Bioimaging of botulinum toxin and hyaluronate hydrogels using zwitterionic near-infrared fluorophores

Background: The injection of botulinum toxin (BTX) to reduce facial wrinkles is one of the most frequently performed plastic surgery procedures. The biocompatible hydrogels are injected with BTX for effective tissue augmentation. However, it is difficult to determine the interval of injection for effective tissue augmentation. Method: BTX and hyaluronate (HA) hydrogels were labeled with zwitterionic (ZW) near-infrared (NIR) fluorophores and visualized for 3 weeks after injection to BALB/c nude mice. Results: BTX-ZW conjugates and diaminohexane (DAH)-HA-ZW hydrogels were successfully prepared by the conventional EDC/NHS chemistry. Using the NIR fluorescence imaging, we confirmed that approximately 10% of BTX-ZW conjugates and 50% of DAH-HA-ZW hydrogels remained 3 weeks post-injection. Conclusion: This bioimaging technique using invisible NIR fluorescence light can be exploited for various biomedical applications. © The Author(s).