Coated NiTi Alloy Research Articles

Biofilm inhibition and bactericidal activity of NiTi alloy coated with graphene oxide/silver nanoparticles via electrophoretic deposition

Biofilm formation on medical devices can induce complications. Graphene oxide/silver nanoparticles (GO/AgNPs) coated nickel-titanium (NiTi) alloy has been successfully produced. Therefore, the aim of this study was to determine the anti-bacterial and anti-biofilm effects of a GO/AgNPs coated NiTi alloy prepared by Electrophoretic deposition (EPD). GO/AgNPs were coated on NiTi alloy using various coating times. The surface characteristics of the coated NiTi alloy substrates were investigated and its anti-biofilm and anti-bacterial effect on Streptococcus mutans biofilm were determined by measuring the biofilm mass and the number of viable cells using a crystal violet assay and colony counting assay, respectively. The results showed that although the surface roughness increased in a coating time-dependent manner, there was no positive correlation between the surface roughness and the total biofilm mass. However, increased GO/AgNPs deposition produced by the increased coating time significantly reduced the number of viable bacteria in the biofilm (p < 0.05). Therefore, the GO/AgNPs on NiTi alloy have an antibacterial effect on the S. mutans biofilm. However, the increased surface roughness does not influence total biofilm mass formation (p = 0.993). Modifying the NiTi alloy surface using GO/AgNPs can be a promising coating to reduce the consequences of biofilm formation.

Evaluation of NaOH pre-treatment on the corrosion behavior and surface characteristics of hydroxyapatite coated NiTi alloy

Successful short-term implementation of nickel-titanium (NiTi) alloys as implants has been a motivation for the development of long-term applications. However, rendering these as safe implant materials is challenging. The major problem associated with the use of NiTi for in-vivo applications is the potential risk of Ni release from the implant surface due to the corrosive environment of the body. Various methods including surface treatment techniques with acid and alkali solutions and application of biocompatible coatings have been used to overcome these difficulties. In particular, NaOH pre-treatment has been commonly performed for surface activation of the substrate material to enhance the adhesion properties of coatings. The present work investigates the effect of NaOH pre-treatment on the hydroxyapatite (HA) coating and the resulting corrosion behavior of and cell response to HA coated NiTi wires. Microstructural examinations showed that the coating integrity deteriorated with prior NaOH treatment which also increased the corrosion rate as evidenced by potentiodynamic measurements. XPS analysis revealed heightened Ni levels on the sample surfaces and cytotoxicity tests showed decreased cell viability for the samples with pre-treatment. Absence of NaOH pre-treatment led to lower contact angle values pointing to higher biocompatibility.

Corrosion Resistance of Graphene oxide/Silver Coatings on Ni\u2013Ti alloy and Expression of IL-6 and IL-8 in Human Oral Fibroblasts

Graphene based materials (GBMs) have potentials for dental and medical applications. GBMs may cause changes in the levels of cytokine released in the body. This study aimed to study the corrosion resistance of graphene oxide (GO) and GO/silver (GO/Ag) nanocomposite coated nickel-titanium (NiTi) alloy by electrophoretic deposition and to access the viability of human pulp fibroblasts, and the interleukin (IL)-6 and IL-8 expression level. The bare and coated NiTi samples were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, surface profilometry, and X-ray diffraction (XRD). The corrosion resistance of the bare NiTi and coated NiTi samples were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution. The cell viability of human pulp fibroblasts was accessed by the treated culture medium of the bare NiTi and coated NiTi alloys containing 1% fetal bovine serum. IL-6 and IL-8 expression levels were studied by human enzyme-linked immunosorbent assay (ELISA). Data were analyzed using One-way ANOVA (α = 0.05). Both the GO-coated NiTi and GO/Ag-coated NiTi alloys showed better corrosion resistance, a lower rate of corrosion, and higher protection efficiency than the bare NiTi alloy. The coated NiTi alloys were biocompatible to human pulp fibroblasts and showed upregulation of IL-6 and IL-8 levels.

