It enables people who can't use their arms or legs to do simple things again - like eat.
For Jan Scheuerman who has a degenerative nerve disease, it's the first time in 10 years she fed herself.
The arm itself moves in seven dimensions for more natural motion.
Now the next step is to make it implantable.
"Potentially we can use this technology to stimulate muscles in the body to potentially use their own limbs," said Dr. Jennifer Collinger.
For patients like Scheuermann, the benefits are well worth it.
"I feel like I get much more out of this study than it gets out of me," she said.
Doctors say they are learning so much about how the brain moves the body, they are confident the robotic arm will get more quadriplegics moving again.