This article is from the Plastic and Reconstructive Surgery FAQ, by firstname.lastname@example.org (Robert Green) with numerous contributions by others.
Currently, only saline-filled implants are approved for general
use in the United States. There has been experimentation with
soybean oil, peanut oil, and hydro gel as fillers for breast
implants, but these are not approved for general use in the USA,
and it does not appear likely that any of these will be approved
for use in the foreseeable future.