These metals or man-made materials could have biological activity at increased pressure. To be honest, there is very little information on this, but my personal view is that this is unlikely to be a problem for sport divers breathing air or nitrox. We must also ask whether the device could predispose to adiving-related problem, such as decompression illness. It is hard to imagine how a breast implant could do this. For orthopaedic implants, the answer is less certain.
Divers can develop a condition called avascular necrosis, which affects bones.
The cause is debated, but it is related to interference with blood flow to a bone. Clearly, having scews in a bone may have some effect on this process. However, the fact is that there are lots of divers out there with such metal implants in bones and they don't seem to be getting avascular necrosis. The difficulty we have here is that avascular necrosis takes years to show itself. We may have to watch this space.