This paper proposes a triphasic model of intact skin in vivo based on a general phenomenological thermohydromechanical and physicochemical (THMPC) approach of heterogeneous media. The skin is seen here as a deforming stratified medium composed of four layers and made out of different fluid-saturated materials which contain also an ionic component. All the layers are treated as linear, isotropic materials described by their own behaviour law. The numerical simulations of in vivo indentation test performed on human skin are given. The numerical results correlate reasonably well with the typical observations of indented human skin. The discussion shows the versatility of this approach to obtain a better understanding on the mechanical behaviour of human skin layers separately. 1. Introduction Human skin is the largest organ of the human body. The skin protects the body against external influences by preventing fluid loss when exposed to sun, the penetration of undesirable substances in case of pollution, and the development of diseases due to the direct application of external chemical or mechanical loads linked to clinical problems, surgery, or aesthetic treatments. The answers of this barrier to these chemical, biological, mechanical, and thermal loads depend on the person, the site on the body, the age, the health, its nutritional status, its properties, its state (intact or damaged), and its evolutions [1]. Numerous studies have shown that human skin has a stratified structure consisting from the skin outer surface inward of three main layers: the epidermis (composed of the stratum corneum and the viable epidermis), the dermis, and the hypodermis [2–6]. Dryness, microcracks, and loss of elasticity are thought to be influenced by fluid flow and the associated changes in ion concentration as a direct result of mechanical stress states. However, these phenomena are complex to understand and to model due to the strong couplings that exist between them and due to the complex behaviour of the different layers of skin soft tissues. Studies of the mechanical behaviour of human skin have observed that the skin is a stratified nonhomogeneous, anisotropic, nonlinear viscoelastic material which is subjected to a prestress in vivo [7–9]. In addition its properties vary with age, throughout the body and per person. Difficulties arise when trying to obtain quantitative descriptions of mechanical properties of the skin. Numerous mechanical experiments have been performed on the skin: tensile testing, suction methods, torsion tests, and indentation experiments [10–16].
References
[1]
G. L. Wilkes, I. A. Brown, and R. H. Wildnauer, “The biomechanical properties of skin,” Critical Reviews in Bioengineering, vol. 1, no. 4, pp. 453–495, 1973.
[2]
G. Odland, Structure of the Skin, Physiology, Biochemistry and Molecular Biology of the Skin, Oxford University Press, Oxford, UK, 1991, Edited by L.A. Goldsmith.
[3]
C. Sheppard and D. Shotton, Confocal Laser Scanning Microscopy, Royal Microscopical Society Microscopic Handbooks, Bios Scientific Publishers, Oxford, UK, 1997.
[4]
M. Rajadhyaksha, S. González, J. M. Zavislan, R. R. Anderson, and R. H. Webb, “In vivo confocal scanning laser microscopy of human skin II: advances in instrumentation and comparison with histology,” Journal of Investigative Dermatology, vol. 113, no. 3, pp. 293–303, 1999.
[5]
Y. Pan, E. Lankenau, J. Welzel, R. Birngruber, and R. Engelhardt, “Optical coherence—gated imaging of biological tissues,” IEEE Journal on Selected Topics in Quantum Electronics, vol. 2, no. 4, pp. 1029–1034, 1996.
[6]
J. Ginefri, I. Darasse, and P. Crozat, “High-temperature superconducting surface coil for in vivo microimaging of the human skin,” Magnetic Resonance in Medicine, vol. 45, pp. 376–382, 2001.
[7]
J. De Rigal and J. L. Leveque, “In vivo measurement of the stratum corneum elasticity,” Bioengineering and the Skin, vol. 1, no. 1, pp. 13–23, 1985.
[8]
J. L. Leveque, J. De Rigal, P. G. Agache, and C. Monneur, “Influence of ageing on the in vivo extensibility of human skin at a low stress,” Archives of Dermatological Research, vol. 269, no. 2, pp. 127–135, 1980.
[9]
A. Rochefort, Propriétés Biomécaniques Du Stratum Corneum: Modélisation Rhéologique—Application à La Cosmetology, Thèse de Doctorat, Université de Franche-Comté, Besan？on, France, 1986.
[10]
P. G. Agache, C. Monneur, J. L. Leveque, and J. De Rigal, “Mechanical properties and Young's modulus of human skin in vivo,” Archives of Dermatological Research, vol. 269, no. 3, pp. 221–232, 1980.
