The purpose of this study was to evaluate the usefulness of TiO2 layer to improve hemocompatibility of 316LVM stainless steel. The TiO2 layers studied in this work were deposited from TiCl4 and H2O in a low-pressure Atomic Layer Deposition (ALD) reactor taking into account number of cycles and process temperature. As a part of the research electrochemical studies of the layer after 28 days exposure to artificial plasma were carried out. In particular, potentiostatic, potentiodynamic and impedance studies were conducted. The obtained results were the basis for selection of surface treatment method dedicated to blood-contacting stainless steel implants

A. Hyla

D. Nakonieczny

M. Basiaga

W. Walke

English

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171METALURGIJA 56 (2017) 1-2, 171-174M. BASIAGA, W. WALKE, D. NAKONIECZNY, A HYLAPHYSIOCHEMICAL PROPERTIES OF TiO2 NANOPARTICLE THIN FILMS DEPOSITED ON STAINLESS STEELReceived – Primljeno: 2016-05-16Accepted – Prihvaćeno: 2016-10-05Preliminary Note – Prethodno priopćenjeM. Basiaga, W. Walke, D. Nakonieczny, A. Hyla Faculty of Biomedical Engineering, Silesian University of Technology, Zabrze, PolandThe purpose of this study was to evaluate the usefulness of TiO2 layer to improve hemocompatibility of 316LVM stainless steel. The TiO2 layers studied in this work were deposited from TiCl4 and H2O in a low-pressure Atomic Layer Deposition (ALD) reactor taking into account number of cycles and process temperature. As a part of the research electrochemical studies of the layer after 28 days exposure to artificial plasma were carried out. In particular, poten-tiostatic, potentiodynamic and impedance studies were conducted. The obtained results were the basis for selec-tion of surface treatment method dedicated to blood-contacting stainless steel implants.Key words: TiO2, 316LVM, ALD method, polarization, electrochemical impedance spectroscopy (EIS)INTRODUCTIONThe main problem of the use of steel 316LVM in blood-contact implants applications is the hemocompat-ibility. Currently, a lot of research is focused on improv-ing its quality by modifying the surface. The most popu-lar methods of surface modification used for medical products are chemical methods (eg. chemical passivation, sol-gel method) and electrochemical (eg. anodic oxida-tion, glow-processing) [1-3]. These methods do not pro-vide the constancy of the geometrical characteristics of the entire length of the implants and especially in their miniaturized forms (coronary stents). In this context, forward-looking method enables uniform application of the surface layer depostion is the ALD (Atomic Layer Deposition) [3-9]. This method allows for the practical use as precursors the chemical elements witch high he-mocompatibility (eg. Ti, Si, Zr, C) [4, 6]. ALD is charac-terized by sequentiality, which involves alternately intro-ducing the reagent into the process-chamber in which the film deposition takes place. Each introduction of precur-sor is followed by introduction of an inert gas (eg. nitro-gen) to remove by-products of reactions occurring in the process. In addition to the geometrical characteristics of the surface remaining unchanged deposited layers, ALD method has other advantages such as follows: reproduc-ibility, ability to deposit very thin layers at low tempera-tures range. Research executed by the authors [3, 5, 9] have shown that titanium oxide formed on the surface of implants influenced favorably the improvement of im-plants hemocompatibility. This phenomenon, in turn, had a positive impact for improving the functional properties of the implant.ISSN 0543-5846METABK 56(1-2) 171-174 (2017)UDC – UDK 669.295-541.451:669.15:541.135:612.843.1-620.197.6=111Earlier investigations of the studied authors [9] also demonstrated a favorable effect of the TiO2 layer which improves the electrochemical properties. The authors also showed the impact of application performance to the final layer quality. They clearly prove that the slayer of TiO2 deposited with ALD method in 500 cycles mode in the temperature range between 200 – 300 °C has a suitable barrier properties for Ni and Fe ions. Due to the fact that the implant stays in the body for a long period of the time, and for the first few days after implantation it is in direct contact with blood, and therefore it is ap-propriate to determine possible changes resulting sur-face layer. Hence, the authors attempted to assess the electrochemical properties TiO2 layer treated to the 28 days of exposure in conditions simulating the human blood environment. The comparison was aimed to test the stability of the layer and thus its barrier