Poly(ethylene glycol)-poly(L-lactide) star block copolymer hydrogels crosslinked by metal-ligand coordination

The aqueous solution behavior and thermoreversible gelation properties of pyridine-end-functionalized poly(ethylene glycol)poly(L-lactide) (PEG(PLLA)8py) star block copolymers in the presence of coordinating transition metal ions were studied. In aqueous solutions, the macromonomers self-assembled into micelles and micellar aggregates at low concentrations and formed physically crosslinked, thermoreversible hydrogels above a critical gel concentration (CGC) of 8% w/v. In the presence of transition metal ions like Cu(II), Co(II), or Mn(II), the aggregate dimensions increased. Above the CGC, the gelsol transition shifted to higher temperatures due to the formation of additional crosslinks from intermolecular coordination complexes between metal ions and pyridine ligands. Furthermore, as an example, PEG(PLLA)8py hydrogels stabilized by Mn(II)pyridine coordination complexes were more resistant against degradation/dissolution when placed in phosphate buffered saline at 37 degrees C when compared with hydrogels prepared in water. Importantly, the stabilizing effect of metalligand coordination was noticeable at very low Cu(II) concentrations, which have been reported to be noncytotoxic for fibroblasts in vitro. These novel PEG(PLLA)8py metallo-hydrogels, which are the first systems to combine metalligand coordination with the advantageous properties of PEGPLLA copolymer hydrogels, are appealing materials that may find use in biomedical as well as environmental applications like the removal of heavy metal ions from waste streams. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012