This is actually not that true, what exactly are you saying with "replaced certain circtuits in the brain with man-made equivalents and it continues to work"? I'm certain I never saw something "man-made" like that used to "replace circuits in the brain" and it "continuing to work", in fact this would probably get a nobel for the creator if this was really proven.
Also, we don't have evidence that the processes in the brain are replicable at all, if for example Penrose's theories are correct (or any other non-reductionist that accepts the need for local identity and/or metaphysical properties for the consciousness). You need to assume A LOT of things in order to get this theory some credit, and many things we are literally unable to explain (like consciousness itself) should be reduced to those assumptions in order to make it work (for example, you must assume that is not the gooey stuff that gives rise to the consciousness in the first place, that it does not need very extremely specific conditions to exist, and so on). This line of thinking is kinda dangerous.
Also, we don't have evidence that the processes in the brain are replicable at all, if for example Penrose's theories are correct (or any other non-reductionist that accepts the need for local identity and/or metaphysical properties for the consciousness). You need to assume A LOT of things in order to get this theory some credit, and many things we are literally unable to explain (like consciousness itself) should be reduced to those assumptions in order to make it work (for example, you must assume that is not the gooey stuff that gives rise to the consciousness in the first place, that it does not need very extremely specific conditions to exist, and so on). This line of thinking is kinda dangerous.