Visualization of lubricating films between artificial head and cup with respect to real geometry

The aim of this study is to propose a novel experimental approach enabling in-situ observation of film formation within hip joint replacements with respect to real geometry (including radial clearance) of rubbing surfaces. A pendulum hip joint simulator in combination with thin film colorimetric interferometry was employed for film thickness evaluation between metal femoral head and glass acetabular cup lubricated by bovine serum solution. Glass acetabulum was developed according to dimensions of artificial cup so the real radial clearance between components was considered. The pendulum, deflected at an initial position, was released and allowed to oscillate freely in the flexion–extension plane; therefore the transient character of motion was considered. Maximum central film thickness of 232 nm was measured at the beginning of the experiment. After a short time it decreased and became quite stable (around 90 nm) until the end of the measurement. The preliminary results shown that novel experimental approach seems to be a very powerful tool for studying lubrication processes within artificial hip joints while considering different loading and kinematic conditions, influence of geometry, clearance and material combination of contact pairs.