The fractal self-assembly of the silk protein sericin

Abstract

Silk consists primarily of two proteins-a fibrous core protein, fibroin, and a glue protein, sericin, which envelops the fibroin fibers with sticky layers thus helping in the formation of cocoon, achieved by cementing the silk fibers together. Sericin, a water soluble protein, has traditionally been discarded in silk processing, despite great potential for use as a biomaterial. Here we show that this glue protein, sericin, has the ability to form self-assembled nano and microstructures with hierarchical self-similarity across length scales in the form of a diffusion-limited, fractal assembly. Sericin obtained from two silkworms, a domesticated mulberry Bombyx mori and a wild non-mulberry Antheraea mylitta, were studied, with particular insight into its structure and morphology as it dried on a surface. High-resolution atomic force microscopy was used to image the self-assembled protein, with investigations on the various factors that influenced this process. We describe the self-assembly patterns formed by the sericin protein and analyze the images based on the theory of diffusion limited aggregation to explain the fractal nature of these architectures observed. The unique physical behavior and fractal nature of this glue protein may represent a key step in understanding its biological relevance as well as the role it plays in the assembly and formation of silks.

Fractal-like structures in colloid science

“…A relevant example in this sense is the silk protein sericin, whose self-assembly can be directed toward objects having different fractality (such as nanofibrils, hydrogels or films) by properly changing environmental (i.e., solvent) conditions [99]. Given a good control on the aggregate structure, it can be envisaged how different classes of protein-based biomaterials will represent an interesting direction for both research and industrial applications.…”

Extraction conditions of Antheraea mylitta sericin with high yields and minimum molecular weight degradation

“…However, no standard method for the Na 2 CO 3 extraction has been previously reported, as in the case of B. mori. Various concentrations of Na 2 CO 3 are used, and the treatment times and temperatures also differ [9,10,[13][14][15]. Therefore, we more closely considered the extraction conditions when using Na 2 CO 3 as the agent to extract sericin from A. mylitta.…”

“…In the case of the sodium chloride solution, the A. mylitta cocoons are immersed in a 1% NaCl solution and stirred overnight at room [11,12]. Currently, a sodium carbonate solution is widely used for the extraction of AmS [9,10,[13][14][15]. Normally, 0.02 M or 0.2% Na 2 CO 3 solutions are used, and the cocoons are boiled for 30 or 60 min, either with or without pressure.…”

“…Kundu et al [9][10][11][12][13][14][15] have extensively studied the novel application of the A. mylitta sericin (AmS). In these studies, two types of solutions for the extraction of AmS have been used, namely, a sodium chloride solution and a sodium carbonate solution.…”

Template-assisted Synthesis of Polymer - Li Composites with Fractal Patterns

“…[14] In contrast, the theory of self-organizing dissipative fractal structures has attracted much attention in explaining the growth and the assembly of fractal aggregates. [15][16][17][18][19] Potential applications have been realized in various scientific fields, especially in materials science in investigating the synthesis of fractal crystals. Fractal material science takes into account the relation between the parameters of fractal structures and the dissipative properties of alloys.…”