Characterization of Ground Silk Fibroin through Comparison of Nanofibroin and Higher Order Structures

Abstract

Silk fibroin, a biodegradable component of silk, is increasingly used for various applications and studied intensively. Recently, a technique for preparing nanofibers without using chemicals has been gaining attention from the environmental impact and safety perspectives. This study focuses on the structure observation of ground silk fibroin (GF) prepared using a grinding method, which is a physical nanofibrillation method. The fabricated nanofiber samples were examined in detail using the X-ray diffraction (XRD), differential scanning calorimetry (DSC), micro Raman spectroscopy, and atomic force microscopy (AFM) techniques. The nanofibrillated structures were observed in both GF and regenerated silk fibroin (RF) samples prepared using the conventional method. As results, AFM images showed that the nanofibril diameter of GF was about 1.64 nm and that of RF was about 0.32 nm. Methanol treatment induced a structural transition from a random coil to a β-sheet for the RF film, but it had no effect on the GF film. Thus, it is suggested that the grinding method provides not only ultrafine silk fibroin nanofibers without using toxic reagents but also resistance to reagents such as methanol.

Robust Nanofiber Mats Exfoliated From Tussah Silk for Potential Biomedical Applications

“…The XRD patterns of TSF nanofiber mats showed diffraction peaks around 16.8°(0.53 nm), 20.3°(0.44 nm), and 24.1°(0.37 nm) assigned to β-sheet structure, confirming the similar result to the FTIR analysis ( Fu et al, 2011 ). It is consistent with previous studies that the physical shearing breaks only the weak interfaces between nanofibers in silk but does not destroy the strong β-sheet crystal structure in nanofibers ( Okahisa et al, 2019 ; Wang et al, 2020a ; Narita et al, 2020 ). So, the secondary structure of silk fibroin can be well retained by this moderate approach.…”

Silk Powder from Cocoons and Woven Fabric as a Potential Bio-Modifier

“…However, the presence of the bands corresponding to β-sheets of amide I and amine III indicate the crystalized regions of fibroin regardless to milling process. The bands at 3062, 2935, and 2876 cm −1 related, respectively, to C-N-H bending, CH 3 asymmetric stretching, and CH 3 asymmetric stretching visible in all Raman spectra demonstrate that fibroin structure were well preserved [17].…”

“…The peak at 1660 cm −1 related to the amide I of β-sheets C=O stretching [16] is present in all spectra at comparable intensity and the same value of Raman shift. β-sheets structure of amine III is also visible for all samples as the bands at 1221 and 1256 cm −1 [17]. The intensity of the band at 1221 cm −1 decreased for the powders, especially for raw and degummed cocoons, in comparison to 1256 cm −1 band related to disordered form of β-sheets amide III.…”

Toughening Wet‐Spun Silk Fibers by Silk Nanofiber Templating

“…Silk nanomaterials including SNs can be prepared using either top-down deconstruction or bottom-up regeneration. Topdown SNs can be exfoliated directly from B. mori silk without destroying the fibroin crystalline structure within the nanofibril using a range of physical (e.g., by ultrasonication, [23] milling, [24] stone grinding, [25] and homogenizating [26] ) or chemical fibrillation strategies. [27,28] Using mechanical fibrillation, various allsilk pseudocomposites have been reported, including porous scaffolds made from HFIP-based regenerated silk solution reinforced with spherical silk microparticles (1-10 μm).…”