NOVEL DRUG DELIVERY SYSTEM
Incorporating them into carbon nanotubes modifies the electrical behaviour of fullerenes, creating regions with varying semiconductive properties, thus offering potential applications in nanoelectronics. Their properties vary according to wavelength, thus finding applications in telecommunications. Since fullerenes are empty structures with dimensions similar to several biologically active molecules, they can be filled with different substances and find medical applications.
Figure: 6 Schematic representation of a modified fullerene
B) Carbon nanotubes:
Discovered barely a decade ago, carbon nanotubes are a new form of carbon molecule. Wound in a hexagonal network of carbon atoms, these hollow cylinders can have diameters as small as 0.7 nm and reach several millimeters in length. Each end can be opened or closed by a fullerene half-molecule. These nanotubes can have a single layer (like a straw) or several layers (like a poster rolled in a tube) of coaxial cylinders of increasing diameters in a common axis. Multilayer carbon nanotubes can reach diameters of 20 nm.
The small dimensions of carbon nanotubes, combined with their remarkable physical, mechanical and electrical properties, make them a unique material. They display metallic or semiconductive properties, depending onhow the carbon leaf is wound on itself. The current density that a nanotube can carry is extremely high and can reach one billion amperes per square metre, making it a superconductor. Light and flexible, the mechanical strength of carbon nanotubes is more than sixty times greater than that of the best steels, even though they weigh six times less. They also present a very large specific surface area, are excellent heat conductors , and display unique electronic properties, offering a threedimensional configuration. They have a great capacity for molecular absorption. Moreover, they are chemically and thermally very stable.
Figure: 7 Schematic representation ofmonolayer or multilayer carbon nanotubes or nanotubes containing other elements
Nanowires are conductive or semiconductive particles with a crystalline structure of a few dozen nm and a high length/diameter ratio. Silicon, cobalt, gold or copper-based nanowires have already been produced. They are used to transport electrons in nanoelectronics. They could be composed of different metals, oxides, sulphides and nitrides.
D) Carbon nanofoams
Carbon nanofoams are the fifth known allotrope of carbon, after graphite, diamond, carbon nanofibers and fullerenes. In carbon nanofoam, islands of carbon atoms, typically from 6 to 9 nm, are randomly interconnected to form a very light, solid and spongy three-dimensional structure, which can act as a semiconductor. Carbon nanofoams display temporary magnetic properties.
E) Quantum dots
An important field of research for about the past five years, quantum dots (also called nanocrystals or artificial atoms) represent a special form of spherical nanocrystals from 1 to 10 nm in diameter. They have been developed in the form of semiconductors, insulators, metals, magnetic materials or metallic oxides. The number of atoms in quantum dots, which can range from 1,000 to 100,000, makes them neither an extended solid structure nor a molecular entity. The principal research studies have focused on semiconductor quantum dots, which display distinctive quantal effects depending on the dimensions. The light emitted can be adjusted to the desired wavelength by changing the overall dimension.
Figure: 8 Different forms of quantum dots showthe organization of the individual atoms
Dendrimers represent a new class of controlled-structure polymers with nanometric dimensions. They are considered to be basic elements for large-scale synthesis of organic and inorganic nanostructures with dimensions of 1 to 100 nm, displaying unique properties. Dendrimers allow precise, atom-by-atom control of the synthesis of nanostructures according to the desired dimensions, shape and surface chemistry. Given that dendrimers can be developed to display hydrophilic or hydrophobic characteristics, their uses can be highly diversified. With different reactive surface groupings, their abundant use is particularly envisioned in the medical and biomedical field. Compatible with organic structures such as DNA, they can also be fabricated to interact with metallic nanocrystals and nanotubes or to possess an encapsulation capacity or display a unimolecular functionality.
G) Other nanoparticles
Some nanoparticles tend to agglomerate and form structures in chains or with multiple branches. This category normally includes welding fumes, silica fumes, carbon black and other nanoparticles, which are often synthesized by flame pyrolysis. These nanoparticles may include metals, metallic oxides, semiconductors, ceramics and organic material. They may also include composites with a metallic core and an oxide or alloy coating, for example. Colloids, which have been known for a long time, are nanometric dimensions. These nanoparticles will not be considered in this study.
2.3 Nanoparticle characterization tools
The characterization of nanomaterials and the understanding of their behaviour is fundamental to the development of new applications and the reproducible and reliable production of nanomaterials. Process nanometrology uses precision instruments with very high sensitivity, capable of measuring at dimensions that are often less than a nanometer. These instruments allow manipulation of individual atoms and measurement of lengths, shapes, forces, masses, electrical properties and other physical properties. They also use electron beam techniques, including high-resolution transmission electron microscopy. Scanning probe techniques include scanning tunneling microscopy and atomic force microscopy. Optical manipulators allow manipulation and measurement of individual atoms.
3. DEVELOPMENT AND PRODUCTION OF NANOPARTICLES
Development of nanoparticles and nanotechnologies is currently one of the most active research fields worldwide. Several industrialized countries are making it a strategic priority for sustainable technological, economic and societal development. Indeed, in 2001 it was estimated that the potential world market would reach one thousand billion1 US dollars by 2015. In 2003, the British Department of Trade and Industry estimated that there would be a world market of US$100 billion by 2005 (Arnall, 2003). The creation of the US Nanobusiness Alliance, the Europe Nanobusiness Association and the Asia-Pacific Nanotechnology Forum, whose shared objective is to commercialize nanoproducts, clearly illustrates the expected magnitude of these markets and the international competition in the field. Quebec is doing likewise via NanoQuebec.
