Skin penetration and stabilization of formulations containing microfine titanium dioxide as physical UV filter

Microfine titanium dioxide (TiO(2)) has become a frequently used physical UV filter in sunscreen formulations. Penetration of microfine TiO(2) into human skin seems to be possible because of the mean particle size of 20 nm. The small particle size results in a high surface activity of the primary particles and causes a formation of agglomerates in the formulation. The aim of this study was to investigate the in vivo and in vitro penetration behaviour of the physical UV filter into human skin. Furthermore, a stable sunscreen formulation with microfine TiO(2) which does not penetrate into the skin should be developed. According to our experiments, microfine TiO(2) penetrates deeper into human skin from an oily dispersion than from an aqueous one. Therefore, an o/w emulsion containing the dispersed micropigment in the aqueous phase was manufactured. Microfine TiO(2) cannot penetrate into human skin from this emulsion, but the storage stability of the formulation is very low at different temperatures. The encapsulation of the micropigment into liposomes does not result in a better stability but it causes a higher penetration depth of the particles into the skin.     

Sunblocking efficiency of various TiO(2)-loaded solid lipid nanoparticle formulations(1)

In this study, titanium dioxide (TiO(2)) was incorporated into solid lipid nanoparticle (SLN) formulations using both classical and novel preparation methods. The SLNs were investigated by evaluating their stabilities and physicochemical characteristics. UV-protection abilities of formulations were investigated using in vitro Transpore and Sun To See(TM) test methods. Results have been discussed by comparing the classical SLN formulation with the novel SLN, hybrid SLN (H-SLN) and the emulsion formulations. The results showed the superiority of the H-SLN formulations compared with the classical SLN; all SLN formulations were better when compared with the emulsion formulations considering the UV protection. Incorporation of TiO(2) as a sunscreen agent into SLN formulations gives opportunity to produce stable and safe formulations with reduced amount but high UV-protection ability.     

Nanostructured lipid carriers as novel carrier for sunscreen formulations

Incorporation of sunscreens into lipid carriers with an increased sun protection factor (SPF) has not yet been fully accomplished. In the present paper, the effectiveness of a sunscreen mixture, incorporated into the novel topical delivery systems, i.e. solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC), used as ultraviolet (UV) protector enhancers with a distinctly higher loading capacity has been developed and evaluated. SLN and NLC were produced by hot high pressure homogenization technique in lab scale production. Size distribution and storage stability of formulations were investigated by laser diffractometry and photon correlation spectroscopy. Nanoparticles were characterized by their melting and recrystallization behaviour recorded by differential scanning calorimetry. Lipid nanoparticles produced with a solid matrix (SLN and NLC) were established as a UV protection system. The loading capacities for molecular sunscreens reported before now were in the range of 10-15%. It was possible to load NLC with up to 70% with molecular sunscreen, which is appropriate to obtain high SPFs with this novel UV protection system. The developed formulations provide a beneficial alternative to conventional sunscreen formulations. The UV protective efficacy of the lipid particles varied with the nature of lipid and UV wavelength.     

Contact angle measurement - a reliable supportive method for screening water-resistance of ultraviolet-protecting products in vivo

Substantivity of sunscreen formulations is affected by the wash-out rate of ultraviolet-absorber and -reflector compounds in water. Water-resistance of sunscreen formulations is currently determined according to a standardized European Cosmetic Toiletry and Perfumery Association (COLIPA) protocol, encompassing the determination of a minimal erythemal dose before and after a defined immersion step in water. It can be supposed that the higher the wettability of a treated skin area, the higher is the wash-out rate of sunscreen compounds. This present report addresses the validity of determining the wettability of treated skin alone as a measure for the water-resistance of sunscreen products. The report addresses the robustness, accuracy and congruence of a recently developed wettability test, based on the measurement of the contact angle (CA) of a sessile water drop on treated skin areas. Contact angle data of 66 sunscreen formulations are compared with the corresponding results of 81 water-resistance tests, using the sun protection factor (SPF)/immersion/SPF method. Sunscreen products tested by the CA method were applied to the skin of the volar forearm of test subjects at a defined dose and drying-time, using a standardized application and recording device. Contact angles between a sessile water drop and skin were recorded by a Charge-Coupled Device (CCD) camera and subjected to automatic contour analysis. Taking the SPF/immersion/SPF method as gold standard, accuracy parameters of the CA method were determined. By using an appropriate cut-off level of CAs, the CA method has a specificity and positive-predictive value of 100%, and turns out to be a reliable screening method to identify water-resistant formulations. Based on our findings, those formulations that give CAs above 30 degrees may be categorized water-proof without further testing by the COLIPA water-resistance method.     

