Are shape-shifting “soft machines” in our future? Scientists develop light-sensitive material

Researchers at Lawrence Livermore National Laboratory have developed a new type of soft material that can change shape in response to light, a discovery that could advance “soft machines” in fields from robotics to medicine.

The new material called liquid crystal elastomer (LCE) is made by incorporating liquid crystals into the molecular structure of a stretchable material. By adding gold nanorods to the LCE material, scientists and engineers created photosensitive inks and 3D printed structures that could bend, crawl and move when exposed to a laser causing localized heating in the material.

As described in their article published in the journal Matter, the LLNL team, along with collaborators from Harvard University, North Carolina State University and the University of Pennsylvania, used a direct-ink printing technique to build a variety of light-sensitive objects, including cylinders capable of rolling, asymmetrical “caterpillars”. ” that could move forward and lattice structures that oscillated. By combining shape morphing and photoreactivity, the researchers said this new type of material could change the way people perceive machines and materials.

“At LLNL, we have been focused on developing static materials and architectures for some time,” said lead researcher Caitlyn Krikorian (Cook).

“We’ve created complex types of structures like hierarchical networks, and we’ve even started to explore more responsive materials, like shape memory polymers, which have a point shape memory response. But the lab didn’t have not really in depth creating architectures that can go from a 3D type of shape change to 3D. This project begins to show how architecture and these new materials can have unique modes of actuation that we haven’t studied before .

The researchers said the new material could be used to create a “soft machine” – a type of machine made from these flexible LCE composite materials – capable of responding to external stimuli and even imitating movements and behaviors living organisms.

Soft robots made from shape-changing material could crawl, swim or fly and explore environments too difficult or dangerous for humans to access, such as caves or space. Soft machines could also be used in medical applications, such as implantable devices that can adapt to body movements, or prosthetic limbs that move like natural limbs, and other applications that are not possible with machines made from rigid materials, such as metal or plastic. .

“Rigid robots might not be ideal for interacting with humans, so we need more compliant systems and materials,” said the paper’s lead author, Michael Ford, who began work on reactive materials while he was a postdoctoral fellow at Carnegie Mellon University.

“You start with the components that make up our robots, and one of those components is an actuator. That’s where these materials come in; they could potentially be an actuator. This reduces computational complexity; you create a material which eliminates on-board components.”

The researchers said the movement of the LCE material is primarily driven by a process known as photothermal actuation, which involves the conversion of light energy into thermal energy, resulting in a mechanical response of the material. Driven by the interaction between light, gold nanorods and the LCE matrix, the process allows the printed structures to exhibit dynamic and reversible movements in response to external stimuli.

“When you have this composite material – in this case, these gold nanorods in these liquid crystal elastomers – it has a photothermal effect,” Cook explained.

“With (infrared) light, it creates a heating effect, which causes misalignment of the aligned molecules. During this misalignment process, if there is uniform heating, you will have an overall shape change. But in this case we can have localized heat change, which is how you can make these localized regions of shape transform to do things like locomotion.

In the study, researchers used a computer vision system involving cameras and tracking software to control the movement of a printed cylinder. The tracking system monitored the position of the rolling cylinder and continuously adjusted the position of the laser to grid the edge of the cylinder. This continuous monitoring and adjustment allowed the cylinder to maintain its rolling motion in a controlled manner.

By leveraging computer vision with photothermal cylinder actuation, researchers have achieved a sophisticated level of manipulation of software machine motion, demonstrating the potential of advanced control systems in the field of software robotics and machinery. software. The team also showed that responsiveness could be controlled so that soft machines could perform useful tasks, such as a moving cylinder carrying a wire.

“(Lead author Ford) has done an impressive job using computer vision to control the locomotion of the printed cylinder and using a raster laser to force it to move,” said co-author Elaine Lee.

“But once you started getting into much more complex movements, like using different dithering speeds and light intensities on a printed grating, making it move in different modes, these were actually apart from what our high-performance computing (HPC) simulations “we were able to predict, because these codes expect uniform heating or stimuli across this network.”

“So using computer vision and machine learning to learn the actuation speeds and doses of light that can cause locomotion of this printed architecture will push us much further in understanding the reaction of our materials.”

The researchers said there were still some challenges to overcome before the material could be used in practical applications. The team found that the structures created could flip or exhibit other unpredictable movements, making it difficult to design specific movement patterns.

They said they will continue to work on models that can describe complex motion to better design future machines and develop new materials and manufacturing techniques to create more durable, more reliable and more efficient soft machines for a variety of applications. New control systems and computer algorithms could also allow software machines to move and interact with their environment more intelligently and autonomously, they said.

Cook said the team plans to integrate responses to different types of stimuli, beyond thermal and light stimuli, into areas such as humidity and energy absorption and the conditions the material might meet in space. She added that the team plans to launch a new strategic initiative at the lab to focus on autonomous materials and “move the needle” toward sentient materials.

“We are all thinking about ways to make materials more autonomous and more sentient, able to sense, respond, be programmed, learn, decide and communicate,” Cook said.

“These liquid crystal elastomers are reactive materials: they are capable of detecting and responding to stimuli, and they will respond repeatedly each time, but they have no sense of memory or way of learning the stimuli repeated and react accordingly. doesn’t yet have any other way of communicating other than potentially being able to couple it with some type of mechanical computing. These are really the materials we’re striving for, and it could take five to ten years of effort.”