The effects of particle size, density and shape on margination of nanoparticles in microcirculation

In the recent past, remarkable advances in nanotechnology have generated nanoparticles of different shapes and sizes, which have been shown to exhibit unique properties suitable for biomedical applications such as cancer therapy and imaging. Obviously, all nanoparticles are not made equal. This becomes evident when we consider their transport behavior under blood flow in microcirculation. In this work, we evaluated the effect of critical physical characteristics such as the particle shape, size and density on a nanoparticle's tendency to marginate towards the vessel walls in microcirculation using an in vitro model. The wall deposition of nanoparticles was tested in a fibronectin-coated microfluidic channel at a physiologically relevant flow rate. Different classes of nanoparticles (liposome, metal particles) of different sizes (60-130 nm), densities (1-19 g ml(-1)) and shapes (sphere, rod) displayed significantly different deposition as a result of different margination rates. The smaller-sized and the oblate-shaped particles displayed a favorable behavior as indicated by their higher margination rates. Notably, the particle density showed an even more essential role, as it was observed that the lighter particles marginated significantly more. Since nanoparticles must escape the flow in order to approach the vascular bed and subsequently extravascular components for meaningful interactions, the design of nanoparticles strongly affects their margination, a key factor for their ultimate in vivo effectiveness.     

Tailoring mechanical properties of aerogels for aerospace applications

Silica aerogels are highly porous solid materials consisting of three-dimensional networks of silica particles and are typically obtained by removing the liquid in silica gels under supercritical conditions. Several unique attributes such as extremely low thermal conductivity and low density make silica aerogels excellent candidates in the quest for thermal insulation materials used in space missions. However, native silica aerogels are fragile at relatively low stresses. More durable aerogels with higher strength and stiffness are obtained by proper selection of silane precursors and by reinforcement with polymers. This paper first presents a brief review of the literature on methods of silica aerogel reinforcement and then discusses our recent activities in improving not only the strength but also the elastic response of polymer-reinforced silica aerogels. Several alkyl-linked bis-silanes were used in promoting flexibility of the silica networks in conjunction with polymer reinforcement by epoxy.     

In situ chemical reduction of Cr(VI) in groundwater using a combination of ferrous sulfate and sodium dithionite: a field investigation

A field study was conducted to evaluate the performance of a ferrous iron based in situ redox zone for the treatment of a dissolved phase Cr(VI) plume at a former industrial site. The ferrous iron based in situ redox zone was created by injecting a blend of 0.2 M ferrous sulfate and 0.2 M sodium dithionite into the path of a dissolved Cr(VI) plume within a shallow medium to fine sand unconfined aquifer formation. Monitoring data collected over a period of 1020 days after more than 100 m of linear groundwater flow through the treatment zone indicated sustained treatment of dissolved phase Cr(VI) from initial concentrations between 4 and 8 mg/L to less than 0.015 mg/L. Sustained treatment is assumed to be primarily due to the reduction of Cr(VI) to Cr(III) by ferrous iron adsorbed to, precipitated on, and/or incorporated into aquifer iron (hydr)oxide solid surfaces within the treatment zone. Precipitated phases likely include FeCO3 and FeS based on saturation index considerations and SEM/EDS analysis. The detection of solid phase sulfites and thiosulfates in aquifer sediments collected from the treatment zone more than 2 years following injection suggests dithionite decomposition products may also play a significant role in the long-term treatment of the dissolved phase Cr(VI).     

Multidentate adsorbates for self-assembled monolayer films

The spontaneous adsorption of organic molecules on a variety of planar and nonplanar substrates, that is, self assembly, can generate films just one molecule thick. These nanoscale, self-assembled monolayer (SAM) films have been extensively used to engineer surfaces with well-defined properties. Their utility has been demonstrated in a wide range of applications, including wetting, adhesion, lubrication, patterning, and molecular recognition. Many SAM systems have been investigated, but alkanethiols adsorbed on gold are the most successful combination. This pairing offers a variety of advantages, including the ability to tune precisely the interfacial properties of a surface through the well-established organic synthetic methodologies that have been developed for preparing custom ω-terminated alkanethiols. Alkanethiolate monolayers are moderately stable at room temperature; however, these films degrade over time and readily desorb upon moderate heating. This shortcoming limits the use of SAMs in applications involving elevated temperatures or harsh environments. Accordingly, new adsorbates with multiple bonding moieties have been created to enhance the stability and versatility of SAMs. In this Account, we examine a variety of multidentate adsorbate structures that have been used to generate SAMs on planar substrates and on nanoparticles. Each of these chelating adsorbates (bidentates and tridentates) has been designed to generate well-defined organic monolayer films with multiple attachment points to the underlying substrate. This bonding arrangement allows the formation of SAMs with enhanced stability through the entropy-driven "chelate effect". The research examined here demonstrates that multidentate adsorbates provide robust films: they enable the use of SAMs under conditions that are incompatible with SAMs derived from normal alkanethiols. Another advantage offered by multidentate adsorbates is the capacity for new paradigms in thin-film composition. In particular, appropriately designed chelating adsorbates can be engineered to have two or more chemically distinct terminal groups that are covalently linked to the same underlying headgroup, without adding steric bulk that might prove detrimental to the resultant assembly. This strategy allows the generation of homogeneously mixed multicomponent surfaces, overcoming the problem of phase separation or "islanding" that is pervasive when two or more chemically distinct adsorbates are used to form mixed SAMs. Such homogeneously mixed films offer the opportunity to fine-tune the interfacial properties of a substrate and to create unique heterogeneous interfaces that are well defined by the chemical composition of the tailgroups exposed at the surface. The insight derived from these studies opens the door to new uses for SAMs, both in surface engineering applications (such as corrosion resistance and soft lithographic patterning) and in the stabilization and manipulation of nanoparticles.     

