DELIVERY SYSTEMS
oligomer Horny layer Granulous layer
Spinous layer Basal layer
Hypodermis Dermis
Chitin
Figure 2: Diversified skin release of chitin block-polymer-nanoparticles dependent on size.
charged. HA is, in fact, a polyanion, which can interact with the polycationic CN by electrostatic forces.18
Through this method the CN acidic suspension is added drop wise under constant stirring to polyanionic HA suspension and vice versa. Due to the complexation between oppositely charged species, CN undergoes ionic gelation and precipitate to form micro and nano lamellae or spherical particles positively or negatively charged on their surface, depending on the method of preparation (Fig. 4).
Thus, it is also possible to entrap within the nanoparticles different active ingredients, hydro or liposoluble, via the use of pre-selected tensides. The active ingredients and the tensides are solubilised into the water suspension of CN or HA or in both, before going on with the ionic gelation.
The obtained medium size of nanoparticles was between 250 nm and 400 nm. However the size of the particles can be controlled by controlling the size of aqueous droplets. The particle size of the final product depends upon the nature and molecular weight of the active ingredient and the tenside, speed of stirring, pH of environment, as well as concentration of the anionic and cationic polymer and the stabilising agent (i.e. tenside). The obtained nanolamellae or nanospheres have been separated by filtration followed by successive washing with water. Soon after, they were also purified by centrifugation, re-suspended in demineralised water and atomised in a stream of hot air by spray-drying technique. The obtained CN nano particles entrapping lutein have been
96 PERSONAL CARE April 2012
controlled for their load and entrapping capacity in comparison with chitosan and amorphous chitin, as shown on Table 1. Moreover, also controlled was the releasing capacity of lutein from the nanoparticles together with the obtained medium size dimension. The highest and most regular release of lutein was obtained from the CN nanoparticles in which the dimensions were the lowest compared to chitosan and amorphous chitin.
It is useful to underline that the superficial electrical charges of the nanoparticles greatly influence their penetrability through the stratum corneum. As shown in Figure 5, and reported elsewhere by in vitro and in vivo studies,10,11
positively charged
nanocapsules (i.e. CN-HA nanoparticles) had the ability to easily load active lutein, controllably releasing it at a level of different skin layers, and as a function of storage time. It has been shown that positively charged nanoparticles are able to increase skin penetration of lutein or other active ingredients, overcoming the stratum corneum barrier function, while negatively charged nanoparticles (i.e.
CN-HA nanoparticles) remain at the level of the outermost corneocytes. What is the supposed mechanism of action? Probably the positive electrical charges, covering the nanoparticles, have the possibility to change the physical properties of the stratum corneum, temporally increasing the diffusivity of the entrapped active ingredients. Also, electropopration, sonophoresis or iontophoresis are able to create spaces of penetration among corneocytes and lipid lamellae by their mechanical energy. However, the major advantage of these nanocapsules is their 100% natural composition and the possibility to manipulate their properties, such as surface charges and size, so that the relative release of the entrapped active ingredients may arrive at the level of the designed skin layers. The release of active ingredients from CN particulate systems generally involves three different mechanisms: Release from the surface of nanoparticles.
Release due to co-polymer erosion. Diffusion through the swollen rubbery matrix (Fig. 6).19
Table 1: Nanoparticle yield, lutein loading content and entrapment efficiency of different kinds of chitin and chitosan complexed with hyaluronic acid.
Polymer Chitosan-HA-Lutein
Nanoparticle Lutein loading Entrapment Particle mean yield (%)
33±9
Amorphous Chitin-HA-Lutein 31±10 Crystal-Chitin HA (CN) Lutein 42±9
Note: all measurements were performed in triplicate. CN: Chitin nanofibrils; HA: Hyaluronic acid.
content (%) efficacy (%) 10±3
18±3 35±3
32±5 40±5 66±6
size (nm) 458±14
355±13 185±13
Mavi Diffusion System (MDS)
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