Norbornene-Functionalized Chitosan Hydrogels and Microgels via Unprecedented Photoinitiated Self-Assembly for Potential Biomedical Applications

Access to biocompatible self-assembled gels and microgels is of great interests for a variety of biological applications from tissue engineering to drug delivery. Here, the facile synthesis of supramolecular hydrogels of norbornene (nb)-functionalized chitosan (CS-nb) via UV-triggered self-assembly in the presence of Irgacure 2959 (IRG) is reported. The in vitro stable hydrogels are injectable and showed pH-responsive swelling behavior, while their structure and mechanical properties could be tuned by tailoring the stereochemistry of the norbornene derivative (e.g., endo- or -exo). Interestingly, unlike other nb-type hydrogels, the gels possess nanopores within their structure, which might lead to potential drug delivery applications. A gelation mechanism was proposed based on hydrophobic interactions following the combination of IRG on norbornene, as supported by 1 H NMR. This self-assembly mechanism was used to access microgels of size 100–150 nm, which could be further functionalized and showed no significant toxicity to human dermofibroblast cells.