Nanospheres preparation procedure

Figure 2. Schematic representation of the nanosphere preparation procedure.

Figure 7. Preparation procedure for precipitating technique. Shown also is the schematic illustration of the diffusion stranding mechanism for nanosphere formation that occurs during the precipitation method.

Both nanospheres and nanocapsules are prepared from either a polymerization reaction of dispersed monomers or from a solvent dispersion procedure using preformed polymers. In many instances, the latter procedure using preformed polymer is desirable, as potential reactions between drug and monomer are avoided and the potential toxicity of residual monomers, surfactant, and initiator is reduced [37], The final properties of nanoparticles, such as their size, morphology, drug loading, release characteristics, and biodisti-bution, are all influenced by the method of preparation [38],... 

This procedure is also referred to as the precipitation method and was first reported by Fessi et al. [105]. In this type of preparation, as shown in Figure 7, the polymer is dissolved in a water-miscible solvent and then poured under stirring into a nonsolvent, which is usually water. This leads to the polymer precipitating as nanospheres. Prior emulsification and inclusion of surfactants are not necessary. 

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. 

Similarly, the decomposition of Fe(CO)5 by thermolysis produces metal nanoparticies, the size and shape of which may be controlled by the surrounding medium. For example, a fairly complex procedure was employed for the fabrication of nanorods. Small iron nanospheres are first prepared by thermolysis of Fe(CO)s in the presence of TOPO. Addition of this solution to excess Fe(CO)5 in TOP at 320 °C leads to the production of nanorods... 

Titanium oxide/polystyrene core-shell nanospheres have been prepared using a combined sol-gel/microwave-assisted emulsion polymerization procedure using a modified domestic oven. The sol-gel process gave stable Ti02 colloids that were used as seeds for the subsequent polymerization step accomplished in 1.5 h at 70 °C. 

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