Research on a natural sunscreen from Chinese herbs

To compare the difference in SPF values between a synthetic sunscreen and a sunscreen derived from Chinese herbs, by using optical and biological methods, we observed the effects of these sunscreens by photochemical reaction, sun protection factor (SPF) values, and UV absorption. The results showed that the synthetic sunscreen was more effective in UV absorption than the sunscreen derived from natural Chinese herbs. When they were tested biologically, it was found that the sunscreen derived from Chinese herbs was able to improve skin tonicity, as well as reduce the itching, photoerythema, squamation, burning, and reddening caused by the excessive UV radiation, while the synthetic sunscreen could not improve these conditions of the skin, and even induced some side-effects in the skin with photoerythema. By comparing the in vivo SPF values of the two types of sunscreen, they were found to be mainly similar. The results indicate that the SPF value was related to both a photo-reaction and a biological reaction. The sunscreen derived from natural Chinese herbs, although having low UV absorption, was able to exhibit the same SPF value as the synthetic sunscreen because of its biological effects.     

Solubilisation de filtres-UV dans des melanges ternaires de phases apolaires, optimisation par l'utilisation de reseaux centres

This paper is concerned with the solubility of UV filters. Emulsions are perfect formulations used for sunscreens, but to give the skin silky feel without being greasy, the oily phase content is low. Considerations of sunscreen solubility can help to solve specific problems of stability in formulations. It is important to determine what solvent dissolves them and what mixture of solvent improves their solubility. Two water insoluble sunscreens were tested at several concentrations in various non-polar solvents. A strategy with simplex centroid design was used to optimize this work. The graphical interpretation of the data assists our understanding of the solubility of UV filters.     

Prediction of the percutaneous penetration of ultra-violet filters used in sunscreen formulations

The application of a mathematical model to estimate the extent of transdermal absorption of UV-filters commonly used in sunscreen formulations is described. Percutaneous penetration is not a factor that has been properly addressed in the literature and the penetration/time profiles generated here suggest that significant amounts of certain of these compounds may penetrate the skin and enter the systemic circulation. The results presented indicate that further research in this area is necessary and the authors suggest that in vitro experiments with human skin are conducted with both current and new UV filters to quantify the degree of dermal penetration of these substances.     

Characterization of the mineral content of a physical sunscreen emulsion and its distribution onto human stratum corneum

When using physical sunscreens, protection and aesthetic aspects are directly related to particle size and mineral distribution onto skin. These investigations aimed to characterize the different mineral raw materials entering into the composition of a specific sunscreen emulsion and to assess the distribution of the sunscreeen agents at the surface of human stratum corneum. X-ray diffractometry revealed the crystallographic features of the TiO2 and ZnO crystals. Frequency distributions of crystal length and aspect ratio were determined for the zinc oxide which presented the largest particle size and varying shapes. Scanning and transmission electron microscopy disclosed structural information. The results reported in this study specify the characteristics of the oxide particles involved in the formulation and show a satisfactory mineral distribution along the irregular topography of the skin. No intracellular penetration was noted.     

