The effects of radiation sterilization on the properties of ultrahigh molecular weight polyethylene

Abstract

The effects of radiation sterilization on ultrahigh molecular weight polyethylene were explored by freeze fractures, electron spin resonance, absorption of aqueous media, density measurements, small-angle and wide-angle x-ray scatter, differential scanning calorimetry, infrared and ultraviolet-visible spectrometry, static and dynamic mechanical fatigue measurements, and standard environmental stress cracking measurements. The rate of fluid absorption increased significantly due to the appearance of carbonyl groups. As the fluids were absorbed, density increased and small-angle x-ray scatter (SAXS) intensity diminished slightly, as expected. Small changes in mechanical properties (e.g., tensile properties and dynamic spectrum) were always consistent with the cross-linking which occurs after irradiation; the only significant mechanical deterioration was in the fatigue properties. The nonspherulitic, inhibited crystallinity which characterized this material and which is responsible for its excellent static resistance to environmental stress cracking was not at all changed.

Analysis of ultrahigh molecular weight polyethylene failure in artificial knee joints: Thermal effect on long-term performance

“…10 Two mechanisms responsible for the subsurface damage were proposed in the literature. High von Mises stresses 5,6,20 and ␥ sterilization 11,21,22 (when this was used) are two explanations that were offered as being responsible for this subsurface damage. We propose that the thermal effect plays an important role, especially in the region below the articulating surface of the UHMWPE component.…”

Relationship between morphology and mechanical properties of ultra high molecular weight polythylene :

“…Second, the behavior shown in Figure 16 is clearly not that predicted by equation (4) since there is a decided frequency dependence associated with the time to failure under zero-tension sinusoidal loading. In short, the Bailey criterion does not apply.…”

“…The report covers the second year of a four year project concerned with the relatship between morphology and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) . Various aspects of the UHMWPE being investigated include (1) the establishment of procedures for compression molding (under vacuum) sheets and cylinders of the polymer, (2) the influence of thermal history and molecular weight on the time dependent mechanical behavior such as creep and stress relaxation in both uniaxial extension and compressioii, (3) dynamic fatigue under conditions of zero-tension sinusoidal loading, (4) environmental stress-crack resistance, and (5) the optical and electron microscopy of sheets of the UHMWPE which have been deformed to varying degrees in uniaxial extension. ;-4i' …”

“…It should be borne in mind however that the implants were subject to sterilization by irradiation, a treatment which may have affected their densities [3,4]. The UHMWPE powder is Initially compacted in the mold at room temperature using an arbor press.…”

Is Polyethylene Still the Best Prosthetic Bearing Surface?

“…It is known that gamma irradiation breaks down some of the polymer chains and creates reactive sites in the molecular structure which are more susceptible to oxidative attack. This may lead to progressive degradation of the polymer with time after sterilisation; the predominant mechanical effect is embrittlement (Winslow, Matreyek and Stills 1965;Plester 1970;Nusbaum and Rose 1979;Roe et al 1981;Bostrom et al 1994). Other workers have demonstrated the existence of surface layers with a different morphology from that of the interior of polyethylene prostheses in relation to fusion defects (Wrona et al 1994).…”