Fibrous carbon nanotubes

The field of fullerene chemistry expanded in an unexpected direction in 1991 when Sumio lijima of the NEC Fundamental Research Laboratories in Japan discovered fibrous carbon clusters in one of his fullerene preparations This led within a short time to substances of the type portrayed in Figure 11 7 called single-walled nanotubes The best way to think about this material IS as a stretched fullerene Take a molecule of Ceo cut it in half and place a cylindrical tube of fused six membered carbon rings between the two halves... 

Fig. 1. Comparalive preparation methods for micrometer size fibrous carbon and carbon nanotubes as one-dimensional forms of carbon.

A recently discovered form of fibrous carbon consists of concentric tubes with walls like sheets of graphite rolled into cylinders. These tiny structures, called nanotubes, form strong, conducting fibers with a large surface area. As a consequence, they have unusually interesting and promising properties that have become a major thrust of nanotechnology research (Box 14.1). 

Dalmas F, Dendievel R, Chazeau L, Cavaille JY, Gauthier C (2006) Carbon nanotube-filled polymer of electrical conductivity in composites. Numerical simulation three-dimensional entangled fibrous networks. Acta Materialia 54 2923-2931. 

Over the last decade, novel carbonaceous and graphitic support materials for low-temperature fuel cell catalysts have been extensively explored. Recently, fibrous nanocarbon materials such as carbon nanotubes (CNTs) and CNFs have been examined as support materials for anodes and cathodes of fuel cells [18-31], Mesoporous carbons have also attracted considerable attention for enhancing the activity of metal catalysts in low-temperature DMFC and PEMFC anodes [32-44], Notwithstanding the many studies, carbon blacks are still the most common supports in industrial practice. 

Several nanoparticles having a non-spherical shape have been synthesized, e.g., carbon nanotubes, nanofibers, nanorods, and nanowires which exhibit, similar to asbestos, a fibrous shape. 

Carbon nanotubes (CNTs) currently attract intense interest because of their unique properties which make them suitable for many industrial applications.28 Carbon nanotubes exhibit some of the properties implied in asbestos toxicity. Carbon nanotubes share with asbestos the fibrous habit - long fibers with a diameter of a few nanometers -and a very high biopersistence. On this basis they are suspected to be hazardous and indeed the first studies in vivo14,29,30 have shown an inflammatory response followed by some evolution towards fibrosis. When inhaled, CNTs may thus constitute a possible hazard to human health. The inflammatory and fibrotic responses elicited by CNTs is similar to that caused by other toxic particles which might be the result of oxidative stress caused by particle- and/or cell-derived free radicals. There is no direct experimental evidence of a capacity of carbon nanotubes to generate free radicals similar to silica asbestos and nano sized iron oxide particles. 

Due to their fibrous stracture and remarkable properties, carbon nanotubes are suitable to the production of polymer composites. Their extreme tensile strength... 

Research on fullerenes carried out at NEC Corporation (Japan) and at IBM (United States) led in 1991 to the isolation of fibrous clusters of single-walled carbon nanotubes (SWCNTs) (Figure 11.6). SWCNTs have since been joined by multiwalled carbon nanotubes (MWCNTs) (Figure 11.7) as well as nanotubes containing elements other than carbon. 

Fibrous fillers Nonbiobased Multi wall carbon nanotube (MWCNT) Moon et al. [182], Zhang... 

Recently, nanostructured carbon-based fillers such as Ceo [313,314], single-wall carbon nanotubes, carbon nanohorns (CNHs), carbon nanoballoons (CNBs), ketjenblack (KB), conductive grade and graphitized carbon black (CB) [184], graphene [348], and nanodiamonds [349] have been used to prepare PLA-based composites. These fillers enhance the crystalUza-tion ofPLLA [184,313,314].Nanocomposites incorporating fibrous MWCNTsandSWCNTs are discussed in the section on fibre-reinforced plastics (section 8.12.3). 

Conductive materials in fibrillar shape may be advantageous compared to films due to their inherent properties such as anisotropy, high surface area, and mechanical strength. Fibrous conductive materials are of particular interest in electroactive composites. Fine metal nanoparticles, carbon fibers, and carbon nanotubes have been efficiently distributed in an insulating polymer matrix in order to improve both electrical and mechanical properties. 

The strategy based on the assembly of conducting carbraiaceous nanomaterials to sepiolite and palygorskite is based on two approaches (1) the development of carbonaceous materials from organic precursors adsorbed on the fibrous clays, and (2) the direct assembly of carbon nanotubes with the fibrous clays. 

Carbon nanotubes are the subject of many research studies from drug delivery systems to many other medical applications. Only a few references and examples have been mentioned here. This dmg delivery application by CNTs constitutes in itself the wide potential of fibrous material for smart implantable medical device designing, going beyond just the biological response impact and including physical and mechanical features. 

Today the synthesis of carbon nanotubes and their incorporation into existing macro-and microtechnologies have led to improvements in the ability to provide a true bio-mimetic microenvironment from engineered nanomaterials. In addition to chemically interesting features previously mentioned, these fibrous devices also include smart physical and mechanical behaviors. 

For this reason, it has been proposed to focus on physical features, reviewing only one specific material, carbon nanotubes, rather than attempting to list material features that may induce potential improvement of fibrous implantable medical devices from biointegration and efficiency points of view. 

First, we note the improvement of the mechanical characteristics of implantable devices that incorporate carbon nanotubes. Even if it is quite difficult to identify which one of stmctural, material chemistry, mechanical strength or other features prevails in a fibrous implantable device s success, it is assumed that carbon nanotubes strength may have a positive impact on soft tissues matrix. 

---