Advances in Chemical Engineering and Science, 2013, 3, 10-16
http://dx.doi.org/10.4236/aces.2013.33A3004 Published Online August 2013 (http://www.scirp.org/journal/aces)
Improved Hemolytic Performance of Blood Pump with
Fluorine-Doped Hydr ogenated Amorphous Carbon Coating
Yasuharu Ohgoe1*, Masanori Hiratsuka2, Hirohito Sumikura3, Kazuyoshi Fukunaga4,
Akihiko Homma1, Kenji K. Hirakuri5, Akio Funakubo1, Yasuhiro Fukui1
1Division of Electronic and Mechanical Engineering, Tokyo Denki University, Saitama, Japan
2Nanotec Corporation, Nanotec Corporation, Chiba, Japan
3Department of Artificial Organs, National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan
4Department of Clinical Engineering, Faculty of Health Sciences, Kyorin University, Tokyo, Japan
5Department of Electrical and Electronic Engineering, Tokyo Denki University, Tokyo, Japan
Received May 10, 2013; revised June 10, 2013; accepted July 10, 2013
Copyright © 2013 Yasuharu Ohgoe et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Fluorine-doped hydrogenated amorphous carbon (a-C:H:F) film was deposited on a flow-straightener, impeller and dif-
fuser surface (SUS 304) of an enclosed-impeller type flow blood pump using the ionization deposition method with a
source gas of C6F5H. The surface characteristics of the a-C:H:F film were examined using atomic force microscopy,
X-ray photoelectron spectroscopy, and measurements of surface roughness, friction and surface potential. The a-C:H:F
film tends to increase surface roughness and the negative surface charge. In addition, the surface energy and friction
decrease with fluorine dopant in the a-C:H film. To estimate the hemolytic performance of a blood pump with the
a-C:H:F film coating, the amount of hemolysis was measured using a mock circulatory system (in vitro test) with 500
mL of pig blood containing sodium citrate. In vitro test was conducted for 180 min with the blood flow and pump head
maintained at 5 L/min and 100 mmHg, respectively. The a-C:H:F film coating reduced the amount of hemolysis and
improved the hemolytic performance. Decreasing the surface energy and negative surface charge of the a-C:H:F film
contributes to the improvement of the hemolytic performance. The a-C:H:F film coating is thus expected to be utilized
in medical technology as a surface coating technology for artificial heart blood pumps.
Keywords: Fluorine-Doped a-C:H Film; Hemolytic Performance; Artificial Heart Blood Pump
1. Introduction
A ventricular assist device (VAD) is an important in-
strument in treating heart failure. With the development
of heart surgery, VADs have been used as a bri-
dge-to-transplant or destination therapy [1-3]. The VAD
provides effective blood circulation support until a donor
heart becomes available for transplant, improves other
organ function, improves exercise performance, and en-
ables participation in cardiac rehabilitation [4]. In recent
years, the VAD has also been considered for long-term
implantation as a destination therapy. The circulatory
support can provide symptomatic relief and improved
survival for those who do not have access to cardiac
transplantation [5-7]. A VAD generally consists of a
pump unit that is either implanted in the abdomen or is
outside the body, a control system and an energy supply.
VADs can be divided into two main categories: dis-
placement pumps and rotary pumps [1,8,9]. Energy
transfer in displacement pumps is characterized by peri-
odic changes of the working space as a pulsation,
whereas in rotary pumps, the energy transfer to the fluid
is established by velocity changes within the impeller
vanes. Rotary pumps are designed to work in a constant
speed mode of mechanical circulatory support, thus, in
principle, produce non-pulsatile flow. Compared with
displacement pumps, the rotary type pumps have advan-
tages of compactness, no valves, simpler control aspects,
lower power consumption, lower relative cost, and a
more simplistic design, which results in smaller size and
increased reliability [2,8,10]. However, the fluid dynamic
forces in centrifugal blood pump impellers contribute to
the destruction of red blood cells because the rotational
speed leads to harsh interactions between the impeller
and red blood cells [11-13]. Thus, hemolysis is caused by
*Corresponding author.
