Fibrillar Network Dynamics during Oscillatory Rheology of Supramolecular Gels

Abstract

Supramolecular gels are three-dimensional network structures formed by the hierarchical self-assembly of small molecules through weak noncovalent interactions. On the basis of the various interactions contributed by specific functional groups/moieties, gels with different architectures can be constructed that are smart to the external stimuli such as pH, type of solvent, stress, temperature, etc. In the present work, we explore the oscillatory shear response of supramolecular selfassembled systems formed by the low-molecular-weight (LMW) gelator based on difunctionalized amino acid, florenylmethoxycarbonyl (Fmoc)lysine(Fmoc), Fm−K(Fm) in aqueous buffer solution, at two different pH (6 and 7.4). Small amplitude oscillatory shear (SAOS) reported weak frequency dependence of moduli indicating a gel-like network structure. Large amplitude oscillatory shear (LAOS) indicated flow regimes dictated by yielding and subsequent network dynamics analogous to cagelike soft glassy events reported for colloidal systems. The three interval thixotropy test (3iTT) indicated recovery of moduli due to regelation contributed by the reversible interactions. A generalized network model framework is utilized to investigate the transient network characteristics of the Fm−K(Fm) gels. The "network creation" and "network loss" rates were chosen as exponential functions of scaled shear stress (= t G ( ) 12 τ ) to effectively describe the complex response. On the basis of the insights, possible mechanisms to explain the differences/similarities in the response at different pH are speculated. It is further illustrated that the modeling strategy can be extended to supramolecular gels of different classes because of the commonality/universality of their response features under oscillatory shear.

Self-Assembly, Bioactivity, and Nanomaterials Applications of Peptide Conjugates with Bulky Aromatic Terminal Groups

“…The distinct self-assembled structures were ascribed to conformational differences, as revealed by spectroscopic probes of secondary structure and X-ray diffraction . In related work, Fmoc-K­(Fmoc) has been shown to form fibrillar gels in aqueous buffer solutions with distinct pH-dependent rheological properties . Fmoc-K­(Fmoc)­D, another conjugate with a double branched Fmoc structure, forms hydrogels with a very low critical gel concentration .…”

“… 77 In related work, Fmoc-K(Fmoc) has been shown to form fibrillar gels in aqueous buffer solutions with distinct pH-dependent rheological properties. 78 Fmoc-K(Fmoc)D, another conjugate with a double branched Fmoc structure, forms hydrogels with a very low critical gel concentration. 79 The hydrogels are suitable for 2D or 3D cell culturing and hybrid gels of this conjugate with polyaniline (prepared by oxidative polymerization in situ) show metal-like electrical conductivity as well as DNA binding ability.…”

YAFAF-Based Hydrogel: Characterization, Mechanism, and Factors Influencing Micro-organization

“…At a peptide concentration of 0.5 mg/mL, the sample was a clear liquid, while “snow flake”-shaped self-assemblies were observed in the solvents, as shown in Figure b. The value of the storage modulus ( G ′) of samples at a concentration of 0.1 and 0.5 mg/mL was less than that of the loss modulus ( G ″), as shown in Figure a, indicating that the sol–gel transition had not even occurred . When the concentration of the peptide exceeded 1 mg/mL, the self-assemblies organized into fibers and bands and cross-linking occurred.…”

“…The value of the storage modulus (G′) of samples at a concentration of 0.1 and 0.5 mg/ mL was less than that of the loss modulus (G″), as shown in Figure 7a, indicating that the sol−gel transition had not even occurred. 52 When the concentration of the peptide exceeded 1 mg/mL, the self-assemblies organized into fibers and bands and cross-linking occurred. With further increases of the peptide concentration, the self-assemblies formed 3D networks, as shown in panels c−g of Figure 7.…”

Short Peptide-Based Smart Thixotropic Hydrogels

“…In advanced studies, Shanmugam’s group already established that the presence of an additional Fmoc group (AA11) to prepare the hydrogelator of twin Fmoc-capped L-Lys induced thixotropicity in the hydrogel [ 9 ]. Later, in 2020, Deshpande’s group, in collaboration with Shanmugam’s group, reported the same Fmoc-functionalized L-Lys, which forms a supramolecular gel at pH 6 and 7.4 with a three-dimensional fibrillar network ( Figure 2 I) [ 69 ]. The gels are thixotropic in nature and exhibited a slow improvement in recovery percentage from 73.9 to 76.5, while the deformation percentage decreased from 26.1 to 23.6 ( Figure 2 J, Table 1 ).…”