In vitro estimation of reduction in strength and wear resistance of UHMWPE for joint prostheses due to lipid‐induced degradation

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is used as a bearing surface of joint prostheses and has been reported to absorb lipids such as squalene (SQ) and cholesterol esters in vivo. These lipids have been suggested by in vitro studies using SQ as a model lipid to have the potential to induce polymer degradation. However, the impact of lipid-induced degradation on the strength and wear resistance of UHMWPE is unknown. In this study, lipid-induced degradation was simulated by SQ absorption and subsequent accelerated aging, and its influence on the strength and wear resistance of UHMWPE was investigated using wear, fatigue crack growth, and delamination testing. Lipid-induced degradation was found to have little impact on fatigue crack growth rates and delamination resistance. These results were consistent with previous reports that lipid-induced degradation is localized near the surface. However, we also found that lipid-induced degradation increased the wear rate of both non-crosslinked and crosslinked UHMWPE by a factor of 2.5 and 14, respectively. These results indicate that lipid-induced degradation may affect the durability and long-term clinical outcome of joint replacements due to increased wear of UHMWPE.

In vitro evaluation of delamination resistance of PEEK and CFR-PEEK

“…To overcome this problem, a test method involving the use of a U-shaped sliding pattern with a length and width of 10 and 1 mm, respectively, was developed. 7,22,23 The delamination resistance of various UHMWPE materials could be ranked using this test method, and the results were consistent with those obtained in other in vitro and retrieval studies of both hip and knee implants. 7 Moreover, Brockett et al 24 performed a wear study simulating an artificial knee joint and reported the occurrence of delamination of PEEK and CRF-PEEK, indicating that implants fabricated from PEEK materials may involve a risk of delamination.…”

“…Delamination tests were conducted using a twodimensional pin-on-plate wear test machine (M. S. Tec, Kyoto, Japan), as previously described. 7,23 However, we used alumina ceramic as the material of the load pin instead of Co-Cr alloy because carbon fibers tend to damage the Co-Cr metal alloy. The alumina ceramic pins, having a mirror-polished hemispherical end with a radius of 3 mm, were used to apply a compression load of 196 N. A U-shaped sliding pattern with a length and width of 10 and 1 mm, respectively, was applied to the plate specimen at a sliding velocity of 30 mm/s.…”

Research progress on the oxidation behavior mechanism and the design of antioxidant methods of artificial polymer acetabular cup

“…Squalene's intrusive radicals cause the oxidation of UHMWPE artificial joints by removing hydrogen atoms from UHMWPE chains. Sakoda et al 55,56 further simulated lipid‐induced degradation by squalene uptake and subsequently accelerated aging and investigated the impact of lipid‐induced degradation on UHMWPE the strength and wear resistance of UHMWPE by abrasion, fatigue crack extension, and delamination tests. The results showed that the lipid‐induced degradation was limited to the vicinity of the surface and had little effect on the fatigue crack extension rate and delamination resistance.…”

Six decades of UHMWPE in reconstructive surgery

“…In this context, a study on the aging process of 150-kGy irradiated UHMWPE, with Vitamin-E [114], exhibited higher oxidative stability for 36 months than those of other UHMWPE forms. OI is not only affected by the chemistry of crosslinked or sterilized UHMWPE, but also by factors such as different types of lipids, especially squalene (SQ), present in lubricants around the UHMWPE prosthesis, which play a significant role in inducing biodegradation [115,116].…”