fabbingmachines.com Such machines could evolve from the 3-D printers currently used by industrial engineers for “rapid prototyping.” They design parts in computer-aided design programs and feed the designs to 3-D printers to make working plastic models. A 3-D printer has a small nozzle that scans back and forth across a surface, depositing tiny droplets of quick-hardening plastic. After each scan, the nozzle moves up a notch and scans again until it has built up the complete object, layer by layer. With multiple nozzles or a means of swapping supply cartridges, the machine can create objects made of many different materials. An electronic circuit, for example, can be made by combining an organic semiconductor, metallic inks and ceramic insulators.