It is not obligatory to wash artificial limbs when doing wudoo’
Question

My foot was amputated, praise be to Allah, and replaced with an artificial limb. Do I have to wash it [when doing wudoo’] and wipe over it if I am wearing a sock on it?
Praise be to Allah.If the foot has been cut off from the shin and the ankle and foot are gone, and you wear an artificial limb in its place, then you do not have to wash it; you are exempt from having to wash this amputated foot, and you do not have to wipe over the artificial foot. But if any part of the foot, from the ankle downwards, remains, then you must wash this remaining part, and if you wear something over it to cover it, such as a khuff (leather slipper) or sock, then you may wipe over it.
Al-Muntaqa min Fatawa ash-Shaykh Saalih al-Fawzaan (2/36)