The core objective of nanoparticles is to control and manipulate biomacromolecular constructs and supramolecular assemblies that are critical to living cells in order to improve the quality of human health. By definition, these constructs and assemblies are nanoscale and include entities such as drugs, proteins, DNA/RNA, viruses, cellular lipid bilayers, cellular receptor sites and antibody variable regions critical for immunology and are involved in events of nanoscale proportions. The emergence of such nanotherapeutics/diagnostics will allow a deeper understanding of human longevity and human ills that include cancer, cardiovascular disease and genetic disorders. A technology platform that provides a wide range of synthetic nanostructures that may be controlled as a function of size, shape and surface chemistry and scale to these nanotechnical dimensions will be a critical first step in developing appropriate tools and a scientific basis for understanding nanoparticles.
Conventional preparations like solution, suspension or emulsion suffer from certain limitations like high dose and low availability, first pass effect, intolerance, instability, and they exhibit fluctuations in plasma drug levels and do not provide sustained effect, therefore there is a need for some novel carriers which could meet ideal requirement of drug delivery system. Recently nanoparticles delivery system has been proposed as colloidal drug carriers. Nanoparticles (NP) are a type of colloidal drug delivery system comprising particles with a size range from 10 to 1000 nm in diameter. Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials (Buzea et al., 2007). The key advantages of nanoparticles are (1) improved bioavailability by enhancing aqueous solubility, (2) increasing resistance time in the body (increasing half life for clearance/increasing specificity for its cognate receptors and (3) targeting drug to specific location in the body (its site of action). This results in concomitant reduction in quantity of the drug required and dosage toxicity, enabling the safe delivery of toxic therapeutic drugs and protection of non target tissues and cells from severe side effects (Irving, 2007). It is increasingly used in different applications, including drug carrier systems and to pass organ barriers such as the blood-brain ophthalmic barrier, cell membrane etc. (Abhilash, 2010). They are based on biocompatible lipid and provide sustained effect by either diffusion or dissolution (Cavalli et al., 1995; Müller et al., 2000; Yang et al., 1999 ; zur Mühlen and Mehnert, 1998).
2. Drug release from nanoparticles
The nanoparticle is coated by polymer, which releases the drug by controlled diffusion or erosion from the core across the polymeric membrane or matrix. The membrane coating acts as a barrier to release, therefore, the solubility and diffusivity of drug in polymer membrane becomes the determining factor in drug release. Furthermore release rate can also be affected by ionic interaction between the drug and addition of auxillary ingredients. When the drug is involved in interaction with auxillary ingredients to form a less water soluble complex, then the drug release can be very slow with almost no burst release effect (Chen et al., 1994).
To develop a successful nanoparticulate system, both drug release and polymer biodegradation are important consideration factors. In general, drug release rate depends on (1) solubility of drug, (2) desorption of the surface bound/ adsorbed drug, (3) drug diffusion through the nanoparticle matrix, (4) nanoparticle matrix erosion/degradation and (5) combination of erosion/diffusion process (Mohanraj and Chen, 2006). Thus solubility, diffusion and biodegradation of the matrix materials govern the release process.
3. Types of nanoparticles
Extensive libraries of nanoparticles, composed of an assortment of different sizes, shapes, and materials, and with various chemical and surface properties, have already been constructed. The field of nanotechnology is under constant and rapid growth and new additions continue to supplement these libraries. The classes of nanoparticles listed below are all very general and multi-functional; however, some of their basic properties and current known uses in nanomedicine are described here.
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and cylindrical ones are called carbon nanotubes or buckytubes. Fullerenes are similar in structure to the graphite, which is composed of stacked grapheme sheets of linked hexagonal rings, additionally they may also contain pentagonal (or sometimes heptagonal) rings to give potentially porous molecules (Holister et al., 2003). Buckyball clusters or buckyballs composed of less than 300 carbon atoms are commonly known as endohedral fullerenes and include the most common fullerene, buckminsterfullerene, C60. Megatubes are larger in diameter than nanotubes and prepared with walls of different thickness which is potentially used for the transport of a variety of molecules of different sizes (Mitchell et al., 2001). Nano “onions” are spherical particles based on multiple carbon layers surrounding a buckyball core which are proposed for lubricants (Sano et al., 2001). These properties of fullerenes hold great promise in health and personal care application. The versatile biomedical applications are enlisted in Table 1.
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