Photopatternable Clickable Hydrogels: Orthogonal Control over Fabrication and Functionalization

Clickable hydrogels were fabricated using dendron polymer conjugate based triblock copolymers containing orthogonally functionalizable dendrons. Because of their well-defined chemical composition, the dendron-based hydrogels provide control over the number of reactive groups in the hydrogel so that the desired (bio)molecules can be immobilized with tailored density within the hydrogel matrix. Well-defined hydrogel precursors were obtained using the copper-catalyzed azide-alkyne click cycloaddition between second and third polyester dendrons bearing an alkyne group at their focal point and linear poly(ethylene glycol) (PEG) diazides PEG2kDa, PEG4kDa, and PEG6kDa. The surfaces of the outer dendron-based blocks were decorated with methacrylate and alkyne groups, the former necessary for photo-cross-linking, while the latter clickable alkyne groups would enable efficient postfunctionalization of hydrogels. The degree of cross-linking and the amount of reactive alkyne units available for postgelation functionalization of the hydrogels were tuned by adjusting the stoichiometry of the orthogonally reactive groups on the dendrons. Hydrogels containing alkyne groups were synthesized via photopolymerization with gelation efficiencies between 91 and 99%. Water uptake of these hydrogels in aqueous media could be tuned between SOO and 3010% by varying the length of PEG as well as generation and substitution of the dendrons. Successful covalent modification of these hydrogels via the azide alkyne click reaction was demonstrated by attachment of the fluorescent dye bodipy and immobilization of the protein streptavidin onto biotinylated hydrogels. Importantly, it was demonstrated that the amount of protein immobilization can be tuned varying the amount of ligand incorporated in the hydrogel using the clickable alkyne-based reactive handles. Three-dimensional hydrogel micropatterns on silicon oxide surfaces were fabricated using either micromolding in capillaries or via photo-cross-linking using a photomask. These reactive micropatterns were amenable to efficient functionalization in a tailored manner by using the Huisgen-type click cycloaddition reaction.