Inspired by Prehistoric Woven Baskets, University of Michigan Invents New Material

Knitted materials can withstand repeated compression without deformation and can be used to manufacture robots, exoskeletons, automotive parts, building components, and more.

According to foreign media reports, engineers at the University of Michigan have drawn inspiration from prehistoric basket-weaving techniques and discovered that woven materials can recover their original shape after repeated strong compression, whereas continuous sheets of the same material deform permanently. The related research paper was published in the journal *Physical Review Research*. The modular platform used in the paper to assemble woven joints can be applied to any field where elasticity and stiffness are crucial, including soft robotics, automotive components, and architectural structures.

Image source: University of Michigan

Guowei Wayne Tu, the first author of the paper and a Ph.D. student in Civil and Environmental Engineering at the University of Michigan, accidentally came across an article tracing the origin of basket weaving back to around 7500 BC. Researchers began to ponder whether there are reasons beyond geometry and aesthetics that have allowed this ancient craft to endure to the present day.

“We know that weaving is an effective method to create 3D shapes using strip-like materials such as reeds and bark, but we suspect that there must be inherent mechanical advantages,” said Evgueni Filipov, associate professor of civil and environmental engineering and mechanical engineering at the University of Michigan, and the corresponding author of the study.

This study reveals these mechanical advantages: high stiffness, suitable for bearing loads; high resilience, suitable for long-term use. "I am very pleased to be able to apply the advantages of ancient woven baskets to the modern engineering field of the 21st century," Filipov added. "For example, lightweight woven materials used in robots can also help make humans safer during human-machine collisions."

To test mechanical properties, the research team vertically wove polyester film strips (approximately the width of a pinky finger and the thickness equivalent to two sheets of copy paper) together to assemble a three-dimensional structure. They transformed this two-dimensional weave into a three-dimensional metamaterial—a type of synthetic composite material whose structure imparts physical properties not found in natural materials.

Tu stated: "While modern metamaterials are usually designed for electromagnetic, optical, or acoustic properties, people have been manufacturing mechanical metamaterials through weaving and other structural methods for thousands of years."

The structures adopted four different angular arrangements, combining three, four, five, and six planes, respectively. For comparison, the team assembled the same structures with continuous non-woven polyester films. They then tested them by gradually compressing both types of structures.

A pair of rectangular boxes with a height of 17 cm returned to their original shape after being compressed by 1 cm. When compressed further, the continuous structure was permanently damaged, while the woven structure remained intact even when compressed by 14 cm (less than 20% of its original height).

High-resolution 3D scanning identifies points of material bending deformation caused by stress concentration on continuous structures. In contrast, woven structures redistribute the stress over a larger area, thereby preventing permanent damage.

The research team then studied stiffness, which was measured by the force required to compress the structure from the top or to bend it by pushing from the side. They compared four corner structures with a continuous structure made of the same polyester film. In all experiments, the stiffness of the woven material was 70% that of the continuous material, which overturns the misconception that woven systems are inherently flexible.

In testing more complex configurations, an L-shaped structure similar to a robotic arm can vertically support 80 times its own weight—like lifting a heavy bag at the waist—and can bend upward as easily as a human arm.

Image source: University of Michigan

A quadruped woven robot prototype, referred to as "Dog" by researchers, can withstand 25 times its own weight while still being able to move its legs and walk. When overloaded, the woven dog robot returns to its original shape and can bear the same weight again.

"Using these basic angular modules, we can design and easily create woven surfaces and structural systems with complex spatial geometries that are both rigid and flexible. These angle-based woven structures have great potential in future engineering design," Tu said.

As one of its applications, researchers have designed a concept of a woven exoskeleton that can adjust the hardness of different parts of the body, thereby providing a reusable shock absorption function while in motion.

Looking to the future, we hope to integrate active electronic materials into these woven structures, enabling them to become “smart” systems that can sense the external environment and change shape according to different application scenarios," Filipov said.