Processing of Lipid Nanodispersions into Solid Powders by Spray Drying
Spray drying is a promising technology for drying lipid nanodispersions. These formulations can serve as carrier systems for poorly water-soluble active pharmaceutical ingredients (APIs) that are loaded into the lipid matrix to improve their bioavailability. Once the API-loaded nanocarriers have been further processed into solid dosage forms, they could be administered orally, which is usually preferred by patients. Various solid lipids as well as oils were used in this study to prepare lipid nanodispersions, and it was shown that their nanoparticulate properties could be maintained when lactose in combination with SDS was used as matrix material in the spray-drying process. In addition, for lipid nanoemulsions loaded with fenofibrate, a good redispersibility with particle sizes below 300 nm at a lipid content of 26.8 wt.% in the powders was observed. More detailed investigations on the influence of the drying temperature yielded good results when the inlet temperature of the drying air was set at 110 °C or above, enabling the lactose to form an amorphous matrix around the embedded lipid particles. A tristearin suspension was developed as a probe to measure the temperature exposure of the lipid particles during the drying process. The results with this approach indicate that the actual temperature the particles were exposed to during the drying process could be higher than the outlet temperature.
Introduction
The current study started with investigations on tristearin nanodispersions initially focusing on the identification of a suitable matrix material for embedding the lipid particles upon spray drying, as well as an optimized formulation for preparing the nanodispersions by high-pressure homogenization. To evaluate the transferability of the optimized formulation to other lipid nanocarrier systems, various dispersions of oils and solid lipids were spray-dried and the redispersibility of the lipid-containing powders in water was tested. Nanoemulsions loaded with the model API fenofibrate were also included in these investigations. In the last part of this study, the time- and formulation-dependent polymorphic transformation of tristearin nanoparticles was used to further investigate the effect of the drying temperature on the physical state of the particles [21,22]. While triglycerides are known to crystallize first in the metastable α-polymorphic form and then transfer to the more ordered and stable β-modification [23,24], a suspension containing mainly nanoparticles in the β-polymorphic form was spray-dried and the content of particles that had melted during the process was evaluated in dependence on the drying temperature.
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Materials
Various solid lipids as well as oils were used for the preparation of lipid nanodispersions. Solid glycerides: Compritol (mono-, di-, and triesters of behenic acid, Compritol 888; Gattefossé, Saint-Priest Cedex, France), tristearin (Dynasan 118), tripalmitin (Dynasan 116), and trimyristin (Dynasan 114; all from Hüls/Condea, Witten, Germany; all kind gifts from the manufacturer). Oils: Miglyol (medium-chain triglycerides, Miglyol®812; Caesar&Loretz, Hilden, Germany), refined soybean oil (Roth, Karlsruhe, Germany), and refined rapeseed oil (Caelo, Hilden, Germany). Lipid dispersions were stabilized with the polymers PVA (polyvinyl alcohol, Mowiol 3-83; Kuraray Europe, Hattersheim, Germany) or HPMC (hydroxypropyl methyl cellulose, Pharmacoat 606; Shin-Etsu Chemical Eo., Tokyo, Japan; kind gift from Harke Pharma, Mülheim an der Ruhr, Germany) and the surfactant SDS (sodium dodecyl sulphate; Roth, Karlsruhe, Germany). The following matrix materials were used during spray drying: lactose (lactose monohydrate; Meggle, Wasserburg am Inn, Germany; kind gift from the manufacturer), mannitol (D-mannitol; Sigma-Aldrich, Taufkirchen, Germany), and sucrose (D(+)-saccharose; Roth, Karlsruhe, Germany). The poorly water-soluble API fenofibrate (FENO; Novartis Pharma AG, Basel, Switzerland; kind gift) was used as a model substance. Tetrahydrofuran (THF; Sigma-Aldrich, Taufkirchen, Germany) was used for characterization purposes. Bidistilled water was used in all experiments.