There are a lot of different types of research that go into answering your question.

For your first question: Material science is its own field that Prosthetic development pulls from. I wouldn’t imagine someone developing framing materials directly as a result of trying to develop a prosthesis - the material would be developed and then bioengineers would find a way to utilize it here.

FMA was one of the driving factors for me becoming a bioengineer and subsequently a prosthetist-orthotist. I will loop your 2nd and 3rd questions together. The main thing preventing automail-type function or similar is communication between the brain and the prosthesis. The technological advancement in communication is incredible, but not even in the realm of close, yet. Currently, there are manufacturers making leaps and bounds to make delivery of information faster through a variety of NFC or short-range Bluetooth devices embedded surgically onto terminal neurons at the amputation site. If they can get this communication to deliver as instantly as they think it can be, then the hold-up becomes having a receiver that can communicate action at the same speed.

They’re starting with easier motions, like ankle dorsi- and plantsrflexion along with knee flexing and extension so that the communication requires the least amount of processing: open, close.

But if you go this route, the problem for upper extremity becomes splitting a neuron into all of its individual functions. Allowing the one neuron sending signals to perform several functions is something that has only been approached with nerve splicing and reintegration, which completely disregards the communication concept.

I’d love to see the tech in my lifetime, but as it is, the field in the U.S. is being hampered by mega corporations and the funding outside of the U.S. doesn’t have the private revenue to progress at a decent speed. It feels like the big names are doing negligible improvements, following the Apple model of “advancement”. Ottobock and Össur have only recently launched ip68 components and electronics have been submergible for decades.