Use of fracture mechanics theory in lifetime predictions for alumina and bioglass-coated alumina.

The fatigue behavior of alumina and bioglass-coated alumina was determined in air and biological test environments by the dynamic fatigue test technique in which strength is measured as a function of stressing rate. The good correlation found between the test data and fracture mechanics theory indicates that fatigue failure is controlled by the slow crack growth of preexisting flaws and that fracture mechanics theory can be used in making failure predictions for alumina and bioglass-coated alumina in biological environments. Thus, it is believed that lifetime predictions can be made for ceramic implants on the basis of short-term test data utilizing fracture mechanics principles.     

Estimation of the minimum number of test specimens for fatigue testing of acrylic bone cement

In the literature on fatigue testing of acrylic bone cements, data sets of various sizes have been used in different test series for the same cement formulation. There are two important consequences of this situation. First, it means that some test series last much longer than others, with all the implications for the cost of testing. Second, it makes drawing conclusions about the fatigue performance of a cement, based on the results of different literature series, a problematic issue. Clearly then, a recommendation as to what should be the minimum number of test specimens to use that would allow for confidence in the results of the statistical treatment of the test results (Gmin) would be desirable. In the present work, a method that could be used to culminate in such a recommendation is described. This method involves (i) obtaining experimental fatigue test results and (ii) analyzing those results using the Weibull probability distribution function and other statistical methods. This methodology is illustrated using fatigue life results obtained from uniaxial tension-compression fatigue tests on specimens fabricated from the polymerizing dough of one commercially available acrylic bone cement. For a tolerable error of 5%, we estimated Gmin to be either 7 (if the fatigue life results are treated using the two-parameter Weibull distribution function) or 11 (if the fatigue life results are treated using the three-parameter Weibull distribution function). To be on the conservative side, we therefore recommend that Gmin be 11. Three key limitations of the methodology presented here are discussed.     

Effects of simulated functional loading conditions on dentin, composite, and laminate structures

Use of composite restorations continues to increase, tempered by more potential problems when placed in posterior dentition. Thus, it is essential to understand how these materials function under stress-bearing clinical conditions. Because mastication is difficult to replicate in the laboratory, cyclic loading is frequently used within in vitro evaluations but often employs traditional fatigue testing, which typically does not simulate occlusal loading because higher stresses and loading frequencies are used, so failure mechanisms may be different. This investigation utilized relevant parameters (specimen size, loading frequency) to assess the effects of cyclic loading on flexural mechanical properties and fracture morphology of (coronal) dentin, composite, and dentin-adhesive-composite "laminate" structures. Incremental monitoring of flexural modulus on individual beams over 60,000 loading cycles revealed a gradual increase across materials; post hoc comparisons indicated statistical significance only for 1 versus 60k cycles. Paired specimens were tested (one exposed to 60k loading cycles, one to static loading only), and comparisons of flexural modulus and strength showed statistically significantly higher values for cyclically loaded specimens across materials, with no observable differences in fracture morphology. Localized reorganization of dentin collagen and polymer chains could have increased flexural modulus and strength during cyclic loading, which may have implications toward the life and failure mechanisms of clinical restorations and underlying tooth structure.     

Qualitative similarities in cognitive impairment associated with 24 h of sustained wakefulness and a blood alcohol concentration of 0.05%

Previous studies that have quantified fatigue-related cognitive impairment as blood alcohol concentration (BAC) equivalents have been limited by two issues: the effect of practice on tests of cognition and, more importantly, the statistic used to quantify change in cognitive performance. The current study addressed these issues by adopting an ABACA design, which allowed for the adequate control of practice effects, and by using effect size metrics, which enabled direct comparisons to be made in performance impairments as a result of fatigue (i.e. sustained wakefulness of 24 h) and alcohol (i.e. BAC of 0.05%). Cognitive performance under the fatigue and alcohol conditions required the use of the CogState battery. It was demonstrated that fatigue caused greater impairment than alcohol on the speed of continuous attention and memory and learning, and on the accuracy of complex matching. Alcohol was more detrimental than fatigue only on the accuracy of memory and learning. Performances on the remaining tasks were the same for both the fatigue and alcohol conditions. These differences and similarities in performance impairment are discussed emphasizing the deleterious cognitive effects of relatively short periods of sustained wakefulness.     

