Deformation and Failure Mechanisms of Element-Substituted Thermoelectric Type-I and Type-VIII Clathrates

Clathrates are potential "phonon-glass, electron-crystal" thermoelectric semiconductors, whose structure of polyhedron stacks is very attractive. However, their mechanical properties have not yet met the requirements of industrial applications. Here, we report the ideal strength of element-substituted type-I and type-VIII clathrates and the shear deformation mechanism by using density functional theory. The results show that the framework element is the determinant of the intrinsic mechanical properties of the clathrates and is affected by sequential weakening of Si-Ge-Sn. The highest ideal shear strength is 8.71 GPa for I-Ba8Au6Si40 along the (110)/[001] slip system, which is attributed to the formation of higher-energy Si-Si covalent bonds. Meanwhile, the ideal shear strength of Ba-filled I/VIII clathrates (4.51/2.65 GPa) is higher than that of Sr-filled clathrates (3.64 GPa/1.91 GPa). In addition, the strength and ultimate strain of VIII-Ba8Ga16Sn30 can be significantly increased by the structural coordination accommodating with the stiffness of the Ga-Ge bond to achieve simultaneous bond breaking. Our findings demonstrate that the element substitution strategy is an effective approach for designing highly robust clathrates.

Optimization of Mechanical and Thermoelectric Properties of SnTe-Based Semiconductors by Mn Alloying Modulated Precipitation Evolution

Multiscale defects engineering offers a promising strategy for synergistically enhancing the thermoelectric and mechanical properties of thermoelectric semiconductors. However, the specific impact of individual defects, in particular precipitation, on mechanical properties remains ambiguous. In this work, the mechanical and thermoelectric properties of Sn1.03- x Mnx Te (x = 0-0.30) semiconductors are systematically studied. Mn-alloying induces dense dislocations and Mn nano-precipitates, resulting in an enhanced compressive strength with x increased to 0.15. Quantitative calculations are performed to assess the strengthening contributions including grain boundary, solid solution, dislocation, and precipitation strengthening. Due to the dominant contribution of precipitation strengthening, the yield strength of the x = 0.10 sample is improved by ≈74.5% in comparison to the Mn-free Sn1.03 Te. For x ≥ 0.15, numerous MnTe precipitates lead to a synergistic enhancement of strength-ductility. In addition, multiscale defects induced by Mn alloying can scatter phonons over a wide frequency spectrum. The peak figure of merit ZT of ≈1.3 and an ultralow lattice thermal conductivity of ≈0.35 Wm-1  K-1 are obtained at 873 K for x = 0.10 and x = 0.30 samples respectively. This work reveals tha precipitation evolution optimizes the mechanical and thermoelectric properties of Sn1.03- x Mnx Te semiconductors, which may hold potential implications for other thermoelectric systems.

Strain-Induced Defect Evolution for the Construction of Porous Cu2-xSe with Enhanced Thermoelectric Performance

Superionic Cu2-xSe, with disordered and even liquid-like Cu ions, has been extensively studied as a high efficiency thermoelectric material. However, the relationship between lattice stability and microstructure evolution in Cu2-xSe under strain, which is crucial for its application, has seldom been explored in previous research. In this study, we investigate the impacts of hydrostatic compression strain on the microstructural evolution and, consequently, its implications for thermoelectric performance. Molecular dynamics (MD) simulations show that high hydrostatic compression strain could induce local diffusion of Cu ions and Se twin evolution, resulting in the breaking and reforming of Cu-Se dynamic bonds and the unstable Se sublattice. The subsequent annealing process of the destabilized structure promoted Se evaporation from the sublattice and resulted in lotus-seedpod-like pores. The reduced sound velocity and intensified phonon scattering, due to pores, lead to a reduction in the lattice thermal conductivity from 0.44 W m-1 K-1 to 0.24 W m-1 K-1 at 800 K, a decrease of approximately 45%, in the porous Cu1.92Se sample. These findings reveal the relationship between stability and defect evolution in Cu2-xSe under high hydrostatic compression, offering a straightforward strategy of defect engineering for designing unique microstructures by leveraging the instability in superionic conductor materials.

Synergetic Enhancement of Strength-Ductility and Thermoelectric Properties of Ag2 Te by Domain Boundaries

Simultaneously improving the mechanical and thermoelectric (TE) properties is significant for the engineering applications of inorganic TE materials. In this work, a novel nanodomain strategy is developed for Ag2 Te compounds to yield 40% and 200% improved compressive strength (160 MPa) and fracture strain (16%) when compared to domain-free samples (115 MPa and 5.5%, respectively). The domained samples also achieve a 45% improvement in average ZT value. The domain boundaries (DBs) provide extra sites for dislocation nucleation while pinning the dislocation movement, resulting in superior strength and ductility. In addition, phonon scattering induced by DBs suppresses the lattice thermal conductivity of Ag2 Te and also reduces the weighted mobility. These findings provide new insights into grain and DB engineering for high-performance inorganic semiconductors with robust mechanical properties.

