Many superheroes wear capes. But Batman’s imposing floor-length cloak is legendary. The twisting sheath not only adds to the Dark Knight’s mystique but also transforms into a rigid fabric that allows him to fly for extended periods. Now, engineers at the California Institute of Technology (Caltech) and Nanyang Technological University (NTU) in Singapore have replicated the shape-shifting material in real life.
“We wanted to make materials that can change stiffness on command,” says study author and Caltech professor of mechanical engineering and applied physics, Chiara Daraio. “We’d like to create a fabric that goes from soft and foldable to rigid and load-bearing in a controllable way.”
The researcher says materials that change properties are already available. “Think about coffee in a vacuum-sealed bag. When still packed, it is solid, via a process we call ‘jamming,'” she explains. “But as soon as you open the package, the coffee grounds are no longer jammed against each other, and you can pour them as though they were a fluid.”
However, due to their disconnected shapes, coffee particles can only “jam” when compressed. The engineers were looking for materials that could “jam” when pushed together or pulled apart. “That’s the key,” Daraio says. “We tested a number of particles to see which ones offered both flexibility and tunable stiffness, and the ones that only jam under one type of stress tended to perform poorly.”
The 3D printed polymer fabric, revealed by the team on August 13, 2021, draws inspiration from ancient chain mail armor. It comprises hollow octahedrons — 8-sided triangular shapes— linked together to form a flexible fabric.
The team demonstrated the material’s shape-shifting ability by sealing it in a vacuum-sealed chamber. The pliable material instantly became 25 times more rigid. It was also a lot stronger and able to support a load of 3.3 pounds (1.5 kilograms) — more than 50 times its weight.
They then further tested the material’s strength by dropping a small steel ball — first when the fabric was in relaxed state and then when it was rigid. The ball’s impact deformed the flexible material by 26 millimeters. However, when the fabric was hardened, the impact was reduced to just 3 millimeters.
The scientists, who published their findings in the journal Nature on August 11, 2021, believe the innovative polymer material could have many uses. “These fabrics have potential applications in smart wearable equipment: when unjammed, they are lightweight, compliant, and comfortable to wear; after the jamming transition, they become a supportive and protective layer on the wearer’s body,” said study co-author and NTU assistant professor Dr. Yifan Wang.
The team’s next goal is to improve the material’s durability. Dr. Yifan told New Atlas, “To further increase the material’s stiffness and strength, we are now working on fabrics made from various metals including aluminum, which could be used for larger-scale industrial applications requiring higher load capacity, such as bridges or buildings.”