Fatigue crack propagation resistance of highly crosslinked polyethylene

A higher degree of cross-linking has been shown to improve wear properties of ultra-high molecular weight polyethylene in laboratory studies. However, cross-linking can also affect the mechanical properties of ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was determined for electron beam cross-linked ultra-high molecular weight polyethylene and compared with gamma irradiation cross-linked and noncross-linked polyethylene fatigue specimens. Crosslinking was done with different dosages of irradiation followed by melting. For one irradiation dose (50 kGy) extrusion and molding processes were compared. A fracture mechanics approach was used to determine how the degree of cross-linking affects resistance to crack propagation in ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was reduced in proportion to the irradiation dose. The type of irradiation (gamma or electron beam) or manufacturing method (extrusion or molding) did not affect fatigue crack propagation resistance. The reduced fatigue strength of highly cross-linked ultra-high molecular weight polyethylene could lead to mechanical failure in conditions that are associated with cyclic local tensile stresses.     

A chronic bile duct and intravenous cannulation model in conscious rabbits for pharmacokinetic studies.

In the development of novel pharmaceutical compounds, pharmacokinetic parameters, such as the extent of biliary excretion, must be characterized. Pharmacokinetic studies in nonrodent species, typically dogs, are generally required for new drug approvals. However, in some cases, rabbits may be a more desirable model. We developed a surgical procedure for the intermittent or continuous collection of bile for long-term use. This surgery involves the removal of the gallbladder and cannulation of the proximal and distal aspects of the common bile duct using a 40 cm flexible surgical-grade cannula. The cannula loop is passed subcutaneously and exteriorized between the scapulae to divert bile flow. During use, the proximal cannula segment is attached to a collection container placed in a nylon torso jacket worn by the animal, and the distal segment of catheter is sealed with a stainless-steel adapter. An auricular catheter, secured by ligatures, is placed aseptically into the lateral ear vein and the tip is advanced to the cranial vena cava for serial blood collection. Daily infusions of a heparinized saline "lock" ensure patency. These procedures have been used in 18 rabbits for up to 1 month without clinical complications. Complete blood counts, biochemical profiles, body weights, and bile flow were monitored weekly and reflected normal enterohepatic circulation.     

Resuscitative Endovascular Balloon Occlusion of the Aorta vs Pre-Peritoneal Packing in Patients with Pelvic Fracture

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A comparison of the mismatch negativity and a differential waveform response

A mismatch negativity response (MMN) and a new differential waveform were derived in an effort to evaluate a neural refractory or recovery effect in adult listeners. The MMN was elicited using oddball test runs in which the standard and deviant stimuli differed in frequency To derive the differential waveform, the same standard and deviant stimuli were presented alone. MMN responses were obtained by subtracting the averaged responses to standards from the deviants. The differential waveforms were obtained by subtracting the averaged responses to standards presented alone from deviants presented alone. Scalp topography for the MMN and differential waveforms were similar. A significant (p <.05) positive and negative correlation was found between the earlier and later components of the bimodal MMN and the NI and P2 component of the differential waveform, respectively. Further, N1 and P2 of the differential waveform were significant (p <.05) predictor variables of early and late peak amplitudes of the MMN. These results suggest that refractory effects may overlay/modify the morphology of the MMN waveform.     

Cleaning products and work-related asthma

To describe the characteristics of individuals with work-related asthma associated with exposure to cleaning products, data from the California-, Massachusetts-, Michigan-, and New Jersey state-based surveillance systems of work-related asthma were used to identify cases of asthma associated with exposure to cleaning products at work. From 1993 to 1997, 236 (12%) of the 1915 confirmed cases of work-related asthma identified by the four states were associated with exposure to cleaning products. Eighty percent of the reports were of new-onset asthma and 20% were work-aggravated asthma. Among the new-onset cases, 22% were consistent with reactive airways dysfunction syndrome. Individuals identified were generally women (75%), white non-Hispanic (68%), and 45 years or older (64%). Their most likely exposure had been in medical settings (39%), schools (13%), or hotels (6%), and they were most likely to work as janitor/cleaners (22%), nurse/nurses' aides (20%), or clerical staff (13%). However, cases were reported with exposure to cleaning products across a wide range of job titles. Cleaning products contain a diverse group of chemicals that are used in a wide range of industries and occupations as well as in the home. Their potential to cause or aggravate asthma has recently been recognized. Further work to characterize the specific agents and the circumstances of their use associated with asthma is needed. Additional research to investigate the frequency of adverse respiratory effects among regular users, such as housekeeping staff, is also needed. In the interim, we recommend attention to adequate ventilation, improved warning labels and Material Safety Data Sheets, and workplace training and education.