Antibacterial properties and corrosion resistance of Cu and
Ag/Cu porous materials
Hemin Jing,1,2 Zhiming Yu,1 Li Li3
1
Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72,
Shenyang 110016, China
2
Anhui Key Laboratory of Metal Materials and Processing, School of Materials and Engineering,
Anhui University of Technology, Maanshan, 243002, China
3
Liaoning Scientific Academy of Microbiology, Wenhua Road 22, Chaoyang 122000, China
Received 20 May 2007; revised 2 July 2007; accepted 1 August 2007
Published online 13 December 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.31688
Abstract: The porous materials of Cu and Ag/Cu were
successfully prepared by the electrodeposition on a precursor of conventional polyamide foam. The microstructure of
the porous materials was observed by scanning electron
microscope. Their porosity and specific surface area were
measured. The inhibition effect of Cu porous materials
against E. coli was also investigated. The broad-spectrum
of antibiosis of the Cu and Ag/Cu porous materials were
characterized. The corrosion resistance of Cu, Ag/Cu coatings was also compared. The shape and size of pores are
uniform in three directions for the porous materials. Their
porosity may reach above 95% and specific surface area is
beyond 12.8 m2/m3. The antibacterial test results show
that the Cu porous materials not only exhibited high antibacterial effect and good broad-spectrum antibacterial
properties, but also excellent persistent antibacterial effects;
the antibacterial effects, and broad-spectrum of antibiosis
were greatly improved through the deposition of a thin
Ag coating on the surface of Cu porous material. Ó 2007
Wiley Periodicals, Inc. J Biomed Mater Res 87A: 33–37,
2008
INTRODUCTION
spectrum antibiosis, overcome the drawbacks of organic antibacterial materials, and have high antibacterial activity against both bacteria and funguses.4–6 Silver has been long known to be a potent antibacterial
agent with a very broad spectrum of activity and has
been used safely in medicine for many years.7–12 TiO2
nanoparticles containing Agþ have been widely used
as a filler in the manufacture of antibacterial plastics,
coatings, functional fibers, dishware, and medical
facilities because Agþ has a strong antibacterial activity against many kinds of bacteria even at lower concentrations.13–16 Microstructure and antibacterial
properties of AISI 420 stainless steel implanted with
copper ions were investigated by Dan et al.17 It was
concluded that an increase in pH had a greater effect
on the corrosion behavior of Ti-6Al-4V and Ti-6Al7Nb than on Ti-13Nb-13Zr in PBS and that the addition of protein to the PBS reduced the influence of
pH on the corrosion behavior of all the alloys, and
the annealed Cu-implanted SS possessed not only
excellent antibacterial property, but also keeps good
corrosion resistance.18,19 However, few articles were
concerned with the antibacterial property of porous
inorganic material.
With scientific and technological advances, much
attention is paid to the sanitation, safety, and health
of environments. Therefore, daily appliances are
being increasingly designed with antibacterial feature.1 In the past, organic antibacterial materials
were widely used,2 because of their low cost and
high inhibitory effect on bacterial growth. However,
their antibacterial effects cannot last for a long time.
On the other hand, organic compound pollutions
have produced various problems in living conditions, public health, and industrial fields. To solve
these problems, new antibacterial materials have
been demanded and studied.3
Inorganic antibacterial materials containing antibacterial metals like silver, copper, zinc with good
properties of long lasting, stability, safe and broadCorrespondence to: Z. Yu; e-mail: zmyu@imr.ac.cn
Contract grant sponsor: Prophase Research Expert Item
of State Major Basic Research Project of MOST, China; contract grant number: 2005CCA00500
Ó 2007 Wiley Periodicals, Inc.
Key words: porous material; antibacterial properties; Cu;
Ag/Cu; corrosion resistance
34
JING, YU, AND LI
In this study, the microstructure of Cu porous material was observed, whose porosity and specific surface area were measured. The inhibition effect of Cuporous materials against E. coli was investigated.
The broad-spectrum of antibiosis of the Cu and Ag/
Cu porous material were evaluated. The corrosion
resistance of Cu and Ag/Cu coatings was discussed.
EXPERIMENTAL PROCEDURE
Preparation of materials
Conventional foam of polyamide with thickness of
about 2 mm was used as precursor material, for making
the Cu porous materials. After conducting treatment, copper coatings with thickness of about 20 lm were deposited
on the precursor by electroplating. Then, heat treatment
was carried out at 7008C for 2 h in argon atmosphere.
