Nanocapsule formation

Mechanism of nanocapsules formation by the emulsion-diffusion process. Journal of Colloid and Interface Science, 317, 458-4-68. 

Fessi H, et al. Nanocapsule formation by interfacial polymer deposition following solvent displacement. Int J Pharm 1989 55 R1. 

Fig. 21 Scheme of nanocapsule formation. The template liposome with homogeneously distributed monomers is irradiated with UV light, resulting in the formation of a fortified liposome. After lipid removal, the 2D polymer network constitutes an intact hollow nanocapsule. Reprinted with permission from [112]. Copyright 2006, American Chemical Society... 

Paiphansiri U, Tangboriboonrat P, Landfester K (2007) Antiseptic nanocapsule formation via controlling polymer deposition onto water-in-oU miniemulsion droplets. Macromol Symp... 

The presence of the surfactant SDS influences nanocapsule formation in two ways With increasing SDS cmicentration, the nanocapsules become smaller. At the same time, with decreasing size of the nanocapsule, the coverage of the nanoobjects (before evaporation of the solvent, the nanodroplets after the evaporatimi, the nanoparticles or nanocapsules) by SDS increases, leading to a decrease in the interfacial tension of droplel/water and copolymer/water. The interfacial tension between copolymer and water ( 0.035 N/m) without surfactant is considerably smaller than the interfacial tension between hexadecane and water ( 0.054 N/m). Thus, in the case of a low concentration of SDS and subsequent coverage of the nanoobjects by SDS, the interfacial tension of the copolymer/water interface is lower than that of the hexadecane/water interface therefore as the thermodynamically most stable structure, nanocapsules are expected to be formed (Fig. 54a). 

There are many other examples in which a solid-derived colloidal approach is being developed and used—such as nanocapsule formation (Self-Assembly of Polymers into Soft Nanoparticles and Nanocapsules, Soft Mat-ter). These colloidal systems can be considered as being... 

H. Fessi, J.P. Puisieux, N. Devissaget, N. Ammoury, and S. Benita, Nanocapsule formation by interfacial polymer deposition following solvent displacement. International Journal of Pharmaceutics, 55 (1), R1-R4,1989. 

Other techniques of nanocapsule formation are discussed by Marty et al, [192]. Colloidal systems for drug delivery are reviewed in [193]. Most involve surfactants at some stage in their preparation, either to solubilize monomer, to disperse monomers in solvents or to stabilize emulsions in the preparation of protein microspheres or microcapsules. 

Different sized nanocapsules are formed by a miniemulsion polymerization of variety of monomers in the presence of larger amounts of hydrophobe [117]. Hydrophobe and monomer form a common miniemulsion before polymerization, whereas the polymer is immiscible with the hydrophobe and phase-separates throughout the polymerization to form particles with a morphology consisting of a hollow polymer structure surrounding the hydrophobe. Differences in the hydrophilicity of oil and polymer turned out to be the driving force for the formation of nanocapsules. In the case of poly(methyl methaciylate) (PMMA) and hexadecane (HD), the pronounced differences in hydrophilicity are suitable for direct nanocapsule formation. In the case of styrene as the monomer, the hydrophilicity of the polymer phase has to be adjusted in order to favor the nanocapsule structure, which is done either by the addition of an appropriate comonomer or initiator. 

Table 1. Formation of filled nanocapsules. Elements in shadowed boxes are those which were encapsulated so far. M and C under the chemical symbols represent that the trapped elements are in metallic and carbide phases, respectively. Numbers above the symbols show references.

Having already examined the use of the LbL method to make various nanocapsules, including polymer nanocapsules, and having already encountered the use of star polymers for catalyst encapsulation, we turn our attention to other methods for the formation of polymeric nanocapsules. Useful reviews of the formation of these capsules using various methods are available [78-84]. 

Letchford K, Burt H (2007) A review of the formation and classification of amphiphilic block copolymer nanoparticulate structures micelles, nanospheres, nanocapsules and polymersomes. Eur J Pharm Biopharm 65 259-269... 

