What you see here are hydrogels--squishy, aqueous semi-solids--being turned into tiny machines. By wiring a copper electrode to hydrogels (in any shape), researchers from North Carolina State University can stiffen sections of the gels, making them change into more rigid shapes. They call the process "ionoprinting," since it works through a reaction caused by inserting copper ions into the gel. Mold a gel into, say, a claw shape, as they do here, and the hydrogels can tighten or release on command.
So, why did they do that? Well, hydrogels are similar enough to human tissue to where they can go through the body without causing harm. So it makes sense that researchers would be interested in finding applications for them (some potentially could be used as drug-delivery systems, or as scaffolding for real tissue). The project here is not as effective as a metal claw, of course, but it can be made on a tiny scale and eventually used for biomedical tools. Also: useful for playing an extra-small version of that claw prize-grab game.