- Abstract This paper describes the preparation and characterization of a three-dimensional, porous sponge made from the marine polysaccharide alginate for creating a cell-matrix transplant to replace damaged organs or tissues. The sponge is prepared by a three-step procedure: first gelation of the alginate with bivalent cations, followed by freezing of the hydrogel and finally lyophilization to produce a porous sponge. The pattern and the extent of sponge porosity, as well as its mechanical properties, were influenced by the concentration and the type of alginate (guluronic to mannuronic ratio, and viscosity), the type and concentration of the cross-linkers and the freezing regime. By controlling these variables, macroporous sponges (pore size of 70–300 μm) that are suitable for cell culture and neovascularization were achieved. Fibroblasts seeded within the sponges preferred the pores, where they maintained a spherical shape. The alginate sponges conserved their initial volume for at least 3 months. It appears that alginate sponges may provide an excellent support for cell transplantation.