The Effects of Mindfulness-Based Interventions on Diabetes-Related Distress,Quality of Life,and Metabolic Control Among Persons with Diabetes: A Meta-Analytic Review

Mindfulness-based interventions (MBIs) have improved psychological outcomes for multiple chronic health conditions, including diabetes. A meta-analytic review of the literature was conducted on all located studies (n = 14) investigating MBIs that targeted diabetes-related distress (DRD) and diabetes-related outcomes among people with Type 1 and Type 2 diabetes. PsychInfo, PubMed, Medline, and Web of Science were searched for MBIs that were designed to improve DRD and other secondary outcomes, including quality of life and measures of metabolic control. A meta-analysis of these outcomes uncovered small-to-moderate effect sizes for intervention studies measuring pretreatment to posttreatment changes in DRD and metabolic control among treatment group participants. However, the pretreatment to follow-up comparisons for DRD and metabolic control were small and unreliable. For control groups, all pre-treatment to post-treatment and pre-treatment to follow-up comparisons were unreliable for all outcomes. A moderate effect size for treatment-control comparisons was found for intervention studies measuring quality of life outcomes at posttreatment, but not at follow-up comparisons. All other effect sizes for treatment-control comparisons were unreliable. Limitations and implications for MBIs among individuals with diabetes are discussed.     

A study of the fatigue properties of small diameter wires used in intramuscular electrodes

Single and multi-strand stainless steel and cobalt-nickel alloy wires, with strand diameters from 26 to 46 microns, were fatigue tested using a modified rotating bending test to determine what factors are most important in controlling fatigue life. The relation between cyclic strain and cyclic life was determined for each material by cyclically straining test specimens at various strain ranges and recording the number of cycles to failure. The results show that (a) the fatigue curves of the 316LVM, MP35N, DBS, and Syntacoben wires are very similar and have many of the same fatigue characteristics of specimens of large cross section. (b) Multi-stranded wires have the same average fatigue life as their individual constituent strands, but the variance of that life is smaller. (c) Deformities in the wire, which are created during the manufacturing, appear to have the effect of shortening the fatigue life of these small section wires. (d) Observation of wire fracture surfaces show a relatively small crack propagation zone and a large fast fracture zone suggesting that most of the fatigue life of these small wires is in the original crack formation, which creates a large stress concentration and quickly leads to wire failure. (e) The size of the wire cross sectional area is of secondary importance compared to the amplitude of the maximum cyclic strain of the individual strands in determining fatigue life of the cable. To maximize the fatigue life of electrodes in vivo, the highest fatigue life for a given bending radius of curvature is desired. This suggests wire strands should be manufactured at the smallest diameter possible (without introducing structural flaws) to maximize service life.     

Comparative fatigue behavior and toughness of remelted and annealed highly crosslinked polyethylenes

Highly cross-linked polyethylenes (HXLPEs) have been incorporated into the hip replacement armamentarium based on their improved wear resistance. However, two different methods of thermal treatment separate the orthopedic community as strategies to control potential long-term oxidation, and controversy remains with problems in the long-term use of acetabular liners (long-term oxidation, rim fracture after impingement, etc.). Meanwhile, the mechanical properties of HXLPEs that may alleviate these problems are still unclear. On the other hand, HXLPEs are scarcely used in knee replacements, as there exists concern about the probably reduced fatigue and fracture performances of these materials. Thus, our aim was to compare the effects of both thermal treatment regimes on mechanical properties and to associate these findings with the material microstructure. The fatigue behavior of annealed and remelted HXLPEs was characterized using short-term cyclic stress-strain, long-term fatigue, and fatigue crack propagation tests. On the other hand, impact tests, tensile experiments, and the J-integral multispecimen method allowed us to assess toughness. Microstructure features such as crosslink density, crystallinity percentage, and lamellar thickness were investigated by swelling measurements, differential scanning calorimetry, and transmission electron microscopy, respectively. This study confirms that annealing preserves mechanical properties better than remelting from both fatigue and fracture resistance points of view, and it remarks that a suitable selection of irradiation and stabilization conditions is needed to achieve optimal mechanical performances of ultra high molecular weight polyethylenes for each specific total joint replacement.     

