Self-Assembled Polyvinyl Alcohol–Tannic Acid Hydrogels with Diverse Microstructures and Good Mechanical Properties

Fabrication of hydrogels with unique microstructures and better mechanical properties through the self-assembly of commercially available synthetic polymers and small molecules is of great scientific and practical importance. A type of physical hydrogels is prepared by the self-assembly of polyvinyl alcohol (PVA) and tannic acid (TA) in aqueous solution with a low PVA-TA concentration (0.5-6.0 wt %) at room temperature. With the increase of the PVA-TA concentration, the water content of the hydrogels increases, and the content of TA in the hydrogels decreases from 23.1 to 6.4%. The driving force for the self-assembly is proven to be the hydrogen bonding between PVA and TA, which also induces the crystallization of PVA chains. The self-assembled PVA-TA hydrogels have diverse morphologies that change from microspheres to oriented porous structures with the increase of the PVA-TA concentration, and these structures are all composed of nanosized particles, fibers, and/or sheets. Most of the self-assembled PVA-TA hydrogels show good mechanical properties. The highest tensile strength and elastic modulus of the PVA-TA hydrogel prepared with 1.0 wt % PVA-TA concentration are about 84 and 30 kPa, respectively. This self-assembly method would lead to the fabrication of more hydrogels with unique microstructures and properties for practical applications.