TiO2 nanoparticles as UV protectors in skin

Doctoral dissertation

Alexey Popov

Optoelectronics and Measurement Techniques Laboratory

University of Oulu, November 21, 2008

2

Outline• Solar spectrum• UV action spectrum• Titanium dioxide: crystal forms• Skin structure• Tape stripping technique• TiO2 nanoparticles in horny layer• Calculations by Mie theory• Model of SC with TiO2 nanoparticles• Effect of TiO2 nanoparticles• Comparison with experiment• Conclusion I

3

• EPR setup and samples• Spectrum of sun simulator• TiO2 nanoparticles

• EPR measurements• Conclusion II

4

Solar spectrumAbsorption in stratosphereSolar spectrum

UV rangeUVC: 100 – 280 nm (absorbed by ozone layer)UVB: 280 – 315 nmUVA: 315 – 400 nm

Wavelength, um Wavelength, nm

reach Earth’s surface

5

280 300 320 340 360 380 400

0.000

0.001

0.002

0.003

0.004

0.005

0.006 UVB UVA

Har

mfu

l effe

ctiv

enes

s, r

.u.

Wavelength, nm

UV action spectrum

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

200 400 600 800 1000 1200 1400

0.00.20.40.60.81.01.21.41.61.8 Solar spectrum

Sp

. ir

rad

ian

ce

, W

*m-2*n

m-1

Wavelength, nm

6

Titanium dioxide: crystal forms

RutileAnatase

Courtesy “Millenium Chemicals”

7

Skin structure

An OCT image of human skin in vivo (flexor forearm)

epidermis

stratum corneumepidermis

dermis

Photograph of human corneocytes on a tape strip obtained by Ar+ laser scanning microscopy (λexcit = 488 nm); image size is 250 um x 250 um.

8

Pressing of the tape by a roller Removing of the adhesive film

Application of the emulsion Homogeneous distribution

J. Lademann at al., J. Biomed. Opt.. 10, 054015 (2005).

Tape stripping technique

9

0

0

Depth, um

Conc. TiO2 particles, ug/cm2

0

0

2014

Volume concentration of TiO2: V

M

V

V

V

M

V

VNC

0

0

00

0

A.P. Popov et al., J. Opt. Technol. 73, 208-211 (2006).

In-depth particles distribution

TiO2 nanoparticles in horny layer

0 2 4 6 8 10 12 14 16 18 20

0

2

4

6

8

10

12

14

16

d = 100 nm

Con

c. T

iO2

part

icle

s, u

g/cm

2

Depth, um

10A.P. Popov et al., J. Biomed. Opt. 10, 064037 (2005).

Qs = s / (d2) – scattering efficacy factors – scattering cross-sectionQa = a / (d2) – absorption efficacy factora – absorption cross-sectiond – particle diameter

Opt. properties of TiO2 particles(rutile modification)

Calculations by Mie theory

, нм Re(n) – i·Im(n)

310 3.56 – i1.720

400 3.13 – i0.008

500 2.82 - i0.00040 60 80 100 120 140 160 180 200

0.00

0.01

0.02

0.03

0.04

= 500 nm

= 400 nm

= 310 nm[Q

a+Q

s(1-

g)]

/d, n

m-1

Diameter of TiO2 nanoparticle, nm

11

air

epidermis

Optical parameters for SC without nanoparticles (adopted from V.V. Tuchin, 1998)

A = s(1)/(s

(1) +sm)

d

CQ

V

N sss

5.1)1(

- scat. coef. of nanoparticles

d

CQ

V

N aaa

5.1)1(

- abs. coef. of nanoparticles

)()1()()( HGMie pApAp

hybrid phase function

2/32

2

)cos21(1

41

)(

ggg

pHG - SC phase function

smss )1(- scat. coef.

amaa )1(- abs. coef.

