900-mhz nonthermal atmospheric pressure plasma jet for biomedical applications
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900-MHz Nonthermal Atmospheric PressurePlasma Jet for Biomedical Applications
Jun Choi, Abdel-Aleam H. Mohamed, Sung Kil Kang, Kyung Chul Woo,Kyong Tai Kim, Jae Koo Lee*
A portable microwave-excited atmospheric pressure plasma jet (APPJ) using a coaxial trans-mission line resonator is introduced for applications of plasma biomedicine. Its unique featureincludes the portability andno need formatching network and cooling systemwith high powerefficiency, operating at 900MHzwith low ignitionpower less than 2.5W in argon at atmosphericpressure. The temperature at the downstream ofthe APPJ stays less than 47 8C (�320K) during5min of continuous operation. The optical emis-sion spectrum of the APPJ shows various reactiveradicals such as OH, NO, and O which are respon-sible for biomedicine. The APPJ was applied toinvestigate the acceleration of blood coagulation,which occurredwithin 20 s of plasma treatment invitro andwithin 1min in vivo. This is significantlyfaster than the natural coagulation.
Introduction
Nonthermal atmospheric pressure plasma sources are in
great demand for biomedical applications including cancer
cell treatment,[1] sterilization,[2] and coagulation.[3] Ideally,
the plasma generated should have low power and low gas
temperature. Furthermore, plasma sources should operate
at atmospheric pressure, have low cost and a long
operational life. Diverse plasma devices with different
J. K. Lee, J. Choi, A.-A. H. Mohamed, S. K. KangDepartment of Electronic and Electrical Engineering, PohangUniversity of Science and Technology, Pohang 790-784, Republicof KoreaFax: (þ82) 54 279 2903; E-mail: [email protected]. H. MohamedDepartment of Physics, Faculty of Science, Taibah University,Almadinah Almunawwarah, Saudi ArabiaDepartment of Physics, Faculty of Science, Beni-Suef University,Beni-Suef, EgyptK. C. Woo, K. T. KimDepartment of Life Science, Pohang University of Science andTechnology, Pohang 790-784, Republic of Korea
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power sources and electrode configurations have been
presented that partially fulfill these conditions.[4] The
plasma sources can be operatedwithDC,[5,6] low-frequency
(kHz),[7] RF,[8,9] microwave,[10,11] and pulsed power.[12]
Microwave-excited plasmas at atmospheric pressure
havebeendeveloped for surfacemodification,[11] analytical
purposes,[13] and biomedical applications including ster-
ilization[14] and detoxification.[15,16] These plasmas are
useful because the energy of the ions that strike the
electrodes in the high-frequency devices is very low due to
the collisionality of the sheath[17–19] and the low sheath
potential that develops at microwave frequency.[20] In
addition, the size of the device can be reduced as the
microwave operating frequency increases. For operating
frequencies of 900MHz and 2.45GHz, a number of low-cost
power modules and solid-state components are available
because they have been developed for mobile communica-
tions systems. Thus microwave-excited microplasmas
operating at low power may meet the need for long-
lifetime devices capable of operating at atmospheric
pressure.[10]
In this study, we propose a portable, matching-network-
free microwave-excited atmospheric pressure plasma jet
DOI: 10.1002/ppap.200900079
900-MHz Nonthermal Atmospheric Pressure Plasma . . .
(APPJ) based on a coaxial transmission line resonator (CTLR)
and show a potential use of biomedical applications.
Experimental Part
Configuration of Device
The device has been designed to minimize power losses and
maximize the power efficiency based on an analytic model and
finite elementmethod (FEM) simulation.We reported the electrical
characteristics of thedevice in detail in thepreviouswork.[21] In the
device (Figure 1), the resonator consists of a quarter wavelength of
coaxial line (characteristic impedance¼50V) connected tothe feed
power by a subminiature type A (SMA) connector (Figure 1a). One
endof thecoaxial line iselectricallyopen (Figure1b)andtheother is
short-circuited to resonate at the exciting frequency. Therefore, at
resonance, the current is zero and the voltage is maximal at the
open end where the plasma is discharged. A metal tip is used to
reduce thegapdistance to40mmand toenhance theelectricfield to
ignite the plasma.
Theoverall lengthof thedevice is83mm,which isone-quarterof
the wavelength of 900-MHz radiation. At resonance, the input
impedance of the CTLR is real and its value depends on the location
of the power feed as Equation (1):
Fig(a)
Plasma
� 2010
Zin � 4Z0 sin bl1ð Þal
V (1)
where Zin is the input impedance of the resonator, Z0 the
characteristic impedance of the coaxial transmission line, l the
1length fromfeedingpoint to shortport, j the complexnumberffiffiffiffiffiffiffi�1
p,
l the wavelength for the given frequency and dielectric constant
(er¼ 1 for air), a the attenuation constant, and b¼ 2p/l is the phaseconstant of the coaxial line, i.e., k¼ b – ja the complex propagation
constant or wave number. Accordingly, the CTLR is powered at a
point by an SMA connector where the input impedance to the
device is 50V. This eliminates the need formatchingnetworks and
the power losses that they cause.
