| abstract |
A silicone gel-like material having a reduced content of extractable silicone fluid and having rheological properties approximating human tissue. The gel-like material or "pseudogel" is useful for filling an implantable prosthesis. Prior art silicone gel-filled prosthetic implants contain a high proportion of extractable free silicone fluid. The free silicone fluid within an implant may enter the host's body by diffusion through the prosthetic shell or by rupture of the outer envelope of the prosthesis. The present filler material, or pseudogel, is produced by controlling the cross-linking of the silicone polymer network such that every polymer chain contains only terminal reactive vinyl groups but not all of the reactive groups participate in the cross-linking reaction. In a preferred embodiment, the polymeric vinyl-terminated starting fluids are selected so that the average molecular weights of the polysiloxane polymers comprising the fluid fall into two or three distinct ranges. The cross-linker, which is composed of a siloxane molecule containing silicon hydride groups, is selected to have a relatively low molecular weight and a relatively high Si-H content. By controlling the cross-linker concentration, essentially all the chains can be made to react, but in such a way that chains are only reacted at one end and function as non-extractable diluents between the cross-linked longer chains. The resulting pseudogel exhibits low extractability and is suitable for filling a soft-tissue prosthesis such as a breast prosthesis having a flexible outer shell which contains the pseudogel. |