Nanobots promise a breakthrough in medicine by letting doctors study and treat you without invasive surgery or relatively ineffective drugs. But they face a couple of key problems: it's not easy to steer them to where they're needed, and getting rid of them is difficult when they're finished. Researchers might have a solution: make them out of natural materials that are guaranteed to break down. They've crafted nanobots (not pictured) using the sort of spirulina algae you can find in health food stores. The natural composition not only lets them biodegrade gracefully, but makes them relatively easy to control and track.