- Email: [email protected]
Improvement of the biocompatibility and mechanical properties of surgical tools with TiN coating by PACVD
Thin Solid Films 435 (2003) 102–107
Improvement of the biocompatibility and mechanical properties of surgical tools with TiN coating by PACVD Jeongwon Parka,*, Duk-Jae Kima, Yoon-Kee Kima, Keun-Ho Leea, Ki-Hoon Leeb, Hoon Leec, Saeyoung Ahnc a
Plasma Technology Center, Institute for Advanced Engineering, Yongin P.O. Box 25, Kyonggi-Do 449-860, South Korea b Plasma Systems and Materials Co. Ltd, Yongin P.O. Box 25, Kyunggi-Do 449-860, South Korea c Solco Biomedical, 34-6, Kumam-ri, Seotan-myun, Pyungtaik, Kyonggi-Do 451-850, South Korea
Abstract TiN film has been applied for medical cutting tools to improve the mechanical properties such as surface hardness and wear resistance, and also to provide the biocompatible property of the surgical tools. TiN film has been deposited by using a plasmaassisted chemical vapor deposition system. Bipolar-pulsed DC discharge has been used for optimal plasma discharge condition, and the gas mixture of TiCl4, N2, H2 and Ar has been used. TiN layer enhanced the surface hardness of 2000 kgymm2 HK0.01 and the corrosion property of the film. The corrosion resistance of TiN films has been estimated using Hank’s solution and the corrosion rates of bare stainless steel substrate and the specimen coated with TiN were 1300 and 66 nAycm2, respectively. TiN film also shows a good biocompatibility in the standard cytotoxicity test (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), which is the normal method for ensuring the biocompatibility of a medical tool. In the standard cytotoxicity test, we obtained an excellent characteristic of biocompatibility from the medical tool coated with TiN layer. This means that the TiN-coated specimen is free of harmful extractables or has not much of them to cause any acute effects even under exaggerated conditions with isolated cells. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: PACVD; TiN; Biocompatibility; Surgical tools; Corrosion resistance; Cytotoxicity
1. Introduction Recently various surface coating technologies have been performed to enhance the important functional properties such as lubricity, biocompatibility and antimicrobial effect for medical devices and surgical tools w1–6x. Stainless steels are still well known materials for medical tools due to their reasonably good mechanical properties as well as good corrosion resistance. However, this material has proven to be relatively poor corrosion resistive in Hank’s solution and the surface hardness is relatively low compared to Ti and its alloys. Advanced biomaterials should possess several required properties such as excellent fatigue and tensile strength, superior corrosion and wear resistance, good hardness and an effective biocompatible property w7–12x. In this study, we investigated various mechanical properties and biocompatible effects of plasma-assisted chemical vapor *Corresponding author. E-mail address: [email protected] (J. Park).
deposition (PACVD) TiN layer with the deposition condition for surgical tools. TiN layers have been deposited on the surface of surgical tools with various gas ratios of N and TiCl4 and bipolar discharge pulse (q550 V, y550 V) and unipolar discharge pulse (y550 V, 0 V) were used as an input power. 2. Experimentals TiN film has been deposited on the surgical tools using PACVD (PlaTeg Co.) which has been already described in detail elsewhere w1x. The deposition temperature was 500 8C and negative bias voltage was fixed at 550 V during the unipolar-pulsed (y550 V, 0 V) plasma discharge process for 4 h. In the bipolar process, negative and positive voltages are fixed at y550 and 550 V, respectively. Auxiliary heaters set inside chamber walls heated the specimen, and the temperature was measured by thermocouples. The working gases were led into the chamber from the gas bottle, and controlled by mass-flow controller (MFC). TiCl4 was used as
0040-6090/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090Ž03.00412-7
J. Park et al. / Thin Solid Films 435 (2003) 102–107 Table 1 Composition of Hank’s solution used in the experiment Components
Gram
Components
Gram
Water NaCl Na2HPO4Ø2H2O MgSO4Ø7H2O
1000 ml 8.00 g 0.06 g 0.20 g
CaCl2 KCl KH2PO4 NaHCO3
0.14 0.4 0.06 0.35
