Devices that change size/shape via osmotic pressure

implantable device in the body of an animal, wherein said device comprises a solute-absorbing encapsulated water membrane water permeable polymer, wherein (1) said polymer is a block copolymer containing a hard segment of polyurethane and / or polyurea and soft segment selected from the group consisting of polyalkylene oxides, polyalkylene carbonates, polysiloxanes and branched, or (b) linear hydrocarbons or said polymer comprises one selected from the groups membrane consisting of polyurethane elastomers, elastomers crosslinked silicone copolymers containing silicone elastomers polyolefin, wherein said membrane has a thickness of 0, 0254-0, (1 to 16 mil) 4,064 mm and has a transmission rate of water vapor by the process E96BW ASTM top 100 g / m2 / day to 0, 0254 mm (1 mil) thick, a force greater than 3447 strain, 35 KPa (500 psi), and a permeability to said lower 10-3 cm2 / s solute, and wherein he said solute is capable of providing said device with a pressure of about 0, 6895 KPa (0, 1 psi) or higher for a period of at least 24 h.