The result, after several years, was the Luke Arm
Dean Kamen assembled an all-star team of mechanical engineers, electrical engineers, software engineers, and clinical researchers, and they got to work. For eight years, they put their heads together to come up with something pretty darn cool: the Luke Arm, which comes in three configurations -- depending on how much of his or her arm an amputee has lost -- and is powered by little motors to move and rotate flexibly at a bunch of different points including the shoulder, elbow, and wrist.
Of course, the fingers also had to be really agile to make the grape scenario work without turning every casual snack into an impromptu jelly-making session. The team solved the puzzle by pre-programming the arm with different grip patterns that you'd use in regular life (think picking up a beer bottle versus holding a spoon to eat your cereal). By cycling through these grip options, the user can apply the appropriate amount of strength to various objects.