J. Cosmet. Sci., 59, 263–289 (July/August 2008)True porosity measurement of hair: A new way to study hair damage mechanisms

The purpose of this study was the development of a microbiological method for the assessment of the ultraviolet (UV) screening effect of sunscreen preparations and determination of their sun protection factor. The method is based on the lethal effect of UV radiation on Escherichia coli and the protective ability of sunscreens. The time of UV exposure required for the reduction of the E. coli viable count by 90% (decimal reduction time, DRT) was used as the photoprotection assessment parameter. The method was tested by assessing the effect of selected experimental variables on the DRT. The suitability of the method as a quality control tool for sunscreen preparations was then checked by assessing the influence of selected formulation variables on the photoprotective effect of a series of o/w emulsion formulations with different compositions. The method proved valid for detecting changes in the photoprotective effect of a market sunscreen product as a result of modifying experimental conditions. It also proved valid for ranking market sunscreen products according to their UV screening effect. Equally important, the method could successfully detect changes in the photoprotective effect of sunscreen test formulations as a function of the concentration and type of the sunscreen agents.     

J. Cosmet. Sci., 59, 385–398 (September/October 2008)Evaluation of liposomal and conventional formulations of octyl methoxycinnamate on human percutaneous absorption using the stripping method

The objective of this study was to determine the influence of vehicles on the penetration of octyl methoxycinnamate (OMC), as a UV absorber, to the stratum corneum by the stripping method. The experimental formulations consisted of a conventional o/w emulsion and multilamellar and small unilamellar liposomes (MLVs and SUVs) containing OMC. MLVs containing OMC were prepared by the fusion method and then converted to SUVs by probe sonication. Various formulations were then applied onto the midvolar forearms of six volunteers at a dose of 2 mg cm^-2. After determined timepoints, the stripping method was conducted whereby 22 tape strips were applied and subsequently divided into different stripping groups. The sunscreen agent was assessed by HPLC while the SPF (sun protection factor) of the formulations was determined in human volunteers in accordance with the Australian standard. Overall the results indicate that skin accumulation of OMC in MLVs was significantly greater than in the o/w emulsion and SUVs. Furthermore, SUV's penetration into the deeper skin layers was significantly greater than MLV's and that of a conventional o/w emulsion. Also, higher amounts of OMC were recovered from the upper layers of the stratum corneum than from the deeper layers in all the formulations tested. Finally, the SPF of the liposomes containing OMC was slightly greater than that of the control lotions at a similar concentration of OMC. In conclusion, the result of this study indicates that an MLV prepared by the fusion method could be a better vehicle for OMC as a sunscreen since it has a slightly better SPF compared to a conventional formulation and more remains in the stratum corneum, reducing its penetration to the deeper layers.
Address all correspondence to M. R. Jaafari.     

Enhanced degradation in nanocomposites of TiO2 and biodegradable polymer

Nanocomposites of titamium dioxide (TiO2) particles and biodegradable poly (butylene succinate) (PBS) were fabricated by melt-blending using a high-shear extruder. TiO2 particles were highly dispersed in the PBS matrix by high-shear processing, and the addition of TiO2 particles into PBS did not decrease its mechanical strength. The photocatalytic decomposition and biodegradable properties of the nanocomposites were evaluated by UV irradiation or enzymatic degradation methods in vitro. It was found that both the esterase enzyme and UV irradiation decomposed the nanocomposites. Photocatalytic decomposition of PBS clearly depended on the size and dispersibility of TiO2 particles in PBS polymer. Higher dispersibility and smaller size of TiO2 particles were effective on the photocatalytic oxidation of PBS. In addition, decomposition rate under a simultaneous UV irradiation treatment and immersion in an enzyme solution was higher than those under UV irradiation or immersion in an enzyme solution. These results indicate that the nanocomposites can easily be decomposed not only by an enzyme in soil or compost, but also by photocatalytic oxidation of TiO2 under sunlight.     

The Outermost Stratum Corneum Layer is an Effective Barrier Against Dermal Uptake of Topically Applied Micronized Titanium Dioxide

