Role of Free Catecholamine in Thiol-Ene Crosslinking for Hyaluronic Acid Hydrogels with High Loading Efficiency of Anticancer Drugs

Abstract

Background: Hyaluronic acid (HA) is a widely used polysaccharide in biomedical field because of its excellent biocompatibility. Its chemical structure can be modified with various functional groups. Recently, dopamine has been tethered onto the polymeric backbone to ensure long-term stability and tissue adhesiveness of HA hydrogel. However, the radical scavenging effect of dopamine on typical photo-induced crosslinking for hydrogels has not been specifically studied. Methods: Photo-crosslinkable norbornene-modified HA (NorHA) was synthesized and crosslinked by dithiothreitol containing dopamine at different concentrations. During in situ ultraviolet light-triggered crosslinking, storage moduli were monitored using an oscillatory rheometer. Additionally, the amount of thiol utilized for HA crosslinking was investigated under the presence and absence of dopamine. Finally, doxorubicin was encapsulated in the hydrogels, and the drug loading efficiency and release kinetics were measured. Results: Adding dopamine into the NorHA pre-gel solution delayed the gelation time, yet the final storage modulus of the hydrogel remained constant. That is, dopamine might partially consume the energy required for thiol-ene reaction to generate semiquinone radicals. Furthermore, the residual thiols which were not involved in the crosslinking decreased when the hydrogel was formed at a high concentration of dopamine, indicating the formation of Michael adducts of semiquinone and thiols. Interestingly, the presence of dopamine in the hydrogel increased the loading efficiency of the hydrophobic drugs due to pi-pi stacking and hydrogen bonding between dopamine and drugs. Conclusion: The presence of free catecholamines in a photo-crosslinkable polymer can delay the gelation time but improve the drug loading efficiency.