Enzyme-Immobilized Oxoammonium Nanogels: A Biocompatible and Injectable Platform for Enhanced Enzyme Stability and Reusability

We report redox-responsive, oxoammonium-functionalized nanogels for mild, injectable, noncovalent enzyme immobilization. Amphiphilic PEG-<i>b</i>-poly(PMA-<i>co</i>-GMA) prepared by Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization was oxidized to nitroxide/oxoammonium states, forming nanogels that electrostatically complex with anionic proteins. Increasing oxoammonium content (30-70%) boosted encapsulation (85-98%) and loading (26-47%). Lipase and paraoxonase-1 (PON1) retained or exceeded native activity; the highest-charge formulation delivered 2.5-5-fold higher specific activity and >80% activity after five reuse cycles. Circular dichroism (CD) and polymer-only controls verified preserved secondary structure and no background catalysis. Reduction of pendant oxoammonium groups with glutathione, followed by mild acidification (pH 6) regenerated neutral nitroxides and triggered release. The nanogels were colloidally stable, shear-thinning, and cytocompatible (>90% cell viability), and PON1-loaded gels showed potent antioxidant and lipid-protective effects. This tunable, biocompatible platform stabilizes and recycles enzymes under gentle aqueous conditions and enables on-demand release for therapeutic delivery and biocatalysis.