Delivering Actives via Solid Lipid Nanoparticles and Nanostructured Lipid Carriers: Part II, Nanoparticle Characterization

Jan 1, 2012 | Contact Author | By: Johann W. Wiechers, PhD, JW Solutions; and Eliana B. Souto, PhD, University Fernando Pessoa
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Title: Delivering Actives via Solid Lipid Nanoparticles and Nanostructured Lipid Carriers: Part II, Nanoparticle Characterization
SLNsx NLCsx nanoparticlex deliveryx crystallinityx
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Keywords: SLNs | NLCs | nanoparticle | delivery | crystallinity

Abstract: The characterization of SLN or NLC nano-sized particles is considered. There are, in principle, four different types of chemicals in an SLN or NLC that have different influences: an active ingredient, which can degrade; lipids that influence particle size, crystallization and morphology; surfactants that influence agglomeration; and finally, water.

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Part I of this review on SLNs and NLCs discussed the differences between these two systems, as well as their production methods and selection criteria for constituents.1 In Part II, the characterization of these nano-sized particles is considered. There are, in principle, four different types of chemicals in an SLN or NLC that have different influences: an active ingredient, which can degrade; lipids that influence particle size, crystallization and morphology; surfactants that influence agglomeration; and finally, water. Table 1 provides an overview of these influences, which will be discussed here in arbitrary order. Various characterization methods relate to these influences, including: loading capacity (LC), encapsulating efficacy (EE), crystallinity and crystallinity index (CI), morphology, particle size and polydispersity index (PI). The chemical stability of the active ingredient and lipid components of the nanoparticle, the in vitro release of the active, and the rheology of the nanoparticle-containing formulation are also influences. These will be discussed in greater depth in part III of this series in March 2012.

Characterization methods such as LC, EE, and the chemical stability and in vitro release of the active are all based on active/lipid interactions, whereas characterization methods such as rheology and occlusion are dependent upon the interaction of all components of the formulation. Many of the characterization methods discussed in this article are based on measurements performed by Teeranachaideekul et al.2 These authors incorporated ascorbyl palmitate into NLCs composed of different lipids, i.e., glycerol monostearate (GMS), cetyl alcohol (CA) and beeswax (BW), and used various techniques to characterize the particles.

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This is an excerpt of an article from GCI Magazine. The full version can be found here.

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Table 1

Table 1. Overview of how SLN/NLC characteristics may be linked to classes of ingredients

Table 2

Table 2. The formulations used by Fang et al. in the described studies; modified from Reference 20

Figure 1

Figure 1. X-ray diffraction patterns of bulk lipid before and after heating to 90°C for 1 hr during NLC production; reproduced with permission from Reference 2.

Figure 2

Figure 2. DSC thermograms of blends of glyceryl behenate (a solid lipid)/sunscreen mixture with increasing amount of lipid (30%, 40%, 50%, 60%, 70% and 80%), as well as the bulk lipid; modified from Reference 11.

Figure 3

Figure 3. Different morphologies of lipid nanoparticles; a) a 2 x 2-μm 3D AFM scan of AP-loaded GMS-based NLCs; b) a 1 x 1-μm SEM picture of AP-loaded BW-based NLCs; c) a 5,000-fold magnification of a glycerol palmitostearate-based SLN; and d) a 5 x 5-μm AFM photograph of a lipid nanoparticle; sources: a) and b), Reference 2; c) Reference 6; d) Reference 14; reproduced with permission.

Figure 4

Figure 4. A possible relationship exists between particle size and zeta-potential, as shown for the four formulations described in Table 2. Smaller particles, i.e., oil droplets, are obtained at larger zeta-potentials. The measured data taken from Reference 20 is plotted in red and identifies the second point (with the zeta-potential of -42 mV) as an outlier. The blue line represents the overall trend when this point is ignored. This suggests the steric effect of the emulsifier polysorbate-80 is approx. 100 nm, as indicated by the dashed line.

a

 a The described equation is proprietary to Malvern Instruments Ltd., Malvern, Worcestershire, United Kingdom.

b

b The DTS version 4.1 software described is produced by Malvern Instruments Ltd.

c

c Tween 80 (INCI: Polysorbate 80) is a product of Kanto Chemical, Tokyo, Japan.

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