Everybody seems to be getting a bit ahead of themselves here. Before we can even begin to think about answering the question of what it would take for machines to be sentient, we'd have to have some idea of what it takes for us to be sentient. You can reply that it's the connections between neurons in the brain, but this doesn't at all address
how this creates sentience.
Bluejay mentioned the ability to disobey as a criterion of sentience, but how do we even know that we have the ability to disobey? I don't mean in the simplistic sense of disobeying an instruction from somebody - computers can do that ('Illegal operation'; 'file not found' etc.). The implication seemed to be about disobeying your own programming, and I don't see any reason to assume that people can do that. How could we distinguish between someone disobeying the deterministic processes which determine how their brain works and somebody obeying them?
DevilsAdvocate talked about 'striving against biological and physical rules' but, again, how could we know if this is ever done? The human brain is an incredibly complex piece of work, and somebody acting contrary to their reproductive success (which is, I assume, the sort of thing you mean) doesn't mean they're acting against any biological or physical rules. It could just mean that, despite being like it is because brains like this have tended to favour reproductive success in the past, there's no guarantee that it always will in all circumstances.
Nobody has any clear idea how sentience is created, so we can't know what it would take to create it, is all I suppose I'm trying to say.