When Tony Stark saw how making weapons affected the world around him, he gave it all up to become an iron (gold-titanium alloy) hero. In real-life, Tony is just as helpful.

Below, Robert Downey Jr., working with Albert Manero, OneNote, and The Collective Project, visited seven-year-old Alex to give him an Iron Man-style prosthetic limb. Downey Jr. did everything in character — he even brought along one of the gauntlet props from the films — and it’s amazing.

These are inexpensive, 3D-printed limbs that can be manufactured for maybe 1% of what high-end prostheses run. Developed in conjunction with students at UCF, the limbs function by attaching three sensors to the skin of the wearer. When little Alex flexes his arm muscles, those sensors respond by sending signals to tiny motors, which pull and release wires running through the arm’s fingers.

This actually isn’t the first time that Alex has been gifted with a totally awesome, inexpensive prosthetic limb. Derek Muller of the YouTube science show Veritasium had a chance to speak with Alex and explain the science behind this admirable project:

The advantage of 3D-printed limbs is that the base material can be cheaply and quickly replicated and enlarged as children outgrow the arms. Until 3D printing technology came along, there were few affordable options for children with missing limbs. As Tony Stark knows, supporting technology that can help us, rather than hurt us, is real heroism.