Injectable bottlebrush triblock copolymer hydrogel crosslinked with ferric ions

Metal ionically crosslinkable hydrogels are useful in many fields; however, it is difficult to design and synthesize them rationally. In this study, we synthesized ABA bottlebrush triblock copolymers, whose A block is poly(acrylic acid) (PAA) and B block is poly(oligo (ethylene glycol) methyl ether acrylate) (POEGA), by atom transfer radical polymerization. The obtained bottlebrush triblock copolymers, PAA-POEGA-PAAs, showed low viscosity at relatively high polymer concentrations and behaved as a Newtonian fluid below 20 wt% in aqueous solutions. The solutions were gelled by mixing with ferric ions after exceeding the overlap concentration. The G’ of the hydrogels increased sharply at the region of semi-dilute solutions before reaching the entanglement concentration. Thanks to the water-retention and steric effect of the bottlebrush structure of POEGA blocks, precipitation of the copolymers did not occur, but in situ and rapid gelling was possible via chelation of ferric ions by PAA blocks.