Sieving and sorting cells

What’s he building in there?

the Fulcrum
Published: Sept 6

The problem

The microscopic world of E. coli and other bacteria is a mixed-up place. Some bacteria can swim from location to location—but a storm of random collisions with thermally raging fluid particles knocks the microscopic microbes for a loop. This diffusive mixing makes it next to impossible to keep bacteria with different mutations separate from each other.

The researcher

Yuguo Tao is a post-doctoral researcher in the department of physics at the University of Ottawa. Tao is a computational biophysicist who builds computer models to simulate the life of a cell. By letting many of these virtual cells move around, compete for food, divide, and eventually die, Tao has studied the behaviour of assemblies of many cells, such as the colonies of cells that form the living films on your bathtub or behind the tap of your kitchen sink.

The project

Tao is interested in building geometries that can trap cells of one type but not of another. With future devices of this kind, cells could be sorted, and diffusive mixing could be overcome.
One existing system that is able to do this is a wall with funnel-shaped openings. Previous experiments on E. coli using this setup have shown a difference in cell concentration between the two sides of the wall.

The key

Tao’s simulations show cells that don’t swim and only diffuse randomly will be found in equal concentrations on both sides of the wall, but cells whose motion is made up of random swimming (like E. coli) become concentrated toward the right-hand side of the funnels. The better they swim, the more concentrated the cells become.
Cells that swim are organized by the funnels: the number on the right and left sides of the wall is determined by cell size, rigidity and ability to swim. So by arranging many of these walls in a row, Tao can sort cells by their physical properties and keep different populations separate from each other.