M. BASIAGA et al.: THE EFFECT OF EO AND STEAM STERILIZATION ON THE MECHANICAL ...
153–158
THE EFFECT OF EO AND STEAM STERILIZATION ON THE
MECHANICAL AND ELECTROCHEMICAL PROPERTIES OF
TITANIUM GRADE 4
VPLIV EO IN STERILIZACIJE S PARO NA MEHANSKE IN
ELEKTROKEMIJSKE LASTNOSTI TITANA GRADE 4
Marcin Basiaga, Witold Walke, Zbigniew Paszenda, Anita Kajzer
Silesian University of Technology, Faculty of Biomedical Engineering, Zabrze, Poland
marcin.basiaga@polsl.pl
Prejem rokopisa – received: 2014-09-23; sprejem za objavo – accepted for publication: 2015-03-09
doi:10.17222/mit.2014.241
Currently, various modifications to surfaces are made more and more frequently in order to improve implants’ haemocom-
patibility. The main criterion determining the applicability of the respective surface-modification method is obtaining a product
featuring suitable functional properties. These properties depend to a great extent on the corrosion resistance in the environment
of human blood. Subject-matter literature does not devote much attention to the sterilisation process for titanium and cpTi alloys
with surface modifications. A problem that still remains unsolved is the selection of a proper test showing the full characteristics
of their behaviour contact with a blood environment during the time that the implant is used. Therefore, the authors of this study
made an attempt to evaluate the impact of medical sterilisation methods, i.e., the ethylene oxide anodic oxide and SiO2 layer, by
means of the sol-gel method. The efficiency of the suggested technology for oxide layer application was evaluated on the basis
of mechanical and electrochemical tests. Sterilisation in ethylene oxide and steam had a favourable influence on the
electrochemical and mechanical properties of cpTi, irrespective of the method of surface preparation. In order to simulate real
conditions, the tests were performed in artificial plasma at a temperature of T = 37 ± 1 °C and pH = 7.0 ± 0.2. The results proved
the diversification of electrochemical properties of the oxide layers, depending on the technological parameters of its
application. The suggestion of proper variants of the surface modification with the application of electrochemical and chemical
methods is of long-range importance and will contribute to the development of technological conditions with specific
parameters for the creation of oxide layers on metallic implants made of cpTi.
Keywords: cpTi (Grade 4), SiO2, TiO2, mechanical properties, electrochemical properties
Vedno pogosteje se opravljajo razli~ne modifikacije povr{ine, da bi se izbolj{ala hemokompatibilnost vsadkov. Glavni kriterij, ki
dolo~a uporabnost metode za modifikacijo povr{ine je, da proizvod poka`e primerne funkcionalne lastnosti. Te lastnosti so v
veliki meri odvisne od korozijske odpornosti v ~love{ki krvi. Obstoje~a literatura ne posve~a velike pozornosti postopku
sterilizacije titana in cpTi zlitin z modificirano povr{ino. Problem, ki {e ni re{en, je izbira primernega preizkusa, ki bi pokazal
vse zna~ilnosti o obna{anju stika s krvjo med uporabo vsadka. Zato so avtorji v tej {tudiji poizkusili oceniti vpliv medicinskih
metod sterilizacije, kot je etilen oksid anodni oksid in SiO2 plast izdelano s pomo~jo metode sol-gel. Predlagana tehnologija
uporabe oksidnega sloja je bila ocenjena z mehanskimi in elektrokemijskimi preizkusi. Sterilizacija v etilen oksidu in pari je
imela ugodne vplive na elektrokemijske in mehanske lastnosti cpTi, ne glede na na~in priprave povr{ine. Za simulacijo realnih
pogojev so bili preizkusi izvr{eni v umetni plazmi pri temperaturi T = 37 ± 1 °C in pH = 7,0 ± 0,2. Dobljeni rezultati so potrdili
razli~nost v elektrokemijskih lastnostih oksidnih plasti, odvisno od tehnolo{kih parametrov njene uporabe. Predlog ustreznega
na~ina spremembe povr{ine z uporabo elektrokemijskih in kemijskih metod je dolgoro~no pomemben in bo prispeval k razvoju
tehnolo{kih pogojev s specifi~nimi parametri nastajanja plasti oksidov na kovinskem implantatu iz cpTi.
