ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Finite Element simulation of human skin deformation
behaviour during a sliding friction test
D. Gad 1 , R. Lewis 1 , S. E. Franklin 1,2 , R. M. J. Voncken 2 , M. Kwiatkowska 3 , M.J. Carré 1 , K. Hendriks 2
1. ABSTRACT
This work is a continuation of previous research concerning the friction and deformation behaviour of human skin.
Kwiatkowska et al. measured the skin friction and deformation behaviour in-plane and perpendicular to the sliding direction
during in vivo reciprocating sliding of a smooth steel ball probe against human forearm skin. They found that the skin is
compressed in front of the probe, forming a „bow-wave‟, and stretched behind as a consequence of friction and lateral skin
displacement. This study provided much useful information regarding skin behaviour during a friction test.
In the current work, the experiments carried out by previously have been simulated using the Finite Element Method in
order to improve the understanding of the relationships between skin friction and skin deformation behaviour and to provide
validating data for further use of the numerical approach for human skin modelling. This understanding is important in
optimizing the design of consumer products that interact with the skin in a mechanical way, e.g. to improve the tactile “feel”.
Keywords: Skin, Friction, Deformation, Finite Element Method, Bioengineering.
2. INTRODUCTION
The Finite Element (FE) method has been using in many branches of industry since the second half of the 20th century
(Clough, et al., 1999). Simplicity and good results even for intricate non-linear problems gave the finite element method an
advantage over other methods. The FE approach gives many benefits such as time and money savings and is a method that
can be very flexible and easy to use for product and process optimisation (E. Keeve, 1998). This is the reason why FE
modelling is irreplaceable in many companies in the world. Already for many years FE modelling has been used in
bioengineering as well as for the more traditional engineering fields. Clearly modelling of biomaterials presents great
challenges due to their nature and the variability apparent, particularly in humans. FE modelling of human skin is of growing
interest in medicine with a wide range of possible applications such as physiological analysis, surgery planning and
interactive simulation (H. Delingette, 1998).
The main aim of this work is reconstruction of deformation behaviour of human skin during a friction test (for which
experimental data is already available (M. Kwiatkowska et al., 2009)) using an FE method.
The human skin is composed of four layers (stratum corneum, epidermis, dermis and hypodermis). The skin is very often
considered as a viscoelastic homogenous material (C.Pailler-Mattéi, 2006). Every layer has different structure, mechanical
properties, thickness etc. Moreover, the mechanical properties of human skin are dependent on the loading and environmental
conditions. The physical properties are also different for the different parts of the human body. This is the reason why many
researchers‟ around the world try to create a model of human skin for different parts the human body.
The biggest problem during the construction of a model of human skin is accessibility and satisfactorily describing the
multi-physical and mechanical properties of human skin. In many publications mechanical properties of human skin can be
found, but the values vary greatly (S. Diridollou et al., 2001) (M. Kwiatkowska et al., 2009) (Geerligs, 2009) (F.M. Hendriks,
2005) (F. M. Hendriks, 2003). This facet is obvious because skin properties change with age, sex, temperature, moisture etc.
Moreover, the mechanical properties are determined by different methods such as: suction, torsion, indentation, stretching
etc. (Giavazzi, et al., 2010) (Finlay, 1970) (Boyer, et al., 2009). In the literature, many authors have been trying to describe
mechanical properties by using a Young‟s modulus for the skin. This theory assumes that mechanical properties of soft tissue
are linear in the stress/strain relationship. Unfortunately, the reality is more complex, because linear behaviour is only correct
for a relative strain up 20% (Y.C. Fung, 1993). A different option is modelling dependent on the deformation range. In the
small deformation hypothesis or large deformation hypothesis the Green-Lagrange formulation is used to link the stress and
strain tensors in a linearized form by neglecting the second order term (O.C. Zienkiewicz et al., 1989). The Green-Lagrange
1 University of Sheffield, Department of Mechanical Engineering, Sir Frederick Mappin Building, Mappin Street, Sheffield, S1 3JD, UK
2 Philips Research, High Tech Campus 7, 5656AE Eindhoven, The Netherlands
3 West Pomeranian University of Technology, Szczecin, Institute of Materials Science and Engineering, Piastow Av. 19, 73-310
Szczecin, Poland
1