Biomolecularly stimuli-responsive tetra-poly(ethylene glycol) that undergoes sol–gel transition in response to a target biomolecule

Stimuli-responsive polymers that undergo a sol–gel transition in response to changes in environmental factors such as pH and temperature have attracted considerable attention for biomedical applications such as drug reservoirs for controlled release and scaffolds for tissue engineering. Although numerous stimuli-responsive polymers that undergo a sol–gel transition have been reported, the literature contains few accounts of biomolecularly stimuli-responsive polymers that undergo a sol–gel transition in response to a specific biomolecule. In previous studies, we designed biomolecule-responsive hydrogels that undergo changes in volume in response to a target biomolecule; the strategy involves using biomolecular complexes as dynamic cross-links in the gel networks. In the present study, we designed biotin-conjugated four-armed poly(ethylene glycol) (biotinylated Tetra-PEG) as biomolecular stimuli-responsive sol–gel transition polymers that underwent the phase transition from a sol to a gel state in response to avidin as a target biomolecule. When avidin that forms a biomolecular complex with biotin was added to a buffer solution containing biotinylated Tetra-PEG, the solution transformed to a gel state immediately. However, the addition of a buffer solution with free biotin to the resulting hydrogel induced its dissociation to a sol state. The sol–gel transition of a buffer solution with biotinylated Tetra-PEG was directly affected by polymer concentration and the biotin/avidin molar ratio. The phase diagram of the sol–gel transition of biotinylated Tetra-PEG in a buffer solution as a function of polymer concentration and the biotin/avidin molar ratio is presented.