A bunch of tightly compressed office staples can work wonders. Even if it is made of many separate parts, an entangled mass can be difficult to pull apart and behave almost like a single solid body.
But those same shackles can quickly come undone. Appropriate vibration or movement allows the staples to separate and return to a loose collection of individual pieces.
Researchers in UW Boulder’s Paul M. Reddy Department of Mechanical Engineering believe this unusual combination of strength and reversibility could help inspire a new generation of engineered materials. By designing particles that intertwine in the same way as staples, they hope to create a material that is strong, malleable, and potentially recyclable.
“We have been experimenting with the idea of building blocks and geometries for years, but only recently have we started to look at particles intertwined and intertwined with each other,” said Professor François Barcella, leader of the Institute for Advanced Materials and Bioinspiration. “We are excited about the combination of properties obtained from these systems and believe this technology has the potential to move in many different directions.”
The results of this research have recently applied physics journal.
How entangled particles create strength
The research focuses on a phenomenon known as “entanglement,” which occurs when particles become entangled and form bonds with each other.
Tangle is common in nature. For example, a bird’s nest relies on a network of intertwined twigs and fibers to maintain its structure. Bone also gains strength through the interaction of hard mineral components and soft proteins.
The CU Boulder team wanted to understand how similar principles could be used to create engineered materials. Their study pointed to one important factor: the shape of the particles themselves.
“Take sand as an example. Sand has a smooth, convex shape, which means it cannot intertwine from particle to particle,” said Yuhan Song, a doctoral student. “However, we found that changing the shape of a sand grain can dramatically affect its behavior and mechanical properties, including the particle’s ability to bond with other particles.”
To investigate further, the researchers used Monte Carlo simulation, a computational technique that allows them to study how different particle shapes interact. Their goal was to identify shapes that maximize entanglement.
Why staple-shaped particles stand out
After identifying a promising design through simulation, the team conducted pickup tests to observe how the particles behaved in real-world conditions.
The results revealed that “two-legged” particles, similar to staples, produced the highest degree of entanglement. The researchers also discovered that this shape offers some unexpected benefits.
One of the most remarkable aspects was its ability to combine tensile strength and toughness, two properties that are difficult to achieve simultaneously with conventional materials.
“Our intertwined granular materials using staple-like particles demonstrate both high strength and toughness at the same time,” said PhD student Saeed Pezeshki.
The staple-like particles also exhibited another unusual feature. They can rapidly combine into stronger structures and then rapidly separate again.
By applying different vibration patterns, the researchers were able to control how tightly the particles became entangled. Mild vibrations promote particle entanglement and strengthen the material, while stronger vibrations unwind the network.
“It’s a strange material because it’s clearly not a liquid, but it’s also not completely solid, which opens up new and interesting engineering possibilities,” Barcella said. “Working with these tangled bundles of particles feels very remote and exotic.”
Potential applications in construction and robotics
Researchers believe this technology could ultimately support more sustainable construction approaches.
In the future, bridges, buildings, and other large structures may be built using intertwined materials that can be later disassembled rather than demolished. Such materials can be reused or completely recycled at the end of their useful life.
This concept could also be applied to robotics.
“I was talking with other students who believe this technology could be used for swarm robotics, where small robots can intertwine to perform a task and unravel when finished,” Pezeshki said.
“Yes, it’s like the liquid metal T-1000 from Terminator 2. It can change shape and slip under a door and return to human size on the other side,” Barcella added. “It’s expensive and difficult to scale, but that’s what everyone cares about.”
Testing even more powerful particle designs
The team is now moving on to the next stage of their research.
Their latest experiments focus on a new particle design that includes additional protruding “legs.” Researchers compare its shape to the sharp burrs that stubbornly stick to shoes and clothing outdoors. They believe these additional features could create even stronger entanglement effects and unlock new possibilities for future materials.
