Abstract: A modified polysaccharide material which comprises: (1) polysaccharide covalently bonded to a synthetic polymer; (2) the synthetic polymer being made from (a) a polymerizable compound which is capable of being covalently coupled directly or indirectly to said polysaccharide, and (b) one or more polymerizable compounds containing (i) an ionizable chemcial group, (ii) a chemical group capable of transformation to an ionizable chemical group, (iii) a chemical group capable of causing the covalent coupling of the compound (b) to an affinity ligand or a biologically active molecule or (iv) a hydrophobic compound.