Klju~ne besede: cpTi (Grade 4), SiO2, TiO2, mehanske lastnosti, elektrokemijske lastnosti
1 INTRODUCTION
Literature does not devote much attention to the steri-
lisation process for titanium and cpTi alloys with surface
modification.1,2 In recent years there has been a dynamic
development in pure titanium coating methods, aimed at
improving the hemocompatibility.3,4 Surface-layer modi-
fication methods must be selected in a way that does not
cause phase or structural transitions, or precipitation
processes in the base material. It has a particular
significance for the geometry of implants having small
cross-sectional areas or small-radii edges (stents or heart
valves). For this reason, surface-layer modification for
titanium and its alloys uses low-temperature methods,
and especially anodic oxidation coating and the sol-gel
method. The properties of TiO2 layers obtained through
the process of anodic oxidation and SiO2 layers obtained
with the sol-gel method depend on the properties of the
titanium surface and the process parameters. The deve-
lopment and verification of conditions for coating cpTi
with layers of TiO2 and SiO2 characterized by high
hemocompatibility was the topic of previous papers pub-
lished by the authors.5–7 The safety of a medical device
involving contact with blood is also related to the ne-
cessity of observing the appropriate procedures, pre-
venting the transfer of pathogenic microorganisms into
the human body. Such procedures are aimed at the remo-
val and efficient elimination of microorganisms and the
obtaining of sterile medical devices complying with
certain specified quality requirements. A medical device
is considered sterile when it achieves a Sterility Assur-
Materiali in tehnologije / Materials and technology 50 (2016) 1, 153–158 153
UDK 669.295:544.6:532.6 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 50(1)153(2016)
ance Level (SAL) of 10–6. Therefore, in order to deter-
mine the impact of the procedure on the properties of the
proposed surface layers, the authors subjected cpTi
samples to steam sterilization and ethylene oxide sterili-
zation. These two methods of medical sterilization are
currently the most frequently used for devices having
contact with blood. Taking the sterilization process into
consideration will allow the characterization of the
physical and chemical properties of the proposed surface
layers in a more complete way, which has a significant
influence on reducing the incidence of failures in the
treatment of cardiovascular diseases.
2 MATERIALS AND METHODS
The study material was Grade 4 cpTi in the form of
disks of the following dimensions: diameter, d = 14 mm,
thickness, g = 2 mm. The samples were subjected to
metal finishing consisting of mechanical grinding and
electrolytic polishing, and then coating with layers of
SiO2 and TiO2 based on two methods. The SiO2 layer was
applied using the sol-gel method with the following
process parameters: v = 3.0 cm/min, T = 430 °C, t = 60
min. The silica precursors were: tetraethyl orthosilicate
(TEOS), Si(OC2H5)4 and tetramethyl orthosilicate
(TMOS), Si(OCH3)4. Other reagents included ethyl
alcohol (EtOH) and water. On the other hand, the TiO2
layer was applied with the use of anodic oxidation at a
potential of 100 V in an electrolyte based on phosphoric
and sulphuric acids. Later, the prepared samples were
subjected to ethylene oxide sterilization and steam
sterilization. Ethylene oxide sterilization was conducted
during a 12-hour cycle of exposure to ethylene oxide at
30 °C. After the process, the samples were ventilated for
2 h with the use of an EOGas series sterilizer from An-
dersen Products. The cycle yielded a Sterility Assurance
Level SAL of 10–6. The process was controlled by means
of a chemical indicator, a biological indicator and an
ethylene oxide exposure indicator. The steam steriliza-
tion was performed in a Basic Plus autoclave at tempe-
rature, T = 134 °C, pressure, p = 2.1 bar, and time, t = 12
min.
