**5. Applications of nanocapsules in therapeutics**

Nanotechnology has revolutionized cancer diagnosis and therapy. Protein engineering and materials science have contributed to the development of new nanosystems for drug delivery. The major features of nanoparticles for their application in drug delivery are particle size and size distribution. These determine the capacity to reach the target, drug distribution and toxicity, and influence charge and drug release, as well as the stability of nanoparticles. Smaller nanoparticles present a larger surface/volume ratio; in this case, the drug, which is closer to the surface, is expected to be released at a higher speed. Because of their small size, these nanoparticles can cross the sore endothelium, the intestinal epithelium, for example, in tumors, and enter microcapillaries of 5–6 microns diameter, and it also enables them to be selectively captured by cells and cause drug accumulation in certain places. On the other hand, the smaller the particle size, the more the risk of aggregation during the storage, transport, and manipulation. With respect to bigger particles, they allow for a larger drug per particle encapsulation, which derives in a slower release. Therefore, particle size control results in a regulation of the drug release rate. Moreover, size also affects polymeric degradation. In the case of cancer treatment, the aforementioned properties are fundamental; due to their small size, nanoparticles can access tumors and concentrate there through the EPR effect (enhanced permeability and retention). To the moment, many nanotechnological systems have been developed and tested as anticancer drug carriers, however, difficulty arises from the fact that these drugs do not differentiate healthy from tumoral cells. For that reason, it is necessary to investigate strategies that permit systems to reach the tumor specifically [1, 53].

As to the surface properties of nanoparticles, hydrophobicity influences their destiny, as it determines the level of blood components (such as opsonin) that will join them. It is essential to minimize opsonization to prolong the circulation of nanoparticles in blood. With this goal, nanoparticles can be coated with hydrophilic/surfactant and/or biodegradable polymers, such as PEG, polyethylene oxide, poloxamer, poloxamine, and polysorbate 80 (Tween 80) [1]. Targeted delivery can be active or passive. In the first case, the active principle or the nanosystem must conjugate to a specific ligand from the cell or tissue, whereas when the delivery is passive, the drug is released in the target organ. Nanocarriers concentrate preferably in tumors,

*Lipid and Polymeric Nanocapsules DOI: http://dx.doi.org/10.5772/intechopen.103906*

inflammatory sites, and at antigen sampling sites due to the EPR effect of the vasculature. Anti-neoplastic, anti-viral drugs, and several other drugs are unable to cross the BBB. Nanoparticles with Tween 80 and those formulated with hyper-osmotic mannitol, which breaks the strong unions present, have been proved to be able to cross the BBB and provide a sustained release of drugs for the treatment of brain tumors. Once the target is reached, nanoparticles from biodegradable hydrophobic polymers become like a reservoir and start releasing the active compound in a continuous way. This type of system is usually employed to improve bioavailability and sustained release, and even to solubilize drugs for systemic delivery, and the systems adapt to protect bioactives from enzymatic degradation by nucleases and proteases, for instance [1].