C
opyright © 2013 SciRes. ACES

Y. OHGOE ET AL. 11
the high-speed rotation of the impeller in mechanical
circulatory support devices, and the damage is mainly
due to the interaction with solid surfaces. Therefore, an
important factor in the development of devices, such as
artificial heart blood pumps is the reduction of hemolysis
and thrombus formation; and minimizing the level of
hemolysis is a key development task to avoid thrombus
formation [11].
Hydrogenated amorphous carbon films (a-C:H), in-
cluding diamond-like carbon (DLC), have been the focus
of considerable research efforts due to their electrical,
mechanical, and chemical properties [14,15]. The prop-
erties of a-C:H films are mainly determined by sp3 and
sp2 bonding hybridization of the carbon atoms and the
relative concentration of these bonds [16]. The combina-
tion of these properties makes many applications avail-
able for a-C:H film coatings. a-C:H films have also
shown promising results in hemocompatible coating
technology. To date many types of a-C:H films have
been applied to medical devices [17-24].
A thrombus is formed by platelet adhesion followed
by aggregation and spreading. Therefore, the low surface
energy of a-C:H films has prompted investigation of such
coatings for improvement of medical devices that require
anti-thrombogenic properties. Hasebe and colleagues re-
ported that fluorine-doping of a-C:H (a-C:H:F) films
results in a significant reduction of Young’s modulus and
the surface free energy, meaning these films could be
useful for blood contacting medical devices [20,23]. The
numbers of platelets adhering to a-C:H:F films were re-
ported to be significantly lower than that with a-C:H
films, and the number and activation of adherent platelets
was reduced with a-C:H:F films [23].
In this study, a-C:H:F film coatings were investigated
for an enclosed-impeller type axial flow blood pump that
circulates blood under high speed rotation of an impeller.
The purpose of such a coating is to improve the hemo-
lytic performance of the blood pump. However, the im-
peller of an axial flow type blood pumps requires con-
tinuous rotation at high speed to perform blood circula-
tion as a primary function. Therefore, to apply a-C:H:F
film coatings to the impeller, it is necessary to investigate
the effect of improvement of the hemolytic performance
and applicability to the high-speed rotation of the impel-
ler.
2. Materials and Methods
2.1. Film Deposition
A schematic diagram of the ionization deposition method
is shown in Figure 1. The direct current ion source con-
sists of a tantalum filament, a tungsten anode electrode
and a molybdenum reflector. The ionization method was
used to deposit a-C:H:F onto SUS 304 substrate (753513,
The Nilaco Corporation, Tokyo, Japan; 200 × 200 mm2,
1 mm thick). The characteristics of the a-C:H:F films
were compared with a conventional a-C:H film deposited
under the same conditions to determine the effect of fluo-
rine doping. C6F5H and C6H6 source gases were decom-
posed to produce a-C:H:F and a-C:H films, respectively.
Each film was deposited using a gas flow of 3 sccm and
a substrate bias of 2.0 kV. The resultant films were ap-
proximately 1 μm thick (Table 1). The surface morphol-
ogy and friction of the films was investigated using ato-
mic force microscopy (AFM; JSPM-5200, Jeol Ltd, To-
kyo, Japan) and a friction tester (FPR-2100, Rhesca Co.,
Ltd, Tokyo, Japan). The friction test was conducted using
an aqueous glycerol solution with the viscosity adjusted
to simulate human blood (33 wt%, 20˚C). In addition, the
surface characteristics were measured using surface po-
tential meter (KSV SPOT1, KSV Instruments Ltd., Hel-
sinki, Finland) and X-ray photoelectron spectroscopy
(XPS; JPS-9000MC, Jeol Ltd, Tokyo, Japan) with Mg
Kα radiation.
Figure 1. Schematic diagram of the ionization deposition
method used to prepare a-C:H:F and a-C:H film coatings.
Table 1. Deposition of a-C:H:F and a-C:H film preparation
conditions employed for the ionization method.
Sauce
gas
Gas
pressure
(Pa)
Substrate
bias (kV)
Thickness
(μm) Substrate
a-C:H:F
film C6F5H
a-C:H filmC6H6
6.7×10
-4 3 1 SUS 304

Y. OHGOE ET AL. 12
2.2. Immersion Test circulation circuit was filled with 500 mL of pig blood
containing 50 mL sodium citrate and in vitro testing was
conducted for 180 min with a blood flow rate of 5 L/min,
a pump head of 100 mmHg, and an impeller speed of ca.