The tests were performed on samples coated with
SiO2 and TiO2 (cpTi+SiO2 and cpTi+TiO2), coated with
SiO2 and TiO2 and subjected to steam sterilization
(cpTi+SiO2+steam and cpTi+TiO2+steam), and coated
with SiO2 and TiO2 and subjected to ethylene oxide
sterilization (cpTi+SiO2+EO and cpTi+TiO2+EO). In
order to assess the impact of a given type of medical
sterilization on the mechanical and electrochemical
properties of the proposed cpTi surface modifications,
the authors selected electrochemical potentiodynamic
and impedance tests. The assessment of the mechanical
properties, in turn, consisted of a measurement of the
layer adhesion to the base and a measurement of the
hardness.
The investigation of the electrochemical properties
began with potentiodynamic tests and registration of the
polarization curves. The measurement facility consisted
of a potentiostat with a PGP-201 generator, an electro-
chemical cell with a set of electrodes (platinum PtP-201
electrode the auxiliary and calomel electrode as the
reference), and a solution (250 mL) functioning as artifi-
cial plasma (pH = 7.0 ± 0.2). The artificial plasma during
the test had a temperature T = 37.0 ± 1 °C. Corrosion
tests started by determining the open-circuit potential
EOCP for no current flowing. Anodic polarization curves
were registered from the initial potential value, Estart =
EOCP – 100 mV. The potential change took place in the
anodic direction at a speed of 0.16 mV/s.8–10 After
obtaining an anodic current density of 1 mA/cm2 or the
measurement range +4000 mV, the polarization direction
was changed in order to register the formation of any
hysteresis loop. Further, electrochemical impedance
spectroscopy (EIS) tests were conducted using an
AutoLab PGSTAT 302N system equipped with an FRA2
module. The measurement system was used in the fre-
quency range 104–10–3 Hz, with a sinusoidal voltage
amplitude of the stimulating signal of 10 mV. The impe-
dance spectra were determined and the measurements
matched to an equivalent circuit by means of the
least-squares method. The impedance spectra of the
studied system were presented in the form of Nyquist
plots for various frequencies and Bode plots.11
The mechanical properties were then tested, with the
properties of interest being the adhesion of the layers to
the base and their hardness. The adhesion of the layers to
the base was tested using the scratch-test method on an
open platform equipped with a CSM Micro-Combi-
Tester in compliance with the standard.12 The test in-
volved generating a scratch with an indenter (Rockwell-
type diamond cone), gradually increasing the load on the
indenter. The assessment of the critical load, Lc, was
made on the basis of registered acoustic emission
changes, friction force and coefficient, as well as
observations from the light microscope integrated into
the platform. The tests were performed at increasing
loads in the range 0.03–20 N and for the following para-
meters: load rate 10 N/min, table speed 1.5 mm/min,
scratch length 3 mm. The instrumental hardness
measurement was performed using the Oliver-Pharr
method, with the use of a Berkovich indenter on the open
platform Micro-Combi-Tester by CSM Instruments. The
loading and unloading rate amounted to 0.40 mN/min,
while the loading force exerted on the indenter was 0.20
mN.13
3 RESULTS
Polarization curves registered during the potentiody-
namic tests were the basis for a determination of the
characteristic quantities describing the pitting-corrosion
resistance of cpTi with a modified surface layer before
and after sterilization (steam and EO) (Figure 1 and
Table 1).
