2.5D\nHierarchical Structuring of Nanocomposite Hydrogel\nFilms Containing Cellulose Nanocrystals

Abstract

Although\ntwo-dimensional hydrogel thin films have been applied\nacross many biomedical applications, creating higher dimensionality\nstructured hydrogel interfaces would enable potentially improved and\nmore biomimetic hydrogel performance in biosensing, bioseparations,\ntissue engineering, drug delivery, and wound healing applications.\nHerein, we present a new and simple approach to control the structure\nof hydrogel thin films in 2.5D. Hybrid suspensions containing cellulose\nnanocrystals (CNCs) and aldehyde- or hydrazide-functionalized poly­(oligoethylene\nglycol methacrylate) (POEGMA) were spin-coated onto prestressed polystyrene\nsubstrates to form cross-linked hydrogel thin films. The films were\nthen structured via thermal shrinking, with control over the direction\nof shrinking leading to the formation of biaxial, uniaxial, or hierarchical\nwrinkles. Notably, POEGMA-only hydrogel thin films (without CNCs)\ndid not form uniform wrinkles due to partial dewetting from the substrate\nduring shrinking. Topographical feature sizes of CNC–POEGMA\nfilms could be tuned across 2 orders of magnitude (from ∼300\nnm to 20 μm) by varying the POEGMA concentration, the length\nof poly­(ethylene glycol) side chains in the polymer, and/or the overall\nfilm thickness. Furthermore, by employing adhesive masks during the\nspin-coating process, structured films with gradient wrinkle sizes\ncan be fabricated. This precise control over both wrinkle size and\nwrinkle topography adds a level of functionality that to date has\nbeen lacking in conventional hydrogel networks.