Published on March 9, 2014
NANOMATERIALS IN SUN-SCREEN UV PROTECTION BY, A. POOJA SHUKLA M.Tech (NANO) 1821310006
HOW SMALL….??? Nanoparticles are one-twentieth the thickness of a human hair. Nanoparticles are smaller than 100 nanometres and invisible to the human eye – a nanometre is 0.000001 millimetre. Microfine particles are smaller than those used in conventional white zinc sunscreens, however are larger than nanoparticles – usually in the range of 100 to 2500 nanometres.
PROPERTIES….??? NANOTECHNOLOGY, is already making today’s products: Lighter Stronger Faster Smaller More Durable
WHAT ARE SUN RAYS…?? The sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV) High Energy Low Energy Each kind is distinguished by a characteristic wavelength, frequency and energy Higher energy radiation can damage our skin
SKIN DAMAGE The kind of skin damage is determined by the size of the energy packet ( E = h x f) The UV spectrum is broken into three parts: Very High Energy (UVC) High Energy (UVB) Low Energy (UVA) • As far as we know, visible and IR radiation don’t harm the skin
SKIN DAMAGE • Very high energy radiation (UVC) is currently blocked by the ozone layer (ozone hole issue) • High energy radiation (UVB) does the most immediate damage (sunburns) • But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term damage
SUN RADIATION SUMMARY Radiation Type Characteristic Wavelength (l) UVC ~200-290 nm (Short-wave UV) UVB UVA ~290-320 nm (Mid-range UV) ~320-400 nm (Long-wave UV) Vis ~400-700 nm IR ~700-120,000 nm Increasing Wavelength Energy per Photon Increasing Energy High Energy Medium Energy % of Total Radiation Reaching Earth Effects on Human Skin Visible to Human Eye? ~0% DNA Damage No Sunburn DNA Damage Skin Cancer No Tanning Skin Aging DNA Damage Skin Cancer No ~43 % None Currently Known Yes ~49% Heat Sensation (high l IR) No (<1% of all UV) ~.35% (5% of all UV) ~6.5% Low Energy Lower Energy Lowest Energy (95 % of all UV)
NANOPARTICALS IN SUN-SCREEN The nanoparticles used in sunscreens and other consumer products may have novel biological and physical properties, which can lead to unusual effects – both good and bad. Nanoparticles found in sunscreens are either titanium dioxide or zinc oxide.
WHY USE SUN-SCREEN….?? Too much unprotected sun exposure leads to: Premature skin aging (e.g. wrinkles) Sunburns Skin cancer
WHY NANOMATERIALS IN SUN- SCREEN…?? Sunscreens made with zinc oxide and titanium dioxide generally score well because: they provide strong sun protection with few health concerns they don’t break down in the sun zinc oxide offers good protection from UVA rays – titanium oxide less so, but better than most other active ingredients.
Inorganic UV Filters NANOMATERIALS….?? Titanium dioxide (TiO2) and zinc oxide (ZnO) pigments are commonly used in personal care products to provide protection against UVA and UVB They attenuate UV light by absorption and scattering They are usually surface coated to minimize photo-catalytic activity. They are typically produced as finer crystals from the same feed stocks and with similar processes as pigmentary grades.
Manufacturing is a two step process : Process The production of TiO and ZnO 2 1. Purification of the raw material 2. Growing of crystals (primary particles) of the desired size They are two different processes for TiO2, known as sulfate and chloride, and three for ZnO, known as American, French and Wet. Crystals are grown at high temperatures to the required sizes : 200 nm and above (pigmentary grades) and finer than 200 nm (attenuation grades). Attenuation grades 10nm Pigmentary grades 200nm
Surface Treatment of Inorganic UV Filters Pigment type (primary particle size) Surface Treatment Pigmentary TiO2 (410 nm) Attenuation grade TiO2 (30 - 50 nm) Attenuation grade ZnO (15 - 35 nm) Treatment Rate * None 4.76 2% Methicone < 0.01 Alumina 0.13 3% Lecithin 0.033 None 1.83 3% Methicone < 0.01 M. Kobayashi and al., Cosm & Toil., Vol. 112, No. 6, p83, 1997 * Rate constant of the first order reaction of oxydation of acetalydehyde It is common industry practice to use surface treated inorganic UV filters when formulating sunscreens.