precursor and led into the reactor by the nitrogen carrier gas, and TiCl4 was controlled by MFC in the unit of gramyhour. The thickness of TiN layer was measured by using scanning electron microscopy (SEM). The crystallographic phases of the TiN films were determined by X-ray diffraction (XRD) using monochromatized Cu Ka radiation (40 kV, 40 mA) using a Siemens D5000. X-ray photoelectron spectroscope (XPS, Physical Electronics PHI 5700 ESCA System) and Auger spectroscopy were used to determine the surface elemental distributions and the chemical compositions of the films. The toughness of coated layers could be gained by performing scratch tests and the load was continuously increased up to 100 N at a loading rate of 10 Nymin. To measure the coating fracture toughness of the layers, acoustic emission (AE) was utilized to detect the load at the first coating fracture. The surface hardness was measured by Knoop hardness mode of micro-hardness tester with 10-g force during 10 s. The corrosion tests were carried out after masking with silicon sealant. The exposure area of the corrosion test was 0.2 cm2. The electrode cell was equipped with a platinum counter electrode and a saturated calomel electrode (SCE). All electrode potentials are referred to the SCE scale in Hank’s solution at room temperature. Table 1 shows the composition of Hank’s solution used
103
in these experiments and the sweep rate setting was 1 mVys. In standard cytotoxicity tests (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), cell monolayers are grown to near confluence in flasks and are then exposed to test or control articles directly or indirectly by means of fluid extracts. In the elution test, which is widely used, extracts are obtained by placing the test and control materials in separate cell culture media under standard conditions (for example, 3 cm2 or 0.2 gyml of culture medium for 24 h at 37 8C). Each fluid extract obtained is then applied to a cultured-cell monolayer, replacing the medium that had nourished the cells to that point. In this way, test cells are supplied with a fresh nutrient medium containing extractables derived from the test article or control. The cultures are then returned to the 37 8C incubator and periodically removed for microscopic examination at designated times for as long as 3 days. Cells are observed for visible signs of toxicity such as a change in the size, appearance of cellular components, and a disruption in their configuration in response to the test and control materials. 3. Results and discussions 3.1. XRD analysis Fig. 1 shows the XRD analyses of phase compositions depending on the gas rates of TiCl4, 3, 5 and 7 gyh, respectively. The deposition temperature was 500 8C and negative bias voltage was fixed at y550 V during the unipolar pulse discharge process. As shown in Fig. 1, phase transition in films was observed and main peaks are TiN (1 1 1), TiN (2 0 0) and TiN (2 2 0). Those TiN peak intensity have been maximized at 3 gy
Fig. 1. XRD patterns of the TiN films as a function of the TiCl4 gas flow ratio at unipolar plasma voltage (y550 V).
J. Park et al. / Thin Solid Films 435 (2003) 102–107
104
Fig. 2. XRD patterns of the TiN films with different plasma power source at 3 gyh TiCl4 rate.
h of TiCl4 gas rate. This means that gas rate of 3 gyh of TiCl4 is the best-designed gas parameter for an optimized plasma discharge condition for TiN coating process using this PACVD system. Fig. 2 shows XRD patterns from TiN films deposited using different types of power source such as bipolar pulse discharge (q550 V, y550 V) and unipolar pulse discharge (y550 V) at 500 8C. The relative intensity of (1 1 1) and (2 0 0) peaks is much bigger when using a bipolar pulse power source. This may be due to the fact that the crystallography of TiN film is pretty much depending on the mode of plasma power source. This means that the movement of the active particles using a bipolar power source is much favorable for the oriented growth mechanism of TiN film due to the alternative change of electric field near the sample substrate.
3.3. X-SEM morphology, scratch test and surface hardness test The thickness of TiN layer is 1.6 mm from the SEM image in Fig. 5a. We can see in Fig. 5b that the AE signal after the critical load for PACVD TiN on stainless steel changes at 71 N rapidly, which is relatively higher than that of PVD TiN films w3,4x. Higher ion energy and flux density of ionized titanium and nitrogen species generated by PACVD process produce stronger chemical adsorption on the surface compared to the PVD process, which improve the adhesion. Also, we obtained 2000 kgymm2 HK0.01 of the surface hardness by Knoop hardness mode of micro-hardness tester with 10-g force during 10 s. 3.4. Corrosion test
3.2. XPS and Auger spectra analysis In order to investigate the chemical composition of the deposited TiN-coated layers, XPS and Auger spectroscopy were used. Fig. 3 shows XPS survey spectra of the TiN film at bipolar pulse discharge and 3 gyh TiCl4 gas rate. The carbon and oxygen contaminants are detected only on the surface of the TiN film. The chemical composition of the TiN layers is very uniform throughout the depth. The chemical concentrations of Ti, N and Cl are 52.0, 43.7 and 4.3 at.%, respectively, as shown in Fig. 4. Titanium content is slightly richer than nitrogen content in TiN-coated layer as previous reports w13x.
