The Bronx physicist, who lost part of his arm at one week old due to a birth defect, found artificial limbs cumbersome, clunky and less mobile than billed. That all changed last month when he became the world's first person to be outfitted with Open Bionics' new 3D-printed Hero FLEX robot arm, a cutting-edge attachment for above-elbow amputees. Within an hour of the procedure, the Bronx-based scientist, 43, was accomplishing tasks he rarely did with previous prosthetics -- like holding his dog's leash, or opening drink containers unaided for the first time.