Zac Vawter, who is fitted with an experimental "bionic" leg, is silhouetted on the Ledge at the Willis Tower in Chicago. Vawter, who is in training to climb to the top of the tower using the new prosthesis, recently took the elevator to the 103rd floor to see the view after an afternoon of work in the lab.

Biomedical engineer Annie Simon, left, and research prosthetist Elizabeth Halsne fit an experimental "bionic" prosthetic leg on Zac Vawter at the Rehabilitation Institute of Chicago.

Dr. Levi Hargrove, lead researcher for the Rehabilitation Institute of Chicago's Center for Bionic Medicine, holds an experimental 'bionic' prosthetic leg.

Physical therapist assistant Suzanne Finucane, right, helps Zac Vawter as he practices walking at the Rehabilitation Institute of Chicago.

Chloe Mills, 1-year-old daughter of Army Staff Sgt. Travis Mills and his wife Kelsey, crawls past her father's walking legs in his boyhood home in Vassar, Mich., on Oct. 4, 2012.

Mills, right, is helped with his home legs by his father, Dennis Mills.

Kelsey Mills helps her husband navigate the newly installed ramp at his boyhood home.

Travis Mills rides in the back of a Jeep during the homecoming parade on Thursday, Oct. 4. Mills, his wife, Kelsey, and their 1-year-old daughter, Chloe, were the grand marshals of Vassar High School's homecoming parade.

Julie Best, a friend of Travis Mills, cheers as he rides in the homecoming parade.

Actresses wait for their turn to walk on stage during a performance of "Suenos," or "Dreams," at the Casa de la Cultura theater in Quito, Ecuador, Sept. 21, 2012.

Cast members mingle backstage at the Casa de la Cultura theater in Quito, Ecuador, Sept. 21.

Singer Jennyfer Avila, experiencing a bout of stage fright, is comforted by her father prior to her performance in "Suenos," or "Dreams," at the Casa de la Cultura theater in Quito, Ecuador, Sept. 21.

A cast member holds still as her make-up is applied and hair is brushed in preparation for her performance in "Suenos," or "Dreams," at the Casa de la Cultura theater in Quito, Ecuador, Sept. 21.

Cast members wave goodbye to the audience as the curtain closes at the end of their performance of "Suenos," or "Dreams," one of Ecuador's most successful musicals, at the Casa de la Cultura Theater in Quito, Ecuador, Sept. 21.

Johan Jonker from South Africa plays a joke with his game partners by pretending to retrieve the ball from the hole using his amputated arm during the South African Disabled Golf Open in Langebaan, South Africa on Monday. The South African Disabled Golf Open is one of the top disabled golf tournaments in the world with more than 60 competitors competing over the 3 day event. People suffering from any number of physical disabilities including arm and leg amputees, hemiplegics, paraplegics, stroke victims, blind and deaf people that are able to grip the club with at least one hand and hit the ball can compete.

Neal Merry from Wales plays a shot during the South African Disabled Golf Open.

Hokom Al, a disabled woman, uses her foot to hold a spoon of sugar as she makes coffee for neighbors.

Hokom Al, a disabled woman, uses her mouth to hang clothes to dry in a rural area in Khartoum on March 7.

Demonstrators representing the group People First gather on the steps of the Alabama Statehouse in Montgomery, Ala., Tuesday, March 22, 2011. The group held a rally calling for the closure of the the W.D. Partlow Developmental Center in Tuscaloosa, a state residential facility for people with intellectual disabilities.