The corrosion resistance of sample coated with TiN using PACVD after plasma nitride process has been measured and compared with that of untreated material. In deaerated Hank’s solution at 20 8C, potentiodynamic measurements generated a family of polarization curves of potential (relative to SCE) vs. current density, as presented in Fig. 6. The results of corrosion potential (Ecorr) and corrosion rate (Icorr) from polarization curves are given in Table 2. In the comparison with the corrosion potential (Ecorr) of the bare stainless steel substrate (y820 mVSCE), Ecorr was clearly increased by applying the TiN coating, reaching y350 mVSCE. Corrosion current density is commonly utilized as an important parameter to evaluate the kinetics of corrosion
J. Park et al. / Thin Solid Films 435 (2003) 102–107
105
Fig. 3. XPS depth-concentration profiles of the TiN film at bipolar pulse discharge and 3 gyh TiCl4 gas rate. (a) Ti 2p; (b) N 1s; (c) Cl 2p; (d) C 1s.
reactions. The corrosion rate is normally proportional to the corrosion current density measured through polarization. In this study, the bare stainless steel substrate corroded (dissolved) far more quickly than PACVD TiN-coated specimen. The corrosion rate of bare stainless steel substrate and TiN-coated specimen are 1300 and 66 nAycm2, respectively.
obtained optimized XRD peaks of TiN (2 0 0), TiN (1 1 1) and TiN (2 2 0) at 3 gyh of TiCl4 gas rate. The relative intensity of those peaks using a bipolar pulse discharge power source is much bigger than using a unipolar-pulsed discharge source. This indicated that the
3.5. Cytotoxicity test The biocompatibility of PACVD TiN-coated sample has been determined from the results of cytotoxicity test at Korean Test Laboratory. Cytotoxicity test provides a reasonably good possibility for ensuring the biocompatibility of the samples. In standard cytotoxicity test methods (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), we obtained a negative cytotoxicity properties as shown in Table 3. It indicates that a material is free of harmful extractables or has not much of them to cause acute effects even under exaggerated conditions with isolated cells. 4. Conclusions TiN film properties have been examined using XRD, SEM, AES and Hank’s solution corrosion test. We
Fig. 4. Auger depth-concentration profiles of the TiN film at bipolar pulse discharge and 3 gyh TiCl4 gas rate.
106
J. Park et al. / Thin Solid Films 435 (2003) 102–107 Table 2 Comparison of the electrochemical parameters of samples determined from the polarization curves
Bare stainless steel substrates PACVD TiN
Fig. 5. (a) Cross-sectional SEM image from TiN film grown by PACVD and (b) AE curve generated during scratch test of TiN-coated sample (at bipolar-pulsed discharge and TiCl4 gas: 3 gyh).
Corrosion potential Ecorr (mV)
Corrosion rate Icorr (nAycm2)
y820 y350
1300 66
crystallography of TiN film much depends on the mode of plasma power source. The chemical concentrations of the film were 52.0 at.% of Ti, 43.7 at.% of N and 4.3 at.% of Cl, respectively. The chemical composition of TiN film according to the depth of the film was very uniform and 4.3 at.% of Cl content was not affected by the corrosion property of the film. For thickness of 1.6 mm of TiN film, AE signal was observed at 71 N. This interface bonding strength of the TiN layer is reasonably high compared to the TiN film deposited using PVD. In this study, the corrosion rate of bare stainless steel substrate and TiN-coated specimen are observed at 1300 and 66 nAycm2, respectively. The corrosion property of TiN layers are expected to be much higher than that of untreated stainless steels. Testing for cytotoxicity is a relatively reasonable step toward ensuring the biocompatibility of a medical device. In standard cytotoxicity test methods (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), we obtained a negative cytotoxicity, which means that TiN layer is free of harmful extractables or has not much of them to cause acute effects under exaggerated conditions with isolated cells. These results indicate that TiN layers are believed to provide practical improvements of biocompatibility for surgical tools. However, it is certainly not enough evidence that a material can be considered as perfect biocompatible.
