Abstract
Introduction
Ultra high molecular weight polyethylene (UHMWPE) has been used successfully as a bearing material in hip, knee, and shoulder joint replacements. However, there are problems to cause a failure in UHMWPE component, which are wear behavior and creep deformation. Continuous bearing motion and dynamic load have occurred to UHMWPE wear debris caused osteolysis in periprosthetic tissue and to plastic deformation of joint component, and subsequent aseptic loosening of components. Therefore, many studies have being carried out in order to reduce wear debris and to improve mechanical strength from UHMWPE, and there is tremendous improvement of mechanical property in UHMWPE from gamma irradiated conventional UHMWPE (GIPE), highly crosslinked PE (XLPE), and XLPE with vitamin E1, 2. Friction has a significant one of the factors effect on the wear and creep deformation. In this study, the short-term frictional behaviors of three typical types of GIPE, remelted XLPE (R-XLPE), and s annealed XLPE (A-XLPE), and XLPE with Vitamin E against Co-Cr alloy were compared under three levels of contact pressures which occured in hip, knee, and shoulder joints.
Methods
Friction tests were conducted with UHMWPE against Co-Cr alloy by using pin-on-disk type triboteter. For test, tribotester performed in a repeat pass rotational slidintg motion with a velocity of 60rpm. Applied contact pressure selected three kinds of levels, 5, 10, and 20MPa which were within the range of maximum contact pressures for total hip, knee, and shoulder joint replacements. To analyze the frictional effect of UHMWPE type, it conducted t-test and p-values less than 0.05 were used to determine the statistically significant difference.
Results
In this study, it was observed that coefficients of friction (COF) were affected by various conditions, kinds of materials and applied load. We can reveal the frictional behavior of UHMWPE in various contact pressures. The average of the COF measured that GIPE was 0.029∼0.0423, R-XLPE was 0.018∼0.031, A-XLPE was 0.023∼0.038, and XLPE with Vitamin E was 0.013∼0.027 under 5, 10, and 20MPa.
Discussion
COF of R-XLPE, A-XLPE, and XPLE with Vitamin E were lower than GIPE for all levels of contact pressures. This study showed the trend that COF decreased as contact pressure increased. Also, XPLE with Vitamin E has lowest frictional values among UHMWPEs. In the viewpoint of applied load, it was decreased as a contact pressure increased for COF of GIPE, RXLPE, and AXLPE against Co-Cr alloy. COF of GIPE, XLPEs, and XLPE with Vitamin E against Co-Cr alloy were as low as using bio materials compared with the COF of cartilage to cartilage, which was about 0.024.
Conclusions
In conclusion, average COF of XLPE with Vitamin E was significantly lower than those of R-XLPE and A-XLPE. XLPEs showed much lower COF than GIPE.
