Influence of the load modelling during gait on the stress distribution in a femoral implant

Introduction

When designing and installing implants, stress analyses should be performed in conditions close to those of everyday use. Specifically, for femoral implants, cyclic loading during gait has been demonstrated to produce fatigue failure. However, there is still no consensus in the literature regarding which modelling procedure is the most appropriate to simulate implant working conditions. This work proposes a method for realistic load modelling of the human body during gait based on flexible multibody dynamics.

Method

The proposed dynamic method was applied to a case study of a lower limb implant that failed by fatigue. The computed stresses were compared to the stresses obtained using the other three methods found in the literature, which are principally based on static or quasi-static load modelling.

Results

For all compared methods, the maximum computed stress was located in the same region of the implant. The maximum stress provided using flexible multibody dynamics was equal to 346 MPa, which was 355% greater than the maximum value given by the static method and 18% greater than the value given by the quasi-static method.

Discussion and conclusion

The proposed dynamic method was in agreement with the conclusions of the previous failure analysis performed on the broken implant. Conversely, the static and quasi-static methods were not representative of the real loading conditions induced by gait. Moreover, the dynamic method emphasizes the pertinence of evaluating the fluctuations in the critical stress during the gait cycle, which is mandatory when studying fatigue failures.

     

Optimization of the fault-current limiting transformer

The fault current limiting transformer (FCLT) presented by J. Brochu et al. (see IEEE Trans. Power Delivery, vol.13, p.233-40, 1998) was designed with the purpose of increasing the total capacity of a transformer station without increasing short-circuit currents. In situations where such an IPC is closely coupled with parallel transformers, the FCLT installation can be simplified. The purpose of this letter is to describe the enhanced capabilities and outline the basic design criteria for this innovative IPC application. An application example provides typical component ratings, space requirements, and a budget cost estimate     

Pregnancy outcome following maternal use of the new selective serotonin reuptake inhibitors: a prospective controlled multicenter study

CONTEXT: Although a large number of women of reproductive age use new selective serotonin reuptake inhibitors (SSRIs) and half of all pregnancies are unplanned, no data exist on the safety of these agents for the human fetus. OBJECTIVE: To assess fetal safety and risk of fluvoxamine, paroxetine, and sertraline. DESIGN: A prospective, multicenter, controlled cohort study. SETTING: Nine Teratology Information Service centers in the United States and Canada. PATIENTS: All women who were counseled during pregnancy following exposure to a new SSRI and followed up by the participating centers. Controls were randomly selected from women counseled after exposure to nonteratogenic agents. MAIN OUTCOME MEASURES: Rates of major congenital malformations. RESULTS: A total of 267 women exposed to an SSRI and 267 controls were studied. Exposure to SSRIs was not associated with either increased risk for major malformations (9/222 live births [4.1%] vs 9/235 live births [3.8%] in the controls, relative risk, 1.06, 95% confidence interval, 0.43-2.62) or higher rates of miscarriage, stillbirth, or prematurity. Mean (SD) birth weights among SSRI users (3439 [505] g) were similar to the controls (3445 [610] g) as were the gestational ages (39.4 [1.7] weeks vs 39.4 [1.9] weeks). CONCLUSION: The new SSRIs, fluvoxamine, paroxetine, and sertraline, do not appear to increase the teratogenic risk when used in their recommended doses.     

Replacement of isoleucine-47 by threonine in the HPr protein of Streptococcus salivarius abrogates the preferential metabolism of glucose and fructose over lactose and melibiose but does not prevent the phosphorylation of HPr on serine-46

Budding of retroviruses from polarized epithelial Madin-Darby canine kidney cells (MDCK) takes place specifically at the basolateral membrane surface. This sorting event is suspected to require a specific signal harbored by the viral envelope glycoprotein and it was previously shown that, as for most basolateral proteins, the intracytoplasmic domain plays a crucial role in this targeting phenomenon. It is well known that tyrosine-based motifs are a central element in basolateral targeting signals. In the present study, site-directed mutagenesis was used to generate conservative or non-conservative substitutions of each four intracytoplasmic tyrosines of the human immunodeficiency virus (HIV-1) envelope glycoprotein. This approach revealed that the membrane-proximal tyrosine is essential to ensure both the basolateral localization of envelope glycoprotein and the basolateral targeting of HIV-1 virions. Substitutions of the membrane-proximal tyrosine did not appear to affect incorporation of envelope glycoprotein into the virions, as assayed by virion infectivity and protein content, nor its capability to ensure its role in viral infection, as determined by viral multiplication kinetics. Altogether, these results indicate that the intracytoplasmic domain of the HIV-1 envelope glycoprotein harbors a unique, tyrosine-based, basolateral targeting signal. Such a tyrosine-based targeting signal may play a fundamental role in HIV transmission and pathogenesis.     

