Solid but fluid: New materials reconfigure their entire crystal structure in response to humidity

(Press-News.org) NEW YORK, March 11, 2026 — Most solid materials we rely on, from steel, to plastics and ceramics, are designed to have specific properties. Whether a material is soft and flexible, or stiff and tough depends on how molecules within the material are organized. That stability is useful, but it comes at a cost: once made, these materials' properties are fixed, and they rarely adapt to their environment.

A new study published in the journal Matter (Cell Press) and led by researchers at the Advanced Science Research Center (ASRC) at the CUNY Graduate Center challenges that assumption, demonstrating solid materials that can reversibly reorganize their internal structure and dramatically change their properties in response to small environmental cues such as humidity.

Inspired by the dynamic behavior of proteins, the international research team created peptide-based crystalline solids that can switch among several entirely different architectures—while remaining intact and mechanically robust. In some cases, the transformation can be triggered simply by changing humidity, almost as easily as breathing on the material.

“Nature shows us that stability and adaptability don’t have to be opposites,” said Xi Chen, the study’s principal investigator and a faculty member with CUNY ASRC’s Nanoscience Initiative and City College of New York’s Chemical Engineering department. “Proteins are generally quite stable, yet they can adapt their shape and motions to local environmental conditions to perform specific functions. Our goal was to bring that same principle into solid-state materials.”

Learning from nature’s smallest building blocks

In living systems, proteins are dynamic molecules that constantly shift between different shapes in response to their environment. These structural rearrangements are central to their function, enabling proteins to adapt their structure and properties as conditions change. Water plays a central role in these dynamics, not only stabilizing specific structures but also facilitating conformational changes. Replicating this dynamic reconfiguration behavior in synthetic solids has been a long-standing challenge.

To create these dynamic solids, the researchers used the same molecular building blocks that make up all proteins. Rather than mimicking whole proteins, the team repurposed amino acids as a versatile chemical toolbox for materials design. This approach allowed them to capture the adaptability seen in living systems while working within a much simpler, robust, and well-controlled synthetic platform.

“Short peptides give us access to stripped-down versions of protein behavior,” explained the study’s co–principal investigator Rein Ulijn, founding director of CUNY ASRC Nanoscience Initiative and Distinguished Professor of Chemistry at Hunter College. “They’re simple enough to design systematically, but still rich enough to encode sometimes surprisingly complex and dynamic behavior. What is especially exciting here is that we could achieve dynamic reconfiguration in the solid state, so without the presence of liquid water, something that is hard to achieve with proteins.”

A solid that can switch its internal architecture

Using a combination of confined water and flexible molecular interactions, the team introduced peptide-based solids that can reversibly switch among multiple topologically distinct crystalline structures. Most notably, the researchers demonstrated the first rapid, solid-state conversion from a layered, soft van der Waals structure to a very stiff, hexagonally packed architecture. This transformation is driven by humidity changes, but without destroying the crystal.

“These are not small tweaks or gentle breathing motions,” said Vignesh Athiyarath, the first author of this work. “The material completely reorganizes how its molecules are packed. That kind of transformation has been extremely rare in solid-state systems.”

Because internal topology determines how stiff or flexible a material is, these structural transitions lead to large, controllable changes in mechanical and optical properties. Unlike most adaptive materials, which only allow minor expansion or contraction, these peptide-based solids access fundamentally different packing modes.

Water as both structure and fuel

A key discovery of the work is the role of confined water. Rather than being a passive occupant of the crystal, water acts as both a structural component and an energy source, enabling the material to move between multiple stable states.

More broadly, the work bridges a critical gap between static synthetic solids and dynamic biological matter, showing that even minimal, biologically inspired building blocks can yield solid materials with unprecedented adaptability.  Their simplicity opens the door to lower production costs and easier large-scale manufacturing, a key hurdle for bringing adaptive materials into real-world technologies.

Partner Institutions
University of North Carolina at Charlotte; Abdus Salam International Centre for Theoretical Physics; Scuola Internazionale Superiore di Studi Avanzati (SISSA); New York Structural Biology Center

Funding Support
Army Research Office; National Science Foundation; Office of Naval Research; Air Force Office of Scientific Research; National Institutes of Health; European Research Top of Form

 

About the Advanced Science Research Center at the CUNY Graduate Center

The Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC) is a world-leading center of scientific excellence that elevates STEM inquiry and education at CUNY and beyond. The CUNY ASRC’s research initiatives span five distinctive, but broadly interconnected disciplines: nanoscience, photonics, neuroscience, structural biology, and environmental sciences. The center promotes a collaborative, interdisciplinary research culture where renowned and emerging scientists advance their discoveries using state-of-the-art equipment and cutting-edge core facilities.

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