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Nanotechnology and Skin Delivery: Infinitely Small or Infinite Possibilities?

Figures

  • Figure 1. Theoretical predictions of particle penetration

    Figure 1. Theoretical predictions of particle penetration

    Figure 1. Theoretical predictions of particle penetration as performed by Michael S. Roberts, School of Medicine, University of Queensland, Princess Alexandra Hospital, Australia. (Reproduced with the author’s permission from Reference 10).
    Figure 1. Theoretical predictions of particle penetration
  • Figure 2. Histological sections demonstrating the penetration depth

    Figure 2. Histological sections demonstrating the penetration depth

    Figure 2. Histological sections demonstrating the penetration depth of particle-containing emulsions and non-particle-containing emulsions in the hair follicles of pig ear skin (laser scanning microscopy measurements). Left a): particle-containing emulsion; right b): non-particle-containing emulsion. (Taken with permission from Reference 14.)
    Figure 2. Histological sections demonstrating the penetration depth
  • Figure 3. Kinetics of the storage of nanoparticles

    Figure 3. Kinetics of the storage of nanoparticles

    Figure 3. Kinetics of the storage of nanoparticles a) in the hair follicles and b) in the stratum corneum. (Taken from Reference 15.)
    Figure 3. Kinetics of the storage of nanoparticles
  • Figure 4.The effect of particle size on the UV attenuating properties of titanium dioxide.

    Figure 4.The effect of particle size on the UV attenuating properties of titanium dioxide.

    Figure 4. The effect of particle size on the UV attenuating properties of titanium dioxide. Reduction of particle size moves the peak of UV attenuation to shorter wavelengths and also improves the transparency. However, the SPF efficacy is considerably reduced when the particle size is too small. The smallest particles (about 20 nm) do not exhibit real UV-protective benefits any longer, not even in the UVB, but such particles are still larger than the size of the quantum dots that were shown to penetrate pig26 and rat skin.27 (Modified from Reference 29.)
    Figure 4.The effect of particle size on the UV attenuating properties of titanium dioxide.
  • Figure 5. Schematic representation of the size-dependent occlusive effect of lipid nanoparticles

    Figure 5. Schematic representation of the size-dependent occlusive effect of lipid nanoparticles

    Figure 5. Schematic representation of the size-dependent occlusive effect of lipid nanoparticles; a) an aqueous dispersion of either solid lipid nanoparticles or nanostructured lipid carrier (diameter 500 nm), in comparison with b) a solid lipid microparticle dispersion (diameter 1 µm). (Reproduced with permission from Reference 34.)
    Figure 5. Schematic representation of the size-dependent occlusive effect of lipid nanoparticles
  • Figure 6: Cumulative amount of ketorolac

    Figure 6: Cumulative amount of ketorolac

    Figure 6. The cumulative amount of ketorolac as a function of time from elastic and rigid vesicle formulations across human skin in vitro. Elastic vesicles were clearly more effective in the enhancement of ketorolac transport across the skin. (Reproduced with permission from Reference 37.)
    Figure 6: Cumulative amount of ketorolac
By: Johann W. Wiechers, PhD, JW Solutions
Posted: December 19, 2008, from the January 2009 issue of Cosmetics & Toiletries.

Once the reader accepts a standard definition of nanotechnology, such as that offered by The Royal Society and The Royal Academy of Engineering,1 and then reads my definition of skin delivery available elsewhere (see Two Definitions),2,3 and then realizes that micro- and nanoparticles accumulate in the furrows and ridges on the skin surface where they act as a reservoir, then they are ready to ask the question answered in this article: Do nano-particles penetrate human skin?

Nanoparticles have been defined as single particles with a diameter less than 100 nm,4 which includes titanium
dioxide in transparent, inorganic sun care products, and is usually extended to 200 nm to include the zinc oxide in those products. But nanoparticles are only a subset of nanomaterials, which can also include cyclodextrins and liposomes. While cyclodextrins do not represent a nanotechnology in this author's opinion, liposomes do. However, liposomes will not be discussed in this article because unlike nanoparticles that are intended to rest on the skin, liposomes were specifically designed to penetrate the skin. Thus, the nanoparticles addressed in this article are solid particles with a diameter less than 200 nm.

Consider the following quote:
"In one of the most dramatic failures of regulation since the introduction of asbestos, corporations around the world are rapidly introducing thousands of tonnes of nanomaterials into the environment and onto the faces and hands of hundreds of millions of people, despite the growing body of evidence indicating that nanomaterials can be toxic for humans and the environment."

This is the first sentence of the executive summary of the May 2006 Friends of the Earth report, Nano-materials, sunscreens and cosmetics: small ingredients, big risks. 5 It is also found in the introduction and on the back cover of the same report. With such emphasis on this statement, one would think there is something fundamentally wrong with nanotechnology. The best way to analyze this is to study whether the "growing body of evidence" actually supports the claim that "nanomaterials can be toxic for humans and the environment."

The Risk
Two things are essential for nanomaterials to constitute a risk, as suggested by The Friends of the Earth report. Humans need to be exposed to the nanoparticles and there needs to be an intrinsic safety hazard of these materials. Are humans indeed being exposed to tons of these materials by the various industries?