Uses of compositions comprising carboxypolysaccharides (CPS) including carboxymethyl cellulose (CMC) and polyethylene glycols (PEGs) are provided where the PEG is a PEG-epoxide covalently linked to the CPS in the presence of NH4OH. In certain embodiments, the PEG attaches to only one CPS, forming a decorated CPS. In other embodiments, bi-functional PEG molecules are attached to adjacent CPSs, thereby forming a covalently cross-linked composition. Such compositions can be used as space-filling materials, load-bearing materials, anti-adhesion compositions, drug delivery vehicles, and lubricants of tissues and medical instruments.