Designing Thermally Stable DNA Hydrogels via Entropically-Driven Acridine Intercalation

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• Supramolecular hydrogels rely on reversible bonds, often exothermic, leading to rapid relaxation with heat.
• Entropy-dominated associations offer temperature-stable mechanical properties, but tuning strategies are limited.
• Acridine-based DNA-intercalating supramolecular hydrogels (Acr-PEG DISHs) present a model system for investigating environmental influences on reversible cross-linking.

Purpose of the Study:

• To investigate how environmental variables, specifically ionic strength, salt concentration, ion identity, and pH, regulate reversible cross-linking dynamics in Acr-PEG DISHs.
• To understand the role of electrostatic screening and transition state entropy in modulating hydrogel mechanical properties.
• To identify key environmental factors for tuning the behavior of entropy-driven supramolecular polymer networks.

Main Methods:

• Preparation of Acr-PEG DISHs using DNA and a bis-intercalating cross-linker at a concentration of 50 mg/mL DNA and 4 mM cross-linker.
• Systematic evaluation of hydrogel properties across a range of ionic strengths (0.004–0.17 M), salt concentrations (0–0.75 M), different ion identities (monovalent and multivalent), and varied pH.
• Rheological measurements to determine relaxation dynamics and elasticity, including calculation of transition state entropy using Eyring analysis.

Main Results:

• Increasing ionic strength significantly enhanced hydrogel elasticity and slowed relaxation dynamics, with relaxation times increasing from ~30–100 s to ~55–625 s.
• At elevated salt concentrations (~0.5 M), electrostatic screening dominated network behavior, increasing transition state entropy.
• Monovalent ion identity modulated dissociation kinetics (Na+ < Li+ < K+), while multivalent ions destabilized the network. pH variations showed minimal impact due to ionic strength masking effects.

Conclusions:

• The ionic environment is a critical factor for tuning the dynamics of entropy-driven supramolecular hydrogels.
• Systematic control over hydrogel elasticity and relaxation behavior can be achieved by manipulating ionic strength and salt composition.
• These findings provide a foundation for designing advanced, environmentally responsive supramolecular materials with tailored mechanical properties.