Ok so its not really a 3D printing as it uses foam, but its still a fun and interesting concept! Apparently the idea has come from swiftlets, who use saliva to build nests.
Dr Mirko Kovac, from the Department of Aeronautics at Imperial, says: “Swiftlets are like beautiful flying factories that can navigate often treacherous, dark environments to find a suitable place to build nests. Amazingly, they carry inside of them all the materials they need to build their own home. We have taken these traits and adapted them in robotics. Robots that mimic these birds could have enormous benefits, helping humans in construction and in hazardous situations.”
You can read more from the Imperial College London article