Air was used as a dielectric of the coaxial line to make the
working gas flow through the device through two gas holes at the
short end of the device. This use of air as a dielectric for the coaxial
line reduces power loss and improves the power efficiency of the
CTLR.Consequently, theCTLR is capableof self-ignitingbelow2.5W
ure 1. The configuration of the CTLR operating at 900MHzside view (b) front view (c) nonthermal microwave-excited APPJ.
Process. Polym. 2010, 7, 258–263
WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
input power[21] in argonunder awide range of pressures, including
atmosphericpressure.The lengthof theAPPJ canbevaried from5to
15mm (Figure 1c) depending on the gas flow rate and input power.
Experimental Setup
A signal generator (Agilent N5181A) and a microwave power
amplifier (AR 60S1G3) were used to supply power to the CTLR
(Figure 2). The forward and reflected powers were measured
simultaneously using two directional couplers (Narda 3202B-20),
two sets of power sensors (Agilent N1921A, HP 8482A), and power
meters (Agilent N1911A, HP EPM-441A). In this experiment, we
used a commercial signal source and a large size of a microwave
power amplifier. However, a compact power amplificationmodule
includingdirectional couplersandpowersensors isquite feasible to
manufacture and we are developing it on a printed circuit board
and eventually on a chip for the hand-held plasma sourceworking
on microwave power.
The emission spectrum of the APPJ was characterized by optical
emission spectroscopy, using a 750mm focal length scanning
monochromator (Dong Woo Optron Monora 700i) equipped with a
built-in high-sensitivity photomultiplier tube (PMT, Hamamatsu
R928) with a 2400gr �mm�1 grating blazed at 240nm. The
monochromator collects light using an optical fiber. In this work,
thefiberwasorientedperpendicular to the longaxisofAPPJ,with its
tip2mmfromtheAPPJ.Duringall spectroscopicmeasurements, the
discharge was operating at atmospheric pressure using argon flow
in ambient air.
Blood samples from a mouse (CBA/N strain) were used to
investigate coagulationbydirect and indirect contactwith theAPPJ.
A10ml of bloodwasplacedonaslideglassand treated invitrobythe
plasmaover9mmdistancefromthenozzleofCTLR.A tail-cutmouse
was applied to evaluate the blood coagulation in vivo by the APPJ.
Results and Discussion
HFSS Simulation and Description of AtmosphericPressure Plasma Jet (APPJ)
To investigate the electric field (E-field) distribution at the
open end of the device before the plasma ignites, a
simulation based on the FEM was performed using a
commercial package (Ansoft HFSS). The HFSS simulation
(Figure3) showsthatattaching themetal tipat theopenend
of the CTLR increases the E-field to 5� 106V �m�1 for 1W
Figure 2. Experimental setup for the APPJ based on the CTLR.
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J. Choi, A.-A. H. Mohamed, S. K. Kang, K. C. Woo, K. T. Kim, J. K. Lee
Figure 3. HFSS simulation of the CTLR with 40mm gap distanceand 1W input power (a) E-field distribution in the direction offront view (Figure 1b) (b) E-field radiation in the direction of sideview (Figure 1a) at the open end of the device before plasmaignition. (The inset is a magnification of E-field for each figure).
a)
260
input power (Figure 1b and 3a). The CTLR can ignite the
argon plasma with the auxiliary tip using less than 3W
input power at atmospheric pressure. Inserting the metal
tip to theCTLRdidnotcauseanysignificantperturbation for
the overall electromagnetic behavior of the resonator such
as a shift of resonant frequency. The E-field is radiated only
fromtheopenendof thedeviceanddecreases to zerowithin
5mm (Figure 3b). This confinement of the E-field prevents
unwanted electromagnetic interference and allows the
array of the device to enlarge the plasma treatment area.
Once the plasmawas ignited, themetal tipwas removed
from the CTLR. Figure 4(a) shows the APPJs by the CTLR
Figure 4. Microwave-excited APPJs and temperature measure-ment (a) argon APPJ pictures in ambient air by the CTLR with3W as a function of gas flow rate (b) temperature at the down-stream of the APPJ at 5 slm gas flow and 3W input power for5min of continuous measurement.
