Au@Hg nanoalloy formation through direct amalgamation: Structural, spectroscopic, and computational evidence for slow nanoscale diffusion

Dynamic core-shell nanoparticles have received increasing attention in recent years. This paper presents a detailed study of Au-Hg nanoalloys, whose composing elements show a large difference in cohesive energy. A simple method to prepare Au@Hg particles with precise control over the composition up to 15 atom% mercury is introduced, based on reacting a citrate stabilized gold sol with elemental mercury. Transmission electron microscopy shows an increase of particle size with increasing mercury content and, together with X-ray powder diffraction, points towards the presence of a core-shell structure with a gold core surrounded by an Au-Hg solid solution layer. The amalgamation process is described by pseudo-zero-order reaction kinetics, which indicates slow dissolution of mercury in water as the rate determining step, followed by fast scavenging by nanoparticles in solution. Once adsorbed at the surface, slow diffusion of Hg into the particle lattice occurs, to a depth of ca. 3 nm, independent of Hg concentration. Discrete dipole approximation calculations relate the UV-vis spectra to the microscopic details of the nanoalloy structure. Segregation energies and metal distribution in the nanoalloys were modeled by density functional theory calculations. The results indicate slow metal interdiffusion at the nanoscale, which has important implications for synthetic methods aimed at core-shell particles.

Osseointegration: the slow delivery of BMP-2 enhances osteoinductivity

Although the placement of dental and orthopedic implants is now generally a safe, reliable and successful undertaking, the functional outcome is less assured in patients whose bone-healing capacity is compromised. To enhance peri-implant osteogenesis in these individuals, BMP-2 could be locally administered. However, neither a free suspension nor an implant-adsorbed depot of the agent is capable of triggering sustained bone formation. We hypothesize that this end could be achieved by incorporating BMP-2 into the three-dimensional crystalline latticework of a bone-mineral like, calcium-phosphate implant coating, where from it would be liberated gradually - as the inorganic layer undergoes osteoclast-mediated degradation - not rapidly, as from an implant-adsorbed (two-dimensional) depot. To test this postulate, we compared the osteoinductive efficacies of implant coatings bearing either an incorporated, an adorbed, or an incorporated and an adsorbed depot of BMP-2 at a maxillary site in miniature pigs. The implants were retrieved 1, 2 and 3 weeks after surgery for the histomorphometric analysis of bone formation within a defined 'osteoinductive' space. At each juncture, the volume of newly-formed bone within the osteoinductive space was greatest around implants that bore a coating-incorporated depot of BMP-2, peak osteogenic activity being attained during the first week and sustained thereafter. In the other groups, the temporal course of bone formation was variable, and the peak levels were not sustained. The findings of this study confirm our hypothesis: they demonstrate that we now have at our disposal a means of efficaciously augmenting and expediting peri-implant bone formation. Clinically, this possibility would render the process of implant placement a safer and a more reliable undertaking in patients whose bone-healing capacity is compromised, and would also permit a curtailment of the postoperative recovery period by a forestallment of the mechanical-loading phase.

Slow release antibiotics for treatment of septic arthritis in large animals

The search for an effective treatment for septic arthritis is ongoing. Current therapies are expensive since they require repeated joint lavage and long term antibiotic treatment. Local application of antimicrobial drugs is advantageous because high concentrations can be attained at the infection site, although repeated injections increase the risk of superinfection of the joint. Thus, slow release formulations, which have the advantage of local treatment yet single application of the drug, are appealing. Antibiotics used in slow release formulations are selected for tissue compatibility, an appropriate antibacterial spectrum, and stability both during the mixing procedure and within the carrier during the release period. Ideally the carriers should be bioresorbable. Promising reports on the clinical use of poly(methyl methacrylate) (PMMA) mixed with several different antibiotics, and of collagen sponges impregnated with gentamicin, should encourage the search for formulations optimally adapted to veterinary medical requirements.

