1. Corrosion behavior of nickel–titanium continuous-casted alloysMinja Miličić Lazić, Dijana Mitić, Katarina Radović, Igor Djordjević, Peter Majerič, Rebeka Rudolf, Branimir Grgur, 2024, izvirni znanstveni članek Opis: Variations in the corrosion behavior of biomedical NiTi alloys in Cl− containing and acidic
environments present a problem with their biological implantation. The objective of this research
was to evaluate the synergy of the microstructure, the corrosion behavior, and the biocompatibility of
novel continuous-cast NiTi alloys and to compare them with commercial NiTi alloys. The two alloys
have a practically identical nominal chemical composition, but they differ in production technology.
The continuous casting technology involved vacuum induction melting of the basic components
and vertical continuous casting, while the commercial NiTi alloy was produced through a process of
casting, hot rolling, and forming into square shapes. The microstructure was revealed to determine
the surface area and size of grains. The corrosion of a commercial nickel–titanium alloy and one
prepared by a novel continuous casting method in acidic and chloride-containing solutions was
studied via analytical and electrochemical tests. Localized corrosion characteristics related to oxide
properties, when exposed to 9 g L−1 NaCl solution, were examined with focused ion beam analysis
and subsequent microchemical analysis of the formed corrosive products. Corrosion potential over
time and the oxide film resistance were analyzed using linear polarization measurements. To obtain
a preliminary estimate of biocompatibility, human fibroblast cells were used in indirect contact,
i.e., alloy conditioning medium. The continuous casting method resulted in a reduction in the
average grain size in comparison to the commercial sample and better corrosion stability of the
sample in an acidic environment. Also, in a solution of 9 g L−1 NaCl the commercial sample showed
high values for the corrosion current density (jcorr = 6 µA cm−2), which indicated low corrosion
resistance, while the continuous casting sample possessed much better corrosion stability and lower
values for the corrosion current density (jcorr = 0.2 µA cm−2). In line with that, elemental analysis of
the corroded surfaces showed higher Cl− ion deposition over the surface layer of the commercial
sample, suggesting local oxide breakdown. Moreover, NiTicc reached a value three times higher
for polarization resistance (Rp = 270 kΩ cm2) over time in comparison to the commercial sample
(Rp~100 kΩ cm2). Biocompatibility evaluation showed that human fibroblast cells exhibited altered
metabolic activity. An MTT assay showed that cells’ mitochondrial activity dropped below that of
control cells in the presence of both materials’ supernatants.
Ključne besede: nickel–titanium, corosion behaviour, electrochemical testing, NiTi biocompatibility
Objavljeno v DKUM: 30.06.2025; Ogledov: 0; Prenosov: 7
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2. Experimental investigation of the biofunctional properties of nickel–titanium alloys depending on the type of productionMinja Miličić Lazić, Peter Majerič, Vojkan Lazić, Jelena Milašin, Milica Jakšić, Dijana Trišić, Katarina Radović, 2022, izvirni znanstveni članek Opis: Nickel–titanium alloys used in dentistry have a variety of mechanical, chemical, and
biofunctional properties that are dependent on the manufacturing process. The aim of this study
was to compare the mechanical and biofunctional performances of a nickel–titanium alloy produced
by the continuous casting method (NiTi-2) with commercial nitinol (NiTi-1) manufactured by the
classical process, i.e., from remelting in a vacuum furnace with electro-resistive heating and final
casting into ingots. The chemical composition of the tested samples was analyzed using an energy
dispersive X-ray analysis (EDX) and X-ray fluorescence (XRF). Electron backscatter diffraction (EBSD)
quantitative microstructural analysis was performed to determine phase distribution in the samples.
