A method for the manufacture of a solid porous separation material based on a polysaccharide, said method comprising the steps of: (a) providing an aqueous solution (I) of a polysaccharide, (b) solidifying the solution, preferably by transforming the solution to a gel, and (c) optionally crosslinking the polysaccharide, with the proviso that, if step (c) is present, steps (b) and (c) may be carried out simultaneously. The method is characterized in that the polysaccharide provided in step (a) is modified by being inter-molecularly crosslinked to an extent such that the viscosity of the solution (I) is at least 110%, preferably at least 200%, of the viscosity of an aqueous solution (II) of the corresponding polysaccharide which has not been intermolecularly crosslinked and which is present in the same concentration as the inter-molecularly crosslinked polysaccharide is in solution (I)