Phác họa cấu trúc tự nhiên

Tạp chí Khoa học - Công nghệ Thủy sản

Số 1/2014

THOÂNG BAÙO KHOA HOÏC

NATURAL STRUCTURES DESIGN
PHÁC HỌA CẤU TRÚC TỰ NHIÊN
Kroisova Dora1, Ron Jiri2
Ngày nhận bài: 21/8/2013; Ngày phản biện thông qua: 12/02/2014; Ngày duyệt đăng: 10/3/2014

TÓM TẮT
Mục đích của bài báo là nghiên cứu một số bề mặt cấu trúc tự nhiên, thiết kế thông minh và sáng tạo trên bề bặt của
chúng nhằm ứng dụng chúng vào công nghiệp. Bề mặt lá sen (Nelumbo nucifera) được biết đến như một mặt phẳng không
dính nước, bề mặt của rêu (Bryophyta) được xem như một bề mặt ưa nước và da cá mập (Carcharodon Carcharias) như bề
mặt với các thông số rất tốt về thủy cơ đã được lựa chọn để nghiên cứu và phát họa cấu trúc. Ban đầu tất cả các mẫu được
sấy khô trong không khí và sau đó phun lên bề mặt mẫu một lớp hợp kim Au-Pd. Các nghiên cứu về cấu trúc đều được thực
hiện trên kính hiển vi điện tử quét VEGA\\TESCAN với độ phóng đại trong khoảng từ 200 đến 100 000 với điện áp gia tốc
là 10 kV. Thông qua kính hiển vi điện tử quét để có thêm thông tin về cấu trúc của chúng. Phần mềm ImageTool phiên bản
3.0 của Trường Đại học Texas Health Science Center ở San Antonio đã được sử dụng để phân tích hình ảnh của bề mặt tự
nhiên. Công ty KOH-I-NOR PONAS tại Cộng hòa Séc đã hợp tác chọn phác họa các bề mặt cấu trúc này và bây giờ nhiệm
vụ của họ là thử nghiệm trong điều kiện thực tế.
Từ khóa: cấu trúc tự nhiên và cấu trúc nano, thiết kế, kỹ thuật sinh học

ABSTRACT
The aim of this work is studying of natural surface structures, their design preparation and subsequent creation of
the specific surfaces of molds for industrial applications. Lotus leaf surface (Nelumbo nucifera) as a superhydrophobic
plant surface, a leaf surface of a common moss (Bryophyta) as a hydrophilic surface and a shark skin (Carcharodon
carcharias) as a surface with good hydromechanical parameters were selected in order to show how to study and design the
structures. At first all the samples were dried in the air and after that were sputtered by a layer of Au-Pd alloy. The studies
of the natural object structures were performed on a scanning electron microscope VEGA\\TESCAN at magnifications in

the range of 200 to 100000x at 10 kV accelerating voltage. Through the scanning electron microscopy it is possible to get
more information about the structures in order to create their design. Software ImageTool version 3.0, The University of
Texas Health Science Center at San Antonio was used for an image analysis of the selected natural surfaces. The designed
structures of chosen surfaces were prepared in cooperation with KOH-I-NOR PONAS, the Czech Republic Company, and
now their functions are tested in real conditions.
Keywords: natural structures and nanostructures, design, bionics

I. INTRODUCTION
An increasing amount of researchers have
been working on a study of natural plant and animal
surfaces from point of view of material compositions
and structures as well as processes by which are
these objects created. An interest in this type of
materials comes out from the fact that life on the

1

2

Earth has developed for more than 3.5 billion years
which has resulted in practically ideal solutions.
The natural surfaces usually show multilevel
structures beginning on a molecular level through a
nano-scale level and ending on a micro-scale level
where many different material combinations are in
mutual coexistence.

Assoc. Prof. Kroisova: Centre for Nanomaterials, Advanced Technologies and Innovations, Technical University of Liberec,
Czech Republic, Email:
Msc. Ron Jiri: Faculty of Mechanical Engineering, Technical University of Liberec, Czech Republic

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Suitable examples are water repellent plant
leaves surfaces created by various structures where
the microstructure is formed of single surface cells
and the nanostructure is formed by wax particles
secreted on the cells surface. In some cases there
may occurred obvious macrostructure which can
even be visible by the naked eye.
These structures facilitate to leaves to stay
clean because adhered dust and other impurities
hinder a process of photosynthesis [1], [2].
The first studied object was a superhydrophobic
surface of a leaf of an Indian lotus (Nelumbo nucifera).
Other surfaces inspiring to a muse may be for
instance a hydrophilic moss surface ensuring water
and nutrients absorption without necessity of using
a root system.
The structures lessening water flow resistance
could be animal skins - shark skin in case of this
study [3].
II. EXPERIMENTS
For a microscopic evaluation and following
image analysis were chosen samples of the Indian
lotus, the moss and the shark skin. All the samples
were dried in the air and sputtered by a thin layer
of Au-Pd alloy. Observations of the structures were