As part of the mechanical properties, the hardness on the surface of samples was measured with
the static Vickers method. The release of metal ions (Ni, Ti) in artificial saliva (pH 6.5) and lactic
acid (pH 2.3) was measured using a static immersion test. Finally, the resulting corrosion layer was
revealed by means of a scanning electron microscope (SEM), which allows the detection and direct
measurement of the formatted oxide layer thickness. To assess the biocompatibility of the tested
nickel–titanium alloy samples, an MTT test of fibroblast cellular proliferation on direct contact with
the samples was performed. The obtained data were analyzed with the IBM SPSS Statistics v22
software. EDX and XRF analyses showed a higher presence of Ni in the NiTi-2 sample. The EBSD
analysis detected an additional NiTi2
-cubic phase in the NiTi-2 microstructure. Additionally, in the
NiTi-2 higher hardness was measured. An immersion test performed in artificial saliva after 7 days
did not induce significant ion release in either group of samples (NiTi-1 and NiTi-2). The acidic
environment significantly increased the release of toxic ions in both types of samples. However, Ni
ion release was two times lower, and Ti ion release was three times lower from NiTi-2 than from
NiTi-1. Comparison of the cells’ mitochondrial activity between the NiTi-1 and NiTi-2 groups did
not show a statistically significant difference. In conclusion, we obtained an alloy of small diameter
with an appropriate microstructure and better response compared to classic NiTi material. Thus, it
appears from the present study that the continuous cast technology offers new possibilities for the
production of NiTi material for usage in dentistry.
Ključne besede: nickel–titanium, continuous casting, characterization, biofunctional properties, biocompatibility
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 2
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3. Correlating nickel functionalities to selectivity for hydrogen peroxide electrosynthesisMiha Nosan, Dušan Strmčnik, Vasiliy Brusko, Maria Kirsanova, Matjaž Finšgar, Ayrat M. Dimiev, Boštjan Genorio, 2023, izvirni znanstveni članek Ključne besede: nickel oxide, heat-treated graphene oxide, selectivity, oxygen reduction reaction, peroxide formation
Objavljeno v DKUM: 10.05.2024; Ogledov: 231; Prenosov: 24
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4. Development of a novel NiCu nanoparticle-loaded polysaccharide-based hydrogel for 3D printing of customizable dressings with promising cytotoxicity against melanoma cellsLaura Činč Ćurić, Maša Šuligoj, Maja Ibic, Nina Marovič, Boštjan Vihar, Matej Vesenjak, Polona Dobnik-Dubrovski, Nejc Novak, Janja Stergar, Irena Ban, Uroš Maver, Marko Milojević, Tina Maver, 2023, izvirni znanstveni članek Ključne besede: nanoparticle-loaded hydrogels, 3D printed dressings, polysaccharides, nickel-copper nanoparticles, cytotoxic activity
Objavljeno v DKUM: 03.04.2024; Ogledov: 260; Prenosov: 280
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5. Recombination of oxygen atoms on the surface of oxidized polycrystalline nickel : temperature and pressure dependencesDomen Paul, Miran Mozetič, Rok Zaplotnik, Jernej Ekar, Alenka Vesel, Gregor Primc, Denis Đonlagić, 2023, izvirni znanstveni članek Opis: The recombination of neutral oxygen atoms in the ground state on the oxidized nickel samples was studied experimentally in the range of pressures where the maximum density occurs in weakly ionized low-pressure oxygen plasma, i.e. between 40 and 200 Pa. The recombination coefficient was determined in the flowing afterglow. The source of oxygen atoms was plasma sustained in a quartz tube of inner diameter 4.7 mm by a microwave discharge in the surfatron mode. The recombination coefficient was determined in the afterglow chamber, which was a Pyrex tube with an inner diameter of 36 mm. The density of oxygen atoms in the afterglow chamber was varied by adjusting the discharge power, the gas flow, the pressure, and the position of a recombinator. Such flexibility of the experimental system enabled adjustment of the temperature of the oxidized nickel samples independently from the O-atom density in its vicinity or other parameters. The density of oxygen atoms in the afterglow chamber at various system parameters was determined by the Šorli method, which is reliable, and has an accuracy of about 20%. The recombination coefficient was determined by calorimetry. The coefficient was inversely proportional to the square root of the pressure and exponentially to the sample temperature. Systematic measurements performed at various pressures and temperatures enabled empirical formula, which were explained qualitatively by recombination kinetics.
