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Physicists Revealing Mysteries of Biological Fluids

September 26, 2019

A group of physics researchers from UC Merced have revealed that a fluid made from biological molecules found in human cells behaves much like ordinary fluids that are mixed externally, such as paint.

Except in the case of the biological fluids, no external mixing is required — it’s mixing itself.

Professors Linda Hirst and Kevin Mitchell and graduate student Amanda Tan have been collaborating on a project funded by National Science Foundation, and their findings were published recently in the prestigious journal Nature Physics.

“We use microtubules — long filamentous protein assemblies — and kinesin molecular motors,” Hirst explained. “The molecular motors are proteins that convert chemical energy into mechanical motion. In the cell, they move along the microtubules in a ‘walking’ motion to deliver cellular cargo.”

Video of the active nematic with topological defects tracked.

To understand the movements and flows better, Tan attaches microscopic glass beads to the microtubules, and the researchers can visualize how the proteins move, sliding in different directions and causing “defects” — swirls and voids in the fluid.

In these flows, the defects act like a stick you put into paint to stir it, except they do what that stick would do spontaneously.

Hirst said an outcome of the work could be new class of self-mixing active solvents. It could also help shed light on how biological processes work, said Tan, a sixth-year Ph.D. candidate and the paper’s lead author.

All three researchers are members of the Department of Physics, Hirst and Mitchell are affiliated with the NSF CREST Center for Cellular and Biomolecular Machines and Hirst is affiliated with the Health Sciences Research Institute. They and other physicists at UC Merced are studying collective motion and fluid dynamics, and this project is another example of how the researchers are contributing to a larger body of knowledge in that area.

Mitchell, who studies Chaos Theory, has been modeling the flows with graduate and undergraduate students.

“Chaos is good for mixing things, especially viscous fluids,” he said. “Chaos in science is not randomness at all — there’s order to chaos, and this is, in part, about trying to find that order.”