Preparation and characterization of the aesthetic coating on nickel-titanium orthodontic archwire by electrophoretic deposition

The aesthetic coating was prepared on the orthodontic nickel-titanium shape memory alloy archwire by electrophoretic deposition. The surface and cross-sectional morphologies, color, composition, surface roughness, water contact angle and cytotoxicity of the aesthetic coating were investigated, and the microhardness, bonding strength and Ni ions release behavior of the coated NiTi samples after immersed in artificial saliva for 30 days were also measured. The results show that the aesthetic coating with a thickness of approximately 22 μm exhibits a human tooth color and is composed of epoxy resin and TiO2 particles, in which the TiO2 particles are uniformly and diffusely embedded in the epoxy resin matrix. The aesthetic coating greatly increases the surface roughness and contact angle of the NiTi alloy, but has no significant effect on the superelasticity and shape memory effect. There is no statistical different (p > 0.05) in the micorhardness and bonding strength of the coated NiTi alloy before and after immersed in the artificial saliva for 30 days. Moreover, the aesthetic coating can effectively inhibit the release of Ni ions from the NiTi wire, and has no cytotoxic effect on the MG-63 cells, presenting excellent cytocompatibility.

Graphene Oxide/Silver Nanoparticle Coating Produced by Electrophoretic Deposition Improved the Mechanical and Tribological Properties of NiTi Alloy for Biomedical Applications.

The aim of this study was to evaluate the mechanical and tribological properties of graphene oxide/silver nanoparticle (GO/AgNP) coated medical grade nickel-titanium (NiTi) alloy. The alloy substrates were coated using electrophoretic deposition at 30 V for 1, 5, and 10 min and were characterized by SEM, Raman spectroscopy, EDS, and surface profilometer. Mechanical and tribological tests were performed for hardness, Young's modulus, and friction coefficient. The data were analyzed using the Kruskal-Wallis test at a significance level of 0.05 to compare the coatings' roughness, thickness, friction coefficient, and hardness at the different coating times. The GO/AgNP coatings were confirmed with Raman spectroscopy, which demonstrated the presence of D bands and G bands at ∼1300 cm-1 and ∼1600 cm-1. The intensity ratios of the D and G bands (ID/IG) were 0.838, 0.836, and 0.837 in the 1, 5, and 10 min coated groups, respectively. The coating thickness ranged from 0.46-1.34 μm and the mean surface roughness (Ra) ranged from 50.72-69.93 nm. Increasing the coating time from 1-10 min increased the roughness, thickness, and Young's modulus of surface coating. The friction coefficients of the coated NiTi alloy were significantly lower compared with that of the uncoated NiTi allloy (p < 0.001). The GO/AgNP nanocomposite coated NiTi alloy demonstrated improved mechanical strength and a reduced friction coefficient that would be more favorable for biomedical applications.

Enhanced corrosion resistance and bio-performance of Al2O3 coated NiTi alloy improved by polydopamine-induced hydroxyapatite mineralization

Corrosion resistance and bio-performance of NiTi alloy is clinically important for osteointegrated implants with long-term performance. Though Al2O3 coating fabricated on NiTi alloy by the cathodic plasma electrolytic deposition (CPED) could effectively reduce the Ni ions release and improve the corrosion resistance to a large extent, the bioinert nature of Al2O3 coating will inevitably limit the potential for orthopaedic applications. In this study, hydroxyapatite (HA) was coated on the Al2O3 coating via polydopamine (PDA) induced biomimetic mineralization to improve the corrosion resistance, biocompatibility and in vitro bioactivity of the Al2O3-coated NiTi alloy.The surface morphology, phase composition, corrosion resistance, biocompatibility, and in vitro bioactivity of the samples with HA modified Al2O3 (HA/Al2O3) coating were systematically investigated. The results indicated that the Al2O3 coating surface was fully covered with HA minerals. The corrosion resistance of the HA/Al2O3-coated sample was enhanced by more than one order of magnitude than that of the Al2O3-coated NiTi alloy. The concentration of Ni ion release displayed a significant drop from 1.9 μg/mL for the Al2O3-coated NiTi alloy to 0.6 μg/mL for the HA/Al2O3-coated sample. In addition, the HA/Al2O3-coated NiTi alloy could promote the cell proliferation and osteogenic differentiation of human bone marrow mesenchymal stem cells (hMSCs) compared with the mere Al2O3-coated sample. Therefore, introducing the HA modified Al2O3 coating is a promising strategy for improving the corrosion resistance and bio-performance of NiTi alloy osteointegrated implants.

