A Comparative Study on the Dissolution of Argema mimosae Silk Fibroin and Fabrication of Films and Nanofibers

Abstract

Limited studies have been done on silk fibroins of wild silkworm species owing to their relative insolubility in many solvents. In this study, the solubility of Argema mimosae wild silk fibroin in different salts (LiBr, LiCl, Ca(NO3)2, and CaCl2) dissolved in formic acid under varying temperatures was investigated. The dissolution conditions under which the solubility was optimum were optimized using a central composite design approach. The optimum range for solvation of the fibroin were visualized using contour plots. The influence of temperature and salt concentration were found to significantly influence the solvation of the fibroin. Following the successful dissolution of the fibroin, the regenerated silk fibroin solutions were cast to obtain water insoluble films which were used in investigating optimum electrospinning conditions. Average nanofiber diameters in the 110–141 nm range were obtained under optimum electrospinning conditions. The silk forms were characterized using the FTIR, TGA, XRD, and SEM to understand their properties. The investigations revealed that formic acid—salt solvents were effective in the solvation of the wild silk fibroin. Some of the dissolution conditions induced mild effects on the silk fibroin while others were harsh. Furthermore, processing to nanofibers resulted in the degradation of the β-sheets producing nanofibers rich in α-helices. However, post-treatment using methanol and water vapor were effective in restoring β-sheet crystallinity.

Evaluating the Performance of Ball-Milled Silk Fibroin Films for Simultaneous Adsorption of Eight Pharmaceuticals from Water

“…It is reported that to obtain silk powder with a particle size between 2–3 μm requires long milling times, and harsh pre-treatment processes must be employed in addition to the long milling times of up to 40 hrs [ 28 ]. While the powder still showed large aggregates, in the current study, however, the preparation of the silk films was carried out under relatively mild conditions to preserve the integrity of the silk fibroin with a milling time of 90 min [ 23 ].…”

“…A. mimosae cocoons were degummed in a two-step degumming process for 90 min at each time as described in [ 23 ]. The cocoons were firstly boiled in 0.025 mol dm −3 then in 0.01 mol dm −3 Na 2 CO 3 aqueous solutions.…”

“…With over 400 species of wild silk-producing moths in the world, approximately eight types have been successfully beneficiated through various applications. The fabrication of an adsorbent based on silk fibroin presents an opportunity to exploit its physical and surface characteristics to adsorb selected PhACs and remove them from environmental samples [ 22 , 23 , 24 ]. Silk is an attractive material to explore as a potential low-cost adsorbent due to its biocompatibility and biodegradability after use.…”

A low-cost method for developing a β-sheet packed silk fibroin powder for medical application in LMICs

“…However, lithium bromide was replaced with cheaper Ajisawa solution [12][13][14], formic acid as a solvent with lithium chloride and calcium chloride salts [15] for SF dissolution which was further processed into SF powder.…”

“…Silk degumming procedure: 5g of raw silk boiled in 0.02M Na 2 CO 3 solution for 30min, rinsed 3 times with distilled water and dried overnight in a fume hood leaving SF bres [4,14,15].…”