In order to help clarify the controversially discussed dermal uptake properties of micronized titanium dioxide (TiO _ 2), we conducted extensive in vitro dermal absorption studies with 'Franz-type' diffusion cells on excised porcine skin. After biopsies and chemical fixation, the overall localization of TiO _ 2 in the skin was analyzed by means of transmission electron microscopy (TEM). The lateral and vertical distribution of TiO _ 2 within the stratum corneum (SC) was investigated by tape stripping and subsequent scanning electron microscopy (SEM) in combination with energy dispersive X-ray analysis (EDXA). TiO _ 2 was found exclusively on the outermost SC layer. The surface deposit, as displayed by TEM, featured clearly distinguishable agglomerates as well as single particles with a characteristic cubic shape and a primary particle size of about 20-50 nm. Concurrently, SEM/EDXA micrographs first showed an even distribution of TiO _ 2 on the skin surface. After 10-fold stripping, however, TiO _ 2 was found to be localized only in the furrows and not on the partially removed ridges of the skin surface. SEM/EDXA micrographs of the adhesive tape strips revealed a characteristic pattern of stripped material and free regions. This pattern was an imprint of the skin's topography. Hence, tape stripping initially removed TiO _ 2 and SC layers only from the ridges and not from the deeper furrows. Continued stripping increasingly yielded material from the deeper contours of the SC surface. TiO _ 2 was found only in traces in the upper part of the follicle without any evidence of uptake into the follicular epithelium. This indicates that there is not any relevant penetration via the follicular route. We conclude that due to the microtopography of the skin, the strip number normally does not reflect the SC layer number. Accordingly, tape stripping results should always be interpreted with care, especially in the case of topically applied particles, as even higher numbers of subsequent strips may still sample material from the outermost SC layer of the deeper furrows, which could be interpreted falsely as penetrated material. Our results clearly demonstrate that TiO _ 2 homogeneously and completely covers the outermost SC layer. It is neither delivered to the SC nor to the underlying skin layers when applied topically to porcine skin in vitro in the cosmetic vehicle used here. These findings underscore the safety of this micronized inorganic UV filter.     

In vitro skin permeation of sunscreen agents from O/W emulsions

The effects of different emulsifiers on the in vitro permeation through human skin of two sunscreen agents [octylmethoxycinnamate (OMC) and butylmethoxydibenzoylmethane (BMBM)] were investigated from O/W emulsions. The test formulations were prepared using the same oil and aqueous phase ingredients and the following emulsifier and coemulsifier systems: Emulgade SE((R)) (ceteareth-12 and ceteareth-20 and cetearyl alcohol and cetyl palmitate) and glycerylmonostearate (emulsion 1); Brij 72((R)) (steareth-2), Brij 721((R)) (steareth-21) and cetearyl alcohol (emulsion 2); Phytocream((R)) (potassium palmitoyl-hydrolysed wheat protein and glyceryl stearate and cetearyl alcohol) and glycerylmonostearate (emulsion 3); Montanov 68((R)) (cetearyl glucoside and cetearyl alcohol) (emulsion 4); Xalifin-15((R)) (C(15-20) acid PEG-8 ester) and cetearyl alcohol (emulsion 5). The cumulative amount of OMC that permeated in vitro through human skin after 22 h from the formulations being tested decreased in the order 3 > 1 congruent with 4 > 5 > 2 and was about nine-fold higher from emulsion 3 compared with that from emulsion 2. As regards BMBM, no significant difference was observed as regards its skin permeation from emulsions 1, 3, 4 and 5, whereas formulation 2 allowed significantly lower amounts of BMBM to permeate the skin. In vitro release experiments of OMC and BMBM from emulsions 1-6 through cellulose acetate membranes showed that only emulsions 4 and 5 provided pseudo-first-order release rates only for OMC. The results of this study suggest that the type of emulsifying systems used to prepare an O/W emulsion may strongly affect sunscreen skin permeation from these formulations. Therefore, the vehicle effects should be carefully considered in the formulation of sunscreen products.     

屏蔽型纳米TiO2的结构及其整理棉织物的性能

在纳米TiO2颗粒外层包裹有机物和SiO2，经高温烧灼处理，制备了具有独特中空结构的屏蔽型纳米TiO2，其粒径20nm左右，锐钛矿相的含量80％以上。屏蔽型纳米TiO2具有明显的分解甲醛作用；其中空屏蔽结构阻隔了与被整理物之间的直接接触，光催化活性比未改性纳米TiO2有一定程度的降低，经其整理的棉织物的光催化降强也小得多。     

Surface distribution and depths profiling of particulate organic UV absorbers by Raman imaging and tape stripping

