Solid lipid particles

Westesen and Siekmann [11] used suspensions of colloidal solid lipid particles as well as lyophilizates as delivery systems for the parenteral administration of the drug for its particle morphology determination. 

Solidification of the particles may not be the final step in the formation process of solid lipid particles. Lipidic materials exhibit rich polymorphism [69,70], which may also occur in the dispersed state. In nanoparticles, the polymorphic behavior of the matrix lipids may, however, differ distinctly from that in the bulk material. Polymorphic transitions are usually accelerated in the nanoparticles compared with the bulk lipids [2,62]. In some cases, polymorphic forms not observable in the corresponding bulk materials were detected in lipid nanoparticles [1,65]. Because polymorphism can affect pharmaceutically relevant properties of the particles, such as the drug incorporation capacity [65], corresponding investigations should also be included in the characterization process. As long as polymorphic or other crystalaging phenomena have not terminated, the particle matrix cannot be regarded as static, and alterations of the particle properties may still occur. 

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are the techniques most widely used for the characterization of crystallinity and polymorphism of solid lipid particles. Although DSC is usually more sensitive in detecting crystalline material, XRD is much more reliable in determining the type of polymorph present in the dispersions because it provides structural data. In contrast, DSC can detect the type of polymorph only indirectly via the transition temperatures and enthalpies. Because these parameters may be different from those observed in the bulk material, particularly for small colloidal particles [1,62], assigmnent of polymorphic forms in DSC curves should be supported by x-ray data. 

In DSC the sample is subjected to a controlled temperature program, usually a temperature scan, and the heat flow to or from the sample is monitored in comparison to an inert reference [75,76], The resulting curves — which show the phase transitions in the monitored temperature range, such as crystallization, melting, or polymorphic transitions — can be evaluated with regard to phase transition temperatures and transition enthalpy. DSC is thus a convenient method to confirm the presence of solid lipid particles via the detection of a melting transition. DSC recrystaUization studies give indications of whether the dispersed material of interest is likely to pose recrystallization problems and what kind of thermal procedure may be used to ensure solidification [62-65,68,77]. 

Lucks, S. Muller, R. Medication Vehicles Made of Solid Lipid Particles (Solid Lipid Nanospheres) SLN. PCT Application, WO93/05768, April 1,1993. 

Fig. 32. Representative examples for proton spectra of QlO-loaded solid lipid particles obtained under MAS conditions and variation of the spin-lock duration sl- The pulse sequence used for the -measurements is depicted in the inset. ...

Fig. 33. Comparison of MAS proton spectra for QlO-loaded solid lipid particles (top) with corresponding spectra of the solid lipid cetyl palmitate (centre) and the active ingredient QIO (bottom) ...

Solid lipid particles offer another interesting formulation option for the drug delivery scientist. Solid lipids particles are lipid-based solid colloidal... 

Similar to emulsions, solid lipid particles consist of emulsifier-coated lipid droplets dispersed within an aqueous phase, with the main difference that the lipid phase is at the solid or semi-soUd state. 

In comparison to emulsions, solid lipid particles exhibit an increased chemical protection against degradation, a higher encapsulation efficiency (>90%) and a better controlled release, due to the immobilization of the encapsulated bioactive compound in the solid lipid matrix. ... 

Siekmann B, Westesen K. Solid lipid particles, particles of bioactive agents and methods for the manufacture and use thereof. US patent 5885486, 1999. 

C.C. Trujillo, A.J. Wright, Properties and stability of solid lipid particle dispersions based on canola stearin and Poloxamer 188, J. Am. Oil Chem. Soc. 87 (2010) 715-730. 

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