The wrist-powered prosthetic hands most often are failing due to imperfect printer performance where the parts will split along the grain. The geometry of the gauntlet with slots for velcro straps is especially vulnerable.  

When printed in PLA, the thermoforming is easy because hot water in a tray gets the part up to glass transition temperature.  It can even be formed around the recipients arm with a towel between the skin and the hot part.

When printed in ABS it is trickier because an oven must be used and the part remains in the rubbery state for only a few seconds when exposed to room temperature.  Try setting it on a block of wood on a tray and watch for the wings to droop.  Then take the tray from the oven and form the curves with gloved hands.

The criss-crossed layers maintain their plywood properties after being thermoformed so that the part is very strong like molded plywood boat hulls.

Credits:

The gauntlet design was taken from https://www.youmagine.com/designs/raptor-reloaded-by-e-nable 

The design was created in Tinkercad from the Raptor Reloaded stl file and it can be modified at https://tinkercad.com/things/bgGS12sgROb