The tiny biohybrids, based on zebrafish, are built from paper, plastic, gelatin and two strips of living heart muscle cells. One strip runs along the left side of the robot's body, the other along the right.
The team tested some early samples by artificially activating the muscle cells, [a teammembr] says. Then they put the leftover fish in an incubator and forgot about them for a couple of weeks.
When they finally opened the incubator, "all the fish were swimming by themselves,"
The fish kept swimming for more than three months, sustained by nutrients added to the fluid around them.