What is this sci-fi anime from the 90s involving a mute main character and lab experiment by some mad corporation?
I think you are looking for Baoh.

Baoh is originally a manga series by Hirohiko Araki, who is best
known as the creator of JoJo's Bizarre Adventure. It was serialized
in Weekly Shonen Jump from 1984 to 1985 and was adapted into a
50-minute OVA in 1989.


  Plot Summary: Ikurou Hashizawa was a normal boy until he is captured
  by evil scientists who create the ultimate fighter by attaching a
  parasite, named Baoh, to his brain. The mysterious girl Sumire, who has
  psychic powers, frees him and together they work to avoiding being
  captured by those who want to use their powers.
  
  BAOH (OAV) - Anime News Network



Amazon.com: Baoh (DVD)