Effects of Silk Degumming Process on Physicochemical, Tensile, and Optical Properties of Regenerated Silk Fibroin

Abstract

Sericin removal from silk (degumming) affects material characteristics of silk fibroin (SF). Sodium carbonate is most commonly used for degumming, but numerous alternative methods are available. Herein, a systematic comparison of degumming methods is provided. Sodium carbonate, sodium oleate, trypsin, and ionic liquid are used, and materials are characterized regarding mass loss, SF content, molecular integrity of SF, refractive index, and tensile properties. Complete degumming is achieved within 30 min of using sodium carbonate, but results in significant reduction of molecular weight, shift toward less acidic charge variants, and reduction of yield‐ and rupture force. Sodium oleate and trypsin are inefficient and negatively affect tensile properties, while ionic liquid shows good efficiency and marginal degradation of SF but also reduced yield‐ and rupture force. Refractive index is not affected by degumming. These results allow rational selection of the degumming method and tuning of SF properties for biomedical applications.

Revealing the Influence of the Degumming Process in the Properties of Silk Fibroin Nanoparticles

“…D4 method yielded the minor loss of mass, with only 25.9%. Assuming that only 25-30% of the total weight in the cocoons corresponds to the SS fraction [13,52,53], we can infer that not only sericin but also fibroin have been lost in the D3 treatment, due of the harsh conditions for the fibers, a phenomenon previously described [24].…”

“…Although the degumming using sodium carbonate solution for 30 min has been stated among the studied alternatives as the best degumming process for the production of silk fibroin implantable biomaterials [24], allowing to retain SF integrity and achieve complete sericin removal, for the preparation of nanodrug delivery systems, the harsh treatment D3 is the most effective degumming process, not only because of the size and Z-potential, but also because of the increasing of carboxylate groups in SFN-D3, which improves availability of reactive sites on the particle surface. These carboxylate groups can be easily functionalized by means of carbodiimide coupling [70], providing a more favorable surface as nano carrier-based drug delivery system.…”

“…The obtained SF was dried for 24 h in a fume hood until constant weight. The mass loss after the different degumming methods was calculated, following the method previously described expressed in the equation 1, where m before degumming and m after degumming are the dry mass before and after degumming, respectively [24].…”

High Molecular Weight Silk Fibroin Prepared by Papain Degumming

“…Additionally, sericin serves as an adhesive that hinders slippage between filaments and reinforces the fiber strength [ 23 ]. When Na 2 CO 3 is used as a degumming agent, the temperature of the Na 2 CO 3 solution has a great influence on the strength of the silk fiber after degumming [ 19 , 52 , 53 ]. In this study, the silk fibers were degummed with a boiled Na 2 CO 3 aqueous solution.…”

“…The preferred commercially available degumming agents are based on Na 2 CO 3 and Marseille soap because they have a high degumming efficiency and simple operation [ 18 ]. Sericin can be completely removed from silk when boiled in 0.02 M Na 2 CO 3 for 60 min, but the breaking strength of the resulting silk fibers is significantly reduced by approximately 56% [ 19 ]. When boiled three times in 0.5 g/L Na 2 CO 3 for 30 min and subsequently dissolved in LiBr aqueous solution, the MW of regenerated SF is mainly distributed below 100 kDa [ 18 ], which is far lower than the MW of native SF.…”