High pressure melt homogenization

High-pressure melt homogenization is most frequently used for the preparation of SLN dispersions. As the whole production is carried out at a temperature above the melting point of the lipid, the process can be regarded as homogenization of an emulsion. 

Other preparation methods are based on the dispersion of the molten lipid in the hot water phase by high speed shearing ° ° or sonication, but often the dispersion quality is not as high as, e.g. for high-pressure melt homogenization and a larger fraction of particles with a size in the m-range has to be considered. 

Yang et al. studied the biodistribution of camptothecin-loaded SLN after oral administration in mice in comparison to the drug solution. The SLN were prepared by high-pressure melt homogenization using stearic acid as matrix lipid and soybean lecithin and poloxamer 188 as stabilizers similarly to those used for the study of camptothecin biodistribution after intravenous injection in mice. After oral administration of the lipid nanoparticles, two... 

However, high pressure melt homogenization presents a distinct thermal stress for the formulation and thermally sensitive compounds and drugs may be degraded. If thermal stress is an issue for the respective formulation, the so-called solvent-evaporation method can be used as an alternative. The whole preparation process is carried out at room or slightly lower temperature. By this preparation method, smectic nanoparticles with a mean size distinctly below 100 nm can be obtained. A disadvantage of this method are potential residues of the organic solvent in the final formulations. 

The stabilizer concentrations are w/w and refer to the whole dispersions prior to high pressure melt homogenization. 

To produce mouldings from polystyrene with minimum strain it is desirable to inject a melt, homogeneous in its melt viscosity, at a high rate into a hot mould at an injection pressure such that the cavity pressure drops to zero as the melt solidifies. Limitations in the machines available or economic factors may, however, lead to less ideal conditions being employed. 

The drug dissolved or dispersed in the melted lipid is poured into an aqueous emulsifier phase of the same temperature. By means of a rotor-stator homogenizer (e.g., an Ultra-Turrax), an o/w preemulsion is prepared and is then homogenized at high pressure and at a temperature at least 10°C above the melting point of the lipid. In most cases, nanoemulsion arises after only three to live homogenization cycles at 500 bar. Nanoparticles are formed by cooling the nanoemulsion to room temperature. 

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