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Solid Lipid Nanoparticles (SLN) and Oil-Loaded SLN Studied by Spectrofluorometry and Raman Spectroscopy

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Purpose

Recently, colloidal dispersions made of mixtures from solid and liquid lipids have been described to overcome the poor drug loading capacity of solid lipid nanoparticles (SLN). It has been proposed that these nanostructured lipid carriers (NLC) are composed of oily droplets, which are embedded in a solid lipid matrix. High loading capacities and controlled release characteristics have been claimed. It is the objective of the present paper to investigate these new NLC particles in more detail to obtain insights into their structure.

Methods

Colloidal lipid dispersions were produced by high-pressure homogenization. Particle sizes were estimated by laser diffraction and photon correlation spectroscopy. The hydrophobic fluorescent marker nile red (NR) was used as model drug, and by fluorometric spectroscopy, the molecular environment (polarity) was elucidated because of solvatochromism of NR. The packaging of the lipid nanoparticles was investigated by Raman spectroscopy and by densimetry. The light propagation in lipid nanodispersions was examined by refractometry to obtain further insights into the nanostructural compositions of the carriers.

Results

Fluorometric spectroscopy clearly demonstrates that NLC nanoparticles offer two nanocompartments of different polarity to accommodate NR. Nevertheless, in both compartments, NR experiences less protection from the outer water phase than in a nanoemulsion. In conventional SLN, lipid crystallization leads to the expulsion of the lipophilic NR from the solid lipid. Measurements performed by densimetry and Raman spectroscopy confirm the idea of intact glyceryl behenate lattices in spite of oil loading. The lipid crystals are not disturbed in their structure as it could be suggested in case of oil incorporation. Refractometric data reveal the idea of light protection because of incorporation of sensitive drug molecules in NLC.

Conclusion

Neither SLN nor NLC lipid nanoparticles did show any advantage with respect to incorporation rate compared to conventional nanoemulsions. The experimental data let us conclude that NLC lipid nanoparticles are not spherical solid lipid particles with embedded liquid droplets, but they are rather solid platelets with oil present between the solid platelet and the surfactant layer.

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Acknowledgment

Katja Jores was supported by Deutsche Forschungsgemeinschaft (DFG).

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Authors and Affiliations

  1. Department of Pharmaceutical Technology, Institute of Pharmacy, Free University of Berlin, Kelchstr. 31, 12169, Berlin, Germany

    Katja Jores & Wolfgang Mehnert

  2. Institute of Pharmaceutical Technology and Biopharmacy, Martin Luther University Halle Wittenberg, Wolfgang Langenbeck Str. 4, 06120, Halle/Saale, Germany

    Katja Jores & Karsten Mäder

  3. Department of Pharmacology and Toxicology, Institute of Pharmacy, Free University of Berlin, Königin Luise Str. 2+4, 14195, Berlin, Germany

    Annekathrin Haberland

  4. Institute of Applied Dermatopharmacy, Wolfgang Langenbeck Str. 4, 06120, Halle/Saale, Germany

    Siegfried Wartewig

Authors
  1. Katja Jores
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  2. Annekathrin Haberland
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  3. Siegfried Wartewig
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  4. Karsten Mäder
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  5. Wolfgang Mehnert
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Correspondence to Karsten Mäder.

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Jores, K., Haberland, A., Wartewig, S. et al. Solid Lipid Nanoparticles (SLN) and Oil-Loaded SLN Studied by Spectrofluorometry and Raman Spectroscopy. Pharm Res 22, 1887–1897 (2005). https://doi.org/10.1007/s11095-005-7148-5

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  • DOI: https://doi.org/10.1007/s11095-005-7148-5

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