Compression Induced Deformation Twinning Evolution in Liquid-Like Cu2Se

For practical applications of copper selenide (Cu₂Se) thermoelectric (TE) materials with liquid-like behavior, it is essential to determine the structure-property relations as a function of temperature. Here, we investigate β-Cu₂Se structure evolution during uniaxial compression over the temperature range of 400-1000 K using molecular dynamics simulations. We find that at temperatures above 800 K, Cu₂Se exhibits poor stability with breaking order that is described as a liquid-like or hybrid structure comprising a rigid Se sublattice and mobile Cu ions. A uniaxial load causes accumulated structural heterogeneity that is alleviated by diffusion-induced accommodation of local deformations. With increasing strain, the deformation mode changes into a combination of compression and shear, accompanied by restructuring in terms of twinning. Interestingly, in addition to a plastic behavior rarely found in inorganic semiconductors, we find that higher temperature promotes deformation twinning in liquid-like Cu₂Se, showing the role of thermal instability, including Cu diffusion, in structural adaptation and mechanical modulation. These findings reveal the micromechanism of hybrid structural evolution as well as performance tuning through twinning, which provides a theoretical guide toward advanced Cu₂Se TE materials design.

Electronic Localization Derived Excellent Stability of Li Metal Anode with Ultrathin Alloy

Lithium metal is an ideal anode for next-generation high-energy-density batteries. However, lithium dendrite growth has impeded its commercial application. Herein, fabricating Li-based ultrathin alloys with electronic localization and high surface work function via depositing Bi, Al, or Au metals on the surface of copper foil for in situ alloying with lithium is proposed. It is discovered that the electronic localization can induce self-smoothing effect of Li ions, as a result, significantly suppressing the growth of dendritic lithium. Meanwhile, the high surface work function can effectively alleviate side reactions between the electrolyte and lithium. With the as-obtained ultrathin alloys as anodes, excellent cycling performance is achieved. The half cells run stably after more than 120 cycles under high capacity of 4 mAh cm^-2 . The S||Bi/Cu-Li full cell delivers a specific capacity of 736 mAh g^-1 after 200 cycles. This work provides a new strategy for fabricating long-life and high-capacity lithium batteries.

Deformation and Failure Mechanisms of Thermoelectric Type-I Clathrate Ba8Au6Ge40

Type-I clathrate Ba₈Au₆Ge₄₀, possessing an interesting structure stacked by polyhedrons, is a potential "phonon-glass, electron-crystal" thermoelectric material. However, the mechanical properties of Ba₈Au₆Ge₄₀ vital for industrial applications have not been clarified. Here, we report the first density functional theory calculations of the intrinsic mechanical properties of thermoelectric clathrate Ba₈Au₆Ge₄₀. Among the different loading directions, the {110}/⟨001⟩ shearing and ⟨110⟩ tension are the weakest, with strengths of 4.51 and 6.64 GPa, respectively. Under {110}/⟨001⟩ shearing, the Ge-Ge bonds undergo significant stretching and twisting, leading to a severe distortion of the tetrakaidecahedral cage, giving rise to the fast softening of the flank Au-Ge bonds. At a strain of 0.2655, the Au-Ge bonds suddenly break, resulting in the collapse of the cage and the failure of the material. Under a ⟨110⟩ tension, the stretching of the Ge-Ge bonds keeps accelerating the softening of the Au-Ge bonds in the top/bottom hexagons, which releases the stress and disables the structure. The Au-Ge bonds are more rigid, contributing two-thirds of the structural deformation resistance. This work provides a new insight to understand the failure mechanisms of type-I clathrates with varied framework constitutions, which should help inform the design of robust thermoelectric clathrate materials.

Order-Tuned Deformability of Bismuth Telluride Semiconductors: An Energy-Dissipation Strategy for Large Fracture Strain

In addition to thermoelectric (TE) performance tuning through defect or strain engineering, progress in mechanical research is of increasing importance to wearable applications of bismuth telluride (Bi₂Te₃) TE semiconductors, which are limited by poor deformability. For improving dislocation-controlled deformability, we clarify an order-tuned energy-dissipation strategy that facilitates large deformation through multilayer alternating slippage and stacking fault destabilization. Given that energy dissipation and dislocation motions are governed by van der Waals sacrificial bond (SB) behavior, molecular dynamics simulation is implemented to reveal the relation between the shear deformability and lattice order changes in Bi₂Te₃ crystals. Using the disorder parameter (D) that is defined according to the configurational energy distribution, the results of strain rates and initial crack effects show how the proper design of the initial structure and external conditions can suppress strain localization that would cause structural failure from the lack of energy dissipation, resulting in large homogeneous deformation of Bi₂Te₃ nanocrystals. This study uncovers the essence of the tuning mechanism in which highly deformable Bi₂Te₃ crystals should become disordered as slowly as possible until fracture. This highlights the role of the substructure evolution of SB-defect synergy that facilitates energy dissipation and performance stability during slipping. The disorder parameter D provides a bridge between micro/local mechanics and fracture strain, hinting at the possible mechanical improvement of Bi₂Te₃ semiconductors for designing flexible TE devices through order tuning and energy dissipation.

