Heterogeneous molecular packing and water effects on the mechanical behaviour of silk-inspired β-sheet crystallites: A steered molecular dynamics study

Abstract

Bombyx-mori silk fibroin (SF) features outstanding mechanical properties, arising from its beta-sheet content. This study investigates the effect of heterogenous molecular packing and water environment on the mechanical behaviour of silk-inspired beta-sheet crystallites using steered molecular dynamics (SMD) simulation technique. Two distinct antipolar antiparallel crystallite models were constructed based on experimental Silk II structures, differing intermolecular packing arrangements, instead of widely used highly ordered theoretical model of beta-sheet structure. Results of pull-out simulations of six different beta-chains reveal that heterogeneous molecular packing introduces location-dependent mechanical strength, which cannot be predicted based on chain region (core vs. surface) only. Water selectively weakens the surface and corner chains while either ineffective or slightly enhances the strength via hydrogen bond bridges formed prior to ultimate rupture. It also smoothens the stick-slip motion and expedites complete dissociation. Our finding provides atomistic insights into structure-mechanical relationship silk fibroin and highlight the critical role of packing heterogeneity and aqueous environment in tuning silk-based materials for biomedical and engineering applications.