Effect of C‑Terminal Residue on the Phase Behavior and Properties of β‑Sheet Forming Self-Assembling Peptide Hydrogels

This study investigates how hydrophobic and hydrophilic modifications at the C-terminus of the base peptide, KFEFEFKFK (KbpK), affect the hydrogel macroscopic properties. By the incorporation of phenylalanine (F, hydrophobic) and lysine (K, hydrophilic) residues, four variants, KbpK-K, KbpK-F, KbpK-KF, and KbpK-FK, were designed and evaluated. pH–concentration phase diagrams and Fourier transform infrared confirmed clear links showing how peptide hydrophobicity and charge influence β-sheet formation and macroscopic phase behavior. Hydrophobic modifications enhanced β-sheet formation, promoting denser fiber networks and stable gelation across a broad pH range, while hydrophilic modification reduced lateral association and gelation strength. Transmission electron microscopy and small-angle X-ray scattering revealed consistent fiber diameters and confirmed stronger self-assembly with increasing hydrophobicity. Rheological analysis showed that all samples exhibit viscoelastic, shear-thinning behavior with higher storage moduli observed for more hydrophobic peptides. These findings demonstrate how subtle peptide modifications modulate fiber assembly, network architecture, and hydrogel mechanics, enabling the design of tunable, injectable peptide-based hydrogels for biomedical applications.