Fig. 6. Polarization curves of the samples in deaerated Hank’s solution at 20 8C.
J. Park et al. / Thin Solid Films 435 (2003) 102–107
107
Table 3 The result of cytotoxicity (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods)
Sample (1) Sample (2) Sample (3) Negative counter sample (1) Negative counter sample (2) Negative counter sample (3) a
State of cell monolayera
Cell of nonintracytoplasmic granules (%)
Changed to rounded cell (%)
Cell lyses (%)
Grade (%)
Reactivity
(q) (q) (q) (q) (q) (q)
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
None None None None None None
(q), perfect; (y), imperfect.
Therefore further investigation should be considered for the practical application of the material. References w1 x w2 x w3 x w4 x w5 x
D.-J. Kim, Surf. Coat. Technol. 116–119 (1999) 906–910. S.R. Bradbury, Vacuum 56 (2000) 173–177. L. Hultman, Vacuum 57 (2000) 1–30. R. Gunzel, Surf. Coat. Technol. 142–144 (2001) 978–983. S. Xiao, Thin Solid Films 334 (1998) 173–177.
I. Efeoglu, Mater. Charact. 46 (2001) 311–316. T.A. Beer, Surf. Coat. Technol. 120–121 (1999) 238–243. H.-H. Huang, J. Cryst. Growth 225 (2001) 540–543. S. Ma, Surf. Coat. Technol. 142–144 (2001) 1023–1027. H.K. Tonshoff, Surf. Coat. Technol. 116–119 (1999) 524–529. D.-H. Kuo, Surf. Coat. Technol. 135 (2001) 150–157. R.I. Masel, Principles of Adsorption and Reaction on Solid Surfaces, John Wiley & Sons, Inc, New York, 1996, pp. 108–234. w13x M. Nordin, M. Larsson, Surf. Coat. Technol. 116–119 (1999) 108–115.
w6 x w7 x w8 x w9 x w10x w11x w12x
Improvement of the biocompatibility and mechanical properties of surgical tools with TiN coating by PACVD Jeongwon Parka,*, Duk-Jae Kima, Yoon-Kee Kima, Keun-Ho Leea, Ki-Hoon Leeb, Hoon Leec, Saeyoung Ahnc a
Plasma Technology Center, Institute for Advanced Engineering, Yongin P.O. Box 25, Kyonggi-Do 449-860, South Korea b Plasma Systems and Materials Co. Ltd, Yongin P.O. Box 25, Kyunggi-Do 449-860, South Korea c Solco Biomedical, 34-6, Kumam-ri, Seotan-myun, Pyungtaik, Kyonggi-Do 451-850, South Korea
Abstract TiN film has been applied for medical cutting tools to improve the mechanical properties such as surface hardness and wear resistance, and also to provide the biocompatible property of the surgical tools. TiN film has been deposited by using a plasmaassisted chemical vapor deposition system. Bipolar-pulsed DC discharge has been used for optimal plasma discharge condition, and the gas mixture of TiCl4, N2, H2 and Ar has been used. TiN layer enhanced the surface hardness of 2000 kgymm2 HK0.01 and the corrosion property of the film. The corrosion resistance of TiN films has been estimated using Hank’s solution and the corrosion rates of bare stainless steel substrate and the specimen coated with TiN were 1300 and 66 nAycm2, respectively. TiN film also shows a good biocompatibility in the standard cytotoxicity test (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), which is the normal method for ensuring the biocompatibility of a medical tool. In the standard cytotoxicity test, we obtained an excellent characteristic of biocompatibility from the medical tool coated with TiN layer. This means that the TiN-coated specimen is free of harmful extractables or has not much of them to cause any acute effects even under exaggerated conditions with isolated cells. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: PACVD; TiN; Biocompatibility; Surgical tools; Corrosion resistance; Cytotoxicity
1. Introduction Recently various surface coating technologies have been performed to enhance the important functional properties such as lubricity, biocompatibility and antimicrobial effect for medical devices and surgical tools w1–6x. Stainless steels are still well known materials for medical tools due to their reasonably good mechanical properties as well as good corrosion resistance. However, this material has proven to be relatively poor corrosion resistive in Hank’s solution and the surface hardness is relatively low compared to Ti and its alloys. Advanced biomaterials should possess several required properties such as excellent fatigue and tensile strength, superior corrosion and wear resistance, good hardness and an effective biocompatible property w7–12x. In this study, we investigated various mechanical properties and biocompatible effects of plasma-assisted chemical vapor *Corresponding author. E-mail address: [email protected] (J. Park).
