Deoxyribonucleic acid (DNA) hydrogels are a unique class of programmable, biocompatible materials able to respond to complex stimuli, making them valuable in drug delivery, analyte detection, cell growth, and shape-memory materials. However, unmodified DNA hydrogels in the literature are very soft, rarely reaching a storage modulus of 10 3 Pa, and they lack functionality, limiting their applications. Here, a DNA/small-molecule motif to create stiff hydrogels from unmodified DNA, reaching 10 5 Pa in storage modulus is used. The motif consists of an interaction between polyadenine and cyanuric acid-which has 3-thymine like faces-into multimicrometer supramolecular fibers. The mechanical properties of these hydrogels are readily tuned, they are self-healing and thixotropic. They integrate a high density of small, nontoxic molecules, and are functionalized simply by varying the molecule sidechain. They respond to three independent stimuli, including a small molecule stimulus. These stimuli are used to integrate and release DNA wireframe and DNA origami nanostructures within the hydrogel. The hydrogel is applied as an injectable delivery vector, releasing an antisense oligonucleotide in cells, and increasing its gene silencing efficacy. This work provides tunable, stimuli-responsive, exceptionally stiff all-DNA hydrogels from simple sequences, extending these materials' capabilities.

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A significant barrier to biological applications of DNA structures is their instability to nucleases. UV-mediated thymine dimerization can crosslink and stabilize DNA nanostructures, but its effect on DNA strand hybridization fidelity and function is unclear. In this work, we first compare a number of methods for DNA irradiation with different wavelengths of light and different photosensitizers. We demonstrate that all approaches can achieve nuclease protection; however, the levels of DNA offtarget crosslinking and damage vary. We then describe mild irradiation conditions intended to safeguard DNA against nuclease degradation. We demonstrate up to 25× increase in serum stability while minimizing off-target damage and maintaining functions such as hybridization efficiency, gene silencing, aptamer binding, and DNA nanostructure formation. Our methodology requires no complex instruments beyond a UV light source and no synthetic modification of the DNA itself, allowing for applications in numerous areas of nucleic acid therapy and nanotechnology.