Designing Thermally Stable DNA Hydrogels via Entropically‐Driven Acridine Intercalation

ABSTRACT

Physically cross‐linked hydrogels formed through supramolecular interactions typically relax more rapidly upon heating because reversible bond formation is often exothermic. In contrast, entropy‐dominated associations can generate materials that maintain or strengthen mechanical properties with temperature. However, strategies to systematically tune entropy‐driven behavior in polymer networks remain limited. Here, we investigate how environmental variables regulate reversible cross‐linking in acridine‐based DNA‐intercalating supramolecular hydrogels (Acr‐PEG DISHs). Hydrogels composed of 50 mg mL ^{− 1} DNA and 4 mM bis‐intercalating cross‐linker were evaluated across buffer compositions with ionic strengths of I ≈ 0.004–0.17 M, salt concentrations from 0–0.75 M, different ion identities, and varied pH. Increasing ionic strength produced more elastic networks with slower relaxation dynamics, increasing relaxation times from ∼30–100 s in low‐ionic‐strength buffers to ∼55–625 s in PBS. At elevated salt concentrations (∼0.5 M), electrostatic screening dominated network behavior and increased transition state entropy by Eyring analysis. Although monovalent salts produced similar elastic responses, ion identity modulated dissociation kinetics (Na ⁺ < Li ⁺ < K ⁺ ), whereas multivalent ions destabilized the network. In contrast, pH‐dependent studies showed only minor effects because citrate‐phosphate ionic strength masked acridine protonation. These findings identify the ionic environment as a powerful handle for tuning entropy‐driven supramolecular hydrogel dynamics.