Multiaxial fatigue behavior of conventional and highly crosslinked UHMWPE during cyclic small punch testing

Previous observations of reduced uniaxial elongation, fracture resistance, and crack propagation resistance of highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) have contributed to concern that the technology may not be appropriate for systems undergoing cyclic fatigue loading. Using a "total life" approach, we examined the influence of radiation crosslinking on the fatigue response of UHMWPE under cyclic loading via the small punch test. Our goal in this study was to evaluate the suitability of the small punch test for conducting miniature-specimen, cyclic loading, and fatigue experiments of conventional and highly crosslinked UHMWPE. We subjected four types of conventional and highly crosslinked UHMWPE to cyclic loading at 200 N/s and at body temperature in a small punch test apparatus. After failure, the fracture surfaces were characterized with the use of field emission scanning electron microscopy to evaluate the fatigue mechanisms. Cyclic small punch testing under load control was found to be an effective and repeatable method for relative assessment of the fatigue resistance of conventional and highly crosslinked UHMWPE specimens under multiaxial loading conditions. For each of the four conventional and highly crosslinked UHMWPE materials evaluated in this study, fatigue failures were consistently produced according to a power law relationship in the low cycle regimen, corresponding to failures below 10000 cycles. The fatigue failures were all found to be consistent with a single source of initiation and propagation to failure. Our long-term goal in this research is to develop miniature-specimen fatigue testing techniques for characterization of retrieved UHMWPE inserts.     

左心耳封堵器体外疲劳耐久性试验方法

目的心房颤动是临床上常见的心律失常之一,左心耳封堵术是在传统药物治疗之外发展的通过微创介入封堵左心耳以达到预防血栓栓塞目的的新技术。左心耳封堵器在体内承受周期循环载荷可能会导致封堵器的固定盘发生疲劳断裂,威胁患者生命,并且血流对阻流膜的冲击造成阻流膜破裂导致封堵效果不佳。因此需要建立一种疲劳耐久性试验方法去评估封堵器在人体中的耐疲劳性能。方法首先根据医药行业标准YY 0808—2010确定疲劳试验采用直径控制法;然后确定在疲劳试验中左心耳封堵器的规格、振幅;最后进行疲劳试验获得封堵器在1900万次疲劳(内皮化时间点)和3.8亿次疲劳(10年疲劳时间点)后的状态。结果1900万次疲劳后,阻流膜无破损、缝合线无松脱掉落、金属部位无断裂,封堵器未移动;3.8亿次疲劳后,左心耳封堵器金属部位无断裂、无磨损。结论本研究可为研发和生产左心耳封堵器的企业及科研机构提供一种便捷、高效的疲劳耐久性评价方法。     

Chronic fatigue syndrome and fibromyalgia: clinical assessment and treatment

Chronic fatigue syndrome (CFS) and fibromyalgia (FM) are closely related illnesses of uncertain etiology. This article reviews the research literature on these biobehavioral conditions, with an emphasis on explanatory models, clinical evaluation of comorbid psychiatric disorders, assessment of stress factors, pharmacologic and alternative therapies, and cognitive-behavioral treatment studies. Furthermore, clinical protocols suitable for professional practice are presented based on an integration of the authors' clinical observations with published data. The article concludes with the recognition that mental health professionals can offer substantial help to these patients.     

Fatigue behavior of packable composites

The aim of this study was to investigate the flexural fatigue behavior of 11 packable composites. Of each material 30 rectangular samples (1.2 x 5 x 35 mm) for flexural fatigue test were prepared. The clamped fracture strength and flexural fatigue limit (FFL) of each material were determined using a custom-made fatigue machine, after storage of the samples for one month in water at 37 degrees C. All data were analyzed using one-way ANOVA and Bonferroni/Dunn's test for multiple comparisons (p<0.05). Regression analysis was used to evaluate the relationship between elastic modulus (Abe et al., 2001), clamped fracture strength or FFL and inorganic filler fraction (vol%). The fracture strengths of all but two materials were in between those of the compact-filled densified composites and the microfine ones. The FFL of the packable composites tested were significantly lower than those of the compact-filled densified composites. Three of the tested materials showed even significantly lower FFL than did the microfine composites. There were statistically significant relationships between both the elastic modulus and the volumetric filler fraction (R(2)=0.974, p=1.990 x 10(-7)). The great diversity in packable composites makes clinical assessment necessary with regard to a justified use in posterior teeth.     

