He then put design software online so that—in theory, at least—anyone in the world who downloaded the software and had access to a commercial 3-D printer and $60 worth of plastic could make their own handgun.

It was a demonstration that not only sparked a lively debate on gun control in the U.S. and abroad, but also threw a spotlight on a vibrant, fast-developing manufacturing technology that could change the shape of the future.

Invented in the mid-1980s, it is a printer that uses plastic, wax, resin, paper, gold, titanium—a whole host of materials—instead of ink to create a solid, three-dimensional object. In much the same way that your desktop printer is directed to print the words in a document, the