Seashells inspire a better way to recycle plastic

Researchers from Georgia Tech have created a material inspired by seashells to help improve the process of recycling plastics and make the resulting material more reliable.

The structures they created greatly reduced the variability of mechanical properties typically found in recycled plastic. Their product also maintained the performance of the original plastic materials.

The researchers said their bio-inspired design could help cut manufacturing costs of virgin packaging materials by nearly 50% and offer potential savings of hundreds of millions of dollars. And, because less than 10% of the 350 million tons of plastics produced each year is effectively recycled, the Georgia Tech approach could keep more plastic out of landfills.

Aerospace engineering assistant professor Christos Athanasiou led the study, which was published in the journal Proceedings of the National Academy of Sciences (PNAS).

Why are plastics recycled so infrequently? And when they are recycled, why can’t they be widely reused?

Recycled plastics aren’t pristine materials — they’re a chaotic mix of past lives. Every bottle, bag, and wrapper brings its own history of additives, stress, and degradation. When we recycle them mechanically by melting them all down, we get a material that’s weaker than virgin plastic — and wildly unpredictable. Unpredictability is a dealbreaker.

That’s why recycled plastics rarely make it back into products that need strength, safety, or consistency like construction materials, car components, or autonomous delivery vehicles. They simply can’t be trusted to perform.

Why can seashell structure offer clues for improvement?

Nature doesn’t purify. It organizes.

Seashells, like nacre, are made of brittle minerals glued together by soft proteins. They’re not flawless, but they’re robust. The secret is in the architecture: hard “bricks” connected by soft “mortar,” creating a system that dissipates energy and controls failure. That’s a fundamentally different design philosophy from how we typically engineer materials, where uniformity and purity are the paths to reliability.

Nature embraces variability and makes it manageable through structure. We borrowed that insight.

What did you create, and how did you test it?

We took chopped-up sheets of recycled high-density polyethylene (HDPE) — the same plastic used in industrial stretch wrap — and reassembled them into layered composites inspired by seashells. Think of it as a synthetic nacre structure: stiff plastic “bricks” joined by a softer “mortar” made from a commercial adhesive polymer, engineered to absorb stress and control failure.

To test it, we pulled these bio-inspired structures apart using a custom-built mechanical setup. We captured their behavior in real time, from initial deformation to crack initiation to propagation to final failure.

Then we developed a new model — a first-of-its-kind uncertainty-aware Tension Shear Chain model. Rather than just assessing how stiff and strong the material was, our model also provided a measure of confidence of how reliably it performed under tension.

What were the results?

We reduced the variability in maximum elongation — a key measure of mechanical performance — by over 68%. Normally, recycled plastics are all over the place in mechanical performance. Our structured composites were consistent. That’s a key requirement for any real-world application.

In other words: we built a structure you can trust, using materials you normally can’t.

HDPE stretch film is the clear material that wraps products stacked on pallets. It can’t do the same job again once it’s been recycled?

Not quite. Stretch film needs to be both strong and flexible. But once it's exposed to sunlight, stress, and heat, its molecular structure changes. Recycling it blindly is like reusing a parachute without checking for rips. Our bio-inspired design doesn’t just reuse the plastic — it restores its reliability, making high-performance reuse possible.

You’re in the School of Aerospace Engineering. This work doesn’t appear to be related to airplanes, rockets, or space. What’s the connection?

Designing the next generation of aerospace systems requires thinking across disciplines and pushing beyond conventional materials. For example, one of the biggest challenges in space engineering is creating structures that don’t fail in unpredictable, extreme environments. Whether it’s a reusable rocket part or a shelter on Mars, we need materials that are resilient across their entire lifecycle.

Our PNAS study tackles a fundamental mechanics problem: how do you build reliable structures from unreliable materials? That’s not just a recycling question. It’s a future-of-space question.

What’s next?

We’re scaling this approach to work with a wider range of recycled plastics while pairing them with greener, bio-based adhesives to make the entire structure more sustainable. At the same time, we’re exploring how this strategy could support off-Earth construction, where recycling and reusing materials is a necessity. NASA’s Lunar Recycling Challenge, for example, points to a future where waste becomes the building block of survival.

CITATION: Georgiou, D., Sun, D., Liu, X, Athanasiou, C. Suppressing Mechanical Property Variability in Recycled Plastics via Bio-inspired Design. Proceedings of the National Academy of Sciences (Vol 122, 2025). https://doi.org/10.1073/pnas.2502613122.