A study on stress corrosion cracking and hydrogen embrittlement of AZ31 magnesium alloy

The stress corrosion cracking (SCC) behavior and pre-exposure embrittlement of AZ31 magnesium alloy have been studied by slow strain rate tensile (SSRT) tests in this paper. It is showed that AZ31 sheet material is susceptible to SCC in distilled water, ASTM D1.387 solution, 0.01 M NaCl and 0.1 M NaCl solution. The AZ31 magnesium alloy also becomes embrittled if pre-exposed to 0.01 M NaCl solution prior to tensile testing. The degree of embrittlement increased with increasing the pre-exposure time, It is proposed that both the pre-exposure embrittlement and SCC were due to hydrogen which reduces the cohesive strength. i,e,. hydrogen embrittlement, (c) 2005 Elsevier B.V. All rights reserved.

Mechanical vibration preserves bone structure in rats treated with glucocorticoids

Glucocorticoids are an important cause of secondary osteoporosis in humans, which decreases bone quality and leads to fractures. Mechanical stimulation in the form of low-intensity and high-frequency vibration seems to be able to prevent bone loss and to stimulate bone formation. The objective of this study was to evaluate the effects of mechanical vibration on bone structure in rats treated with glucocorticoids. Thirty 3-month-old adult male Wistar rats were randomized to three groups: control (C), glucocorticoid (G), and glucocorticoid with vibration (CV). The G and GV groups received 3.5 mg/kg/day of methylprednisolone 5 days/week for a duration of 9 weeks, and the C group received vehicle (saline solution) during the same period. The CV group was vibrated on a special platform for 30 min per day, 5 days per week during the experiment. The platform was set to provide a vertical acceleration of 1 G and a frequency of 60 Hz. Skeletal bone mass was evaluated by total body densitometry (DXA). Fracture load threshold, undecalcified bone histomorphometry, and bone volume were measured in tibias. Glucocorticoids induced a significantly lower weight gain (-9.7%) and reduced the bone mineral content (-9.2%) and trabecular number (-41.8%) and increased the trabecular spacing (+98.0%) in the G group, when compared to the control (C). Vibration (CV) was able to significantly preserve (29.2%) of the trabecular number and decrease the trabecular spacing (+ 26.6%) compared to the G group, although these parameters did not reach C group values. The fracture load threshold was not different between groups, but vibration significantly augmented the bone volume of the tibia by 21.4% in the CV group compared to the C group. Our study demonstrated that low-intensity and high-frequency mechanical vibration was able to partially inhibit the deleterious consequences of glucocorticoids on bone structure in rats. (C) 2010 Elsevier Inc. All rights reserved.

The intercalated disc of monkey myocardial cells and Purkinje fibers as revealed by scanning electron microscopy

The intercalated discs of working myocardium and Purkinje fibers of the monkey heart were examined by scanning and transmission electron microscopy. The NaOH/ultrasonication technique resulted in the digestion of connective tissue and a separation of the intercellular junctions of intercalated discs, such that these could be visualized three-dimensionally. The intercalated discs of ventricular myocytes, atrial myocytes and Purkinje fibers vary considerably in number and configuration, as do the intercalated discs of the three different layers of the ventricular myocardium. Myocytes in the subepicardial, middle and subendocardial layers of the ventricle have 1-3, 4-5 and 5-6 intercalated discs at the end of these cells, respectively, Those in the endocardial layer are characterized by the presence of small laterally-placed intercalated discs. Atrial myocytes and Purkinje fibers usually only have 1-2 intercalated discs, Individual intercalated discs in ventricular myocytes have complicated stairs with 10-30 steps and corresponding risers, while those of atrial myocytes and Purkinje fibers have simple stairs with 1-3 steps and risers, Steps equivalent to the plicate segments are characterized by densely-packed microplicae and finger-like microprojections which greatly increase surface area in vertricular myocytes, Microprojections in atrial myocytes and Purkinje fibers are sparse by comparison, Risers equivalent to the interplicate segments containing large gap junctional areas are most numerous in left ventricular myocytes, followed by right ventricular myocytes, Purkinje fibers and atrial myocytes in decreasing order. The geometric arrangement of the various types of myocytes may be related with impulse propagation. Large intercalated discs of cell trunks and series branches may participate in longitudinal propagation, while small laterally-placed ones may be the site of transverse propagation.