deposition (PACVD) TiN layer with the deposition condition for surgical tools. TiN layers have been deposited on the surface of surgical tools with various gas ratios of N and TiCl4 and bipolar discharge pulse (q550 V, y550 V) and unipolar discharge pulse (y550 V, 0 V) were used as an input power. 2. Experimentals TiN film has been deposited on the surgical tools using PACVD (PlaTeg Co.) which has been already described in detail elsewhere w1x. The deposition temperature was 500 8C and negative bias voltage was fixed at 550 V during the unipolar-pulsed (y550 V, 0 V) plasma discharge process for 4 h. In the bipolar process, negative and positive voltages are fixed at y550 and 550 V, respectively. Auxiliary heaters set inside chamber walls heated the specimen, and the temperature was measured by thermocouples. The working gases were led into the chamber from the gas bottle, and controlled by mass-flow controller (MFC). TiCl4 was used as
0040-6090/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090Ž03.00412-7
J. Park et al. / Thin Solid Films 435 (2003) 102–107 Table 1 Composition of Hank’s solution used in the experiment Components
Gram
Components
Gram
Water NaCl Na2HPO4Ø2H2O MgSO4Ø7H2O
1000 ml 8.00 g 0.06 g 0.20 g
CaCl2 KCl KH2PO4 NaHCO3
0.14 0.4 0.06 0.35
precursor and led into the reactor by the nitrogen carrier gas, and TiCl4 was controlled by MFC in the unit of gramyhour. The thickness of TiN layer was measured by using scanning electron microscopy (SEM). The crystallographic phases of the TiN films were determined by X-ray diffraction (XRD) using monochromatized Cu Ka radiation (40 kV, 40 mA) using a Siemens D5000. X-ray photoelectron spectroscope (XPS, Physical Electronics PHI 5700 ESCA System) and Auger spectroscopy were used to determine the surface elemental distributions and the chemical compositions of the films. The toughness of coated layers could be gained by performing scratch tests and the load was continuously increased up to 100 N at a loading rate of 10 Nymin. To measure the coating fracture toughness of the layers, acoustic emission (AE) was utilized to detect the load at the first coating fracture. The surface hardness was measured by Knoop hardness mode of micro-hardness tester with 10-g force during 10 s. The corrosion tests were carried out after masking with silicon sealant. The exposure area of the corrosion test was 0.2 cm2. The electrode cell was equipped with a platinum counter electrode and a saturated calomel electrode (SCE). All electrode potentials are referred to the SCE scale in Hank’s solution at room temperature. Table 1 shows the composition of Hank’s solution used
103
in these experiments and the sweep rate setting was 1 mVys. In standard cytotoxicity tests (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), cell monolayers are grown to near confluence in flasks and are then exposed to test or control articles directly or indirectly by means of fluid extracts. In the elution test, which is widely used, extracts are obtained by placing the test and control materials in separate cell culture media under standard conditions (for example, 3 cm2 or 0.2 gyml of culture medium for 24 h at 37 8C). Each fluid extract obtained is then applied to a cultured-cell monolayer, replacing the medium that had nourished the cells to that point. In this way, test cells are supplied with a fresh nutrient medium containing extractables derived from the test article or control. The cultures are then returned to the 37 8C incubator and periodically removed for microscopic examination at designated times for as long as 3 days. Cells are observed for visible signs of toxicity such as a change in the size, appearance of cellular components, and a disruption in their configuration in response to the test and control materials. 3. Results and discussions 3.1. XRD analysis Fig. 1 shows the XRD analyses of phase compositions depending on the gas rates of TiCl4, 3, 5 and 7 gyh, respectively. The deposition temperature was 500 8C and negative bias voltage was fixed at y550 V during the unipolar pulse discharge process. As shown in Fig. 1, phase transition in films was observed and main peaks are TiN (1 1 1), TiN (2 0 0) and TiN (2 2 0). Those TiN peak intensity have been maximized at 3 gy
Fig. 1. XRD patterns of the TiN films as a function of the TiCl4 gas flow ratio at unipolar plasma voltage (y550 V).