Attenuation of UV light is influenced by particle size. Scattering of visible light (whitening effect) is influenced by particle size and the difference between the refractive index of the pigment and the surrounding media. Maximum scattering occurs when size equals 1/2 the wavelength and particles are uniformly dispersed (Mie theory). Wavelength Particle size
TiO2 Dispersions in Cyclopentasiloxane 195 60 35 15 10 nm 195 195 60 35 15 10 nm 195 60 60 35 15 10 nm 35 15 10 nm 10nm TiO2 (110 nm dispersion particle size) makes transparent dispersions for all skin types. All dispersions diluted in Cyclopentasiloxane (to 20% TiO2)
Particle Size and UV attenuation UVB / UVA 100 - 120 nm balance 7.0 - 8.0 120 - 150 nm 3.4 - 5.5 11 - 55 20 nm 130 - 160 nm 2.0 9 35 nm 150 - 180 nm 1.5 - 2.0 7 - 17 150 nm > 250 nm 1.1 2.6 20 nm 130 - 180 nm 1.0 - 1.1 30 - 37 60-100 nm 180 - 250 nm 1.1 6.3 120 nm ZnO Dispersion particle size 15 nm TiO2 Primary particle size 10 nm Pigment > 250 nm 0.9 2.9 (1) Transparency 308/360 extinction ratio : indication of UVB/UVA balance (2) 308/524 extinction ratio : indication of transparency (1) 70 - 90 (2)
Conclusions Attenuation grade Titanium Dioxide and Zinc Oxide are produced using the same processes as larger pigmentary grades. They are usually surface coated to minimize their photo-catalytic activity. TiO2 and ZnO attenuate UV light according to their particle size : Small primary particle sizes (10 - 15 nm) are necessary to produce dispersions (100 - 150 nm) transparent to visible light and efficient against UVB. ZnO and larger TiO2 (35 - 150 nm) are more efficient against UVA. The particle size of pigmentary grades are appropriate to scatter visible light, but they are not efficient at attenuating UV light or effective as sunscreens.
With all of this possible damage, it pays to wear sunscreen, but which one should you use? PRODUCTS….???
Do the shape and size of the particles affect sun protection? Yes. The smaller they are, the better the SPF protection and the worse the UVA protection. Manufacturers must strike a balance: small particles provide greater transparency but larger particles offer greater UVA protection. The form of zinc oxide most often used in sunscreens is larger and provides greater UVA protection than the titanium dioxide products that apply clear on the skin. Do the nanoparticles in sunscreen penetrate the skin? No. Some studies indicate that nanoparticles can harm living cells and organs, but there is no evidence that zinc oxide and titanium dioxide nanoparticles penetrate skin in any significant quantities. Could nanoparticles that penetrate the skin cause skin damage when energized by sunlight? Possibly but unlikely, since the materials don’t penetrate deep enough in skin to reach living skin cells.
APPLICATION Blocks UVA and UVB radiation Full SPF protection Protects from SKIN RASHES Avoids SKIN CANCER Avoids SKIN AGING Twenty different skin cancer lesions
REFERENCES 1. Images : source internet 2. http://en.wikipedia.org/wiki/Sunscreen 3. Nano-ingredients in sunscreen, The need for regulation, july 2012 4. Nanotechnology and cosmetics, November 2008 5. http://www.ewg.org/2013sunscreen/nanoparticles-in-sunscreen/ 6. http://spie.org/x33993.xml 7. http://www.uvawareness.com/sunscreen-info/sunscreen-information.php 8. http://www.cancer.org.au/preventing-cancer/sun-protection/nanoparticlesand-sunscreen.html 9. http://www.csiro.au/en/Portals/Publications/Brochures--FactSheets/sunscreens-FAQ.aspx
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