Solid Lipid Nanoparticles
Solid lipid nanoparticles are a new generation ofcolloidal drug carrier systems and consist of surfactant-stabilized lipids that are solid both at room and body temperatures [52]. They combine the advantages of liposomes, polymeric nanoparticles, and emulsions while minimizing some of their individual disadvantages [53,54]. They typically contain a hydrophobic solid matrix core with a phospholipid coating. The hydrophobic tail regions of the phospholipid are embedded into the core matrix and that is why the core exclusively possesses a hydrophobic nature. So it is to be expected that the solid lipid nanoparticles have a higher entrapment efficiency for hydrophobic drugs in the core compared with conventional liposomes [53] (Fig. 6.7).
The solid lipid nanoparticles are suitable for intravenous administration and can be successfully dispersed in aqueous or aqueous-surfactant solutions. Other advantages of solid lipid nanoparticles include easy scale-up and low cost of production, relative
Figure 6.7 Schematic representation of the structures of liposome and solid lipid nanoparticles.
Nanoparticulate Systems for Therapeutic and Diagnostic Applications 115
Table 6.2 Examples of lipids and surfactants used in solid lipid nanoparticle preparations [53]
|
Lipids |
|
|
Triglycerides |
Tricaprin, trilaurin, trimyristin, tripalmitin, tristearin |
|
Hard fats |
Witepsol W 35, Witepsol H 35, Witepsol H 42, Witepsol E 85 |
|
Others |
Glyceryl monostearate (Imwitor 900), glyceryl behenate (Compritol 888 ATO), glyceryl palmitostearate (Precirol ATO 5), cetyl palmitate, stearic acid, palmitic acid, decanoic acid, behenic acid |
|
Surfactants (emulsifiers and coemulsifiers) |
Soy lecithin, egg lecithin (Lipoid E 80), phosphatidylcholine, poloxamer 188, 182, and 407, poloxamine 908, Tyloxapol, polysorbate 20, 60, and 80, sodium cholate, sodium glycocholate, taurocholic acid sodium salt, taurodeoxycholic acid sodium salt, butanol, butyric acid, dioctyl sodium sulfosuccinate, monooctylphosphoric acid sodium
nontoxic nature, biodegradable composition, and stability against aggregation or coalescence. Other crucial features include the protection offered to the entrapped drugs and prolonged drug release from the matrix [53].
Solid lipid nanoparticles are prepared by using solid lipids (e.g., purified triglycerides, fatty acids, steroids, orwaxes), emulsifiers, and water [52]. Table 6.2 summarizes the lipids and emulsifiers currently prevalent in research for solid lipid nanoparticle preparation.