M. BASIAGA et al.: THE EFFECT OF EO AND STEAM STERILIZATION ON THE MECHANICAL ...
154 Materiali in tehnologije / Materials and technology 50 (2016) 1, 153–158
The corrosive potential registered for the samples
before sterilization assumed the following values:
cpTi+TiO2 – Ecorr = –235 mV and cpTi+SiO2 – Ecorr =
–178 mV. In the case of the samples subjected to anodic
oxidation and sterilization, the corrosive potential was:
cpTi+TiO2+steam – Ecorr = –142 mV and cpTi+TiO2+EO
– Ecorr = –170 mV, while for the samples coated with
silica and sterilized it was: cpTi+SiO2+steam – Ecorr =
–121 mV and cpTi+SiO2+EO – Ecorr = –121 mV.
Regardless of the surface-modification method and the
medical sterilization method, no hysteresis loop was
observed, which shows that the analysed samples
polarized up to potential value of +4000 mV are fully
resistant to pitting corrosion (Figure 1 and Table 1).
Table 1: Results of potentiodynamic test (mean measurement values)
Tabela 1: Rezultati potenciodinami~nega preizkusa (srednje izmerje-
ne vrednosti)
Surface Ecorr, mV Rp, M cm2
cpTi+TiO2
inital state –235 4.02
EO –170 43.70
steam –142 30.58
cpTi+SiO2
inital state –178 0.47
EO –121 9.20
steam –121 1.30
M. BASIAGA et al.: THE EFFECT OF EO AND STEAM STERILIZATION ON THE MECHANICAL ...
Materiali in tehnologije / Materials and technology 50 (2016) 1, 153–158 155
Figure 3: Impedance spectra for the sample cpTi(SiO2): a) Nyquist
plot, b) Bode diagram
Slika 3: Spekter impedance za vzorec cpTi(SiO2): a) Nyquist diagram,
b) Bode diagram
Figure 1: Anodic polarisation curves of sample: a) cpTi(TiO2), b)
cpTi(SiO2)
Slika 1: Krivulje anodne polarizacije vzorcev: a) cpTi(TiO2), b)
cpTi(SiO2)
Figure 2: Impedance spectra for the sample cpTi(TiO2): a) Nyquist
plot, b) Bode diagram
Slika 2: Spekter impedance za vzorec cpTi(TiO2): a) Nyquist
diagram, b) Bode diagram
The impedance spectra determined during the EIS
tests indicate diversified kinetics during the process
taking place in the surface layers formed on the cpTi
base before and after medical sterilization (Figures 2
and 3). The impedance spectra were analysed with the
use of equivalent circuits, and their resultant impedances
described (Figure 4 and Table 2). The best conformity
between the model spectra and the experimental spectra
obtained from the artificial plasma was achieved in the
following circuits:5,6,11
• circuit indicating the existence of a double layer,
where Rs is the resistance of the artificial plasma,
CPEp is a constant phase element modelling the
capacity of the surface zone of the material, with a
highly developed surface, Rp – an element modelling
the solution resistance in this zone, Rct and CPEdl –
resistance and capacity of the oxide layer (Figure
4a),
• circuit including also CPEpore – an element represent-
ing the capacity of a double (porous) layer and an
Rpore resistor representing the electrolytic resistance in
the pores (Figure 4b).
In the case of the cpTi+TiO2+steam sample, the layer
was triple. This was a result of the penetration of the
artificial plasma into the surface layer, resulting from the
fact that the oxide layer created during anodic oxidation
was destroyed by the steam, and recreated deeper inside,
up to the layer adjacent to the base. In the remaining
samples, the presence of a layer with high surface
development was observed. The layer functioned as an
additional barrier protecting the material against the
corrosive environment.