Electrolytic deposition of hydroxyapatite/calcium phosphate-heparin/gelatin-heparin tri-layer composites on NiTi alloy to enhance drug loading and prolong releasing for biomedical applications

Although the initial success of bare metal stents has significantly reduced the restenosis rate for percutaneous transluminal coronary angioplasty from 35% to 25%, the biological mechanism such as vascular smooth muscle cells (VSMCs) proliferation and neo-intimal hyperplasia still may induce in-stent restenosis (ISR). Therefore, some drug eluting stents have been introduced to reduce ISR. In this study, heparin (Hep) combined with calcium phosphate (CaP) and gelatin (Gel), without any additive or solvent, is co-deposited on hydroxyapatite (HA) coated NiTi alloy in order to enhance the drug load and the sustaining release for promoting the hemo-compatibility of NiTi substrate. Polarization tests were carried out in several solutions to investigate deposition mechanisms. Heparin contained composite coatings were characterized by X-ray diffractometry, Field emission scanning electron microscope, Fourier transform infrared spectroscopy, toluidine blue colorimetric assay, UV–visible spectrometer and kinetic clotting tests. The consequences indicate that heparin accompanied respectively with CaP, and Gel through ionic bonds can be loaded on the NiTi alloy. The porous post-HA coating can dramatically enhance the heparin content from 148 for the single layer coating (CaP-Hep) to 325 μg/cm2 for the tri-layer coating (HA/CaP-Hep/Gel-Hep), also resulting in the heparin release duration from 1 to >35 days, supposed to meet the requirement to prevent the proliferation of VSMCs. Both the drug content and releasing time are remarkable. As the result of clotting tests in vitro, drug loaded composite coatings reveal good anticoagulant property which is proportional to the cumulative content of drug release in an hour, indicating no denaturalization of heparin found during the electrochemical process.

Enhanced corrosion resistance and hemocompatibility of biomedical NiTi alloy by atmospheric-pressure plasma polymerized fluorine-rich coating

To improve the corrosion resistance and hemocompatibility of biomedical NiTi alloy, hydrophobic polymer coatings are deposited by plasma polymerization in the presence of a fluorine-containing precursor using an atmospheric-pressure plasma jet. This process takes place at a low temperature in air and can be used to deposit fluoropolymer films using organic compounds that cannot be achieved by conventional polymerization techniques. The composition and chemical states of the polymer coatings are characterized by fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the coated and bare NiTi samples is assessed and compared by polarization tests and electrochemical impedance spectroscopy (EIS) in physiological solutions including simulated body fluids (SBF) and Dulbecco's Modified Eagle's medium (DMEM). The corrosion resistance of the coated NiTi alloy is evidently improved. Protein adsorption and platelet adhesion tests reveal that the adsorption ratio of albumin to fibrinogen is increased and the number of adherent platelets on the coating is greatly reduced. The plasma polymerized coating renders NiTi better in vitro hemocompatibility and is promising as a protective and hemocompatible coating on cardiovascular implants.

