If scientists were to create a well-functioning human brain, I suggest it probably would have to involve the brain being part of an anatomically well-functioning body, whether the body is human or humanoid or mechanical (in which case one would have a cyborg of some kind). Philosophers have entertained bizarre thought experiments in which human brains function in vats and are subject to systematic, misleading electro-chemical stimulation, but I suggest this would not be a case of a WELL-FUNCTIONING human brain. It would instead by in a profoundly dysfunctional situation. Are there good philosophical reasons for thinking that it is impossible for scientists to create something that is anatomically an exact replica of a human being such as you and me? Some might argue that "being human" essentially involves the reproductive and nurturing processes that we underwent (and so they would seek to rule out conceptually the idea that a human brain and body can be manufactured in a lab), but this would (in my view) be strained (not obvious). I rather think it is in principle to produce a replica. What about consciousness? I am inclined to think the nature and reality of consciousness would impede the project of scientifically constructing a "well-functioning human brain."
As someone who is firmly confident that consciousness is the most obvious fact about our lives (I am not at all tempted by those who seek to deny the existence of consciousness or the mental), I am led to think that if there is a physical replica of me (and I am conscious), then the replica will be conscious. This would not, however, be the equivalent of asserting that consciousness is itself physical. One might hold that consciousness (as a non-physical state) supervenes or emerges because of the laws of nature or because of the inherent causal powers of physical objects and relations or because of an act of God, and so on. Even so, while I note that this is my inclination, it seems to be possible that (in contemporary jargon in philosophy of mind) there may be zombies -- beings who are physically indistinguishable from conscious embodied beings but who lack consciousness. This is a highly controversial claim. You might do a search for Dean Zimmerman on zombies for further reflection.