M. BASIAGA et al.: THE EFFECT OF EO AND STEAM STERILIZATION ON THE MECHANICAL ...
156 Materiali in tehnologije / Materials and technology 50 (2016) 1, 153–158
Figure 4: Physical models of an electrical equivalent system for a corrosion system: metal – solution5,6,11
Slika 4: Fizikalni modeli ekvivalentnega elektri~nega sistema za korozijski sistem: kovina – raztopina5,6,11
Table 2: EIS analysis results
Tabela 2: Rezultati EIS-analize
Surface
Rs/
cm2
Rpore/
cm2
CPEpore Rp/
kcm2
CPEp Rct/
Mcm2
CPEdl
Y0/–1cm–2s–n n Y0/–1cm–2s–n n Y0/–1cm–2s–n n
cpTi+TiO2
inital state 19 – – – 968 0.2083E-6 0.89 4.26 0.1852E-5 0.81
EO 18 – – – 700 0.1460E-6 0.96 4.40 0.1901E-6 0.93
steam 18 112 0.2092E-6 0.94 817 0.5091E-6 0.90 3.66 0.2417E-5 0.82
cpTi+SiO2
inital state 18 – – – 188 0.6605E-5 0.93 1.59 0.2065E-4 0.88
EO 19 – – – 224 0.1730E-5 0.83 3.00 0.6317E-5 0.75
steam 17 – – – 160 0.9806E-5 0.85 2.40 0.2664E-4 0.85
Table 3: The results of adhesion of the layer on the cpTi substrate
Tabela 3: Rezultati adhezije plasti na podlago iz cpTi
Failure of the layer
The value of registered indenter load Fn/N
cpTi+SiO2 cpTi+TiO2
inital state steam EO inital state steam EO
Measurment 1 Delamination Lc1 2.59 2.89 2.79 2.71 1.66 1.87
Complete break Lc2 7.58 4.32 4.05 5.35 2.67 2.58
Measurement 2 Delamination Lc1 3.78 3.26 1.95 2.96 1.67 1.65
Complete break Lc2 5.76 4.55 2.59 4.95 2.56 2.37
Measurement 3 Delamination Lc1 3.38 2.41 2.01 3.33 1.82 1.78
Complete break Lc2 6.16 4.88 2.89 5.08 2.89 2.12
Average Delamination Lc1 3.25 2.85 2.25 3.00 1.71 1.76
Complete break Lc2 6.50 4.58 3.08 5.12 2.70 2.35
Standard
deviation
Delamination Lc1 ±0.60 ±0.42 ±0.46 ±0.31 ±0.09 ±0.11
Complete break Lc2 ±0.95 ±0.28 ±0.77 ±0.20 ±0.16 ±0.23
The results of the tests of adhesion of the analysed
layers to the base material are presented in Table 3 and
Figures 5 and 6. Regardless of the sterilization method,
the results indicate the impairment of adhesion of the
layers coated by both anodic oxidation and the sol-gel
method in comparison to the baseline samples. This can
be seen from the values of the parameters determined on
the basis of the measurements (Table 3). It was observed
that for the samples not subjected to sterilization, the
critical load causing layer delamination inwards and
outwards was Lc2 = 6.50 N (cpTi+SiO2 – sol-gel method)
and Lc2 = 5.12 N (cpTi+TiO2 – anodic oxidation). After
sterilization (both steam and EO sterilization), the cri-
tical load value decreased to: Lc2 = 4.58 N (cpTi+SiO2+
Steam), Lc2 = 3.08 N (cpTi+SiO2+EO) for the sol-gel
method, and Lc2 = 2.70 N (cpTi+TiO2+Steam), Lc2 =
2.35 N (cpTi+TiO2+EO) for the anodic oxidation. Re-
gardless of the type of sample, no acoustic emission
signal was registered, which indicated that the bond
energy between the base and the coating was too low. No
significant changes between steam and EO sterilization
were observed.
The next step involved the hardness testing of the
layers. The results of the measurements are shown in
Table 4. The results do not show any significant diffe-
rences between the samples after steam and ethylene
oxide sterilization and the baseline samples.
Table 4: The results of nanohardness of the layers
Tabela 4: Rezultati meritve mikrotrdote plasti
i.c.