Improvement of corrosion resistance and antibacterial effect of NiTi orthopedic materials by chitosan and gold nanoparticles

Biocomposite consists of gold nanoparticles (AuNPs) and a natural polymer as Chitosan (CS) was electrodeposited over NiTi alloy to improve biocompatibility, biostability, surface corrosion resistance and antibacterial effect for orthopedic implantation. The forming process and surface morphology of this biocomposite coats over NiTi alloy were studied. The results showed that the nm-scale gold particles were embedded in the composite forming compact, thick and smooth coat. Elemental analysis revealed significant less Ni ion release from the coated NiTi alloy compared with the uncoated one by 20 fold. Furthermore, the electrochemical corrosion measurements indicated that AuNPs/CS composite coat was effective for improving corrosion resistance in different immersion times and at all pH values, which suggests that the coated NiTi alloys have potential for orthopedic applications. Additionally, the efficiencies of the biocomposite coats for inhibiting bacterial growth indicate high antibacterial effect.

Biomimetic deposition of apatite coatings on biomedical NiTi alloy coated with amorphous titanium oxide by microarc oxidation

The biomedical NiTi alloy was treated by microarc oxidation (MAO) in H3PO4 electrolyte using DC power supply. The amorphous titanium oxide coating with porous and rough structure was formed on NiTi alloy. The MAO treated NiTi was soaked in a simulated body fluid (1·0SBF) to investigate the biomimetic deposition of apatite on the surface of titanium oxide coated NiTi alloy. It was found that titanium oxide coated NiTi alloy shows an excellent apatite forming ability after soaking in a simulated body fluid (1·0SBF) for 28 days, while no apatite forming ability was observed on bared NiTi alloy, even though soaking time is up to 28 days. The Fourier transformed infrared and X-ray photoelectron spectroscopy results showed that apatite deposited on MAO treated NiTi is a kind of incorporated and Ca deficient apatite.

Tantalum coated NiTi alloy by PIIID for biomedical application

Plasma immersion ion implantation deposition (PIIID) technique was employed to fabricate tantalum coatings on NiTi alloys with the aim to obtain a more adherent, corrosion resistant and radiopaque coatings in our present study. The surface characteristics and corrosion behavior were investigated by SEM, AFM, XRD, AES, XPS and electrochemical measurement. The results show that a relatively rough, dense and adhesive tantalum coating has been successfully fabricated on NiTi alloy by the PIIID method with the thickness of about 3.3μm. The surface topography of the tantalum coatings is characterized by regularly spaced grain facets. The coating is combined with a mixture of predominantly α-phase tantalum with a small concentration of β-phase tantalum. The outmost surface of the coating is oxidized, consisting of majority of stoichiometric Ta2O5 and a small quantity of Ta2O5−X. It can be concluded that the dense and adhesive tantalum coatings on NiTi alloy improve its corrosion resistance, implying the decrease of Ni ions released into human body fluids.

Effect of micro-arc oxidation surface modification on the properties of the NiTi shape memory alloy

In this paper, the effects of micro-arc oxidation (MAO) surface modification (alumina coatings) on the phase transformation behavior, shape memory characteristics, in vitro haemocopatibility and cytocompatibility of the biomedical NiTi alloy were investigated respectively by differential scanning calorimetry, bending test, hemolysis ratio test, dynamic blood clotting test, platelet adhesion test and cytotoxicity testing by human osteoblasts (Hobs). The results showed that there were no obvious changes of the phase transformation temperatures and shape memory characteristics of the NiTi alloy after the MAO surface modification and the coating could withstand the thermal shock and volume change caused by martensite-austenite phase transformation. Compared to the uncoated NiTi alloys, the MAO surface modification could effectively improve the haemocopatibility of the coated NiTi alloys by the reduced hemolysis ratio, the prolonged dynamic clotting time and the decreased number of platelet adhesion; and the rough and porous alumina coatings could obviously promote the adherence, spread and proliferation of the Hobs with the significant increase of proliferation number of Hobs adhered on the surface of the coated NiTi alloys (P < 0.05).