Model of SC with TiO2 nanoparticles

, nm sm, mm-1 am, mm-1

310 240 60

400 200 23

Optical parameters for SC with nanoparticles

12

30 60 90 120 150 180 2100

20

40

60

80 = 310 nm = 400 nm

Ab

sorp

tio

n (

SC

wit

h T

iO2)

, %

Diameter of TiO2 particles, nm

(a)

30 60 90 120 150 180 2100

5

10

15

20

25 = 310 nm = 400 nm

Dif

fus

e r

efl

ec

tan

ce

, %

Diameter of TiO2 particles, nm

(b)

30 60 90 120 150 180 210

0

10

20

30

40

50 = 310 nm = 400 nm

Tra

nsm

issi

on

, %

Diameter of TiO2 particles (d), nm

(c)

Effect of TiO2 nanoparticles

Absorption in the upper part of the horny layer (1-um-thick, with TiO2 particles) (a), reflectance from (b) and transmittancethrough (c) the whole 20-um-thick horny layer of the incident radiation with = 310 and 400 nm.

13

0% 5% -- -- --0

20

40

60

80

100%

Concentration of 122-nm TiO

2 particles, %

(a)

The effect of the optimal TiO2 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

0% 5% -- -- --0

20

40

60

80

100 Transmission Total reflection Absorption in lower part Absorption in upper part

%

Concentration of 62-nm TiO

2 particles, %

(b)

Effect of TiO2 nanoparticles

A.P. Popov et al., J. Biomed. Opt. 10, 064037 (2005).

14

200 300 400 500 600 700 800

2

4

6

8

10

Ext

inct

ion,

tim

es

Wavelength, nm(a)

Experiment Simulations

max at = 360 nm

Comparison with experiment

ExperimentNanoparticles UV-TITAN M 160 (Kemira, Finland) in absorbing emulsion (L’Oréal, France) Monte Carlo simulationsTiO2 particles (d = 100 nm, C = 0.2%) in transparent medium (thickness 20 um, nm = 1.4)

0 50 100 150 200

0

5

10

15

20

25

30

35

40

[Qa+

Qs*

(1-g

)]/d

, 10

3 nm

-1

Diameter of TiO2 particles, nm

(b)

max at d = 98 nm

= 360 nmnTiO2 = 3.54 - i*0.16nm = 1.4

15

Conclusion IOptimal sizes of TiO2 nanoparticlesfor attenuation of: 310-nm UV light are 62 nm,400-nm UV light are 122 nm.

Good correlation with experiment

16

EPR setup and samples

EPR setup (1.5 GHz)

Punch biopsies from porcine ears

Placebo with PCA and TiO2 (diam. 400 nm, 0, 25 nm) on glass plates, 2 mg/cm2

17

Spectrum of sun simulator

18

TiO2 nanoparticles

d = 25 nm (a) d = 400 nm (b)

TEM photos (TiO2 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

0 100 200 300 400 50002468

10121416

TiO2: d = 25 nm

TiO2: d = 400 nm

Raman shift, a.u. (a)

Rama

n sign

al, a.

u.

0 200 400 600 800 1000

0

5

10

15

20

25

= 335 nm= 310 nm

Q a/d, 10

3 *nm-1

Diameter of TiO2 particles, nm(b)

Signal of Raman scattering (a);relative absorption efficiency factor (Qa/d) for two wavelengths (b)

TiO2 nanoparticles: anatase

20

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

EP

R s

igna

l, a.

u.

Time, min.

TiO2 d = 25 nm

5 samples no UV UV

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4TiO

2 d = 400 nm

5 samples no UV UV

EP

R s

ign

al,

a.u

.

Time, min.

EPR measurements

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Placebo5 samples

no UV UV

EP

R s

ign

al,

a.u

.

Time, min.

EPR signals from placebo with TiO2 particles on glass slides

21

EPR measurements

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

TiO2 d = 25 nm

immediately4 samples

no UV 3 min UV

EP

R s

ign

al,

a.u

.

Time, min.0 2 4 6 8 10 12 14 16 18 20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

TiO2 d = 400 nm

immediately4 samples

no UV 3 min UV

EP

R s

ign

al,

a.u

.

Time, min.

EPR signals from placebo with 25- (a) and 400-nm (b) TiO2 particles on porcine skin

(a) (b)

A.P. Popov et al., J. Biomed. Opt. 14, xxxxxx (2009).

22

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Skin (porcine)immediately6 samples

no UV 3 min UV

EP

R s

ign

al,

a.u

.

Time, min.

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Placeboimmediately6 samples

no UV 3 min UV

EP

R s

ign

al,

a.u

.

Time, min.

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

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