Does Texturing of UHMWPE Increase Strength and Toughness?: A Pilot Study

Abstract

Background Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear resistance than conventional UHMWPE but lower strength and toughness. To produce crosslinked UHMWPE with improved mechanical properties, the material can be treated before crosslinking by tension to induce molecular alignment (texture). Questions/purposes We asked how (1) the microstructure of UHMWPE evolves when subjected to tension and (2) whether the new microstructure (texture) increases strength and toughness. Methods We analyzed microstructure evolution of UHMWPE by small-and wide-angle xray scattering and scanning electron microscopy. We then developed a method to characterize the local strength and toughness of undeformed and textured UHMWPEs by means of nanoscratch tests along and perpendicular to the specimen axis. In three samples we determined the scratch characteristics in terms of deformation mode, coefficient of friction (l), and viscoelastic recovery (r). Results Before the tensile process, the scratch behavior of UHMWPE was characterized by a l ranging from 0.64 to 0.68, no cracking, and r ranging from 0.58 to 0.60. Microfibrillar morphologic features resulted from the tensile process. The new microstructure had an increased strength (r = 0.78) and decreased toughness (cracking + l = 0.77) perpendicular to the fibril axis and decreased strength (r = 0.53) and increased toughness (no cracking + l = 0.55) parallel to the fibril axis. Conclusions Textured UHMWPE behaves like a fiber composite with high strength and toughness in well-defined directions. However, the effect of crosslinking on these specific properties is unknown and therefore it is important to verify that the properties are retained. If wear resistance of crosslinked-textured UHMWPE is at least as high as that of crosslinked UHMWPE, novel medical devices made of crosslinked-textured UHMWPE could be developed and clinically tested.

Impact of microextrusion and addition of graphite nanoplatelets on bulk and surface mechanical properties of UHMWPE

“…It is supposed that when such a morphology is submitted to tension, a stress transfer occurs from domains having a low‐strength, i.e., domains whose texture is perpendicular to tensile direction, to domains having a high strength, i.e., domains whose texture is along tensile direction. The ability of e‐PE to withstand stress is locally linked to a high involvement of tie molecules and entanglements in the textured‐domains with chains oriented along tensile direction 16, 17. This high strength may be responsible for an important strain recovery after unloading 18.…”

“…The surface recovery is similar for the three materials ( r of about 65%). As stipulated in the article of Addiego et al,16 the lower the coefficient of friction, the lower the work done during the viscoelastoplastic deformation generated by scratching. Consequently, e‐PE is characterized by a low scratching work that may be due to a higher consolidation when compared to PE and e‐PE/g, as shown by SEM (Fig.…”

The influence of electron beam irradiation, plastic deformation, and re‐irradiation on crystallinity degree, mechanical and sclerometric properties of GUR 1050 used for arthroplasty

“…The stress relief annealing is applied at the end of most of those methods to form the polyethylene structure and properties. It reduces the anisotropy of properties and removing a substantial part of free radicals stabilizes polyethylene from chemical point of view (oxidation resistance) …”

Properties of ultra‐high‐molecular‐weight polyethylene with a structure modified by plastic deformation and electron‐beam irradiation

“…In the majority of methods applied to alter the PE structure and properties, posttreatment annealing is additionally used to stabilize the structure. It reduces the residual stresses and anisotropy of properties and chemically stabilizes PE (in terms of oxidation resistance) by the recombination of a significant fraction of free radicals 10–13. However, such a posttreatment annealing is sometimes omitted 14…”

“…In the case of a modified material demonstrating a preferred orientation and anisotropic properties, the location of the sample, especially the orientation of the working surface of the acetabular cup of the endoprosthesis with respect to the direction of that orientation, is of utmost importance. An increase in the resistance to wear by 3–5 times is frequently observed in such systems but only when the plane of the tribological interaction is parallel to the direction of the prior deformation, whereas the direction of movement/sliding is preferentially perpendicular to that deformation direction 11–14. Marrs et al12 suggested, however, that such a significant improvement in the tribological properties can be achieved only in the case of a bidirectional or multidirectional movement during the interaction with a smooth surface of the CoCr counterspecimen.…”