Nanohardness HIT, MPa
cpTi+SiO2 cpTi+TiO2
inital
state steam EO
inital
state steam EO
Measurement 1 1181 1304 1082 1236 1434 1171
Measurement 2 1236 1278 923 913 1247 1241
Measurement 3 1021 1189 1120 1021 1156 1089
Average 1146 1257 1041 1056 1279 1167
Standard
deviation ±152 ±60 ±104 ±164 ±141 ±76
4 CONCLUSIONS
The correct selection of physical and chemical pro-
perties is a significant issue in the process of adjusting
the functionalities of cardiac implants,14 and has a direct
impact on the final quality of medical devices. Physical
and chemical devices are shaped by means of various
types of metal finishing.14,15 The influence of various
types of titanium alloy finishing on orthopaedic implants
has been demonstrated by Szewczenko et al.16. He has
shown that the method of base preparation has a crucial
influence on the physical and chemical properties of the
anodic oxide coating. Paszenda has proposed chemical
surface modifications of the Cr-Ni-Mo steel intended for
cardiac implants in order to achieve a higher hemo-
compatibility.17 The literature review indicates that there
are no comprehensive works devoted to a possible
change of properties during medical sterilization.18–20
Therefore, the authors of this paper focused on an
assessment of the possible changes to the mechanical
and electrochemical properties of a coating subjected to
pressurized steam sterilization and ethylene oxide
sterilization. The tests on the samples following medical
sterilization processes have shown differences in relation
to those samples that did not undergo sterilization.
Pressurized-steam sterilization caused a change in the
corrosive potential value towards positive values and
increased the polarization resistance, regardless of the
surface-modification method. For the TiO2-coated sam-
ples, it stopped the diffusion processes stemming from
the anodic oxidation and caused the formation of an
additional layer with a highly developed surface, which
functioned as an additional barrier protecting the mate-
rial against the corrosive environment and increasing the
ion-transfer resistance. In the case of the SiO2 layer, this
type of sterilization did not cause significant changes to
M. BASIAGA et al.: THE EFFECT OF EO AND STEAM STERILIZATION ON THE MECHANICAL ...
Materiali in tehnologije / Materials and technology 50 (2016) 1, 153–158 157
Figure 6: Results of the adhesion tests of the sample cpTi+SiO2+EO
Slika 6: Rezultati preizkusa adhezije vzorca cpTi+SiO2+EO
Figure 5: Results of the adhesion tests of the sample cpTi+TiO2+EO
Slika 5: Rezultati preizkusa adhezije vzorca cpTi+TiO2+EO
the corrosive resistance of cpTi. The mechanical proper-
ties, on the other hand, remained unchanged, regardless
of the type of metal finishing. However, the adhesion to
the base was weaker in comparison to those samples not
subjected to sterilization, which may be caused by the
restructuring of the surface oxides under the influence of
a sterilizing agent, which has a direct impact on the
strength of the bonds between the chemical compounds,
such as between TiO2/Ti2O3 and the base. Ethylene oxide
sterilization of the samples with a modified surface also
caused changes to their electrochemical and mechanical
properties. As in the case of pressurized-steam steriliza-
tion, the samples coated with TiO2 and SiO2 had a better
resistance to corrosion in contact with the artificial
plasma. On the surface of the samples coated with TiO2,
the presence of an additional porous layer has been ob-
served. This is the result of the partial degradation of the
oxide layer and an increase in its porosity, which, as a
consequence, leads to much weaker adhesion to the base.
In the scratch test, a decrease in the critical load causing
delamination of the layer towards the base was observed.
In conclusion, the study has shown the significant
influence of medical sterilization on the physical and
chemical properties of the TiO2 and SiO2 layers. It has
been proved that, regardless of the surface layer type, the
choice of the sterilizing method is an important issue. A
SiO2 layer applied with the sol-gel method exhibited a
higher electrochemical stability. In the future, the authors
plan further work to help identify the chemical compo-
sition and chemical compounds formed as a result of the
sterilization processes and possible changes to the layer
thickness.
