Distephano: I thought you were dead!
Ripley 8: Yeah, I get that a lot.
[Ripley is staring at a fork.]
Vriess: Fork.
Ripley: Fuck.
Call: Jesus Christ, Jonner, what do you put in this shit? Battery acid?
Johner: Just for color.
Gediman: You are a beautiful, beautiful butterfly.
Ripley 8: So, who do I have to fuck to get off this boat?
Johner: I can get you off. Maybe not the boat, but...
Answer: This is just speculation (and I haven't watched the movie for ages) but the operation is done with medical equipment in a facility designed for studying Aliens, which the military knows a little about. Maybe it is made of futuristic acid proof material.
If the surgical tools were acid proof, surely the floors of the cells that contain the grown alien specimens would also be acid proof; but that is how they escape, by sacrificing one of their own in order to spill acid blood onto the floor.
Well, you can imagine any acid-proof metal is probably very expensive. They can't make the entire station out of that stuff. Surgical equipment is probably necessary for their research, so they make an exception.
lionhead