(609c) Dynamic, Reversible Control of Biomaterial Properties Using DNA

The ability to dynamically control the mechanical properties of biomaterials is critical for regenerative medicine applications. For example, matrix stiffness controls the differentiation of stem cells, or the metastasis of cancer cells. However, most methods for tuning the mechanical properties of 3D hydrogels are not reversible, or involve potentially harmful stimuli like UV light. Here we use DNA as a programmable crosslinker to reversibly change the stiffness of gelatin hydrogels. We modified DNA with a methacrylate moiety, allowing it to be crosslinked along with methacrylated gelatin (GelMA). By tuning the amount of pre-formed DNA crosslinks relative to GelMA, we were able to tune the stiffness of the hydrogels obtained from 0.5 – 2 kPa, as measured by an AFM-based method. The crosslinkers contained single-stranded toehold sequences, allowing them to be broken by adding fully complementary displacement strands. The stiffness of the formed hydrogels could be tuned through the amount of displacement strand added, and the process was reversible: adding more crosslinker restored the stiffness to the original value. We explored various crosslinker lengths, designs, and geometries (including branched and more rigid multi-helical DNA tiles), demonstrating the straightforward tunability of DNA. The use of GelMA allows for photopatterning of hydrogels into micron-sized patterns, and cells could be incorporated into the materials and responded to the reversible changes in stiffness. DNA-based crosslinking also enables spatial patterning of stiffness, and will allow for incorporation of multiple ligands in a programmable manner to impart the gels with bioactivity. We will also outline chemical strategies for incorporating DNA into other biomaterial scaffolds, such as hyaluronic acid or PEG, demonstrating the versatility of our approach. We envision that DNA-based control of stiffness will allow for programmable and reversible control of hydrogel properties, and lead to advanced biomaterials for regenerative medicine, tissue engineering, and fundamental biological studies.