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

Hlobsile Kgomo,Somandla Ncube,Mathew M Nindi,Simiso Dube,Temesgen Girma Kebede,Vimbai Mhuka

doi:10.3390/polym13040549

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.

Highlights

Silk is a natural protein polymer produced by various insects including silkworms.Interest in silk fibroin (SF) from silkworms is due to its outstanding mechanical properties, high thermal stability, and other superior properties including biodegradability
The first one being “no dissolution” which was characterized by a swollen fiber, but no regenerated silk fibroin (RSF) solution could be collected, no films were obtained from such systems
The results show that some solvent systems induced only mild effects to the silk fibroin during processing, while others were harsh resulting in changes in the thermal stability of the fibroin

Summary

Introduction

Silk is a natural protein polymer produced by various insects including silkworms.Interest in silk fibroin (SF) from silkworms is due to its outstanding mechanical properties, high thermal stability, and other superior properties including biodegradability. Silk fiber has evolved into a fascinating material that has been used mainly as sutures in the medical field over the years because of its biodegradability [1]. It has been explored for potential application in different areas including such as tissue engineering and controlled drug delivery [2,3]. The general approach in obtaining pure SF is via a degumming process to remove sericin This sericin is a hydrophilic protein that binds the SF fibers together to form a compact cocoon. Various reviews on electrospinning have highlighted advantages of this technique, notably, the production of nano-scale fibers with a large surface area to volume ratio which has been found to improve their applicability and performance in a variety of applications [4,5,6,7]

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Results

Conclusion