Crystallization of LiNbO3 and NaNbO3 in niobiosilicate glass–ceramics

Although glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry-dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO₃ in a 35SiO₂–30Nb₂O₅–35Li₂O mol% composition and crystallization of LiNbO₃ and NaNbO₃ in a 35SiO₂–30Nb₂O₅–25Li₂O–10Na₂O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion-controlled one-dimensional growth. Adding Na₂O to the glass composition increases the inter-diffusivity of ions which causes LiNbO₃ to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time-temperature-transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO₃ is ∼650°C and for NaNbO₃ is ∼715°C.     

Kinetics of shrinkage and shape evolution during liquid phase sintering of tungsten heavy alloy

A numerical model describing gravity-induced shape distortion and densification during solid and liquid phase sintering is proposed. The constitutive formulation is based on the continuum theory of sintering and implemented in commercial finite element software. Simulations under gravity-induced stress are attempted on the basis of the model parameters where viscosity is assumed to be temperature and porosity dependent. Viscosity is assessed through shrinkage and shrinkage rate data obtained experimentally from dilatometry over a controlled temperature regime. Effects of temperature, heating rate, and liquid phase formation on porosity evolution are analyzed. Additionally, sample studies on the influence of heating rate, gravity, friction coefficient, aspect ratio, and volume on the predicted distortion profiles after sintering of a tungsten heavy alloy are also presented. These numerical results are compared with experimental data from the literature.     

Giant Electrocaloric Response Over A Broad Temperature Range in Modified BaTiO3 Ceramics

A giant electrocaloric effect (ECE) near room temperature is reported in a lead‐free bulk inorganic material. By tuning Ba(Zr_xTi_1–x)O₃ compositions which also exhibit relaxor ferroelectric response to near the invariant critical point, the Ba(Zr_xTi_1–x)O₃ bulk ceramics at x ～ 0.2 exhibit a large adiabatic temperature drop of 4.5 K, a large isothermal entropy change of 8 J kg^?1 K^?1, and a large EC coefficient (|ΔT_c/ΔE| = 0.52 × 10^?6 KmV^?1 and ΔS/ΔE = 0.93 × 10^?6 J m kg^?1 K^?1 V^?1) over a 30 K temperature range. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications.     

Aquatic hypoxia is an disrupter and impairs fish reproduction

There is increasing concern that certain chemicals in the aquatic environment can disrupt endocrine systems, leading to reproductive impairment and threatening survival of wild populations of invertebrates, fish, bird, reptiles, and wildlife. For the first time, we report that hypoxia is also an endocrine disruptor and poses a significant threat to the reproduction and hence sustainability of fish populations. Serum levels of testosterone, estradiol, and triiodothyronine significantly decreased in carp (Cyprinus carpio) upon chronic exposure to hypoxia. These hormonal changes were associated with retarded gonadal development in both male and female carp, reduced spawning success, sperm motility, fertilization success, hatching rate, and larval survival, indicating that adverse effects of hypoxia on reproductive performance resulted from endocrine disruption. Since aquatic hypoxia commonly occurs over thousands of square kilometers in aquatic systems worldwide, our results imply that endocrine disruption and reproductive impairment in fish may be a widespread environmental problem.     

Several Modulation Techniques for a Pulsewidth Modulated Inverter

Pulsewidth modulation of a six-step inverter can be accomplished in different ways. Comparisons between different modulation techniques are based primarily on harmonic content in the output waveform and circuit constraints imposed by semiconductor characteristics. Adaptive ratio is a modulation scheme which combines the beneficial features of several available techniques and makes the necessary compromises to optimize the operating characteristics of a modulated six-step inverter.