Rapid collagen-directed mineralization of calcium fluoride nanocrystals with periodically patterned nanostructures

Collagen fibrils present periodic structures, which provide space for intrafibrillar growth of oriented hydroxyapatite nanocrystals in bone and contribute to the good mechanical properties of bone. However, there are not many reports focused on bioprocess-inspired synthesis of non-native inorganic materials inside collagen fibrils and detailed forming processes of crystals inside collagen fibrils remain poorly understood. Herein, the rapid intrafibrillar mineralization of calcium fluoride nanocrystals with a periodically patterned nanostructure is demonstrated. The negatively charged calcium fluoride precursor phase infiltrates collagen fibrils through the gap zones creating an intricate periodic mineralization pattern. Later, the nanocrystals initially filling the gap zones only expand gradually into the remaining space within the collagen fibrils. Mineralized tendons with organized calcium fluoride nanocrystals acquire mechanical properties (indentation elastic modulus ∼25.1 GPa and hardness ∼1.5 GPa) comparable or even superior to those of native human dentin and lamellar bone. Understanding the mineral growth processes in collagen may facilitate the development of tissue engineering and repairing.

Synthesis of monodisperse rod-shaped silica particles through biotemplating of surface-functionalized bacteria

Mesoporous silica particles of controlled size and shape are potentially beneficial for many applications, but their usage may be limited by the complex procedure of fabrication. Biotemplating provides a facile approach to synthesize materials with desired shapes. Herein, a bioinspired design principle is adopted through displaying silaffin-derived 5R5 proteins on the surface of Escherichia coli by genetic manipulations. The genetically modified Escherichia coli provides a three-dimensional template to regulate the synthesis of rod-shaped silica. The silicification is initiated on the cell surface under the functionality of 5R5 proteins and subsequentially the inner space is gradually filled. Density functional theory simulation reveals the interfacial interactions between silica precursors and R5 peptides at the atomic scale. There is a large conformation change of this protein during biosilicification. Electrostatic interactions contribute to the high affinity between positively charged residues (Lys4, Arg16, Arg17) and negatively charged tetraethyl orthosilicate. Hydrogen bonds develop between Arg16 (OH), Arg17 (OH and NH), Leu19 (OH) residues and the forming silica agglomerates. In addition, the resulting rod-shaped silica copy of the bacteria can transform into mesoporous SiOx nanorods composed of carbon-coated nanoparticles after carbonization, which is shown to allow superior lithium storage performance.

Grain Boundaries Softening Thermoelectric Oxide BiCuSeO

Engineering grain boundaries (GBs) are effective in tuning the thermoelectric (TE) properties of TE materials, but the role of GB on mechanical properties, which is important for their commercial applications, remains unexplored. In this paper, we apply ab initio method to examine the ideal shear strength and failure mechanism of GBs in TE oxide BiCuSeO. We find that the ideal shear strength of the GB is much lower than that of the ideal single crystal. The atomic rearrangements accommodating the lattice and neighbor structure mismatch between different grains leads to the much weaker GB stiffness compared with grains. Failure of the GBs arises from either the distortion of the Cu-Se layers or the relative slip between Bi-O and Cu-Se layers. This work is crucial to illustrate the deformation of GBs, laying the basis for the development and design of mechanically robust polycrystalline TE materials.

Enhanced Strength Through Nanotwinning in the Thermoelectric Semiconductor InSb

The conversion efficiency (zT) of thermoelectric (TE) materials has been enhanced over the last two decades, but their engineering applications are hindered by the poor mechanical properties, especially the low strength at working conditions. Here we used density functional theory (DFT) to show a strength enhancement in the TE semiconductor InSb arising from the twin boundaries (TBs). This strengthening effect leads to an 11% enhancement of the ideal shear strength in flawless crystalline InSb where this theoretical strength is considered as an upper bound on the attainable strength for a realistic material. DFT calculations reveal that the directional covalent bond rearrangements at the TB accommodating the structural mismatch lead to the anisotropic resistance against the deformation combined with the enhanced TB rigidity. This produces a strong stress response in the nanotwinned InSb. This work provides a fundamental insight for understanding the deformation mechanism of nanotwinned TE semiconductors, which is beneficial for developing reliable TE devices.

Micro- and Macromechanical Properties of Thermoelectric Lead Chalcogenides

Both n- and p-type lead telluride (PbTe)-based thermoelectric (TE) materials display high TE efficiency, but the low fracture strength may limit their commercial applications. To find ways to improve these macroscopic mechanical properties, we report here the ideal strength and deformation mechanism of PbTe using density functional theory calculations. This provides structure-property relationships at the atomic scale that can be applied to estimate macroscopic mechanical properties such as fracture toughness. Among all the shear and tensile paths that are examined here, we find that the lowest ideal strength of PbTe is 3.46 GPa along the (001)/⟨100⟩ slip system. This leads to an estimated fracture toughness of 0.28 MPa m^1/2 based on its ideal stress-strain relation, which is in good agreement with our experimental measurement of 0.59 MPa m^1/2. We find that softening and breaking of the ionic Pb-Te bond leads to the structural collapse. To improve the mechanical strength of PbTe, we suggest strengthening the structural stiffness of the ionic Pb-Te framework through an alloying strategy, such as alloying PbTe with isotypic PbSe or PbS. This point defect strategy has a great potential to develop high-performance PbTe-based materials with robust mechanical properties, which may also be applied to other materials and applications.

