“It was pretty amazing how well the experimental data and numerical simulation matched,” Eckert said. In fact, it matched so closely that Carenza’s first response was that it must be wrong. The team jokingly worried that a peer reviewer might think they’d cheated. “It really was that beautiful,” Carenza said.
The observations answer a “long-standing question about the type of order present in tissues,” said Joshua Shaevitz, a physicist at Princeton University who reviewed the paper (and did not think they’d cheated). Science often “gets murky,” he said, when data points to seemingly conflicting truths—in this case, the nested symmetries. “Then someone points out or shows that, well, those things aren’t so distinct. They’re both right.”
Form, Force, and Function
Accurately defining a liquid crystal’s symmetry isn’t just a mathematical exercise. Depending on its symmetry, a crystal’s stress tensor—a matrix that captures how a material deforms under stress—looks different. This tensor is the mathematical link to the fluid dynamics equations Giomi wanted to use to connect physical forces and biological functions.
Bringing the physics of liquid crystals to bear on tissues is a new way to understand the messy, complicated world of biology, Hirst said.
The precise implications of the handoff from hexatic to nematic order aren’t yet clear, but the team suspects that cells may exert a degree of control over that transition. There’s even evidence that the emergence of nematic order has something to do with cell adhesion, they said. Figuring out how and why tissues manifest these two interlaced symmetries is a project for the future—although Giomi is already working on using the results to understand how cancer cells flow through the body when they metastasize. And Shaevitz noted that a tissue’s multiscale liquid crystallinity could be related to embryogenesis—the process by which embryos mold themselves into organisms.
If there’s one central idea in tissue biophysics, Giomi said, it’s that structure gives rise to forces, and forces give rise to functions. In other words, controlling multiscale symmetry could be part of how tissues add up to more than the sum of their cells.
There’s “a triangle of form, force, and function,” Giomi said. “Cells use their shape to regulate forces, and these in turn serve as the running engine of mechanical functionality.”
Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.