Nanodispersion, aqueous

H Ibrahim, C Bindschaedler, E Doelker, P Buri, R Gurny. Aqueous nanodispersions prepared by a salting-out process. Int J Pharm 87 239-246, 1992. 

E Allemann, R Gurny, E Doelker. Preparation of aqueous polymeric nanodispersions by a reversible salting-out process, influence of process parameters on particle size. Int J Pharm 87 247-253, 1992. 

The reprecipitation strategy lies in the conversion of the products dissolved in a suitable organic solvent into nanodispersed systems in a different medium by a precipitation/condensation procedure. On the other hand, the ion-association strategy can produce ion-based dye nanoparticles in pure aqueous media by utilizing a water-insoluble ion-pair formation reaction. The following example shows the size-dependent absorption properties for the cation-based pseudoisocyanine (PIC see the chemical structure in Fig. 4) dye nanoparticles. 

To increase dispersion or surface area of salt-enzyme preparations in organic media, a method of preparing surfactant-assisted salt enzyme nanodispersions (SSENDs) was explored. The goal was to create a fine dispersion of the salt enzyme lyophilized particles with the use of a siufactant prior to lyophilization by creation of a fine emulsion, followed by removal of solvent and water by lyophilization. Microscopic observation of the emulsion indicated a submicron dispersion of the aqueous phase in the solvent. The results of the ertzyme assay using SSENDs catalyst is shown in Table 3. This experiment was conducted in hexane to determine if such a preparation can enhance activity of the enzyme because posdyophilization addition of the surfactant did not improve the rate of the reaction. The results show that a two- to threefold higher rate can be obtained by preparation of the salt-SC using the SSENDs preparation method. 

Much work has focused on improving aqueous coating efficiency and quality by a multitude of methods. But there has been less focus on the huge impact particle size may potentially have on film quality particularly when at the nanoscale. This is not to say nanodispersions of polymers are not available on the market, but simply that a direct comparison of the same polymer in micro- and nanoscale has not been carried out. 

F. Roelofs, W. Vogelsbetger, Dissolution kinetics of nanodispersed y-alumina in aqueous solution... 

Exclusively submicron particles obtained by high pressure homogenization were used in a study which compared skin interaction of GMO-based cubic nanoparticles (with additional vesicular structures as observed by cryo-TEM) with that of other lipidic nanoparticles with compact liquid, crystalline or thermotropic liquid crystalline matrix structure. The cubic nanodispersion, which was stable with respect to particle size for 15 months of storage at room temperature, increased skin permeation of the model substance corticosterone (used in trace amounts in this study) compared to the other types of lipid nanoparticles. Permeation from all lipidic dispersions was, however, lower than from an aqueous solution which was attributed to the retention of a certain fraction of the drug in the lipid nanoparticles. Considering only the drug present in the aqueous phase of the dispersion as available for transport through the epidermis, the presence of cubic GMO particles increased permeation by the factor 2.4. 

Characteristic features of emulsions which are used to extract and concentrate substances from aqueous solutions are examined. The effects of surfactant and carrier concentrations and external and internal phase compositions upon the properties of the extracting emulsions are discussed. Several mathematical models for the rheological curves are considered, and regions of adequacy of the models are determined. An influence of nanodispersion formation on mass transfer through the interface and on the properties of the extracting emulsions for cholesterol is demonstrated. 

Special conditions for pre-treatment of the initial emulsion to enhance nanodispersion formation have been developed. An additional amount of ethanol (10-25 %) is first incorporated into the internal phase of the extracting emulsion. The resulting emulsion is contacted with an aqueous buffer solution of pH equal to that of the internal aqueous phase and then with doubly distilled water or an aqueous buffer at pH 7.4. During this process some of the ethanol diffused from the internal phase of the emulsion into the external aqueous solution which stimulates nanodispersion formation. 

Figure 11 shows the period for half separation of the external aqueous phase in the emulsions as a fimction of the ethanol concentration with and without this pretreatment. As can be seen, repeating the pre-treatment three times produces an eightfold enhancement in stability of the emulsion to coalescence. Although almost all of the nanodispersion is formed during the pre-treatment step, this is not detrimental to the extraction properties of the emulsion. 

Drops of the nanodispersion can play the role of transfer agents leading to transmembrane transfer of water to the internal phase (i.e. swelling of the emulsion) which is undesirable. Thus in addition to the surfactant and carrier molecules, droplets of the nanodispersion may also be a major contributor to water transport from the external aqueous phase into the internal aqueous phase. 

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