Moreover, Ag thin film of about 100 nm was coated on the
surface of the Cu porous materials to expand its broadspectrum of antibiosis as well as to promote its antibacterial effect.
The microstructure and the physical property
The morphology images of the Cu porous materials
were observed by scanning electron microscope (SEM). By
comparing the mass of porous material with that of solid
material, the porosity of the Cu porous materials was
0
determined. The porosity is given by e ¼ mm
m 3 100%
where e is the porosity, m is the mass of bulk material,
and m0 is the mass of porous material.
Specific surface area of the porous materials was measured by the permeation method, which is given by
ffi
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
e3 ADP
S ¼ 14 ð1e
, where S is the specific surface area, e is
Þ2 hdQ
the porosity, A is the area of the porous materials for the
permeation measurement D P is the press difference
between the two sides, d is the thickness of the porous
materials, h is the conglutination coefficient, and Q is the
flux of nitrogen gas, which passes the porous materials.
Antibacterial test
Firstly, porous materials of Cu or Ag/Cu were prepared
with the same exposed area of 20 mm 3 20 mm. For microbiological experimentation, Escherichia coli (ATCC 8099),
Candida albicans (ATCC 10231), Staphylococcus aureus (ATCC
6538), Bacillus atrophaeus (ATCC 9372), and Saccharomyces
cerevisiae (ATCC 18824) were selected as indicators. All
glass wares (F110 mm) and samples were sterilized in autoclave at 1218C for 20 min before experiments. Test bacteria
inoculated on beveled the nutrient agar medium plates
were incubated at 378C for 24 h, whose store time is less
than 30 days at 0–58C after incubation. The composition of
mediums is shown in Table I.
Before the antibacterial experiment, the aforementioned
test bacteria were inoculated on an agar plate and incubated at 378C for 24 h. Each day, the test bacteria were
inoculated one time within 2 weeks. The 0.2-mL of fresh
bacteria solution was dripped onto the surface of specimen
and then the specimen was put into the sterilized glass
ware in which 5 mL of sterilized water was injected. After
the specimen was cooled, 0.2 mL of bacterial was again
dripped onto the surface of specimen and the specimen
was covered with an aseptic polyethylene film to ensure
that the bacterial solution was in close contact with the
surface of the specimen. The specimen with the bacterial
solution was incubated at 378C for 24 h. Subsequently, the
number of bacterial colonies was counted. Each evaluation
was carried out in triplicate and values obtained were
averaged to given the final data.
To evaluate the persistent antibacterial effects of Cu porous material, the used samples were used in the experiment which had been tested for 72 h. Before the experiment, the used samples were first ultrasonically cleaned
for 10 min in acetone solution.
The corrosion resistance of Cu and Ag/Cu coatings
The SUS 304 stainless steel was used as the substrate
material, whose dimension is 25 3 25 3 2 mm. Firstly, Cu
film of about 15 lm was deposited on the substrate surface
by electroplating. The samples coated with Cu film were
divided into two groups. One group directly used to corrosion test; for another group, Ag film was deposited on the
surface of Cu coating. Finally, the coated samples were
TABLE I
The Composition of the Mediums (g)
Bacteria Composition
Beef extract
Peptone
Yeast extract
Glucose
Sodium chloride
Agar powder
Potato
Water
Ph
E coli (ATCC8099)
5
10
5
5
5
16
1000 mL
7.0
Journal of Biomedical Materials Research Part A
S. aureus (ATCC6538)
B. atrophaeus (ATCC9372)
3
5
3
5
5
16
5
16
1000 mL
7.0–7.2
1000 mL
7.0–7.2
C. albicans (ATCC10231)
20
16
200
1000 mL
Natural
ANTIBACTERIAL PROPERTIES AND CORROSION RESISTANCE OF Cu AND Ag/Cu
prepared with the same exposed area. Polarization measurements were performed in 3.5% NaCl solution by means
of the conventional electric cells with three electrodes on a
332 electrochemical measurement system (EG&G Princeton
Applied Research) with a saturated calomel (SCE) reference electrode and a platinum counter electrode. All
potentials are referred to SCE. Scanning rate was 5 mV/s.
RESULTS AND DISCUSSION
Microstructure and physical properties of Cu
porous material
Figure 1 shows the SEM image of the Cu porous
material. It can be seen that the shape and size of
pores is uniform in three directions, whose maximum diameter is about 0.6 mm. The calculation
results show that the porosity is about 95%. The specific surface area is above 12.8 m2/m3. The specific
surface area of Cu porous material is much higher
than that of solid materials.