3.1 Worldwide research efforts
A study published in 2002 concluded that, from 1989 to 1998, the rate of increase of scientific publications on nanomaterials increased annually by 27%. This data indicated that over 30 countries were involved in research in this field, the most active being the United States, Japan, China, France, Great Britain and Russia, which accounted for 70% of publications. Also in 2002, Holister concluded that 455 private companies and 271 academic institutions and government entities were already involved in researching short-term applications in nanotechnology around the world. Since then, this field has continued to grow.
Over the past five years, many countries have developed strategic plans and decided to invest massively in nanotechnology research. This will result in an ongoing increase in scientific articles on the subject and a wider variety of research topics. Roco (2001, 2003) reported that government investments had risen from US$432 million in 1997 to over $2.98 billion in 2003.
Worldwide research efforts are currently estimated at over US$8 billion for the year 2005 alone, about 40% of which would come from the private sector. A detailed review of international investments was carried out by Waters (2003) and by the European Commission (2004a). Despite these colossal investments aimed at development of new commercial applications, research in the occupational health and safety field is still in its infancy.
Five leading Asian countries are heavily involved in research into the development of new products: Japan, China, South Korea, Taiwan and Singapore. Japan is the most important Asian stakeholder in the field and has a completely integrated development policy, which the government sees as the key to the country’s economic recovery. In 2003, the Japanese government invested the equivalent of US$800 million in the nanotechnology field, while the private sector invested an additional $830 million. The British Department of Trade and Industry reported, in 2002, that the first 1 One thousand billion or one million million carbon nanotube and fullerene production plants were under construction in Japan.
The European Union’s 6th Framework Program, known as Nanoforum, allocated US$1.44 billion for the 2002-2006 period and is seeking to develop a European research and communications network integrating all aspects of nanotechnology, ranging from business to science and information intended for the general public. In May 2004, the Commission adopted a plan in which it proposed a safe, integrated and responsible European strategy. Following broad consultations of its members, the 7th Framework Program , proposes to increase the European Union’s R&D investments to strengthen Europe’s global position in this field.
One of the specific objectives of this European initiative is long-term interdisciplinary research to understand the phenomena involved, master the processes and develop research tools. There is particular interest in nanobiotechnologies, nanoengineering techniques, implications for the fields of health and medical systems, chemistry, energy, optics, food and the environment. This European program also covers production and processing of multifunctional materials, the involvement of engineering for the development of materials, and the development of new processes and flexible and intelligent manufacturing systems. The specific initiatives of several countries must be added to these European efforts. Waters (2003) estimates that the aggregate European investments will range between $3.8 billion and $7.8 billion in 2002-2006. However, private enterprise seems to be much less active than in the United States or Japan. Among the most active European countries are Germany, Great Britain, France, Switzerland, Belgium and the Netherlands. Other European countries are also active in nanotechnology R&D, but their investments are more limited: Ireland, Luxembourg, Italy, Austria, Denmark, Finland, Sweden and Norway.
3.2 The most actively studied nanoparticles
The most active research in the nanoparticle field concerns carbon nanotubes, which are expected to have a wide variety of applications in numerous fields. In particular, the use of nanotubes is being considered in electronics, in electrochemistry, as mechanical reinforcements for high-performance composites, as cathode ray transmitters, as a means of energy production or hydrogen storage, or as templates for the creation of other nanostructures, such as production of metallic nanowires by filling carbon tubes. The exceptional strength of the bonds uniting the carbon atoms in a nanotube structure makes them an ideal candidate as reinforcing agents in composites. Among the other uses envisioned, carbon nanotubes could be employed as sensors for high-resolution imaging, in nanolithography, in production of nanoelectrodes or as vectors to transport drugs to specific locations in the human body.
3.3 Polymers used in nanoparticles
As name only suggest polymeric nanoparticles are nanoparticles which are
prepared from polymers. The drug is dissolved, entrapped, encapsulated or
attached to a nanoparticles and depending upon the method of preparation,
nanoparticles, nanospheres or nanocapsules can be obtained. Nanocapsules
are vesicular systems in which the drug is confined to a cavity surrounded by
a polymer membrane, while nanospheres are matrix systems in which the
drug is physically and uniformly dispersed.
In recent years, biodegradable polymeric nanoparticles have attracted
considerable attention as potential drug delivery devices in view of their
applications in drug targeting to particular organs/tissues, as carriers of DNA
in gene therapy, and in their ability to deliver proteins, peptides and genes
through a per oral route of administration.
Classification: Polymers are classified as:
A) Natural polymers:
· Gums (Ex. Acacia, Guar, etc.)
· Sodium alginate
B) Synthetic polymers:
· Poly(2-hydroxy ethyl methacrylate).
· Poly(N-vinyl pyrrolidone).
· Poly(methyl methacrylate).
· Poly(vinyl alcohol).
· Poly(acrylic acid).
· Poly(ethylene-co-vinyl acetate).
· Poly(ethylene glycol).
· Poly(methacrylic acid).
· Polylactides (PLA).
· Polyglycolides (PGA).
· Poly(lactide-co-glycolides) (PLGA).
Originally, polylactides and polyglycolides were used as absorbable suture material. The main advantage of these degradable polymers is that they are broken down into biologically acceptable molecules that are metabolized and removed from the body via normal metabolic pathways. However, biodegradable materials do produce degradation by-products that must be
tolerated with little or no adverse reactions within the biological environment.
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