Superstrengthening Bi_{2}Te_{3} through Nanotwinning

Bismuth telluride (Bi_{2}Te_{3}) based thermoelectric (TE) materials have been commercialized successfully as solid-state power generators, but their low mechanical strength suggests that these materials may not be reliable for long-term use in TE devices. Here we use density functional theory to show that the ideal shear strength of Bi_{2}Te_{3} can be significantly enhanced up to 215% by imposing nanoscale twins. We reveal that the origin of the low strength in single crystalline Bi_{2}Te_{3} is the weak van der Waals interaction between the Te1 coupling two Te1─Bi─Te2─Bi─Te1 five-layer quint substructures. However, we demonstrate here a surprising result that forming twin boundaries between the Te1 atoms of adjacent quints greatly strengthens the interaction between them, leading to a tripling of the ideal shear strength in nanotwinned Bi_{2}Te_{3} (0.6 GPa) compared to that in the single crystalline material (0.19 GPa). This grain boundary engineering strategy opens a new pathway for designing robust Bi_{2}Te_{3} TE semiconductors for high-performance TE devices.

Multi-Scale Microstructural Thermoelectric Materials: Transport Behavior, Non-Equilibrium Preparation, and Applications

Considering only about one third of the world's energy consumption is effectively utilized for functional uses, and the remaining is dissipated as waste heat, thermoelectric (TE) materials, which offer a direct and clean thermal-to-electric conversion pathway, have generated a tremendous worldwide interest. The last two decades have witnessed a remarkable development in TE materials. This Review summarizes the efforts devoted to the study of non-equilibrium synthesis of TE materials with multi-scale structures, their transport behavior, and areas of applications. Studies that work towards the ultimate goal of developing highly efficient TE materials possessing multi-scale architectures are highlighted, encompassing the optimization of TE performance via engineering the structures with different dimensional aspects spanning from the atomic and molecular scales, to nanometer sizes, and to the mesoscale. In consideration of the practical applications of high-performance TE materials, the non-equilibrium approaches offer a fast and controllable fabrication of multi-scale microstructures, and their scale up to industrial-size manufacturing is emphasized here. Finally, the design of two integrated power generating TE systems are described-a solar thermoelectric-photovoltaic hybrid system and a vehicle waste heat harvesting system-that represent perhaps the most important applications of thermoelectricity in the energy conversion area.

Structure and Failure Mechanism of the Thermoelectric CoSb3/TiCoSb Interface

The brittle behavior and low strength of CoSb₃/TiCoSb interface are serious issues concerning the engineering applications of CoSb₃ based or CoSb₃/TiCoSb segmented thermoelectric devices. To illustrate the failure mechanism of the CoSb₃/TiCoSb interface, we apply density functional theory to investigate the interfacial behavior and examine the response during tensile deformations. We find that both CoSb₃(100)/TiCoSb(111) and CoSb₃(100)/TiCoSb(110) are energetically favorable interfacial structures. Failure of the CoSb₃/TiCoSb interface occurs in CoSb₃ since the structural stiffness of CoSb₃ is much weaker than that of TiCoSb. This failure within CoSb₃ can be explained through the softening of the Sb-Sb bond along with the cleavage of the Co-Sb bond in the interface. The failure mechanism of the CoSb₃/TiCoSb interface is similar to that of bulk CoSb₃, but the ideal tensile strength and failure strain of the CoSb₃/TiCoSb interface are much lower than those of bulk CoSb₃. This can be attributed to the weakened stiffness of the Co-Sb framework because of structural rearrangement near the interfacial region.

Effects of calcination temperatures on photocatalytic activity of SnO2/TiO2 composite films prepared by an EPD method

SnO2/TiO2 composite films were fabricated on transparent electro-conductive glass substrates (F-doped SnO2-coated glass:FTO glass) via an electrophoretic deposition (EPD) method using Degussa P25 as raw materials, and were further characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), UV-vis diffuse reflectance spectra and Photoluminescence spectra (PL). XRD and XPS results confirmed that the films were composed of TiO2 and SnO2. FESEM images indicated that the as-prepared TiO2 films had roughness surfaces, which consisted of nano-sized particles. The effects of calcination temperatures on the surface morphology, microstructures and photocatalytic activity of SnO2/TiO2 composite films were further investigated. All the prepared SnO2/TiO2 composite films exhibited high photocatalytic activities for photocatalytic decolorization of Rhodamine-B aqueous solution. At 400 degrees C, the SnO2/TiO2 composite films showed the highest photocatalytic activity due to synergetic effects of low sodium content, good crystallization, appropriate phase composition and slower recombination rate of photogenerated charge carriers.

Primary lateral sclerosis: A heterogeneous disorder composed of different subtypes?

OBJECTIVE

To determine identifiable subgroups of patients with primary lateral sclerosis (PLS) with distinct clinical features as a first step in identifying patients likely to have the same disorder.

METHODS

Twenty-five patients meeting previously proposed diagnostic criteria for PLS were seen for examination, measurement of gait and finger tapping speed, and physiologic tests to assess motor pathways. Motor cortex excitability and central motor conduction time were assessed with transcranial magnetic stimulation. Brainstem motor pathways were assessed by the acoustic startle reflex. MRS was performed in a subgroup of patients to assess metabolites in the motor cortex.

RESULTS

Fifty-six percent of the patients with PLS had a similar pattern of symptom progression, which the authors termed ascending. In these patients spasticity began in the legs and progressed slowly and steadily. Spasticity in the arms developed 3.6 years after the legs, on average, and speech impairment followed 1.5 years later. Motor evoked potentials were absent. MRS showed a mean reduction of N-acetylaspartate/creatinine in the motor cortex. The remaining patients with PLS had heterogeneous patterns of symptom progression and physiology.

