Scientists have announced a revolution in 3D printing. Rather than building things up layer by layer, which is the traditional approach, University of Florida scientist Tommy Angelini prints things inside a gel material using a hollow needle. The gel contains tiny particles that mean it moves easily when pushed by the needle but otherwise remains as a solid, supporting whatever has been printed inside it. Right now it reproducibly prints tumours for testing anti-cancer drugs. Long term, entire human organs look likely, as he explains to Chris Smith...