IN VITRO SPF DETERMINATION ON HD6 PMMA 249 INFLUENCE OF C.B. PRETREATMENT ON ROUGHNESS OF THE HD6 SUBSTRATE The second criterion checked was the surface roughness in the presence of the cocamido- propyl betain fi lm. The values obtained (Table III) were compared with those obtained with a petrolatum fi lm applied on the HD6. The amphoteric pretreatment has a lower infl uence on the roughness substrate compared with petrolatum pretreatment. The C.B. treatment makes a very thin fi lm whose roughness will not affect the SPF results. INFLUENCE OF C.B. PRETREATMENT ON THE WETTABILITY OF THE HD6 SUBSTRATE The contact angles between a 10-μl drop of ionized water and HD6 PMMA plates with and without pretreatment were measured. The values (Table IV) show the hydrophilic nature of PMMA (contact angle of 63°). In the presence of C.B. pretreatment the sub- strate becomes highly hydrophilic (θ=14.9). INFLUENCE OF C.B. PRETREATMENT ON THE SPREADING OF TWO SELECTED PRODUCTS SPF investigations were performed with two different bases, an O/W emulsion and a gel. Both these formulae were chosen according to their respective poor and good correlations with the in vivo values. Sample A with poor in vitro/vivo correlation. Product A is selected in this study because HD6 plates failed to reproduce the in vivo SPF value. It is interesting, however, to mea- sure the SPF of such a product on the amphoteric pretreated HD6 in order to compare the results. The in vitro SPF results (Table V) obtained with the same operator on untreated plates (5.59) were much lower than those obtained on the pretreated HD6 (18.46), which are in line with the in vivo values. It is therefore necessary to understand why untreated HD6 failed to give a result close to the in vivo value, whereas it works on the pretreated plates in the case of sample A. Table III Mean Values of the Different Roughness Parameters for the Untreated PMMA and Pretreated PMMA Plates Roughness parameters Ra Rp Rv Rdq Rsk Rku A1 A2 Ssc Vvv Untreated PMMA plate 4.70 10.80 12.83 10.60 -0.22 3.64 213.83 550.83 0.032 9.50E-07 PMMA plate + TegoBetain F50 3.54 9.38 8.43 6.91 0.30 3.87 309.40 296.00 0.017 6.54E-07 PMMA plate + petrolatum 2.42 6.85 4.57 3.59 0.78 4.45 279.00 99.46 0.008 4.69E-07 Table IV Values of the Contact Angle (θ) between Deionized Water and the Substrate before and after Pretreatment 10 μl deionized water Untreated HD6 Pretreated HD6 Contact angle θ 63 14.9

JOURNAL OF COSMETIC SCIENCE 250 Figure 4a shows a clear separation of both phases of emulsion A, in contact with the molded plate. After stabilization, it results in multiple non-covered areas the poor cover- age of the surface may explain why the SPF value is lower than the results expected with the fi lters used (Table V). A poor distribution reduces the intensity of the absorption (15). Figure 4b shows that in the presence of C.B. pretreatment, a slight separation of the product phases during spreading on the PMMA is observed by microscopic visualization. After stabilization, it results in a uniform covered area and a good fi lter distribution, which could explain the higher SPF corresponding to the in vivo value. WETTABILITY MEASUREMENTS BETWEEN SAMPLE A AND THE UNTREATED AND PRETREATED HD6 The contact angles between sample A and the HD6 plates were measured with and with- out C.B. The values reported in Table VI signifi cantly decrease in the presence of C.B., refl ecting a better contact between product A and the HD6 PMMA substrate in the presence of the 12-mg C.B. treatment. The C.B. pretreatment improves the attraction of sample A on the PMMA surface, resulting in a better distribution and a higher in vitro SPF. Sample B with good in vitro/vivo correlation. In contrast to sample A, sample B yields results in line with the in vivo value (Table VII) whatever the level of the hydrophilicity of the HD6. MICROSCOPIC OBSERVATIONS In the case of untreated as well as treated PMMA plates, both phases of product B remain homogenous (Figure 5) during the spreading on PMMA. After stabilization, it results in a homogenous fi lm distribution. The distribution of sample B is homogenous in both cases, which explains the similar SPF values. In the case of sample B, the wettability measurements are also in accordance with the in vitro SPF results. In fact, the lowest value of the contact angle measured on an untreated Table V Mean Values of In Vitro SPF for Sunscreen Product A Sample A (in vivo SPF = 16) Untreated PMMA plate PMMA plate + TegoBetain F50 Mean SPF 5.59 18.46 Std. SPF 0.36 1.2 Cov. SPF 6.50% 6.52% Figure 4. (a) Microphotography on untreated HD6. (b) Microphotography on C.B.- treated HD6.