Plasma Process. Polym. 2010, 7, 258–263
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without the tip at 3W input power and gas flow ranged
from 2 to 10 slm. The average length of the APPJ (Lp) was
9.14mm in the given condition. The APPJ showed stable
operationup to 6 slm (cross-sectional area of thenozzlewas
125.6mm2 and effective gas flow speedwas 0.8m � s�1) gas
flow rate and changed to turbulent-like mode for higher
flow rate than 6 slm. The Lp was maximal at 6 slm and
getting shorter as the gas flow increased. Figure 4(b)
presents the measured temperature of the downstream of
the APPJ (�9mm from the nozzle) at 3W input power and
5 slm (0.66m � s�1 of effective gas flow speed), which is a
stable operation condition of the APPJ. The temperature
was measured by a fiber optic sensor (FISO FTI-10). As a
result of continuous measurement for 5min, the gas
temperature of the APPJ did not exceed 47 8C (�320K).
Analysis of Optical Emission Spectrum
The rotational temperature of theAPPJwas estimated from
the OH (A2Sþ!X2P), v(0–0) band using LIFBASE[22]
(Figure 5). The discharge is far from equilibrium and the
rotational temperature of OHmolecules in the discharge is
b)
Figure 5. Gas temperature of the APPJ (a) optical emission spec-trum of OH band of the CTLR with 1.5W input power and 6 slmargon gas flow rate at atmospheric pressure compared withLIFBASE calculations of OH band for 450 and 550K (b) dependenceof the gas temperature on the microwave input power at atmos-pheric pressure.
DOI: 10.1002/ppap.200900079
900-MHz Nonthermal Atmospheric Pressure Plasma . . .
Figure 7. NO radical emission of the microwave-excited APPJ at8 slm argon flow and 3W input power.
�450–550Kwhen input power is 1.5Wand gas flow rate is
6 slm (Figure 5a). This temperature decreases with increase
in distance from the CTLR open end and no thermal effect
was observed in the downstream of the APPJ (Figure 1c). At
6 slm, the gas temperature increases linearly from 500K at
1.5W to 620K at 3.5W (Figure 5b) due to gas heating as the
input power to the APPJ increases (i.e., the difference
between the forward and reflected power). These results
are consistent with observations in other high pressure
plasmas.[23] The dominant gas heating mechanism in
microwave-excited argon microplasma at atmospheric
pressure is the elastic collisions between electrons and
atoms,[24] so the observed heating is probably a conse-
quence of the increase in electron density.[25] Above 3.5W,
the gas temperature stabilized, which agrees with results
reported for air plasma[26] and could result from the
enlargement of the plasma dimension as a function of
increasing input power.
Figure 6 shows the optical emission spectra from 200 to
900nm. Because the argon APPJ was flushed into the
ambient air, argon lines dominate the 700–900nm and the
energetic charged particles and excited argon species can
stimulate the ground-state oxygen molecules. As a result,
b)
a)
Figure 6. Optical emission spectra of the microwave-excited APPJat 2mm from the nozzle with 4W input power and 8 slm argongas flow rate (a) 200–600nm and (b) 600–900nm.
Plasma Process. Polym. 2010, 7, 258–263
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they present strong emission lines of argon species as well
as highly reactive species such as nitrogen species (230–
280nm) andOH radicals (309nm) in Figure 6(a) and atomic
oxygen lines (777.4 nm) in Figure 6(b). Emission bands
corresponding to nitric oxide (NO) were observed in the
emission spectra (Figure 7) of the APPJ. The NO radical of
nonthermalatmosphericpressureplasmacanhelpregulate
blood coagulation and accelerate wound treatment.[27]
Thehighgas temperatureat the ignitionpointof theAPPJ
is likely to contribute the NO formation[28,29] and the APPJ
cools down at the afterglow due to the flow ofworking gas.
Themechanism of NO production in nonthermal plasma is
controlledby reactionsofatomicnitrogenwithO2andO3as
follows.[30]
Nþ O2 ! NOþ O (2)
Nþ O3 ! NOþ O2 (3)
Toaccelerate (2) and (3), thenitrogenmolecules shouldbe
dissociated to atomic nitrogen by the impact of electrons. A
recent computational work shows that the microwave
discharge can generate high population of energetic
electrons.[20] This presents the microwave-exited plasma
has high possibility to produce atomic nitrogen and NO
abundantly. In addition, the NO generation is favored by
the gas temperature by the following equation:
k ¼ 1:5� 10�11 exp � 3 600
Tg
� �cm3 �mol�1 � s�1 (4)
where k is the rate coefficient of the reactions and Tg is the
gas temperature.[31] As Equation (4), it is noted that
the reaction rate constant is dependent on the gas
temperature. The NO production, therefore, increases with
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J. Choi, A.-A. H. Mohamed, S. K. Kang, K. C. Woo, K. T. Kim, J. K. Lee
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increase in the gas temperature at the ignition point of the
APPJ. The NO radical has multiple biological functions:
regulation of blood vessel tone, blood coagulation,
immune system and early apoptosis, etc.[29] Furthermore,
NO shows anti-microbial effect and strong sterilization
activity of bacteria.[14] It is suggested that the microwave-
excited discharge presented could be a good candidate for
biomedical applications, particularly inflammation
remedy, healing of wound surface, and stimulation of
regenerative processes.
