A shear-induced network of aligned wormlike micelles in a sugar-based molecular gel. From gelation to biocompatibility assays

Abstract

A new low molecular weight hydrogelator with a saccharide (lactobionic) polar head linked by azide-alkyne click chemistry was prepared in three steps. It was obtained in high purity without chromatography, by phase separation and ultrafiltration of the aqueous gel. Gelation was not obtained reproducibly by conventional heating-cooling cycles and instead was obtained by shearing the aqueous solutions, from 2 wt% to 0.25 wt%. This method of preparation favored the formation of a quite unusual network of interconnected large but thin 2D-sheets (7nm-thick) formed by the association side-by-side of long and aligned 7nm diameter wormlike micelles. It was responsible for the reproducible gelation at the macroscopic scale. A second network made of helical fibres with a 10-13nm diameter, more or less intertwined was also formed but was scarcely able to sustain a macroscopic gel on its own. The gels were analysed by TEM (Transmission Electronic Microscopy), cryo-TEM and SAXS (Small Angle X-ray Scattering). Molecular modelling was also used to highlight the possible conformations the hydrogelator can take. The gels displayed a weak and reversible transition near 20°C, close to room temperature, ascribed to the wormlike micelles 2D-sheets network. Heating over 30°C led to the loss of the gel macroscopic integrity, but gel fragments were still observed in suspension. A second transition near 50°C, ascribed to the network of helical fibres, finally dissolved completely these fragments. The gels showed thixotropic behaviour, recovering slowly their initial elastic modulus, in few hours, after injection through a needle. Stable gels were tested as scaffold for neural cell line culture, showing a reduced biocompatibility. This new gelator is a clear illustration of how controlling the pathway was critical for gel formation and how a new kind of self-assembly was obtained by shearing.

Wet spinning and radial self-assembly of a carbohydrate low molecular weight gelator into well organized hydrogel filaments

“…Applying well-controlled external triggers should bring interesting self-assembling effects and may result in new kinds of self-assembled materials with more controlled properties. Some studies described the use of shear stress, 26,[29][30][31][32][33] controlled reagent exchanges in microfluidic devices, [34][35][36][37][38] electrical 39 or magnetic fields, 40,41 surface effects [42][43][44] or ice growth 45 to control self-assembly. While microfluidics is often used to control the self-assembly of micelles, particles, liquid crystals and some polymers, 46,47 it is scarcely the case for molecular gels.…”

Advanced Methods for the Characterization of Supramolecular Hydrogels

“…TEM and the cryo-EM techniques gave size and shape details about the hydrogel that could be related to a gelation mechanism, which varied with concentration and preparation method, with visual differences between images from each microscopy technique (Figure 6). For example, for the 2 wt% hydrogel, which was prepared via shearing, big flexible sheets and twisted helical fibers were observed; both of these structures also had fibrous substructures, with the TEM, cryo-TEM, and cryo-SEM technologies providing information regarding spacing and fiber lengths to the nm [18].…”

“…While we sometimes rely on studies with a broader focus to be able to explain the techniques, in each section we include examples of how these methods have been used with supramolecular hydrogels to specifically illustrate the relevant information that can be obtained from this characterization. [14] with permission, ©2019-Royal Society of Chemistry; (b) from [15] under the terms of a CC-BY license, ©2014-American Chemical Society; (c) from [16] under the terms of the Creative Commons Attribution License, ©2014-the authors and published by Beilstein-Institut; (d) from [17] with permission, ©2019-Royal Society of Chemistry; (e) from [18] with permission, ©2017-Elsevier; and (f) from (i) [19] under the terms of a CC-BY license, ©2020-American Chemical Society and (ii) [20] under the terms of the Creative Commons Attribution License, ©2007-the authors and published by PLoS ONE.…”

Carbohydrate Derived Organogelators and the Corresponding Functional Gels Developed in Recent Time

“…Incorporation of a rigid triazole moiety as a spacer through the Cu(I) catalyzed click reaction has also been created for synthesizing a new compound ( 21 , Figure 16), derived from the lactobionic acid amide, as polar head group, which gave a shear-induced thixotropic gel [80]. Of these, the hydrogel exhibited interesting behavior due to the polymorphism with respect to the gelator concentration.…”