COLLAGEN EVALUATION 339 Figure 7. SEM images of thin films of three collagens for cosmetic use: (1) AteloHelogen®, (2) Collasol®, and (3) CLR Collagen®. Scale bars are shown. as a clear solution, showed an essentially featureless film, confirming the lack of par­ ticulate or fibrous components. On the other hand, the Collasol®, which was a white turbid sample, showed extensive fibrous structures (Figure 7, panel 2). Of interest was the CLR Collagen® sample, which, although presenting as a fairly clear solution, showed a range of black or grey zones under SEM (Figure 7, panel 3). The nature of these spots is not clear. OTHER TECHNIQUES A range of other techniques may also be valuable in assessing collagen for certain applications. These include determination of viscosity and solubility, over a range of pH values to match formulation requirements density refractive index and lipid content. Microbiological content and immunological response may also be issues of concern. CONCLUSIONS The collagen samples examined m the present study show a wide range in various

340 JOURNAL OF COSMETIC SCIENCE properties. This range suggests that one of these collagens could probably be selected to meet specific manufacturing needs. The tests that have been described allow the poten­ tial collagens to be evaluated, and different batches to be compared for quality assurance. The tests that should be applied to samples will depend on the needs of the particular formulation being developed. A key property of collagens, their water-binding capacity, may also be measured, but this data needs to be treated with care, as the salt present in certain preparations can lead to false interpretations. Of the collagens examined, Atelo­ Helogen® was monomeric and particularly pure, both biochemically and in the absence of salts. The country of origin may be a consideration at present due to risk of any viral or prion-based contamination. Thus, non-bovine collagens may also be preferred as there may be less risk of disease transmission. In this respect, the chicken collagen, Atelo­ Helogen®, is intrinsically more stable than marine collagens. Consumer sensitivity to avian collagens is potentially low, and comparable to mammalian collagens despite the structural differences (data not shown). It has also been suggested that collagen could permeate intact skin and augment the collagenous tissue. This seems implausible, however, as collagen molecules would be too large and too well bound to penetrate the stratum corneum (32). Should collagen or fragments pass into the underlying tissue, they would be unable to participate in the complex biosynthetic pathway that charac­ terizes collagen deposition in tissue (7). Evidence has been presented that confirms that this augmentation does not occur in skin with intact stratum corneum (33). Indeed, the lack of skin penetration should minimize sensitivity issues. ACKNOWLEDGMENTS We thank N. Bartone for assistance with amino acid analysis, G. Heath for assistance with IR spectroscopy, S. McCarthy for assistance with DSC, and Dr J. Ward for assis­ tance with scanning electron microscopy. We thank our suppliers for the gifts of collagen preparations. REFERENCES (1) P. Morganti, S. D. Randazzo, and A. Cardillo, Role of insoluble and soluble collagen as skin mois­ turizer,]. Appl. Cosmetol., 4, 141-152 (1986). (2) J. A. M. Ramshaw, Collagen, Cosmet. Aerosols Toiletr., 1, 22-25 (1986). (3) J. Bella, B. Brodsky, and H. M. Berman, Hydration structure of a collagen peptide, Structure, 3, 893-906 (1995). (4) R. D. B. Fraser, T. P. MacRae, and E. Suzuki, Chain conformation in the collagen molecule,]. Mol. Biol., 129, 463--481 (1979). (5) J. Bella, M. Eaton, B. Brodsky, and H. M. Berman, Crystal and molecular structure of a collagen-like peptide at 1.9 A resolution, Science, 266, 75-81 (1994). (6) R. A. Berg and D. J. Prockop, The thermal transition of a non-hydroxylated form of collagen. Evidence for a role for hydroxyproline in stabilizing the triple-helix of collagen, Biochem. Biophys. Res. Commun., 52, 115-120 (1973). (7) J. F. Bateman, S. Lamande, and J. A. M. Ramshaw, "Collagen Superfamily," in Extracellular Matrix: Vol. 2. Molecular Components and Interactions, W. D. Camper, Ed. (Harwood Academic Publishers, Amsterdam, 1995), pp. 22-67. (8) B. J. Rigby and M. S. Robinson, Thermal transitions in collagen and the preferred temperature range of animals, Nature, 253, 27-279 (1975).