22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Treatment of poly(ethylene terephthalate) foils by atmospheric pressure air
dielectric barrier discharge and its influence on cell growth
O. Kylián1, A. Kuzminova1, M. Vandrovcová2, A. Shukurov1, A. Shelemin1, D. Slavínská1, L. Bačáková2 and
H. Biederman1
1
Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, V Holešovickách 2,
CZ-18000 Praha 8, Czech Republic
2
Institute of Physiology, Academy of Sciences of the Czech Republic, Vídeňská 1083, CZ-14220 Prague 4, Czech
Republic
Abstract: Effect of atmospheric pressure DBD plasma in air on PET foils was
investigated. It was shown that plasma treatment, depending on its duration, is capable to
modify morphology, chemical composition, surface energy and surface mechanical
properties of PET foils. In addition attachment and growth of cells on PET foils may be
positively influenced by plasma treatment. However, this effect is strongly linked with cell
type.
Keywords: plasma treatment, DBD plasma, surface modification, cells growth
1. Introduction
Polymers are employed in impressive range of fields
including for instance food packaging, flexible
electronics, textile industry or biomedical applications.
The popularity of polymers is connected with their
advantageous bulk properties such as optical
transparency, high thermal stability, high strength-toweight ratio, good flexibility or barrier properties.
However, the use of common polymers is in many cases
hampered by their low surface energy or insufficient
biocompatibility. Because of this, additional treatment of
polymeric materials is often necessary in order to improve
their surface properties. From this point of view
treatment of polymers by dielectric barrier discharge
(DBD) sustained in air at atmospheric pressure receives
increasing attention that results in large number of studies
that were published in the last decade (e.g., [1-12]). This
is mainly due to the fact that DBD plasma treatment is
easy to implement, time and cost effective, and since no
solvents are needed also environmentally friendly.
In this study, we focus on the determination of air DBD
plasma treatment effect on surface properties of
poly(ethylene terephthalate) (PET) foils as well as on
cells growth on PET foils exposed to DBD plasma.
2. Experimental details
A schematic sketch of DBD set-up that was used for the
treatment of PET foils is presented in Fig. 1 and described
in previous study [12]. The plasma was sustained in
laboratory air between two parallel planar electrodes. The
rectangular top electrode was made of stainless steel and
enabled scanning along the length of the bottom
electrode. The bottom electrode was a grounded steel
plate covered with 1 mm thick sintered alumina. The
distance between both electrodes was 1.5 mm.
P-III-6-29
Fig. 1. Schematic of DBD system used for treatment of
PET foils.
PET foils (thickness 50 µm, Goodfellow) were placed
on the bottom electrode. The upper powered electrode,
which was driven with a high voltage low frequency
power supply, operated at 30 W, was scanned over the
strips with constant scanning speed 40 mm/s. At this
scanning speed, the surface of the foil was during 1 scan
exposed to plasma for 0.5 seconds. In order to evaluate
the effect of treatment duration on properties of PET foils,
number of scans was varied from 2 up to 64 scans, which
corresponds to treatment times up to 32 seconds.
Chemical composition of PET foils before and after
DBD treatment was determined by X-ray photoelectron
spectroscopy (XPS) using a XPS spectrometer equipped
with a hemispherical analyzer (Phoibos 100, Spec) and
Al Kα X-rays source (1486.6 eV, 200W, Specs). The
wettability and surface energy of PET foils was measured
by the sessile droplet method using deionized water and
diiodomethane (Sigma Aldrich). Morphology of PET
surfaces was evaluated by atomic force microscopy
(AFM, Quesant Q-scope 350) in the semi-contact mode
using NSC-16 silicon cantilevers. The complex Young’s
modulus of the surface layers of the foils was assessed via
nano-DMA (Hysitron, Triboscope 75 with a
nano-DMAIII module combined with an AFM
1
80
70
20
10
Intensity [a.u.]
292
290
0
5
10
15
20
25
30
35
Treatment time [s]
C-O
288
286
284
282
Binding energy [eV]
Fig. 3. High resolution C1s XPS peak of untreated PET
(top) and PET foil treated 1 second by DBD (bottom).
C-O
C-O
538
0
C-C
C-H
O-C=O
O-C-OH
60
30
C-O
C-C/C-H 54%
C-O
25%
O-C=O/ O-C-OH 21%
Intensity [a.u.]
Atomic concentration [%]
C
O
N
C-C
C-H
O-C=O
O-C-OH
Intensity [a.u.]
3. Results
The first step of this study was evaluation of influence
of DBD plasma treatment on the surface chemical
composition of PET foils. It was observed that already
1 second plasma treatment led to rapid increase of atomic
concentration of oxygen from 23% up to 29%, which was
on expense of carbon atomic concentration that decreased
from 77% to 70%. In addition, nitrogen peak was
observed in XPS spectra of DBD treated PET foils;
corresponding N atom concentration as determined by
XPS was around 1%.
However, the atomic
concentrations of C, O and N were not largely influenced
by plasma treatment duration as can be seen in Fig. 2.
C-C/C-H 63%
C-O
21%
O-C=O/ O-C-OH 16%
Intensity [a.u.]
microscope Ntegra Prima, NT-MDT) with a standard
Berkovich-type indentor.
For biological tests two cell types were used - Saos-2
human osteoblast-like cells and HUVEC human umbilical
vein endothelial cells.
536
534
C=O
C=O
532
C-O 53%
C=O 47%
C-O 63%
C=O 37%
530
528
Binding energy [eV]
Fig. 2. Elemental composition of surface of PET foil in
dependence on DBD treatment time.
Fig. 4. High resolution O1s XPS peak of untreated PET
(top) and PET foil treated 1 second by DBD (bottom).
