Multi-stimulus-responsive biocompatible natural anionic surfactant/anionic additive mixed system

Developing natural biosurfactant-based smart hydrogels with low-toxicity, biocompatibility and multi-stimulus-responsiveness is of great importance in fundamental and applied science. Based on the strategy of hydrogen bonding and steric hindrance regulation, multi-stimulus-responsive hydrogels were constructed using electrostatically repulsive sodium deoxycholate (NaDC) and sodium salt of trans -ortho-methoxycinnamic acid ( trans -NaOMCA). The rheological and DLS techniques, TEM, optical microscopy, 1 H NMR, FT-IR and UV–vis spectrometers were used to investigate the stimulus-responsiveness and the controlled release of model drug. Molecular dynamics (MD) simulations were performed to provide molecular insights into the effect of stimuli on self-assembly, type and number of hydrogen bonds, etc. This study provides a new method to construct multi-stimulus-responsive hydrogels using anionic surfactant and anionic photoresponsive additive. The NaDC/ trans -NaOMCA/H 2 O mixed system exhibits reversible pH- and CO 2 -responses. FT-IR and 1 H NMR spectra results and MD simulations reveal that, the formation and breaking of bridging hydrogen bonds involving H 3 O + (including the acid salt structures) play key roles in reversible sol ⇌ gel transition, and the bridging hydrogen bonds between DC − and trans -OMCA − lead to a synergistic effect during the formation of HAc- and CO 2 -induced hydrogels. In addition, the HAc-induced hydrogels are thermosensitive and photoresponsive, exhibiting the stimulus-responsiveness of both NaDC and trans -NaOMCA. The stimulus-responsive mechanism has been proposed. The investigation of the release of methylene blue from the prepared hydrogels will provide guidance for practical applications.