Competitive Binding of Bilirubin and Fatty Acid on Serum Albumin Affects Wear of UHMWPE

Total Joint Replacement (TJR) devices undergo standardized wear testing in mechanical simulators while submerged in a proteinaceous testing solution to mimic the environmental conditions of artificial joints in the human body. Typically, bovine calf serum is used to provide the required protein content. However, due to lot-to-lot variability, an undesirable variance in testing outcome is observed. Based on an earlier finding that yellowish-orange serum color saturation is associated with wear rate, we examined potential sources of this variability, by running a comparative wear test with bilirubin; hemin; and a fatty acid, oleic acid, in the lubricant. All these compounds readily bind to albumin, the most abundant protein in bovine serum. Ultrahigh molecular weight polyethylene (UHMWPE) pins were articulated against CoCrMo discs in a pin-on-disc tribometer, and the UHMWPE wear rates were compared between lubricants. We found that the addition of bilirubin increased wear by 121%, while hemin had a much weaker, insignificant effect. When added at the same molar ratio as bilirubin, the fatty acid tended to reduce wear. Additionally, there was a significant interaction with respect to bilirubin and hemin in that UHMWPE wear rate decreased with increasing fatty acid concentration. We believe the conformational change in albumin by binding bilirubin makes it more likely to form molecular bridges between UHMWPE and the metal counterface, thus increasing adhesive wear. However, fatty acids compete for binding sites on albumin, and can prevent this conformational change. Hence, the protein is stabilized, and the chance for albumin to form bridges is lowered. Ultimately, UHMWPE wear rate is driven by the competitive binding of bilirubin and fatty acid to albumin.

Wear performance of inverted non-conforming bearings in anatomic total shoulder arthroplasty

Background Glenoid component failures still represent the most common complication in total shoulder arthroplasty. These failures depend on several factors, including ultra-high molecular weight polyethylene (UHMWPE) wear. One reason for UHMWPE wear in total shoulder arthroplasty may be the current use of a spherical prosthetic humeral head against a radially mismatched UHMWPE glenoid component, which leads to reduced glenohumeral translations, glenoid edge loading and high translational forces during shoulder motions. The aim of this study was to assess the in vitro wear of an anatomic total shoulder prosthesis with non-spherical non-conforming bearings with inverted conventional materials. Methods The wear of a vitamin E-blended UHMWPE non-spherical humeral head articulating against a non-conforming titanium-niobium nitride (TiNbN)-coated metallic glenoid was tested using a joint simulator. The wear test was performed by applying a constant load of 756 N with angular motions and translations. Results After 2.5 million cycles, the mean wear rate of the humeral head was 0.28 ± standard deviation (SD) 0.45 mg/million cycles. Conclusion The low wear rate of the vitamin E UHMWPE humeral head supports the use of non-spherical non-conforming bearings with inverted conventional materials in anatomic total shoulder arthroplasty.

Manufacturing, oxidation, mechanical properties and clinical performance of highly cross-linked polyethylene in total hip arthroplasty

Ultra-high molecular weight polyethylene (UHMWPE) continues to be the gold standard bearing surface in total hip arthroplasty (THA) for nearly 5 decades. Highly cross-linked UHMWPE (HXLPE) was adapted for routine use in the early 2000s to reduce the revision rates related to wear, osteolysis, and aseptic loosening resulting from conventional UHMWPE wear. Since its inception, consistent evidence showing reduced wear rates and osteolysis supports the use of HXLPE in THA. High quality studies demonstrating the advantage in long term survivorship of HXLPE over conventional UHMWPE are emerging. Though retrieval studies have demonstrated evidence of in vivo oxidation and fatigue related damage at the rim of the first generation HXLPE liners, clinical significance of this remains to be seen. Second-generation sequentially annealed and vitamin E containing HXLPE liners demonstrate improved mechanical properties, resistance to oxidation, and equivalent wear rates in comparison to their first-generation counterparts, but long term success remains to be seen.

The Contact Simulation Comparison of UHMWPE to the Crosslink Intensity Effect

Ultra High Molecular Weight Polyethylene called UHMWPE is a unique polymer material that has excellent physical and mechanical properties. UHMWPE material is frequently used in prosthesis. One example of UHMWPE uses in prosthesis is acetabular liner which is one component for Total Hip Joint Replacement (THR) and can also be found for bearing surfaces on the knee, ankle, shoulder, and connective tissue of the joint. UHMWPE material is made by compression molding process. However, UHMWPE wear often causes the failure of artificial hip joints. Therefore, a treatment to reduce the crosslink method is performed. The purpose of this study was to determine the crosslink effect in UHMWPE material. The method used for this analysis is ABAQUS 6-13 software. On bipolar model, the 3000 N load is applied in the FEM model. The crosslink dose used in this analysis was 50kgy, 75kgy, and 100kgy. The results obtained are that UHMWPE that has received by gamma irradiation treatment can receive a smaller stress distribution. The results of the simulation for UHMWPE without irradiation produced 0.759 stress distributions; 50kgy crosslink dose has 0.666 stress distributions; 75kgy crosslink dose has 0.662 stress distributions; and 100kgy crosslink dose has 0.660 stress distributions. This result proved that UHMWPE which has received crosslink can receive a better stress distribution. For the result crosslink with 100kgy dose received the best number of stress distributionss.