Scientists Created a Material Inspired by Staples That Can Lock Solid or Fall Apart in Seconds
Picture a handful of office staples stuffed into a box. Even though each staple is a completely separate object, the whole bundle resists being pulled apart. The pieces hook around each other and behave almost like a single solid chunk of material. That ordinary observation sent a team of engineers at the University of Colorado Boulder down a research path that could eventually change construction, robotics, and materials science as we know it.
The research team, led by Professor Francois Barthelat of the Laboratory for Advanced Materials and Bioinspiration, focused on a concept called entanglement. Entanglement happens when particles — the individual pieces that make up a material — become so interwoven and interlinked that they hold each other in place. This is not a new idea in nature. Bird nests stay together because twigs and fibers weave around each other, and human bone gets its strength from a mix of hard mineral crystals and flexible proteins that interact and support one another. The CU Boulder team wanted to recreate that same principle using engineered particles that they could design and test from scratch.
Their first major finding was that shape matters enormously. PhD student Youhan Sohn explained it using sand as an example. Sand grains are smooth and rounded, so they slide past each other easily and cannot hook together. But change the shape of those grains — give them angles, curves, or legs — and suddenly the particles can grab onto their neighbors and form a much more connected network. To figure out which shapes worked best, the team ran Monte Carlo simulations, a type of computer modeling that tests thousands of random variations to find the most effective design. The simulations pointed clearly to one winner: a two-legged shape, almost identical to a staple.
When the researchers tested real staple-shaped particles in the lab, the results matched what their simulations predicted, and then some. The tangled network of staple particles showed two mechanical properties at the same time that are notoriously hard to combine. The first is tensile strength, which is resistance to being pulled or stretched apart. The second is toughness, which is the ability to absorb force without cracking or breaking suddenly. Most engineered materials trade one for the other. Glass is strong under steady pressure but shatters with impact. Rubber absorbs impact but stretches easily. The staple-shaped entangled material managed both, making it genuinely unusual.
What made the discovery even more striking was the role vibrations played. The researchers found they could control the material's behavior simply by changing the intensity of vibrations applied to it. Gentle vibrations encouraged the particles to settle into tighter, more interlocked arrangements, making the material stronger. More intense vibrations broke those connections apart, causing the whole structure to rapidly come undone and return to a loose collection of individual pieces. Professor Barthelat described it as something that does not fit neatly into any existing category: not quite solid, not quite liquid, but genuinely its own strange thing.
That weirdness is exactly what excites the team about potential real-world uses. In construction, buildings and bridges are typically demolished at the end of their life, sending enormous amounts of material to landfill. A structure built from entangled particles could instead be carefully vibrated apart, with every piece collected and reused in an entirely new building. That kind of circular approach, where nothing is wasted, is something engineers and environmental scientists are actively trying to develop across many industries, and entangled materials could offer a practical path forward.
Robotics is another frontier. PhD student Saeed Pezeshki described conversations with colleagues about using the technology in swarm robotics, where many small robots could physically entangle into a larger combined shape to accomplish a task and then disentangle and separate again when finished. Professor Barthelat compared the concept to the shape-shifting liquid metal robot from the science fiction film Terminator 2 — a machine that can compress through a gap and then reform on the other side. Scaling the technology up to that level is still a major challenge, but the underlying physics that would make it possible is exactly what the team is now investigating.
Their next experiments involve particles with additional protruding legs, inspired by the spiky burrs that stick to your clothing after a walk through tall grass. Those extra legs are expected to create even stronger entanglement effects and could push the material's properties even further. With each new particle design, the team gets closer to understanding just how far this unusual approach to building materials can go.
Source: ScienceDaily