The latest science (including safety) on nanotechnology and skin penetration.

1
The latest science (including safety) on
nanotechnology and skin penetration.

• Michael Roberts PhD DSc
• School of Medicine
• University of Queensland
• Princess Alexandra Hospital
• Australia

2
Nanotechnology skin penetrationeg Physical
sunscreens (TiO2, ZnO)

• TiO2 or ZnO nanoparticles
• are colorless water-resistant insoluble
  materials
• are non-toxic
• Zn essential element (DNA polymerases, DNA
  stability)

• Dermal risk issues
• Exposure
• Absorption
• Intrinsic Toxicity

Penetrate skin
Apparent cut off MW500 0.9 nm
100 m
10-1 m
10-2 m
10-3 m
10-4 m
10-5 m
10-6 m
10-7 m
10-8 m
10-9 m
10-10 m
(1 m)
(1 mm)
(1 µm)
(1 nm)
(100 nm)
(0.1 nm)
(10 nm)
RBC (7 ?m)
Hair (80 ?m)
Salicylic acid (0.5 nm)
ZnO nanoparticles (20-50 nm)
Water (0.3 nm)
Rhinovirus (20 nm)
3
Exposure absorption

• In general
• Nanoparticles preferentially accumulate in hair
  follicle openings
• Stratum corneum penetration limited to upper
  layers

4
Our experiences zinc oxide nanoparticles
applied to human skin

• Epidermal membrane in Franz cells with PBS
  DC-30 2
• ZinClear o/w sunscreen placebo for 24 hr
• Zn assayed using ICP-MS after acidifying solution
• TEM

TEM of coated ZnO
Spectral transmittance in aqueous solution
Cross et al Skin Physiol Pharmacol, in press
PCS size distribution
5
Our experiences zinc oxide nanoparticles

• Conclusion
• Electron micrographs of human skin show ZnO
  nanoparticle mineral components present on the
  surface of the skin around desquaming
  corneocytes
• No penetration into the underlying intact
  stratum corneum was observed
• Multiphoton images also showed zinc oxide 10nm
  Cerium Oxide was retained in follicle openings
  around desquamating corneocytes
• Stretching or flexing the skin did not affect
  particle distribution stays on stratum corneum
  surface

Cross et al Skin Physiol Pharmacol, in press
6
Our experiences zinc oxide nanoparticles
Receptor phase penetration of Zinc through human
epidermal membrane (ug/cm2) over 24hrs. Mean SE,
n8 (formulation treatments), n3 (placebo base
and untreated control).
Total absorbed less than 0.03 of product applied
as 10?l/cm2
Note Gamer et al (2006) pig skin recoveries of
0.8-1.4 of dose
Treatment
Conclusion Zinc penetration may be observed but
is likely to be negligible and as hydrolysed to
zinc rather than as zinc oxide
Cross et al Skin Physiol Pharmacol, in press
7
Titanium dioxide Zinc oxide in a topical
sunscreen
Dussert et al Int J Cosm Sci 19 119-129 (1997)
8
Titanium dioxide stratum corneum follicular
levels after stripping in vivo
Some absorption into upper layers of stratum
corneum, but no penetration
Lademann et al., 1999
9
Other studies

• Negatively charged fluorescein particles of 50
  and 500nm penetrated pig skin whereas 100 200
  did not nor did neutral positively charged
  particles (Kohli Alpar, 2004) (not found with
  carboxylated nanoparticles in human skin)
• Polystyrene NPs, 20 and 200 nm to pig skin
  (Alvarez-Roman et al., 2004)
• No penetration into epidermis / dermis
• Accumulation in follicle orifice
• But no penetration from follicle
• Nano titanium oxide 10-100nm retained on
  outermost layer of human skin in vivo after 6 hr
  with none being detected in deeper SC, epidermis
  or dermis in punch biopsies (Pflucker et al,
  2001 Schulz et al 2002)

10
Quantum dots pig skin.But

• Quantum dots penetrate porcine skin
• All 3 coated materials had penetrated by 8 hr
• Localisation affected by surface charge
• Conclude skin could serve as entry point for a
  diversity of engineered nanostructures

• Pig
• pH 8.3 PEG, pH 9.0 COOH, peg
• Perfused
• Lymph nodes

11
But fate also depends on what you do to the skin?

1µm flexing 30 min
2 4µm remain on surface

• Red fluorescein iso-thiocyanate (FITC) -
  conjugated dextran beads to human skin (back) for
  30min.
• Skin either flexed at 45, 20 flexes/minute (
  with double-sided tape) or left flat, for 15, 30,
  or 60 min

1µm flexing 60 min
0.5µm entry via a tear
0.5 µm flexing 60 min

• Flexing time critical for 0.5 1 µm beads
  penetration into epidermis
• 15 min seen in 2 of 11 skin samples (18)
• 30 min - in 5 of 12 samples
• 60min - in 9 of 16 samples also penetration
  into the dermis for two samples
• No particle penetration observed without flexing
  at any time or size!!!

10µm
Tinkle Environ Health Perspect 2003
12
Confirmation by tape stripping sem
Surface, 0 strips
Particles
After 10 strips

• Hydrated 24-48hr
• Mechanical force particle size (100nm-500nm) ?
  penetration? Not seen for ZnO 30nm flexed
• No diffuse reflectance
• No particles in follicle

After 20 strips
Tinkle Environ Health Perspect 2003
13
What do we predict? - Desquamation matters!
Consider the Molecular Volume Dependence of the
Epidermal Exposure Concentration Css of Soluble
Compounds following Stratum Corneum penetration
to predict likely penetration of insoluble
particles
Adapted from Magnusson et al., J. Invest.
Dermatol. 122993, 2004
In vitro
14
Conclusion of exposure absorption

• The available data suggests that it is unlikely
  that significant amounts of ZnO or TiO2 will
  penetrate through the stratum corneum either
  directly or via the hair follicles to result in
  any local or systemic toxicity
• Conclusion is similar to Australias Therapeutic
  Goods Agency (TGAs) perspective
• ..The weight of current evidence is that they
  remain on the surface of the skin in the outer
  dead layer (stratum corneum) of the skin.

Acknowledgements Australian National Health
Medical Research Council (NHMRC), Advanced
Nanotechnology, my staff (Dr M Sarkar, Dr O
Jepps, Dr S Cross, Dr J Grice), colleagues (Dr A
Zyvagin, Dr Y Anissimov) graduate students