Biomaterials made of polymers, metals or their alloys, ceramics and their composites, are used as implants to restore or to replace the damaged soft and hard tissue/organ functions for an intended time period. Biomaterials made of synthetic materials are very simple materials compared to their natural counterparts, they only replace very simple functions of the damaged tissue during healing. Natural tissues have been used for both soft and hard repair and replacement, but they do have serious limitations such as: shortage of donor tissue, donor site morbidity, unpredictable resorption characteristics, immunogenic response, risk of disease transmission, and ethical limitations. Tissue engineering is a relatively new approach, in which healthy mammalian cells are used with supporting matrices, usually made of either natural or synthetic polymers as composite bioartificial implants. Primary cells, especially embryonic stem cells, cell lines, hybridomas, genetically modified cells are considered as potential sources for this application. Both closed and open matrices are used as support matrices. Nondegradable and biocompatible microcapsules and hollow fibers are utilized in closed systems, especially for immunoprotection of the transplanted cells. Biodegradable polymers, both natural and synthetic are used in the preparation of bioartificial implants carrying only autogenic cells.