Investigations into the role of water concentration on mechanical behavior and nanomechanics ofBombyx morisilk fibroin using molecular dynamics simulations

M Patel and DK Dubey and SP Singh, JOURNAL OF MATERIALS SCIENCE, 55, 17019-17045 (2020).

DOI: 10.1007/s10853-020-05249-3

Bombyx morisilk fibroin (B. moriSF) 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. moriSF 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 ofB. moriSF at the building block level under varying hydration conditions. In current investigation, tensile mechanical behavior of two characteristic computational models ofB. moriSF, 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 ofB. moriSF 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 hydratedB. moriSF nanostructure, which is useful for explorations in silk-based biomaterials.

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