ABSTRACT
Hyaluronic acid (HA) is a naturally occurring polysaccharide that is commonly used in cosmetic, wound healing, and tissue regeneration applications because of its biocompatibility and intrinsic biological activities. However, the rheological behavior of unmodified HA is not ideal for many of these. In particular, whereas chain entanglements result in an increase in viscosity, they do not prevent flow from delivery sites under zero-shear conditions. It would be of significant benefit if strategies could be developed in which robust but reversible cross-links could be incorporated within the material to allow the formation of a gel under static conditions. In developing a modification strategy, the extent of functionalization should be low to preserve the biological activities of HA. Therefore, this study focused on attaching peptides that self-assemble into ß-sheets to HA to modify the viscosity at low shear rates. It was found that the peptide sequence (LS)(4) forms ß-sheets in aqueous media and when reacted with HA using EDC/HOBt coupling to give 6.0 ± 1.5% modification the peptide-modified HA exhibits significant increases in low-shear viscosities in comparison with the unmodified HA. However, this increase in viscosity was observed only at lower polymer concentrations and at low shear rates, suggesting that network formation is sensitive to external forces and may change at high concentrations. At higher shear rates and at higher polymer concentrations the viscosity profile of the modified HA matches that of the unmodified HA, indicating that the peptide interactions were disrupted or ineffective under these conditions. The rheology of the peptide-modified HA was also compared with samples of HA reacted with the same molar ratio of aniline, but we found that the aniline-modified HA displayed behavior comparable to that of the unmodified HA, which demonstrates that the ß-sheet peptide modification technique is superior to the technique used in commercial products, such as Hyaff, at low degrees of functionalization.
