From the article:
The body is made of a dark gray NTPT carbon, a special composite that’s lightweight, strong, and has a distinctive surface pattern reminiscent of Damascus steel. Inside the sapphire container at the top is the movement for controlling the nib. It’s made mostly of titanium and has 12 jewels to keep the rhodium-plated gears moving smoothly. The whole thing is finished by hand to the same specifications as Richard Mille’s watch movements.
The mechanical system itself is based on that of a minute repeater. You hit the button, and a system of gears and springs slowly transfers energy at a constant rate to send the nib sliding out of the front of the barrel. Instead of giving it an external winding system that would require a small bit of human labor, Richard Mille engineered the winding mechanism into the barrel of the pen itself; putting the cap on sends the nib back into its home, generating enough energy for the next deployment. It’s a deceivingly complex solution to a difficult problem you’ve never thought about.