J. Park et al. / Thin Solid Films 435 (2003) 102–107
104
Fig. 2. XRD patterns of the TiN films with different plasma power source at 3 gyh TiCl4 rate.
h of TiCl4 gas rate. This means that gas rate of 3 gyh of TiCl4 is the best-designed gas parameter for an optimized plasma discharge condition for TiN coating process using this PACVD system. Fig. 2 shows XRD patterns from TiN films deposited using different types of power source such as bipolar pulse discharge (q550 V, y550 V) and unipolar pulse discharge (y550 V) at 500 8C. The relative intensity of (1 1 1) and (2 0 0) peaks is much bigger when using a bipolar pulse power source. This may be due to the fact that the crystallography of TiN film is pretty much depending on the mode of plasma power source. This means that the movement of the active particles using a bipolar power source is much favorable for the oriented growth mechanism of TiN film due to the alternative change of electric field near the sample substrate.
3.3. X-SEM morphology, scratch test and surface hardness test The thickness of TiN layer is 1.6 mm from the SEM image in Fig. 5a. We can see in Fig. 5b that the AE signal after the critical load for PACVD TiN on stainless steel changes at 71 N rapidly, which is relatively higher than that of PVD TiN films w3,4x. Higher ion energy and flux density of ionized titanium and nitrogen species generated by PACVD process produce stronger chemical adsorption on the surface compared to the PVD process, which improve the adhesion. Also, we obtained 2000 kgymm2 HK0.01 of the surface hardness by Knoop hardness mode of micro-hardness tester with 10-g force during 10 s. 3.4. Corrosion test
3.2. XPS and Auger spectra analysis In order to investigate the chemical composition of the deposited TiN-coated layers, XPS and Auger spectroscopy were used. Fig. 3 shows XPS survey spectra of the TiN film at bipolar pulse discharge and 3 gyh TiCl4 gas rate. The carbon and oxygen contaminants are detected only on the surface of the TiN film. The chemical composition of the TiN layers is very uniform throughout the depth. The chemical concentrations of Ti, N and Cl are 52.0, 43.7 and 4.3 at.%, respectively, as shown in Fig. 4. Titanium content is slightly richer than nitrogen content in TiN-coated layer as previous reports w13x.
The corrosion resistance of sample coated with TiN using PACVD after plasma nitride process has been measured and compared with that of untreated material. In deaerated Hank’s solution at 20 8C, potentiodynamic measurements generated a family of polarization curves of potential (relative to SCE) vs. current density, as presented in Fig. 6. The results of corrosion potential (Ecorr) and corrosion rate (Icorr) from polarization curves are given in Table 2. In the comparison with the corrosion potential (Ecorr) of the bare stainless steel substrate (y820 mVSCE), Ecorr was clearly increased by applying the TiN coating, reaching y350 mVSCE. Corrosion current density is commonly utilized as an important parameter to evaluate the kinetics of corrosion
J. Park et al. / Thin Solid Films 435 (2003) 102–107
105
Fig. 3. XPS depth-concentration profiles of the TiN film at bipolar pulse discharge and 3 gyh TiCl4 gas rate. (a) Ti 2p; (b) N 1s; (c) Cl 2p; (d) C 1s.
reactions. The corrosion rate is normally proportional to the corrosion current density measured through polarization. In this study, the bare stainless steel substrate corroded (dissolved) far more quickly than PACVD TiN-coated specimen. The corrosion rate of bare stainless steel substrate and TiN-coated specimen are 1300 and 66 nAycm2, respectively.
obtained optimized XRD peaks of TiN (2 0 0), TiN (1 1 1) and TiN (2 2 0) at 3 gyh of TiCl4 gas rate. The relative intensity of those peaks using a bipolar pulse discharge power source is much bigger than using a unipolar-pulsed discharge source. This indicated that the
3.5. Cytotoxicity test The biocompatibility of PACVD TiN-coated sample has been determined from the results of cytotoxicity test at Korean Test Laboratory. Cytotoxicity test provides a reasonably good possibility for ensuring the biocompatibility of the samples. In standard cytotoxicity test methods (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), we obtained a negative cytotoxicity properties as shown in Table 3. It indicates that a material is free of harmful extractables or has not much of them to cause acute effects even under exaggerated conditions with isolated cells. 4. Conclusions TiN film properties have been examined using XRD, SEM, AES and Hank’s solution corrosion test. We
Fig. 4. Auger depth-concentration profiles of the TiN film at bipolar pulse discharge and 3 gyh TiCl4 gas rate.
