Prosthetic components, UHMWPE

Vitamin E is soluble in UHMWPE (around 3% by weight), while it is insoluble in water and in the synovial fluid, and therefore it cannot be drawn out from the UHMWPE prosthetic components. UHMWPE films with 0.5% of vitamin E irradiated in air at lOOkGy after 60 days in water at 70°C do not show loss of vitamin E or degradation products [62]. This behavior is similar, but in an opposite way, to the diffusion of the apolar products present in the synovial fluid (cholesterol, ester of cholesterol, squalene) [63]. 

Implantable prosthetic bearings may be constructed from a composite material having a first layer and a second layer (20). The first layer has an articulating surface defined therein, whereas the second layer has an engaging surface defined therein for engaging either another prosthetic component or the bone itself. The first layer is constructed of a UHMWPE, whereas the second layer is constructed of a copolymer of ethylene and an acrylate. 

The origins of consolidation-related oxidation are not clear yet, but the processing conditions of the UHMWPE bar or sheet, together with the influence of the machining of the prosthetic component, have been proposed as contributing factors. Poor consolidation of the UHMWPE powder during processing. 

Typical GC/MS analysis of the soluble fraction extracted from a retrieved UHMWPE prosthetic component. 

Distribution of Oxidized Compounds in the New UHMWPE Prosthetic Components... 

UHMWPE prosthetic components in vivo are in intimate contact with joint fluid, basically a filtered component of blood s plasma, rich in lipids and triglycerides. 

Costa L, Bracco P, del Prever EB, Luda MP, TrossareBi L. Analysis of products diffused into UHMWPE prosthetic components in vivo. Biomaterials 2001 22(4) 307-15. 

When polytetrafluoroethylene (PTFE) was Introduced in the early 1960 s the life of total replacement hip joints was limited to about three years by the poor wear characteristics of the polymer. When ultra-high molecular weight polyethylene (UHMWPE) replaced PTFE, the rate of penetration of the metallic component into the polymeric component was reduced to such an extent that loosening emerged as a major aspect of prosthetic life. There is, nevertheless, a need to pursue studies of the wear of prosthetic materials to facilitate the development of satisfactory materials which can be used with confidence in long-life prostheses. 

Bracco P, Brach del Prever EM, Cannas M, Luda MP, Costa L. Oxidation behaviour in prosthetic UHMWPE components sterilised with high energy radiation in a low oxygen environment. Polym Degr Stab 2006 91 2030-6. 

R. Lee, A. Essner, A. Wang, and W. L. Jaffe. Scratch and wear performance of prosthetic femoral head components against crosshnked UHMWPE sockets. Wear 267,1915-1921 (2009). 

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