Technological watch

Photo- and pH-dually responsive hydrogel containing spirooxazine groups

Abstract The development of a low-cost and multifunctional sensing and monitoring device would be a meaningful endeavor. In this research, a novel spirooxazine with a two double-bonded structure, designated as (1-butyl-3,3-dimethylspiro[indoline-2,3’-naphtho[2,1-b] [1, 4]oxazine]-5,8’-diyl)bis(methylene)bis(2-methylacrylate) (SO-DB), was successfully synthesized and incorporated as a functional cross-linker into a polyhydroxyethyl methacrylate hydrogel system. Notably, this hydrogel system based on a single responsive component exhibits photo-pH dual responsiveness, which avoids the addition of multiple components that may affect other properties of the hydrogel. Particularly, in comparison to traditional surface grafting and physical blending, crosslinking with SO-DB leads to the formation of a denser and stronger three-dimensional polymer network in the stimuli-responsive hydrogel. Under UV light irradiation, spirooxazine absorbs energy and undergoes cleavage of the Cspiro-O bond, transforming the molecule from a colorless closed-ring state to an open-ringed photomerocyanine (PMC) state. Under acidic conditions, hydrophobic spirooxazine undergoes a reversible protonation open-ring reaction, forming a stable intermediate form, a protonated photomerocyanine (PMCH). Furthermore, the addition of SO-DB as a crosslinking agent to the hydrogel system increases its stability and fatigue resistance, and maintains good repeatability over 24 light cycles and 7 pH cycles without performance loss. Such approach to generate stimulus-responsive hydrogels could have great potential in both wearable biosensors and food packaging field.

Publication date: 21/01/2024

Journal of Polymer Research


This project has received funding from the Bio Based Industries Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 837761.