Wear factors UHMWPE

Each test specimen was subjected to a constant load and a fixed cycle of reciprocating motion. Long term wear tests were performed with the total sliding distance in each case extending to several hundred km. The material removed by wear was monitored by periodic measurements of the weight of the UHMWPE wear pins on a Mettler microbalance with a sensitivity of 1 g Density measurements enabled volume loss (V) against sliding distance (X) relationships to be established at each load (P) and wear factors (k) were then determined from the relationship. 

The earlier suggestion by Dowson et alj( 3) that for the dry wear of UHMWPE against stainless steel there was an optimum Initial surface finish corresponding to a minimum wear factor, has been confirmed by further detailed and extensive studies by Glllls( ) and Dlab( 3). These experiments indicate that the optimum (Ra) is slightly less than 0.1 jjm and In the range 0.05 to 0.1 ym. 

The distinctive characteristics observed for the wear factors as functions of counterface roughness and the Intersection of the traces at a value of (Ra) of about 0.01 jjm provides an explanation of the contradictory views which are held about the influence of environment on the wear of UHMWPE. It is now clearly evident that comparisons must be related to the counterface roughness. 

Has the above discussion, it is understood that wear of UHMWPE primarily occurred due to adhesive, abrasive, subsurface cracks and delamination. These wear phenomena were affected by several factors, which are not inherent material properties of the articulating surface. A reduction of wear volume is always desirable to increase the longevity of the bearing surface. It was attempted by using various fillers as reinforcing materials in UHMWPE. Although a wide variety of fillers was used, MWCNTs were chosen for discussion in the present chapter in relevance to their superior properties. A detailed discussion on the... 

Since 1962, UHMWPE also has been used in orthopedics as a bearing material in artificial joints. Each year, about 1.4 million joint replacement procedures are performed aroimd the world. Despite the success of these restorative procedures, UHMWPE implants have only a finite lifetime. Wear and damage of the UHMWPE components is one of the factors limiting implant longevity. 

With chain material of regular acetal, wear strip material of UHMWPE, a comer angle of 90 degrees, and well-lubricated operation, the comer factor from Table 12-7 is 1.20. 

The main problem with total hip system is the loosening of the acetabular component, which is caused by wear debris. For this reason alumina is used only in the head of femur since numerous clinical studies indicates that alumina/ultrahigh molecular weigh polyethylene (UHMWPE) pair reduces wear debris by a factor of 10 or greater [19],... 

Under ideal (in vitro) circumstances, the magnitude of the wear reduction for first-generation highly crosslinked UHMWPEs is proportional to the absorbed dose, but in practical terms the perceived wear reduction is also influenced by experimental study design, including such factors as the radiographic wear measurement technique (Chapter 28) and the choice of control material used as a comparison (Chapter 20). The choice of irradiation source (gamma or e-beam) does not substantially influence wear resistance... 

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