Solid dispersions cooling process

Urea Urea has been used both to form solid dispersions by the cooling of urea-drug mixtures and to directly coat drug-laden particles in melt-coating operations. It has a melting point of approximately 130°C and is highly soluble in water. A variety of urea-drug dispersions obtained from melt processes... 

Van den Mooter et al. prepared solid dispersions of tamazepam in PEG 6000 and polyvinylpyrrolidone K30 (PVP K30) by the fusion (melting) and cooling process. In contrast to the very slow dissolution rate of pure temazepam, the dispersion of the drug in the polymers enhanced the dissolution rate considerably. This can be attributed to improved wettability and dispersibility and a decrease of the crystalline fraction of the drug. 

In contrast, there are no solvents used in HME processes for manufacturing amorphous solid dispersions. Instead, the mixture of crystalline drug and polymer are heated to a temperature at which the components melt or form a eutectic, and then flash cooled, resulting in a dense amorphous glassy solid. The solid is then milled to achieve uniform particle size distribution, which is then processed into the final formulation. Therefore, the milling step will determine particle size and surface area, which in turn is related to the dissolution rate of the solid. 

Figure 5 displays the SEM and TEM images of Ag core/poly(ADA)-shell hybridized NCs [50], Actually, Ag core was clearly covered with almost uniform poly(ADA) shell. The thickness of the shell was about 5 nm, and the morphology of the core/shell nanostructure in the present hybridized NCs was dependent remarkably on microwave irradiation conditions [50], For example, the above-mentioned microwave irradiation condition is the most desirable, and the core/shell nanostructure could not be formed successfully when the irradiation condition was 500 W, 20 s or 200 W, 40 s. After co-reprecipitation, the dispersion liquid is considered to be a mixture of Ag NPs and ADA NCs. The heated ADA NCs were probably partially melted by microwave irradiation, and may easily collide and fuse with Ag NPs at the elevated temperature. As a result, molten ADA monomer could adsorb effectively on the surface of Ag core, and was then recrystallized to form solid-state polymerizable ADA shell during the cooling process after microwave irradiation [50]. The present co-reprecipitation and microwave-irradiation method is available for the fabrication of another type of metal-core/ji-conjugated polymer-shell hybridized NCs [107]. 

Liposphere formulations are prepared by solvent or melt processes. In the melt method, the active agent is dissolved or dispersed in the melted solid carrier (i.e., tristearin or polycaprolactone) and a hot buffer solution is added at once, along with the phospholipid powder. The hot mixture is homogenized for about 2 to 5 min, using a homogenizer or ultrasound probe, after which a uniform emulsion is obtained. The milky formulation is then rapidly cooled down to about 20°C by immersing the formulation flask in a dry ice-acetone bath, while homogenization is continued to yield a uniform dispersion of lipospheres. 

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