Robust multi-responsive supramolecular hydrogel based on a mono-component host-guest gelator

Area of Science:

• Supramolecular chemistry
• Materials science
• Polymer chemistry

Background:

• Stimuli-responsive supramolecular hydrogels are challenging to create due to the need to balance gelator solubility and gelation.
• Mono-component host-guest hydrogels require careful design for controlled self-assembly and responsiveness.

Purpose of the Study:

• To synthesize and investigate novel azobenzene-modified beta-cyclodextrin derivatives as mono-component hydrogelators.
• To explore the impact of alkyl chain length on hydrogel properties, including solubility, gelation ability, and responsiveness.

Main Methods:

• Synthesis of three beta-cyclodextrin derivatives with varying alkyl chain lengths (beta-CD-Azo-Cn).
• Characterization of host-guest interactions using UV-visible and ROESY NMR spectroscopy.
• Evaluation of hydrogel properties, including minimum gelation concentration (MGC), self-supporting ability, and gel-sol transition temperature.

Main Results:

• Alkyl chain length significantly affects the solubility and gelation of beta-cyclodextrin derivatives.
• Beta-cyclodextrin-azobenzene derivative with an eight-carbon alkyl chain (beta-CD-Azo-C8) exhibited the lowest MGC.
• The hydrogels demonstrated responsiveness to external stimuli like heating, competing guests/hosts, and UV irradiation.
• Hydrogels formed with >8 wt% gelator showed good self-supporting ability (storage modulus >104 Pa) and a gel-sol transition near body temperature.

Conclusions:

• Successfully developed stimuli-responsive mono-component host-guest hydrogels based on azobenzene-modified beta-cyclodextrins.
• Demonstrated the critical role of alkyl chain length in tuning hydrogelator performance.
• Highlighted the potential of these hydrogels for biological material applications due to their properties and body-temperature transition.