A spatiotemporal controllable crosslinking route for preparing tough tissue-like anisotropic PVA hydrogel

Highly ordered and multi-layered assembly structures endow biological tissues with excellent and unique mechanical properties. Up to now, it is difficult to prepare artificial materials with the tissue-like structures through the traditional gelation routes for the lack of a spatiotemporal controllable cross-linking strategy. Here we propose a dynamic borate ester bonds assisted method to realize the spatiotemporal controllable cross-linking of PVA hydrogel, which make it feasible to prepare biomimetic anisotropic PVA hydrogel architectures. In this work, the directional alignment and re-crosslinking of the polymer chains can be performed as needed. The fracture strength of the obtained anisotropic hydrogel can reach ∼8.0 MPa, which is about 34 and 12 times that of the hydrogels obtained by freezing-thawing and salting-out respectively. Highly ordered structure and good anti-swelling of the hydrogels obtained by this method are determined by Polarizing microscope, X-ray diffraction and Scanning electron microscope. Various tissue-like hydrogels with hierarchical uniaxial or multi-layered assembly are prepared with this method. This study provides a facile, friendly and spatiotemporal controllable route to prepare tough biomimetic hydrogel architectures, which have potential application in biomedical engineering or soft machines.