Embryonic cells are stressed

When a mechanical force is applied to an object, that object deforms and withstands physical stress.

Think of applying a force to stretch a rubber band. It stretches and withstands mechanical tension. If you cut it, that tension is relaxed and the rubber band pings back to its preferred length.

If you understand that, you’re well on your way to understanding a central tenant of biomechanics. Each cell in the embryonic neural tube acts like a little rubber band, stretching its neighbours. To work out how much tension a cell is withstanding we have to cut it and measure how far it pings (we call this “recoil”).

So how do you cut a cell? Cells are far too tiny to cut them with anything physical like a scalpel. Instead we use a high-powered laser to very precisely cut a cell border. In the image above you will see the laser cut indicated by a red line as the white borders around cells ping apart. These cells should be pulling the neural tube closed, so by cutting them we can infer whether they were doing their job correctly.