Antibacterial performance
Table II presents some results obtained by antibacterial tests against E. coli (3.5 3 106 cfu/mL) and S. aureus (1 3 106 cfu/mL), respectively. From the Table II,
it follows that, the Cu porous material has very strong
antibacterial activity against both E. coli and S. aureus.
The percentage of dead cells reached 99.3% after
20-min incubation and 100% after only 40-min incubation; against S. aureus, the percentage of dead cells
reached 98.4% after 20-min incubation, 99.3% after
40-min incubation, and 100% after 60-min incubation.
The antibacterial effects of Cu porous material against
S. aureus is worse than that of against E. coli. It may be
attributed to the S. aureus a typical Gram-positive bac-
35
TABLE II
The Antibacterial Effects of the Cu Porous Material
Viable Cell Count (cfu/mL)
Bacteria
E. coli
S. aureus
Start
6
3.5 3 10
1.0 3 106
20 min
40 min
60 min
10
7
0
3
0
0
terium which has a thicker cell wall compared with E.
coli a typical gram-negative bacterium. Moreover,
Yamamoto and coworkers reported that both the percentages of dead cells reached 99% after 24-h incubation, by NASSAM3/#400 austenitic stainless steel containing Cu of 3.8% against E.coli with a start colony
forming unit of 2.5 3 105 cfu/mL and against S. aureus
with a start colony forming unit of 2.3 3 105 cfu/mL,
respectively.20 It can be seen that the specific gravity
of Cu porous material is less than 0.445 g/cm3, which
is close to the Cu content (0.296 g/cm3) of the NASSAM3 austenitic stainless steel (0.04C-0.50Si-1.80Mn9.0Ni-18.0Cr-3.80Cu, wt%). However, the antibacterial
activity of the former is greater than that of the latter,
when against E. coli and S. aureus. It can be considered
that the excellent antibacterial effect of the Cu porous
material is due to its large surface area and high surface activity. Furthermore, from Table II, it can be seen
that the viable cell count was seven after 20-min incubation, three after 40-min incubation and zero after 60min incubation, against S. aureus. The reason may be
that the Cu2þ ions concentration was not enough to
kill all S. aureus after 40-min incubation. This means
that Cu2þ ions were slowly released into the medium
from the Cu porous material.
By contacting with 50 mL of 1 3 108, 1 3 109, and
1 3 1010 cfu/mL E. coli-containing water for 24 h,
the persistent antibacterial effects of Cu porous material were evaluated and the results are shown in
Table III. Table III shows that the Cu porous materials still have excellent antibacterial effects, which has
been used for 72-h. Although the start colony forming unit is as high as 1 3 109 cfu/mL, the percentage
of dead cells also reached 100% after 24-h incubation. It can be considered that the Cu porous material may be repeatedly used after proper cleanout.
Table IV shows some results achieved by testing
the inhibition effect of the Cu porous material
against E.coli, S. aureus, C. albicans, and B. atrophaeus
for 1, 6, and 24 hr. It can be seen that the Cu porous
TABLE III
The Persistent Antibacterial Effects of the Cu Porous
Materials Against E. coli for 24 h
Figure 1.
The SEM image of the Cu porous material.
Start (cfu/mL)
1 3 1010
1 3 109
1 3 108
Antibacterial rate (%)
96.5
100
100
Journal of Biomedical Materials Research Part A
36
JING, YU, AND LI
TABLE IV
The Broad-Spectrum of Antibiosis for the Cu
Porous Material
Antibacterial Rate (%)
Bacteria
E. coli
S. aureus
C. albicans
B. atrophaeus
TABLE VI
The Antibacterial Effects of the Ag/Cu Porous Material
Against S. cerevisiae (ATCC 18824)
Start (cfu/mL)
Antibacterial rate (%)
1 3 105
100
1 3 106
100
1 3 107
100
Start (cfu/mL) After 1 h After 6 h After 24 h
1.0
1.0
4.8
1.0
3
3
3
3
108
106
106
106
100
100
99.2
–
100
100
100
–
100
100
100
3.9
material has well broad-spectrum of antibiosis. For
E.coli (1 3 108cfu/mL) and S. aureus (1.0 3 106 cfu/
mL) after 1 h, both of the percentage of dead cells
reached 100%; for C. albicans (4.8 3 106 cfu/mL) after 6 h, the percentage of dead cells also reached
100%. However, the Cu porous material almost has
not the inhibition effect against B. atrophaeus. From
Table IV combining with Tables II and III, it is clear
that the Cu porous materials not only exhibited high
antibacterial effect and good broad-spectrum antibacterial properties, but also excellent persistent antibacterial effects.
