What is the opinion of Islam about using artificial hair that is fixed on the head especially for bald men? Allah created us with hair? What ablution and sterilizing [al-Taharah] if he fixed it while he has ablution?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is no harm in implanting artificial hair to the head. This act is not considered as changing the nature created by Allah, rather it is a treatment permitted in Sharia. The evidence for this permissibility is the Hadith reported by Abu Dawood that "Arfajah Ibn Asa'd who had his nose cut off at the battle of al-Kilab got a silver nose, but it developed a stench, so the Prophet (Peace and blessing be upon him) ordered him to get a gold nose".(Abu Dawood).
As for how to make the Taharah after fixing it is as following:
If removing and fixing such hair does not cause hardship for the using person then he has to remove it during his ritual purity as to be able to wash or wipe the head. If it is removed only for the medical reasons or removing it causes much hardship or any harm then removing it during Ghsul or Wudu is not compulsory but the person has only to wipe over it.
Allah knows best.