Discovery Defies Physics, Illuminates Cell Movement

UW-Madison engineers find surprising "negative viscosity" that propels cells, rather than impedes them.

Jan. 31, 2026 at 3:15am

Got story updates? Submit your updates here. ›

University of Wisconsin-Madison engineers have made a surprising discovery that upends understanding of how cells move. Using a pioneering method to directly measure viscosity in a group of cells, the researchers found regions of cells with "negative viscosity" that propel cells forward rather than impeding their movement, which goes against standard physical rules.

Why it matters

This advance can enable researchers to develop better models for cell motion, which could lead to future applications for human health, such as ways to speed up wound healing or facilitate essential processes in tissue development. The discovery of negative viscosity reframes the problem and shows that viscosity can be either positive or negative, which hadn't been considered before.

The details

In experiments, the researchers used optical imaging to analyze how a single layer of epithelial cells deformed a soft gel surface as they migrated across it. This allowed them to calculate how much force the cells produced. Their analysis revealed there were regions of cells where the viscosity, unexpectedly, was negative. This surprising discovery implies that these regions of cells are injecting energy into the flow, rather than dissipating it, which goes against standard physical rules. However, the researchers found that regions of cells with negative viscosity had elevated metabolic activity, reflecting an increased energy demand in these cells.

  • The findings were published on December 4, 2025 in the journal PRX Life.

The players

Jacob Notbohm

An associate professor of mechanical engineering at the University of Wisconsin-Madison who led the research.

Molly McCord

A PhD student at the University of Wisconsin-Madison who developed a new approach for analyzing the data and revealed the regions of cells with negative viscosity.

Got photos? Submit your photos here. ›

What they’re saying

“This advance can enable researchers to develop better models for cell motion, which could lead to future applications for human health, such as ways to speed up wound healing or facilitate essential processes in tissue development.”

— Jacob Notbohm, Associate Professor of Mechanical Engineering (Mirage News)

“When we started this project, our question was how big is the number for viscosity. But we've now learned that we should be asking a different question: Is this number positive — or negative? This discovery reframes the problem and shows that it's meaningful to treat this viscosity as being either positive or negative, which hadn't been considered before.”

— Jacob Notbohm, Associate Professor of Mechanical Engineering (Mirage News)

The takeaway

This surprising discovery of "negative viscosity" that propels cells, rather than impedes them, could lead to new insights and applications in fields like wound healing and tissue development by enabling researchers to develop better models for how cells move collectively.