Martin Vincent Bloedorn has designed a 3D printed prosthetic hand that functions just like human hand, but it uses actuated motors with a linkage which drives each finger via a threaded rod. The motor and drive screw are both capable of lifting a couple of pounds, and the servo motor potentiometer provides feedback to judge the position of each finger and drives the electronics involved. According to Bloedorn the key to the design was to make the Biohand relatively inexpensive to produce. Rather than using tendon-like bands, the fingers in the hand are actuated individually and make use of a 4-bar linkage which synchronizes the movement of the proximal and distal phalanges. You can read the whole story here: http://3dprint.com/76855/biohand-low-cost-prosthetic/