An injection port assembly for a tissue expander and/or mammary prosthesis comprising a composite silicone matrix having embedded fiber layers. The composite matrix materials may cover or extend from the outside perimeter of the injection port assembly and provide self sealing polymeric materials if punctured by a needle. The tissue expander and injection port assemblies and structures may be formed of MR scannable materials. The injection port structures may have palpation lumps for locating the injection port structure subsequent implantation. The injection port structure may be remotely located from the tissue expander and connected thereto via tubing.
