Fabrication and Characterization of Self Entangling Hydrogel Helices

Entanglements define properties across a broad range of length scales from the molecular scale toughening of hydrogels to the collective behavior of California blackworms. Synthetic materials that self-entangle offer opportunities for control over porosity, gelation, and mechanical properties, but there are only a few prior reports of such materials. To investigate entanglements at the meso-scale, micron scale helices capable of shape morphing around physiological temperature are fabricated from thin films via photolithography. The helices are composed of two hydrogel layers, each layer with compositions of hydrophilic co-monomers that adjust their respective temperature sensitivity and swelling behavior. Patterning a rectangle of the first, less temperature sensitive polymer, with thin stripes of the second, more temperature sensitive polymer on top yields a helix capable of inverting curvature at elevated temperature due to a swelling mismatch. Varying the stripe parameters (e.g., width, spacing, direction) allows for precise control over the resulting helix geometry. When these ribbons are in high concentration and undergo shape morphing, they entangle, ultimately forming a gel-like structure. Ongoing work involves the extensive characterization of entanglement via oscillatory shear rheology and microscopy, across various temperature changes and helix geometries.