Delivering Actives via Solid Lipid Nanoparticles and Nanostructured Lipid Carriers: Part III, Stability and Efficacy

Mar 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 III, Stability and Efficacy
nanoparticlesx deliveryx activesx SLNsx NLCsx
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Keywords: nanoparticles | delivery | actives | SLNs | NLCs

Abstract: Part I of this review on Solid Lipid Nanoparticles (SLNs) and Nanostructured Lipid Carriers (NLCs) discussed the differences of these two delivery systems for cosmetic actives, as well as their production methods and selection criteria for constituents. In Part II, the characterization of these nano-sized particles was considered. In Part III, presented here, their stability and efficacy are considered; Part IV will address their application in cosmetics.

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JW Wiechers and EB Souto, Delivering actives via solid lipid nanoparticles and nanostructured lipid carriers: Part III, stability and efficacy, Cosm & Toil 127(3) 164-173 (Mar 2012)

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Editor’s note: Part I of this review appeared in October 2010. Part II appeared in January 2012; Part III is presented here, and Part IV appeared in May 2012.

Part I of this review on Solid Lipid Nanoparticles (SLNs) and Nanostructured Lipid Carriers (NLCs) discussed the differences of these two delivery systems for cosmetic actives, as well as their production methods and selection criteria for constituents. In Part II, the characterization of these nano-sized particles was considered. In Part III, presented here, their stability and efficacy are considered; Part IV addresses their application in cosmetics.

Active and Lipid Chemical Stability

The reason for including an active in a nanoparticle is not only to enhance skin delivery or controlled-release rate, but also, like liposomes and other deformable vesicles, to create a barrier to chemicals that may negatively influence the stability of the active. The following section deals with a couple of relevant cosmetic examples, illustrating how this can be investigated. The chemical stability of both the active and the lipid excipient can be at stake and are discussed separately here.

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Figure 1. Percentage of retinol that remains in SLNs (black markers) and in oil

Figure 1. Percentage of retinol that remains in SLNs (black markers) and in oil

The percentage of retinol that remains in SLNs (black markers) and in oil, as a function of time; reproduced from Reference 1, based on data from Reference 2

Figure 2. The release rate of active ingredients as a function of the type of nanoparticle formulation

Figure 2. The release rate of active ingredients as a function of the type of nanoparticle formulation

The release rate of active ingredients as a function of the type of nanoparticle formulation; an active-enriched a) shell or core affects the release rate. A less solid NLC (Formula C in Figure 2b) shows an even higher release rate but is slow relative to the immediate release observed from c) emulsion or gel-type formulations; sources: a) and b), Reference 6; c), Reference 7.

Figure 3. The penetration of Nile Red into pig skin

Figure 3. The penetration of Nile Red into pig skin

Following an 8-hr application period, the penetration of Nile Red into pig skin via: a) cream; b) SLN; c) NLC 1 (SLN + oleic acid); and d) NLC 2 (SLN + glyceryl tricaprylate/caprate); within the images, a = the stratum corneum, b = epidermis and c = dermis. Photos were produced by superimposing normal light and fluorescence images of the same area; black bar corresponds to 100 μm; reproduced with permission from Reference 15.

Figure 4. Cyproterone acetate penetration into human skin in vitro

Figure 4. Cyproterone acetate penetration into human skin in vitro

Cyproterone acetate penetration into human skin in vitro; dispersions of drug loaded carrier systems (0.05%) were applied to cryo-conserved human skin for 6 hr. Particulate dispersions were tested in parallel to, and delivery expressed relative to, an o/w cream. NE = nano-emulsion; SLN = solid lipid nanoparticle; NLC-O = nanostructured lipid carrier + oleic acid; NLC-M = nanostructured lipid carrier + caprylic/capric triglycerides; MS = microspheres; * = a statistically significant difference in delivery over the cream (p < 0.05); reproduced with permission from Reference 13.

Figure 5. Electron micrograph of an air-dried SLN dispersion

Figure 5. Electron micrograph of an air-dried SLN dispersion

An electron micrograph of an air-dried SLN dispersion showing that the lipids coagulate and form a solid lipid film on the surface of skin. Based on occlusivity measurements, there should still be micro-channels in this film, although they are not visible. Reproduced with permission from Reference 23.

Figure 6. The occlusion factor of lipid nanoparticles

Figure 6. The occlusion factor of lipid nanoparticles

The occlusion factor of lipid nanoparticles; with identical lipid content, reducing the particle size leads to an increase in particle number, and a) the film becomes denser, increasing the occlusion factor. At a given particle size, increasing the lipid concentration increases the number of particles, density of the film, and therefore b) the occlusivity factor. By varying the size and lipid concentration, the occlusion can be fine tuned. The film becomes denser due to the creation of multiple layers of nanoparticles, c) if the lipid content is kept constant; source, a) and b), Reference 1.

Biography: Eliana B. Souto, PhD, University Fernando Pessoa

Eliana B. Souto, PhD

Eliana B. Souto, PhD, is an assistant professor at the Faculty of Health Sciences, University Fernando Pessoa in Porto, Portugal. She coordinates the Biopharmaceutical Chemistry Unit of the doctoral program in Biotechnology and Health, and the Euro-PhD in Advanced Drug Delivery from Galenos Network. Souto obtained her doctorate at the Institute of Pharmacy, Free University of Berlin, Germany. Her research group is devoted to the design, development and characterization of lipid nanocarriers for the controlled topical delivery of drugs and dermatocosmetics.

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