1,100 rpm. After the circulation test, the total hemoglo-
bin concentration in the pig blood was determined by the
cyanmethemoglobin method based on a standard hemo-
globin concentration curve from UV-vis absorption mea-
surements (U-1500, Hitachi, Ltd., Tokyo, Japan) at an
absorbance wavelength of 540 nm.
As a preliminary experiment, blood adhesion at the
a-C:H:F film surface was investigated under static condi-
tions. The a-C:H:F sample was fully immersed in 50 mL
of pig blood containing 5 mL sodium citrate for 180 min
under static conditions at 37˚C (Figure 2). After immer-
sion, the sample was rinsed in distilled water and the
amount of protein accretion at the sample surface was
estimated by the adenosine triphosphate (ATP) biolumi-
nescence method using a lumitester (PD-20, Kikkoman
Food Products Company, Tokyo, Japan). Monitoring of
the amount of ATP is typically used as a surface cleaning
test [25] and the amount of luminescence is proportional
to the amount of ATP and adenosine monophosphate
(AMP) present in the sample. The luminescence was
measured with the lumitester and the results are given in
relative light units (RLU) [25,26].
3. Results and Discussion
3.1. Film Deposition
a-C:H:F was successfully deposited on SUS 304 sub-
strates. The surface roughness of the a-C:H:F was meas-
ured using AFM and was determined to be uniform and
smooth on the SUS 304 substrate. The surface roughness
results shown in Table 2 indicate the a-C:H:F film was
significantly rougher than the a-C:H film, but similar to
the SUS 304 substrate. Yu, et al. reported that the in-
creased surface roughness of fluorinated amorphous car-
bon films was possibly caused by preferential etching of
fluorine because the films were not ideally isotropic [28].
The surface roughness was reported to increase with the
amount of fluorine dopant in the a-C:H film [29]. The
growth of fluorinated a-C:H films is dependent on the
competing deposition and etching processes. In the pre-
sent work, the surface roughness of the a-C:H:F film
showed the same tendency as that reported by Yu, et al.
2.3. Hemolysis Test
Figure 3 shows the enclosed-impeller type flow blood
pump, a schematic diagram of the driving parts for cir-
culation, and the hemolysis test system with mock circu-
lation. The in vitro test system with mock circulation
consists of a flow-straightener, impeller, diffuser, a flexi-
ble tube, and a flow meter (T402, Transonic Systems Inc.,
New York, USA). Maruyama, et al. reported that the
threshold surface roughness obtained for rapid increase
in hemolysis was 0.8 μm or greater [11,27]. In this ex-
periment, to avoid the influence of surface roughness on
hemolysis, the surface roughnesses of the flow-straigh-
tener, impeller, and diffuser, which were made of SUS
304, were treated to less than 0.6 μm by electrolytic pol-
ishing. After electrolytic polishing, a-C:H:F was depos-
ited on the parts by the ionization method (Table 1). The
film thickness was controlled to 1 μm and the surface
roughness was measured using a surface roughness tester
(SJ 400, Mitsutoyo Co., Kanagawa, Japan). The mock
The friction coefficient of the a-C:H:F film surface is
shown in Table 2. The friction coefficient of the SUS
304 surface was reduced from 0.18 to 0.14 by coating
with the a-C:H:F film. The reduction of the friction coef-
ficient by C6F5H plasma deposition on the SUS 304 sur-
face is due to a substantial decrease in the polar compo-
nent of the surface energy.
The chemical composition of the a-C:H:F film surface
Figure 2. Schematic diagram of the immersion test. The a-C:H:F and a-C:H films, and the SUS 304 substrate (without coat-
ing) were fully immersed in 50 mL pig blood containing 5 mL sodium citrate for 180 min under static conditions at 37˚C.
After immersion, the samples were rinsed in distilled water and the amount of protein accretion at the sample surface was
estimated using the adenosine triphosphate (ATP) test.

Y. OHGOE ET AL. 13
Table 2. Surface characteristics of a-C:H:F and a-C:H films, and the SUS 304 substrate surface.
