Utilizing Frémy's Salt to Increase the Mechanical Rigidity of Supramolecular Peptide-Based Gel Networks

Abstract

Peptide-based supramolecular gels are an important class of biomaterials that can be used for biomedical applications ranging from drug delivery to tissue engineering. Methodology that allows one to readily modulate the mechanical properties of these gels will allow yet even a broader range of applications. Frémy's salt is an inorganic salt and long-lived free radical that is known to oxidize phenols. Herein, we show that Frémy's salt can be used to dramatically increase the mechanical rigidity of hydrogels formed by tyrosine-containing self-assembling β-hairpin peptides. When Frémy's salt is added to pre-formed gels, it converts tyrosine residues to o-quinones that can subsequently react with amines present within the lysine side chains of the assembled peptide. This results in the installation of chemical crosslinks that reinforce the gel matrix. We characterized the unoxidized and oxidized gel systems using UV-Vis, transmission electron microscopy and rheological measurements and show that Frémy's salt increases the gel rigidity by nearly one order of magnitude, while retaining the gel's shear-thin/recovery behavior. Thus, Frémy's salt represents an on-demand method to modulate the mechanical rigidity of peptide-based self-assembled gels.

Antibacterial Gel Coatings Inspired by the Cryptic Function of a Mussel Byssal Peptide

“…Although the positional dependence of DOPA oxidation is certainly playing a role in determining material cohesion, any positional effects of subsequent quinone crosslinking cannot be ruled out. [38,39] Lastly, the Tyr-control gels show no H 2 O 2 production as expected. Both the DOPA-and Tyr-containing hydrogels display shear-thin/recovery behavior over multiple cycles (Figure 3C), suggesting they can be delivered by syringe injection.…”

“…To test the hypothesis that lysine and DOPA (Ÿ) residues within Mfp-5 could impart antibacterial activity, we identified an amino acid sequence within the native protein that is particularly rich in these two residues. [6] We prepared the peptide fragment, denoted Mfp-5 29-47 DOPA, as well as a control peptide, Mfp-5 [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Tyr, where all of the DOPA residues were replaced by tyrosine, Figure 1C. This allows one to evaluate the effects of DOPA separate from lysine.…”

“…All of the peptides studied herein were synthesized by Fmoc-based solid phase peptide synthesis, purified by reverse phase liquid chromatography (LC), and their primary structure characterized by LC-mass spectroscopy, Figures S1-S10 (Supporting Information). Gratifyingly, Figure 1C (left panel) shows that the parent peptide can indeed produce H 2 O 2 in a manner that is dependent on peptide concentration, reaching values higher than 0.5 × 10 −3 m. In contrast, no H 2 O 2 was produced by the control Mfp-5 [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Tyr peptide indicating that DOPA is necessary for the production of the chemical oxidant. We then examined the antibacterial activity of the peptides against a clinically relevant Grampositive methicillin-resistant Staphylococcus aureus (MRSA) bacteria strain with reduced susceptibility to vancomycin [25] by broth microdilution.…”

Peptide-Based Supramolecular Hydrogels as Drug Delivery Agents: Recent Advances

“…However, for some applications in which stiffer hydrogels are required, this may not be enough. One approach to overcome this limitation was recently described by Schneider et al, who utilized Frémy’s salt to increase the stiffness of the supramolecular networks [ 72 ]. They report that the addition of Frémy’s salt to their novel gelation system resulted in the conversion of the phenol group of the tyrosine residue into a reactive o -quinone group, which readily reacts with the amine groups present on the lysine residues of the assembled peptide, and thus covalent cross-links are introduced into the system.…”

Spatiotemporally-regulated multienzymatic polymerization endows hydrogel continuous gradient and spontaneous actuation

“…In recent years, functionally gradient materials (FGMs) with gradually varied microstructure from one region to another region, have received extensive attention and are the focus of a rapidly developing research hotspot, involving the fields of engineering mechanics, tissue engineering, cell engineering, diagnostics, as well as other multidisciplinary integrations [7][8][9][10][11][12]. Hydrogels formed by three-dimensional hydrophilic polymer networks and water have the benefit of tunable mechanical performance among other cumulative properties, and have been broadly applied as intelligent soft actuators, biological scaffolds, and drug delivery system [13][14][15][16][17][18][19][20][21][22][23][24]. A combination of hydrogel and FGM, gradient hydrogels not only have the characteristics of continuous or quasi-continuous changes in molecular structure, chemical composition, and macroscopic properties, but also have good biocompatibility, high permeability to small molecules, and smart responsiveness, thus, gradient hydrogels have the potential to be used as cellular substrates and biological scaffold [25][26][27][28].…”