This article talks about a replacement foot that was made for a duck born with a reversed foot. There's a useful technique described in there: because the replacement foot had to be flexible, the prosthetic maker first used 3D prints to prototype, and then made the final part by casting it with silicon rubber.
http://www.cnet.com.au/disabled-duck-gets-new-foot-thanks-to-3d-printing-339344725.htm
