Harvard researchers built a living robot out of rat hearts

The stingray-bot is made up of four distinct layers: a silicone substrate that forms its body, a skeletal system made of gold wire, a second layer of silicone that insulates the skeleton and, finally, 200,000 genetically-engineered rat cells. Those cells are designed to contract when exposed to a specific wavelength of light. When they do, the robot effectively swims in the same undulating manner as its namesake. What's more, the "biological life-form," as lead researcher, Kit Parker, describes it, automatically follows the light source as it swims through the nutrient-rich liquid that keeps its cells alive, allowing it to be remotely controlled. The bio-bot can't survive outside of the lab yet.