CONCLUSIONS

Patients with PLS with an ascending progression of symptoms form a distinct clinical subgroup that may be amenable to investigations of etiology and treatment.

Effects of deletion of streptokinase residues 48-59 on plasminogen activation

Streptokinase (SK) is a thrombolytic agent widely used for the clinical treatment of clotting disorders such as heart attack. The treatment is based on the ability of SK to bind plasminogen (Pg) or plasmin (Pm), forming complexes that proteolytically activate other Pg molecules to Pm, which carries out fibrinolysis. SK contains three major domains. The N-terminal domain, SKalpha, provides the complex with substrate recognition towards Pg. SKalpha contains a unique mobile loop, residues 45-70, absent in the corresponding domains of other bacterial Pg activators. To study the roles of this loop, we deleted 12 residues in this loop in both full-length SK and the SKalpha fragment. Kinetic data indicate that this loop participates in the recognition of substrate Pg, but does not function in the active site formation in the activator complex. Two crystal structures of the deletion mutant of SKalpha (SKalpha(delta)) complexed with the protease domain of Pg were determined. While the structure of SKalpha(delta) is essentially the same as this domain in full-length SK, the mode of SK-Pg interaction was however different from a previously observed structure. Even though mutagenesis studies indicated that the current complex represents a minor interacting form in solution, the binding to SKalpha(delta) triggered similar conformational changes in the Pg active site in both crystal forms.

Effects of dietary phytoestrogen on global myocardial ischemia-reperfusion injury in isolated female rat hearts

We investigated the effects of phytoestrogen on global myocardial ischemia-reperfusion injury in five groups of female rats. A high-phytoestrogen group (HPE) was ovariectomized (Ovx) and fed a diet containing soybean protein and a high-isoflavone soy extract. Another Ovx group of rats was fed the same diet as the HPE group but treated with the estrogen receptor blocker ICI-182,780 (HPE + ICI). A third group of Ovx rats was fed a diet containing soybean protein alone (low-phytoestrogen content; LPE). A fourth Ovx group was fed a diet free of phytoestrogen (Ovx). The fifth group of rats was sham ovariectomized (sham). Hearts from all rats were subjected to 30 min of global, hypothermic (4 degrees C), cardioplegic ischemia and 120 min of normothermic (37 degrees C) reperfusion with oxygenated Krebs-Henseleit buffer. Compared with either the sham or the HPE group, the Ovx and HPE + ICI groups had significantly decreased first derivative of left ventricular pressure (dP/dt), coronary flow rate (CFR), nitrite production and mitochondrial respiratory function and significantly increased Ca2+ accumulation and myocardial histological and ultrastructural injury. The CFR of the LPE group was significantly different from that of either Ovx or HPE + ICI group but the dP/dt, nitrite production, Ca2+ accumulation, and mitochondrial function were not. Our results indicate that diets containing phytoestrogen extract play a cardioprotective role in global myocardial ischemia-reperfusion in female rats.

Regional characteristics of sulfur and lead isotope ratios in the atmosphere at several Chinese urban sites

Sulfur and lead isotope ratios in the atmosphere were measured at several selected sites (Harbin, Changchun, Dalian, Waliguan, Shanghai, Nanjing, Guiyang) in China and Tsukuba (Japan), to reveal regional sources characteristics over Eastern Asia. Average S isotope ratios for SO2 and sulfate in the atmosphere in China were close to those of the coals used in each region, indicating a considerable contribution of coal combustion to the sulfur compounds in the atmosphere. Most northern cities had around 5% sulfur isotope ratio, while Guiyang, a southwestern city in China, showed a considerably lower sulfur isotope ratio (about -3%) because of the unusually light sulfur isotope ratio of coals in this region. These were considerably different from the value (-1.4%) for Tsukuba (Japan). Lead isotope ratios also suggested that coal combustion considerably contributed to atmospheric lead in some cases in China. At the same time, influences by the emission of Chinese lead ores were also observed in northern cities. Seasonal variations of both sulfur and lead isotope ratios indicated the existence of a certain amount of industrial sources other than coal combustion. In addition, fractionation effect between SO2 and sulfate showed a seasonal tendency (high in winter (0-6%) and low in summer (-1-3%)), suggesting the oxidation pathway of SO2 changed seasonally.

Effect of estrogen on global myocardial ischemia-reperfusion injury in female rats

We investigated the effects of estrogen on global myocardial ischemia-reperfusion injury in rats that were ovariectomized (Ovx), sham-operated, or ovariectomized and then given 17beta-estradiol (E(2)beta) supplementation (Ovx+E(2)beta). Hearts were excised, cannulated, perfused with and then immersed in chilled (4 degrees C) cardioplegia solution for 30 min, and then retrogradely perfused with warm (37 degrees C), oxygenated Krebs-Henseleit bicarbonate buffer for 120 min. The coronary flow rate, first derivative of left ventricular pressure, and nitrite production were all significantly lower in Ovx than in sham-operated or Ovx+E(2)beta hearts. However, coronary flow rates or nitrate production were not consistently different throughout the entire reperfusion period. Ca(2+) accumulated more in Ovx rat hearts than in sham-operated or Ovx+E(2)beta hearts, and mitochondrial respiratory function was lower in Ovx hearts than in hearts from the other two groups. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of Ovx rat hearts but not in hearts from either of the other groups. Hematoxylin-basic fuchsin-picric acid-stained sections revealed fewer viable myocytes in hearts from the Ovx group than from the sham or Ovx+E(2)beta group. Transmission electron microscopy demonstrated more severely damaged mitochondria and ultrastructural damage to myocytes in Ovx rat hearts. Our results indicate that estrogen plays a cardioprotective role in global myocardial ischemia-reperfusion injury in female rats.

