A single word, written in roman letters and out of context makes it it little difficult to find the right answer.
Yet, "saisei" means regeneration and "iryou" medicine, medical care.
Thus, you are probably dealing with therapeutic attempts at restoring damaged/impaired functions or structures. This can be achieved in many ways, including surgery, rehabilitation etc.
None of my dictionaries lists this term, but you should be comfortable with something like "regenerative medicine".