A cross-section of skeletal muscle in this light micrograph shows the individual, parallel muscle fibers (red). These fibers work in concert to power movement. Thomas Deerinck, NCMIR/ScienceSource hide caption

toggle caption Thomas Deerinck, NCMIR/ScienceSource

Dennis Aabo Sorensen tests a prosthetic arm with sensory feedback in a laboratory in Rome in March 2013. Patrizia Tocci/Lifehand 2 hide caption

toggle caption Patrizia Tocci/Lifehand 2

Larry Bonassar shows off an ear that he and his colleagues at Cornell University built out of living cartilage cells with the help of a 3-D printer. Lindsay France/Cornell University Photography hide caption

toggle caption Lindsay France/Cornell University Photography