A droplet of protein hangs in the air, and the water inside it slowly drifts away. The protein gets crowded and starts assembling into neat little crystals, much the way salt settles at the bottom of a glass of seawater. Scientists wanted to understand why these crystals sometimes come out tough and sometimes crumble at the lightest touch. So they added polyethylene glycol to the droplet, a substance made of long chains that look like strings of beads. And they found something surprising: the length of the string decides the fate of the crystal.
With long chains, the protein quickly lined up in rows, but then the crystals lost their order and broke down. With short chains, the opposite happened: the protein resisted crystallizing for a long time, yet once it assembled, it held firm to the very end. The secret seems to be that short chains cling to the protein and keep a bit of water around it. That water acts like a lubricant, preventing the crystal from cracking when the droplet is nearly dry. Nobody knew this before, and now it's simply a matter of choosing a shorter polymer to get reliable crystals for studying proteins and developing drugs.
A droplet with a volume of 10 microliters evaporates in the levitator in roughly 20 minutes, and over that time the protein concentration climbs from 50 to 500 mg/ml, that is, by a factor of 10.
In Stanislaw Lem's novel Solaris, the ocean creates structures that cannot be understood by earthly methods; here, by contrast, we see how a simple polymer governs the birth and death of protein crystals in a droplet suspended in midair.