Particle, drug delivery systems

MAJOR APPLICATIONS Membranes, chromatographic resins, size exclusion particles, drug delivery systems. 

Nanomaterials are particles between 1 and 100 nm in diameter. They have properties that differ from the properties of atoms and from those of bulk materials and are used to create miniature circuits and drug delivery systems. 

Xylans from beech wood, corncobs, and the alkaline steeping liquor of the viscose process have been shown to be applicable as pharmaceutical auxiliaries [3]. Micro- and nanoparticles were prepared by a coacervation method from xylan isolated from corncobs [150]. The process is based on neutralization of an alkaline solution in the presence of surfactant, which was shown to influence both the particle size and morphology. They are aimed at applications in drug delivery systems. 

A large variety of drug delivery systems are described in the literature, such as liposomes (Torchilin, 2006), micro and nanoparticles (Kumar, 2000), polymeric micelles (Torchilin, 2006), nanocrystals (Muller et al., 2011), among others. Microparticles are usually classified as microcapsules or microspheres (Figure 8). Microspheres are matrix spherical microparticles where the drug may be located on the surface or dissolved into the matrix. Microcapsules are characterized as spherical particles more than Ipm containing a core substance (aqueous or lipid), normally lipid, and are used to deliver poor soluble molecules... 

As discussed earlier, noncollagenous proteins, particularly albumin and to a lesser extent gelatin, in the form of microspheres and nanoparticles continue to be exploited as drug delivery systems. Oppen-heim (71) and Speiser (72) reviewed the technology developed to produce ultrafine particles, often referred to as nanoparticles. 

Solubilization of vinylpyrrolidone, acrylic acid, and A,A -methylene-bis-acrylamide in AOT-reversed micelles allowed the synthesis in situ of a cross-linked polymer with narrow size distribution confined in the micellar domain. These particles displayed high entrapment efficiency of small hydrophilic drugs and have been considered interesting drug delivery systems [239],... 

Silica particles A novel drug-delivery system. Advanced Materials, 16, 1959-1966. 

Schiraldi et al. [64] have developed this kind of material by combining silica particles and pHEMA. pHEMA is a biocompatible hydrogel that has been widely studied in the past decades due to its chemical-physical structure and mechanical properties. It has been widely used in ophthalmic prostheses (contact or intraocular lenses), vascular prostheses, drug delivery systems and soft-tissue replacement [65]. These authors have shown that by incorporating silica nanoparticles, the resulting hybrid material is highly biocompatible and promotes bone cell adhesion and proliferation of bone cells seeded on it.1 ... 

Clearly, the definitive characteristic of any nanoparticulate drug delivery system will be its submicrometer diameter. Sizing such particles in the suboptical region can be difficult as the measuring technique itself may alter size and properties by either hydrating or aggregating the particles. This will have a profound influence on the size of the particle [59]. Haskell [134] has discussed the various optical techniques available to measure the size of nanoparticles. 

Many proteins and protein-like materials are precipitated from aqueous solution by the application of heat or the addition of electrolyte, and this general reaction can be used to prepare solid particles with various particle size ranges. Under the right conditions these particles can be made reproducibly and serve as drug delivery systems in their own right, being especially suitable for the delivery of other proteins or polypeptides. 

Most coacervates explored as drug delivery systems consist of particles dispersed in a liquid continuum. The questions as to how these systems are made and how they may be presented as drug delivery systems depends to a large degree on the individual formulator. 

What was interesting about this study is that it was possible to demonstrate that the sugar was adsorbed onto the internal gelatin particle matrices as well as the visible external particle surface (Table 8.3). This factor needs to be taken into account in any studies on the use of gelatin particles as drug delivery systems, especially if the initial production process is likely to have any influence on the intrinsic characteristics of the matrix. 

FIGURE 10.3 Schematic presentation of lipid based drug delivery systems. Micelles (right) are composed of a solid lipid core with the polar heads exposed to the aqueous environment. Liposomes (left) are particles with a hpid bilayer surrounding an aqueous core. Drug can be encapsulated in the hydrophobic regions of the lipid particle, in the aqueous environment of the liposome, or adsorbed to the surface of the lipid particle. 

The variety of materials which can be incorporated into polyelectrolyte multilayers makes them attractive to use as biosensors [431], Polyelectrolyte multilayers can also be formed on curved surfaces of small particles [432], After adsorption, the core particle can be chemically dissolved and a hollow polyelectrolyte capsule remains. These capsules are selectively permeable for small molecules like water or certain dyes. The permeability can be tuned externally by varying the ion strength, pH, temperature and solvent nature [433 135], Therefore, it has been suggested to use them as selective membranes for separation, as well as a possible drug delivery system. The adjustment of their size and permeability allows us to exploit them as micro- or nanocontainers for chemical synthesis and crystallization. 

In many cases in drug development, the solubility of some leads is extremely low. Fast dissolution rate of many drug delivery systems, for example, particle size reduction, may not be translated into good Gl absorption. The oral absorption of these molecules is usually limited by solubility (VWIImann et al., 2004). In the case of solubility limited absorption, creating supersaturation in the Gl Luids for this type of insoluble drugs is very critical as supersaturation may provide great improvement of oral absorption (Tanno et al., 2004 Shanker, 2005). The techniques to create the so-called supersaturation in the Gl Luids may include microemulsions, emulsions, liposomes, complexations, polymeric micelles, and conventional micelles, which can be found in some chapters in the book. 

Vinogradov, S., Batrakova, E. and Kabanov. A. (1999b) Poly(ethylene glycol)-polyethyleneimine NanoGel particles novel drug delivery systems for antisense oligonucleotides. Colloids and Surfaces B Biointerfaces, 16, 291-304. 

Janes, K.A., P. Calvo, and M.J. Alonso. 2001. Polysaccharide colloidal particles as delivery systems for macromolecules. Adv Drug Deliv Rev 47 83. 

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