In situ crosslinked hydrogels formed using Cu(I)-free Huisgen cycloaddition reaction

BACKGROUND: 'Click' chemistry, or the 1,3-dipolar cycloaddition of organic azides with alkynes, has been evaluated for many biomedical purposes; however, its utility in crosslinking hydrogels in situ is limited by the toxicity of the requisite copper(I) catalyst. We report the first use of catalyst-free Huisgen cycloaddition to generate crosslinked hydrogels under physiological conditions using multivalent azide-functionalized polymers and an electron-deficient dialkyne crosslinker. RESULTS: Water-soluble azide-functionalized polymers were crosslinked with an electron-deficient dialkyne crosslinker to form hydrogels at physiological temperature without the addition of copper(I) catalyst. Crosslinking was confirmed using scanning electron microscopy, Fourier transform infrared and H-1 NMR analyses. Flow by vial inversion and dynamic rheological methodologies were implemented to evaluate gelation kinetics at 37 degrees C of variable polymer compositions, concentrations and stoichiometric ratios. Kinetic studies revealed gelation in as little as 12 h at 37 degrees C, although strong gels that withstand inversion were observed by 1-8 days. CONCLUSION: The ability to form hydrogel networks under mild conditions demonstrates the potential viability of the catalyst-free 'click' crosslinking chemistry for in situ gelling and other biological applications. Further chemical modifications in the crosslinking moieties, as well as polymer and crosslinker conformations, are expected to enhance gelation kinetics to a more biomedically practical rate. (C) 2009 Society of Chemical Industry