A water insoluble, biocompatible composition that is formed by a method which
combines,
in an aqueous mixture, a polyanionic polysaccharide, a nucleophile, and an activating
agent, under conditions sufficient to form the composition. Also, a water insoluble,
biocompatible composition that is formed by a method which combines, in an aqueous
mixture, a polyanionic polysaccharide, a modifying compound, a nucleophile and
an activating agent under conditions sufficient to form the composition.