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Nanotechnology and Skin Delivery: Infinitely Small or Infinite Possibilities?
By: Johann W. Wiechers, PhD, JW Solutions
Posted: December 19, 2008, from the January 2009 issue of Cosmetics & Toiletries.
- Figure 1. Theoretical predictions of particle penetration
- Figure 2. Histological sections demonstrating the penetration depth
- Figure 3. Kinetics of the storage of nanoparticles
- 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 6: Cumulative amount of ketorolac
page 12 of 13
Finally, to achieve penetration the formulation must be massaged into the skin to open the orifice surrounding the hair follicles. However, the nanomaterials used in cosmetics such as the metal oxides are too rigid to penetrate, too big to penetrate, and are effectively cleared away from the skin by sebum flow, hair growth and desquamation, and we humans are simply not hairy enough to allow them to penetrate.
This suggests endless opportunities for nanotechnology in cosmetics, but this is also not true. The only reasons that particulate systems are used are purely cosmetic. Customers prefer transparent sunscreen formulations and for that, nano-sized particles are required. The skin moisturization and elasticity and lubrication benefits offered by the lipid nanomaterials are really secondary benefits, for which many other cosmetic ingredients are available that could offer more effect for less cost.
Therefore, it can be concluded that both the risks and the benefits of nanotechnology in cosmetics are exaggerated but it remains strange that there is a perceived risk for those topically applied nanoparticles such as the metal oxides for which there is no evidence of skin penetration, whereas there is no perceived risk for those topically applied nanomaterials such as elastosomes and flexible liposomes for which there is evidence of skin penetration. The latter is correct; the former may hopefully have changed after reading all these pages.
Despite this cautionary note, the future of nanotechnology in cosmetics is bright and shiny. This author foresees the main future benefits of nanotechnology to come from the combination of nano-sized materials and trans-follicular delivery, another topic soon to be discussed in Cosmetics & Toiletries magazine. Frum, for instance, concluded in 2007 that this route of penetration may account for up to 60% of all skin penetration of soluble materials.39 Combine this potential with the capability of nanomaterials to accumulate in the transfollicular orifice that acts as a long-term reservoir, and the following options will become a reality.
First, include solutes into SLNs and NLCs that accumulate in the orifice and subsequently diffuse out of these nano-sized delivery systems and provide a long-term delivery. Second, nano-sized solids with some minimal fat solubility will automatically accumulate in the orifice and then be delivered. Finding the right solubilities will be the challenge to get this to work but when successful, delivery from nano-sized particles will become gigabig.