Sterility is required for medical devices use in invasive medical procedures, and for some situations in the food industry. Sterilization of heatsensitive or porous materials or devices, such as endoscopes, porous implants, liquid foodstuff, and liquid medicine, poses a challenge to current technologies. There has been a steady interest in using high-pressure carbon dioxide as a process medium for new sterilization technology. Among the potential advantages are that CO 2 may sterilize at low temperatures. This paper is a review of the technical and patent literature, including analysis of the microorganisms studied, important operating parameters, and deactivation mechanisms. The current research status and challenges are summarized at the end of this paper.

The mechanism of lubrication in normal human joints depends on loading and velocity conditions. Boundary lubrication, a mechanism in which layers of molecules separate opposing surfaces, occurs under severe loading. This study was aimed at characterizing the phospholipid composition of the adsorbed molecular layer on the surface of normal cartilage that performs as a boundary lubricant. The different types of phospholipid adsorbed onto the surface of cartilage were isolated by extraction and identified by chromatography on silica gel paper and mass spectroscopy. The main phospholipid classes identified were quantified by a phosphate assay. Gas chromatography and electrospray ionization mass spectrometry were used to further characterize the fatty acyl chains in each major phospholipid component and to identify the molecular species present. Phosphatidylcholine (41%), phosphatidylethanolamine (27%) and sphingomyelin (32%) were the major components of the lipid layer on the normal cartilage surface. For each lipid type, a mixture of fatty acids was detected, with a higher percentage of unsaturated species compared to saturated species. The most abundant fatty acid observed with all three lipid types was oleic acid (C18:l). Additional work to further quantify the molecular species using electrospray ionization mass spectrometry is recommended.

Function and wear of total knee arthroplasties were compared by analysis of damage patterns on polyethylene tibial inserts retrieved from patients (Group R) with inserts obtained after in vitro force-controlled knee joint wear simulation. Two simulator input profiles were evaluated, including standard walking (Group W), and combined walking and stair descent (Group W þ S), simulating varied activities and a more severe physiological environment. Damage regions on all inserts were quantitatively assessed. On average, inserts in all groups had internally rotated damage patterns and the greatest articular deformation in the lateral compartment. These patterns were more pronounced in Group W þ S compared to Group W. Deformation rates of simulated inserts were analogous to about six years of physiologic function. However, both groups of simulated inserts generally underestimated the magnitude of damage area and extent observed on retrieved inserts, consistent with differences in the simulator's tibiofemoral contact mechanics and those known to occur in patients during functional activities. Modification of simulator inputs, such as the increased anteroposterior excursion and more severe loading conditions in Group W þ S, can generate greater wear volume, larger damage areas, and increased surface deformation rates compared to standard inputs. ß

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