New Liquid Crystal Elastomer Fiber Makes Shape-Shifting Fabrics a Reality

Researchers from the Massachusetts Institute of Technology (MIT) and Northeastern University have developed a new fiber, named FibeRobo, that can reversibly change its shape in response to different temperature stimuli.

The fiber, which is compatible with traditional textile manufacturing machines, could have practical applications in high-performance wear, compression garments and other adaptive clothing, the scientists say.

The research was presented at the Association for Computing Machinery (ACM) Symposium on User Interface Software and Technology 2023.

Liquid crystals enable new, production-ready, shape-shifting fiber

What if, instead of buying a new coat for the winter months, your summer jacket could morph its shape to become a better insulator as temperatures fall? That future might not be very far off, as a growing number of researchers have dedicated themselves to making adaptable smart fabrics.

“We use textiles for everything. We make planes with fiber-reinforced composites, we cover the International Space Station with a radiation-shielding fabric, we use them for personal expression and performance wear. So much of our environment is adaptive and responsive, but the one thing that needs to be the most adaptive and responsive — textiles — is completely inert,” said Jack Forman, a graduate student in the MIT Media Lab and lead author of the new research paper.

Previous attempts to create a reactive shape-changing fabric have been a limited success. One fiber, known as a shape-changing alloy, does function; but it only contracts by around 5% of its original size, doesn’t self-reverse and will stop functioning after more than a handful of actuations. Another alternative, the McKibben actuator, is driven pneumatically and so requires an air compressor to use.

In pursuit of a simpler solution – a fiber that actuates silently, reversibly and to a greater degree – the MIT and Northeastern researchers set out to find a completely new approach. They eventually settled on a unique type of polymer fiber; a material known as liquid crystal elastomer (LCE).

Liquid crystals are made up of a series of slightly crosslinked molecules that can effectively flow like a liquid, but when allowed to settle stack into a periodic crystal arrangement. The LCE material operates in a similar fashion, using liquid crystal structures incorporated into a stretchy elastomer network.

FibeRobo is an LCE material that is responsive to changes in heat. As the fiber heats up, the liquid crystal molecules begin to fall out of alignment and pull the elastomer network closer together, causing the full fiber to contract significantly. As the fiber cools down, the molecules begin to return to their original positions, allowing the material to stretch back out to its full size. 

The making of FibeRobo

Making a fiber such as FibeRobo is an intricate process. The researchers found that by carefully mixing certain chemicals in with the LCE fiber synthesis, they could delicately control the final properties of the fiber – including its thickness and the temperature at which it begins to actuate.

Crucially, they were able to find a preparation technique that results in the FibeRobo actuating at skin-safe temperatures, making it suitable for wearable fabrics. This is another aspect where previous attempts at creating actuating fibers fell short, the researchers say.

“There are a lot of knobs we can turn. It was a lot of work to come up with this process from scratch, but ultimately it gives us a lot of freedom for the resulting fiber,” Forman said.

To make FibeRobo, a thick and viscous LCE resin is heated and then slowly extracted through a thin nozzle. Ultraviolet (UV) lights cure the resin as it is extruded to an appropriate thickness. Once cured, the resulting fiber is dipped in oil to receive a slippery outer layer and cured again, this time with stronger UV lights to form a fiber that is both very strong and very smooth. In a final processing step, the fiber is spooled up and dipped in powder so that it can be easily fed into machines for textile manufacturing.

“At the end of the day, you don’t want a diva fiber. You want a fiber that, when you are working with it, falls into the ensemble of materials — one that you can work with just like any other fiber material, but then it has a lot of exciting new capabilities,” Forman said.

The team says that, from the point of chemical synthesis to the finished spool, the entire process takes roughly a day and produces around a kilometer of ready-to-use fiber.

The researchers say that FibeRobo can contract up to 40% of its size without bending and is producible with a low-cost setup for a final cost of around 20 cents per meter – which is around 60 times cheaper than other competing shape-changing fibers.

The future of smart fabrics

The compatibility of FibeRobo with widely used textile machinery makes it well-suited for commercial use, the researchers say. They have also developed several prototypes using the fiber, to demonstrate its possible application in a wide variety of fields.

One of these was a compression jacket made to fit Forman’s dog, which made use of a standard industrial knitting machine. The jacket was also special in that it was set up so that it would actuate and “hug” the dog based on a Bluetooth signal from Forman’s smartphone; pet compression jackets are commonly used to alleviate separation anxiety by mimicking the feeling of a hug while the pet’s owner is away.

The team also created an adaptive sports bra using the material, done using an embroidery technique, that would contract and offer more support when the wearer begins exercising.

Looking to the future, the researchers say that they want to conduct more research with different adjustments to the fiber’s chemical makeup, in the hopes that it can be made recyclable or biodegradable. They also want to streamline the initial polymer synthesis process in order to make the creation of the fiber more accessible to those without chemistry wet lab experience.

Reference: Forman J, Kilic Afsar O, Nicita S, et al. FibeRobo: Fabricating 4D fiber interfaces by continuous drawing of temperature tunable liquid crystal elastomers. In: Proceedings of the 36th Annual ACM Symposium on User Interface Software and Technology. ACM; 2023:1-17. doi:10.1145/3586183.3606732

This article is a rework of a press release issued by the Massachusetts Institute of Technology. Material has been edited for length and content.