I recently re-watched the first season of the sci-fi anime series Ghost in the Shell: Stand Alone Complex. It's an excellent piece of work. While the show is neither Christian nor Catholic, it raises interesting issues for Catholic theology. One such issue concerns prosthetic bodies and marriage.
A number of characters on the show are cyborgs, or humans with fully functioning prosthetic bodies. Most of their humanity, physically speaking, is in the approximate 3% of their brain that is still the original flesh-and-blood they were born with. Everything else is their prosthetic body and brain.
While this technology is far from real-life, very similar technology is likely to develop as the science of engineering artificial human body parts develops.
So the question then becomes whether marriage and the marriage act would be appropriate for persons with prosthetic bodies?
In Catholic ethics, intentional frustration of the procreative faculty of a given act (by artificial contraception, or by other methods) is considered an intrinsic and grave evil.*
Prosthetic bodies, at least as imagined by Ghost in the Shell, are certainly not impotent, as at least a few episodes of the series seem intent on pointing out. But they do seem contraceptive or rather to act as contraceptives, or at least to be sterile or infertile.
Sterility in itself would be no problem for a Catholic couple. But if the prosthetic body itself acts as a sort of contraceptive, this seems to change the game. I suspect for those of us who call ourselves Catholics, the morality of marrying and the marital act where prosthetic bodies are concerned will hinge largely on the question of whether those bodies are considered artificially contraceptive, or merely infertile or sterile.
Perhaps the situation is most analogous to that of women who have had hysterectomies.** In this case the intent of the procedure in the first place would seem to play a role. If that is the case then erhaps that procedure, not the marital acts following it, would be the act which one could properly call right or wrong or should at least take the primary focus in theological-ethical discussions.
* This doesn't mean all contraception is the worst evil ever (lots of things are grave and intrinsically evil in Catholic tradition), but it does mean that it cannot be considered in Catholic moral tradition to be a "good" thing.
** One might ask why I'm not noting vasectomies here--I considered it, but a good key difference is that as far as I know, while not all men in marital situations are expected to reverse them, vasectomies are not candidates as moral actions in Catholic theology, whereas hysterectomies can be for medical reasons.