Blood Coagulation
We investigated whether the APPJ could accelerate blood
coagulation, both in vitro and in vivo. Blood samples were
collected from a healthy mouse (CBA/N strain). The blood
was treated with ethylene diamine tetra-acetic acid in the
concentration of 5mmol � l�1which is an anti-coagulant for
inhibiting fast blood coagulation naturally in the air. To
quantify in vitro coagulation rates, a 10-ml sample of this
bloodwas placed on a slide glass (Figure 8a–c) and the APPJ
was applied to the blood at 3W input power and 3 slm gas
flow rate. Measurements were replicated at least three
times for each sample. Untreated blood did not coagulate
during the measurements (Figure 8a). The blood started to
coagulate after 10 s of plasma treatment (Figure 8b) and
was completely coagulated after 20 s of treatment
(Figure 8c). This result is comparable to a previous report[27]
and the role of atmospheric nonthermal plasma in
blood coagulation was studied by Kalghatgi et al.[3]
To investigate the effect of gas flow, same 10-ml blood
samples were treated by argon gas at 3 slm for 10 and 20 s.
Although coagulation was observed in the test, the effect
Figure 8. In vitro and in vivo blood coagulation using APPJ at 3.5Winput power and 3 slm argon flow rate: (a) control; (b) aftertreatment for 10 s; (c) after treatment for 20 s [10ml anti-coagu-lated blood was used for (a–c)]; (d) side-view (noncontact) of invitro blood coagulation after treatment for 30 s; (e) in vivocoagulation of bleeding for living mouse.
Plasma Process. Polym. 2010, 7, 258–263
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was minor. Indirect coagulation was also observed
(Figure 8d) after 30 s of treatment when the APPJ was held
3mm away from the blood sample. Even though the APPJ
didnot contact theblooddirectly, coagulationoccurred. The
noncontact coagulation may result from various radicals
generated from the APPJ and minor thermal effect. In fact,
the gas temperature of the APPJ did not exceed 38.3 8C on
average during 20 s treatmentwhich is slightly higher than
the human body temperature (Figure 4b).
To quantify the effect of plasma application on coagula-
tion in vivo, the mouse was anesthetized and the tail was
cut to inducebleeding (Figure 8e). At first,we left the cut tail
without any treatment. The bleeding stopped naturally
within 5–6min. When the APPJ was applied, the blood
started to coagulate at once and changed toa clotwith time.
Furthermore, this clot closed the wound and reduced the
amount of bleeding. The bleeding usually stopped within
1min with the plasma treatment. This work shows the
potential of the microwave-excited APPJ as a medical
method for rapid and thermally safe coagulation.
Conclusion
In summary, we have developed a portable microwave-
excitedAPPJ that uses a coaxial transmission line resonator
operating at 900MHz with low power. HFSS simulation
based on FEM demonstrated that the E-field distribution at
the open end of the CTLR was �106V �m�1 and that the
metal tip caused no significant perturbation. The APPJ
shows highly reactive species including OH, NO, and O
radicals. The emission spectrumof theOHbandwasused to
determine the gas temperature of an APPJ using argon in
ambient air. The APPJ was clearly nonthermal and the
gas temperature increased from 500 to 620K for given
input power. In in vitro tests tomeasurewhether using the
APPJ accelerates blood coagulation significantly, this
process began after 10 s of treatment and was completed
within 20 s. In vivo blood coagulation was observed after
less than 1min of plasma treatment. These results indicate
that this APPJ has potential possibility for biomedical
applications including coagulation, wound healing, and
sterilization.
Acknowledgements: The authors are grateful to Top EngineeringCo. for lending their microwave power amplifier for theexperiment. This work was supported by the Korea Science andEngineering Foundation (KOSEF) grant funded by the Koreagovernment (MOST) (no. R01-2007-000-10730-0), and the KoreaMinistry of Education, Science, and Technology through its BrainKorea 21 program.
Received: July 6, 2009; Revised: November 10, 2009; Accepted:November 18, 2009; DOI: 10.1002/ppap.200900079
DOI: 10.1002/ppap.200900079
900-MHz Nonthermal Atmospheric Pressure Plasma . . .
Keywords: atmospheric pressure plasma jet (APPJ); blood coagu-lation; microwave discharges; nonthermal plasma; plasmatreatment
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