Charge-Mixed Nanogels for siRNA Delivery: Concurrent Optimization of Efficacy and Safety via Structure-Activity Relationships.

Cationic nanogels are efficient polymeric vectors for siRNA delivery but often raise toxicity concerns. To address this efficacy-toxicity trade-off, we present a charge-mixed nanogel platform that reconciles high delivery potency with excellent biocompatibility. Specifically, a library of cationic nanogels was synthesized with precise control over charge composition, size, and cross-linking degree, enabling systematic investigation of their effects on delivery performance and toxicity. Our findings reveal that delivery efficiency is cooperatively modulated by charge, size, and cross-linking degree, whereas toxicity reduction is primarily achieved by diluting the positive charge density through incorporation of anionic units. The established structure-activity relationship identified an optimal formulation comprising 80% cationic and 20% anionic monomers, with a hydrodynamic radius of approximately 83 nm and a cross-linking degree of 20% using a disulfide-based cross-linker. This design enables intracellular glutathione-responsive dissociation and efficient siRNA release. The engineered charge-mixed nanogels demonstrate potent gene silencing (83.0%) and antitumor efficacy (84.3%), alongside notably reduced cellular and systemic toxicity. Collectively, this work provides rational design principles for cationic nanocarriers and establishes a promising vector platform that effectively overcomes the efficacy-toxicity dilemma for advanced siRNA therapeutics.