Viscoelastic recovery of creep-deformed ultra-high molecular weight polyethylene (UHMWPE)

Viscoelastic creep recovery of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time and applied pressure for both static and dynamic loading. Unirradiated extruded GUR 4150HP UHMWPE specimens were compressed by using static and dynamic (1-Hz sinusoidal) loads with clinically relevant (hip) peak pressures of 2, 4, and 8 MPa in 37°C bovine serum for 10 000 minutes. Thereafter, loads were removed and the thicknesses of the specimens were measured periodically in air for up to 10 000 minutes. The creep strains recovered as a function of log time for all pressures in both static and dynamic loading. Regardless of load amplitude, load type, and radial location from which the specimens were machined from the extruded rod stock, approximately 51% of the total creep deformation was ultimately recovered, and 73% of the recovered creep strain occurred during the first 1000 min after unloading. These data emphasize the need to account for the amount of creep recovery when estimating wear rates with in vivo radiographic penetration measurements and the dimensions of retrieved implants.