Shear-Thinning and Rapidly Recovering Hydrogels of Polymeric Nanofibers Formed by Supramolecular Self-Assembly

The self-assembly of amphiphilic polymers into worm-like micelles represents a versatile approach to create hydrogels, where interactions and functionalities are widely customizable by the chemistry of the hydrophilic block. However, processing options for such gels remain a bottleneck as fragmentation is often irreversible due to the limited dynamics of the assemblies. We demonstrate here that shear-thinning hydrogels can reversibly be formed by amphiphilic polymers, which assemble into supramolecular polymer nanofibers due to additional directing hydrogen bonds. The addition of bifunctional cross-linkers resulted in robust gels, which feature a surprisingly strong shear-thinning character but recover fully in the absence of shear stress despite the lack of a dynamic exchange of individual building blocks. In addition to increasing the concentration, the strength of the gel can be tuned by varying the content or the length of the bivalent cross-linker. Low viscosities under shear load and the rapid recovery (<5 s) after relief of the strain facilitates an effortless extrusion through even thin needles and subsequent formation of self-supporting structures in a printing process. The polymer covered fiber structure further bestows the gels with an excellent stability in various conditions and good biocompatibility while minimizing cell adhesion. The mesh sizes of the gel allow even large macromolecules to diffuse, but retardation is nevertheless observed for small molecules due to the dense polymer brush structure. This unique set of properties renders these polymer fiber hydrogels a versatile and easily processable scaffold for future applications, for example as an adaptable cell scaffold or injectable drug depots.

Automated summary

This study demonstrates the formation of shear-thinning hydrogels by amphiphilic polymers, which assemble into supramolecular polymer nanofibers through additional hydrogen bonds. The addition of bifunctional cross-linkers results in robust gels that exhibit strong shear-thinning behavior and can fully recover in the absence of shear stress. The low viscosity under shear load and rapid recovery make these gels suitable for easy extrusion and printing processes. Furthermore, the polymer-covered fiber structure provides excellent stability and biocompatibility to the gels.