Tape stripping in conjunction with scanning Raman microscopy was used for assessing the lateral and vertical distribution of an organic particulate UV filter, methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), in a sunscreen formulation. On the volar forearms of three volunteers, 1 mg cm(-2) formulation containing 10% MBBT was applied, and the average amount of MBBT was measured by Raman scanning microscopy in 15 consecutive tape strippings. The recovery of MBBT was 91.1% with 30.2% localizing on the skin surface (first strip), 42.5% in the upper stratum corneum (strips 2-5) and from 3.6 down to 0.8% in each of the 10 consecutive layers. The concentration of surface deposits of MBBT differed by a factor of 300 between folds, furrows and pores on the one hand and the interjacent ridges on the other hand. Seventy-five per cent of the applied particles occupied a fifth of the evaluated area - where concentrating in folds and furrows - as was confirmed by 3-D reconstruction. On interjacent ridges, 8.6% of MBBT distributed as very thin films preferentially. MBBT localized at sites not connected with the surface, such as in truncated pores or as potentially penetrated material amounted to 0.06% or to a twentieth of the 1.4% found in the lowest skin strippings. Scanning Raman microscopy in combination with tape stripping documented the lateral and vertical distribution quantitatively and at cellular (12.5 μm) lateral resolution. Our results confirmed an earlier report on the vertical distribution of organic particles applied to skin and was in line with similar reports on TiO(2) distribution.     

Technological strategies to improve photostability of a sunscreen agent

Due to the reduction of the ozone layer, there is an increasing need of effective UV protection systems with minimized side-effects. Trans-2-ethylhexyl- p -methoxycinnamate ( trans -EHMC) represents one of the most widely used sunscreen compound. Several studies demonstrated that trans -EHMC is unstable following UV irradiation both in solution and in emulsion formulations. Moreover, various reports of photocontact sensitization induced by trans -EHMC have appeared in the literature. Consequently, in order to ensure adequate efficacy and safety for this sunscreen agent, there is a need for new carrier systems to enhance trans -EHMC photostability. In the present study the photostability of the filter in different formulation types (emulsion–gel, gel and emulsion) with various ingredients is evaluated. In addition, nanoparticles based on poly- D , L -lactide-co-glycolide (PLGA) as carrier for trans -EHMC are investigated. The influence of nanoparticle matrix on the photochemical stability of the sunscreen agent is also presented. The results obtained demonstrated that PLGA nanoparticles are effective in reducing the light-induced degradation of the sunscreen agent. Moreover, the choice of formulation type and the excipients used play an important role in order to obtain a stable cosmetic product containing trans -EHMC.     

Reconstructed human epidermis as an efficient tool in the evaluation of the effects of UV irradiation and of the photoprotective capacities of a sunblock

In this study, we used a spectroscopic method, found effective in measuring sunscreen photo-degradation results in terms of a photoabsorption decrease. The traditional approach was to measure variations in well-known parameters such as the absolute in vitro sun protection factor (SPF) or the relative UVA/UVB ratio after a controlled dose of UV radiation. However, these parameters fail to fully reflect the product's photochemical behavior. Variation in the SPF mainly depicts changes in UVB filtration, and variation in the relative parameter UVA/UVB ratio can be subjected to misinterpretation, as is the case for products in which a parallel loss of photoabsorption is observed in the UVA and UVB regions. In our laboratory, we developed a new approach using pure spectroscopic UVA and UVB attenuation factors called UVA attenuation factor and UVB attenuation factor. Attenuation factors are defined here as the inverse of the arithmetic mean of the transmittance data, taken either from the UVB region (290–320 nm, 1 nm steps) or the UVA region (320–400 nm, 1 nm steps). Using these two new spectroscopic indices, the photochemical behavior of a sunscreen formula can be assessed in each UV region. The general procedure consists of applying two UV doses to a film of sunscreen previously spread on a roughened polymethylmethacrylate plate and then measuring the UV transmission versus wavelength before and after the irradiation process. We tested different UV filters in a cosmetic base to demonstrate the efficacy of the method.     

