New graft copolymers of hyaluronic acid and polylactic acid: Synthesis and characterization

New graft copolymers have been synthesized, using hyaluronic acid (HA) as a hydrophilic backbone and polylactic acid (PLA) as an aliphatic polyester in order to obtain new polymeric derivatives of HA able to hydrophobically associate in an aqueous medium. Hyaluronic acid with low molecular weight was made soluble in organic solvent by transformation to its tetrabutylammonium (TBA) salt. Using the HA–TBA derivative, the reaction was performed in dimethylsulfoxide adding as a reagent the N-hydroxysuccinimide derivative of PLA. Two HA–PLA graft copolymers have been synthesized and characterized by FT-IR, 1H NMR spectroscopy and gel permeation chromatography. The interaction between these samples and an aqueous medium has been evaluated by rheological measurements. The obtained data evidenced that both HA–PLA graft copolymers show in aqueous medium a clear tendency for hydrophobic interaction dependent on the amount of PLA chains linked to the HA backbone.