A carrier and a method for preparing it are provided for use in the delivery of therapeutic agents. A polysaccharide is reacted with an oxidizing agent to open sugar rings on the polysaccharide to form aldehyde groups. The aldehyde groups are reacted to form covalent oxime linkages with a second polysaccharide and each of the first and second polysaccharide is selected from the group consisting of hyaluronic acid, dextran, dextran sulfate, chondroitin sulfate, dermatan sulfate, keratan sulfate, heparan, heparan sulfate and alginate.