Effects of\nDiffusing Squalene on the Plastic Deformation\nof Ultrahigh-Molecular-Weight PolyethyleneInsights from Molecular\nDynamics Simulations

Ultrahigh-molecular-weight\npolyethylene (UHMWPE) stands out as\na popular artificial joint material. However, wear limits its service\nlife, which is mainly caused by accumulation of plastic deformation.\nThe plastic deformation on the frictional interface reflects the early\nwear of UHMWPE. To investigate the effect of squalene, a typical component\nin the body fluid, on the tribological properties of UHMWPE at microscopic\nscale, the diffusion behavior of squalene into polyethylene and its\ninfluence on the plastic deformation of polyethylene are discussed\nusing the molecular dynamics (MD) simulation. The lubrication model\nshows that polyethylene reconstructed from the interface to lower\nsubstrate, with refactor gaps between polyethylene chains. This promotes\nsqualene molecules to gradually diffuse into polyethylene from these\ngaps and causes the polyethylene structure to become loose. On the\nother hand, in the diffused model, squalene in polyethylene substrates\nincreases the plastic deformation of polyethylene. The separation\nof squalene reduces the interaction strength between adjacent polyethylene\nchains and accelerates the disentanglement of polyethylene. The flexibility\nof “CC” bonds in squalene allows the continuous\nadjustment of its spatial structures to adapt the space between polyethylene\nchains. The squalene fragments will not hinder the plastic flow of\npolyethylene.