The effects of lubricant composition on in vitro wear testing of polymeric acetabular components

Abstract

Lubricant composition is known to affect in vitro (simulator) wear of polymeric acetabular components. Clinical acetabular components, fabricated from both ultrahigh molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE), were tested against cobalt-chromium 32-mm ball heads, with the use of various lubricants, with different compositions and concentrations of bovine and calf serum as well as hyaluronic acid, in tests which lasted one million cycles. The type of proteins and their relative concentration in the lubricant affected the wear rate of both UHMWPE and PTFE. Increasing protein concentration reduced the UHMWPE wear rate but increased the PTFE wear rate. For a given total protein concentration, increasing the albumin/globulin (A/G) ratio led to a significant reduction in the wear rate for PTFE. A similar but smaller effect was found for UHMWPE. The relative wear-rate ratio between PTFE and UHMWPE depends on both the total protein concentration and the specific protein concentration (albumin/globulin ratio). The average clinical wear rates for both PTFE and UHMWPE and the average wear-rate ratios between them were reproduced when the serum lubricant contained total protein concentration and A/G ratio within normally observed physiological ranges. It is recommended that lubricants for simulator testing be standardized to control total protein content as well as albumin/ globulin ratio.

In contact observation of model synovial fluid lubricating mechanisms

“…Proteins which passed through the contact formed thick deposited films on the metallic surface. This observation is supported by other 3 studies [13][14][15] which reported thick protein deposits on joint surfaces after in vitro and in vivo (explant) use. It is usually suggested that these films act as a protective surface layers reducing adhesion and wear [15].…”

The use of self-mating PEEK as an alternative bearing material for cervical disc arthroplasty: a comparison of different simulator inputs and tribological environments

“…The use of saline resulted in the highest wear rate of 0.89 ± 0.08 and 1.23 ± 0.07 mm 3 /Mc (Groups 4 and 5, respectively). The higher wear rate for Group 4 was expected, given that saline lacks any lubricating proteins [30], and yielded the opposite result of polymer on metal articulations [17,18]. Given the lack of evidence for third body wear from the imaging assessment for Group 5 as compared to Group 4, it is believed that slow dissolution of the coating and/or physical removal of the HA coating during specimen handling during testing is responsible for the difference in mass loss; the cycle intervals were decreased to minimize handling of the coated devices.…”

“…For example, an increase in the sliding distance a bearing surface travels can result in increased wear [15,16]. Decreasing the quantity of protein in the lubricant can increase the wear rate of UHMWPE on CoCr and decrease the wear rate of PTFE on CoCr, but testing both in a zero protein fluid yields unrealistically low wear rates for both as compared to clinical retrieval analyses [17,18]. In addition, multidirectional or ''cross-shear'' motion can increase the wear rate by an order of magnitude [19][20][21][22] or not have an effect at all [23].…”

The Synovial Lining and Synovial Fluid Properties after Joint Arthroplasty

“…Joint simulator studies have been performed for decades but there are often large differences between labs in the properties of the lubricants used to conduct the tests [42,[57][58][59]. The conditions that these simulations are run under also differ markedly from joint function in vivo including the volume and temperature of the fluids.…”