Substrate roughness (nm) Friction Contact angle (deg) Surface potential (mV)
a-C:H:F film 16.14 ± 2.69 0.14 105.9 ± 5.0 -0.75
a-C:H film 7.79 ± 3.51 0.17 99.6 ± 3.1 -0.31
SUS 304 substrate
(without coating) 18.34 ± 4.37 0.18 101.6 ± 3.6 -0.17
(a)
(a)
(b)
(b)
Figure 4. Decomposed XPSs spectrum for (a) a-C:H:F
the bonding within the film as C-CF bonds decrease
(c)
Figure 3. (a) Enclosed-impeller of axial flow blood pump. (b)
Schematic diagram of the driving parts for blood circula-
tion. (c) Hemolysis test system employed for mock circula-
tion.
was estimated using XPS. Figure 4(a) and (b) show the
XPS C1s spectra for the a-C:H:F and a-C:H films depos-
ited on SUS 304 substrates, respectively. The main fea-
ture of the a-C:H film was an asymmetric peak at 284.6
eV, which indicates π-bonding. The C1s spectrum of the
a-C:H:F film was decomposed into 5 peaks correspond-
ing to C-F2 (292.8 eV), C-F (290.6 eV), C-CF (288.0 eV),
C-O (286.0 eV), and C-C (285.4 eV). The surface free
energy of the a-C:H:F film was reported to be reduced
C
1
film. (b) XPS C1s spectrum for a-C:H film.
in
and CF and CF2 bonds increase [29,30]. Water contact
angle measurement was carried out using the θ/2 method
with a digital camera. The contact angles for the a-C:H:F
and a-C:H films, and the SUS 304 substrate were 105.9˚
± 5.0˚, 99.6˚ ± 3.1˚ and 101.6˚ ± 3.6˚, respectively. The
surface roughness generally affects contact angle meas-
urements. Yu, et al. reported a decrease in the contact
angle (larger surface energy) with increasing surface
roughness [28]. However, in the present work, the sur-
face roughness increased with increasing contact angle
(smaller surface energy). Hasebe, et al. and Yu, et al. re-
ported that the surface roughness and microstructure
have a negligible influence on the surface energy [23,28],
with increasing fluorine content, which is due to changes

Y. OHGOE ET AL. 14
which is consistent with the present results.
Fluorine is a termination radical in C-C networks and
co
3.2. Immersion Test
TP bioluminescence for protein
3.3. Hemolysis Test
sited on the surface of the flow-
nsequently decreases cross-linking, which leads to new,
more open structural arrangements that can lead to a de-
crease in the density of a film [29-31]. The addition of
fluorine also results in a decrease in the hardness and stress
of a film [29,30]. These results indicate that a-C:H:F film
becomes more graphitic with increasing fluorine concen-
tration [28]. In addition, fluorine atoms are very electro-
negative and so will carry some degree of negative
charge. The surface of the a-C:H:F film was increased to
more negative potentials, as shown in Table 2.
Figure 5 shows the A
accretion on the a-C:H:F and a-C:H films, and on the
SUS 304 substrate after the immersion test. The surface
of a-C:H:F film had a low luminescence level, and thus a
low ATP concentration, which indicates that the a-C:H:F
film tends to weaken the protein adhesion of blood com-
pared with the other samples is due to negative charge
polarity. The high electronegativity of fluorine gives car-
bon-fluorine bonds a significant polarity or dipole mo-
ment. Therefore, it was expected that the van der Waals
interaction of the pig blood with the a-C:H:F surface is
reduced by the carbon-fluorine bonds. Platelet adhesion
and activation on the surface of a biomaterial is the most
important factor in determining the hemocompatibility of
a biomaterial, and low platelet adhesion denotes good
hemocompatibility, while a higher degree of platelet ad-
hesion tends to result in the formation of a thrombus
[20].
a-C:H:F film was depo
Figure 5. ATP bioluminescence results for the a-C:H:F and
a-C:H films, and the SUS 304 substrate.
effect of a-C:H:F film coating on the
ance of a blood pump was investigated.
