Surgically implantable tissue expanding device and the method of its use

A surgically implantable device for expanding skin and mucous tissue comprises a partially collapsed sealed envelope formed from a material which is permeable to extracellular body fluid. The envelope contains a material which establishes an osmotic potential across the envelope wall. Body fluid crosses the membrane to fill the envelope. As the envelope fills it expands the adjacent tissue. In use, the partially collapsed envelope is surgically implanted under the tissue to be expanded and is allowed to absorb fluid whereby expansion of the bag and subsequent tissue expansion is accomplished. A variety of surgical procedures using the expanded tissue are possible.