Evaluation of molar teeth and buds in patients submitted to mandible distraction: Long-term results

Background: Despite all benefits offered by mandible distraction, complications and long-term consequences need to be evaluated to define its safety and morbidity. Forty mandible distractions were studied. Panoramic mandible radiographs obtained preoperatively, during distraction, and during the postoperative period were reviewed, with the intention of evaluating development and complications of molar buds and teeth in the distraction area. Methods: The mean patient age was 8.1 years. Twenty-five patients had craniofacial microsomia (one associated with a no. 10 facial cleft), five had temporomandibular joint ankylosis, two had familiar cases of auriculocondylar syndrome, one had a Tessier no. 30 facial cleft, and one had Treacher Collins syndrome. The severity of mandible hypoplasia was Pruzansky grade I in four cases, grade IIA in eight cases, grade 1113 in 16 cases, and grade III in one case. Mean radiographic follow-up was 44.8 months. Results: Molar buds located in the distraction area erupted without any deformity or displacement in 18 sides (45 percent). Fourteen cases presented distalization of a dental bud to a superior position in the mandibular ramus (four migrated back to the original position). Six molar buds presented perforations, four had shape deformities (two caused by dental fracture), and two had dental root injuries followed by root absorption lately. One case developed a dentigerous cyst. Conclusions: Almost half of the patients did not have any molar bud or tooth alterations after mandible distraction, and more than 20 percent presented only bud distalization. Therefore, preventive bud enucleation or tooth extraction should be avoided before mandible distraction.

A transformation toughening white cast iron

An experimental white cast iron with the unprecedented fracture tough ness of 40 MPa m(1/2) is currently being studied to determine the mechanisms of toughening. This paper reports the investigation of the role of strain-induced martensitic (SIM) transformation. The dendritic microconstituent in the toughened alloy consists primarily of retained austenite, with precipitated M(7)C(3) carbides and some martensite. Refrigeration experiments and differential scanning calorimetry (DSC) were used to demonstrate, firstly, that this retained austenite has an ''effective'' sub-ambient M(S) temperature and, secondly, that SIM transformation can occur at ambient temperatures. Comparison between room temperature and elevated temperature K-Ic tests showed that the observed SIM produces a transformation toughening response in the alloy, contributing to, but not fully accounting for, its high tough ness. SIM as a mechanism for transformation toughening has not previously been reported for white cast irons. Microhardness traverses on crack paths and X-ray diffraction (XRD) on fracture surfaces confirmed the interpretation of the K-Ic experiments. Further DSC and quantitative XRD showed that, as heat-treatment temperature is varied, there is a correlation between fracture toughness and the volume fraction of unstable retained austenite.

A single dose of zoledronic acid reverses the deleterious effects of glucocorticoids on titanium implant osseointegration

This study evaluates the effect of zoledronic acid (ZOL) on the osseointegration of titanium implants in rabbits with glucocorticoid (GC)-induced bone loss, and our findings demonstrated that a single dose of ZOL is able to reverse the detrimental effects of GCs on the osseointegration of titanium implants. The purpose of this study is to evaluate the effect of ZOL on the osseointegration of titanium implants in rabbits with GC-induced bone loss. Three groups of six NZW rabbits were treated for 18 weeks with saline (SALINE), GC (methylprednisolone, 0.35 mg/kg three times a week), or GC + ZOL (methylprednisolone + single dose of ZOL, 0.1 mg/kg). The animals received a titanium implant in the left tibia after 6 weeks and were killed at the 18th week. Bone mineral density (BMD) was measured with dual-energy X-ray absorptiometry at baseline, eighth week (W8), and 18th week (W18) after treatment to determine the change upon treatment (a dagger BMD). Histomorphometric and serum bone alkaline phosphatase analysis (BAP) were also performed. At W8, GC group had a significant reduction in lumbar spine and tibia BMD compared with SALINE (p = 0.003 and p = 0.000), as also observed for GC + ZOL group (p = 0.014 and p = 0.003) just 2 weeks after ZOL treatment. In contrast, at W18, the GC + ZOL had an evident BMD rescue with similar lumbar spine and tibia a dagger BMD compared with SALINE (0.043 +/- 0.006 vs. 0.055 +/- 0.009 g/cm(2), p = 0.457 and 0.027 +/- 0.003 vs. 0.041 +/- 0.011 g/cm(2), p = 0.232) and a significantly higher a dagger BMD compared with the GC (p = 0.024 and p = 0.001). Histomorphometry revealed that osseointegration was significantly reduced in GC (tibia cortical thickness and diameter, bone-implant contact, total and peri-implant bone area) whereas GC + ZOL had these parameters similar to SALINE (p > 0.05). Likewise, ZOL reversed the BAP alteration induced by GC. Our findings demonstrated that a single dose of ZOL is able to reverse the detrimental effects of glucocorticoids on the osseointegration of titanium implants, suggesting that ZOL therapy may improve the outcome of bone implants in patients with glucocorticoid-induced osteoporosis.

