A implant assembly (1) includes a frame structure (10) with an inwardly protruding support flange (16), a first frame portion (12) extending above the flange (16) and a second frame portion (14) extending below the flange (16). A first semipermeable membrane (20) is positioned on a first side of the flange (16) and a second membrane (30) is positioned on a second opposite flange side. A first seal (2) is formed at the first frame portion (12) and a second seal (3) is formed at the second frame portion (14) to form an enclosed inner chamber (18) defined by the membranes (20, 30) and the frame structure (10).