Numerical simulation of three-dimensional flow-induced microstructure in a simplified prosthetic hip joint with nematic liquid crystal lubricant

Abstract

The nature of liquid crystalline materials leads to a preferred direction of molecules in the vicinity of solid surfaces that gives them outstanding tribological properties. Intrinsic molecular order of liquid crystalline materials close to the solid boundaries protects the rubbing surfaces against wear. Due to the bio-compatible nature of most lyotropic liquid crystalline materials, they have been considered as viable candidates to be used as bio-lubricants. In order to understand the complex flow patterns and microstructure of liquid crystals, in this paper, start-up flow-induced microstructure of a nematic liquid crystal in a simplified capsular space of prosthetic hip joint was studied using the Landau-de Gennes nematodynamic theory. Flow streamlines, dimensionless pressure distribution, and rheological properties for a liquid crystal and for synovial fluid affected by rheumatoid arthritis (RA) were presented and compared. The liquid crystals exhibited higher degrees of net pressure lifting force across the capsular gap while forming an ordered molecular layer close to the solid surfaces that protects the surface against wearing mechanism while decreasing the coefficient of friction (COF). Formation of molecular microstructure in vicinity of solid surfaces with perpendicular orientation to the normal surface vector was observed.