Calcium ion-sensitive PEG-alginate blend hydrogels formed via thiol-ene photo-click reaction
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Stimuli-responsive hydrogels that exhibit a volume phase change when exposed to physical stimuli are valuable materials for diverse applications. Fabrication of these hydrogels requires selecting either specialized polymers or particular crosslinking mechanisms that can effectively trigger an alteration in the material’s mesh size and network density. In this work, we fabricated a double-network hydrogel using relatively common polymers: poly(ethylene glycol) (PEG) and alginate. The initial network was formed via thiol-ene photo-cross-linking with norbornene-modified PEG and alginate with a dithiol crosslinker (dithiothreitol), and we then modulated the swelling ratios using either calcium ions or a sequestrant. The resulting material features a robust double-network structure combining both chemical and physical crosslinks, with its mechanical and swelling properties easily tuned simply by adjusting the initial mixing ratio of the two polymer components. To demonstrate its utility, we created a bilayer hydrogel strip and tested it as an actuator. When submerged in a solution containing calcium ions, the 1.2 cm strip rapidly bent within 10 min. It then recovered its original shape by soaking in a sequestrant solution. Although the recovery motion took a relatively long time (about 60 min), the material’s reliable reversible bending and rebending highlights its significant potential for use as a responsive actuator. These results indicate that a functional hydrogel-based actuator can be prepared simply by blending PEG/alginate and designing the appropriate geometry.
Abstract
Stimuli-responsive hydrogels that exhibit a volume phase change when exposed to physical stimuli are valuable materials for diverse applications. Fabrication of these hydrogels requires selecting either specialized polymers or particular crosslinking mechanisms that can effectively trigger an alteration in the material’s mesh size and network density. In this work, we fabricated a double-network hydrogel using relatively common polymers: poly(ethylene glycol) (PEG) and alginate. The initial network was formed via thiol-ene photo-cross-linking with norbornene-modified PEG and alginate with a dithiol crosslinker (dithiothreitol), and we then modulated the swelling ratios using either calcium ions or a sequestrant. The resulting material features a robust double-network structure combining both chemical and physical crosslinks, with its mechanical and swelling properties easily tuned simply by adjusting the initial mixing ratio of the two polymer components. To demonstrate its utility, we created a bilayer hydrogel strip and tested it as an actuator. When submerged in a solution containing calcium ions, the 1.2 cm strip rapidly bent within 10 min. It then recovered its original shape by soaking in a sequestrant solution. Although the recovery motion took a relatively long time (about 60 min), the material’s reliable reversible bending and rebending highlights its significant potential for use as a responsive actuator. These results indicate that a functional hydrogel-based actuator can be prepared simply by blending PEG/alginate and designing the appropriate geometry.