properties in human body fluids environment.MATERIAL AND METHODSFor undertaken investigations it was chosen steel 316LVM in the form of discs with an diameter d=14mm and a thickness g=2mm. Surfaces of the specimens were subjected to electrochemical polishing treatment carried out in an acid-bath containing phosphate sulfate. Polishing lasted until a surface roughness was Ra < 0,12 μm recommended for implants used in the circulatory system. In next step the samples were subjected to chemical passivation in 40 % HNO3. These two steps are the basic treatment for forming on the surface of the stainless-steel used for miniaturized geometrical im-plants. Then, for the as-prepared surface was deposited a layer of TiO2 with ALD method. TiO2 films studied in this work were grown from TiCl4 precursor and H2O in a low type low-pressure ALD reactor [4]. The deposi-172M. BASIAGA et al.: PHYSIOCHEMICAL PROPERTIES OF TiO2 NANOPARTICLE THIN FILMS DEPOSITED... METALURGIJA 56 (2017) 1-2, 171-174tion process consisted of repeated ALD cycles. Each cycle included a TiCl4 pulse, purge time, H2O pulse and another purge time. TiO2 layer was deposited at 500 cy-cles at 200 °C and 300 °C. In the last step the samples were sterilized with eth-ylene oxide. Then specimens were immersed in a solu-tion of artificial plasma at a temperature of T = 37 °C for 28 days. In order to identify the phenomena occurring at the interface and thus assess the suitability of the proposed surface modification potentiostatic, po-tentiodynamic, impedance investigations were execut-ed. In addition, samples were examined in the Scanning Electron Microscopy (SEM) and Atomic Force Micros-copy (AFM) to determine the surface topography and morphology. Tests of resistance for pitting corrosion was performed by potentiodynamic polarization curves. The test rig consisted a potentiostat (VoltaLab PGP201), reference electrode (saturated calomel electrode SCE type KP-113), the auxiliary electrode (platinum elec-trode type PtP-201), the anode (the test sample) and a PC with software (VoltaMaster). The change of the po-tential was occurred in the direction of the anode at a rate of 0,16 mV/s. to the anodic current density of 1 mA/cm2. In turn, the test of resistance to crevice corro-sion resistance was performed by potentiostatic method with the change in current density at a potential of + 800 mV at t = 15 min. The test rig in this step was the same as previous. Impedance measurements (EIS) were car-ried out using the measurement system AutoLab PG-STAT 302N provided with the module 2 FRA (Frequen-cy Response Analysis). The test rig used the same elec-trode arrangement as in corrosion tests. Impedance spectra of the test are shown in the form of a Nyquist diagrams for different frequencies (104 - 10-3 Hz) and in the form of a Bode diagrams. The voltage amplitude of the sinusoidal excitation signal was 10 mV. Obtained EIS-spectra diagrams were interpreted by the least-squares fitting to the electrical equivalent circuit. Poten-tiodynamic, potentiostatic and impedance studies was performed in an simulation environment: artificial plas-ma (chemical composition complies with the recom-mendations of the ISO-standard [10]), at temperature T = 37±1 °C and pH = 7,0 ± 0,2. Due to the significant influence on the early and late cardiac system-reactions an atomic force microscope using a non-contact mode for as-prepared surface samples was performed. The scanned area is 10 x 10mm with a resolution of 256 x 256. Additional observations was performed with scan-ning electron microscope ZEISS SUPRA 35 detector type SE (Secondary Electrons) for secondary electrons in the magnification range 1 000 – 70 000x.RESULTSPotentiodynamic studies have shown that exposure to artificial plasma has reduced resistance for the pitting corrosion regardless of the applied temperature of depo-sition process – Figure 1. Rp and Eb values were de-creased for the samples after exposure (T = 200 °C (E) - Ecorr = - 180 mV, Rp = 10 kWcm2 and Eb = + 595 mV; T = 300 °C (E) - Ecorr = - 157 mV, Rp = 17 kWcm2 and Eb = + 624 mV) relative to the baseline (T = 200 °C - Ecorr = - 214 mV, Rp = 415 kWcm2 and Eb = + 1 584 mV; T = 300 ° C - Ecorr = - 138 mV, Rp = 276 kWcm2 and Eb = + 1 608 mV). The TiO2 barrier layer after exposure in the plasma was not well resistant also to crevice corro-sion - Figure 2. The presence of the double layer (porous) with low electrochemical properties (Rpore) have been also con-firmed in impedance studies (EIS) - Table 1, Figure 3Prepared layer was characterized by a large surface development which could cause penetration of metal ions and also a small chemical stability. In