Formic Acid Regenerated Mori, Tussah, Eri, Thai, and Muga Silk Materials: Mechanism of Self-Assembly

Abstract

Flexible and water-insoluble regenerated silk materials have caught considerable interest due to their mechanical properties and numerous potential applications in medical fields. In this study, regenerated Mori (China), Thai, Eri, Muga, and Tussah silk films were prepared by a formic acid-calcium chloride (FA) method, and their structures, morphologies, and other physical properties were comparatively studied through Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray scattering (WAXS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). FTIR results demonstrated that the secondary structures of those five types of silk films are different from those of their respective natural silk fibers, whose structures are dominated by stacked rigid intermolecular β-sheet crystals. Instead, intramolecular β-sheet structures were found to dominate these silk films made by FA method, as confirmed by WAXS. We propose that silk I-like structures with intramolecular β-sheets lead to water insolubility and mechanical flexibility. This comparative study offers a new pathway to understanding the tunable properties of silk-based biomaterials.

Influence of the Casting Concentration on the Mechanical and Optical Properties of FA/CaCl2-Derived Silk Fibroin Membranes

“…et al and Zhang et al [33,37]. While all these works have a similar sequence of process steps, they focus on different aspects of the FA/CaC2 manufacturing chain [33][34][35][36][37]…”

“…The aim of this study was to evaluate the production processes and the resulting properties of casted silk fibroin membranes fabricated via formic acid (FA) and calcium chloride (CaCl 2 ) dissolution. In recent years there have been several works that have established this novel dissolving process using FA/CaCl 2 as an integral part of the regeneration process of silk fibroin [33][34][35][36][37]. Though this technique has recently evolved and is now recognized as a fast and cheap manufacturing method, it has scarcely been investigated so far.…”

Comparative Study of Silk-Based Magnetic Materials: Effect of Magnetic Particle Types on the Protein Structure and Biomaterial Properties

“…Mori silk cocoons were purchased from Treenway Silks (Lakewood, CO, USA). To remove the sericin coatings, silk cocoons were first degummed as reported previously [ 10 ]. An amount of 10 g of silk cocoons was added to 3 L boiling DI water with 6.36 g of NaHCO 3 (Sigma-Aldrich, St. Louis, MO, USA).…”

“…Silk fibroin protein materials have shown excellent tensile strength, flexibility and biocompatibility [ 10 , 11 , 12 ]. Natural silk fibers are composed of sericin coating and silk fibroin proteins.…”

“…For instance, the mechanical properties of silk fiber can be enhanced by a high content of β-sheet crystals [ 19 , 20 ]. The highly crosslinked silk fibril network structure through β-sheet crystals is believed to also cause the insolubility of the regenerated silk materials in water and many mild organic solvents [ 10 , 21 ]. Different types of silk materials, such as silk films, gels, particles and fibers, have shown great potential in biomedical applications [ 22 , 23 , 24 , 25 ], and by manipulating their secondary structure, one can control the release time and dose during targeted drug delivery [ 18 , 26 ].…”