MIT Team Flips Nanoparticle Dogma: Flexibility, Not Rigidity, Builds New Materials

Both approaches have drawbacks. "The methods for defining stickiness that have been developed are always bespoke: They work for one material, at one size scale, in one condition," Macfarlane explains. "It's good for studying, but you can't do much with it."

Both methods also demand that surface connectors, called ligands, stay rigid to hold specific angles. That requirement has shaped the field's thinking for two decades.

What did the researchers actually do?

They inverted the rulebook.

"It's the exact opposite of what the dogma has been for 20 years: that you need to make connector ligands rigid, and any deviation causes assembly to fail," Macfarlane says. "We showed if you just crank it all the way to the opposite extreme, it works just as well."

Macfarlane's group has spent years making particles from polymer grafts. In the new system, flexible ligands carry charged tips. Opposite charges attract, so the ligands bend to connect. As particles come together, the ligands reorganize — and that reorganization itself limits how many neighbors each particle can grab.

Instead of dictating bond direction through complicated synthesis, the team let the bonds find their own most stable arrangement. "The ligands can then reorganize as the particles come together, and that reorganization itself limits how many neighbors each particle can bind," Macfarlane says.

In experiments led by MIT PhD candidate Nicholas Sbalbi, the researchers controlled the connections by changing nanoparticle sizes and ligand chain lengths. They then assembled particles into crystal structures not previously observed.

"Without having to predesign where the particles connect or what their shapes are, we can control the number of bonds each particle has," Macfarlane says. "It allows us to lower the number of bonds each particle has and make lattices we have never seen before."

Joining Macfarlane and Sbalbi on the paper are University of Delaware doctoral student Stephen Kronenberger, MIT undergraduate Hana Shinzawa, Matthew Ye PhD '26, and former University of Delaware professor Arthi Jayaraman.

How close is this to real-world materials?

The researchers frame the work as a step toward getting custom nanoparticle materials out of the lab and into products.

"We in the nanoparticle assembly community talk about having completely independent control over what your particle is and what assembly it goes into," Macfarlane says. "In theory, that should be the case. In reality, it absolutely has not been."

The approach establishes ligand flexibility as a scalable route to customized material structures. That matters because dense packing narrows the applications. "This offers a way to get less dense formations of nanoparticles, and that's where a lot of the interesting applications are," Macfarlane says.

The work received partial support from the National Science Foundation, the Department of Energy, the U.S. Army and the U.S. Navy. The study demonstrates the concept in the lab; commercial designer materials will take further work.