Simulation of the Aging Face

Mazza, Edoardo; Papes, O.; Rubin, M. B.; Bodner, S. R.; Binur, N. S.

doi:10.1115/1.2746388

Cited by 14 publications

(9 citation statements)

References 22 publications

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“…However, this seems to be a reasonable first assumption, since most current expanders have well-designed textures to promote mild tissue in-growth, primarily to prevent expander migration [9]. To address these potential limitations, we are currently refining the elastic model, the growth model, and the boundary conditions, to render our future simulations more realistic, and place it on an idealized face [43]. …”

Section: Discussionmentioning

confidence: 99%

Stretching skin: The physiological limit and beyond

Tepole

Gosain

Kuhl

2012

International Journal of Non-Linear Mechanics

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The goal of this manuscript is to establish a novel computational model for skin to characterize its constitutive behavior when stretched within and beyond its physiological limits. Within the physiological regime, skin displays a reversible, highly nonlinear, stretch locking, and anisotropic behavior. We model these characteristics using a transversely isotropic chain network model composed of eight wormlike chains. Beyond the physiological limit, skin undergoes an irreversible area growth triggered through mechanical stretch. We model skin growth as a transversely isotropic process characterized through a single internal variable, the scalar-valued growth multiplier. To discretize the evolution of growth in time, we apply an unconditionally stable, implicit Euler backward scheme. To discretize it in space, we utilize the finite element method. For maximum algorithmic efficiency and optimal convergence, we suggest an inner Newton iteration to locally update the growth multiplier at each integration point. This iteration is embedded within an outer Newton iteration to globally update the deformation at each finite element node. To illustrate the characteristic features of skin growth, we first compare the two simple model problems of displacement- and force-driven growth. Then, we model the process of stretch-induced skin growth during tissue expansion. In particular, we compare the spatio-temporal evolution of stress, strain, and area gain for four commonly available tissue expander geometries. We believe that the proposed model has the potential to open new avenues in reconstructive surgery and rationalize critical process parameters in tissue expansion, such as expander geometry, expander size, expander placement, and inflation timing.

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Section: Discussionmentioning

confidence: 99%

Stretching skin: The physiological limit and beyond

Tepole

Gosain

Kuhl

2012

International Journal of Non-Linear Mechanics

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“…Skin hydration level, contributions of the specific skin layers, as well as the anisotropic and Current research on skin mechanics aims at capturing the above-mentioned properties and integrating them into theoretical/analytical [116,118,128] and numerical models (e.g. linear viscoelastic or hyperelastic models) [62,116,125,126,[137][138][139][140], previously validated for elastomers and polymers, to develop and implement improved and more realistic mechanical finite element models of human skin.…”

Section: Mechanical Properties Of Human Skinmentioning

confidence: 99%

Tribology of Skin: Review and Analysis of Experimental Results for the Friction Coefficient of Human Skin

2011

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In this review, we discuss the current knowledge on the tribology of human skin and present an analysis of the available experimental results for skin friction coefficients. Starting with an overview on the factors influencing the friction behaviour of skin, we discuss the up-to-date existing experimental data and compare the results for different anatomical skin areas and friction measurement techniques. For this purpose, we also estimated and analysed skin contact pressures applied during the various friction measurements. The detailed analyses show that substantial variations are a characteristic feature of friction coefficients measured for skin and that differences in skin hydration are the main cause thereof, followed by the influences of surface and material properties of the contacting materials. When the friction coefficients of skin are plotted as a function of the contact pressure, the majority of the literature data scatter over a wide range that can be explained by the adhesion friction model. The case of dry skin is reflected by relatively low and pressureindependent friction coefficients (greater than 0.2 and typically around 0.5), comparable to the dry friction of solids with rough surfaces. In contrast, the case of moist or wet skin is characterised by significantly higher (typically [1) friction coefficients that increase strongly with decreasing contact pressure and are essentially determined by the mechanical shear properties of wet skin. In several studies, effects of skin deformation mechanisms contributing to the total friction are evident from friction coefficients increasing with contact pressure. However, the corresponding friction coefficients still lie within the range delimited by the adhesion friction model. Further research effort towards the analysis of the microscopic contact area and mechanical properties of the upper skin layers is needed to improve our so far limited understanding of the complex tribological behaviour of human skin.

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“…This implies that our virtual tissue expansion resembles a creep test under constant loading, while clinical tissue expansion resembles a relaxation test under constant deformation. Last, a more realistic model should incorporate the real expander to account for effects like interface sliding or shear [59], and, ideally, also an idealized face [45]. In addition, the expander base which we have here modeled as fixed and undeformable, should ideally be modeled as soft bedding.…”

Section: Example Of Skin Expansion and Growthmentioning

confidence: 99%

Growing skin: A computational model for skin expansion in reconstructive surgery

Tepole

Ploch

Wong

et al. 2011

Journal of the Mechanics and Physics of Solids

113

106

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The goal of this manuscript is to establish a novel computational model for stretch-induced skin growth during tissue expansion. Tissue expansion is a common surgical procedure to grow extra skin for reconstructing birth defects, burn injuries, or cancerous breasts. To model skin growth within the framework of nonlinear continuum mechanics, we adopt the multiplicative decomposition of the deformation gradient into an elastic and a growth part. Within this concept, we characterize growth as an irreversible, stretch-driven, transversely isotropic process parameterized in terms of a single scalar-valued growth multiplier, the in-plane area growth. To discretize its evolution in time, we apply an unconditionally stable, implicit Euler backward scheme. To discretize it in space, we utilize the finite element method. For maximum algorithmic efficiency and optimal convergence, we suggest an inner Newton iteration to locally update the growth multiplier at each integration point. This iteration is embedded within an outer Newton iteration to globally update the deformation at each finite element node. To demonstrate the characteristic features of skin growth, we simulate the process of gradual tissue expander inflation. To visualize growth-induced residual stresses, we simulate a subsequent tissue expander deflation. In particular, we compare the spatio-temporal evolution of area growth, elastic strains, and residual stresses for four commonly available tissue expander geometries. We believe that predictive computational modeling can open new avenues in reconstructive surgery to rationalize and standardize clinical process parameters such as expander geometry, expander size, expander placement, and inflation timing.

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Simulation of the Aging Face

Cited by 14 publications

References 22 publications

Stretching skin: The physiological limit and beyond

Stretching skin: The physiological limit and beyond

Tribology of Skin: Review and Analysis of Experimental Results for the Friction Coefficient of Human Skin

Growing skin: A computational model for skin expansion in reconstructive surgery

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