Modelling the human epidermis in vitro: tools for basic and applied research

Culture models of tissues and organs are valuable tools developed by basic research that help investigation of the body functions. Modelling is aimed at simplifying experimental procedures in order to better understand biological phenomena, and consequently, when sufficiently characterized, culture models can also be utilized with high potential in applied research. In skin biology and pathology, the development of cultures of keratinocytes as monolayers has allowed the elucidation of most functional and structural characteristics of the cell type. Beside the multiple great successes that have been obtained with this type of culture, this review draws attention on several neglected characteristics of monolayer cultures. The more sophisticated models created in order to reconstruct the fully differentiated epidermis have followed the monolayers. The epidermal reconstruction produces all typical layers found in vivo and thus makes the model much less simple, but only this kind of model allows the study of full differentiation in keratinocyte and production of the cornified barrier. In addition to its interest in basic research, the reconstructed epidermis is currently gaining a lot of interest for applied research, particularly as an alternative to laboratory animals in the chemical and cosmetic industry. Today several commercial providers propose reconstructed skin or epidermis, but in vitro assays on these materials are still under development. In order to be beneficial at long term, the validation of assays must be performed on a material whose availability will not be interrupted. We warn here providers and customers that the longevity of in vitro assays will be guaranteed only if these assays are done with well-described models, prepared according to published procedures, and must consider having a minimum of two independent simultaneous producers of similar material

Mesure absolue de la section efficace totale de création de paires, près du seuil, au moyen d'une source d'énergie variable

The author presents results of absolute measurements of the total pair production cross section in germanium, near threshold, using a source of photons of variable energy. These measurements are made for energies ranging between 1 240 and 1 263 keV, 1 180 and 1 207 keV and between 1 057 and 1 110 keV, by steps of 2.85 keV. These results and those obtained with radioactive sources are compared with the predictions of different theories.L'auteur présente des résultats de mesures absolues de la section efficace totale de création de paires dans le germanium, près du seuil, au moyen d'une source de photons d'énergie variable. Ces mesures sont faites pour des énergies comprises entre 1 240 et 1 263 keV, 1 180 et 1 207 keV et entre 1 057 et 1 110 keV par pas de 2,85 keV. L'auteur compare ces résultats et ceux obtenus au moyen de sources radioactives avec les différentes prédictions théoriques

Mesure absolue de la section efficace totale de création de paires près du seuil

The author present results of an absolute measurement of the total pair production cross section in germanium, near threshold. The photons, produced by a collimated radioactive source, have energies ranging between 1 063 and 2 754 keV. The results are compared to the predictions of different theories (Born approximation, exact calculation without and with screening effects).L'auteur présente des résultats d'une mesure absolue de la section efficace totale de création de paires dans le germanium, près du seuil. Les énergies des photons, produits par une source collimatée, sont comprises entre 1 063 et 2 754 keV. L'auteur compare ces résultats avec les prédictions des différentes théories (approximation de Born, calcul exact sans et avec effet d'écran)