Hierarchical networks of anisotropic hydrogels based on cross-linked Poly(vinyl alcohol)/Poly(vinylpyrrolidone)

Construction of hierarchical networks of anisotropic hydrogels has attracted much attention recently. We developed a simple strategy to fabricate anisotropic hydrogels with rich structural hierarchy and tunable mechanical properties by using the minor polymer as the performance and network regulators in this work. Poly(vinyl alcohol) (PVA)/poly(vinylpyrrolidone) (PVP) solution was used as precursor to build networks across multiple length scales via the directional freezing/salting-out treatments. The presence of PVP, as minor component, promoted the formation of the bridging fibers across the oriented channel-like pores. Thus, as-prepared two-component anisotropic hydrogels revealed superior mechanical strengths as compared to the two-component isotropic hydrogels or the single-component anisotropic ones. On the other hand, the formation of this dendritic structure improved the strength perpendicular to aligned direction, and therefore, the PVA/PVP anisotropic hydrogels possessed more balanced mechanical performance. In brief, PVP acted as the roles of network and performance regulators in this kind of anisotropic hydrogels. This work provides an interesting way to regulate morphology and overall properties of the PVA based anisotropic hydrogels.