Novel route to fatigue-resistant fully sintered ultrahigh molecular weight polyethylene for knee prosthesis

The role of entanglements in obtaining a homogeneous product of ultrahigh molecular weight polyethylene (UHMW-PE) has been explored. Studies performed in this report show that a disentangled state before melting is a prerequisite to obtain homogeneous products of an intractable polymer like UHMW-PE. The disentangled state is obtained directly from the reactor by controlling the polymerization conditions or in the solid state when there is enhanced chain mobility along the c axis of a unit cell. The disentangled state is maintained in the melt over a period of time, invoking implications in polymer rheology. This approach is applicable to polymers in general. The homogeneous fully sintered UHMW-PE, obtained for the first time, shows a considerable decrease in oxygen permeability and an increase in toughness and fatigue resistance. Such homogeneous products of UHMW-PE are beneficial in highly demanding applications, especially in knee prosthesis, where the polymer is used as an inlay between the human bone and a metal or ceramic part, which slides against the polyethylene component during normal gait.