DNA-Intercalating Supramolecular Hydrogels for Tunable Thermal and Viscoelastic Properties

Abstract

Polymeric supramolecular hydrogels (PSHs) leverage the thermodynamic and kinetic properties of non-covalent interactions between polymer chains to govern their structural characteristics. As these materials are formed via endothermic or exothermic equilibria, their thermal response is challenging to control without drastically changing the nature of the chemistry used to join them. In this study, we introduce a novel class of PSHs utilizing the intercalation of double-stranded DNA (dsDNA) as the primary dynamic non-covalent interaction. The resulting dsDNA intercalating supramolecular hydrogels (DISHs) can be tuned to exhibit both endothermically or exothermically driven binding through strategic selection of intercalators. Bifunctional polyethylene glycol (M_W~2000 Da) capped with intercalators of varying hydrophobicity, charge, and size (acridine, psoralen, thiazole orange, and phenanthridine) produced DISHs with comparable moduli (500-1000 Pa), but unique thermal viscoelastic responses. Notably, acridine-based cross-linkers displayed invariant and even increasing relaxation times with temperature, suggesting an endothermic binding mechanism. This methodology expands the set of structure-properties available to biomass-derived DNA biomaterials and promises a new material system where a broad set of thermal and viscoelastic responses can be obtained due to the sheer number and variety of intercalating molecules.

Keywords: Biomaterials; DNA Intercalations; Entropy driven gelation; Supramolecular hydrogels.

Figure 1.

a) Relationship of material properties to thermodynamics properties and their corresponding enthalpy and entropy-driven interactions. The exact mathematical relations are not shown b) Schematic of a DISH displaying reversible intercalation as an inter-strand cross-linker c) Enthalpies and entropies of binding for various intercalators determined by viscometry.^[20]

Figure 2.

a) Structures of intercalators and their assigned acronyms b) Photograph of DISHs used in this study (left to right) Acr-PEG, Pso-PEG, Thi-PEG, and Phen-PEG under ambient light (left image) and 365 nm light (right image) c) UV/Vis spectra of Thi-PEG with DNA (left) and Thi-PEG in buffer (right) at increasing concentrations.

Figure 3.

a) Representative frequency sweeps conducted at 1 % strain from 0.01 to 100 rad/s at 27 °C, 37 °C, and 47 °C. DISHs were compared to 5 % (w/w) DNA sample. Top to bottom: DNA, Acr-PEG, Pso-PEG, Thi-PEG, and Phen-PEG. b) Frequency sweeps replotted as a function of tan δ. We note that at hight frequency the efects of instrument inertia cause slight fluctuations in the observed moduli.

Figure 4.

a) Representative normalized stress relaxation plots conducted at 2 % strain and 5 rad/s. Each plot was fit to the KWW function at 27 °C, 37 °C, and 47 °C. DISHs Top to bottom: Acr-PEG, Pso-PEG, Thi-PEG, and Phen-PEG. b) Bar graphs comparing tau values extracted from triplicate runs at temperatures 27 °C, 37 °C, and 47 °C. Error bars represent standard error.