Ključne besede: heterogenous surface recombination, recombination coefficient, nickel, nickel oxide, temperature
Objavljeno v DKUM: 25.03.2024; Ogledov: 243; Prenosov: 26
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6. EXAFS and IR analysis of electrochromic $NiO_x$/$NiO_xH_y$ thin filmsJana Padežnik Gomilšek, Romana Cerc Korošec, Peter Bukovec, Alojz Kodre, 2008, izvirni znanstveni članek Opis: Electrochromic (EC) thin films of $NiO_x$ and $NiO_xH_y$ are prepared by sol-gel method from nickel chloride precursor and deposited onto a suitable substrate by dip-coating technique. The development of the structure with thermal treatment is investigated by EXAFS and IR spectroscopy in two series of films, with high and low concentration of chloride as counter ions. In the former, the predominant structure before thermal treatment is nickel hydroxide. The baking induces condensation, yet with no trace of NiO. In the latter group, colloidal particles are indicated, on which acetate groups are adsorbed or coordinated. At the maximum EC-response the formation of NiO grains is established by EXAFS and IR.
Ključne besede: electrochromism, thin films, nickel oxide, nickel hydroxide, EXAFS
Objavljeno v DKUM: 18.08.2017; Ogledov: 1423; Prenosov: 109
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7. The correlation between pain perception among patients with six different orthodontic archwires and the degree of dental crowdingEvgenija Marković, Janko Ferčec, Ivana Ščepan, Branislav Glišić, Nenad Nedeljković, Jovana Juloski, Rebeka Rudolf, 2015, izvirni znanstveni članek Opis: Introduction: Forces generated in orthodontic treatment with fixed appliances create tension and compression zones in the periodontal ligament resulting in a painful experience for patients. In the first phase of orthodontic treatment, when leveling of teeth is needed, nickel-titanium (NiTi) archwires can be completely engaged in brackets, even in the cases of extreme crowding, exerting small forces. There is a great individual variation in the pain perception related to the application of orthodontic forces.
Objective: The aim of this study was to investigate the pain perception among patients with dental crowding after insertion of six different NiTi orthodontic archwires as a part of fixed appliances in the first stage of orthodontic treatment.
Methods: The study was conducted on a sample of 189 orthodontic patients receiving one of six different either superelastic or heat activated NiTi archwires, in the first phase of orthodontic treatment. Pain perception was evaluated in groups of patients with different degree of crowding. The modified McGill Pain Questionnaire with Visual Analogue Scale was used to evaluate the quality and intensity of pain. Statistical analysis was performed using simple descriptive statistics, and Pearson`s chi-square test with statistical significance of p<0.05.
Results: Majority of patients reported pain as discomfort or pressure of moderate intensity caused by chewing or biting, started within 12 hours, carried on for 3-4 days, and decreased over time without self-medication.
Conclusion: No correlation was found between pain perception among patients with different types of NiTi archwires and the degree of crowding.
Ključne besede: nickel-titanium archwires, pain, dental crowding, orthodontics
Objavljeno v DKUM: 04.08.2017; Ogledov: 1293; Prenosov: 359
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8. Microstructure of NiTi orthodontic wires observations using transmission electron microscopyJanko Ferčec, Darja Feizpour, Borut Buchmeister, Franc Rojko, Bojan Budič, Borut Kosec, Rebeka Rudolf, 2014, izvirni znanstveni članek Opis: This work presents the results of the microstructure observation of six different types of NiTi orthodontic wires by using Transmission Electron Microscopy (TEM). Within these analyses the chemical compositions of each wire were observed in different places by applying the EDS detector. Namely, the chemical composition in the orthodontic wires is very important because it shows the dependence between the phase temperatures and mechanical properties. Micro- structure observations showed that orthodontic wires consist of nano-sized grains containing precipitates of Ti2Ni and/or TiC. The first precipitated Ti2Ni are rich in Ti, while the precipitated TiC is rich in C. Further investigation showed that there was a difference in average grain size in the NiTi matrix. The sizes of grains in orthodontic wires are in the range from approximately 50 to 160 nm and the sizes of precipitate are in the range from 0,3 μm to 5 μm.
