Investigations into the role of water concentration on mechanical behavior and nanomechanics of Bombyx mori silk fibroin
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Investigations into the role of water concentration on mechanical behavior and nanomechanics of Bombyx mori silk fibroin using molecular dynamics simulations Mrinal Patel1, Devendra K. Dubey1,*, and Satinder Paul Singh1 1
Mechanical Engineering Department, Indian Institute of Technology, Delhi, New Delhi 110016, India
Received: 30 April 2020
ABSTRACT
Accepted: 10 August 2020
Bombyx mori silk fibroin (B. mori SF) is emerging as a promising biomaterial for its application in biomedical field such as hard and soft tissue engineered grafts considering it is a load-bearing polymer with biocompatible and biodegradable characteristics. B. mori SF being a biopolymer is made up of amino acids (residues) comprising crystalline and amorphous domains at nanoscale. In general, mechanical behavior of a biomaterial is actively governed by its chemical environment. Extent of water present in silk can significantly affect its mechanical behavior and alter structural functions at the molecular level. Hence, it is essential to understand the mechanical behavior and molecular deformation mechanics of B. mori SF at the building block level under varying hydration conditions. In current investigation, tensile mechanical behavior of two characteristic computational models of B. mori SF, along the fiber axis, under varying hydration levels (0 to 70 wt%) has been studied using molecular dynamics simulations. Elastic modulus values in the range of 7 to 11 GPa and 8 to 13 GPa were obtained for the two models for varying hydration levels. Analyses reveal that the hydrophobic effect has a dominating role at lower hydration levels resulting in an enhanced interaction between protein chains. This results in mechanical strengthening of B. mori SF nanostructure. However, at higher hydration levels, the osmotic pressure plays a dominating role, resulting into screening of interatomic interaction between protein chains thus giving a weakening effect. Overall, this work contributes toward developing an understanding of mechanistic interactions between different protein phases (amorphous and crystalline regions) and water in hydrated B. mori SF nanostructure, which is useful for explorations in silk-based biomaterials.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Handling Editor: Yaroslava Yingling.
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https://doi.org/10.1007/s10853-020-05249-3
J Mater Sci
Introduction Silk fiber is a naturally occurring protein polymer and a promising biomaterial possible owing to its biocompatibility and tunable biodegradability [1–3]. Silk has been investigated as biomaterial, also given its favorable mechanical properties like strength and stiffness complementing to the requirements of grafts/scaffolds in biomedical applications [2, 3]. Worldwide, most of the silk fibers are produced by the Bombyx Mori (B. mori) silkworms [3]. B. mori silk has a elastic modulus, tensile strength, toughness and extensibility in the range of 300–800 MPa, 7–18 GPa, 6 9 104 J/kg and 15–25%, re
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