3D printing in the horseshoe world probably was done first in some high-tech factory in Asia, but let's give some credit to Curtis Burns in the United States, who has been using 3D printing in the design of Polyflex glue-on shoes. Watch for Mucho Macho Man to run in the Breeders Cup Classic wearing shoes derived from this 3D printing technology on Saturday. (photo courtesy of Curtis Burns/Polyflex Horseshoes)