Dear RLee,
I SERIOUSLY doubt that the "friends that say they have been treated by a doctor with a series of collagen injections" - really know what they were really injected with. This is tragic.
Collagen is a cow derived dermal (skin) filler which was popular in the 1980's to late 1990's when new, better and longer lasting fillers began to appear and take its place. The injection of Collagen any deeper than the dermis (such as to fill lips aka "Paris Lips" has been outlawed by the FDA because of potential complications). It is CERTAINLY never used to fill buttocks by any ethical, professional Plastic surgeons.
EVEN IF your friends were injected with REAL Collagen (now owned by the Allergan corp), by someone who is either too stupid to know, too callous to care, it still would cost a fortune to augment buttocks, where commonly 500 t- over 1,000 cc of fat are needed for a full correction. (Multiply 1,000 cc (small correction) by 300 to 400 dollars PER 1 cc syringe and it becomes obvious that that could not have happened.
I would guess your friends were injected by a NON - Plastic surgeon (not a member of the American Society of Plastic Surgeons, www.PlasticSurgery.org) with an illicit substance, probably silicone, hydrogel or who knows what.
Not a pretty picture either way...
http://www.cosmeticsurgeryspecialists.org/realboardcertification.html#
