I don't think there's anything bad about wondering that at all. While people generally don't die from kidney stones nowadays (although sometimes they still do), they are widely acknowledged as producing some of the most severe pain that humans can experience (sometimes they're not bad, or even painless, but when they are painful, boy howdy does it hurt).

Just speculating, I'd guess that while artificial kidneys might possibly develop stones, they wouldn't be painful, as the artificial kidney probably wouldn't be connected to the patient's nervous system.