Journal of Biosciences and Medicines, 2016, 4, 33-37
Published Online March 2016 in SciRes. http://www.scirp.org/journal/jbm
http://dx.doi.org/10.4236/jbm.2016.43006
How to cite this paper: Nagayama, K., Kurihara, T., Amano, Y. and Tanahashi, M. (2016) Particle Simulation of Skin Basal
Layer Formation. Journal of Biosciences and Medicines, 4, 33-37. http://dx.doi.org/10.4236/jbm.2016.43006
Particle Simulation of Skin Basal Layer
Formation
Katsuya Nagayama1, Takeshi Kurihara1, Yasuko Amano2, Masanori Tanahashi2
1Kyushu Institute of Technology, Fukuoka, Japan
2Kao Corporation, Tokyo, Japan
Received 2 October 2015; accepted 10 March 2016; published 17 March 2016
Abstract
There has been increasing concern regarding the cosmetic aspects of skin in recent years. Compu-
tational simulation can be useful in understanding the mechanism underlying skin formation. The
bottom of the epidermis is called the basal layer and is very undulation. In this study, we focus on
the basal layer formation. We created a particle model, which forms an undulation basal layer and
regenerates the basal layer formation by numerical simulation. At first, two-dimensional basal
layer formation without epidermal turnover was simulated. The results showed film shape changes
and the stability, as a layer in the process of long-ti me with an increase and decrease of basal cells.
Next, the model was applied to three-dimensional basal layer formation with epidermal turnover.
As the structure of the basal layer was deformed, the upper structure of the epidermis comprising
the cells divided from the basal layer also became irregular. The simulation results accurately
represented and reproduced the three-dimensional basal layer formation and epidermis turnover
process.
Keywords
Numerical Simulation, Skin Formation, Particle Model, Basal Layer
1. Introduction
Skin is the largest organ of the human body. We can diagnose epidermal conditions and provide appropriate care
particularl y because the epidermis is the most external part of the skin. In recent years, there has been an in-
creasing concern regarding the cosmetic aspects of skin care in both men and women, prompting research stu-
dies on anti-ageing therapy and cosmetics.
The epidermis consists of four differentiated layers. In particular, the basal layer, which is at the bottom of
epidermis, is undulationly formed. This undulationness is considered to be associated with spots and ageing.
Therefore, it is important to elucidate the mechanism of the formation of an undulation basal layer. However,
there are many unexplained phenomena in skin metabo lis ma nd the formation of undulation layers because the in
situ observation of basal layer formation is difficult.
Computational simulation can be useful in further understanding the mechanisms of skin development, and

K. Nagayama et al.
34
several models have been proposed [1]-[4]. However, the analysis of the epidermis requires an ability to not on-
ly increase and decrease epidermal cells but also to assess the transition of cell shape and physical properties.
For this reason, previous methods are not good at analyzing all the four layers of the epidermis with their re-
spective characters, simultaneously. Thus, in this study, we propose a particle model that can handle complex
biological phenomena, including cell interactions such ascell division, motion, deformation, and transition
[5]-[7]. Furthermore, we believe that it is a suitable method for simulating skin formation. We developed an
analytical method for studying the formation and turnover process of the skin using the particle model [8]-[10].
This study conducted the numerical simulation of cutification, which includes basal layer undulation ness, us-
ing the particle method. The particle method can simulate three-dimensional skin formation with cornification
and by changing physical properties, whereas also being able to increase and decrease basal cell production. Our
aim was to elucidate the phenomena of epidermis formation using this model to contribute to medical skin
treatment and the development of cosmetics.
2. Analysis Object and Model Description
2.1. Analysis Object
Figure 1 depicts a cross-section of the skin [11], and the roles of each cell layer are described. The epidermis is
the outermost layer of the skin and is primarily composed of cells called keratinocytes. The epidermis consists
of four layers. A basal layer, which is the lowest layer of the epidermis, provides new cells by dividing each day.
The dividing cells are called the prickle layer, which are pushed and moved up toward the skin surface, trans-
forming into the granular layer and stratum corneum, which finally detaches from the skin surface. Skin cells
change not only in their shape but also in their physical properties during this process. This process is referred to
as turnover and occurs at approximately 4-week intervals. Dermis is located under the epidermis, and is divided
by the basal layer. Furthermore, capillaries in the dermis supply nutrition and oxygen for basal cells.
2.2. Model Description
The particle model [5]-[7] is introduced to simulate the epidermis formation process [8]-[10]. The model con-
siders the interaction between the particles and pursues motions of the particles in a Lagrangian way. This me-
thod is suitable for analysis with large deformations, or when the numbers of calculation points are changing.
The cellular particles move in response to inter-particle forces, such as volume conservation force and spring
force. The volume conservation force works to keep the distance between the particles. Because of the repulsive
force, particles eventually move to a stable distance. The spring force works to make the continuum of the cel-
lular particles structural. Spring force has already introduced cornification into our model [8]-[1 0]. In this paper,
we describe the application of spring force to the basal layer. The actual basal layer maintains a layer with film
shape, which includes undulationness. To introduce this film shape to our model, we use spring force to produce
intervals in basal cells. Moreover, the distance which spring force works to is variable because it can fill the
gaps generated by the basal layer. By summing up these forces from the surrounding particles, the particles
gradually move to the position of the force balance.
In addition, each basal cell is a stem cell and can divide into two daughter cells. This division has three pat-
terns as shown in Figure 2 [12] [13]. Pattern.1 is where both cells become basal cells, and Pattern.2 is where
one cell remains as a basal cell and another cell becomes a prickle cell, while in Pattern.3, both cells change into
prickle cells. Each basal cell follows a pattern among these three patterns at random. We modeled the basal layer
Figure 1. Cross-section of the skin [11].
Corneum
Granular layer
Prickle layer
Basal layer
Epidermis
Dermis
Corneum
Granular layer
Prickle laye r
Basal laye r
Epidermis
Dermi s

