I was thinking about this nit for awhile. Artificial flowers do fulfill one purpose of flowers, i.e. decoration. And the parent is right that most other "artificial" things serve to fill in for some original purpose of the natural thing. But the real point is they don't have to fill all the purposes, or even most of them. An artificial eye could be made of glass or it could be a camera a thousand miles away... in the first case, it's just there in someone's head for show, fulfilling the aesthetic purpose of an eye. In the second case it's there for the purpose of seeing something and fills no aesthetic need at all. So an artificial neuron could fill any one of many functions... it could even just be a big plastic model of a neuron in a doctor's office.

Artificial hearts pump blood similarly to how submarines swim: typically with some form of rotor.