Here's a soft robotic stingray made of light-controlled rat heart muscle

A bio-engineering team at Harvard made a tiny robotic stingray from "a pinch of rat cardiac cells, a pinch of breast implant, and a pinch of gold," says Kit Parker, who lead the project. "That pretty much sums it up, except for the genetic engineering."

From PopMech:

Parker's robotic stingray is tinya bit more than half an inch longand weighs only 10 grams. But it glides through liquid with the very same undulating motion used by fish like real stingrays and skates. The robot is powered by the contraction of 200,000 genetically engineered rat heart-muscle cells grown on the underside of the bot. Even stranger, Parker's team developed the robot to follow bright pulses of light, allowing it to smoothly twist and turn through obstacle courses. The fascinating robot was unveiled today in the journal Science.