AIUI the electrons only travel a short way, then knock an electron out of the atom they're joining, which then moves on in its turn. So there isn't a huge migration of electrons into and out of the wire.
The cells in our body are a bit different, as it's actually cells replicating and old cells dying that causes the renewal.
Given how small electrons are, it's more likely that it's repeated thermal expansion and contraction, plus vibration, that eventually causes a screw to loosen. And of course there's always the chance that whoever did it up didn't do it up tightly enough.