K. Nagayama et al.
35
using function of film shape and stem cells having abilities to follow three patterns. When basal cells increase,
the film shape suffers a change, because the increase in basal cells presses them against other cells. Besides,
when basal cells decrease, surrounding basal cells fill the gap and keep the film shape.
3. Results and Discussion
Two cases of simulation were performed. One is two-dimensional basal layer formation without epidermal turn-
over to check the basal layer shape. Another is three-dimensional basal layer formation with epidermal turnover
to simulate close to real phenomena.
3.1. Two-Dimensional Basal Layer Formation
Figure 3 presents the simulation results of two-dimensional basal layer formation without epidermal turnover.
Figures 3(a)-(c) are taken after 45, 100, and 1000 days of analysis time, respectively. Red colour indicates that
the particle is moving upward, light green indicates it is stationary, a nd blue indicates it is moving downward.
The results show film shape changes and the stability, as a layer in the long-time process with an increase and
decrease of basal cells.
3.2. Three-Dimensional Basal Layer Formation with Epidermal Turnover
Figure 4 and Figure 5 present the simulation results of three-dimensional basal layer formation with epidermal
turnover. Figures 4(a)-(d) are taken after 45, 100, 300, and 1000 days of analysis time, respectively. From the
basal layer (blue), prickle cells (green) split and move up, which then develop into the granular layer (yellow).
Finally, the corneum (red) peels off. The cells in the course of the spinous layer transform within the stratum
corneum, from spherical-shaped into elliptical-shaped cells, by extending in the horizontal direction to form the
skin. Figure 4 shows formation of natural undulationness of the basal layer and the stability of a film shape as a
Figure 2. Cell division of basal layer cell [12] [13] .
(a) (b) (c )
Figure 3. Results of two-dimensional basal layer formation simulation. (a) 45 days; (b) 100 days; (c) 1000 days.
(a) (b) (c) (d)
Figure 4. Results of three-dimensional skin formation simulation (Side view). (a) 45 days; (b) 100 days; (c) 300 days; (d)
1000 days.
Basal cell
Prickle cell
8%
84%
8%
Probability
Pattern.1
Pattern.2
Pattern.3
50[μm]Corneum
Granular layer
Dermi s
Prickle layer
Basal layer

K. Nagayama et al.
36
(a) (b) (c) (d)
Fig ure 5. Results of three-dimensional skin formation simulation (Top-down view of basal layer). (a) 45 days;
(b) 100 days; (c) 300 days; (d) 1000 days.
layer in the process of long-time epidermal formation with an increase and decrease of basal cells. Moreover, the
basal layer plays a role in the film function because particles do not get mixed up between the prickle layer and
dermis. Figure 5 only displays the basal layer of the same model as Figure 4. However, it should be noted that
this result is the top-down view of the analysis domain. Although there are partial biases by increasing and de-
creasing the basal cell layer, particles are placed uniformly in the whole of the basal layer. In addition, undula-
tionness is formed all over the field.
4. Conclusion
In this study, the basal layer formation and the epidermis turnover were modeled using the particle model. We
created a particle model which forms an undulation basal layer and regenerates the basal layer formation by nu-
merical simulation. At first, two-dimensional basal layer formation without epidermal turnover was simulated.
The results showed film shape changes and the stability, as a layer in the long-time process with an increase and
decrease of basal cells. Next, the model was applied to three-dimensional basal layer formation with epidermal
turnover. As the structure of the basal layer was deformed, the upper structure of the epidermis comprising cells
divided from the basal layer also became irregular. The simulation results accurately represented and reproduced
the three-dimensional basal layer formation and epidermis turnover process.
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