- Abstract Two approaches for cell transplantation and new tissue constructions are discussed. In one case, a novel synthetic polyphosphazene has been synthesized that can be gelled by simply adding ions to it at room temperature under aqueous conditions. This polymer has been shown to be compatible for several different cell types. Microcapsular membranes based on the complex of this polymer with poly( l -lysine) allow the inward diffusion of nutrients to nourish the encapsulated cells, but are impermeable to antibodies. In a second approach, biodegradable polyesters have been designed as scaffolds for liver cells and cartilage cells to aid in organ regeneration. Design of the polymer scaffold including the characterization of the surface chemistries for cell attachment, as well as in-vitro and in-vivo data on cell behavior are presented.