The fibrous shape of carbon nanotubes (CNTs) raises concern that they may pose an asbestos-like inhalation hazard, leading to the development of diseases, especially mesothelioma. Direct instillation of long and short CNTs into the pleural cavity, the site of mesothelioma development, produced asbestos-like length-dependent responses. The response to long CNTs and long asbestos was characterized by acute inflammation, leading to progressive fibrosis on the parietal pleura, where stomata of strictly defined size limit the egress of long, but not short, fibers. This was confirmed by demonstrating clearance of short, but not long, CNT and nickel nanowires and by visualizing the migration of short CNTs from the pleural space by single-photon emission computed tomographic imaging. Our data confirm the hypothesis that, although a proportion of all deposited particles passes through the pleura, the pathogenicity of long CNTs and other fibers arises as a result of length-dependent retention at the stomata on the parietal pleura.

Suspicion has been raised that high aspect ratio nanoparticles or nanofibers might possess asbestos-like pathogenicity. The pleural space is a specific target for disease in individuals exposed to asbestos and by implication of nanofibers. Pleural effects of fibers depends on fiber length, but the key threshold length beyond which adverse effects occur has never been identified till now because all asbestos and vitreous fiber samples are heterogeneously distributed in their length. Nanotechnology advantageously allows for highly defined length distribution of synthetically engineered fibers that enable for in-depth investigation of this threshold length. We utilized the ability to prepare silver nanofibers of five defined length classes to demonstrate a threshold fiber length for acute pleural inflammation. Nickel nanofibers and carbon nanotubes were then used to strengthen the relationship between fiber length and pleural inflammation. A method of intrapleural injection of nanofibers in female C57Bl/6 strain mice was used to deliver the fiber dose, and we then assessed the acute pleural inflammatory response. Chest wall sections were examined by light and scanning electron microscopy to identify areas of lesion; furthermore, cell-nanowires interaction on the mesothelial surface of the parietal pleura in vivo was investigated. Our results showed a clear threshold effect, demonstrating that fibers beyond 4 µm in length are pathogenic to the pleura. The identification of the threshold length for nanofiber-induced pathogenicity in the pleura has important implications for understanding the structure-toxicity relationship for asbestos-induced mesothelioma and consequent risk assessment with the aim to contribute to the engineering of synthetic nanofibers by the adoption of a benign-by-design approach.

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The use of fibre-shaped nanomaterials in commercial applications has met with concern that they could cause health effects similar to those seen with pathogenic fibres such as certain forms of asbestos. Of the attributes which form the fibre pathogenicity paradigm, fibre length is thought to be a critical factor in determining fibre toxicity. We have previously shown that carbon nanotubes display such length-dependent pathogenicity but it remains unclear if other forms of fibrous nanomaterials conform to the fibre pathogenicity paradigm. As such, our aim is to determine the generality of this hypothesis by asking whether a radically different form of fibrous nanomaterial, nickel nanowires, show length-dependent pathogenicity. Our results indicate that nickel nanowires synthesised to be predominantly long (>20 μm) show the ability to elicit strong inflammation in the mouse peritoneal model in a dose-dependent manner; inflammation or fibrosis was not seen with the short (<5 μm) nanowires. This length-dependent response was also seen after lung aspiration and within a macrophage in vitro model adding further weight to the contention that fibre length is an important driver of hazard potential. This may have important implications when considering the hazard posed by fibrous nanomaterials and their regulation in workplaces.

It is possible to suppress convection and dispersion of a paramagnetic liquid by means of a magnetic field. A tube of paramagnetic liquid can be stabilized in water along a ferromagnetic track in a vertical magnetic field, but not in a horizontal field. Conversely, an ''antitube'' of water can be stabilized in a paramagnetic liquid along the same track in a transverse horizontal field, but not in a vertical field. The stability arises from the interaction of the induced moment in the solution with the magnetic field gradient in the vicinity of the track. The magnetic force causes the tube of paramagnetic liquid to behave as if it were encased by an elastic membrane whose cross-section is modified by gravitational forces and Maxwell stress. Convection from the tube to its surroundings is inhibited, but not diffusion. Liquid motion within the paramagnetic tube, however, exhibits vorticity in tubes of diameter 1 mm or less-conditions where classical pipe flow would be perfectly streamline, and mixing extremely slow. The liquid tube is found to slide along the track almost without friction. Paramagnetic liquid tubes and antitubes offer appealing new prospects for mass transport, microfluidics, and electrodeposition.fluid dynamics ͉ magnetism ͉ Maxwell stress ͉ microfluidics M ass transport in miscible liquids is usually dominated by convection. When a drop of colored solution falls into a glass of water, it quickly disperses because of convection driven by density differences and the initial velocity distribution. The relevant dimensionless quantity is the Péclet number Pe, the ratio of the time scales for diffusion and dispersion. This number, defined aswhere D is the diffusion constant, l is a characteristic dimension of the system, and v is the liquid velocity, is usually much greater than 1. A typical value of D for ions in solution is 10 Ϫ9 m 2 ⅐s Ϫ1 (1); the dimension l of our glass is ϳ0.1 m and v d may be ϳ1 mm⅐s Ϫ1 , so Pe ϳ 10 5 . The drop of ink disperses in the glass of water in less than a minute, but to achieve mixing by diffusion would take a time of order l 2 / 2 D (1), which is about a fortnight. A magnetic field can suppress convection in the following way: Magnetization is induced in a paramagnetic liquid by an external field, and a magnetic field gradient is created by means of ferromagnetic material to exert a force on the induced magnetization. With an appropriate field configuration, it is possible to confine the paramagnetic liquid in a stable shape. The field gradient force density on an element with uniform magnetization M in an external field H 0 is F m ϭ 0 ٌ͑M⅐H 0 ͒.[2]A more general expression, valid when the specific magnetization is independent of density, as it is for dilute solutions, is (2, 3):