Nanoscale friction and adhesion mechanisms in articular cartilage top layer hydrated interfaces: Insights from atomistic simulations

Abstract This study investigates nanoscale adhesion and frictional behavior of an idealized cartilage-cartilage top layer atomistic contact model with nanoconfined water at the interface under range of load using three dimensional molecular dynamics (MD) simulations. Analysis reveals that water significantly replaces the cohesive interactions with adhesive at regions of unhydrated cartilage-cartilage contact by engulfing water molecules. These water molecules improve the load-bearing capacity and reduces frictional forces at the interface. Interfacial water also inhibits debonding at the interface during pull-off test at higher loads. Sliding tests reveal that at higher load-induced confined geometries there is a significant reduction in the frictional forces up to five times in comparison to dry collagen-collagen contact. Interaction energy curves predict that water molecules completely wet the collagen and thus provide an in-situ interfacial lubrication. Finally, the intermolecular interactions unveil the presence of substantial amount of water molecules at the interfaces to reduce friction drastically at the interface employing water-water interactions. Overall, a hydrated atomistic model for top layer cartilage-cartilage lubricated contact is developed and studied for adhesion and friction behavior and underlying mechanisms which is useful for understanding in-vivo boundary lubricated interfaces and design enhanced implant solutions.