performed on a scanning electron microscope (SEM)
VEGA\\TESCAN at magnifications in the range of
200 to 100000x at 10 kV accelerating voltage.
SEM images of the sample surface structures
were used for the image analysis which aim was
finding dimensions and geometry of the micro and
nanoparticles. Software ImageTool version 3.0, The
University of Texas Health Science Center at San
Antonio was used for the image analysis.
The images were tresholded and transferred to
binary images, i.e. bright areas (peaks of the surface
cells of the lotus) on the SEM images were
transferred to white colour and areas among the
cells to black colour. The images were purified
from noise (spots and smears). Some cells on the
SEM images were joined together which would be
evaluated as a one cell instead of two ones. This
problem was treated by a “watershed” function. After
a segmentation of the epidermal cells a cell density
ρcells was evaluated. Another step was a contact area
ratio between liquid and solid phase fLSmicro
evaluation (i.e. a sum of the white areas divided by
the whole image area). The same policy was applied
to get fLSnano values. A figure 1 shows the origin area
from which was measured the cells density ρcells and
outlines of the contact areas [4].

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Số 1/2014

Figure 1. Upper side of the Indian lotus leaf with the applied
image analysis on the SEM image [4]
The image analysis evaluated these values:
Cells density:
ρcells
= 3205
[mm-2]
= 0,101 [-]
Contact area ratio
fLSmicro
= 0,241 [-]
fLSnano

There can be counted which area is equal to
a single cell from the cell density ρcells assuming
hexagonal layout of the cells. The single cell area
multiplied by fLSmicro corresponds with an area which
is in contact with liquid from which was derived a
contact diameter dcont written bellow:

On the basis of the image analysis a model of
a form for fabrication has been designed. The value
of dcont from the analysis (Fig. 2 up) is adequate to
a value of a formations which should be fabricated
(Fig. 2 down).
A density of the fabricated formations, their
pitches and geometric layout should also be adequate to the studied natural surface [4].

Figure 2. Models of natural surface structure (up)

and its transformation to technical form (down) [4]


Tạp chí Khoa học - Công nghệ Thủy sản

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III. RESULTS AND DISCUSSION
With the usage of the SEM and image analysis, the evaluation of three different types of natural objects
was performed.
The lotus leaf is known for its specific characteristic which is a high hydrophobicity. This characteristic
is achieved by the microstructure and the nanostructure of the leaf surface which may also be increased by
chemical composition of the surface waxes on the nanoscale level.
By the surface analysis, data about the shapes, layouts, dimensions and densities of the cells and
the waxes have been achieved. There is no possibility of identical structural analogy fabrication by current
conventional methods.
A following tab. 1 shows a contact angles and their hysteresis, the epidermal cell densities, the micro and
nano contact area ratios and derived contact diameters with heights and pitches between asperities (epidermal
cells) for 4 chosen hydrophobic surfaces.
Tab. 1. Geometric parameters of chosen hydrophobic plants
Micro
Contact Epidermal
contact
angle
cell density
area ratio
hysteresis
ρcells
fLSmicro
[°]

[mm-2]
[-]

Nano
contact
area ratio
fLSnano
[-]

Contact
diameter
dcont [µm]

Plant name

Contact
angle
[°]

Epidermal Epidermal
cell height cell pitch
H [µm]
P [µm]

Indian lotus*
(Nelumbo Nucifera)

146,7
± 3,5

1,4 ±
0,9

3205

0,101

0,241

6,6

12,2

17,7

Cock’s-foot*
(Dactylis glomerata)

146,7
± 1,9

2,1 ±
1,3

3764

0,201

0,190

8,3

9,0

16,3

St John’s wort*
(Hypericum perforatum)

151,6
± 1,5

1,7 ±
1,0

1562

0,114

0,249

9,6

11,3

25,3

Poinsettia*
(Euphorbia Pulcherrima)

146,3
± 5,0

1,4 ±
0,9

2022

0,098

0,168

7,9

6,8

22,2

* All the values were measured on the upper side of dehydrated leaves

1. Indian lotus (Nelumbo nucifera)

Figure 3. Typical structure of the Indian lotus surface. Convex epidermal cells (the upper image) covered by the tiny wax rods
(the lower image). SEM images [4]

The Indian lotus is a thermo-philic tropic swamp plant which originates from India. Almost circular leaves
emerge from swamp water as well as their blossoms. Despite growing in backwater the lotus remains perfectly
clean a dried which is ensured by its hierarchic structure formed by the microscale concave cells with hollow
nanoscale wax rods on the cells surfaces. The length of the wax rods is about 600 nm and its diameters (inner
and outer) about 100 nm (fig. 4). Besides being clean, this structure also ensures self-cleaning ability.

There was found out by the image analysis that the cell density ρcells is 3205 mm-2 and hollow rods density
ρwaxes was approximately 6 mil. mm-2. This nanostructure with such a huge density and a nanoparticles shape is
unfabricatable by current technologies. Fig. 4 shows the measured dimensions on models [4].

