Carbon nanotubes as nanoscale mass conveyors.

The development of manipulation tools that are not too 'fat' or too 'sticky' for atomic scale assembly is an important challenge facing nanotechnology. Impressive nanofabrication capabilities have been demonstrated with scanning probe manipulation of atoms and molecules on clean surfaces. However, as fabrication tools, both scanning tunnelling and atomic force microscopes suffer from a loading deficiency: although they can manipulate atoms already present, they cannot efficiently deliver atoms to the work area. Carbon nanotubes, with their hollow cores and large aspect ratios, have been suggested as possible conduits for nanoscale amounts of material. Already much effort has been devoted to the filling of nanotubes and the application of such techniques. Furthermore, carbon nanotubes have been used as probes in scanning probe microscopy. If the atomic placement and manipulation capability already demonstrated by scanning probe microscopy could be combined with a nanotube delivery system, a formidable nanoassembly tool would result. Here we report the achievement of controllable, reversible atomic scale mass transport along carbon nanotubes, using indium metal as the prototype transport species. This transport process has similarities to conventional electromigration, a phenomenon of critical importance to the semiconductor industry.

Communications: Nanomagnetic shielding: High-resolution NMR in carbon allotropes.

The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of (13)C high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the largest diamagnetic shifts (down to -68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.

Detonation synthesis of carbon nano-onions via liquid carbon condensation.

Transit through the carbon liquid phase has significant consequences for the subsequent formation of solid nanocarbon detonation products. We report dynamic measurements of liquid carbon condensation and solidification into nano-onions over ∽200 ns by analysis of time-resolved, small-angle X-ray scattering data acquired during detonation of a hydrogen-free explosive, DNTF (3,4-bis(3-nitrofurazan-4-yl)furoxan). Further, thermochemical modeling predicts a direct liquid to solid graphite phase transition for DNTF products ~200 ns post-detonation. Solid detonation products were collected and characterized by high-resolution electron microscopy to confirm the abundance of carbon nano-onions with an average diameter of ∽10 nm, matching the dynamic measurements. We analyze other carbon-rich explosives by similar methods to systematically explore different regions of the carbon phase diagram traversed during detonation. Our results suggest a potential pathway to the efficient production of carbon nano-onions, while offering insight into the phase transformation kinetics of liquid carbon under extreme pressures and temperatures.

A Force on the Crown and Tug of War in the Periodontal Complex.

The load-bearing dentoalveolar fibrous joint is composed of biomechanically active periodontal ligament (PDL), bone, cementum, and the synergistic entheses of PDL-bone and PDL-cementum. Physiologic and pathologic loads on the dentoalveolar fibrous joint prompt natural shifts in strain gradients within mineralized and fibrous tissues and trigger a cascade of biochemical events within the widened and narrowed sites of the periodontal complex. This review highlights data from in situ biomechanical simulations that provide tooth movements relative to the alveolar socket. The methods and subsequent results provide a reasonable approximation of strain-regulated biochemical events resulting in mesial mineral formation and distal resorption events within microanatomical regions at the ligament-tethered/enthesial ends. These biochemical events, including expressions of biglycan, decorin, chondroitin sulfated neuroglial 2, osteopontin, and bone sialoprotein and localization of various hypertrophic progenitors, are observed at the alkaline phosphatase-positive widened site, resulting in mineral formation and osteoid/cementoid layers. On the narrowed side, tartrate-resistant acid phosphatase regions can lead to a sequence of clastic activities resulting in resorption pits in bone and cementum. These strain-regulated biochemical and subsequently biomineralization events in the load-bearing periodontal complex are critical for maintenance of the periodontal space and overall macroscale joint biomechanics.

Therapeutic effect of neutralizing endogenous IL-18 activity in the collagen-induced model of arthritis.

Two distinct IL-18 neutralizing strategies, i.e. a rabbit polyclonal anti-mouse IL-18 IgG and a recombinant human IL-18 binding protein (rhIL-18BP), were used to treat collagen-induced-arthritic DBA/1 mice after clinical onset of disease. The therapeutic efficacy of neutralizing endogenous IL-18 was assessed using different pathological parameters of disease progression. The clinical severity in mice undergoing collagen-induced arthritis was significantly reduced after treatment with both IL-18 neutralizing agents compared to placebo treated mice. Attenuation of the disease was associated with reduced cartilage erosion evident on histology. The decreased cartilage degradation was further documented by a significant reduction in the levels of circulating cartilage oligomeric matrix protein (an indicator of cartilage turnover). Both strategies efficiently slowed disease progression, but only anti-IL-18 IgG treatment significantly decreased an established synovitis. Serum levels of IL-6 were significantly reduced with both neutralizing strategies. In vitro, neutralizing IL-18 resulted in a significant inhibition of TNF-alpha, IL-6, and IFN-gamma secretion by macrophages. These results demonstrate that neutralizing endogenous IL-18 is therapeutically efficacious in the murine model of collagen-induced arthritis. IL-18 neutralizing antibody or rhIL-18BP could therefore represent new disease-modifying anti-rheumatic drugs that warrant testing in clinical trials in patients with rheumatoid arthritis.

Elastic discontinuity due to ectopic calcification in a human fibrous joint.

