Hurricane-like flows revealed in curved cellular membranes

Vortices show up everywhere in nature, from milk poured into coffee, to hurricanes and ocean eddies. But there is one place where they’ve been long overlooked: biological membranes.

Studies of flows in biological membranes typically assume the membrane is flat, when many cellular membranes have curved surfaces. Samanta and Oppenheimer set out to study the topological effects of curvature on flows in membranes, finding flows similar to those seen in Earth’s atmosphere and oceans.

Using a spherical membrane model, the authors studied fluid flows generated by rotating proteins embedded in curved biological membranes. They based their model on rotating ATP synthase proteins, which are found on the highly curved endoplasmic reticulum in the mitochondria cells. Theoretical calculations showed how the membrane shape created new vortices not seen in flat models.

“It turned out that membrane curvature and topology can indeed influence profoundly the dynamics of these rotating proteins as well as the fluid flows they generate in the membrane,” said author Rickmoy Samanta.

While the study was specific to vortex flows caused by rotating proteins, the findings can be informative to a wide class of active inclusions, colloids, and microswimmers on curved surfaces. The authors hope their findings will motivate more studies and experiments on cell membranes and other surfaces.

“A detailed knowledge of such flows will shed light on possible mechanisms of mixing in biological viscous fluids as well as serve as a guiding principle to engineer molecular rotors, artificial microswimmers and nanocarriers in targeted drug delivery,” Samanta said.

Source: “Vortex flows and streamline topology in curved biological membranes,” by R. Samanta and N. Oppenheimer, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0052213 .