Twelve-year-old Leon McCarthy (R) rests his prosthetic hand on a MarkerBot Replicator 2 Desktop 3D Printer, while talking to the company's CEO Bre Pettis, at the new MakerBot store in Boston, Massachusetts November 21, 2013. McCarthy, whose prosthetic hand is made of parts printed from a MakerBot 3D printer, broke a piece of it last week while playing football, so he printed a new finger to repair it. (Photo by Brian Snyder/Reuters)
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