Abstract
The molecular weight (MW) of regenerated silk fibroin (RSF) decreases during degumming and dissolving processes. Although MW and the MW distribution generally affect polymer material processability and properties, few reports have described studies examining the influences of MW and the distribution on silk fibroin (SF) material. To prepare different MW SF fractions, the appropriate conditions for fractionation of RSF by ammonium sulfate (AS) precipitation process were investigated. The MW and the distribution of each fraction were found using gel permeation chromatography (GPC) and SDS-polyacrylamide electrophoresis (SDS-PAGE). After films of the fractionated SFs formed, the secondary structure, surface properties, and cell proliferation of films were evaluated. Nanofiber nonwoven mats and 3D porous sponges were fabricated using the fractionated SF aqueous solution. Then, their structures and mechanical properties were analyzed. The results showed AS precipitation using a dialysis membrane at low temperature to be a suitable fractionation method for RSF. Moreover, MW affects the nanofiber and sponge morphology and mechanical properties, although no influence of MW was observed on the secondary structure or crystallinity of the fabricated materials.
Highlights
Because the solubility of protein generally depends on the temperature, we inferred that the different fractionation profiles based on temperature derived from the protein solubility [32]. 20SF-addition method (AM) might be difficult to precipitate at 37 ◦ C because of its higher solubility than at 4 ◦ C
Fractionation of silk fibroin (SF) from regenerated silk fibroin (RSF) aqueous solution was performed by precipitation of the ammonium sulfate (AS) solution
Amino acid analysis revealed a different composition in the lowest molecular weight (MW) fractionated
Summary
Silk has been examined for its application as a biomaterial in medicine, especially in the tissue engineering field, due to the biosafety it has exhibited during its long and extensive use for surgical sutures [1]. Silk fiber has been reported to be an excellent textile material for practical use as a surgical scaffold in regenerative medicine [2], many studies have examined the fabrication of silk proteins beyond silk fibers to include films [3], gels [4], sponges [5], and nanofibers [6] adapted for medical use. The sericin protein layer, which is regarded as triggering inflammation and foreign body reactions, has been removed before any medical application by degumming through boiling in a weak alkali solution such as Na2 CO3 [7].
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