This metal-based material could revolutionise soft robots

Researchers have created a new metal-based material for use in soft robots.

A new process called "graphene oxide-enabled templating synthesis" creates the new material for use in soft robots.

“Origami robots” are state-of-the-art soft, flexible robots that could find use in drug delivery in human bodies, search and rescue missions in disaster environments, and humanoid robotic arms.

Because these robots need to be flexible, they are often made from soft materials such as paper, plastic, and rubber. To be functional, sensors and electrical components are often added on top, but these add bulk to the devices.

Combining metals such as platinum with burned paper (ash), the new material has enhanced capabilities while maintaining the foldability and lightweight features of traditional paper and plastic. In fact, the new material is half as light as paper, which also makes it more power efficient.

Prosthetics and soft robots

These characteristics make the new material a strong candidate for making flexible and light prosthetic limbs which can be as much as 60% lighter than their conventional counterparts. Such prosthetics can provide real-time strain sensing to give feedback on how much they are flexing, giving users finer control and immediate information—all without the need for external sensors which would otherwise add unwanted weight to the prosthetic.

This lightweight metallic backbone is at least three times lighter than conventional materials used in the fabrication of origami robots. It is also more power-efficient, enabling origami robots to work faster using 30% less energy. The new material is also fire-resistant, making it suitable for use in robots that work in harsh environments. The new material can withstand burning at about 800 C (1,472 F) for up to 5 minutes.

In addition, the conductive material has geothermal heating capabilities on-demand—sending a voltage through the material causes it to heat up, which helps to prevent icing damage when a robot works in a cold environment. These properties could help create light, flexible search-and-rescue robots that can enter hazardous areas while providing real-time feedback and communication.

How they made the new material

Researchers create the metal-based material through a new process called “graphene oxide-enabled templating synthesis.” They first soak cellulose paper in a graphene oxide solution, before dipping it into a solution made of metallic ions such as platinum. The material then burns in an inert gas, argon, at 800 C (1,472 F) and then at 500 C (932 F) in air.

The final product is a thin layer of metal—90 micrometers (μm), or 0.09mm—made up of 70% platinum and 30% amorphous carbon (ash) that is flexible enough to bend, fold, and stretch. Other metals such as gold and silver can also be used.

The work appears in the journal Science Robotics.

Team leader Chen Po-Yen used a cellulose template cut out in the shape of a phoenix for his research. “We are inspired by the mythical creature. Just like the phoenix, it can be burnt to ash and reborn to become more powerful than before,” says Chen, assistant professor at NUS Chemical and Biomolecular Engineering.

Conductive backbones

The team’s material can function as mechanically stable, soft, and conductive backbones that equip robots with strain sensing and communication capabilities without the need for external electronics.

Being conductive means the material acts as its own wireless antenna, allowing it to communicate with a remote operator or other robots without the need for external communication modules. This expands the scope of origami robots, such as working in high-risk environments (e.g. chemical spills and fire disaster) as remote-control untethered robots, or functioning as artificial muscles or humanoid robotic arms.

“We experimented with different electrically conductive materials to finally derive a unique combination that achieves optimal strain sensing and wireless communication capabilities,” says Yang Haitao, doctoral student at NUS Chemical and Biomolecular Engineering and the first author of the study. “Our invention therefore expands the library of unconventional materials for the fabrication of advanced robots.”

Chen and his team are now looking to add more functions to the metallic backbone. One promising direction is to incorporate electrochemically active materials to fabricate energy storage devices such that the material itself is its own battery, allowing for the creation of self-powered robots. The team is also experimenting with other metals such as copper, which will lower the cost of the material’s production.