No abstract

The processing techniques available for ultra‐high molecular weight polyethylene (UHMWPE) do not lead to a homogeneous material. The processed material exhibits particle boundaries (fusion defects) reflecting the powder flakes of the virgin resin. Hot isostatic pressing has been used in this study as a possible technique to produce a homogeneous, defect‐free material, and to study the effect of processing parameters on consolidation and other properties. The extent of consolidation was determined by optical microscopy using thin sections, and by scanning electron microscopy using cryofractured and solvent‐etched specimens. Processing temperature is the most important variable affecting consolidation; fusion defects can be eliminated by increasing the processing temperature. This is sometimes accompanied by the appearance of spherulties; however, the degree of crystallinity, melting point, and density remain constant. DMA results show that the molecular weight between entanglements increases and the entanglement structure changes with an increase in processing temperature. Polym. Eng. Sci. 44:1848–1857, 2004. © 2004 Society of Plastics Engineers.

Radiation crosslinked ultrahigh molecular weight polyethylene (UHMWPE) is the bearing surface material most commonly used in total joint arthroplasty because of its excellent wear resistance. Crosslinking agents such as peroxides can also effectively increase wear resistance but peroxide crosslinked UHMWPE has low oxidative stability. We hypothesized that the addition of an antioxidant to peroxide crosslinked UHMWPE could improve its oxidation resistance and result in mechanical, tribological, and oxidative properties equivalent to currently utilized radiation crosslinked UHMWPEs. Various vitamin E (0.1-1.0 wt % and peroxide concentration (0.5-1.5 wt %) combinations were studied to investigate changes in crosslink density, wear rate, mechanical properties, and oxidative stability in comparison to radiation crosslinked UHMWPE. Peroxide crosslinking was more efficient as compared to radiation crosslinking in the presence of vitamin E with the former resulting in lower wear rate with vitamin E concentrations above 0.3 wt %. The tensile mechanical properties were comparable to and the impact strength was higher than those of the clinically relevant radiation crosslinked controls. We also determined that gamma sterilization of peroxide crosslinked vitamin E blends improved wear resistance further. In summary, peroxide crosslinking of vitamin E-blended UHMWPE may provide a feasible and economical alternative to radiation for achieving clinically relevant properties for total joint implants using UHMWPE. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1379-1389, 2017.

Neonatal respiratory morbidity or being Caucasian were the population-specific independent risk factors for RSVH in 32-36 weeks of GA in Ireland, whereas the other identified independent risk factors mirrored those established in previous studies.