Ključne besede: orthodontic wires, nickel-titanium orthodontic wire, NiTi wire, shape memory alloys, SMA wires, microstructure, transmission electron microscopy, TEM, average grain size
Objavljeno v DKUM: 03.07.2017; Ogledov: 1524; Prenosov: 129
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9. The characterisation of nanosized nickel-zinc ferrites synthesized within reverse micelles of CTAB/1-hexanol/water microemulsionVuk Uskoković, Mihael Drofenik, Irena Ban, 2004, izvirni znanstveni članek Opis: Stoichiometric nanocrystalline nickel-zinc ferrites were synthesized by a reverse micelle method following a multi-microemulsion approach. Different pH values were chosen for the alkali precipitating reaction during the synthesis of different powders. Synthesized, as-dried and subsequently calcined powders were characterized in terms of their magnetic properties. XRD analyses and specific-surface area measurements were used to determine the average particlesizes of the synthesized samples. DCS and TGA measurements were performed to reveal the phase transitions within the samples at elevated temperatures, whereas TEM was used to view and record the microstructure of the nanosized ferrite samples. A possible mechanism of the formation of the synthesized NiZn-ferrite was also discussed.
Ključne besede: magnetic materials, magnetic nanoparticles, microemulsion synthesis, nickel, iron, fine powders, Ni-Zn ferrites, reverse micelle method
Objavljeno v DKUM: 01.06.2012; Ogledov: 2071; Prenosov: 58
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10. Response of monocyte-derived dendritic cells to rapidly solidified nickel-titanium ribbons with shape memory propertiesSergej Tomić, Rebeka Rudolf, Mihael Brunčko, Ivan Anžel, V. Savić, Miodrag Čolić, 2012, izvirni znanstveni članek Opis: Ni-Ti Shape Memory Alloys (SMAs) have attracted considerable attention as biomaterials for medical devices. However, the biocompatibility of Ni-Ti SMAs is often unsatisfactory due to their poor surface structure. Here we prepared Rapidly Solidified (RS) Ni-Ti SMA ribbons by melt-spinning and their surface was characterised by Augerelectron spectroscopy, X-ray photoelectron spectrometry and scanning electron microscopy. The biocompatibility of the produced ribbons and their immunomodulatory properties were studied on human monocyte-derived dendritic cells (MoDCs). We showed that melt-spinning of Ni-Ti SMAs can form a thin homogenous oxide layer, which improves their corrosion resistance and subsequent toxicity to MoDCs. Ni-Ti RS ribbons stimulated the maturation of MoDCs, as detected by changes in the cells' morphology and increased expression of HLA-DR, CD86, CD40 and CD83 molecules. However, Ni-Ti RS ribbons enhanced the tolerogenic properties of immature MoDCs, which produced higher levels of IL-10 and IL-27, driving the differentiation of IL-10- and TGF-β-producing CD4+T cells. On the other hand, in the presence of lipopolysaccharide, an important pro-inflammatory biomolecule, Ni-Ti RS ribbons enhanced the allostimulatory and Th1 polarising capacity of MoDCs, whereas the production of Th2 and Th17 cytokines was down-regulated. In conclusion, Ni-Ti RS ribbons possess substantial immunomodulatory properties on MoDCs. These findings might be clinically relevant, because implanted Ni-Ti SMA devices can induce both desired and adverse effects on the immune system, depending on the microenvironmental stimuli.
Ključne besede: nickel-titanium alloy, biocompatibility, cytokines, immunomodulation, monocyte-derived dendritic cells
Objavljeno v DKUM: 01.06.2012; Ogledov: 2084; Prenosov: 460
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