Ultra High weight Molecular Weight Polyethylene


    TKR COMPONENTS WOTH UHMWPE Tibial           Insert

UHMW Polyethylene - Long hydrocarbon chain held together by covalent bonds. 

Exists in two forms - 

        1. Disorganized amorphous phase

        2. More organized crystalline phase

How is this material manufactured ?

   Zeigler Process 

    1.Ethylene gas polymerized at a low temperature, low pressure environment catalyst Titanium Chloride        produces a fine UHMWPE powder.

    2. Then the powder processed in one of the following methods-

            - Ram extrusion produces bar stock, lowest quality

            - sheet compression moulding -higher quality 

            - Direct compression moulding - expensive shape of final component 

            - machining - - UHMWPE bar, sheets or moulded components shaped into final form

            - Sterilization and packaging - gamma irradiation ,gas plasma or ethylene oxide. 

    How can its material properties be manipulated ? 

            By making cross-linked Polyethylene

   Bombarding material with an electric beam or gamma irradiation which causes chain session of double covalent bonds, followed by rebonding either by oxidation or by cross linking.

    Annealing to prevent oxidation and reduction of shelf half life.

    Adding antioxidants e.g. Vitamin E 

    Advantages - 80-100 % reduction in vivo wear

Disadvantages - brittle , increased risk of fractures 


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