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This review is based on selected reports from 2004 to 2014 and provides a comprehensive and updated overview of the state of the art related to the drug delivery advantages of polymeric nanocapsules, which are a specific type of polymeric nanoparticles used for improvement of biological effects. Special attention is given to the application of nanocapsules to increase the chemical and photostability of drugs, to modulate the interaction with cells and tissues, to reduce adverse effects of drugs, and to increase the drug efficiency and/or bioavailability. Moreover, this review covers in vitro and in vivo studies, highlighting interesting examples of drugs from several therapeutic classes for which efficacy is improved by encapsulation in different types of nanocapsules, especially in lipid-core nanocapsules. We also briefly present the first results obtained so far attesting to the safety of using polymeric nanocapsules for drug delivery.

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This work explored the effect of the encapsulation in polymeric nanocapsules, as well as of the incorporation of such nanoparticles in a chitosan hydrogel, on the skin adhesion and skin penetration/permeation of capsaicinoids (capsaicin and dihydrocapsaicin), which are used as topical analgesic to treat chronic pain. The skin experiments were performed using a modified (drug adhesion and drug diffusion) and a normal Franz diffusion cell (drug diffusion) with porcine skin as membrane. The AUC0-h of the washability profile (% washed away vs. time) determined for the formulation combining both factors studied (chitosan hydrogel containing drug-loaded nanocapsules) was 198.88 +/- 10.05/153.53 +/- 5.99, for capsaicin and dihydrocapsaicin respectively, significantly lower than the values observed for the chitosan hydrogel containing free drug (291.57 +/- 3.83/278.18 +/- 5.28) and for the hydroxyethyl cellulose containing drug-loaded nanocapsules (245.47 +/- 13.18/197.69 +/- 15.78). By adequate fitting to the monoexponential first order equation, the washing rate values indicated that the nanocapsules were more efficient in increasing the drugs skin adhesion than the chitosan gel. Regarding the skin penetration/permeation study, after washing the skin, the formulation which presented the lowest washing rate (chitosan gel containing nanocapsules) was the one which led to a higher amount of capsaicinoids in the skin layers (epidermis and dermis). Without washing the skin, the nanoencapsules caused retention of the drugs in the outer skin layer (epidermis). In conclusion, the skin adhesion of the nanocapsules and their capability of controlling the drug diffusion were shown. Combining chitosan gel to nanocapsules led to a formulation of great skin bioadhesion.

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For an improved understanding of the relevant particle features for cutaneous use, we studied the effect of the surface charge of acrylic nanocapsules (around 150nm) and the effect of a chitosan gel vehicle on the particle penetration into normal and stripped human skin ex vivo as well as local tolerability (cytotoxicity and irritancy). Rhodamin-tagged nanocapsules penetrated and remained in the stratum corneum. Penetration of cationic nanocapsules exceeded the penetration of anionic nanocapsules. When applied on stripped skin, however, the fluorescence was also recorded in the viable epidermis and dermis. Cationic surface charge and embedding the particles into chitosan gel favored access to deeper skin. Keratinocytes took up the nanocapsules rapidly. Cytotoxicity (viability<80%), following exposure for ≥24h, appears to be due to the surfactant polysorbate 80, used for nanocapsuleś stabilization. Uptake by fibroblasts was low and no cytotoxicity was observed. No irritant reactions were detected in the HET-CAM test. In conclusion, the surface charge and chitosan vehicle, as well as the skin barrier integrity, influence the skin penetration of acrylic nanocapsules. Particle localization in the intact stratum corneum of normal skin and good tolerability make the nanocapsules candidates for topical use on the skin, provided that the polymer wall allows the release of the active encapsulated substance.

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Aim: To evaluate the effect of cationic coating of polymeric nanocapsules in sunscreen formulations on the in vitro skin penetration of benzophenone-3. Methods: Benzophenone-3-loaded nanocapsules were prepared by the interfacial deposition of poly(Ε-caprolactone) and coated by using a chitosan solution. The nanoparticles were characterized and incorporated in hydrogels. The presence of nanoparticles in hydroxyethyl cellulose gels was observed by transmission electron microscopy and photon correlation spectroscopy. Penetration studies were carried out using Franz cells with porcine skin membranes. Results: Benzophenone-3-loaded chitosan-coated nanocapsules presented a mean size of 202 ± 7 nm and positive zeta potential (+21 ± 1 mV), while these values for the uncoated nanocapsules were 175 ± 1 nm and –8 ± 1 mV. Penetration profiles showed that a higher amount of benzophenone-3 remained at the skin surface and a lower amount was found in the receptor compartment after the application of the formulation containing chitosan-coated nanocapsules compared to a formulation containing its free form. Conclusions: Hydrogel containing benzophenone-3 chitosan-coated nanocapsules represents an innovative formulation to overcome limitations of sunscreen daily use.