Specific Surface Area of Barrier Mixtures at Various Outgas Temperatures

Specific surface area (SSA) values for Fe–smectite alone and mixtures comprising varying proportions of glacial till were determined by nitrogen-adsorption Brunauer–Emmett–Teller analysis under different outgassing temperatures. Additionally, the extent to which the SSA of a mixture was related to the SSA of its components was investigated. A theoretical value for mixture SSA can be computed by summing the products of component SSA and the corresponding weight fraction. This theoretical estimate may not always yield the same value as measured because of a variety of physical and chemical interactions that can lead to either aggregation or dispersion of the constituent matrix. The results are explained in terms of these interactions and within the context of SSA relevance to barrier performance. For mixtures comprising 90% glacial till and 10% Fe–smectite, measured specific surface areas were consistently higher than predicted values for outgassing temperatures beyond 100°C, with a maximum departure of 4 m2/g. An increase in the net repulsive force between particles is likely responsible for the observed change. A striking feature noted in the microporosity analysis is the collapse of the Fe–smectite interlayer at an outgassing temperature of 200°C, possibly as a result of iron reduction.     

Remodeling and angiotensin II responses of the uterine arcuate arteries of pregnant rats are altered by low- and high-sodium intake

Lowering and increasing sodium intake in pregnant rats evoke opposite changes in renin-angiotensin-aldosterone system (RAAS) activity and are associated with alterations of blood volume expansion. As augmented uterine blood flow during gestation is linked to increased circulatory volume, we wanted to determine if low- and high-sodium intakes affect the mechanical properties and angiotensin II (AngII) responses of the uterine vasculature. Non-pregnant and pregnant rats received a normal sodium (0.22% Na+) diet. On the 15th day of gestation some animals were moved to a low-sodium (0.03%) diet, whereas others were given NaCl supplementation as beverage (saline, 0.9% or 1.8%) for 7 days. All rats were killed after 7 days of treatment (eve of parturition). Uterine arcuate arteries (>100 microm) were set up in wire myographs under a tension equivalent to 50 mmHg transmural pressure. The pregnancy-associated increase in diameter of the uterine arteries was significantly attenuated on the low-sodium diet and 1.8% NaCl supplementation. The arcuate arteries of non-pregnant rats on the low-sodium diet showed markedly increased responses to AngII and phenylephrine (Phe). Pregnancy also resulted in heightened responses to AngII and Phe that were significantly reduced for the former agent in rats on the low-sodium diet. Sodium supplementation of non-pregnant rats did not affect the reactivity of the uterine arteries to AngII, but significantly reduced the effect of Phe (1 micromol/l). High salt also significantly diminished the elevated responses to AngII in the arteries of pregnant animals. It was observed that altered sodium intake affects the mechanical and reactive properties of the uterine arcuate arteries more importantly in pregnant than in non-pregnant rats. Low-salt intake similarly affected the reactivity of the uterine arcuate arteries to AngII and Phe, whereas high-salt intake more specifically affected AngII responses. These results showed that perturbations of sodium intake have major impacts on the structure and functions of the uterine arterial circulation, indicating RAAS involvement in uterine vascular remodeling and function during gestation.     

Structure de PbU2Se5

PbU₂Se₅ crystallizes in a monoclinic unit cell $\text{a}\text{= 8,605}\text{A}\text{?}$; $\text{b}\text{= 7,788}\text{A}\text{?}$; $\text{c}\text{= 12,27}\text{A}\text{?}$; β = 90° of space group $\text{P}\text{2}{}_1\text{c}$, Z = 4. The crystal structure has been determined for 1251 independant reflections and refined to a final R value of 0,068. Two kinds of uranium sites are found; the average U-Se distances are 2,97 Å for eight-coordination and 2,88 Å in seven-coordination. The average Pb-Se distance for eight-coordination is 3,20 Å. This structure explains the solid solution between PbU₂Se₅ and U₃Se₅.     

Rebuttal to comments by R. Dumas

Multibody System Dynamics -