Slow Strain Rate Testing and Stress Corrosion Cracking of Ultra-Fine Grained and Conventional Al-Mg Alloy

Stress corrosion cracking susceptibility was investigated for an ultra-fine grained (UFG) AI-7.5Mg alloy and a conventional 5083 H111 alloy in natural seawater using slow strain rate testing (SSRT) at very slow strain rates between 1E(-5) s(-1), 1E(-6) s(-1) and 1E(-7) s(-1). The UFG Al-7.5Mg alloy was produced by cryomilling, while the 5083 H111 alloy is considered as a wrought manufactured product. The response of tensile properties to strain rate was analyzed and compared. Negative strain rate sensitivity was observed for both materials in terms of the elongation to failure. However, the UFG alloy displayed strain rate sensitivity in relation to strength while the conventional alloy was relatively strain rate insensitive. The mechanical behavior of the conventional 5083 alloy was attributed to dynamic strain aging (DSA) and delayed pit propagation while the performance of the UFG alloy was related to a diffusion-mediated stress relaxation mechanism that successfully delayed crack initiation events, counteracted by exfoliation and pitting which enhanced crack initiation. (C) 2014 Elsevier B.V. All rights reserved.

Slow fertilization of stickleback eggs: the result of sexual conflict?

BACKGROUND: The fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm. The time delay between sequential ejaculations may further influence the outcome of sperm competition. Such a time interval can load the raffle over fertilization if fertilization takes place very fast. Short fertilization times are generally assumed for externally fertilizing fish such as the three-spined stickleback (Gasterosteus aculeatus). In this pair-spawning fish, territorial males often try to steal fertilizations in nests of neighbouring males. This sneaking behaviour causes sperm competition. Sneakers will only get a share of paternity when eggs are not fertilized immediately after sperm release. Contrary to males, females may be interested in multiple paternity of their clutch of eggs. There thus may be a sexual conflict over the speed of fertilization. RESULTS: In this study we used two different in vitro fertilization experiments to assess how fast eggs are fertilized in sticklebacks. We show that complete fertilization takes more than 5 min which is atypically long for externally fertilizing fishes. CONCLUSION: This result suggests that the time difference does not imply high costs to the second stickleback male to ejaculate. Slow fertilization (and concomitant prolonged longevity of sperm) may be the result of sexual conflict in which females aimed at complete fertilization and/or multiple paternity.

Electroencephalographic changes after pediatric cardiac surgery with cardiopulmonary bypass: is slow wave activity unfavorable?

Pediatric cardiac surgery with cardiopulmonary bypass (CPB) is frequently associated with neurologic deficits. We describe the postoperative EEG changes, assess their possible causes, and evaluate their relevance to neurologic outcome. Thirty-one children and five neonates with congenital heart disease were included. EEG recording started after intubation and continued until 22-96 h after CPB. In addition to conventional analysis, spectral analysis was performed for occipital and frontal electrodes, and differences between pre- and postoperative delta power (delta-deltaP) were calculated. Maximum values of occipital delta-deltaP that occurred within 48 h after CPB were correlated with clinical variables and with perioperative markers of oxidative stress and inflammation. Occipital delta-deltaP correlated with frontal delta-deltaP, and maximum delta-deltaP correlated with conventional rating. Distinct rise of deltaP was detected in 18 of 21 children without any acute or long-term neurologic deficits but only in five of 10 children with temporary or permanent neurologic deficits. Furthermore, maximally registered delta-deltaP was inversely associated with duration of CPB and postoperative ventilation. Maximal delta-deltaP was also inversely associated with the loss of plasma ascorbate (as an index of oxidative stress) and plasma levels of IL-6 and IL-8. Slow wave activity frequently occurs within 48 h after CPB. However, our data do not support the notion that EEG slowing is associated with adverse neurologic outcome. This is supported by the fact that EEG slowing was associated with less oxido-inflammatory stress.

Endothelialization of sirolimus-eluting stents with slow and extended drug release in the porcine overstretch model

