Mechanical Properties of Spider Silk for Use As a Biomaterial: Molecular Dynamics Investigations

Silk fibers are naturally produced by arthropods such as silkworm and spiders. They’ve been used for centuries in the textile applications, and in recent decades for biomedical purposes. The silkworm silk fibers are made up of two different proteins, fibroin and sericin. Fibroin is the central inner-core protein rich in glycine, whereas sericin is a glue-like coating that wraps around the fibroin. [1, 2]  Even though silkworm are the most dominant type of silk fibers used for commercial applications, spider silk has found its niche in biomedical applications. Its biocompatibility and excellent mechanical properties give it great potential for commercial biomaterial applications. While large scale harvests of silk from spiders isn’t possible, recombinant production of the silk proteins at a large scale has found new interest in the recent years. Spider silk composites with a combination of a variety of other biomaterials have also been used to improve properties such as bio-compatibility, mechanical strength and controlled degradation. [2] A major constituent of spider silk fibers, are spidroin proteins. These are made up of repetitive segments flanked by conserved non-repetitive domains. The fiber proteins consist of a light chain and a heavy chain that are connected via a single disulfide bond. [1] Present paper employed steered molecular dynamics (SMD) as the principal method of investigating the mechanical properties of nanoscale spider silk protein 3LR2, with a residual count of 134 amino acids. [3]. SMD simulations were performed by pulling on each chain of the protein in the x-direction, while holding the other fixed. The focus of this paper is to investigate the mechanical properties of the nanoscale spider silk proteins with lengths of about 4.5nm in a folded state, leading to understanding of their feasibility in bio-printing of a composite spider silk biomaterial with a blend of various other biomaterials such as collagen. Molecular dynamics modeling is used to simulate, model and analyze mechanical properties of spider silk proteins. An in-depth insight into the deformation and structural properties of the spider silk proteins are of innovative significance for a multitude of bio medical engineering applications. A detailed comprehension of the protein’s mechanical properties is investigated through the fraying deformation behavior studied. A calculated Gibbs free energy value via umbrella sampling corresponds with a complete unfolding of a single chain from a spider silk protein in case of fraying. Force needed for complete separation of each chain from the spider silk protein is analyzed, and discussed in this paper.   

[1]          N. Kasoju and U. Bora, "Silk fibroin in tissue engineering," Adv Healthc Mater, vol. 1, no. 4, pp. 393-412, Jul 2012.

[2]          M. K. Wlodarczyk-Biegun and A. Del Campo, "3D bioprinting of structural proteins," Biomaterials, vol. 134, pp. 180-201, Jul 2017.

[3]          G. Askarieh et al., "Self-assembly of spider silk proteins is controlled by a pH-sensitive relay," Nature, vol. 465, no. 7295, pp. 236-8, May 13 2010.