Effect of hardness on three very different forms of wear

Different abrasive wear tests have been applied to materials with hardnesses ranging from 80 HV (aluminium) to 1700 HV (tungsten carbide). The tests were: dry sand rubber wheel (DSRbrW); a similar test using a steel wheel (DSStlW); a new combined impact-abrasion test (FIA). The DSRbrW results were as expected, giving generally decreasing wear with increasing hardness. White cast irons and tool steels containing coarse, hard carbide particles performed better than more homogeneous materials of comparable hardness. When normalized to load and distance, the DSStlW results for the homogeneous materials were similar to the DSRbrW results. The multi-phase materials performed poorly in the DSStlW test, with volume loss for high-speed steel (880 HV) higher than that of aluminium. Within this group, wear increased with increasing hardness. These unexpected results are explained in terms of (a) differential friction coefficients of wheel and specimen, (b) increased fracture of sand, and (c) introduction of microfracture wear mechanisms. The FIA combined impact-abrasion results lacked clear correlations with hardness. The span of relative wear rates was similar to that reported for materials in ball mills. White cast irons at maximum hardness performed fairly poorly and showed evidence of microfracture. (C) 1997 Elsevier Science S.A.

Vitamin D insufficiency: A risk factor to vertebral fractures in community-dwelling elderly women

Objective:To determine the risk factors for the presence of moderate/severe vertebral fracture, specifically 25-hydroxyvitamin D (25-OHD). Study design: Cross-sectional study conducted for 2 years in the city of Sao Paulo, Brazil including community-dwelling elderly women. Methods: Bone mineral density (BMD), serum 25-OHD, intact parathyroid hormone (iPTH), calcium and estimated glomerular filtration rate (eGFR) were examined in 226 women without vertebral fractures (NO FRACTURE group) and 189 women with at least one moderate/severe vertebral fracture (FRACTURE group). Vertebral fracture assessment (VFA) was evaluated using both the Genant semiquantitative (SQ) approach and morphometry. Results: Patients in the NO FRACTURE group had lower age, increased height, higher calcium intake, and higher BMD compared to those patients in the FRACTURE group (p < 0.05). Of interest, serum levels of 25-OHD in the NO FRACTURE group were higher than those observed in the FRACTURE group (51.73 nmol/L vs. 42.31 nmol/L, p < 0.001). Reinforcing this finding, vitamin D insufficiency (25-OHD < 75 nmol/L) was observed less in the NO FRACTURE group (82.3% vs. 93.65%, p = 0.001). After adjustment for significant variables within the patient population (age, height, race, calcium intake, 25-OHD, eGFR and sites BMD), the logistic-regression analyses revealed that age (OR = 1.09, 95% Cl 1.04-1.14, p < 0.001) femoral neck BMD (OR = 0.7, 95% CI 0.6-0.82, p < 0.001) and 25-OHD <75 nmol/L (OR = 2.38, 95% CI 1.17-4.8, p = 0.016) remains a significant factor for vertebral fracture. Conclusion: Vitamin D insufficiency is a contributing factor for moderate/severe vertebral fractures. This result emphasizes the importance of including this modifiable risk factor in the evaluation of elderly women. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

Transmission electron microscopy of a transformation toughened white cast iron

Transmission electron microscopy has been used to study the microstructure of an experimental white cast iran, in which a combination of modified alloy composition and unconventional heat treatment has resulted in a fracture toughness of 40 MPa m(-1/2). Microstructural features of the alloy that contribute to the toughness improvement and hence distinguish it from conventional white irons have been investigated. In the as-cast condition the dendrites are fully austenitic and the eutectic consists of M7C3 carbides and martensite. During heat treatment at 1130 degrees C the austenite is partially destabilized by precipitation of chromium-rich M7C3 carbides. This results in a dendritic microconstituent consisting of bulk retained austenite and secondary carbides which are sheathed with martensite. The martensite sheaths, which contain interlath films of retained austenite, are irregular in shape with some laths extending into the bulk retained austenite. Emphasis has been placed on the morphology, distribution, and stability of the retained austenite and its transformation products in the dendrites. The implications of these findings on the transformation toughening mechanism in this alloy are discussed.

