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Development of a Ta/TaN/TaNx(Ag)y/TaN nanocomposite coating system and bio-response study for biomedical applications
Abstract
TaN(Ag) composited coatings are being investigated to improve biocompatibility of different biomedical devices due to the mechanical and chemical stability of TaN and bactericidal effect of silver nanoparticles. However, controlling the size, density, shape and especially the release of silver ions (Ag) into the surrounding medium becomes a challenge, since elevated levels of Ag could be cytotoxic. The aim of this work is to design and develop a new Ta/TaN/TaNx(Ag)y/TaN coating system, deposited by unbalanced DC magnetron sputtering technique, presenting an adequate balance between biocompatibility and bactericidal effect for potential applications in biomedical field. For this purpose, four different coating systems were deposited on 316 L stainless steel and silicon (100) samples applying a bias voltage of −30, −60, −90 and −120 V during the deposition of the top layer of TaN to vary its density. This manufacturing strategy allowed controlling the diffusion of silver nanoparticles to the coating surface and the release kinetics of silver ions in simulated body fluid (SBF). Biologic characterization has been performed with MC3T3-E1 pre-osteoblastic cells in terms of cell adhesion and long-term differentiation. Additionally, the adhesion and biofilm formation of the bacteria Streptococcus sanguinis strain in the deposited coating systems of Ta/TaN/TaNx(Ag)y/TaN were analyzed. The results indicated an improvement of cell adhesion and differentiation of the composited coating deposited with a bias of −30 V compared to other coatings. Concordantly, this coating showed the lowest bacterial adhesion and biofilm formation, representing an attractive and suitable composited material for biomedical applications.
... The introduction of Ta into coatings via surface modification technologies is a reliable way to improve the surface and biological properties of biomedical metallic materials [8,10,[13][14][15]. For example, Hee et al. [15] used a filtered cathodic vacuum arc deposition technique-the socalled bio-stable surface treatment-to prepare Ta and related nitride films on TC4 alloy, after which both the Ta and TaN films exhibited improvement in corrosion resistance. ...
... Furthermore, the heterogeneous multilayer coatings are also within the scope of many studies on biocompatible materials. Echavarría et al. [14] developed a new Ta/TaN/TaNx(Ag)y/TaN coating system using unbalanced DC magnetron sputtering. The release of Ag to the osteoblast medium enabled one to improve the cell adhesion and differentiation of the TaNx(Ag)y composite coating so as to achieve an appropriate balance between biocompatibility and bacterial adhesion. ...
Monolayer Ta and multilayer Ti/Zr/Ta and Zr/Ti/Ta coatings were prepared by magnetron sputtering on TC4 substrates to improve the surface friction and wear properties in a simulated body fluid (SBF) environment and an atmospheric environment. Optical microscopy, scanning electron microscopy, laser scanning confocal microscopy and nano scratch testing were employed to establish the structure-property-environment relationships. By controlling the preparation parameters, the outermost layer of all three samples was Ta coating, and the total coating thickness of each sample was about 3 μm. Friction and wear testing revealed that, compared to bare TC4 substrate, and multilayer Ti/Zr/Ta and Zr/Ti/Ta coatings, the monolayer Ta possessed the lowest friction coefficient as well as the minimum wear rate (i.e., calculation result of the wear track width and wear depth). This was mainly attributed to excellent adhesion strength, a particular structure and solid lubrication of the monolayer coating. The same coating sample exhibited a stronger wear resistance in the SBF environment than in the atmospheric environment. Furthermore, the wear behaviors and mechanisms of various coatings under different experimental environments are also discussed.
... For the Ag-CaP system an angle of 77.8°and an energy of 36.75 mJ/m 2 were registered (left), while an angle of 53.5°an energy of 52.01 mJ/m 2 were determined for the CaP coating (right). Both surfaces have a hydrophilic character (being greater for the Ag free CaP coating), as the values obtained for the water contact angle are < 90°and the calculated values for the surface free energy are positive [29,30]. Good biological response in terms of cell adhesion and proliferation has been reported in the literature for hydrophilic surfaces [16,31]. ...