Changes in surface chemical composition of PET foils
after their exposure to DBD plasma were observed also in
high resolution XPS spectra of C1s and O1s peaks. In
case of C1s peak plasma treatment resulted in increase of
components at binding energies 286.3 eV and 288.7 eV
that correspond to C-O and O-C=O or O-C-OH,
respectively. This increase that can be seen in Fig. 3
occurs at the expense of the peak at binding energy
284.7 eV that may be attributed to aromatic CH groups.
In case of O1s peak observed changes suggest decrease of
amount of C=O functional groups (binding energy
531.7 eV) that is counter balanced by relative increase of
abundance of C-O groups at binding energy 533.3 eV (see
Fig. 4). These changes are in good agreement with results
presented and in detail discussed for plasma treatment of
PET foils with Diffuse Coplanar Surface Barrier
Discharge [13].
Changes in surface chemical composition of PET foils
induced by DBD plasma affected also their wettability. It
was found out that the static water contact angle dropped
from 63o down to approximately 30o already after
1 second of plasma treatment. This increase in wettability
is connected with growth of polar part of surface energy
that rose from 8 mJ/m2 for untreated PET to 24 mJ/m2
after 1 second of plasma treatment. This increase is in
agreement with increasing fraction of polar functional
groups observed by XPS. In addition, similarly to XPS
results, prolongation of treatment time did not result in
further changes both in wettability and surface energy.
DBD plasma affects not only the surface chemical
composition and wettability of PET foils, but also their
morphology. As can be seen in Fig. 5, small “bumps”
appeared on PET foils exposed to DBD air plasma. The
size of these surface features was found to increase with
increasing treatment duration, which caused monotonous
increase of the root-mean-square surface roughness from
1 nm measured on untreated PET up to 8 nm measured on
PET foil treated 16 seconds by the DBD.
Nano-indentation tests revealed that the plasma
treatment longer than 4 seconds results in gradual increase
of surface complex modulus E* (see Table 1). This
suggests enhanced cross-linking of the surface layer of
PET foil induced by plasma treatment.
2
P-III-6-29
Fig. 5. AFM scans of untreated and DBD treated PET
foil.
Table 1. Variation of complex modulus with DBD
treatment time.
Treatment time [s]
Complex
modulus
[GPa]
0
3.0
2
2.7
4
2.8
8
6.2
16
8.7
Finally, effect of plasma treatment on growth of two
cell lines was evaluated. It was found that whereas for
Saos cells no significant difference between numbers of
attached cells was observed for untreated and DBD
treated PET foil on day 1 and 3 after seeding (see Fig. 6a),
plasma treatment resulted in dramatic increase of number
of HUVEC cells on PET foils (see Fig. 6b).
Fig. 6. Images of a) Saos and b) HUVEC cells on
untreated PET foils and PET foils exposed for 1 second to
DBD atmospheric pressure air plasma. The images were
acquired 3 days after seeding.
nanoindentation measurements.
According to the
presented results DBD plasma treatment may also
positively influence attachment and growth of cells on
treated PET. However, it was shown as well that in this
case the cell type played a key role: whereas considerably
lower enhancement in initial cells count was observed for
osteoblast-like cells, endothelial cells were found to attach
and grow on DBD pre-treated foils significantly faster as
compared to untreated PET. This finding is of high
importance, since it clearly shows that it is not possible to
generalize results obtained for one particular cell type on
another cell types and thus each cell type has to be
considered separately.
5. Acknowledgement
This work was performed under the COST Action
MP1101 and was supported by the grant LD 12066
financed by the Ministry of Education, Youth and Sports
of the Czech Republic.
6. References
[1] N.Y Cui and N.M.D. Brown. Appl. Surf. Sci., 189,
31 (2002)
[2] P. Esena, C. Riccardi, S. Zanini, et al. Surf. Coat.
Technol., 200, 644 (2005)
[3] K.G. Kostov, A.L.R. dos Santos, R.Y. Honda, et al.
Surf. Coat. Technol., 204, 3064 (2010)
[4] E. Kuffel. IEEE Trans. Plasma Sci., 37,659 (2009)
[5] T. Shao, C. Zhang, K. Long, et al. Appl. Surf. Sci.,
256, 3888 (2010)
[6] C.S. Ren, K. Wang, Q.Y. Nie, D.Z. Wang and
S.H. Guo. Appl. Surf. Sci., 255, 3421 (2008)
[7] G. Borcia, C.A. Anderson and N.M.D. Brown.
Appl. Surf. Sci., 221, 203 (2004)
[8] N. Kormunda, T. Homola, J. Matousek, et al.
Polymer Degrad. Stabil., 97, 547 (2012)
[9] T. Homola, J. Matoušek, B. Hergelová, et al.
Polymer Degrad. Stabil., 97, 886 (2012)
[10] G. Borcia, C. Anderson and N.M. Brown. Appl.
Surf. Sci., 225, 186 (2004)
[11] D.J. Upadhyay, N.Y. Cui, C.A. Anderson and
N.M.D. Brown. Colloids Surf. A: Physicochem.
Engng. Aspects, 248, 47 (2004)
[12] A. Kuzminova, A. Shelemin, O. Kylián, et al.
Polymer Degrad. Stabil., 110, 378 (2014)
[13] T. Homola, J. Matoušek, B. Hergelová, et al.
Polymer Degrad. Stabil., 97, 2249 (2012)
4. Conclusion
Effect of atmospheric pressure DBD plasma in air on
PET foils was investigated. It was shown that plasma
treatment, depending on its duration, is capable to modify
morphology, chemical composition, surface energy and
surface mechanical properties of PET foils as witnessed
by AFM, XPS, contact angle measurements and
P-III-6-29
3