Dendrimers nanosystems

Fig. 8 Nanosystems that may function as simultaneous drug delivery and imaging agents for targeting T cells (a) liposomal systems, (b) solid biodegradable nanoparticulates, and (c) macro-molecular dendrimer complexes. PEG polyethylene glycol, Gd-DTPA gadolininum-diethylene triamine penta acetic acid. (Adapted from [48])...

Figure 8.33 Nanosystems formed by association of dendrimers in aqueous solution. These structures are around 50 nm in diameter.

It is useful, for reasons which are apparent in relation to movement of nanoparticles in vivo, to divide nanosystems into two types, hard and soft, although there are obviously intermediate situations. Hard systems, for example, polymeric nanoparticles and nanocapsules, nanosuspensions or nanocrystals, dendrimers, and carbon nanotubes are neither flexible nor elastic. Hard systems can block capillaries and fenestrae that have dimensions similar to the particles, whereas soft systems can deform and reform to varying degrees. Erythrocytes and many liposomes fall into this category and are thus better able to navigate capillary beds and tissue extracellular spaces. Soft systems include nanoemulsions (microemulsions) and polymeric micelles. 

A plethora of different nanosized particles have been adopted for biomedical and pharmaceutical applications, including inorganic and organic nanoparticles (NPs). The most commonly adopted inorganic NPs include magnetic particles (mainly for imaging), silica particles, metal oxides, carbides, borates, sulfides, hydroxides, and salts (eg, calcium phosphate, calcium carbonate, calcium sulfate). Organic NPs include oil-in-water (0/W) emulsions, double emulsions [water-in-oil-in-water (W/OAV)], and polymer-based NPs. Different polymer-based nanosystems are adopted and include polymer micelles, dendrimers, polymerosomes, and polymeric NPs. 

For DNA and RNA delivery to the central nervous system (CNS), numerous nonviral nanosystems can be employed [10], These include cationic and stealth liposomes, cationic polymers, dendrimers, cyclodextrin, and cell-penetrating peptides (CPPs). In general terms, all these synthetic vectors lack of a cytotropism, i.e., they do not specifically target a single type/subtype of cell, and display different degrees of cytotoxicity. 

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