Investigating\nthe Formation of Polymer–Nanoparticle\nComplex Coacervate Hydrogels Using Polymerization-Induced Self-Assembly-Derived\nNanogels with a Succinate-Functional Core

This paper reports polymer–nanoparticle-based\ncomplex coacervate\n(PNCC) hydrogels prepared by mixing anionic nanogels synthesized by\npolymerization-induced self-assembly (PISA) and cationic branched\npoly­(ethylenimine) (bPEI). Specifically, poly­(3-sulfopropyl methacrylate)<sub>58</sub>-<i>b</i>-poly­(2-(methacryloyloxy)­ethyl succinate)<sub>500</sub> (PKSPMA<sub>58</sub>-PMES<sub>500</sub>) nanogels were\nprepared by reversible addition–fragmentation chain-transfer\n (RAFT)-mediated PISA. These nanogels swell on increasing the solution\npH and form free-standing hydrogels at 20% w/w and pH ≥ 7.5.\nHowever, the addition of bPEI significantly improves the gel properties\nthrough the formation of PNCCs. Diluted bPEI/nanoparticle mixtures\nwere analyzed by dynamic light scattering (DLS) and aqueous electrophoresis\nto examine the mechanism of PNCC formation. The influence of pH and\nthe bPEI-to-nanogel mass ratio (MR) on the formation of these PNCC\nhydrogels was subsequently investigated. A maximum gel strength of\n1300 Pa was obtained for 20% w/w bPEI/PKSPMA<sub>58</sub>-PMES<sub>500</sub> PNCC hydrogels prepared at pH 9 with an MR of 0.1, and\nshear-thinning behavior was observed in all cases. After the removal\nof shear, these PNCC gels recovered rapidly, with the recovery efficiency\nbeing pH-dependent.