... This Ag + can bind to DNA and proteins, affecting the bacterial division and replication. In addition, Ag nanoparticles cause the membrane rupture, inducing the formation of irreversible complex such sulfhydryl orhistidyl, which affect the respiratory enzymes, causing the bacterial death [30,38]. Base on that, we suggest that the antibacterial response shown in the Ag-CaP coating could be interpreted according to the previously described mechanisms. ...
Currently, antibiotic prophylaxis is not sufficient for the treatment of infections associated with implantable materials. For this reason, it is necessary to develop new alternatives, complementary to traditional pharmaceutical methods, in order to treat these infections. This study aims to respond to this need. In it, multi-layer bactericidal silver - calcium phosphate coatings were obtained on Ti-6Al-4V by radio frequency magnetron sputtering. A 4.2 Ag atomic % and Ca/P ratio of 2.15 were measured by energy dispersive X-ray spectroscopy. The structural and phase analysis, performed respectively by micro-Raman spectroscopy and X-ray diffraction, allowed characteristic vibration bands of the CaP and hydroxyl groups, as well as hydroxyapatite peaks, to be appreciated. Additionally, the surface topography was studied by atomic force microscopy, revealing granular morphology with grain size of 191 ± 32 nm and a root mean square of 21.1 nm. Additionally, a water contact angle of 77.8° was registered using a goniometer. The bactericidal effect of the coatings at relatively low Ag concentration (<0.01 mg/L) was observed through an inhibitory halo generation in the culture of the Staphylococcus aureus and Pseudomonas aeruginosa strains. Meanwhile, the non-toxic character, proliferation and adhesion of Saos-2 osteoblast to the coating surface were determined by means of MTT assays, fluorescence and scanning electron microscopy visualization.
... Several multilayered coatings for biomedical applications are proposed in the literature. Among them, those alternating metallic/ceramic layers such as (Ti/TiN) [4], Ta/TaN [5] i.e. (Me/MeN)n. Where "Me" is metal and "n" is the number of alternating bilayers. ...
Multilayer thin coatings (∼ 3 µm in thickness) were deposited using reactive radio frequency magnetron sputtering on Ti-6Al-4V substrate for biomaterial applications. Films are a combination of hard zirconium nitride with pure tantalum, used to manage interfacial stress and to avoid crack growth. Alternating hard/ductile material is a biomimetic design inspired by nature (nacre-inspired materials). Tribocorrosion tests were performed in Hank's solution at 37°C, under open circuit potential by using a ball-on-disc reciprocating tribometer. A tendency to high resistance against corrosion was found for all the samples. Coatings with a top 100 nm thick ZrN layer showed more noble potential as well as a reduction of both the friction coefficient and the wear rate during the sliding phase. The principal wear mechanism is related to a tribocorrosion layer formation.
... Fig. 7 shows the water contact angle and the surface free energy of the Ti-6Al-4V and the deposited coatings. Here, it can be observed that both the TiN coating and the substrate used have hydrophobic behavior, according to the authors of the report [40], since the contact angle was > 90°. On the other hand, the HA-Ag coatings showed a greater water affinity, obtaining a significant reduction in the contact angle and presenting a hydrophilic character. ...
... Additionally, the development of an effective means to increase the surface hardness and wear resistance of titanium alloys is on demand. Numerous methods have been recently proposed for surface modification of metal implants in order to obtain properties required for bone replacement [3]. Research on b Ti-based alloys with non-toxic and osseointegration promoting elements such as Zr, Nb and Ta has increased rapidly during the past decade [4e10]. ...
In this study, Ti-Zr coatings were fabricated by ion-assisted arc-plasma deposition in vacuum. The phase composition, morphology and mechanical properties of the developed thin films were studied. The addition of Zr into Ti resulted in the formation of α’- (Ti,Zr) and α”- (Ti,Zr) solid solutions and mechanical properties change of the prepared alloys. It was revealed that the increase of Zr content in the coating resulted in the increase of nanohardness. The deposited coatings possess reduced modulus of elasticity 77–98 GPa, which is significantly improved compared with Ti substrate, which reveals a modulus of elasticity of 110 GPa. Furthermore, nanoindentation results demonstrate significant improvement of the elastic strain to failure and plastic deformation resistance of the Ti-Zr coatings with the increase of the content of Zr from 11 wt % to 22 wt%. Thus, it is likely that Ti-Zr coatings obtained by ion-assisted arc-plasma deposition possess a high biomedical potential due to synergetic combination of biocompatibility and biomechanical properties.