straightener, enclosed-impeller, and the diffuser. The
surface roughness of these parts was 0.48 μm, while that
for the SUS 304 substrate and the a-C:H film were 0.47
and 0.46 μm, respectively (Table 3). Therefore, it was
expected that there was no influence of surface rough-
ness on the hemolytic performance. The hemolytic per-
formance of a blood pump with a-C:H:F film coating was
determined according to the amount of hemolysis meas-
ured for a mock circulatory system (in vitro tests). Fig-
ure 6 shows the amount of free hemoglobin in the blood
that was released in a hemolysis reaction for the blood
pump with a-C:H:F and a-C:H film coatings, and the
SUS 304 without a coating. The rotational speed of the
impeller in the blood pump was around 11,000 rpm. The
amount of hemolysis was reduced from 1110 mg/dL to
925 mg/dL with the a-C:H:F film coating. There was a
significant difference between the a-C:H:F film coating
and the SUS 304 surface without a coating (P < 0.05).
According to the ATP bioluminescence of the a-C:H:F
film surface, it was expected that the amount of hemoly-
sis was reduced by 20% with the decrease in the surface
energy of the blood contact surface. In addition, the
a-C:H:F film had good stability during the in vitro test.
The negatively charged polarity suppresses platelet
adhesion and fibrinogen adsorption as the platelets and
proteins tend to have a net negative zeta potential [20,23].
In this study, the a-C:H:F film surface resulted in a
higher degree of negative charge polarity. Roy, et al. [20]
studied the effect of fluorine incorporation into a-C:H
films on hemocompatibility. They reported that platelet
adhesion was suppressed as the fluorine concentration
increased and the surface charge became more negative.
This observation is closely related with the C-F2, C-F,
and C-CF surface bonds, because the negative charge of
the surface increased with the fluorine concentration
[20,29]. Yu, et al. also reported that the polar component
of the surface energy was reduced with increasing fluo-
rine concentration [28]. Thus, it is possible to have
higher surface polarization in films with higher fluorine
concentration. Their observations support the present
suggestion that the negatively charged polar component
caused by C-F2, C-F and C-CF surface bonds improves
the hemolytic performance under dynamic high-speed
rotation of the impeller.
4. Conclusion
In this study, the
hemolytic perform
The results indicate that the a-C:H:F film tends to in-
crease the surface roughness and negative charge of the
surface. In addition, the surface friction is decreased with
respect to fluorine doping in the a-C:H film. In in vitro
test, it has been indicated that fluorine in the a-C:H film

Y. OHGOE ET AL. 15
Table 3. Surface roughness of flow-straightener, the en-
closed-impeller, and the diffuser.
Surface roughness (μm)
a-C:H:F film 0.48
a-C:H film 0.47
SUS 304 substrate
(wg) ithout coatin0.46
Figure 6. Hemolytic performance for an axial flow type
blood pump with a-C:H:F film coating, a-C:H film coating
and without coating.
molytic performance of the blood
hiro Seki, a graduate
r conducting the hemolysis
[1] H. Wu, Z. Wang and X. Lv, “Design and Simulation of
Axial Flow Mag
of Informationonic Business, Vol.
,
tends to weaken the protein adhesive properties of blood.
addition, the heIn
pump with a-C:H:F film coating was improved because
the a-C:H:F film coating reduced the amount of hemoly-
sis. Decreasing the surface energy and negative charge of
the surface by coating with the a-C:H:F film was a con-
tributing factor for improvement of the hemolytic per-
formance. The a-C:H:F film coating is thus expected to
be utilized in medical technology as a surface coating
technology for artificial heart blood pumps. However, the
level of hemolysis is still relatively high. Therefore, fur-
ther investigations are required to understand the hemo-
lysis process in blood circulation with dynamic high-
speed rotation of the impeller.
5. Acknowledgements
The authors thank Mr. Taka
Tokyo Denki University, fo
from
test. This research was partially supported by a Grant-in-
Aid for Scientific Research (B), 2010-2012 (22300160)
from the Ministry of Education, Culture, Sport, Science,
and Technology of Japan (MEXT), and the Strategic Re-
search Foundation Grant-aided Project for Private Uni
versities from MEXT, 2008-2012 (S0801023), and the
Research Institute for Science and Technology, Tokyo
Denki University 2013 (Q13L-06).
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