In 2016 I received a commission to create a functional prosthetic hand based off of the Phantom Pain hand used in Metal Gear Solid 5. This was for a client who was born without a left hand and grew tired of his standard claw style prosthetic, but didn't want to shell out thousands of dollars for a motorized medical grade prosthetic. The goal was to create something durable, functional and useful on a budget. My client has very little left of his wrist, meaning the standard active grip system on other 3D printed prosthetics wouldn't work for him, so I designed a passive grip system using retention springs. This allows the fingers to auto-adjust to whatever object they are gripping, and only requires user input to actually open the grip, which is done by pulling the knob at the rear of the forearm section. All 5 fingers normally open and close at once, but there is also a detachable ring connected to the main knob which articulates just the index finger, which can be locked in place to allow greater usability in actions such as typing and pressing buttons.
I have released all design files and build instructions for this prosthetic on Thingiverse as open source files for free, as I want people who actually need a device like this to have easy access to it. The total material cost to reconstruct this prosthetic totals to less then $100.