the gel's properties in response to temperature.
Titanate Nanosheets (TiNSs): These two-dimensional electrolytes are cofacially oriented, meaning they align in parallel layers. This arrangement allows them to synchronously change their electrostatic repulsion, driving the anisotropic deformation.
Directed Peristaltic Crawling: This is the key to the earthworm-like movement, enabling robots to navigate and explore environments in a manner reminiscent of these creatures.

When a visible-light laser is focused on the hydrogel, the gold nanoparticles heat up, causing the PNIPA network to react. This, in turn, triggers a change in the electrostatic repulsion of the TiNSs, leading to rapid and significant expansion (up to 80% of its original length) in a specific direction. By moving the laser along the hydrogel, researchers can create a wave of expansion and contraction, mimicking the earthworm's peristaltic crawl.

The Future of Soft Robotics: Beyond the Earthworm

While this hydrogel actuator is inspired by the earthworm, its potential applications extend far beyond simple crawling. The ability to control deformation with light opens up possibilities for creating adaptable medical devices, miniature robots for environmental monitoring, and even interactive art installations.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1002/ange.201810052, Alternate LINK

Title: An Anisotropic Hydrogel Actuator Enabling Earthworm-Like Directed Peristaltic Crawling

Subject: General Medicine

Journal: Angewandte Chemie

Publisher: Wiley

Authors: Zhifang Sun, Yoshihiro Yamauchi, Fumito Araoka, Youn Soo Kim, Julian Bergueiro, Yasuhiro Ishida, Yasuo Ebina, Takayoshi Sasaki, Takaaki Hikima, Takuzo Aida

Published: 2018-11-05

Everything You Need To Know

How does the anisotropic hydrogel mimic the earthworm's crawling motion?

The anisotropic hydrogel achieves its unique deformation through a combination of gold nanoparticles, a thermoresponsive polymer network made of poly(N-isopropylacrylamide) (PNIPA), and titanate nanosheets (TiNSs). Gold nanoparticles convert light into heat, triggering the PNIPA network to react. This reaction changes the electrostatic repulsion of the TiNSs, leading to expansion in a specific direction. By controlling this process, the material can mimic the earthworm's crawling motion.

What distinguishes anisotropic hydrogels from ordinary hydrogels, and why is this difference important?

Anisotropic hydrogels differ from ordinary hydrogels because they are designed to deform in a specific direction, rather than expanding uniformly. This directional deformation is achieved through the strategic incorporation of components like gold nanoparticles and titanate nanosheets (TiNSs) within a thermoresponsive polymer network composed of poly(N-isopropylacrylamide) (PNIPA). This controlled expansion allows for mimicking complex movements like the earthworm's peristaltic crawl.

Beyond crawling, what are the potential applications for this hydrogel actuator, and how might it revolutionize soft robotics?

This hydrogel actuator's potential goes far beyond mimicking earthworm movement. The ability to control deformation with light allows for creating adaptable medical devices, miniature robots for environmental monitoring, and interactive art installations. The combination of gold nanoparticles, poly(N-isopropylacrylamide) (PNIPA), and titanate nanosheets (TiNSs) opens up possibilities for applications that require precise, controlled movements in diverse environments. Further research could explore applications in targeted drug delivery or creating soft exoskeletons.

Why was the earthworm's crawling motion chosen as a model for this robotic innovation?

The earthworm's crawling motion serves as an inspiration because it allows movement in confined spaces and challenging terrains inaccessible to traditional machines. The peristaltic motion, replicated using anisotropic hydrogels, enables robots to navigate environments where rigid robots would be impractical. By mimicking this natural movement, the anisotropic hydrogel robot, powered by gold nanoparticles, poly(N-isopropylacrylamide) (PNIPA), and titanate nanosheets (TiNSs), can squeeze, expand, and adapt to its surroundings.

What are the implications of using gold nanoparticles, poly(N-isopropylacrylamide) (PNIPA), and titanate nanosheets (TiNSs) for the biocompatibility of these robots?

The use of gold nanoparticles, poly(N-isopropylacrylamide) (PNIPA), and titanate nanosheets (TiNSs) in anisotropic hydrogels has major implications for biocompatibility. The ability to manipulate these materials allows for the design of robots that can interact safely with the human body. Future applications could include creating internal medical devices, drug delivery systems, or even artificial muscles. The potential for using light to control these hydrogels also minimizes the need for bulky and potentially harmful electronic components.