The effect of transient conditions on synovial fluid protein aggregation lubrication

Abstract

Little is known about the prevailing lubrication mechanisms in artificial articular joints and the way in which these mechanisms determine implant performance. The authors propose that interfacial film formation is determined by rheological changes local to the contact and is driven by aggregation of synovial fluid proteins within the contact inlet region. A direct relationship between contact film thickness and size of the protein aggregation within the inlet region has been observed.In this paper the latest experimental observations of the protein aggregation mechanism are presented for conditions which more closely mimic joint kinematics and loading. Lubricant films were measured for a series of bovine calf serum solutions for CoCrMo femoral component sliding against a glass disc. An optical interferometric apparatus was employed to study the effects of transient motion on lubricant film formation. Central film thickness was measured as a function of time for a series of transient entrainment conditions; start-up motion, steady-state and non-steadystate uni-directional sliding, and bi-directional sliding. The size of the inlet aggregations was found to be dependent upon the type of transient condition. Thick protective protein films were observed to build up within the main contact region for all uni-directional tests. In contrast the inlet aggregation was not observed for bi-directional tests. Contact film thickness and wear was found to be directly proportional to the presence of the inlet protein phase. The inlet phase and contact films were found to be fragile when disrupted by surface scratches or subjected to reversal of the sliding direction.

The Effects of Surface Mechanical Deformation and Bovine Serum Albumin on the Tribological Properties of Polyvinyl Alcohol Hydrogel as an Artificial Cartilage

“…It is necessary to study the role of proteins in synovial uids including albumin. Albumin had been studied in lm thickness experiments, and its concentration is 0.7-1.8 g/dl in healthy synovial uid [24,25].…”

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

“…According to the essential effect of surface conformity, introduced by Vrbka et al [16] in combination with direct evidence of the importance of transient conditions pronounced by Myant and Cann [20], it can be concluded that the described experimental approach seems to be a very suitable tool for further investigation of lubrication processes within hip joint replacements, while considering different loading and kinematic conditions, influence of geometry, radial clearance and material combination of contact pairs.…”

Ring-Shaped Surface Microstructures for Improved Lubrication Performance of Joint Prostheses

“…However, the symmetrical geometry of the ring structure can be regarded as a positive attribute and it could have an impact on the formation of a steadier lubricant film. This is because a reversal in flow direction and change in axis can retard, or even prevent the buildup of a protective protein surface layer [28]. Since hip endoprostheses are exposed to multi-axial movements, a symmetrical dimple or rather microstructure is basically favorable.…”

“…It was concluded that film thickness could not be predicted by using the rheology of simple Newtonian fluids in steady state contact conditions. Instead, interfacial film formation was determined by local rheological changes in the contact area and is driven by an aggregation of proteins within the contact inlet region [28,29]. Surface textures, for example, are discontinuities in film thickness that exhibit complex and transient load and kinematic multi-axis cycles.…”