An examination of four models predicting fatigue in multiple sclerosis.

Fatigue is a common symptom of multiple sclerosis (MS) that is purported to cause significant distress and have detrimental effects on daily functioning, social and occupational obligations, and overall well-being. The prevalence of fatigue in MS is high, with 53-87% of patients reporting significant problems with fatigue across different studies reported in the literature. The cause of fatigue in MS is still poorly understood. Some researchers have suggested that fatigue is a direct consequence of the MS disease process, but several studies have failed to find a relationship between disease severity and MS fatigue. A number of investigations have reported that depression and sleep are significantly related to fatigue in MS, as well as to one another. The purpose of the present investigation was to examine the relationships among disease severity, depression, and sleep disturbance in MS, and their possible role in predicting fatigue. Four models were proposed to explore these relationships. The best fitting model showed that all three were significant independent contributors to fatigue in MS, accounting for 43% of the variance, with sleep disturbance reigning as the largest contributor. Furthermore, although disease severity predicted fatigue in our sample, both depression and sleep disturbance emerged as stronger predictors. These findings suggest that, beyond core physical/neurological MS symptomatology, there are other factors that contribute to fatigue in MS, namely, depression and sleep disturbance.     

人工心脏瓣膜疲劳寿命实验装置的驱动与测量电路

按照文献〔１〕提出的以人工心脏瓣膜在体内受力为参数进行体外模拟加速疲劳寿命试验的要求，作者设计了以直线电机为动力的人工心脏瓣膜体外加速疲劳寿命试验装置，为满足该装置的性能要求而设计的一套驱动与测量电路包括波形发生器。心率检测、瓣膜开闭计数和大功率放大器，系统经过调试运行，表明性能符合加速疲劳寿命试验要求，运行稳定可靠。     

Fatigue syndromes: new thoughts and reinterpretation of previous data.

Recently, the author has identified 19 patients who have complained of marked fatigue that had abnormal responses to copper test bracelets or necklaces. At this time, 8 have been shown to have at least one enzyme deficiency in the heme pathway. These patients have been diagnosed with multiple sclerosis, chronic fatigue syndrome and other non-specific diagnoses. A lengthy but still limited review of the literature was performed regarding the following conditions: multiple sclerosis (MS), hepatic porphyria (HP), chronic fatigue syndrome (CFS) and paralytic polio (PP). The text will focus on similar epidemiologies, laboratory findings and clinical courses. Copper as a common but not unique etiologic agent will be discussed; as will the heme pathway, a biologic process that may be disordered in all.     

Microtomography assessment of failure in acrylic bone cement

Micromechanical studies of fatigue and fracture processes in acrylic bone cement have been limited to surface examination techniques and indirect signal analysis. Observations may then be mechanically unrepresentative and/or affected by the presence of the free surface. To overcome such limiting factors the present study has utilised synchrotron X-ray microtomography for the observation of internal defects and failure processes that occurred within a commercial bone cement during loading. The high resolution and the edge detection capability (via phase contrast imaging) have enabled clear microstructural imaging of both strongly and weakly absorbing features, with an effective isotropic voxel size of 0.7 microm. Detailed assessment of fatigue damage processes in in vitro fatigue test specimens is also achieved. Present observations confirm a link with macroscopic failure and the presence of larger voids, at which crack initiation may be linked to the mechanical stress concentration set up by adjacent beads at pore surfaces. This study does not particularly support the suggested propensity for failure to occur via the inter-bead matrix; however crack deflections at matrix/bead interfaces and the incidence of crack arrest within beads do imply locally increased resistance to failure and potential improvements in global crack growth resistance via crack tip shielding.     