Table V shows the results achieved by testing the
inhibition effect of the Ag/Cu porous material
against E. coli, S. aureus, C. albicans, and B. atrophaeus
after 1, 3, and 24-h incubation. From Tables IV and
V, it can be seen that the Ag/Cu porous material
has higher antibacterial effects and much better
broad-spectrum of antibiosis than that of Cu porous
material. Specially, it is evident the antibacterial
properties against B. atrophaeus were greatly
improved through the deposition of a thin Ag coating on the surface of Cu porous material, by comparison with Table IV. From the test results of Ag/
Cu porous material against B. atrophaeus after 1-h,
3-h and 24-h incubation, it can be seen that the percentage of dead cells gradually reaches 97% from
58% with prolonging the incubation time. This suggests that Agþ ions were slowly released into the
medium from the Ag/Cu porous material. Combining with the aforementioned about the characteristic
of Cu2þ release, it can be considered that the concentration of Agþ and Cu2þ in the processed liquid may
be controlled at appropriate level by choosing
proper contact time of the processed liquid with Cu
or Ag/Cu porous material.
The Ag/Cu porous materials possess high antibacterial effects and excellent broad-spectrum of antibiosis. The reason may be attributed to that the ionization energy (7.57 eV) of Agþ is much lower than that
(20.29 eV) of Cu2þ. This means that the formation of
Agþ ions is easier from silver than that of Cu2þ ions
from copper. Therefore, Agþ ions easily interact with
the cell wall, and then silver ions enter the cells and
combined some cell components containing sulfur.21
Ag/Cu porous materials can be expected to have a
promising application for a situation of strict sterility
or high level disinfection.
Moreover, the antibacterial effects of Ag/Cu porous material against S. cerevisiae (ATCC 18824) were
evaluated and the results are shown in Table VI.
From Table VI, it can be seen that the Ag/Cu porous
material exhibited high antibacterial effect. When the
start colony forming unit is as high as 1 3 107 cfu/
mL, the percentage of dead cells also reached 100%
after 24-h incubation. If Ag/Cu porous material may
be used to sterilize in the beer production process, a
vast energy should be saved.
Evaluation of the corrosion resistance
of the porous materials
Figure 2 shows the polarization curves of the Cu
and Ag/Cu coatings in a solution of 3.5% NaCl.
TABLE V
The Broad-Spectrum of Antibiosis for the Ag/Cu
Porous Material
Antibacterial Rate (%)
Bacteria
E. coli
S. aureus
C. albicans
B. atrophaeus
Start (cfu/mL) After 1 h After 3 h After 24 h
1.5
5.6
2.0
5.0
3
3
3
3
108
107
108
108
100
100
100
58
Journal of Biomedical Materials Research Part A
100
100
100
76
100
100
100
97
Figure 2. Polarization curves of the Cu and Ag/Cu coatings in 3.5% NaCl solution.
ANTIBACTERIAL PROPERTIES AND CORROSION RESISTANCE OF Cu AND Ag/Cu
From Figure 2, it can be seen that the Cu coatings
are not resistant to corrosion. The reason may be
that a continuous passive film cannot be formed on
the surface of Cu coating because Cu is not resistant
to pitting corrosion in a solution that contains chlorides.22 By a comparison of the polarization curves of
Cu coating and Ag/Cu coating, it can be found that
a passivity maintaining zone exits in the polarization
curve of Ag/Cu coating. It may be considered that
the pit corrosion resistance was improved by a thin
coating of Ag deposited on the Cu coating. However, it can be seen that the corrosion current of Ag/
Cu coating (Icorr 5 4.6 3 1026 A/cm2) is a little
larger than that of Cu coating (Icorr 5 4.0 3 1026 A/
cm2). This means that the corrosion rate increased by
a thin coating of Ag deposited on the Cu coating.
Therefore, a detailed investigation is required to
improve the corrosion resistance of Ag/Cu porous
material.
CONCLUSIONS
1. The Cu porous materials were successfully prepared by the electrodeposition on the foam of
polyamide. Moreover, Ag/Cu porous materials
were also obtained by coated a thin Ag film on
the surface of the Cu porous material.
2. The Cu porous materials exhibited very strong
antibacterial activity and the persistent antibacterial ability against E. coli. The percentage of
dead cells already reached 100% on E. coli (3.5 3
106 cfu/mL) after 40-min incubation; although,
the start colony forming unit is as high as 1 3
109 cfu/mL, the percentage of dead cells also
reach 100% after 24-h incubation.
