Facile Fabrication of Robust Silk Nanofibril Films via Direct Dissolution of Silk in CaCl₂–Formic Acid Solution

Abstract

In this study, we report for the first time a novel silk fibroin (SF) nanofibrous films with robust mechanical properties that was fabricated by directly dissolving silk in CaCl2-formic acid solution. CaCl2-FA dissolved silk rapidly at room temperature, and more importantly, it disintegrated silk into nanofibrils instead of separate molecules. The morphology of nanofibrils crucially depended on CaCl2 concentrations, which resulted in different aggregation nanostructure in SF films. The SF film after drawing had maximum elastic modulus, ultimate tensile strength, and strain at break reaching 4 GPa, 106 MPa, and 29%, respectively, in dry state and 206 MPa, 28 MPa, and 188%, respectively, in wet state. Moreover, multiple yielding phenomena and substantially strain-hardening behavior was also observed in the stretched films, indicating the important role played by preparation method in regulating the mechanical properties of SF films. These exceptional and unique mechanical properties were suggested to be caused by preserving silk nanofibril during dissolution and stretching to align these nanofibrils. Furthermore, the SF films exhibit excellent biocompatibility, supporting marrow stromal cells adhesion and proliferation. The film preparation was facile, and the resulting SF films manifested enhanced mechanical properties, unique nanofibrous structures, and good biocompability.

Development of regenerative and flexible fibroin‐based wound dressings

“…The tensile strength and elongation at break of GMSF films in dry and wet state were determined using standard testing machine (Zwick), equipped with a 100 N capacity load cell. The test samples (3 × 2 cm) were mounted between grips of the machine and pulled at cross head speed of 10 mm/min . Average tensile properties of five specimens were measured.…”

A novel method to prepare tussah/Bombyx mori silk fibroin-based films

“…The special nanostructure of BSF lm was studied in our previous study. 23 The BSF lm showed nanobrous structure originated from the nanobril-preservation dissolution behavior of broin in CaCl 2 /formic acid. The preserved nanobril endowed the BSF lm with exceptional mechanical properties.…”

Formic Acid

“…Formic acid can be used to dissolve polyamides (e.g., nylon 66 and nylon 46) or silk to prepare fibers and membranes [81][82][83]. It is also a useful component in semiconductor cleaning solutions [84].…”