Myocardial ischemia-reperfusion injury in estrogen receptor-alpha knockout and wild-type mice

We investigated the function of estrogen receptor-alpha in global myocardial ischemia and reperfusion injury in male estrogen receptor-alpha knockout (ERKO) and wild-type mice. Mouse hearts were subjected to 45 min of global ischemia followed by 180 min of reperfusion. The hearts were excised, cannulated, and maintained in a chilled (4 degrees C) cardioplegia solution until warm (37 degrees C) oxygenated Krebs-Henseleit bicarbonate buffer was perfused through the coronary arteries. ERKO hearts started beating later and had a higher incidence of ventricular fibrillation and/or tachycardia than control hearts. Coronary flow rate was significantly lower in ERKO hearts during the 90- and 120-min periods of reperfusion. Ca(2+) accumulation was significantly greater following 30, 90, 120, 150, and 180 min of reperfusion in ERKO hearts. Nitrite production was significantly less in ERKO hearts following 90, 120, and 150 min of reperfusion. Myocardial reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was significantly lower in experimental ERKO hearts. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of ischemia-reperfused ERKO hearts but not in control tissues. Hematoxylin-basic fuchsin-picric acid-stained sections from experimental ERKO hearts had fewer viable myocytes compared with controls. Transmission electron microscopy revealed swollen and fragmented mitochondria with amorphous and granular bodies, loss of matrix, and rupture of cristae in experimental ERKO hearts. This is the first demonstration that estrogen receptor-alpha plays a cardioprotective role in ischemia-reperfusion injury in males.

Lack of involvement of neuronal nitric oxide synthase in the pathogenesis of a transgenic mouse model of familial amyotrophic lateral sclerosis

A subset of familial cases of amyotrophic lateral sclerosis are linked to missense mutations in copper/zinc superoxide dismutase type 1. Patients with missense mutations in copper/zinc superoxide dismutase type 1 develop a paralytic disease indistinguishable from sporadic amyotrophic lateral sclerosis through an unknown toxic gain of function. Nitric oxide reacts with the superoxide anion to form the strong oxidant, peroxynitrite, which participates in neuronal injury in a variety of model systems. Peroxynitrite is an alternate substrate for copper/zinc superoxide dismutase type 1, causing catalytic nitration of tyrosine residues in other proteins. Mutations in copper/zinc superoxide dismutase type 1 may disrupt the active site of the enzyme and permit greater access of peroxynitrite to copper, leading to increased nitration by peroxynitrite of critical cellular targets. To investigate whether neuronal-derived nitric oxide plays a role in the pathogenesis of familial amyotrophic lateral sclerosis, we examined the effects of three different nitric oxide synthase inhibitors: a non-selective nitric oxide synthase inhibitor, nitro-L-arginine methyl ester; a relatively selective inhibitor of neuronal nitric oxide synthase, 7-nitroindazole; and a novel highly selective neuronal nitric oxide synthase inhibitor, AR-R 17,477, in transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 (Gly-->Ala at position 93; G93A) containing a high transgene copy number and a low transgene copy number. AR-R 17,477, but not nitro-L-arginine methyl ester or 7-nitroindazole, significantly prolonged survival in both the high and low transgene transgenic mice. To determine whether neuronal nitric oxide synthase is involved in the pathogenesis resulting from the familial amyotrophic lateral sclerosis copper/zinc superoxide dismutase type 1 mutation, we produced mice with the copper/zinc superoxide dismutase type 1 mutation which lack the neuronal nitric oxide synthase gene. The transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 on neuronal nitric oxide synthase null background do not live significantly longer than transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1. Western blot analysis indicates the presence of two neuronal nitric oxide synthase-like immunoreactive bands in spinal cord homogenates of the neuronal nitric oxide synthase null mice, and residual neuronal nitric oxide synthase catalytic activity ( > 7%) is detected in the spinal cord of the transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 on neuronal nitric oxide synthase null background. This amount of residual activity probably does not account for lack of protection afforded by the disrupted neuronal nitric oxide synthase gene in the familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 mice. Immunological nitric oxide synthase is not detected in the copper/zinc superoxide dismutase type 1 mutant mice at several different ages, thus excluding immunological nitric oxide synthase as a contributor to the pathogenesis of familial amyotrophic lateral sclerosis. Levels of neuronal nitric oxide synthase as well as Ca2+-dependent nitric oxide synthase catalytic activity in the copper/zinc superoxide dismutase type 1 mutant mice do not differ from wild type mice. Endothelial nitric oxide synthase levels may be decreased in the copper/zinc superoxide dismutase type 1 mutant mice. Together, these results do not support a significant role for neuronal-derived nitric oxide in the pathogenesis of familial amyotrophic lateral sclerosis transgenic mice.

