Francois Barthelat

Staple-like particles reveal new path to strong materials

alse6588 — Tue, 14 Apr 2026 17:18:17 +0000

Staple-like particles reveal new path to strong materials alse6588 Tue, 04/14/2026 - 11:18

Alexander Servantez

A tightly packed ball of office staples can be surprisingly strong.Try to pull it apart and the tangled metal resists like a solid object.

But with the right movement or vibration, that same bundle can quickly fall back into loose pieces.

A team of engineers and materials scientists in the Paul M. Rady Department of Mechanical Engineering at �鶹��Ѱ��Boulder are exploring how this uncanny combination of strength and flexibility could inspire a new class of materials built on interlocking particles. By mimicking the way staples lock together and release, the researchers believe these emerging materials can one day form structures that are strong, adaptable and even recyclable.

“We’ve been playing around with the idea of building blocks and geometry for many years, but we started looking at interlocking, entangled particles only recently,” said Professor Francois Barthelat, the leader of the Laboratory for Advanced Materials & Bioinspiration. “We are excited about the combination of properties we can get out of these systems and we believe this technology has the potential to go in many directions.”

Unraveling the research

A bird nest made out of interwoven sticks and fibers.

The work, recently published in the Journal of Applied Physics, focuses on what the researchers call “entanglement”—when multiple particles become intertwined with one another, creating a link.

It’s not a new concept. In fact, nature is filled with examples of objects or materials that tangle and interlock with each other to create strong structures. Think about that giant bird nest on the tree in your neighborhood made out of interwoven sticks and fibers, or the interplay of hard minerals and soft proteins in your bones.

But how can scientists recreate that kind of natural entanglement in manufactured materials? The researchers in Barthelat’s lab say the answer revolves around one key concept: particle shape.

“Let’s take sand as an example. Sand is smooth and convex-shaped, meaning it cannot interlock from grain to grain,” PhD student Youhan Sohn said. “However, we found that if we change the shape of a grain of sand, we can drastically affect its behavior and mechanical properties, including the particle’s ability to link with other particles.”

Once the group came to this realization, they began running Monte Carlo simulations, a type of computational analysis, to predict exactly how the particles interlock with each other. Their goal was to find the optimal geometry that delivered the maximum entanglement.

A video demonstrating a pickup test used to analyze particle entanglement.

After finding the optimal shape, the team performed pickup tests to see how the entangled particles actually behaved.

The tests showed that a “two-legged” particle—similar in shape to a staple—had the greatest potential for entanglement. But the researchers also discovered several unexpected advantages that made the design even more intriguing.

The first was its rare blend of tensile strength and toughness, a combination the researchers say conventional materials rarely achieve simultaneously.

“Our entangled granular material using the staple-like particle demonstrates both high strength and toughness at the same time,” said PhD student Saeed Pezeshki.

Next, was its unique ability to rapidly assemble—and just as quickly come apart.

By applying different vibrational patterns to the material, the team was able to change its level of entanglement on demand. A light vibration, for example, could be used to interlock and strengthen the particles, while a larger vibration could cause them to completely unravel.

“It’s a strange material because it’s obviously not a liquid. However, it’s also not quite solid. This opens new and intriguing engineering possibilities,” Barthelat said. “Handling a bundle of these entangled particles feels very remote and exotic.”

Professor Francois Barthelat at the Triple E Fair showcasing his team's research to help middle school students explore engineering.

PhD student Youhan Sohn guiding middle school students through a series of pickup tests to help them visualize particle entanglement.

PhD student Saeed Pezeshki demonstrating the mechanical behavior of staple-like particles for middle school students.

Reassembling the impact

A close look at a free-standing arch made of crown-leg staples.

One of those possibilities comes in the realm of sustainability. The group believes that one day, large buildings and structures like bridges can be designed using entangled materials, allowing them to be disassembled when no longer needed or even fully recycled.

Or maybe entangled materials can make their way into the world’s next great robotic systems, sort of like the ones you’ve seen in some of your favorite sci-fi movies.

“I was talking with other students who believe this technology can be used in swarm robotics— where small robots can entangle, do a task and then disentangle when they are done,” said Pezeshki.

“Yes, kind of like that liquid metal T-1000 in Terminator 2 who can change shape to slide under a door and then transform back to a human’s size on the other side,” added Barthelat. “It’s expensive and scaling up is a challenge, but it’s something that’s on everybody’s mind.”

A close-up photo showing two spiky burrs in nature.

For now, the group is focused on building out the next phase of their research. They are currently testing a new particle shape with added protruding “legs”—similar to those spiky plant burrs that stick relentlessly to your shoes when you step on them—which they believe can generate even stronger entanglement properties.

But no matter what project they are working on, the team says the most important thing about their work is maintaining the passion and excitement.

“We’re not quite sure where this is going to go, but we’re going to continue the fun,” Barthelat said. “Most people don’t think about making strong materials in this way out of something like staples, because they think it’s counterintuitive. Until they try breaking a bundle of staples in half and see that it’s impossible.

“We love to take a difficult project like this and dig in.”

A tightly packed ball of office staples can be surprisingly strong. Try to pull it apart and the tangled metal resists like a solid object. But with the right movement or vibration, that same bundle can quickly fall back into loose pieces. A team of engineers and materials scientists in the Paul M. Rady Department of Mechanical Engineering at �鶹��Ѱ��Boulder are exploring how this uncanny combination of strength and flexibility could inspire a new class of materials built on interlocking particles.

