Researchers say they've created the world's first "biological" drone, built mostly with materials derived from living things, which, if it crashes, would simply melt away and leave no trace.

Drones have been used to explore and observe remote locations, some for scientific purposes and some for military operations, but the crash of a science drone could contaminate a sensitive environment, while that of a military drone could give away they fact someone's been spying.

Bio-drones that could simply and quickly decompose into a pool of uninteresting gunk would avoid those problems, researchers say.

"No one would know [whether] you'd spilled some sugar water or if there'd been an airplane there," says Lynn Rothschild of NASA's Ames Research Center at Moffet Field in California, where the drone was created.

The greatest part of the biological prototype drone consists of a plant-root-like material known as mycelium, part of a fungus, often grown for use as a sustainable, lightweight material for wine packaging or in surfboard cores.

A New York company, Ecovative Design, which cultivates the material for packaging uses, created the prototype body by growing it into a custom drone shape.

That main shape was then given a protective cover of sticky sheets of cellulose grown from bacteria in a lab, all covered with protein cloned from paper wasps' saliva, which they used to waterproof their nests.

The drone's electronics were printed rather than manufactured, using silver nanoparticle ink.

The drone is not 100 percent biodegradable, at least not yet.

"There are definitely parts that can't be replaced by biology," says design team member Raman Nelakanti of Stanford University. In its first test flights, the drone was lifted into the air with off-the-shelf motors, propellers and a battery from a commercially available mechanical quadcopter.

Those first flights took place in Boston at the International Genetically Engineered Machine competition.

The research team's next step in making the craft disposable is creating the drone sensors from a degradable material, and they are already studying ways to create those sensors from E. Coli bacteria.

Although one expert, aerospace engineer Ella Atkins at the University of Michigan in Ann Arbor, says she is enthusiastic about the concept, she warns of problems if such drones started to degrade and break down before that was desired.

"We don't want biodegradable drones to rain down from the sky and we don't want to litter the land and seas with crashed drones even if they will eventually biodegrade," she says.

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