a new soft tissue implant filling material is disclosed . the material may be polyvinylpyrollidone , polyvinyl alcohol , hydroxypropylmethyl cellulose , polyethylene oxide , hyaluronic acid , sodium or calcium alginate , hydrogel polyurethane , hydroxyethyl starch , polyglycolic acid , polyacrylamide , hydroxyethylmethacrylate , and several naturally derived biopolymers including sodium kinate , seaweed , and agar .