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Watch: Can biological materials inspire better engineering materials?

Anonymous — Wed, 23 Mar 2022 17:53:14 +0000

Watch: Can biological materials inspire better engineering materials? Anonymous (not verified) Wed, 03/23/2022 - 11:53

Francois Barthelat

Department of Mechanical Engineering Professor Francois Barthelat:
Can seashells, fish fins and other biological materials inspire better engineering materials for the future?

Abstract: Current progress in materials science allows us to manipulate the chemistry and micro-architecture of engineering materials towards desired properties. Still, no matter how skilled we are at these techniques, we cannot compete with the advanced materials made by nature for eons. Can nature teach us new tricks to improve the design and capabilities of engineering materials? The answer is a resounding yes and interestingly, some of these tricks are quite counterintuitive.

In this webinar, Professor Francois Barthelat will discuss how patterns of weak regions within mollusk shells and teeth actually makes these materials extremely tough - which inspired his group to create a new type of toughened glass. He will also demonstrate how smaller is not necessarily stronger for fish scales, which inspired new flexible protective gloves, and how the complex structure and mechanics of fish fins could inspire the next generation of soft robotic materials.

Bio: After obtaining his PhD from Northwestern University in 2006, Professor Barthelat founded the Laboratory for Advanced Materials and Bioinspiration at McGill University to explore key structures and mechanisms in natural materials, and to develop new bioinspired, high-performance materials. In 2019 he moved his research activities to �鶹��Ѱ��Boulder. His methods combine theoretical mechanics, numerical modeling, optimization, fabrication and experimental mechanics. Barthelat and his students have discovered new deformation and fracture mechanisms in biological materials including bone, mollusk shells and fish scales. Recently they have also started to explore the mechanics of fish fins as inspiration for next generation morphing materials, and of granular assembly as a pathway to high-performance engineering materials. In parallel, they have pioneered new bioinspired materials designs and innovative material fabrication methods which they are now implementing in engineering applications.

[video:https://www.youtube.com/watch?v=ffzW3fZIC1E]

Watch Department of Mechanical Engineering Professor Francois Barthelat give a seminar on how studying mollusk shells and teeth inspired his group to create a new type of toughened glass.

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ME Course Column: Mechanics of Snow

Anonymous — Thu, 17 Mar 2022 15:45:29 +0000

ME Course Column: Mechanics of Snow Anonymous (not verified) Thu, 03/17/2022 - 09:45

Rachel Leuthauser

The ME Course Column is a recurring publication about the unique classes and labs that mechanical engineers can take while at the �鶹��Ѱ��. Follow the series to understand the core curriculum, discover elective course options and learn the broad applications of mechanical engineering skills.

Most mechanical engineers will work with materials such as metals, polymers, ceramics and composites during their careers. However, a course taught by Department of Mechanical Engineering Professors Francois Barthelat and Franck Vernerey asks students to draw inspiration from another material – snow.

“I am a backcountry skier and as such, you have to learn a lot about avalanches and take courses for safety,” Vernerey said. “You realize there is so much mechanics involved with snow.”

Above: Professors Francois Barthelat and Franck Vernerey
Header image: Barthelat and Vernerey guide students through a slide test.

MCEN 4228/5228: Mechanics of Snow motivates students to look at their environment and the materials around them in an analytical way. The idea behind the course is to teach students the science behind certain phenomena by looking at the fundamentals of snow and ice from the atomic level to the mechanics of the snowpack.

“Snow in itself is an interesting material to study, you do not necessarily think of looking at snow in the context of mechanics of materials, but there is a lot to learn from this approach,” Barthelat said. “This is a great a way to expose students to state-of-the-art experimental and modeling techniques that people use in engineering.”

While studying the properties of natural versus artificial snow, the mechanics of sliding on skis and snowboards, or the conditions that trigger avalanches, students also master theoretical tools such as fracture mechanics and heat transfer. They also learn about the relationship between molecular structures, thermodynamics, and micromechanics, including viscoelasticity.

The professors explained that applying these critical engineering concepts to snow helps students better understand the information. It allows them to see that these concepts are real and happening in our environment.

“We often teach mechanics of materials and students are not always connected to the course because they have not worked with the materials before,” Vernerey said. “They learn the equations but may have difficulties connecting them to the real world. This course allows them to better connect because they already have an idea about the material. They are much more motivated to learn.”

Mechanical engineering students conduct slide tests on a snowboard.

Students in Mechanics of Snow conducted their own research out in the elements on March 10, after Boulder received about four inches of snow. They measured the densities of the fresh and old snow, assessed their compressive strength and calculated the snow’s coefficients of friction on skis and snowboards.

The class will take one more field trip outside to conduct strength and fracture tests on the snow before completing final projects to wrap up the semester. Some students are looking at avalanche conditions, while others are studying the impact mechanics of snowballs or snow construction such as igloos and walls.

“A big takeaway from this course is that students will be exposed to a vast number of topics in engineering and physics,” Barthelat said. “If they need these in their professional life later on, they know that the concepts exist and where to find more information.”

Mechanics of Snow is a technical elective open to upper-level undergraduate and graduate mechanical engineering students.

View all the Mechanical Engineering Technical Elective Courses

MCEN 4228/5228: Mechanics of Snow motivates students to look at natural materials in an analytical way. The idea behind the course is to teach students the science behind certain phenomena by looking at the fundamentals of snow and ice from the atomic level to the mechanics of the snowpack.

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