Effect of Water and Serum Absorption on Wear of Unirradiated and Crosslinked UHMWPE Orthopedic Bearing Materials

Abstract

In addition to confounding mass-based wear measurements in serum-lubricated hip simulator experiments, fluid absorption by the acetabular cups may simultaneously modify the wear resistance of the ultra-high molecular weight polyethylene (UHMWPE) from which they are composed. To decouple the fluid absorption and wear processes enabling clearer investigation of this effect, absorption was first imposed during an initial stage where UHMWPE was exposed to pressurized (10 MPa) fluid. This was followed by a second stage, where resultant wear behavior was assessed by a multidirectional pin-on-flat technique that, though still providing a serum-lubricating environment, does not promote the simultaneous fluid absorption occurring in hip simulator testing. Both unirradiated and highly crosslinked UHMWPE were investigated, each with both bovine calf serum and water soaking exposures of duration to 129 days. The pressurized soaking of a highly crosslinked UHMWPE decreased its wear resistance, causing an increase in wear rate by approximately 50% during subsequent serum-lubricated multidirectional pin-on-flat sliding tests as compared to non-soaked material. The magnitude of this effect did not appear to depend on whether the soaking fluid was water or serum, nor did it appear to depend on soak time provided it was at least of a 14-day duration, during which more rapid transient fluid absorption occurs. Such soaking did not produce as pronounced an effect on unirradiated UHMWPE, as its lack of wear resistance likely causes the absorption-affected surface region to be removed within the earliest stages of sliding contact.     

The application of satellite remote sensing for soil studies in upland areas of Southern Italy

Spectral data can supply useful information on soil spatial variability even when the soil surface is partially masked by vegetation. This paper reports the first results of research aiming to assess the possibilities and limits of satellite remote sensing data for studying soils in the Apennine Mountains of Southern Italy. This region is characterized by the presence of large areas of bare soils during certain times of the year, but also by the dissected terrain which strongly influences the spectral response of soils. The results presented show the potential of satellite remotely-sensed data to broadly predict certain soil parameters, such as organic matter (OM) and calcium carbonate content (CACAR), from radiance values. However, the results of a sub-scene spectral classification, illustrate a greater potential for satellite data to provide useful reconnaisance soil mapping information, which can be tested by limited ground checks