turn, the sub-layers formed during the application of TiO2 by ALD method is characterized by a high resistance for corro-sion which contributed to the high value of the charge transfer resistance Rct. This value has also increased as a result of the impact of artificial plasma which can be Figure 1  Polarization curves of samples with a layer of TiO2 before and after 28 day exposure in artificial plasma solutionFigure 2  Potentiostatic curves determined on a modified surface of steel 316LVM173M. BASIAGA et al.: PHYSIOCHEMICAL PROPERTIES OF TiO2 NANOPARTICLE THIN FILMS DEPOSITED...METALURGIJA 56 (2017) 1-2, 171-174associated with the reconstruction of the TiO2. In addi-tion, it was also found that the 28 day exposure tests did not affect the morphology and topography of the sur-face compared to the initial state - Figure 4.CONCLUSIONSPerformed electrochemical studies showed no sig-nificant differences between the used depostion process temperature (T = 200 °C – 300 °C). Obtained in the voltamperometric studies results shows the negative impact of artificial plasma to corrosion resistance of de-posited layers. Regardless from the process temperature TiO2 layer during exposure underwent rebuild, thereby causing the appearance on the surface of the additional porous layer with low chemical stability. This layer is characterized by low resistance to corrosion in contact with the artificial plasma. On the other hand sublayers of TiO2 as a result of ongoing reaction surface does not deteriorate its barrier properties – Table 1.AcknowledgementsThe project was funded by the National Science Centre allocated on the basis of the decision No. 2014/13/D/ST8/03230REFERENCES[1] W. Walke, Z. Paszenda, M. Basiaga, P. Karasiński, M. Kaczmarek, EIS study of SiO2 Oxide Film on 316L stainless steel for cardiac implants Information Technolo-gies in Biomedicine. Advances in Intelligent Systems and Computing 284. Springer (2014) 403-410[2] A. Kajzer, W. Kajzer, J. Dzielicki, D. Matejczyk, The stu-dy of physicochemical properties of stabilizing plates re-moved from the body after treatment of pectus excavatum. Acta of Bioengineering and Biomechanics 2 (2015) 35-44[3] C.X. Shan, X. Hou, K.-L. Choy, Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposi-tion. Surface & Coatings Technology 202 (2008) 2399-2402[4] L. Aari et al., Atomic layer deposition of TiO2 from TiCl4 and O3. Thin Solid Films 542 (2013) 100-107.[5] D. Siva, Rama Krishna, Y. Sun, Thermally oxidised rutile-TiO2 coating on stainless steel for tribological properties and corrosion resistance enhancement. Applied Surface Science 252 (2005) 1107-1121[6] E. Marin et al., Chemical and mechanical characterization of TiO2/Al2O3 atomic layer depositions on AISI 316 L Table 1 EIS analysis resultsTemperature of process EOCP/ mV Rs/ Ωcm2 Rpore/ kΩcm2CPEpore Rct/ MΩcm2CPEdlY0/ Ω-1cm−2s−n n Ydl/ Ω-1cm−2s−n ndlBefore 28 days exposure200 °C - 268 27 15 0,8268 E-5 0,96 43 0,2002 E-4 0,81300 °C - 227 26 65 0,2328 E-4 0,98 7 0,4322 E-5 0,85After 28 days exposure200 °C - E - 340 27 30 0,1737 E-4 0,86 140 0,8621 E-5 0,86300 °C - E - 475 26 42 0,8225 E-4 0,72 86 0,4873 E-5 0,93Figure 3  Impedance spectra for the modified surface of steel 316LVM: a) Nyquist diagram, b) Bode diagramFigure 4  The morphology and topography of the surface after 28 days exposure, for the layer deposited at T = 200 °C174M. BASIAGA et al.: PHYSIOCHEMICAL PROPERTIES OF TiO2 NANOPARTICLE THIN FILMS DEPOSITED... METALURGIJA 56 (2017) 1-2, 171-174stainless steel. Surface and Coatings Technology 211 25 (2012) 84-88[7] L. Avril et al., TiO2 anatase films obtained by direct liquid injection atomic layer deposition at low temperature. Ap-plied Surface Science 288 1 (2014) 201-207[8] M. R. Saleem, P. Silfsten, S. Honkanen, J. Turunen, Ther-mal properties of TiO2 films grown by atomic layer depo-sition. Thin Solid Films 520 (2012) 5442-5446[9] M. Basiaga, R. Jendruś, W. Walke, Z. Paszenda, M. Kaczmarek, M. Popczyk, Influence of surface modifica-tion on properties of stainless steel used for implants. Ar-chives of Metallurgy and Materials 60 4 (2015) 2965-2969[10] Standard: ASTM F2129 - Electrochemical Corrosion Te-sting of Surgical Implants (Standard Test Method for Con-ducting Cyclic Potentiodynamic PolarizationNote:  The responsible translator for English language is Iwona Bąbel (Learning Center – Future), Poland

Physiochemical properties of TiO2 nanoparticle thin films deposited on stainless steel

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Physiochemical properties of TiO2 nanoparticle thin films deposited on stainless steel

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