On the assessment of oxidative and microstructural changes after in vivo degradation of historical UHMWPE knee components by means of vibrational spectroscopies and nanoindentation

Abstract

This study reports on the suitability of different experimental techniques to evaluate chemical, microstructural and mechanical changes associated with in vivo oxidation encountered in historical polyethylene components. To accomplish this aim, eight traceable tibial inserts were analyzed after revision surgery. The knee bearings were gamma sterilized in air and implanted for an average of 11.5 years after a shelf life no longer than one year. Characterization of oxidation and transvinylene indexes, crystallinity, amorphous and intermediate phase fractions, along with hardness and surface modulus, were performed in transverse sections of each bearing using Fourier transform infrared spectroscopy, Raman spectroscopy, and nanoindentation, respectively. Generally, subsurface maxima in the crystallinity, oxidation index, and hardness were observed at a depth of about 1 mm in all of the bearings. The superior surfaces and anterior-posterior faces of the inserts exhibited significantly higher oxidation and greater crystallinity than the inferior side. These observations suggest that the metallic tray may limit the access of molecular oxygen to the backside of the tibial inserts. We conclude that chemical, physical, and mechanical property data confirm the occurrence of in vivo degradation in the long-term implanted knee components following gamma irradiation in air. Furthermore, infrared spectroscopy alone appeared to provide excellent insight into the oxidation and crystallization state of the in vivo oxidized polyethylene.

Long-term accelerated weathering of HAS stabilized PE and PP plaques: Compliance of ESRI, IR, and microhardness data characterizing heterogeneity of photooxidation

“…The oxidation index (OI) was determined as the ratio of the carbonyl band area (1720 cm À1 ) to the methylene band area (1370 cm À1 ) [24]. The crystallinity index (CI) was calculated using the formula CI ¼ CA/(CA þ 0.3), where CA is the ratio of the area of the band at 1897 cm À1 (assigned to the PE crystalline phase) to the area of the band at 1303 cm À1 (assigned to the PE amorphous phase) [20,25]. The Tinuvin ® 770 stabilizer index (SI) was defined in this work as follows: the difference between area of Tinuvin ® 770 specific band (1170 cm À1 ) and the area of small overlapping PE specific band (1176 cm À1 ) was divided by the intensity of a Tinuvin ® 770 independent standard, where the standard was defined as a ratio of the PE crystalline band area (peak at 1897 cm À1 , see above) and the crystallinity index CI.…”

“…Information on heterogeneity of photoxidation processes inferred from analysis of nitroxide concentration profiles inside polymer plaques provided by ESRI can be complemented with profiles of oxidation index (OI), crystallinity index (CI), stabilizer concentration index (SI) and microhardness (MH), measured as a function of distance from the irradiated surface along the same direction (perpendicular to the irradiated surface of the plaque) [20,21]. The OI, CI and SI profiles can be determined by infrared microspectroscopy [19,22,23].…”

Microstructure, thermooxidation and mechanical behavior of a novel highly linear, vitamin E stabilized, UHMWPE

“…The present findings are in agreement with the three phase model and its evolution upon irradiation, regardless of the polyethylene resin. The three phase model has been also successfully utilized by other researchers in the assessment of microstructure, oxidation-induced, changes in moderately oxidized polyethylene knee retrievals, but its applicability to highly oxidized polyethylene was questioned [30].…”

Silicon Nitride Bearings for Total Joint Arthroplasty

“…Stretching and weakening of the crosslinks promotes reorganization of the polymeric structure and contributes to the formation of free radicals. In gamma-irradiated and artificially aged polyethylene, as is the case for these liners, more favorable conditions for oxidation are expected deeper within the liner as compared to the surface [105][106][107][108]. This might explain the negligible increase of crystallinity on the unworn surface.…”