Structural Transformation and Physical Properties of a Hydrogel-Forming Peptide Studied by NMR,Transmission Electron Microscopy,and Dynamic Rheometer

Peptide-based hydrogels are attractive biological materials. Study of their self-assembly pathways from their monomer structures is important not only for undertaking the rational design of peptide-based materials, but also for understanding their biological functions and the mechanism of many human diseases relative to protein aggregation. In this work, we have monitored the conformation, morphological, and mechanical properties of a hydrogel-forming peptide during hydrogelation in different dimethylsulfoxide (DMSO)/H₂O solutions. The peptide shows nanofiber morphologies in DMSO/H₂O solution with a ratio lower than 4:1. Increased water percentage in the solution enhanced the hydrogelation rate and gel strength. One-dimensional and two-dimensional proton NMR and electron microscopy studies performed on the peptide in DMSO/H₂O solution with different ratios indicate that the peptide monomer tends to adopt a more helical structure during the hydrogelation as the DMSO/H₂O ratio is reduced. Interestingly, at the same DMSO/H₂O ratio, adding Ca²⁺ not only promotes peptide hydrogelation and gel strength, but also leads to special shear-thinning and recovery properties of the hydrogel. Without changing the peptide conformation, Ca²⁺ binds to the charged Asp residues and induces the change of interfiber interactions that play an important role in hydrogel properties.