[11]
C. H. Daly, “Biomechanical properties of dermis,” Journal of Investigative Dermatology, vol. 79, pp. 17–20, 1982.
[12]
C. Escoffier, J. De Rigal, A. Rochefort, R. Vasselet, J.-L. Leveque, and P. G. Agache, “Age-related mechanical properties of human skin: an in vivo study,” Journal of Investigative Dermatology, vol. 93, no. 3, pp. 353–357, 1989.
[13]
J. F. M. Manschot and A. J. M. Brakkee, “The measurement and modelling of the mechanical properties of human skin in vivo-I. The measurement,” Journal of Biomechanics, vol. 19, no. 7, pp. 511–515, 1986.
[14]
C. Pailler-Mattéi and H. Zahouani, “Analysis of adhesive behaviour of human skin in vivo by an indentation test,” Tribology International, vol. 39, no. 1, pp. 12–21, 2006.
[15]
C. Pailler-Mattei, S. Bec, and H. Zahouani, “In vivo measurements of the elastic mechanical properties of human skin by indentation tests,” Medical Engineering and Physics, vol. 30, no. 5, pp. 599–606, 2008.
[16]
A. Barel, W. Courage, and P. Clarys, Suction Method For Measurement of Skin Mechanical Properties : the Cutometer, Handbook of Non-Invasive Methods and the skinCRC Press, Boca Raton, Fla, USA, 1995, Edited by J. Serup and G B E. Jemec.
[17]
J. M. Huyghe and J. D. Janssen, “Thermo-chemo-electro-mechanical formulation of saturated charged porous solids,” Transport in Porous Media, vol. 34, no. 1–3, pp. 129–141, 1999.
[18]
M.-A. Abellan, H. Zahouani, E. Feulvarch, and J.-M. Bergheau, “Modelling water and ion transport through damaged skin,” in Proceedings of the 2nd Euro-Mediterranean Conference on Bioengineering and Biomaterials (EMCBB '12), Fez, Morocco, July 2012.
[19]
M.-A. Abellan, E. Feulvarch, H. Zahouani, and J.-M. Bergheau, “Numerical simulation of in vivo indentation tests: determination of the mechanical properties of human skin,” in Proceedings of the 21e Congrès Fran？ais de Mécanique (CFM '13), pp. 26–30, Ao？t, Bordeaux, France, 2013.
[20]
F. M. Hendriks, D. Brokken, C. W. J. Oomens, D. L. Bader, and F. P. T. Baaijens, “The relative contributions of different skin layers to the mechanical behavior of human skin in vivo using suction experiments,” Medical Engineering and Physics, vol. 28, no. 3, pp. 259–266, 2006.
[21]
A. Hung, K. Mithraratne, M. Sagar, and P. Hunter, “Multilayer soft tissue continuum model: towards realistic simulation of facial expressions, World Academy of Science,” Engineering and Technology, vol. 54, pp. 134–138, 2009.
[22]
P. Jouanna and M.-A. Abellan, “A generalized approach to heterogeneous media,” Transport in Porous Media, vol. 25, no. 3, pp. 351–374, 1996.
[23]
P. M. Van Kemenade, Water and Ion Transport Through Intact and Damaged Skin, DissertatIon, Eindhoven University of Technology, 1998.
[24]
J. Yoon, S. Cai, Z. Suo, and R. C. Hayward, “Poroelastic swelling kinetics of thin hydrogel layers: comparison of theory and experiment,” Soft Matter, vol. 6, no. 23, pp. 6004–6012, 2010.
[25]
Y. Hu, X. Chen, G. M. Whitesides, J. J. Vlassak, and Z. Suo, “Indentation of polydimethylsiloxane submerged in organic solvents,” Journal of Materials Research, vol. 26, no. 6, pp. 785–795, 2011.
[26]
M.-A. Abellan, E. Feulvarch, J.-M. Bergheau, and H. Zahouani, “Coupled fluid flow and ion transport through intact skin,” in Proceedings of the 38e Congrès de la Société de Biomécanique (SB '13), Marseille-Luminy, France, 2013.
[27]
M.-A. Abellan, E. Feulvarch, H. Zahouani, and J.-M. Bergheau, “Contribution à la caractérisation expérimentale et simulation numérique du comportement de la peau humaine in vivo: indentation sans contact,” in Proceedings of the 11e Colloque National en Calculs des Structures (CSMA '13), pp. 13–17, mai, Giens, France, 2013.
[28]
C. Truesdell and R. Toupin, The Classical Field Theories, Handbuch Der Physik III/I, Springer, Berlin, Germany, 1960.
[29]
F. M. Hendriks, Mechanical Behaviour of Human EpiDermal and Dermal Layers in Vivo, Dissertation, Eindhoven University of Technology, 2005.
