Aldo M. Crugnola

On the pressure dependence of the wear of ultrahigh molecular weight polyethylene

Abstract The wear of polyethylene in bovine serum was evaluated as a function of load and molecular weight. The range and distribution of contact loadings simulated those which exist in currently available total hip and total knee prostheses. The wear increased exponentially with load at constant molecular weight. An increasing molecular weight parametrically displaced the exponential curve to higher loads, lowering the overall rate. It is proposed that the behavior of these materials be described in terms of a critical pressure-velocity product although the specific mechanisms for wear acceleration are not known in this case.

On the origins of high in vivo wear rates in polyethylene components of total joint prostheses.

Scanning electron microscope examination of the polyethylene components of 8 total hip and 16 total knee prostheses which had been implanted 4--96 months revealed that in many cases severe wear may not necessarily be caused by the presence of acrylic cement debris or other abrasives. The craters and cracks observed on severely worn surfaces are associated with fusion defects in the plastic itself. The fusion defects were seen to occur as a result of the low temperature necessary to mold ultrahigh molecular weight polyethylene and are (at least at present) difficult to avoid. As a consequence of the above and variability of molecular weight in this material, relatively wide variations in wear rate should be expected even in the absence of acrylic debris.

Effect of γ irradiation on the friction and wear of ultrahigh molecular weight polyethylene

Abstract The effect of sterilization γ irradiation on the friction and wear properties of ultrahigh molecular weight polyethylene (UHMWPE) sliding against stainless steel 316L in dry air at 23 °C was determined. A sliding pin-on-disk apparatus was used. Experimental conditions, in most cases, included a load of 1 kgf (9.8 N), a sliding velocity of 0.061–0.27 m s−1, and a sliding distance of 32000–578000 m. Although sterilization doses of 2.5 and 5.0 Mrad greatly altered the average molecular weight and the molecular weight distribution of UHMWPE, the friction and wear properties of the polymer were not significantly changed. Average wear rates of 1.6 × 10−15m3N−1m−1, 1.3 × 10−15m3N−1m−1 and 1.3 × 10−15m−3N−1m−1 were obtained for the unirradiated, the 2.5 Mrad γ-irradiated and the 5.0 Mrad γ-irradiated specimens respectively. The corresponding average friction coefficients for these three irradiation levels were 0.44, 0.44 and 0.38 respectively.

A method for the quantitative recovery of polyethylene wear debris from the simulated service of total joint prostheses

Abstract The quantitative recovery of polyethylene wear debris is particularly important in the evaluation of the wear of total joint prostheses as it is the only feasible experimental wear parameter and also because of the clinical significance of the rate of release of the debris into the surrounding tissues. A method has been developed to recover the debris from the synovial fluid or serum in the joint; it consists in essence of chemical digestion, filtration and stereological evaluation of the debris volume. This method separates the polyethylene debris from all the other suspended solids present in the joint fluid and can be reliably and reproducibly calibrated. It has revealed that gross differences exist in the wear rates of commercially available total hip prostheses.

The in vivo Biodegradation of Nylon 6 Utilized in a Particular IUD

The particular IUD of this study was composed of a plastic shield and a nylon 6 coated filament tail string. This IUD was unique, in the fact that its tail string was the only one (and has been to date) that consisted of a coated multifilament arrangement. Studies on the tail string have revealed bacteria and debris existing between the outer filaments that are underneath the coating. Other studies have reported that removed devices were found to exhibit an unusually high incidence of breaks in the tail string coating. Studies at the University of Lowell also found that upon examination of devices that had been in vivo for periods of two years or longer, 67% of these devices examined had breaks in the coating of the tail string. Investigations have determined that the design of the tail string was serving as an avenue of transport for the bacteria to bypass the protective cervical mucus barrier and enter the sterile uterine cavity through the breaks in the tail string coating. This mechanism has been suggested to account for the higher frequency of uterine infections associated with this device. Research at the University of Lowell was undertaken to study the degradation of the nylon 6 coating and to determine the in vivo degradation mechanism. The biochemistry of the fluids present in the reproductive tract were carefully documented and the more aggressive ones selected for in vitro trials. The results of the study revealed that the in vivo physical breakdown of the coating may depend upon a series of mechanisms and variables.

Advancing the Plastics Industry Through Education and Research

The Plastics Institute of America is a not-for-profit organization whose members come from industry, academia, and government. Its primary objective is to help advance the growth and progress of the plastics industry through education and research. Corporate members of the PIA include large and small producers of plastics products, commodity and engineering resins, additives for plastics, plastics packaging, and process machinery, as well as educators, international industry associations, government agencies, and trade publications. Major organizations that have representation on PIA’s board of directors include the Society of Plastics Industry, the Society of Plastics Engineers, the Society of Manufacturing Engineers, the Plastics Pioneers Association, and the National Plastics Center.