3. The Ag/Cu porous material has higher antibacterial effects and much better broad-spectrum
of antibiosis than that of Cu porous material.
Specially, it is evident that antibacterial properties against B. atrophaeus were greatly improved
through the deposition of a thin Ag coating on
the surface of Cu porous material.
References
1. Hong IT, Koo CH. Antibacterial properties, corrosion resistance and mechanical properties of Cu-modified SUS 304
stainless steel. Mater Sci Eng A 2005;393:213–222.
37
2. Yokota T, Tochihara M. Kawasaki. Silver dispersed stainless
steels with antibacterial property. Steel Rep 2001;33:88.
3. Kumar VS, Nagaraja BM, Shashikala V, Padmasri AH, Madhavendra SS, Raju BD, Rao KSR. Highly efficient Ag/C catalyst prepared by electrochemical deposition method in controlling microorganisms in water. J Mol Catal A: Chem
2004;223:313–319.
4. Modak SM, Fox CLJ. Binding of silver sulfadiazine to the cellular components of Pseudomonas aeruginous. Biochem Pharmacol 1973;22:2391.
5. Berger TJ, Spadaro JA, Chapin SE, Becker RO. Electrically
generated silver ions: Quantitative effects on bacterial and
mammalian cells. Antimicrob Agents Chemother 1976;9:357.
6. Williams RL, Doherty PJ, Vince DG, Grashoff GJ, Williams DF.
The biocompatibility of silver. Crit Rev Biocompat 1989;5:221.
7. Ersek R. Silver impregnated porcine xenografts for treatment
of meshed autografts. Ann Plast Surg 1984;13:325–330.
8. Hu C. Therapeutic effects of silver nylon dressings with
weak direct current on Pseudomonas aeruginosa infected burn
wounds. J Trauma 1988;28:1488–1492.
9. Liedberg H. Silver alloy coated catheters reduce catheterassociated bacteriuria. Br J Urol 1990:65:379–381.
10. Stamm W. Catheter-associated urinary tract infections: Epidemiology, pathogenesis and prevention. Am J Med 1991;91:65–71.
11. Johnson J. Prevention of catheter-associated urinary tract
infection with asilver oxide coated urinary catheter: Clinical
and microbiologic correlates. J Infect Dis 1990;162:1145–1150.
12. Babycos C. A prospective randomized trial comparing the silver-impregnated cuff with the bedside tunneled subclavian
catheter. J Patenter Enteral Nutr 1993;17:61–63.
13. Zhang WZ, Wei WJ. A nover bactericide with silver ion. Rare
Metal Mater Eng 1996;25:48–51.
14. Spadaro JA, Berger TJ, Barranco SD, Chapin SE, Becker RO.
Antibacterial effects of silver electrodes with weak direct current. Antimicrob Agents Chemother 1974;6:637.
15. Zhang WZ. Review of Silver’s research and production.
World Non-Ferrous Metals 1995;18:18–24.
16. Tomioko TS. Characteristics of antibacterial material ‘‘Amenitop’’
composed of silver complex. Nat Tech Rep 1994;40:39–45.
17. Dan ZG, Ni HW, Xu BF, Xiong J, Xiong PY. Microstructure
and antibacterial properties of AISI 420 stainless steel
implanted copper ions. Thin Solid Films 2005;492:93–100.
18. Trapalis CC, Kokkoris M, Perdikakis G, Kordas G. Study of
antibacterial composite Cu/SiO2 thin coatings. J Sol-Gel Sci
Technol 2003;26:1213–1218.
19. Khan MA, Williams RL, Williams DF. The corrosion behavior
of Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr inprotein solutions. Biomaterials 1999;20:631–637.
20. Ookubo N, Nakamura S, Yamamoto M, Mikyakusu K, Hasegawa M, Munesue Y. Antimicrobial Activity and Basic Properties of Antimicrobial Stainless Steels ‘‘NSSAM Series’’. Nisshin Steel Rep 1998;77:69–81.
21. Feng QL, Wu J, Chen GQ, Cui FZ, Kim TN, Kim JO. A mechanistic study of the antibacterial effect of silver ions on Escherichia coli
and Staphylococcus aureus. J Biomed Mater Res 2000;52:662–668.
22. Banas J, Mazurkiewicz A. The effect of copper on passivity
and corrosion behavior of ferritic and ferritic-austenitic stainless steels. Mater Sci Eng A 2000;277:183.
Journal of Biomedical Materials Research Part A