Mo-Ag-N coatings were prepared by d.c. magnetron sputtering technique from a Mo target with embedded Ag pellets, followed by vacuum annealing at 425, 500, and 600 °C, respectively, for 1 h. SEM, EDS, XRD, nanoindenter, and micro–macro tribometer were used to investigate the influence of Ag content and annealing temperature on their microstructure, surface morphology and mechanical properties. Results demonstrated that as-deposited Mo-Ag-N coatings consisted of fcc γ-Mo2N phase and fcc Ag phase where Ag uniformly distributed into Mo-N matrix. The hardness of Mo-Ag-N coatings initially increased and then decreased with Ag content, reaching the maximum hardness of 32 GPa at 4 at.% Ag, whereas friction coefficient decreased monotonously with Ag content increasing. With the increase of annealing temperature hardness, friction coefficient, and wear resistance were decreased due to the accumulation of a large amount of Ag agglomerates onto surface resulted from high temperature intriguing phase segregation and diffusion.
Surgical devices and tools are manufactured in AISI 420 martensitic stainless steel, due to its hardenability, adequate hardness and acceptable biocompatibility. Nevertheless, many surface modification strategies are being investigated with a view to improving this material by providing it with self-protection against the colonization of bacteria. One such strategy is the use of a TiAlVN-Ag nanocomposite coating to promote bactericidal effect in surgical devices; however, it is necessary to study the electrochemical response of such coatings to aggressive environments that simulate disinfection and sterilization processes. The aim of this work is to study the relationship between the microstructure, chemical phases and the electrochemical and corrosion response of TiAlVN-Ag coating, varying the amount of silver with the target power increase (0, 50, 70, 80 and 100 W). To study the microstructure, chemical phases, scanning and high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction were used. Roughness, microhardness, residual stresses, qualitative adhesion of coatings were estimated by atomic force microscopy, Knoop indentation, profilometer and Rockwell C indentation, respectively. Electrochemical behavior and corrosion protection of coatings were studied using electrochemical impedance spectroscopy and potentiodynamic polarization. TiAlVN-Ag 50W coating showed an improvement in electrochemical behavior and in protection of the steel against corrosion and exhibiting higher hardness than that of the AISI 420 stainless steel substrates. This coating exhibited a dense microstructure and high crystallinity, indicating that the low Ag content does not affect the insulating nature of the coating matrix.
TaZrN coatings were synthesized directly on biomedical grade CoCrMo using radio-frequency magnetron co-sputtering. The mechanical properties, adhesion, wear, and corrosion resistance of the TaZrN coatings on the Cobalt alloy were assessed to determine their potential for hip joint replacement applications. The results indicate the TaZrN coatings are highly adhesive and have a nanocrystalline structure with a Hardness and Young’s modulus of 19 GPa and 297 GPa, respectively. The TaZrN coatings showed a 3% lower wear rate of the polyethylene counterpart and an icorr value 274 times lower than the uncoated CoCrMo alloy. The excellent wear and corrosion resistance of the TaZrN coating suggest that it is a promising coating material for CoCrMo alloy to improve the lifetime of hip joint implants.
Ta–N–Al thin films were produced by reactive sputtering with two different TaAl alloys (Al 10 at.% and 20 at.%) for use as resistive materials for thin film chip resistors. Changing the N2 gas flow of the N2/Ar plasma and the Al ratio in TaAl alloy resulted in different microstructures and electrical properties of the Ta–N–Al thin film. The resistivity of the thin film sputtered by TaAl (Al 20 at.%) alloy was 1.23 times that sputtered by Ta under 20% N2/Ar. After deposition, rapid thermal processing was applied to anneal the thin films for 5 min at 600 °C, 650 °C, and 700 °C under N2 (99.995%) atmosphere, causing the Ta2N and TaN crystalline phase formation. Al in Ta–N–Al was observed to hinder Ta2N and TaN crystalline phase formation during annealing. It is crucial to dope Al ith Ta–N appropriately to obtain a near-zero temperature coefficient of resistance (TCR) after annealing. The TCR of Ta–N–Al thin film, sputtered by TaAl (Al 20 at.%) alloy, was substantially affected by the annealing temperature. However, the thin film sputtered by TaAl (Al 10 at.%) alloy under 16% N2/Ar can achieve a TCR of −1.8 ppm/°C and 1.4 ppm/°C after annealing at 600 °C and 650 °C, respectively.
