Determinants of friction in soft elastohydrodynamic lubrication

Area of Science:

• Biomechanics
• Tribology
• Soft Tissue Engineering

Background:

• Elastohydrodynamic lubrication (EHL) is vital for protecting soft tissues in biological systems like joints and eyes.
• Few studies have investigated the influence of external loads, geometry, and material properties on EHL in soft tissues.

Purpose of the Study:

• To investigate the tribological behavior of soft tissues under varying conditions.
• To determine the impact of sliding velocity, normal load, material properties, and surface geometry on EHL.

Main Methods:

• A 2D finite element simulation was employed to model a fluid layer between a rigid surface and a soft tissue asperity.
• Frictional force, solid deformation, and fluid thickness were computed.
• Double-logarithmic regression was used to analyze scaling relationships.

Main Results:

• Frictional shear force is strongly influenced by velocity, viscosity, and load; moderately by bump length and elasticity; and weakly by bump amplitude.
• Minimum fluid thickness is strongly dependent on velocity and viscosity, with moderate changes due to load, elasticity, amplitude, and length.
• The initial shape of the soft tissue asperity has minimal effect on lubrication outcomes.

Conclusions:

• EHL in soft tissues is primarily governed by fluid dynamics and mechanical loading.
• Shear-induced deformation of symmetrical shapes contributes to load-supporting capabilities in soft tissues.
• This research provides insights into the lubrication mechanisms essential for soft tissue function and health.