The procedure chosen for the preparation of lipid complexes of AmB was nanoprecipitation. This procedure has been developed in our laboratory for a number of years and can be applied to the formulation of a number of different colloidal systems liposomes, microemulsions, polymeric nanoparticles (nanospheres and nanocapsules), complexes, and pure drug particles (14-16). Briefly, the substances of interest are dissolved in a solvent A and this solution is poured into a nonsolvent B of the substance that is miscible with the solvent A. As the solvent diffuses, the dissolved material is stranded as small particles, typically 100 to 400 nm in diameter. The solvent is usually an alcohol, acetone, or tetrahydrofuran and the nonsolvent A is usually water or aqueous buffer, with or without a hydrophilic surfactant to improve colloid stability after formation. Solvent A can be removed by evaporation under vacuum, which can also be used to concentrate the suspension. The concentration of the substance of interest in the organic solvent and the proportions of the two solvents are the main parameters influencing the final size of the particles. For liposomes, this method is similar to the ethanol injection technique proposed by Batzii and Korn in 1973 (17), which is however limited to 40 mM of lipids in ethanol and 10% of ethanol in final aqueous suspension. 

Skiba, M., Nemati, F., Puisieux, F., Duchene, D., Wouessidjewe, D. (1996). Spontaneous formation of drug-containing amphiphilic p-cyclodextrin nanocapsules. International Journal of Pharmaceutics, 145, 241-245. 

Block Copolymers are macromolecules which are composed of blocks usually in linear as it shown in Fig. 3.20, where it is illustrated a classical block copolymer. Main block copolymers are amphiphilic block copolymers having united hydrophilic blocks to hydrophobic blocks. Amphiphilic block copolymer have surfactant properties and form different kinds of associations, such as micelles, nanospheres, nanocapsules and polymersomes This tipe of association can act like excellent vehicles of several active principles. The composition, aggregate formation and the different applications of these materials have been reviewed [112], Figure 3.20 also illustrates the nanoparticulate drug delivery systems formed by amphiphilic block copolymers and their general characteristics. 

When the core is an oily liquid, the surrounding polymer is a single layer of polymer, and the vesicle is referred to as a nanocapsule. These systems have found utility in the encapsulation and delivery of hydrophobic drugs Polymers used for the formation of nanocapsules have typically included polyester homopolymers such as poly(D,L-lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) and poly(caprolactone) PCL [112],... 

As a third possibility, nanocapsules in a miniemulsion system could be achieved using different interfacial reactions in inverse miniemulsions. The formation of polyurea, polythiourea, and polyurethane nanocapsules synthesized through the polyaddition reaction has been described in detail [110-112], The size of the nanocapsules could be controlled by the amount of surfactant used and the addition time of the diisocyanate. The wall thickness was adjusted by the amount of employed monomers. dsDNA molecules were successfully encapsulated into poly-butylcyanoacrylate (PBCA) nanocapsules by anionic polymerization, which took place at the interface between the miniemulsion droplets and the continuous phase [113]. 

The crosslinking of starch at the droplet interface in inverse miniemulsion leads to the formation of hydrogels. The formulation process for the preparation of crosslinked starch capsules in inverse miniemulsion is schematically shown in Fig. 10. The influence of different parameters such as the amount of starch, surfactant P(E/B-fe-EO), and crosslinker (2,4-toluene diisocyanate, TDI) on the capsule size and stability of the system were studied. The obtained capsules were in a size range of 320-920 nm. Higher amounts of starch and surfactant result in a smaller capsule size. The TEM images of crosslinked starch capsules prepared with different amount of crosslinker (TDI) are presented in Fig. 11. The nanocapsules can be employed as nanocontainers for the encapsulation of dsDNA molecules with different lengths [114] and for the encapsulation of magnetite nanoparticles. 

Chouinard, F., Buczkowski, S., and Lenaerts, V. (1994), Poly(alkylcyanoacrylate) nanocapsules Physico-chemical characterization and mechanism of formation, Pharm. Res., 11,869. 

Allowing self-assembly of CDs resulting in the spontaneous formation of nanosize carriers in the form of nanospheres and nanocapsules... 

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