One technique involves a portable bioprinter that could be carried to wounded soldiers on the battlefield where it would scan the injury, take cells from the patient and print a section of compatible skin. Another uses a three-dimensional printer combining donor cells, biofriendly gel and other materials to build cartilage. The 3-D printer was shown at work, building a prototype of an ear during a half-hour demonstration at a Washington science conference. Hod Lipson of Cornell University in New York said it worked much like an ink-jet printer.