Dynamic Viscoelasticity Properties Evaluation of Skin and Developmentof Dummy Skin for Safety Evaluation: Analysis of Deformation Behavior in the Depth Direction of the Skin
Sota KONDO, Yasumi ITO, Tatsuya FUKUOKA, Kazuya CHIGIRA,
UNIVERSITY
Yoshiyuki
KAGIYAMA,
Ryuichi
YAMADA,
andTetsuya
NEMOTO
13thInternational
Symposiumon
Advanced
ScienceOF
YAMANASHI University of Yamanashi, National Center for Geriatrics and Gerontology and Technology in Experimental Mechanics
Oct. 30-Nov. 2, 2018,
E-mail：g18tm011@yamanashi.ac.jp, yasumii@yamanashi.ac.jp
Kaohsiung City, Taiwan (ROC)• G 'and G' 'tend to increase as the pressing amount increases.
• In the range of the pressing amount of 3-6 mm, tan δ has almost the same value regardless of themeasuring position and pressing amount.

introduction• In measures against pressure ulcers and safety evaluation of power assist robots, it
is required to quantitatively evaluate the mechanical mechanism of the load on thehuman body.
• Because there are experiments that are difficult to perform in vivo from theviewpoint of ethics and reproducibility, dummy skin which is very similar inmechanical properties such as viscoelasticity and hardness of living soft tissue like measures against pressure ulcers
skin and muscle is required.
• We have quantitatively evaluated the dynamic viscoelasticity of human skin invivo in men in their 20s. Moreover, by simulating the state of tension of theepidermis against the simulated material simulating the hardness of human skin,
we were able to create a dummy skin whose surface mechanical properties werevery similar to human skin of male in her twenties with hardness and dynamic
safety evaluation
viscoelastic properties in shear direction. 1).
of power assist robots• However, the skin is a hierarchical composite material composed of a plurality ofmaterials of epidermis, dermis, subcutaneous tissue.2).
• In this study, we aim to develop dummy skin that simulates not only the surface
but also the viscoelastic properties of human skin in the depth direction.

Experiment on dummy skin
Materials
dummy skin

Probe

• Hitohada gel which is a material having hardness equivalent to that of human skin
skin was used as a simulated skin material.
• As a pseudoepidermis, the state of the skin in vivo was simulated by applying
tension to a dressing material (Permirol: Nitto Medical Co., Ltd.) used at the timeof treatment of pressure ulcer.
• Since human skin is composed of materials with various different mechanicalproperties, human skin gel of different hardness and thickness was laminated.

Dressing
Hitohada gel
TensionStage

ダミー皮膚模式図

NameA

B

CD

Construction

Singlelayer

Stacking

Stacking

Stackingup

underupunderupunderhardness

5500505thickness[mm]262103103203mm4mmDressing

測定の外観

Hitohada gel

Dummy Skin Schematic Diagram

Results

The measurement procedure is shown below.
① Apply shear deformation to the sample using a probe.
② Measure the shear stress from the sample.
A③ Dynamic viscoelasticity such as elastic component (storageRmodulus G '), viscous component (loss modulus G "), and loss tangent
tan δ is calculated from the measured stress.
Here, the storage modulus G 'and loss modulus G "are the real partand the imaginary part of the complex elastic modulus G *representing dynamic viscoelasticity, respectively. Basic formula ofdynamic viscoelasticity is shown below.
𝐺 ∗ = 𝐺 ′ 𝜔 + 𝐺 ′′ 𝜔(1)𝑡𝑎𝑛𝛿 = 𝐺 ′′ 𝜔 Τ𝐺 ′ 𝜔(2)Frequency [Hz]Strain [%]Probe diameter [mm]human skin
ϕ20, 40
20.4～2.0
dummy skin
ϕ20

Probe

Granting the strain of
the sine wave system

SampleStage

G' 3mmG'' 3mm

G' 4mmG'' 4mm

G' 5mmG'' 5mm

G' 6mmG'' 6mmtanδ

Rheometer (AR550: TA Instruments)

G' 2mmG'' 2mm
900
800
700
600
500
400
300
200
100
00G', G'' [kPa]

