ThisThough they may not realise it, anyone who’s taken the subway at rush hour knows how a red blood cell feels passing through the human spleen. Almost home now, just need to get through the gates; but wait, someone’s ticket isn’t working, the crowd is starting to push, the gates are getting jammed… Maybe you should have called a cab.
Meet Trichoplax adhaerens, a microscopic marine animal from one of the oldest known branches of the evolutionary tree. It looks like a microscopic cell sandwich: two layers of epithelial cells (which make up the surfaces of our organs), with a layer of fibre cells in between.
If you speak to a soft matter physicist these days, within a few minutes the term “active matter” is bound to come up. A material is considered “active” when it burns energy to produce work, just like all sorts of molecular motors, proteins, and enzymes do inside your body. In this study, the scientists are focusing specifically on active polymers. These are long molecules which can burn energy to do physical work. Much of biological active matter is in the form of polymers (DNA or actin-myosin systems for example), and understanding them better would give direct insight into biophysics of all kinds. But polymers are microscopic objects with complex interactions, making them difficult to manipulate directly. To make matters worse, physicists have yet to fundamentally understand the behaviors of active materials, since they do not fit into our existing theories of so-called “passive” systems. In this study, Deblais and colleagues decided to entirely circumvent this problem by working with a much larger and easier-to-study system that behaves similarly to a polymer solution: a mixture of squirming worms in water.