Acknowledgements
The project was funded by the National Science
Centre allocated on the basis of the decision No.
2011/03/B/ST8/06499.
5 REFERENCES
1 P. Karasiñski, Opt. Appl., 35 (2005), 117–128
2 J. Szewczenko, J. Jaglarz, M. Basiaga, J. Kurzyk, E. Skoczek, Prz.
Elektrot., 88 (2012) 12B, 228–231
3 A. Sadeq, Z. Cai, R. D. Woody, A. W. Miller, J. Prosth. Dent., 90
(2003) 1, 10–17, doi:10.1016/S0022-3913(03)00263-4
4 B. Surowska, J. Bieniaœ, M. Walczak, K. Sangwal, A. Stoch, Appl.
Surf. Sci., 238 (2004), 288–294, doi:10.1016/j.apsusc.2004.05.219
5 M. Basiaga, W. Walke, Z. Paszenda, P. Karasiñski, J. Szewczenko,
Biomatt., 4 (2014), 1–6, doi:10.4161/biom.28535
6 M. Basiaga, Z. Paszenda, W. Walke, P. Karasiñski, J. Marciniak, Inf.
Technol. Biomed., 284 (2014), 411–420, doi:10.1007/978-3-
319-06596-0_39
7 W. Walke, Z. Paszenda, M. Basiaga, P. Karasiñski, M. Kaczmarek,
Inf. Technol. Biomed., 284 (2014), 403–410, doi:10.1007/978-
3-319-06596-0_38
8 ASTM F2129-08 Standard Test Method for Conducting Cyclic
Potentiodynamic Polarization Measurements to Determine the
Corrosion Susceptibility of Small Implant Devices, 2008,
doi:10.1520/F2129-08
9 W. Kajzer, A. Kajzer, Prz. Elektrot., 12 (2013), 275–279
10 A. Kajzer, W. Kajzer, J. Semenowicz, A. Mroczka, Sol. St. Phen.,
227 (2015), 523–526, doi:10.4028/www.scientific.net/SSP.227.523
11 M. Kaczmarek, W. Walke, Z. Paszenda, Prze. Elektrot., 12b (2011),
74–77
12 PN-EN 1071-3. Advanced technical ceramics. Determination of
adhesion and other mechanical failure modes by a scratch test, 2007
13 EN ISO 14577-1 Metallic materials-Instrumented indentation test for
hardness and materials parameters-Part1: Test method, 2015
14 J. G³uszek, In¿. Mat., 5 (2002), 351–354
15 L. Gan, J. Wang, A. Tache, N. Valiquette, D. Deporter, R. Pilliar,
Biomat., 25 (2004), 5313–5321, doi:10.1016/j.biomaterials.2003.
12.039
16 J. Szewczenko J. Jaglarz, M. Basiaga, J. Kurzyk, Z. Paszenda, Optica
Applicata, 43 (2013) 1, 173–180, doi:10.5277/oa130121
17 Z. Paszenda, Inf. Tech. Biomed., Adv. Soft Comp., 47 (2008), 15–27,
doi:10.1007/978-3-540-68168-7_2
18 N. Kuromoto, R. Simao, G. Soares, Materials Characterization, 58
(2007), 114–121, doi:10.1016/j.matchar.2006.03.020
19 B. Yang, M. Uchida, H. M. Kim, X. Zhang, T. Kokubo, Biomat, 25
(2004), 1003–1010, doi:10.1016/S0142-9612(03)00626-4
20 H. Song, S. Park, S. Jeong, Y. Park, Journal of Mater. Proc. Techn.,
209 (2009), 864–870, doi:10.1016/j.jmatprotec.2008.02.055
M. BASIAGA et al.: THE EFFECT OF EO AND STEAM STERILIZATION ON THE MECHANICAL ...
158 Materiali in tehnologije / Materials and technology 50 (2016) 1, 153–158