Insights into nanomechanical behavior of B. mori silk fibroin-hydroxyapatite bio-nanocomposite using MD simulations: Role of varying hydroxyapatite content.

Nanocomposite material composed of Bombyx mori Silk Fibroin and hydroxyapatite (B. mori SF-HA) is a potential biomaterial for bone tissue engineering. Here, Bombyx mori Silk Fibroin (B. mori SF) is a flexible and tough organic, polymer phase, and hydroxyapatite (HA) is hard and stiff mineral phase. Knowledge about mechanical deformation behavior together with governing mechanisms, and the role of the two phases (SF and HA phase) and interfacial interactions between them, in B. mori SF-HA biomaterial, at fundamental level is an important factor to consider while developing the tissue grafts. Such nanometer scale behavior is often preferably investigated using molecular dynamics method. Present study aims at understanding the mechanical deformation behavior and associated physical mechanisms in B. mori SF-HA bio-nanocomposite, at nanoscale. For this purpose, computational atomistic models of B. mori SF-HA bio-nanocomposite are developed with varying HA content. Mechanical behavior analysis of these composite models under tensile loading were performed using Molecular Dynamics (MD) simulations. Elastic modulus and tensile strength values in the range of 7-20 GPa and 200-700 MPa, respectively, are obtained for B. mori SF-HA composite, in case of different HA contents, wherein, increased mechanical properties are observed with increase in HA content. Analyses of the deformation trajectories show that the deformation flow behavior in B. mori SF-HA bio-nanocomposites is mainly defined by the soft SF phase. However, energetics analyses show that, the HA phase and SF-HA interfacial interactions also play a considerable role in mechanical performance of B. mori SF-HA bio-nanocomposite. Additionally, interfacial shear strength values in B. mori SF-HA bio-nanocomposite, for different HA contents, have also been obtained. The observations made and insights gained in present work has contribution and impact in gaining an insight into the mechanistic interactions occurring at nanoscale between SF and HA phases in B. mori SF-HA bio-composite.