Thrombogenicity of polyethylene oxide-bonded Dacron sewing ring in a mechanical heart valve

BACKGROUND AND AIM OF THE STUDY

The aim of the study was to evaluate the effect of binding hydrophilic polyethylene oxide (PEO) onto Dacron fibers in the sewing ring of a mechanical heart valve (MHV), in terms of thrombogenicity of the prosthesis.

METHODS

The study was performed in blinded fashion. Six Yorkshire-cross pigs (bodyweight 35-45 kg) were implanted with MHVs, in the mitral annulus, with the PEO-treated sewing ring. An additional five pigs implanted with identical MHVs, but with untreated sewing rings, served as controls. PEO of chain-length 10,000 Da was grafted to Dacron fibers using gamma irradiation. PEO-bonded Dacron fibers (diameter 100 microns) were used to weave the sewing ring, which was then assembled on a titanium stent (OD 25 mm). Autologous platelets were labeled with 111In-tropolone and injected intravenously (850-1250 microCi per injection) into the pigs on removal from cardiopulmonary bypass (CPB). At 20-24 h after surgery, platelet thrombi adherent to MHV components, and shed emboli trapped in the brain, lung, heart, kidneys and other organs/connective tissues were imaged using a gamma camera. The animals were killed and the amounts of thrombi adherent to MHV components and organ-trapped emboli quantified using an ionization chamber and gamma counter.

RESULTS

There was no statistically significant difference in the adhesion of 111In-labeled platelets to either control sewing rings (0.08 +/- 0.06% dose) or PEO-treated rings (0.19 +/- 0.21% dose). The thrombogenicity of MHV components in both animal groups was in the ascending order: Dacron ring > Teflon pledgets > polypropylene sutures > titanium housing > pyrolytic carbon. The number of platelet-emboli trapped in the organs was not significantly different between the two groups.

CONCLUSIONS

Simple modifications may not reduce platelet thrombosis or wound-healing of the sewing ring in the acute phase, at which time several complex processes are activating and inactivating platelets and coagulant factors during CPB and implantation of MHVs.

Recombinant adenovirus is an appropriate vector for endocytotic protein trafficking studies in cultured neurons

Endocytosis of full-length beta-amyloid precursor protein (APP) from the plasma membrane contributes to beta-amyloid peptide (Abeta) secretion, and, hence, potentially contributes to the molecular pathogenesis of Alzheimer's disease. We recently have demonstrated that central neuronal APP is endocytosed in a common vesicular compartment with recycling synaptic vesicle integral membrane proteins, but is then sorted away from synaptic vesicles for retrograde transport to the neuronal soma. For this report, we explore whether recombinant adenovirus can be used to modulate APP expression in cultured central neurons to study APP processing by the endocytotic pathway in these cells. Using a replication-deficient recombinant adenovirus that expresses a lacZ reporter (Ad5/CMV-lacZ), we demonstrate high efficiency of transfection (30-35%) at low viral titer (10-20 MOI), with no significant neuronal toxicity or cytoarchitectural change. In addition, we demonstrate that infection with the control virus does not result in re-direction of endogenous neuronal APP from usual endocytotic pathways. We have prepared, using the same genomic background as the control virus, an adenoviral vector that expresses the neuronal isoform of human APP (Ad5/CMV-APP). Infection with Ad5/CMV-APP at 10-20 MOI results in significantly increased immunoreactivity for endocytosed APP with preservation of usual endocytotic trafficking. These results demonstrate that recombinant adenovirus at low titer is an appropriate and effective vector for protein trafficking/processing studies in cultured central neurons.

Successful prosthetic mitral valve implantation in pigs

Clotting mechanisms, the coagulation cascade, platelet function, and platelet-leukocyte-endothelial cell interactions are all very similar in humans and pigs. Because of these similarities, the authors concluded that the pig would be an ideal model for the study of thromboembolism resulting from prosthetic heart valves. To date, they have successfully recovered a total of 11 pigs (52.9 +/- 8.1 kg), 3 with bioprosthetic valves and 8 with mechanical valves, all in the mitral position (25 mm od). The normal presence of high numbers of pulmonary endothelial macrophages and other unique aspects of porcine cardiovascular and pulmonary function dictate somewhat different surgical protocols than those normally used for human patients and ruminant species. Some of these special procedures include 1) crystalloid prime without the use of plasma volume expanders, especially those with a starch base; 2) pharmacologic protection against arrhythmias (lidocaine, 4 mg/kg); 3) special attention to adequate hypothermic cardioprotection during the time of cross-clamp; 4) the use of shock doses of corticosteroid (prednisolone sodium succinate, 0.5 mg/kg) before removal of the aortic cross-clamp; and 5) positive inotropic support (dopamine, 0.008 mg/kg) while weaning from cardiopulmonary bypass. Gamma camera images of 111In tagged autologous platelets 24 hours after surgery show most thrombi located on the sewing ring with fewer on the pledgets and anchor sutures. The latter observations were confirmed by quantification of platelet deposition using a gamma counter.

