Researchers from Sweden and Germany have successfully developed a groundbreaking hydrogel material from wood that has the ability to shape-shift, expand, and contract under electronic control. The specially-developed hydrogel, made with cellulose nanofibers (CNFs) derived from wood pulp, exhibits remarkable properties that have potential applications in various fields such as robotics, medicine, and biochemical production.

Unlike traditional robotic muscles that rely on air or liquid pressure to expand, this hydrogel muscle gains its flexibility and strength through water movement propelled by electrochemical pulses. By adding conductive carbon nanotubes to the hydrogel, researchers were able to control its electronic swelling, creating what they refer to as electrochemical osmotic hydrogel actuators.

One of the key advantages of this innovative material is its unique porosity, which can be electronically controlled and increased by up to 400 percent. This feature makes the hydrogel an ideal candidate for the development of electrotunable membranes, enabling precise separation and distribution of molecules or drugs in situ.

Moreover, the material’s strength is derived from the alignment of the nanofibers in a uniaxial direction, similar to the grain in wood. This unidirectional swelling generates high pressure, enabling a 15 x 15cm piece of hydrogel to lift a 2-tonne car.

While the current use of this technology is primarily limited to small devices like valves or switches in microfluidics, researchers speculate that it could have potential applications in larger-scale artificial muscles for robots, with underwater robots being one possible future use. Additionally, the material is relatively inexpensive to manufacture, opening up possibilities for commercial production.

The project draws inspiration from the robustness and resilience of plant growth, highlighting the parallels between the material’s expansion capabilities and the forces applied by plants to grow through obstacles such as pavement. The team continues to optimize the material, explore 3D-printing methods for electronic muscles, and study ways to scale up production for commercial use.

Sources:
– KTH Royal Institute of Technology: https://www.kth.se/en/forskning/artiklar/new-robotic-muscle-bends-and-twists-like-trees-1.1155548
– Advanced Materials: https://onlinelibrary.wiley.com/doi/10.1002/adma.202105527