Subclavian Vein an Unusual Access for the Removal of Intravascular Foreign Bodies

Catheter migration or catheter fracture and consequent migration of a fragment is a rare complication that occurs in 1% of the patients. Despite the low incidence, embolization may cause severe and potentially fatal complications, with the mortality rates varying between 24 and 60%. The gold standard treatment for this condition is the extraction of the fragmented catheter by the intravascular percutaneous route, through the common femoral vein. If it is not available, the extraction procedure must be performed through an alternative access. This article describes a fully successful removal of a fragmented catheter by percutaneous intravascular access obtained through the right subclavian vein.

Altered loading patterns and femoral bone mineral density in children with unilateral Legg-Calve-Perthes disease

Maximization of bone accrual during the growing years is thought to be an important factor in minimizing fracture risk in old age. Mechanical loading through physical activity has been recommended as a modality for the conservation of bone mineral in adults; however, few studies have evaluated the impact of different loading regimes in growing children. The purpose of this study was to compare bone mineral density (BMD) in weight-bearing and non-weight-bearing limbs in 17 children with unilateral Legg Calve Perthes Disease (LCPD). Children with this condition have an altered weight-bearing pattern whereby there is increased mechanical loading on the noninvolved normal hip and reduced loading on the involved painful hip. Thus, these children provide a unique opportunity to study the impact of differential mechanical loading on BMD during the growing years while controlling for genetic disposition. BMD at four regions of the proximal femur (trochanter, intertrochanter, femoral neck, total of the regions) was measured using dual energy x-ray absorptiometry (DXA), and the values were compared between the involved and noninvolved sides of the children with LCPD. The BMD of both sides also were compared with normative values based on both chronological and skeletal age data. A significantly higher BMD was found on the noninvolved side over the involved side for all regions (P

Calcium intake and metabolic bone disease after eight years of Roux-en-Y gastric bypass

Background Roux-en-Y gastric bypass (RYGBP) has been found to be the most efficient way to lose weight and maintain the weight loss in morbid obesity. However, with the formation of a new stomach and the modification of intestinal anatomy, there are significant changes on physiological properties of these organs that lead to nutrient deficiency, including calcium. The objectives of this study were to evaluate calcium intake, bone metabolism, and prevalence of metabolic bone disease in women subjected to RYGBP after 8 years. Methods Food frequency questionnaire and 3-day dietary recall, laboratory tests of bone metabolism and bone mineral density were accessed. Results Calcium intake was below the recommendation in all women. Serum PTH and alkaline phosphatase were elevated, whereas vitamin D and urinary calcium were significantly lower. Also, a higher prevalence of metabolic bone disease than the one expected for the normal population at the same age was noted. Conclusion These data suggest that metabolic bone disease could be a complication of this type of surgery.

Scanning electron microscopy as an auxiliary method in the study of exhumed bones

Scanning electronmicroscopy (SEM) has been used in forensic science in many ways. The reports of cases in which SEM has been used as an auxiliary method in the investigation of exhumed bones are rare. In this article, we report an exhumation that was made to determine if a seized weapon could have been used in a homicide. We used SEM to analyze a fracture in the interior of the skull of the victim. The findings described in this article showed us that it is possible to develop new researches in this field. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Partial lesions of the intratemporal segment of the facial nerve: Graft versus partial reconstruction

Objectives: In cases of partial lesions of the intratemporal segment of the facial nerve, should the surgeon perform an intraoperative partial reconstruction, or partially remove the injured segment and place a graft? We present results from partial lesion reconstruction on the intratemporal segment of the facial nerve. Methods: A retrospective study on 42 patients who presented partial lesions on the intratemporal segment of the facial nerve was performed between 1988 and 2005. The patients were divided into 3 groups based on the procedure used: interposition of the partial graft on the injured area of the nerve (group 1; 12 patients); keeping the preserved part and performing tubulization (group 2; 8 patients); and dividing the parts of the injured nerve (proximal and distal) and placing a total graft of the sural nerve (group 3; 22 patients). Results: Fracture of the temporal bone was the most frequent cause of the lesion in all groups, followed by iatrogenic causes (p < 0.005). Those who obtained results lower than or equal to III on the House-Brackmann scale were 1 (8.3%) of the patients in group 1, none (0.0%) of the patients in group 2, and 15 (68.2%) of the patients in group 3 (p < 0.001). Conclusions: The best surgical technique for therapy of a partial lesion of the facial nerve is still questionable. Among these 42 patients, the best results were those from the total graft of the facial nerve.