The HACKberry is a 3D printable electric prosthetic arm created by exiii Inc a Japanese robotics company based in Tokyo and specialised in bionic arms.
The hand works by detecting when nerve and muscle tissue is stimulated by signals from the brain and sends that data to an onboard micro controller to translate into hand and arm movements. The system enables users of the prosthesis to open and close the hand and even control individual fingers.
The hand uses an underactuated mechanism to control precise movements and obtain self-adaptability when grasping different objects with its 3DOF fingers.
Check out the documentation for this project here.