Mechanistic Insights into Hyaluronic Acid Induced Peptide Nanofiber Organization in Supramolecular Hydrogels.

Composite hydrogels composed of low-molecular-weight peptide self-assemblies and polysaccharides are gaining great interest as new types of biomaterials. Interactions between polysaccharides and peptide self-assemblies are well reported, but a molecular picture of their impact on the resulting material is still missing. Using the phosphorylated tripeptide precursor Fmoc-FFpY (Fmoc, fluorenylmethyloxycarbonyl; F, phenylalanine; Y, tyrosine; p, phosphate group), we investigated how hyaluronic acid (HA) influences the enzyme-assisted self-assembly of Fmoc-FFY generated in situ in the presence of alkaline phosphatase (AP). In the absence of HA, Fmoc-FFY peptides are known to self-assemble in nanometer thick and micrometer long fibers. The presence of HA leads to the spontaneous formation of bundles of several micrometers thickness. Using fluorescence recovery after photobleaching (FRAP), we find that in the bundles both (i) HA colocalizes with the peptide self-assemblies and (ii) its presence in the bundles is highly dynamic. The attractive interaction between negatively charged peptide fibers and negatively charged HA chains is explained through molecular dynamic simulations that show the existence of hydrogen bonds. Whereas the Fmoc-FFY peptide self-assembly itself is not affected by the presence of HA, this polysaccharide organizes the peptide nanofibers in a nematic phase visible by small-angle X-ray scattering (SAXS). The mean distance d between the nanofibers decreases by increasing the HA concentration c, but remains always larger than the diameter of the peptide nanofibers, indicating that they do not interact directly with each other. At a high enough HA concentration, the nematic organization transforms into an ordered 2D hexagonal columnar phase with a nanofiber distance d of 117 Å. Depletion interaction generated by the polysaccharides can explain the experimental power law variation d∼c-1/4 and is responsible for the bundle formation and organization. Such behavior is thus suggested for the first time on nano-objects using polymers partially adsorbing on self-assembled peptide nanofibers.

Localized Enzyme-Assisted Self-Assembly in the Presence of Hyaluronic Acid for Hybrid Supramolecular Hydrogel Coating.

Hydrogel coating is highly suitable in biomaterial design. It provides biocompatibility and avoids protein adsorption leading to inflammation and rejection of implants. Moreover, hydrogels can be loaded with biologically active compounds. In this field, hyaluronic acid has been largely studied as an additional component since this polysaccharide is naturally present in extracellular matrix. Strategies to direct hydrogelation processes exclusively from the surface using a fully biocompatible approach are rare. Herein we have applied the concept of localized enzyme-assisted self-assembly to direct supramolecular hydrogels in the presence of HA. Based on electronic and fluorescent confocal microscopy, rheological measurements and cell culture investigations, this work highlights the following aspects: (i) the possibility to control the thickness of peptide-based hydrogels at the micrometer scale (18-41 µm) through the proportion of HA (2, 5 or 10 mg/mL); (ii) the structure of the self-assembled peptide nanofibrous network is affected by the growing amount of HA which induces the collapse of nanofibers leading to large assembled microstructures underpinning the supramolecular hydrogel matrix; (iii) this changing internal architecture induces a decrease of the elastic modulus from 2 to 0.2 kPa when concentration of HA is increasing; (iv) concomitantly, the presence of HA in supramolecular hydrogel coatings is suitable for cell viability and adhesion of NIH 3T3 fibroblasts.