Cooperative Assembly of a Peptide Gelator and Silk Fibroin Afford an Injectable Hydrogel for Tissue Engineering

Silk fibroin (SF) from Bombyx mori has received increasing interest in biomedical fields, because of its slow biodegradability, good biocompatibility, and low immunogenicity. Although SF-based hydrogels have been studied intensively as a potential matrix for tissue engineering, weak gelation performance and low mechanical strength are major limitations that hamper their widespread applicability. Therefore, searching for new strategies to improve the SF gelation property is highly desirable in tissue engineering research. Herein, we report a facile approach to induce rapid gelation of SF by a small peptide gelator (e.g., NapFF). Following the simple mixing of SF and NapFF in water, a stable hydrogel of SF was obtained in a short time period at physiological pH, and the minimum gelation concentration of SF can reach as low as 0.1%. In this process of gelation, NapFF not only can behave itself as a gelator for supramolecular self-assembly, but also can trigger the conformational transition of the SF molecule from random coil to beta-sheet structure via hydrophobic and hydrogen-bonding interactions. More importantly, for the generation of a scaffold with favorable cell-surface interactions, a new peptide gelator (NapFFRGD) with Arg-Gly-Asp (RGD) domain was applied to functionalize SF hydrogel with improved bioactivity for cell adhesion and growth. Following encapsulating the vascular endothelial growth factor (VEGF), the SF gel was subcutaneously injected in mice, and served as an effective matrix to trigger the generation of new blood capillaries in vivo.