The technique of FTIR imaging, in combi nation with a tape-stripping procedure, gives the opportunity to picture and compare the UV fi lter permeation of a specifi c sunscreen product in the SC. A different penetration behavior for the BMDBM between the traditional sunscreen formulation and the sunscreen formulation based on encapsulation technology was detected. With the regular formulation, the UV fi lters presented not only a high concentration on the skin surface as expected but also a signifi cant concentration deep inside the SC, indicating the BMDBM under “free” formulation did not remain on the skin surface but penetrated deep inside the skin. UV fi lters were detected up to the layer six under free formulation after just one single topical application. On the other hand, the same UV fi lters combined with encapsulation technology were observed on the skin surface, and almost no penetration was detected inside the SC. Encapsulated BMDBM (avobenzone) was not detected after the layer one, clearly indicating that the encapsulation technology allowed to keep the UV fi lters at the surface of the skin where they will exert their pur- pose most effi ciently (69) (see Figure 3). Microparticles loaded with BMDBM or wit h combined BMDBM and OCR were pro- duced by the hot emulsion technique, using glyceryl behenate as the lipid material and poloxamer 188 as the surfactant. The LMs were characterized by release studies, scanning electron microscopy, and powder X-ray diffractometry. The BMDBM and OCR loading was 15.2 and 10.6%, respectively. To reproduce the conditions prevalent in commercial sunscreen products, the photo-protective effi cacy of the LMs was evaluated after their Figure 3. FTIR images allow to visualize and compare the BMDBM penetration inside the SC for different skin samples: skin samples treated with formulations F1, F2, and F3 compared with the untreated skin. For each sample, the FTIR images were scanned before (control), after topical application on the sunscreen for- mulation, and after eight sequential tape strips [Cozzi et al. (69)]. JOURNAL OF COSMETIC SCIENCE 318
introduction in a model cream (oil-in-water emulsion), containing a mixture of UVA and UVB fi lters. A small but statistically signifi cant decrease in BMDBM photodegradation was obtained when the UVA fi lter was encapsulated alone into the LMs (the extent of degradation was 28.6% ± 2.4 for nonencapsulated BMDBM and 26.0% ± 2.5 for BM- DBM-loaded microparticles). On the other hand, the co-loading of OCR in the LMs produced a more marked reduction in the light-induced decomposition of microencapsu- lated BMDBM (the UVA fi lter loss was 21.5% ± 2.2). Therefore, incorporation in LMs of BMDBM together with the sunscreen OCR is more effective in enhancing the UVA fi lter photostability than LMs loaded with BMDBM alone (16,80). INCORPORATION IN MESOPOROUS SILICA The effect of incorporating avobenzone (AVO/BMDBM), oxybenzone (OXY) and OMC in mesoporous silica (SBA-15) was investigated by Daneluti et al. Stick formulations containing “free” and “incorporated” UV fi lters (SF1 and SF2, respectively) were prepared. Different physicochemical analytical techniques including N2 adsorption isotherm, small-angle X-ray scattering, and thermogravimetry/derivative thermogravimetry (TG/ DTG) were used to confi rm that OMC had been successfully entrapped in SBA-15. Cutaneous delivery experiments using the porcine skin with quantifi cation by UHPLC- MS/MS demonstrated skin deposition of avobenzone and oxybenzone after different ap- plication times (6, 12, and 24 h). The amounts of OMC and AVO permeated across the porcine skin were below the limit of quantifi cation of the UHPLC-MS/MS method (i.e., concentrations 10 ng mL-1) for application times of 6 and 12 h. However, after applica- tion for 24 h, both UV fi lters were detected in the receiver compartment, and permeation from SF1 and SF2 was not signifi cantly different at 24 h. Regarding the OXY results, this was detected in the receiver compartment after application for 6, 12, and 24 h for both SF1 and SF2 although transdermal permeation from both formulations was signifi - cantly lower at each time point with SF2: SF2 having a 30-, 12-, and 1.5-fold lower OXY permeation than SF1 after 6, 12, and 24 h, respectively. OXY showed the highest capac- ity to permeate the skin at all exposure times. After 24 h, the OXY amount detected in the receptor compartment after application of SF1 was 18.7-fold and 21.5-fold greater than that of AVO and OMC, respectively, whereas for SF2, it was 33-fold and 16.5-fold greater than that of AVO and OMC, respectively. OXY has a slightly lower molecular weight (228.25 g mol-1) than OMC and AVO, but more importantly, it is less lipophilic (log Ko/w 3.79 vs. 5.96 and 4.51, for OMC and AVO, respectively), and this may facilitate partitioning into the viable epidermis and hence transdermal permeation (81). DISC USSION Exte nsive research on the tests used for estimating the permeation behavior of various groups of UV fi lters has been carried out. This has led to the discovery of safe vehicle systems that prevent skin absorption of effi cacious UV fi lters and the development of advanced ones with high photostability and low toxicity. Lipi d carriers seem to be a good alternative to formulate chemical UV fi lters reducing their skin penetration while maintaining good photo-protective abilities. Nano particles seem to be interesting carriers of sunscreen, as demonstrated by the good stability, lower toxicity, lack of phototoxic effect in cells, and no allergic reaction in mice. DISTRIBUTION OF UV FILTERS ON THE SKIN 319
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