Remote hydrogelation by metal-ligand coordination using high intensity focused ultrasound

Abstract

Smart materials have garnered interest due to their potential and versatility in a wide range of applications from tissue engineering, drug delivery, and cosmetics. It should be appreciated that while ultrasound has been utilized as a stimulus for smart materials, including organogels, its application has primarily been focussed below 100 kHz and for chemical scission. To investigate the potential of high intensity focussed ultrasound (HIFU) for gel formation, we synthesized a water-soluble comb-like polymethacrylate copolymer with randomly distributed tridentate ligands. We utilized reversible metal-ion non-covalent interactions in the design of our polymeric system to bind monomeric units together into temporary crosslinking networks or polymeric aggregates. To minimize the immediate formation of the metallogel, other functional groups within the polymer were involved in competitive reversible binding processes with the solvated metal ions. We show that HIFU triggers hydro-metallogelation by breaking the weaker labile interactions that in turn may allow for more favourable metal ion-ligand chelation, resulting in the formation of a gel network. Considering the established targeting potential of HIFU, our results here open a framework for targeted in situ triggered acoustic hydro-metallogelation for biomedical and industrial applications.