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.

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3. Making the assumption that this prediction can be extrapolated from small soluble molecules to bigger solid particles, the maximum flux of a particle can be predicted from the molar volume (MV) using the equation:
log J_max ≈ 3.978 - 5.282 MV.

4. The desquamation rate of the stratum corneum was set at 14 days, meaning that in 14 days the stratum corneum is completely renewed.

5. The return penetration is assumed to be zero, which is in line with experimental findings in the scientific literature.

6. The epidermal clearance was calculated from the flux through the stratum corneum, which can be calculated from the permeability coefficient in equations such as the ones developed by Potts and Guy, Barratt, Mitragotri, etc., that can be calculated from equations that predict the stratum corneum permeability co-
efficient;¹² and

7. When calculating the steady-state epidermal concentrations, it turned out that desquamation had a profound impact on the epidermal concentrations reached. If a safety margin of 100 was applied, the predicted epidermal levels of a solubilized molecule with a molecular weight of 800 would be approximately 10 nmol/mL, whereas that of a particle with a diameter of
30 nm would be 10-18 nmol/mL, which is a factor of 1019 smaller. (See Some Perspective on 10-18 nmol/mL.)