BACKGROUND: Vascular healing of intracoronary stents has been shown to be delayed in drug-eluting stents (DES) due to the cytotoxic compounds on the stent surface that prevent stent ingrowth and endothelialization. The lack of endothelialization explains the occurrence of late and very late stent thrombosis in DES. MATERIALS AND METHODS: In 11 house swines (body weight 38-45 kg), 3 stents were implanted randomly into the 3 large epicardial coronary arteries, namely a bare-metal stent (BMS), a sirolimus-eluting stent with slow-release (SES) and a SES with extended-release (SESXR). Stent length was 18 mm, and stent diameter 3 mm. All stents were of identical design. Animals were followed for 3 (n = 3), 7 (n = 4) and 14 (n = 4) days, respectively. One animal died before implantation due to hyperthermia. On the day of explantation, the animals were euthanized and endothelialization was tested by scanning electron microscopy after drying and sputtering the samples. Endothelial coverage was determined semiquantitatively by 2 observers. RESULTS: Endothelialization was more rapid with BMS and SESXR than SES at 3 and 14 days. At 7 days there were no significant differences between the 2 SES. CONCLUSIONS: Endothelialization of intracoronary stents is faster with BMS and SESXR at 3 days than with SES. These differences persist at 14 days, suggesting delayed vascular healing with the slow-release SES.

DYNAMICS AND CONTROL OF REACTIVE DISTILLATION PROCESS FOR MONOMER SYNTHESIS OF POLYCARBONATE PLANTS

Polycarbonate (PC) is an important engineering thermoplastic that is currently produced in large industrial scale using bisphenol A and monomers such as phosgene. Since phosgene is highly toxic, a non-phosgene approach using diphenyl carbonate (DPC) as an alternative monomer, as developed by Asahi Corporation of Japan, is a significantly more environmentally friendly alternative. Other advantages include the use of CO2 instead of CO as raw material and the elimination of major waste water production. However, for the production of DPC to be economically viable, reactive-distillation units are needed to obtain the necessary yields by shifting the reaction-equilibrium to the desired products and separating the products at the point where the equilibrium reaction occurs. In the field of chemical reaction engineering, there are many reactions that are suffering from the low equilibrium constant. The main goal of this research is to determine the optimal process needed to shift the reactions by using appropriate control strategies of the reactive distillation system. An extensive dynamic mathematical model has been developed to help us investigate different control and processing strategies of the reactive distillation units to increase the production of DPC. The high-fidelity dynamic models include extensive thermodynamic and reaction-kinetics models while incorporating the necessary mass and energy balance of the various stages of the reactive distillation units. The study presented in this document shows the possibility of producing DPC via one reactive distillation instead of the conventional two-column, with a production rate of 16.75 tons/h corresponding to start reactants materials of 74.69 tons/h of Phenol and 35.75 tons/h of Dimethyl Carbonate. This represents a threefold increase over the projected production rate given in the literature based on a two-column configuration. In addition, the purity of the DPC produced could reach levels as high as 99.5% with the effective use of controls. These studies are based on simulation done using high-fidelity dynamic models.

Focal adhesion kinase is a load-dependent governor of the slow contractile and oxidative muscle phenotype

Striated muscle exhibits a pronounced structural-functional plasticity in response to chronic alterations in loading. We assessed the implication of focal adhesion kinase (FAK) signalling in mechano-regulated differentiation of slow-oxidative muscle. Load-dependent consequences of FAK signal modulation were identified using a multi-level approach after electrotransfer of rat soleus muscle with FAK-expression plasmid vs. empty plasmid-transfected contralateral controls. Muscle fibre-targeted over-expression of FAK in anti-gravitational muscle for 9 days up-regulated transcript levels of gene ontologies underpinning mitochondrial metabolism and contraction in the transfected belly portion. Concomitantly, mRNA expression of the major fast-type myosin heavy chain (MHC) isoform, MHC2A, was reduced. The promotion of the slow-oxidative expression programme by FAK was abolished after co-expression of the FAK inhibitor FAK-related non-kinase (FRNK). Elevated protein content of MHC1 (+9%) and proteins of mitochondrial respiration (+165-610%) with FAK overexpression demonstrated the translation of transcript differentiation in targeted muscle fibres towards a slow-oxidative muscle phenotype. Coincidentally MHC2A protein was reduced by 50% due to protection of muscle from de-differentiation with electrotransfer. Fibre cross section in FAK-transfected muscle was elevated by 6%. The FAK-modulated muscle transcriptome was load-dependent and regulated in correspondence to tyrosine 397 phosphorylation of FAK. In the context of overload, the FAK-induced gene expression became manifest at the level of contraction by a slow transformation and the re-establishment of normal muscle force from the lowered levels with transfection. These results highlight the analytic power of a systematic somatic transgene approach by mapping a role of FAK in the dominant mechano-regulation of muscular motor performance via control of gene expression.