In vitro evaluation of the cutaneous penetration of sprayable sunscreen emulsions with high concentrations of UV filters

The aim of this study was to evaluate the possible penetration through human skin of organic and inorganic filters contained in sunscreen emulsions packaged in aerosol cans, using an in vitro method. Experiments were carried out on two different types of emulsion: W/Si and W/O. This study was conducted using static diffusion cells (Franz cells). The determination of organic UV filters [Methylene Bis Benzotriazolyl Tetramethylbutylphenol (MBBT); Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine (BEMT); Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB); Ethylhexyl Methoxycinnamate (EMC); and 2-Ethylhexyl Dimethyl PABA (ED-PABA)] was performed by High Performance Liquid Chromatography (HPLC). Therefore, it was important to develop a single analytical method for the quantification of the five organic filters with the aim of facilitating the experiment. The determination of inorganic filters [titanium dioxide (TiO₂) and zinc oxide (ZnO)] was performed using an emission spectrometric analysis method (ICP-OES). The HPLC and ICP-OES methods were validated. After a penetration test of 24 h duration, the results showed very low penetration only for two of the organic filters (maximum penetration of 1.21 μg cm⁻² h⁻¹ for EMC and 0.14 μg cm⁻² h⁻¹ for MBBT) and no penetration for the inorganic filters. Moreover, more than 50% of each sunscreen agent stayed on the surface on the skin. These results are consistent with those in the literature that presents similar experiments. This study showed that the sprayable sunscreen products developed, which contained high concentrations of UV filters, presented a low level of skin penetration.     

Absorption of materials by or through the living skin

The skin comes into contact with a large range of materials either deliberately or inadvertently. It should be possible to predict the exact transport rates of these materials through the skin as a function of the physicochemical properties of the different compounds. With this sort of knowledge it is possible to predict the exact disposition of compounds and use this in the formulation of new products both in the pharmaceutical and cosmetic field. The information will also be useful from the standpoint of skin toxicology and environmental health. In order to be able to predict this complex process it is necessary to split the overall transport into different component parts. This article will identify these components and provide illustrations. The major areas discussed will be barrier function of the skin, the release properties of different topical formulations and how these may be monitored. Novel means of enhancing the penetration of drugs will be discussed and how some additives that are incorporated into formulations will perhaps alter the barrier function of skin. A mathematical model describing skin penetration has been developed and its use in predicting blood levels will be described. This model has been tested both in animal experiments and in limited human studies and its relevance to these situations will be highlighted.
Absorption cutanée et transcutanée in vivo     

Comparison of sun protection factors determined by an in vivo and different in vitro methodologies: a study with 58 different commercially available sunscreen products

An extensive study on the sun protection factors (SPF) of sun care products was carried out using the COLIPA (The European Cosmetic Toiletry and Perfumery Association) method, which relates to in vivo experiments. Furthermore, in vitro methods were tested with sunscreen formulations that were prepared as films on surface-roughened plates of polymethyl methacrylate (PMMA). One of the in vitro methods, i.e. using the sunscreen tester, has been recently developed, whereas the second has been defined by a pure spectroscopic approach, which is based on spectral transmission measurements of sunscreen films. Altogether 58 different sunscreen formulations, with manufacturer declared SPF values ranging from 4 to 60 and currently available on the European market, were investigated. The quality of correlations with results from the individual products based on the different in vitro methods versus the COLIPA values that were considered as generally accepted standard values was assessed. In this context, also variations because of sample preparation and spectral measurement were discussed. For sunscreen products with in vivo SPF values larger 25, the spectral transmittance within the UVA/UVB range is rapidly decreasing, which is experienced even for products with reduced amounts reaching 0.5 mg cm(-2) and still leading to unsatisfactory correlation of the spectroscopically derived SPF values versus the results from the alternative assays. Opposite to these small amounts, a sunscreen product spread of 2 mg cm(-2) is standard for the in vivo COLIPA method, whereas an area-normalized amount of 1 mg cm(-2) is currently routinely used for the sunscreen tester method. Furthermore, an overview of the individual product characteristics, such as their specific critical wavelengths and their UVA/UVB ratios is provided; both parameters can also be calculated from the spectral absorbances of the standardized sunscreen films.