Osteolysis is the resorption or removal of bone tissue, which is associated with the accumulation of polyethylene particles and misalignment of hip joint implant components. The mechanical properties, adhesion, tribological, and corrosive properties of single-layered tantalum nitride (TaN) coatings on biomedical grade cobalt alloy were evaluated to determine the potential of these coatings to prevent osteolysis in hip joint replacement applications. The TaN coatings were deposited directly on biomedical grade CoCrMo alloy disks using a hybrid system of Plasma Enhanced Chemical Vapor Deposition (PECVD) and Physical Vapor Deposition (PVD) at different deposition temperatures. By increasing the deposition temperature from 350 °C to 500 °C, the mechanical properties and adhesion improved remarkably, without a significant change in the crystal structure according to XRD and XPS results. The ball-on-disk wear testing results showed that the wear rate of the polyethylene balls decreased by 5% when sliding against the TaN-500C sample compared to sliding against the uncoated alloy and was 23% lower than the TaN-350C sample. The electrochemical corrosion results indicated that the TaN coating deposited at 500 °C is about 15% more noble than the uncoated alloy, which allows the rapid formation of a protective passive layer. These results suggest that TaN is a promising coating for CoCrMo alloy to improve the lifetime of hip joint implants.
In this paper, Cu–TiN nanocomposite coatings on titanium alloys were prepared by multi-target co-sputtering system. On this basis, Mg or Ca ions at the same doses were then implanted into the Cu–TiN coatings respectively via plasma immersion ion implantation system (PIII) to further improve their biological properties. The corrosion resistances, protein adhesion rates, in vitro cell proliferation and bacterial inhibition capabilities of Mg ⁺ implanted Cu–TiN and Ca⁺ implanted Cu–TiN were also compared. The results showed that the Mg⁺ implanted Cu–TiN showed (i) improved corrosion behavior, (ii) higher protein adsorption capacity, (iii) ideal cell proliferation and adhesion, (iv) better antimicrobial properties. The research results showed that compared with Ca, Mg and Cu–TiN combined better in osteogenetic and antibacterial activities, which could provide a good choice for the surface modification of medical materials.
The goal of this research is to determine the effect of N2 pressure to argon pressure on the microstructural analysis and corrosion behavior of nanostructured TaN deposited coatings using a reactive DC‐magnetron sputtering (RDCMS) technique. The samples coated microstructure was studied by the X‐ray diffraction (XRD), scanning electron microscope (SEM) and elemental distribution was studied using energy‐dispersive x‐ray spectroscopy (EDS). To investigate the corrosion behavior of nanostructured TaN coatings, the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests were performed in Hank’s physiological solution. The results of different tests revealed that the coating with a content of 17.6% PN2/PAr consisted of hexagonal and orthorhombic TaN phases, had denser microstructure and free pores. This coating showed superior corrosion behavior in comparison to the other ones. Also, the corrosion resistance of this coating raised by increasing the time of immersion from 48 to 168 hours.
In this study, TaN nanostructured coatings were successfully produced on AISI 316 L stainless steel substrates using the reactive DC magnetron sputtering method. Among all of these coating processes, the only variable factor was the percentage of partial pressure of nitrogen gas (PN2) which was attended in the sputtering process. To do this, the percentage of partial pressure of nitrogen gas was chosen in different percentages of 5%, 10% and 15%. After the coatings formation, their microstructure, chemical composition and corrosion behavior were studied. The microstructure of the samples coated was studied by the scanning electron microscope (SEM), their elemental and phase composition by energy diffraction spectroscopy (EDS), X-ray diffraction (XRD) and elemental distribution was carried out by mapping (MAP) analysis. In order to study the corrosion behavior of coatings, the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests were carried out in a simulated body fluid (Ringer's solution). Immersion time of specimens was determined 1, 24, 48 h and 7 days in Ringer's solution. The results of different tests showed that coatings containing 15% nitrogen consisted of hard orthorhombic and hexagonal tantalum nitride phases, had free pores and denser microstructure. This coating exhibited better corrosion behavior than the other two ones in all of the immersion times. The corrosion resistance of this coating also increased by rising immersion time from 1 h to 7 days. In fact, the coating containing 15% of nitrogen being immersed for 7 days with a resistance of 118.68 (MΩ.cm²), had the highest corrosion resistance.
