Ebook Computational biophysics of the skin: Part 2
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Ebook Computational biophysics of the skin: Part 2
Chapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2y, Goethe Center for Scientific Computing, Kettenhofweg 139, 60325 Frankfurt am Main, Germanywittum@gcsc.uni-frankfurt.deComputational modelling and simulation of penetration processes in the skin barrier on multiple biological scales in space and time is increasingly being recognized as a powerful Ebook Computational biophysics of the skin: Part 2tool to develop and to refine hypotheses, focus experiments, and enable more accurate predictions. One area of the ongoing research effort is physioloEbook Computational biophysics of the skin: Part 2
gybased transport models. On the one hand, these are based on first principles and describe processes in the skin mathematically in terms of conservatChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2d function. Particularly, such models provide an understanding how microscopic physiological structure and heterogeneity govern penetration. In this chapter, we describe microscopic geometry models of the skin cells (e.g. corneocytes) and the lipid bilayers of the stratum corneum (SC).Computational Ebook Computational biophysics of the skin: Part 2Biophysics of the SkinEdited by Bernard QuerleuxCopyright © 2014 Pan Stanford Publishing Ptt. ltd.ISBN 978-981-4463-84-3 (Hardcover), 978-981-4463-85-Ebook Computational biophysics of the skin: Part 2
0 (aBook) www.panstanford.com218 Cellular Scale Modelling of the Skin BarnerThe particular focus is on geometries based on tetrakaidekahedra (TKD). ThChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2ption of these membranes, which is complemented by examples of computations in the simulation system UG.8.1 IntroductionThe stratum corneum (SC) (see Fig. 8.1a) is the outermost skin layer of the epidermis of mammals. It consists of corneocytes and a lipid matrix. The corneocytes are dead, keratiniz Ebook Computational biophysics of the skin: Part 2ed, fully differentiated skin cells that arise from the underlying keratinocytes. The corneocytes are embedded in a matrix of lipid bilayers (Fig. 8.1Ebook Computational biophysics of the skin: Part 2
b). The SC incorporates the main barrier function of the skin. It protects the human body against the ingress of pathogens and preserves it also from Chapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2 the result of the special arrangement and geometry of the corneocytes and the chemical properties of the lipid matrix. Micrographs of the sc show that the corneocytes are arranged in staggered columns with different overlapping (see Figs. 8.1 and 8.2).The overlap of the cells depends on the body re Ebook Computational biophysics of the skin: Part 2gion and the differing mechanical stresses. The corneocytes are closely packed, flexible and provide an excellent protective function. The lipid matriEbook Computational biophysics of the skin: Part 2
x consists of free lipid bilayers and lipids, which are covalently bound to the corneocytes. The anchoring of covalently bound lipids occurs via transChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2rm into lipid bilayers with lamellar structure [2,10]. The sc is composed of 10-15 layers of flattened corneocytes according to the body region and has a thickness of about 0.02 mm [4] (see Figs. 8.1a,b).For the numerical simulation of drug diffusion in the sc many different mathematical models exis Ebook Computational biophysics of the skin: Part 2t. They differ in both the physical description, and also in the geometry model of the corneocytes and of the extracellular lipid matrix. One popularEbook Computational biophysics of the skin: Part 2
two-dimensional geometry model is the "brick and mortar" geometry in which corneocytes are represented as bricks and the lipid matrixIntroduction 219aChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2ng brick-and-mortar models (cf. Table 1 of [11]). Obviously, three-dimensional geometry models are also desirable because they can represent the sc more realistic than a two-dimensional model.Figure 8.1(a) Layers of the epithelial skin layer: the epidermis. Modified from [1]. (b) Magnified sketch of Ebook Computational biophysics of the skin: Part 2 two corneocytes A and B with lipid matrix. The lamellar structure of the lipid matrix Is indicated, as well as the network of keratins within the corEbook Computational biophysics of the skin: Part 2
neocytes. Reprinted from [2] with permission from BioMed Central.Figure 8.2 Light micrograph and four different geometric models of the SC: Top left: Chapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2om center: 3D-Model with hexagonal prisms [7]. Bottom right: 3D-Tetrakaldekahedron [8].220 Cellular Scale Modelling of the Skin BarrierThe issue "Modeling the human skin barrier—towards a better understanding of dermal absorption", which was published recently in the journal Advanced Drug Delivery R Ebook Computational biophysics of the skin: Part 2eviews, provides an overview of different mathematical models as well as the state of the art of computational research tools that are employed for moEbook Computational biophysics of the skin: Part 2
delling dermal absorption. We refer for further details, e.g. existing two- and three-dimensional geometry models for the sc, to several articles in tChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2xperimentally observed geometry of the corneocytes is very similar to the space-filling polyhedron tetrakaidekahedron (see Fig. 8.3b), which has an almost optimal surface to volume ratio and is a solution of the Kelvin problem (cf. Section 8.3). The geometry model was suggested in [8,17,53], and lat Ebook Computational biophysics of the skin: Part 2er on applied successfully in [18,19].Figure 8.3(a) Micrograph of soap foam with a tetrakaldekahedron likestructure. Reprinted from [20] with permissiEbook Computational biophysics of the skin: Part 2
on from Nature Publishing Group, (b) Single corneocyte. Reprinted from [21] with permission from Nature Publishing Group.This work is organized as folChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2tetrakai-dekahedron mathematically. In particular, we introduce the necessary parameters for characterizing tetrakaidekahedra. Finally, we provide a mathematical model in Section 8.4 and conclude with computational results in Section 8.5.8.2 Motivation for a stratum CorneumGeometry Model with Tetrak Ebook Computational biophysics of the skin: Part 2aidekahedraUsing microscopic examination of frozen sections of the SC in the 60s the shape of the corneocytes was assumed being hexagonalMotivation foEbook Computational biophysics of the skin: Part 2
r a Stratum Corneum Geometry Model with Tetrakaidekahedra 221[3,22]. Recent studies confirm this structure [23-27]. In 1975 Menton [20,28] first preseChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2f micrographs of the SC (see Fig. 8.2, top left) with the spatial arrangement of soap foam (see Fig. 8.3a). The soap foam is arranged, as the sc, in overlapping columns. This geometry is similar to stacked tetrakaidekahedra (see Fig. 8.2, lower right) [29],Physically one can explain the formation of Ebook Computational biophysics of the skin: Part 2 the tetrakaide-kahedron form of the corneocyte cells as follows: During the differentiation the keratinocytes in the epidermis are packed denser becaEbook Computational biophysics of the skin: Part 2
use they are displaced upwards. Due to its surface tension and mutual pressure, the cells obtain a geometric configuration in which they can be packedChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt University Ebook Computational biophysics of the skin: Part 2nd irregular arranged keratinocytes with different size change to similarly sized and flat corneocytes, which have a columnar arrangement [30,20] (cf. Figs. 8.2 and 8.4a). Also gaps outside the corneocytes are unlikely due to the pressure. The cells have a staggered arrangement and are interdigitate Ebook Computational biophysics of the skin: Part 2d. Such an interdigitating arrangement saves surface. It is tight, elastic and offers an ideal protection.Figure 8.4(a) LM-micrograph of the stratum cEbook Computational biophysics of the skin: Part 2
orneum. Reprinted fromChapter 8Cellular Scale Modelling of the Skin BarrierArne Nagel, Michael Heisig, Dirk Feuchter, Martin Scherer, and Gabriel WittumFrankfurt UniversityGọi ngay
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