Methods

0.5

11.5
Frequency [Hz]22.52mm0.350.3
0.25
0.20.15
0.1
0.05
005mm

0.5

11.5
Frequency [Hz]

3mm

4mm

6mm

22.5

Results of dummy skin A

Pressing amount [mm]2-6Experiment on human skinG' 3mmG'' 3mm

G' 4mmG'' 4mm

G' 5mmG'' 5mm

G' 6mmG'' 6mm

2mm
0.3

500

0.25

400

0.2tanδG', G'' [kPa]G' 2mmG'' 2mm
600

300

0.1

100

0.05

000.5

11.5
Frequency [Hz]22.56mm

0.15

200

05mm

00.5

11.5
Frequency [Hz]22.5

Results of dummy skin DMaterials
Human arm
• The arm center part was taken as the measurement position 1, and the vicinity ofthe elbow as the measurement position 2.
• In order to reduce the influence of the edge of the probe, a probe with a diameterof 20mm was used as the measuring position 1, and a probe with a diameter of
40mm was used as the measuring position 2.
• Measurements were made in the muscle relaxed state.
• The stage temperature was 36 ° C which is the same as the human bodytemperature.
GenderMaleAge
22

Height [cm]175

Weight [kg]70

• G ', G' ', tan δ tend to decrease as the pressing amount increases.
• Due to the occurrence of slip, C could be measured only up to the pressing amount of 4 mm, but in thecase of D with the lower layer thickened up to 6 mm could be measured.
• The same tendency was observed for tan δ between A and D, B and C where the total thickness isequivalent.

測定位置2

測定位置1
計測部位

• Although G ‘and G’ ‘tend to increase as the pressing amount increases, since both increase at the samemagnification, tan δ representing the ratio is almost the same regardless of the measurement position andpressing amount. Therefore, in the current measurement region, the influence on the tan δ due to the pressing
part is small, and the viscoelastic characteristics of the human skin can be quantified. However, because there
is only one subject, it is necessary to verify whether the same tendency will also occur in other subjects fromnow on.
• Dummy skin, G ', G' ', tan δ showed a tendency to decrease with increasing pressing amount, unlike humanskin. This is believed to be due to the fact that the influence of the tension loaded on the surface is reduced as
the pressing amount increases in the dummy skin, and a structural device other than a simple laminate isnecessary.
• As the whole thickness changed, a change was observed in the measurement result of tan δ. Since itcorresponds to the thickness of the arm in vivo, the reproducibility of individual differences such as physiqueand gender is suggested by using this.

Dominant arm
Left
Appearance of measurement

Results
G' 2mmG'' 2mm
250

G' 3mmG'' 3mm

G' 4mmG'' 4mm

G' 5mmG'' 5mm

G' 6mmG'' 6mm

2mm

3mm

4mm

5mm

6mm

0.3
200150tanδ

G', G'' [kPa]

discussion

100Conclusion

0.20.1500000.5

11.5
Frequency [Hz]

22.5

00.5

11.5
Frequency [Hz]22.5

Result of measurement position 1
G' 2mmG'' 2mm60

G' 3mmG'' 3mm

G' 4mmG'' 4mm

G' 5mmG'' 5mm

G' 6mmG'' 6mm

2mm

3mm

4mm

5mm

6mm

Acknowledgments

0.30.2This work was supported by JSPS KAKENHI Grant Number JP16H03134. I would like to thank the Exseal Corporation for providing Hitohada gel ofthe test material.

tanδG', G'' [kPa]

50403020• In this measurement area, the influence on the tan δ due to the pressing site is small, suggesting thepossibility of quantifying the viscoelastic properties of human skin.
• For the preparation of the dummy skin which simulates the characteristics in the depth direction, structuralmeasures other than simple lamination are necessary.
• By changing the thickness of the whole, reproducibility of individual differences such as physique andgender was suggested.

0.1

References

100000.5

11.5
Frequency [Hz]22.50

Result of measurement position 20.5

11.5
Frequency [Hz]22.51) Nishio, Y., Ito, Y., Kishida, R., Kagiyama, Y., and Nemoto, T.: Dynamic Viscoelasticity Properties Evaluation of Skin and Making of Dummy
Skin for Safety Evaluation, The Japanese Society for Experimental Mechanics, Vol.16, No4, (2016), pp.307-314.
2) Oka, H., and Irie, T.: Hihunanbusoshikimoderukanotamenoseitaiteisu (in Japanese), Society of Biomecanisms Japan, Vol.17, No.4, (1993),
pp.216-222.