Zac Vawter for The Wall Street Journal

Zac Vawter has his bionic leg fitted with the help of Elizabeth Halsne, Certified Prosthetist, at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Vawter has been successfully using the experimental thought-controlled bionic leg which allows him to walk, climb stairs, and move the leg while seated. Andrew A. Nelles for The Wall Street Journal

Zac Vawter walks down stairs with his bionic leg at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal

Zac Vawter walks up stairs with his bionic leg at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal

Zac Vawter walks down a ramp as Kim Ingraham, left, Research Engineer, and Dr. Levi Hargrove, center, observe at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal

Zac Vawter lifts his bionic leg as Dr. Levi Hargrove, right, observes at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal

Adjustments are made to Zac Vawter's bionic leg at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal

Zac Vawter walks down a hallway as Elizabeth Halsne, right, Certified Prosthetist, observes at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal

Dr. Levi Hargrove, right, speaks with Zac Vawter, left, while testing his bionic leg at the Rehabilitation Institute of Chicago on Tuesday, Sept. 24, 2013, in Chicago, Ill. Andrew A. Nelles for The Wall Street Journal