Poly(_L-lysine)-<i>block</i>-poly(ethylene glycol)-<i>block</i>-poly(_L-lysine) triblock copolymers for the preparation of flower micelles and their irreversible hydrogel formation

Poly(_L-lysine)-<i>block</i>-poly(ethylene glycol)-<i>block</i>-poly(_L-lysine) (PLys-<i>block</i>-PEG-<i>block</i>-PLys) triblock copolymers formed polyion complex (PIC) with poly(acrylic acid) (PAAc) or sodium poly(styrenesulfonate) (PSS), leading to the formation of flower micelle-type nanoparticles (Nano^Lys/PAAc or Nano^Lys/PSS) with tens of nanometers size in water at a polymer concentration of 10 mg/mL. The flower micelles exhibited irreversible temperature-driven sol-gel transitions at physiological ionic strength, even at low polymer concentrations such as 40 mg/mL, making them promising candidates for injectable hydrogel applications. Rheological studies showed that the chain length of PLys segments and the choice of polyanions significantly impacted irreversible hydrogel formation, with PSS being superior to PAAc for the formation. The incorporation of silica gel nanoparticles into the PIC flower micelles also resulted in irreversible gelation phenomena. The highest storage modulus exceeded 10 kPa after gelation, which is sufficient for practical applications. This study demonstrates the potential of these PIC-based hydrogels as biomaterials with tunable properties for biomedical applications. A polyion complex-based flower micelle, formed by poly(_L-lysine)-<i>block</i>-PEG-<i>block</i>-poly(_L-lysine) triblock copolymers and polyanions, shows irreversible hydrogel formation; incorporating silica enhanced its modulus to exceeding 10 kPa, promising for biomedical applications.