The effect of arc current on the corrosion behaviour of coated NiTi alloy on AISI304 by plasma transferred arc process

In this study, the effect of arc current on the corrosion behaviour of NiTi coating on stainless steel has been investigated. NiTi powder mixture was alloyed on surface austenitic AISI304 by using plasma transferred arc (PTA) method. Surface alloying process is turned out using 80, 90, 100 A current densities and Ar atmosphere which is plasma and protective. The corrosion resistance of the coatings was analyzed by measuring the potentiodynamic polarization scanning (PDS) technique. Results indicate that corrosion resistances of the coatings decrease with increasing the arc current. In addition, the localized corrosion on the surface of produced coating at 100A is more activated than other coatings and the most passive coating in view of corrosion was obtained at produced coating at 80A.

In Vitro Blood Compatibility of Alumina Coatings Prepared by Micro-Arc Oxidation on Biomedical NiTi Alloy

In this paper, the in vitro blood compatibility of micro-arc oxidation (MAO) alumina coatings prepared in different times on biomedical NiTi alloy was studied using hemolysis ratio, dynamic blood clotting and platelet adhesion. The results show that the blood compatibility of the coated NiTi alloy is much better than that of uncoated NiTi alloy and reduces with increasing the micro-arc oxidation treatment times. Therefore, it can be concluded that the blood compatibility of materials is mainly dominated by the surface species contacted with blood within some ranges of surface roughness, not the surface morphologies, and the MAO alumina coatings can effectively improve the blood compatibility of NiTi alloy

Preparation, characterization, corrosion behavior and bioactivity of Ni2O3-doped TiO2 nanotubes on NiTi alloy

Electrochemical anodization has become a prevalent surface modification method for biomaterials nowadays. In this study we prepared Ni2O3-doped TiO2 nanotubes (NTs) on NiTi alloy using electrochemical anodization method and explored its suitability for biomedical applications. Morphology, composition and microstructure of NT films were found to depend on preparation conditions. NT film prepared at 35 V, 45 °C and 10 min had well-defined nanotubular architecture and were composed of TiO2 and a small amount of Ni2O3. Annealing at 450 °C, the film remained amorphous structure, with excellent corrosion resistance. At annealing temperatures of 600 °C, rutile crystalline was formed thus enhanced the bioactivity of the film. Formation of NT film on the surface of NiTi alloy also increased its wettability, especially for 600 °C annealed sample, so the biological response is expected to be improved. Our results indicate that annealing the NT film coated NiTi alloy at 450 °C is desirable for cardiovascular applications. This attributes to its advantages such as the eliminated toxic F species, enhanced corrosion resistance and reduced risk of calcification. For orthopedic applications, annealing at 600 °C is preferred due to its enhanced corrosion resistance and bioactivity.

폴리머 코팅된 NiTi합금 교정선의 표면특성

NiTi alloy has been used for orthodontic wire due to good mechanical properties, such as elastic strength and frictional resistance, combined with a high resistance to corrosion. Recently, these wire were coated by polymer and ceramic materials for aesthetics. The purpose of this study was to investigate surface characteristics of polymer coated NiTi alloy wire for orthodontics using various instruments. Wires (round type and rectangular type) were used, respectively, for experiment. Polymer coating was carried out for wire. Specimen was investigated with field emission scanning electron microscopy(FE-SEM), energy dispersive x-ray spectroscopy(EDS) and atomic force microscopy(AFM). The phase transformation of non-coated NiTi wire from martensite to austenite occurred at the range of <TEX>$14{\sim}15^{\circ}C$</TEX>, in the case of coated wire, it occurred at the range of <TEX>$16{\sim}18^{\circ}C$</TEX>. Polymer coating on NiTi wire surface decreased the surface defects such as scratch which was formed at severe machined surface. From the AFM results, the average surface roughness of non-coated and coated NiTi wire was 13.1 nm, and 224.5 nm, respectively. From convetional surface roughness test, the average surface roughness of non-coated and coated NiTi wire was <TEX>$0.046{\mu}m$</TEX>, and <TEX>$0.718{\mu}m$</TEX>, respectively.

