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 similar to 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.