Facile Maleimide-Hydrazine Reaction to Form Stable Bonds in Dynamic Hydrazone-Cross-Linked Hydrogels

Abstract The hydrazone bond has been extensively used in dynamic hydrogels but is limited in applications where stability is also required. Here, we demonstrate hydrazine cross-linking with both aldehydes and maleimides under physiological conditions (pH = 7.4 and 37 °C), enabling a one-pot reaction to form dynamic hydrazone and stable hydrazinosuccinimide bonds. Using poly(ethylene glycol) (PEG) and hyaluronic acid (HA) functionalized macromers, hydrogel-forming reactions between maleimide and amine-containing functional groups occurred most rapidly with alkyl-hydrazine through an aza-Michael addition mechanism. Hydrazinosuccinimide cross-links also exhibited enhanced stability compared to alkyl-hydrazone and benzyl-hydrazone cross-links. Lastly, hydrazinosuccinimide cross-linked PEG-HA hydrogels were functionalized with a cell-adhesive peptide via hydrazinosuccinimide, thiosuccinimide, or benzyl-hydrazone bonds, and human mesenchymal stem cell migration depended on the cross-linker structure and dynamicity. This reaction between maleimide and alkyl-hydrazine not only expands the range of accessible properties in dynamic hydrazone-cross-linked hydrogels but also broadens the available reactions maleimide can undergo for numerous biomaterial applications.