A new method for quantitation of platelet microthrombi and microemboli from cardiopulmonary bypass in organs using 111In labeled platelets

During cardiopulmonary bypass (CPB), showers of microemboli (ME) distribute among the organs and connective tissues according to regional blood flow. Post CPB, ME were quantified by subtracting residual platelets (RP) in the organs of a group of unoperated control Yorkshire pigs (n = 6) from those of operated pigs. The RP level was minimized by heparinization (300 IU/kg) before death and exsanguination. The number of adherent microthrombi (MT) and ME from the oxygenator (OX), arterial filter (AF), and thoracotomy site were determined using 111In labeled autologous platelets (INPLT) (525-585 microCi administered 24 hr before CPB) in two CPB groups (ACT > 400 sec) of 12 pigs (30-35 kg). CPB was carried out at a flow of 2.5-3.5 L/min at 28 degrees C with a roller or a centrifugal pump, OX (Bentley Univox 1.8 m2), AF (0.25 m2), and cardiotomy reservoir (CR) (Bentley BR: 3,500), for 90 (n = 6) and 180 (CPB 180, n = 6) min. Six pigs underwent thoracotomy without CPB. L-Arginine was infused at a dose of 2 mg/ kg/min during CPB (n = 6). Flow cytometry was used to estimate the circulating ME in blood. MT and organ trapped ME were imaged with a gamma camera and measured with an ion chamber and a gamma counter. ME values (percent of injected INPLT dose) in six organs and four connective tissues were calculated for all five groups. INPLT distribution indicated a uniform distribution of low level platelet MT in the CR and AF. Circulating ME amounted to 2.5% of total platelets. In the CPB circuit, ME generation in AF was the rate-limiting step (n = 4 x 10(5)). Similar studies in organs and tissues suggested the presence of a uniform distribution of the total events of ME (n = 500 x 10(6)). ME increase in brain, lung, liver, and skeletal muscle following thoracotomy and CPB was significant. The low level of ME in ischemia sensitive organs also indicated the presence of a thrombolytic threshold for cumulative ME. ME disaggregation was activated at an early stage to prevent ischemic damage, specifically in the brain. Measurement of trapped ME provided a novel, reliable, and one step method of evaluation of thrombogenicity of a CPB device and drugs.

Benefit of vitamin E, riluzole, and gabapentin in a transgenic model of familial amyotrophic lateral sclerosis

Familial amyotrophic lateral sclerosis (FALS) has been linked in some families to dominant mutations of the SOD1 gene encoding Cu,Zn superoxide dismutase (Cu,ZnSOD). We have used a transgenic model of FALS based on expression of mutant human Cu,ZnSOD to explore the etiology and therapy of the genetic disease. Expression of mutant, but not wild-type, human Cu,ZnSOD in mice places the brain and spinal cord under oxidative stress. This causes depletion of vitamin E, rather than the typical age-dependent increase in vitamin E content as occurs in nontransgenic mice and in mice expressing wild-type human Cu,ZnSOD. Dietary supplementation with vitamin E delays onset of clinical disease and slows progression in the transgenic model but does not prolong survival. In contrast, two putative inhibitors of the glutamatergic system, riluzole and gabapentin, prolong survival. However, riluzole did not delay disease onset. Thus, there was clear separation of effects on onset, progression, and survival by the three therapeutics tested. This suggests the hypothesis that oxidative damage produced by the expression of mutant Cu,ZnSOD causes slow or weak excitotoxicity that can be inhibited in part by alerting glutamate release or biosynthesis presynaptically.

Pathogenic mechanisms in familial amyotrophic lateral sclerosis due to mutation of Cu, Zn superoxide dismutase

Oxidative mechanisms of damage have been implicated indirectly in the damage to brain tissue caused acutely by ischemia or chronically by neurodegenerative diseases. A direct link between pathogenesis and antioxidant enzyme systems has come from studies of a genetic form of amyotrophic lateral sclerosis (ALS). ALS causes the degeneration of motor neurons in cortex, brainstem and spinal cord with consequent progressive paralysis and death. The disease occurs in both sporadic and familial forms. Some 20% of kindreds in which ALS is inherited in an autosomal dominant fashion have mutations in the gene (SOD1) encoding Cu, Zn superoxide dismutase (SOD). Several SOD1 mutations have been shown by ourselves and others to cause motor neuron disease when expressed at high levels in transgenic mice, whereas transgenic mice expressing comparable amounts of wild-type human SOD do not show clinical disease. Thus, we have argued that motor neuron disease is caused by gain-of-function mutations in the human SOD1 gene. Our current experiments investigate the link between mutation of SOD1 and oxidative pathways of damage.

Age-dependent penetrance of disease in a transgenic mouse model of familial amyotrophic lateral sclerosis

The mutation gly93-->ala of Cu,Zn superoxide dismutase (SOD) is found in patients with familial amyotrophic lateral sclerosis and causes motor neuron disease when expressed in transgenic mice. The progression of clinical and pathological disease was studied in a line of mice designated G1H. Clinical disease started at 91 +/- 14 days of age with fine shaking of the limbs, followed by paralysis and death by 136 +/- 7 days of age. Pathological changes begin by 37 days of age with vacuoles derived from swollen mitochondria accumulating in motor neurons. At the onset of clinical disease (90 days), significant death of somatic motor neurons innervating limb muscles has occurred; mice at end-stage disease (136 days) show up to 50% loss of cervical and lumbar motor neurons. However, neither thoracic nor cranial motor neurons show appreciable loss despite vacuolar changes. Autonomic motor neurons also are not affected. Mice that express wild-type human Cu,Zn SOD remain free of disease, indicating that mutations cause neuron loss by a gain-of-function. Thus, the age-dependent penetrance of motor neuron disease in this transgenic model is due to the gradual accumulation of pathological damage in select populations of cholinergic neurons.