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.