1. TiO 2 nanoparticles as UV protectors in skin Doctoral dissertation Alexey Popov Optoelectronics and Measurement Techniques Laboratory University of Oulu, November 21, 2008

2. 2 Outline Solar spectrum UV action spectrum Titanium dioxide: crystal forms Skin structure Tape stripping technique TiO 2 nanoparticles in horny layer Calculations by Mie theory Model of SC with TiO 2 nanoparticles Effect of TiO 2 nanoparticles Comparison with experiment Conclusion I

3. 3 EPR setup and samples Spectrum of sun simulator TiO 2 nanoparticles EPR measurements Conclusion II

4. 4 Solar spectrum Absorption in stratosphereSolar spectrum UV range UVC: 100 – 280 nm (absorbed by ozone layer) UVB: 280 – 315 nm UVA: 315 – 400 nm Wavelength, um Wavelength, nm reach Earth’s surface

5. 5 UV action spectrum A.P. Popov at al., J. Phys. D: Appl. Phys. 38, 2564-2570 (2005).

6. 6 Titanium dioxide: crystal forms RutileAnatase Courtesy “Millenium Chemicals”

7. 7 Skin structure An OCT image of human skin in vivo (flexor forearm) epidermis stratum corneum epidermis dermis Photograph of human corneocytes on a tape strip obtained by Ar + laser scanning microscopy (λ excit = 488 nm); image size is 250 um x 250 um.

8. 8 Pressing of the tape by a rollerRemoving of the adhesive film Application of the emulsion Homogeneous distribution J. Lademann at al., J. Biomed. Opt.. 10, 054015 (2005). Tape stripping technique

9. 9 0 0 Depth, um Conc. TiO 2 particles, ug/cm 2 0 0 20 14 Volume concentration of TiO 2 : A.P. Popov et al., J. Opt. Technol. 73, 208-211 (2006). In-depth particles distribution TiO 2 nanoparticles in horny layer

10. 10 A.P. Popov et al., J. Biomed. Opt. 10, 064037 (2005). Q s =  s / (  d 2 ) – scattering efficacy factor  s – scattering cross-section Q a =  a / (  d 2 ) – absorption efficacy factor  a – absorption cross-section d – particle diameter Opt. properties of TiO 2 particles (rutile modification) Calculations by Mie theory, нм Re(n) – i·Im(n) 310 3.56 – i  1.720 400 3.13 – i  0.008 500 2.82 - i  0.000

11. 11 air epidermis Optical parameters for SC without nanoparticles (adopted from V.V. Tuchin, 1998) A =  s (1) /(  s (1) +  sm ) - scat. coef. of nanoparticles - abs. coef. of nanoparticles hybrid phase function - SC phase function - scat. coef. - abs. coef. Model of SC with TiO 2 nanoparticles, nm  sm, mm -1  am, mm -1 31024060 40020023 Optical parameters for SC with nanoparticles

12. 12 Effect of TiO 2 nanoparticles Absorption in the upper part of the horny layer (1-um-thick, with TiO 2 particles) (a), reflectance from (b) and transmittance through (c) the whole 20-um-thick horny layer of the incident radiation with = 310 and 400 nm.

13. 13 The effect of the optimal TiO 2 particles (sizes 122 (a) and 62 (b) nm) distributed homogeneously within the 1-um-thick upper part (volume concentration 5%) of the 20-um-thick layer for 400- (a) 310-nm (b) light Effect of TiO 2 nanoparticles A.P. Popov et al., J. Biomed. Opt. 10, 064037 (2005).

14. 14 Comparison with experiment Experiment Nanoparticles UV-TITAN M 160 (Kemira, Finland) in absorbing emulsion (L’Oréal, France) Monte Carlo simulations TiO 2 particles (d = 100 nm, C = 0.2%) in transparent medium (thickness 20 um, n m = 1.4)

15. 15 Conclusion I Optimal sizes of TiO 2 nanoparticles for attenuation of: 310-nm UV light are 62 nm, 400-nm UV light are 122 nm. Good correlation with experiment

16. 16 EPR setup and samples EPR setup (1.5 GHz) Punch biopsies from porcine ears Placebo with PCA and TiO 2 (diam. 400 nm, 0, 25 nm) on glass plates, 2 mg/cm 2

17. 17 Spectrum of sun simulator

18. 18 TiO 2 nanoparticles d = 25 nm (a) d = 400 nm (b) TEM photos (TiO 2 in emulsion), magnification: x110 (a) and x22 (b). Scale: bar corresponds either to 0.2 um (a) or 1 um (b). Courtesy E.V. Zagainova

19. 19 Signal of Raman scattering (a); relative absorption efficiency factor (Q a /d) for two wavelengths (b) TiO 2 nanoparticles: anatase

20. 20 EPR measurements EPR signals from placebo with TiO 2 particles on glass slides

21. 21 EPR measurements EPR signals from placebo with 25- (a) and 400-nm (b) TiO 2 particles on porcine skin (a)(b) A.P. Popov et al., J. Biomed. Opt. 14, xxxxxx (2009).

22. 22 EPR measurements EPR signals from placebo on porcine skin (a) and skin (b) without particles A.P. Popov et al., J. Biomed. Opt. 14, xxxxxx (2009).

23. 23 If applied onto glass: small particles of 25 nm in diameter produce an increased amount of free radicals compared to the larger ones of 400 nm in diameter and placebo itself. If applied onto porcine skin: there is no statistically distinct difference in the amount of radicals generated by the two kinds of particles on skin and by the skin itself. This proves that: although particles as part of sunscreens produce free radicals, the effect is negligible in comparison to the production of radicals by skin. Conclusion II