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

Abstract

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.

Rationalizing the Extent of the “Sergeants‐and‐Soldiers” Effect in Supramolecular Helical Catalysts: Effect of Copper Coordination

“…These crosslinks are dynamic by essence and are found to be eliminated when a sufficient amount of “sergeant” is present in the helices. Our work demonstrates that copper or other metal binding groups can be envisaged to introduce dynamic crosslinks in supramolecular materials, thus constituting an alternative strategy to difunctionalized linkers reported to date [80–82] . Not only main chain but also side chain aggregation of supramolecular helices must be considered for the design of elaborated chiral materials.…”

“…Our work demonstrates that copper or other metal binding groups can be envisaged to introduce dynamic crosslinks in supramolecular materials, thus constituting an alternative strategy to difunctionalized linkers reported to date. [80][81][82] Not only main chain but also side chain aggregation of supramolecular helices must be considered for the design of elaborated chiral materials. Improving the extent of the "sergeants-and-soldiers" effect in catalytic BTAs by tuning the aggregation of the supramolecular chains is currently under investigation in our laboratory.…”

Advanced supramolecular design for direct ink writing of soft materials

“…Supramolecularly designed inks for DIW started to attract more awareness in chemistry, materials science, and engineering communities due to their highly dynamic and reversible features. 20,69 3D-printed soft materials with self-healing properties, 59,166,167,192 enhanced mechanical strength, 163,193,194 multiple-stimuli responsiveness, 74,78,144,193 and complex shape-morphing capabilities 203,205,209 have been demonstrated and discussed in this review. These exciting features come from the functional motifs that are hydrogen bonded, 253 host–guest bound, 118 metal–ligand coordinated, 131 or assembled via van der Waals forces.…”

“…12(e)) to construct a supramolecularly crosslinked hydrogel. 167 BTU-PEG 2k -OMe monomers self-assembled to form a weak hydrogel with an elastic modulus of ∼10 Pa. In the presence of the BTU 2 -PEG crosslinker ([monomer]/[crosslinker] = 100), a supramolecularly crosslinked hydrogel was formed ( G ′ ∼ 100 Pa).…”

Trendbericht: Makromolekulare Chemie 2023

“…So entwickelten Brendel, Catrouillet und Mitarbeitende ein strukturviskoses Hydrogel, das sich durch die supramolekulare Selbstassemblierung von Nanofasern bildet. 51) Ganz andere Zell-Material-Interaktionen zeigte das Material von Rodriguez-Emmenegger und Team: ionische Combisome, die sowohl mit Liposomen als auch mit lebenden Bakterien fusionieren. 52) Die relative Häufigkeit von Beiträgen aus der makromolekularen Chemie in der Biomedizin zeigt, wie bedeutend und beliebt dieses Forschungsfeld ist.…”