Dual-reactive hydrogels functionalizable using "Huisgen click" and "Schiff base" reactions

Abstract

Hydrogels incorporating different reactive groups are important platforms for the fabrication of functional materials through the conjugation of diverse molecules. In this study, a dual-reactive hydrogel system was designed utilizing aldehyde and azide groups containing methacrylate monomers. Hydrogels were obtained in the presence of a dimethacrylate crosslinker with a combination of hydrophilic PEG-based monomers via free-radical polymerization. The azide and aldehyde sites of the hydrogel network are reactive towards alkyne and amine functional groups, respectively. The advantage of the different reactivities of these functional groups was demonstrated through the attachment of two different dye molecules onto the hydrogel platform via the "Huisgen click" and "Schiff base" reactions to obtain a sensing platform for various applications, such as indicating change in pH of the environment.

Keywords: Dual-reactive hydrogel; Huisgen click; Schiff base.

Figure 1

Hydrogel synthesis and dual-functionalization through “Huisgen click” and “Schiff base” reactions respectively.

Figure 2

Synthesis procedures and 1H-NMR spectra of OHMA (a) and AHMA (b).

Figure 3

Synthesis of hydrogel network (top), and SEM images of hydrogels H1 and H3 (bottom).

Figure 4

Percentage water uptake versus time graphic of H1, H2, and H3 (left), photographs of H1 and H3 before (right, top), and after swelling in water (right, bottom).

Figure 5

FTIR spectra of hydrogel H1, after functionalization through “Huisgen click” (P-H1), after dual functionalization through the “Schiff Base” reaction (PR-H1), and after treatment with pH 5 acetate buffer (PR-H1-a).

Figure 6

Fluorescence microscopy images of H1 (inset b), and P-H1 upon functionalization with 1-ethynylpyrene (a), Fluorescence images were taken with Hoechst/DAPI (UV); (Excitation BP 350/50, Emission BP 460/50) filter set.

Figure 7

Fluorescence microscopy image of rhodamine functionalized PR-H1 (a, top), and fluorescence image of rhodamine functionalized PR-H1-a after treatment with acid (b, top). Schematic representation of rhodamine group response to acid for PR-H1 (bottom, left). Fluorescence intensity comparison of PR-H1 and PR-H1-a, before and after acid treatment, respectively (bottom, right). Fluorescence images were taken with AF647/CY5(Red); (Excitation BP 620/60, Emission BP 700/75) filter set.