SciFi/Fantasy details help?

Writing SF means the proposed advances must at least be improbable, not impossible. Replacing bone marrow would relieve you of your stem cells, in the main, especially red and white cell production. You would die. Period. That's what bone marrow replacement surgery is all about. 2, Comic-book heroes aside, bones are a living tissue- an organ. Plating them in metal would kill them, They are also a porous tissue, Any extensive fill, would make you heavier, thus slower moving. Muscles move you, not bones. Most attempts in fiction that try to approach this do so with exo-skeletal enhancement, nerve enhancement, or muscle enhancement. Anyway, a SF story is a fiction, and like all fictions, need to focus on something besides the stage props it uses. You need the story first. Even if you manage to double talk the prop around into the realm of feasibility, there must be a story , preferably one that makes even the mention of the prop important to it in some way. More important in what you have said, is the theme of a government capable of manhandling and abusing people in science experiments, something that is not even unregulated in animal experimentation, and reflects a vast social issue. I would reflect on this as a plot point that must be addressed in that kind of story, and is probably what you need to develop it around, not the prop... , .