I am also a prosthetist and have been making prostheses for 30+ years. I love to 3D print items, just be careful of printing this for someone without taking the liability on yourself. I say that because the feet that are commercially printed are tested by the companies through at least 2 million cycles or steps to insure there is no failures of the feet. That may seem like a lot, but it is only about what a person walks in a year. Also the feet we buy from manufactures are rated for specific weight categories and their activities. So if you print this and give it to a person and in a month they fall when climbing steps and their hands are full or crossing a road and it snaps when they are in front of a car, this would be partially your responsibility. I have had components fail on my patients even with all of the testing done and it can be very devastating if they are doing an action that can cause problems if they fall and are not ready for it. The testing and the responsibility of making a foot is one of the reasons the foot itself can be expensive. There are over 200 types of feet now available for amputees in the USA. They range from firm feet to very flexible ones. Costs also range from $500 to over $100,000 for the foot alone depending on the foot. I know it seems like a lot, but think of now what goes into a prosthetic foot and what liabilities there are when you make one.
I think this is a great idea, but just use caution if and when you might make this for someone or for yourself.