Effect of regeneration of liquid silk fibroin on its structure and characterization

Abstract

Silk derived from cocoons of the female silkworm (Bombyx mori) was made into three kinds of test material, degummed fiber, liquid fibroin and regenerated silk fibroin membrane (RSFM). The effect of the silk degumming and fiber dissolution system (SD-FDS) on the molecular structure and properties of silk fibroin were studied in detail. Degumming with Na 2 CO 3 solution had the greatest impact on silk fibroin fiber, resulting in significant reduction of the thermal stability and crystallinity, and the fiber tensile property was only half of that degummed with urea buffer. The moderate degumming solution was urea buffer, followed by strongly alkaline electrolyzed water (SAEW). SDS-PAGE showed that the silk fibroin degummed with 8.0 M urea at 80 C and dissolved in 9.3 M LiBr at 25 C was similar to the natural silk fibroin in vivo, but boiling in Na 2 CO 3 solution leads to serious breakage of the silk fibroin peptide chain. The degree of breakage of the peptide chain is positively correlated with the storage time of liquid silk fibroin. DSC showed the more nearly intact the silk fibroin peptide chain, the higher the thermal decomposition temperature. The regenerated condition of the silk protein is often overlooked during the research process, while our study showed that different silk degumming and fiber dissolution systems will have different influences. The results of this test help us gain a deeper understanding of the effect of silk degumming and fiber dissolution on the molecular structure and properties of silk fibroin and provide important experimental data for screening and using silk protein as advanced functional biomaterials, such as medical tissue engineering materials.

Processing of silk biomaterials

“…Similar with degumming, studies have reported that differences in the molecular weight of regenerated SF also correlates with the extent of protein degradation induced by various factors of the dissolving process, thus contributing to changes in performance of SF-based materials (Yamada et al, 2001;Wang et al, 2011Wang and Zhang, 2013;You et al, 2013). Wang and coworkers studied the effects of fiber dissolution on the molecular chain of SF when using different inorganic solvent systems including LiBr, and CaCl 2 -EtOH .…”

“…A study by Wang et al reported that the thermal and mechanical properties of SF protein were least affected when using 8.0 M urea as the degumming reagent. SF prepared with this degumming procedure showed the least amount of fracturing in the silk peptide chain, yielding the most intact silk protein similar to natural SF found in vivo in the silk glands of the silkworm (Wang and Zhang, 2013).…”

“…Dissolution methods used for solubilizing the degummed SF fibers generally rely on strong chaotropic agents, including concentrated acids, inorganic salts, fluorinated organic solvents, and ionic liquids, to neutralize the hydrogen bonds stabilizing the silk crystal structure (Yamada et al, 2001;Wang et al, 2011Wang and Zhang, 2013;You et al, 2013). Consequently, the conditions of the dissolution process can influence the chemical composition and the molecular structure of the silk protein, affecting its biomaterial properties.…”

Physico-chemical and biological studies on three-dimensional porous silk/spray-dried mesoporous bioactive glass scaffolds

“…The dried fibroin was dissolved with 9.3 M lithium bromide solution at 70°C for 4 h. The viscous sol obtained after dissolution was dialyzed against deionized water for 48 h to remove the salts. 0.5 mL of the obtained regenerated silk fibroin (RSF) solution was placed in a weighing boat and allowed to dry overnight under hood at room temperature to estimate the concentration of the solution, and, if needed, adjusted to be 6% (w/v) by diluting with deionized water [33].…”

CO2-assisted synthesis of silk fibroin hydrogels and aerogels

“…Sericin coats SF chains and the sericin must be removed in a ''degumming'' step-although SF chains can be degraded during this step as a result of the strength of the degumming reagent and degumming time and temperature [23][24][25][26]. The resultant SF molecular weight has a significant effect on the gelation kinetics since the formation of a polymer gel is related to the degree of polymer chain overlap in solution.…”