Superstrong and Tough Hydrogel through Physical Cross-Linking and Molecular Alignment.

Hydrogels are attracting increasing attention due to their potential use in various fields. However, most of the existing hydrogels have limitations in either dissipating mechanical energy or maintaining high stretchability under deformation, thus do not possess high mechanical properties. Herein, poly(vinyl alcohol) (PVA)-tannic acid (TA) hydrogels with both high mechanical strength and stretchability were obtained via a step-by-step physical cross-linking and molecular alignment method. Saline-triggered physical interactions serve as "sacrifice domains" to dissipate energy and endow PVA-based hydrogel with high mechanical strength (≈16 MPa) and stretchability (≈1000%). Due to the reversible arranging and disassociating property of physical interactions, PVA-TA hydrogels show excellent shape memory performance. We further demonstrated an effective approach to fabricate strong and aligned PVA-TA thread. The resultant well-aligned PVA-TA dry thread reveals an ultrahigh mechanical tensile strength of up to 750 MPa, nearly 45 times higher than PVA-TA thread with no alignment. Wide-angle X-ray two-dimensional diffraction images further confirmed the alignment of PVA fibers in stretching direction. In addition, we applied the PVA-TA hydrogel as suture and evaluated the cytotoxicity and biocompatibility of the PVA-TA suture.