Carbon Nanotubes in Physiological Environment
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Carbon Nanotubes in Physiological Environment R. Cué , G. Del Bosque1, A. Sanchez1 1 Instituto Tecnológico y de Estudios Superiores de Monterrey. Ave. Eugenio Garza Sada 2501 Sur, Col. Tecnológico C.P. 64849, Monterrey, N.L., México. 1
ABSTRACT To fully accomplish all promises and hopes on clinical applications of carbon nanotubes, it is crucial to understand their interactions with physiological environment. One of these applications is polymer fillers, and it is important to review the toxicology of carbon nanotubes themselves because some polymer matrices may be biodegradable. Therefore, the interactions with organic molecules such as water, electrolytes, and proteins are reviewed and results of multiple studies on cellular interaction, cytotoxicity, immune response, biodistribution, and biopersistence are further presented. Finally, a section describing the interaction of polymer matrices with carbon nanotube reinforcements and the physiological environment is presented. INTRODUCTION Nanotechnology, as in many other technological fields, poses a risk to human health [1]. Some manufacturing processes involve toxic chemicals or dangerous by-products. Besides, nanoparticle characteristics cannot be compared to the ones of macroscale materials. Carbon nanotubes are not the exception; we cannot assume their toxicological behavior by their chemical composition only. Carbon nanotubes consist of a curved form of graphene (single carbon atom layer of graphite) with diameters ranging in the nanoscale. These nanoparticles have high surface areas, high mechanical strength, chemical and thermal stability, and optimal electronic and conductive properties [2]. These tubes can be either single-walled or have multiple walls one inside the other. On pristine state, carbon nanotubes are extremely hydrophobic, possess carbonaceous and metal impurities, and tend to bundle due to van der Waals attractions [3]. These nanotubes can be refined or purified to remove such impurities by various methods, though the structural surfaces of carbon nanotubes are modified [4]. As mentioned, pristine carbon nanotubes are hydrophobic; hence they need to be modified to make them soluble. This functionalization is done by adsorption, electrostatic interaction or covalent bonding of different molecules [5]. Functionalization not only improves the nanotubes’ hydrophilicity, it also diminishes their tendency to bundle and changes their physiological performance. Another way to reduce aggregation is when carbon nanotubes are triturated in an oscillatory ball mill [6][7] and therefore are called .ground. carbon nanotubes. There are various possible applications of carbon nanotubes, many of them already being developed. Some of these are vaccine [7], gene [5] or drug delivery [4][5][7]-[9] systems. Other possible uses include tissue regeneration [10], cancer cell killing with hyperthermia [5], imaging [8], sensors [4], biomaterials [7], nanofluidic systems [4][11], probes, actuators and nanobots [4]. Because of their exceptional characteristics, carbon n
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