Disease can alter natural ramp-like elastic gradients to steeper step-like profiles at soft-hard tissue interfaces. Prolonged function can further mediate mechanochemical events that alter biomechanical response within diseased organs. In this study, a human bone-tooth fibrous joint was chosen as a model system, in which the effects of bacterial-induced disease, i.e. periodontitis, on natural elastic gradients were investigated. Specifically, the effects of ectopic biomineral, i.e. calculus, on innate chemical and elastic gradients within the cementum-dentin complex, both of which are fundamental parameters to load-bearing tissues, are investigated through comparisons with a healthy complex. Complementary techniques for mapping changes in physicochemical properties as a result of disease included micro X-ray computed tomography, microprobe micro X-ray fluorescence imaging, transmission electron and atomic force microscopy (AFM) techniques, and AFM-based nanoindentation. Results demonstrated primary effects as derivatives of ectopic mineralization within the diseased fibrous joint. Ectopic mineralization with no cementum resorption, but altered cementum physicochemical properties with increasing X-ray attenuation, exhibited stratified concretion with increasing X-ray fluorescence counts of calcium and phosphorus elements in the extracellular matrix in correlation with decreased hygroscopicity, indenter displacement, and apparent strain-relieving characteristics. Disease progression, identified as concretion through the periodontal ligament (PDL)-cementum enthesis, and sometimes the originally hygroscopic cementum-dentin junction, resulted in a significantly increased indentation elastic modulus (3.16±1.19 GPa) and a shift towards a discontinuous interface compared with healthy conditions (1.54±0.83 GPa) (Student's t-test, P<0.05). The observed primary effects could result in secondary downstream effects, such as compromised mechanobiology at the mechanically active PDL-cementum enthesis that can catalyze progression of disease.

Mapping local charge recombination heterogeneity by multidimensional nanospectroscopic imaging.

As materials functionality becomes more dependent on local physical and electronic properties, the importance of optically probing matter with true nanoscale spatial resolution has increased. In this work, we mapped the influence of local trap states within individual nanowires on carrier recombination with deeply subwavelength resolution. This is achieved using multidimensional nanospectroscopic imaging based on a nano-optical device. Placed at the end of a scan probe, the device delivers optimal near-field properties, including highly efficient far-field to near-field coupling, ultralarge field enhancement, nearly background-free imaging, independence from sample requirements, and broadband operation. We performed ~40-nanometer-resolution hyperspectral imaging of indium phosphide nanowires via excitation and collection through the probes, revealing optoelectronic structure along individual nanowires that is not accessible with other methods.

Interlayer forces and ultralow sliding friction in multiwalled carbon nanotubes.

We describe interlayer force measurements during prolonged, cyclic telescoping motion of a multiwalled carbon nanotube. The force acting between the core and the outer casing is modulated by the presence of stable defects and generally exhibits ultralow friction, below the measurement limit of 1.4 x 10(-15) N/atom and total dissipation per cycle lower than 0.4 meV/atom. Defects intentionally introduced in the form of dangling bonds lead to temporary mechanical dissipation, but the innate ability of nanotubes to self heal rapidly optimizes the atomic structure and restores smooth motion.

Shrinking a carbon nanotube.

We report a method to controllably alter the diameter of an individual carbon nanotube. The combination of defect formation via electron irradiation and simultaneous resistive heating and electromigration in vacuum causes the nanotube to continuously transform into a high-quality nanotube of successively smaller diameter, as observed by transmission electron microscopy. The process can be halted at any diameter. Electronic transport measurements performed in situ reveal a striking dependence of conductance on nanotube geometry. As the diameter of the nanotube is reduced to near zero into the carbon chain regime, we observe negative differential resistance.

Ultrahigh frequency nanotube resonators.

We report carbon-nanotube-based electromechanical resonators with the fundamental mode frequency over 1.3 GHz, operated in air at room temperature. A new combination of drive and detection methods allows for unprecedented measurement of both oscillation amplitude and phase and elucidates the relative mobility of static charges near the nanotube. The resonator serves as an exceptionally sensitive mass detector capable of approximately 10(-18) g resolution.

Nanocrystal-powered nanomotor.

We have constructed and operated a nanoscale linear motor powered by a single metal nanocrystal ram sandwiched between mechanical lever arms. Low-level electrical voltages applied to the carbon nanotube lever arms cause the nanocrystal to grow or shrink in a controlled manner. The length of the ram is adjustable from 0 to more than 150 nm, with extension speeds exceeding 1900 nm/s. The thermodynamic principles governing motor operation resemble those driving frost heave, a natural solid-state linear motor.

Packing C60 in boron nitride nanotubes.

We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.

Blockade of endogenous IL-18 ameliorates TNBS-induced colitis by decreasing local TNF-alpha production in mice.

BACKGROUND & AIMS: Interleukin (IL) 18 has proinflammatory effects. IL-18 plays a pivotal role in Th1 responses, but its proinflammatory activities extend beyond Th1 cells, including macrophages and production of tumor necrosis factor (TNF) alpha and IL-1beta. IL-18 is up-regulated in colonic specimens of patients with Crohn's disease. The goal of this study was to evaluate the role of IL-18. METHODS: Activity of IL-18 was neutralized using recombinant human IL-18 binding protein isoform a (rhIL-18BPa) in trinitrobenzene sulfonic acid (TNBS)-induced colitis. RESULTS: Mice treated daily with rhIL-18BPa (8 mg/kg) had significant reductions in clinical score, body weight loss, and colon weight increase compared with saline-treated mice. Histologic analysis showed that rhIL-18BPa-treated mice developed only mild colitis without signs of ulceration, with a mean total score of 9.8 +/- 1.3 points compared with 15.9 +/- 1.1 points observed in saline-treated mice with colitis. Analysis of cytokine levels in colon homogenates showed a significant decrease in TNF-alpha, IL-6, and IL-1beta after rhIL-18BPa treatment but no effect on interferon gamma. The therapeutic potential of rhIL-18BPa treatment was confirmed in TNBS mice that were treated only on days 8 and 9 after the start of the experiment. In these mice, significant reductions in total colitis score and colon weight were also observed. CONCLUSIONS: These findings show that inhibition of rhIL-18BPa bioactivity, via rhIL-18BPa, may be beneficial for the treatment of IBD.