Biomimetic deposition of apatite coatings on micro-arc oxidation treated biomedical NiTi alloy

The biomedical NiTi alloy was treated by micro-arc oxidation in an electrolytes containing sodium aluminate and sodium hypophosphite at 400 V constant voltages for 30 min. The MAO-treated NiTi has a porous microstructure on its surface and coatings consisting only of the γ-Al2O3 phase. The ceramic coating prepared by micro-arc oxidation is composed of Al, Ti, Ni, O, and P with the atomic concentration of 26.98%, 3.67%, 3.33%, 65.30% and 0.72%, respectively. The MAO-treated NiTi was soaked in a simulated body fluid (1.0SBF) to investigate the biomimetic deposition of apatite on the surface of Al2O3 coated NiTi alloy. It was found that Al2O3 coated NiTi alloy shows an excellent apatite-forming ability after soaking in a simulated body fluid (1.0SBF) for 14 days, while no apatite-forming ability was observed on bared NiTi alloy even though soaking time is up to 28 days.

Structure and tribological properties of micro-arc oxidation coatings for reduction of Ni2+ ion release on biomedical NiTi alloy

The ceramic coating was prepared on the NiTi alloy by Micro-arc oxidation (MAO) in a sodium aluminate (NaAlO2) solution at constant current density. The surface of the coating displays a rough, porous structure. The elements of the coatings mainly contain Al, Ti, O, and Ni. The concentration of Ni in the surface is 1.63 at%, which is greatly lower than that of Ni in the NiTi substrate. XPS analysis revealed that Al exist as Al–O bond of Al2O3, Ti existed as Ti4+(TiO2), Ti3+(Ti2O3), Ti2+(TiO), and Ti0(metallic Ti), and Ni exist as Ni2O3, NiO and metallic Ni in the coating surface. Thin-film X-ray diffraction shows that the only Al2O3 phase can be confirmed in the coating. Potentiodynamic polarization curves indicate that the corrosion resistance of the Al2O3 coating is better than that of uncoated NiTi. The amount of Ni leached from coated NiTi sample is 20.97% of that from the uncoated NiTi sample after immersion 40 d. The Tribological behavior of uncoated and coated NiTi alloy was evaluated using a computer-controlled ball-on-disk WTM-1E tribometer.

Improving the biocompatibility of NiTi alloy by chemical treatments: An in vitro evaluation in 3T3 human fibroblast cell

The nearly equi-atomic nickel titanium alloy was coated with calcium phosphates by socking the chemically treated alloy in simulated body fluid in order to prepare bioactive NiTi implants. The biocompatibility of the calcium phosphates coated NiTi alloy was investigated by in vitro 3T3 human embryonic fibroblast cell culture tests. The cells attachment and morphologies were studied using phase contrast light microscope and environmental scanning electron microscope. The mechanically polished and the calcium phosphates coated NiTi samples were well tolerated by the cells, whereas, the controlled pure Ni samples exhibited strong toxicity to the cells. Furthermore, the calcium phosphates coated NiTi samples showed good osteoconductivity.

Mechanical and corrosion study of diamond-like carbon coating on NiTi alloys

Diamond-like carbon (DLC) coatings were prepared on NiTi alloys using plasma immersion ion implantation and deposition. The evaluation of surface hardness using nano-indenter reveals that the DLC coated NiTi alloys is much harder than that of the uncoated sample. The scratch test reveals that the DLC coating has good adhesion strength between the coating and substrate. Anodic polarization has been carried out to examine the electrochemical corrosion behavior of the coated and uncoated samples. The result indicates that the corrosion resistance of the NiTi alloys is improved by the coating.