106
J. Park et al. / Thin Solid Films 435 (2003) 102–107 Table 2 Comparison of the electrochemical parameters of samples determined from the polarization curves
Bare stainless steel substrates PACVD TiN
Fig. 5. (a) Cross-sectional SEM image from TiN film grown by PACVD and (b) AE curve generated during scratch test of TiN-coated sample (at bipolar-pulsed discharge and TiCl4 gas: 3 gyh).
Corrosion potential Ecorr (mV)
Corrosion rate Icorr (nAycm2)
y820 y350
1300 66
crystallography of TiN film much depends on the mode of plasma power source. The chemical concentrations of the film were 52.0 at.% of Ti, 43.7 at.% of N and 4.3 at.% of Cl, respectively. The chemical composition of TiN film according to the depth of the film was very uniform and 4.3 at.% of Cl content was not affected by the corrosion property of the film. For thickness of 1.6 mm of TiN film, AE signal was observed at 71 N. This interface bonding strength of the TiN layer is reasonably high compared to the TiN film deposited using PVD. In this study, the corrosion rate of bare stainless steel substrate and TiN-coated specimen are observed at 1300 and 66 nAycm2, respectively. The corrosion property of TiN layers are expected to be much higher than that of untreated stainless steels. Testing for cytotoxicity is a relatively reasonable step toward ensuring the biocompatibility of a medical device. In standard cytotoxicity test methods (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), we obtained a negative cytotoxicity, which means that TiN layer is free of harmful extractables or has not much of them to cause acute effects under exaggerated conditions with isolated cells. These results indicate that TiN layers are believed to provide practical improvements of biocompatibility for surgical tools. However, it is certainly not enough evidence that a material can be considered as perfect biocompatible.
Fig. 6. Polarization curves of the samples in deaerated Hank’s solution at 20 8C.
J. Park et al. / Thin Solid Films 435 (2003) 102–107
107
Table 3 The result of cytotoxicity (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods)
Sample (1) Sample (2) Sample (3) Negative counter sample (1) Negative counter sample (2) Negative counter sample (3) a
State of cell monolayera
Cell of nonintracytoplasmic granules (%)
Changed to rounded cell (%)
Cell lyses (%)
Grade (%)
Reactivity
(q) (q) (q) (q) (q) (q)
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
None None None None None None
(q), perfect; (y), imperfect.
Therefore further investigation should be considered for the practical application of the material. References w1 x w2 x w3 x w4 x w5 x
D.-J. Kim, Surf. Coat. Technol. 116–119 (1999) 906–910. S.R. Bradbury, Vacuum 56 (2000) 173–177. L. Hultman, Vacuum 57 (2000) 1–30. R. Gunzel, Surf. Coat. Technol. 142–144 (2001) 978–983. S. Xiao, Thin Solid Films 334 (1998) 173–177.
I. Efeoglu, Mater. Charact. 46 (2001) 311–316. T.A. Beer, Surf. Coat. Technol. 120–121 (1999) 238–243. H.-H. Huang, J. Cryst. Growth 225 (2001) 540–543. S. Ma, Surf. Coat. Technol. 142–144 (2001) 1023–1027. H.K. Tonshoff, Surf. Coat. Technol. 116–119 (1999) 524–529. D.-H. Kuo, Surf. Coat. Technol. 135 (2001) 150–157. R.I. Masel, Principles of Adsorption and Reaction on Solid Surfaces, John Wiley & Sons, Inc, New York, 1996, pp. 108–234. w13x M. Nordin, M. Larsson, Surf. Coat. Technol. 116–119 (1999) 108–115.
w6 x w7 x w8 x w9 x w10x w11x w12x