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Biomaterials that can stimulate stem cell differentiation without growth factor supplementation provide potent and cost-effective scaffolds for regenerative medicine. We hypothesize that a scaffold prepared from cellulose and silk blends can direct stem cell chondrogenic fate. We systematically prepared cellulose blends with silk at different compositions using an environmentally benign processing method based on ionic liquids as a common solvent. We tested the effect of blend compositions on the physical properties of the materials as well as on their ability to support mesenchymal stem cell (MSC) growth and chondrogenic differentiation. The stiffness and tensile strength of cellulose was significantly reduced by blending with silk. The characterized materials were tested using MSCs derived from four different patients. Growing MSCs on a specific blend combination of cellulose and silk in a 75:25 ratio significantly upregulated the chondrogenic marker genes SOX9, aggrecan, and type II collagen in the absence of specific growth factors. This chondrogenic effect was neither found with neat cellulose nor the cellulose/silk 50:50 blend composition. No adipogenic or osteogenic differentiation was detected on the blends, suggesting that the cellulose/silk 75:25 blend induced specific stem cell differentiation into the chondrogenic lineage without addition of the soluble growth factor TGF-β. The cellulose/silk blend we identified can be used both for in vitro tissue engineering and as an implantable device for stimulating endogenous stem cells to initiate cartilage repair.

Multiwalled carbon nanotube (MWNT)/poly(vinyl butyral) (PVB) composite nanofibers were prepared by electrospinning, successive twisting and heat treatment. The MWNTs were highly oriented in an electrified thin jet during electrospinning. The heat treatment of the twisted electrospun nanofiber yarns produced the characteristics of the CNT in the composite nanofiber yarns and enhanced their electrical properties, mechanical properties, and thermal properties. The electrical conductivity of the heated yarn was significantly enhanced and showed the maximum value of 154 S cm(-1) for the yarn heated at 400 °C. It is an order of magnitude higher than other electrospun CNT composite materials. These results demonstrated that the novel top-down process based on electrospinning, twisting, and heat treatment provide a promising option for simple and large-scale manufacture of CNT assemblies.

The control of the structure of carbon nanotubes remains a central issue in rapidly developing science and technology. Of the various structural parameters of nanotubes, namely, diameters, number of walls, length, and chirality, it is the control of chirality which presents significant challenges as well as opportunities. It is known from our earlier work that the addition of nitrogen as a heterocyclic compound in the hydrocarbon feedstock leads to the growth of carpets of multiwall nanotubes in which all the walls are either of the armchair or zigzag structure. The research here shows the role of nitrogen in stabilizing iron carbide catalyst particles, the belt nucleation of the nanotubes, the orientational relationship between particle and nanotube structure, and the reconstruction of the surface layers of the carbide in contact with the growing ends of the tubes. By combining the various pieces of new experimental evidence it has proved possible to suggest why such unique types of nanotubes should form...

There is considerable interest in the adhesion of polymers to carbon nanotubes for nanocomposite applications.(1-4) One example is multiwalled carbon nanotubes (MWCNTs) dispersed in nylon 6,6.(5) We will show that high-contrast tomographic reconstructions can be created from plasmon-loss electrons that show the three-dimensional structural complexity of the MWCNT-nylon composite at the nanoscale. Further, by recording a series of energy-loss images at successive tilts, it is possible to interrogate subvolumes to extract energy-loss spectra from the reconstructed "volume spectra".

The article examines the in situ observation of the effect of nitrogen on carbon nanotube synthesis. Environmental TEM (ETEM) is a relatively new technique ideal for in situ measurements. Researchers apply ETEM to study the effect of nitrogen on CNT growth, elucidating the mechanisms by which nitrogen acts, to guide efforts to optimize synthesis. To the best of our knowledge, this is the first in situ TEM study of the effect of nitrogen on CNT growth. Therefore, in the absence of ammonia, carbon should precipitate first, resulting in an interface with pure iron. Pure iron has a higher surface tension with the nanotube, which explains the separation of the CNT and catalyst immediately following carbon precipitation. A carbide particle will have a lower surface tension with the nanotube due to its higher carbon chemical potential and thus maintain its contact. The pure iron catalyst may become carbide following cap separation, but this will not affect CNT nucleation.

It has been demonstrated that dispersion of noble metal nanoparticles in an organic matrix can be achieved by crystallization of amorphous low-molecular-weight nylon-11 in a process called relaxative autodispersion. In the present paper we report the dispersion of Au by acetone vapor-induced crystallization of amorphous polycarbonate films. Crystallization kinetics were examined with infrared spectroscopy. Au dispersion was detected with X-ray photoelectron spectroscopy in conjunction with ion-beam depth profiling and cross-sectional transmission electron microscopy. While vapor sorption in films of some micrometers thickness occurs within minutes at room temperature, crystallization and Au dispersion take place on a time scale of hours. Crystallization gives rise to a strong enhancement of surface roughness measured by atomic force microscopy. The present approach of metal dispersion is not restricted to low-molecular-weight polymers. A model for the dispersion process is proposed.