In vitro fatigue-crack growth and fracture toughness behavior of thin-walled superelastic Nitinol tube for endovascular stents: A basis for defining the effect of crack-like defects

Endovascular stents made of the superelastic nickel-titanium alloy Nitinol are subjected in service to tens of millions of loading cycles and even "single-event" overloads, both of which can potentially result in fracture and/or complete failure of the device. A fracture-mechanics-based methodology can provide a means to quantify relevant material parameters critical to the design against such failures. However, there is a dearth of relevant experimental data in the literature on such fracture-mechanics-based approaches to fatigue in Nitinol; furthermore, that which does exist invariably pertains to product forms that are not appropriate for stent manufacture, e.g., bulk Nitinol bar and strip. Consequently, the current work is focused on characterizing in vitro both subcritical and critical crack growth (fatigue-crack growth and R-curve fracture toughness) behavior in thin-walled ( approximately 400microm thick) Nitinol tubing similar to that used for medical device manufacture (following shape-setting procedures to flatten the material), with a resultant austenite finish temperature of A(f) approximately 25-30 degrees C, identical to self-expanding Nitinol stents. Fatigue-crack growth behavior, measured in Hanks' Balanced Saline Solution over a wide spectrum of growth rates (down to 10(-10)m/cycle) and at a range of positive load ratios (R=0.1-0.7), revealed significantly higher fatigue thresholds than had been previously reported for bulk Nitinol material. In addition, we examine the critical effect of test frequency, as most fatigue experiments on Nitinol have been performed at 30Hz or above, despite the fact that this is far in excess of the frequency of physiological loading. Finally, the fracture toughness properties are characterized in thin-section Nitinol and show marked crack-resistance (R-curve) behavior with a dependence on crack-growth angle (with respect to the tube drawing axis); additionally, measured toughnesses are found to be lower than has been previously reported for bulk Nitinol.     

Effect of Fatiguing Exercise on Longitudinal Bone Strain as Related to Stress Fracture in Humans

Muscular fatigue in the training athlete or military recruit has been hypothesized to cause increased bone strain that may contribute to the development of a stress fracture. Under normal circumstances, muscles exert a protective effect by contracting to reduce bending strains on cortical bone surfaces. In vivo strain studies in dogs show that muscle fatigue following strenuous exercise elevates bone strain and changes strain distribution. However, a similar experiment has yet to be performed in humans. The purpose of this work was to test the hypothesis in humans that strenuous fatiguing exercise causes an elevation in bone strain. It was also hypothesized that this elevation is greater in younger people than in older people due to the decline in muscle strength and endurance that normally occurs with age. To test these hypotheses, strain in the tibiae of seven human volunteers was measured during walking before and after a period of fatiguing exercise. Neither hypothesis was sustained. Post-hoc analysis of the strain data suggests that strain rate increases after fatigue with a greater increase in younger as opposed to older persons. Although not conclusive, this suggests that it is strain rate, rather than strain magnitude, that may be causal for stress fracture. © 1998 Biomedical Engineering Society. PAC98: 8745Dr, 8745Bp, 0180+b     

Comparison of in vivo and in vitro cytogenetic assay results

In vitro mutagenicity assays have largely replaced whole animal studies for screening compounds for genotoxic potential. While numerous comparisons have been made between the results of these assays and cancer assays in rodents, comparisons between in vitro and in vivo mutagenicity studies where the genetic endpoints are the same have not been published. To this extent, the published literature was reviewed for chemicals that had been tested in both in vitro and in vivo cytogenetic assays. Two hundred sixteen chemicals were identified, and definitive test results were obtained for 181 of them. Results from the two assays agreed on 126 of the compounds and of the 55 compounds for which the results did not agree, 53 were positive in vitro and negative in vivo. The proportion of "false positives" and the significance of the two "false negatives" are discussed.     

Future Directions in Father Inclusion,Engagement, Retention,and Positive Outcomes in Child and Adolescent Research

Fathers make important and unique contributions to positive child development. In spite of these findings, the research literature has lagged in the study of the role and impact of fathers on child development and in the development of effective approaches and interventions for fathers. Parameters for additional study include the inclusion of fathers in treatment outcome studies, the engagement of fathers within studies once included, the retention of fathers in interventions and studies once engaged, and the appropriate measurement of father-related outcomes. A systematic review of 64 studies indicated that there is evidence that fathers have been included within multiple studies aimed at improving parenting but that there are relatively fewer studies of other targeted outcomes such as coparenting. A set of recommendations for future directions in the next generation of father-focused studies in the child and adolescent psychology literature is presented, with an emphasis on improving study of the parameters of inclusion, engagement, retention, and measurement of outcomes.