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Figure 4. Models of the surface structure covering leaves of the Indian lotus
- the documentation of the structure [4]

Although the contact angles and hysteresis of
four different hydrophobic leaves are very similar,
geometrical parameters of the leaves vary distinctly.
This variety may be caused by morphology and
geometry of epidermal waxes and their chemical
compositions. Wax morphology varies from tubes
to platelets with different types of arrangement.
Indian lotus possesses hollow tubes with irregular
arrangement while St John’s wort has regular
platelets with spacing which resembles stars with
five tips.
St John´s wort microstructure seems to be the
most profitable because it has the highest contact
angle (151,6 ± 1,5) with the largest dimensions of
asperities which is less difficult for fabrication and
also cheaper. Due to the fineness, variety and wide

morphology of waxes which is currently inimitable
it would be useful to choose St John´s wort
microstructure
dimensions
as
a
default
microstructure and try to deposit nanoasperities
(PECVD) with varying dimensions and find out the
best combination of micro and nanostructure to get
the highest contact angle value experimentally.
2. Moss (Bryophyta)
Mosses are green nonvascular plants of a
small growth with a distinct ability to retain water.
The mosses accept water by the whole surface of
thallus and distribute it by their water conducting
tissues or easily by wettable surfaces. The way how the
mosses manage water enables them to use even
very little amount of rainfall.

42 • TRƯỜNG ĐẠI HỌC NHA TRANG

Figure 5. SEM image of the moss with the obvious
structured surface

The image analysis showed an elongated
hexagonal alignment of the structure. Dimensions
gained from the real structure were used for a fabrication
of a form for plastic material injection. The form has
been fabricated in many dimensional variations with

maintenance of a dimensions ratio and its function
has been currently tested in real conditions.

Figure 6. Model of the moss surface for the form fabrication


Tạp chí Khoa học - Công nghệ Thủy sản

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Figure 7. SEM image of the form surface for the moss
structure fabrication.
Fabricated by KOH-I-NOOR PONAS s.r.o

The mosses are interesting for their ability of
surface water absorption. The model created according
to the SEM images of original moss structure was
served for the form surface fabrication. The form
has been fabricated in cooperation with Department
of Engineering Technology TUL and KOH-I-NOOR
PONAS s.r.o. The function of the form has been
currently tested in real conditions.
3. White shark (Carcharodon carcharias)
A specific shark skin structure is covered by firm
tooth-like scales lessening water flow resistance.
Figure 8 shows the SEM image of shark skin scales
and there are scales dimensions in figure 9. A
scale width varies from 150 to 200 µm, a distance
between longitudal flutes is about 40 µm and a
height of the flutes varies from 10 to 20 µm.

The shark skin surface was characterised on
the basis of the image analysis. A new structure
(figure 10) was fabricated according to the model
but regarding to the large difference from its original
the new structure hasn´t been tested.

Figure 8. SEM image of the shark skin surface
with the obvious scale structure [3]

Figure 9. Model of the shark skin scale as a basis for the
form fabrication

Figure 10. SEM image of the new form surface fabricated
on the basis of the derived dimensions. Fabricated by
KOH-I-NOOR PONAS s.r.o

The shark skin was used for modelling of the
surface with low resistance against the flow in the
water environment. The model with the dimensions
achieved from the SEM images was used to design
of the surface of the fabricated form. From the image
above it is obvious that it was not possible to
fabricate the form surface on a required level
regarding the shape, structure and dimensions.
IV. CONCLUSION
The described image analysis applied to the
images of the natural objects achieved from the
scanning electron microscopy turned out to be a
suitable method to determination of the surface
characteristic parameters such as the size, the

shape and the layout of the cells and the waxes.
The parameters achieved by the image analysis
are sufficient for models design of the form surfaces
fabrication.

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The form fabrication by today´s conventional technologies can reach only a microscale level shapes
but not smaller. Experimental data showed that the most profitable geometry of microscale, based on
the chosen leaves is derived from St John´s wort leave (upper side) with the highest angle (151,6 ± 1,5).
Diameter of the asperities of such form is 9,6 µm, their height 11,3 µm and pitch 25,3 µm.
ACKNOWLEDGEMENTS
The research was supported in part by the Project OP VaVpI Centre for Nanomaterials, Advanced
Technologies and Innovation CZ.1.05/2.1.00/01.0005 and student´s project SGS TUL. The acknowledgement
for cooperation belongs to Ing. P. Kejzlar, prof. P. Lenfeld and workers of KOH-I-NOOR PONAS.

REFERENCES
1. D. Kroisova, 2012. Microstructures and Nanostructurees in Nature. In: Progress in Optics, 57: 93 – 132.
2. J. Ron, 2012. The study of surface structures of chosen natural object and potentials of creating their analogies. In: Diploma thesis.
3. K. Koch and W. Barthlott, 2009. Superhydrophobic and superhydrophilic plant surfaces: an inspiration for biomimetic
materials. In: Philosophical Transactions of the Royal Society A, 367: 1487- 1509.
4. K. Koch and H.J. Ensikat, 2008. The hydrophobic coatings of plant surfaces: Epicuticular wax crystals and their morphologies,
crystalinity and molecular self-assembly. In: Micron, 39: 759-772.

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