" Rachael said, “Do you know what the lifespan of a humanoid robot such as myself is? I’ve been in existence two years. How long do you calculate I have?”

After a hesitation he said, “About two more years.”

“They never could solve that problem. I mean cell replacement. Perpetual or anyhow semi-perpetual renewal. Well, so it goes. "

― Philip K. Dick , Do Androids Dream of Electric Sheep?