She talked about how she used it to cut a steak which was the first that she had been able to eat in a conventional way since her accident of over two years ago. She said, "That was a very big thing for me."
Very often patients fitted with high-tech prosthetic limbs give up after a while and revert to simple devices which although look good have little functionality. However engineers still try to achieve the ideal, a limb controlled by the brain and works well looking like a normal limb.
Mitchell, 26, is only one of six people who is trying out the latest model that has been developed by the Rehabilitation Institute of Chicago. She recalls that with her older prosthetic arm, she was limited to doing only one thing at a time - either open her elbow or open her hand and to achieve that she had to concentrate on a particular muscle at a time.
She said, "It was odd. I had to think, 'OK, my hand is here. Which muscle?'"
She had to concentrate on flexing her pectoral muscle, or the triceps, to get the arms and hand to do what she wanted. "Now I just think about it."
Mitchell often left her old-fashioned artificial arm at home. She said, "It just didn't work well enough to bother wearing it. This might be bigger and feel a little awkward, but the amount of function that I get out of it makes it worth wearing it."
Dr Todd Kuiken, developer of the bionic technology admits that the device is a little crude, weighing five kilograms with one motor extending far beyond her shoulder, with wires and mechanical parts as well as some of the six motors, clearly visible. Her hand is covered with a flesh-colored sheath, and the fingers move awkwardly.
The interface between the body and machine makes the new arm unique. Gregory Dumanian, a plastic surgeon, at Northwestern Memorial Hospital in Chicago assisted Kuiken to move the five nerves that once controlled her arm.
The ends of the nerves were placed in her chest by Dumanian, where they re-grew close to the skin. Electrodes that are placed on the surface of Mitchell's chest send signals which control the arm.
Kuiken said, "The brain doesn't know that these nerves are connected to different tissue or muscle."
For Mitchell thoughts of moving her hand or arm causes an activation of the nerves just as if they were still leading all the way down her arm and into the elbow and fingers. These signals are in turn picked up by the electrodes on her skin, that send commands to the six motors in the electronic arm.