Biocompatible and antibacterial multi-layer coatings of hydroxyapatite (HA)-Ag/SiO2/TiN/Ti were obtained on the Ti-6Al-4V alloy, by means of the magnetron sputtering technique. During characterization of the coatings, the chemical composition was evaluated by energy dispersive X-ray spectroscopy and the phase analysis was carried out by X-ray diffraction. The morphology of the coatings was observed by field emission scanning electron microscopy, while transmission electron microscopy was used to appreciate their structure. The adhesion of the coatings to the substrate was evaluated by micro scratch test. The in vitro biological response was evaluated in terms of cytotoxicity, adhesion and differentiation of mouse mesenchymal stem cells, as well as adhesion and bacterial viability of Staphylococcus aureus strain. Through the compositional study carried out, the deposition of the HA phase was verified, with a Ca/P ratio close to 1.67 and the characteristic diffraction peaks of this compound. The structural study of the coatings evidenced the obtention of multi-layer architectures. The use of an intermediate SiO2/TiN/Ti trilayer was found to improve adhesion between HA-Ag and the substrate by 84%. Finally, the in vitro biological tests carried out indicated a potentially non-toxic character in the coatings. Additionally, an antibacterial effect was registered at low concentrations of Ag (<0.25 mg/L).
AISI 420 stainless steel is currently used in the manufacture of surgical and dental instrumentation due to its hardenability, acceptable biocompatibility and suitable resistance to corrosion in low acid or basic medium. However, it is necessary to increase the wear and corrosion resistance of this type of steel when it is used in certain biomedical applications. Therefore, multiple surface modification strategies have been used in order to overcome these drawbacks in the properties of this material. In this work, TiAlN coatings doped with Ag and Cu nanoparticles in four different quantities (11 at.% to 20 at.%) were deposited onto 420 steel by DC magnetron sputtering technique. The microstructure, and chemical and phase composition, were analyzed by scanning and transmission electron microscopy (SEM/TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction, while roughness was determined using atomic force microscopy (AFM). The electrochemical behavior of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. A reduction in the corrosion current density of the steel substrate was evident once it was superficially modified with the TiAlN matrix coating, which formed a protective barrier to the corrosive medium. The TiAlN(Ag,Cu) coatings developed superior electrochemical activity to the TiAlN matrix, and consequently exhibited higher corrosion current densities. This behavior was accentuated with increased Ag/Cu content in the coating, and it was correlated mainly with the increase in the dissolution rates of silver and copper to the surrounding medium. This suggests a potential bactericidal effect of this kind of coating, which might be considered for potential application in surgical and dental instrumentation.
Most medical instrumentation is manufactured using AISI 420 martensitic stainless steel, due to its acceptable biocompatibility, good hardenability, adequate hardness and resistance to corrosion. However, this steel can be susceptible to contamination with bacteria, representing a potential risk to the patient's health. This research work focused on the development of titanium‑aluminum-nitride coatings doped with silver and copper nanoparticles, TiAlN (Ag,Cu), with an appropriate bactericidal effect. TiAlN coatings doped with four different contents of Ag and Cu (11 at.% to 20 at.%) were deposited onto AISI 420 steel by means of DC unbalanced magnetron sputtering using two composite targets of Ti/Al and Ag/Cu. The diffusion of the Ag,Cu nanoparticles at the sample surface, as well as their quantity, size, shape and distribution, was controlled by appropriate adjustment of the power applied to the Ag/Cu- target, and the temperature and time of the deposition process. The mechanical, tribological and bactericidal properties of the compound depend on, among other factors, the above-mentioned characteristics of the nanoparticles. The microstructure, surface topography, and chemical and phase composition were analyzed by scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. To evaluate the bactericidal effect of the coatings, in vitro inhibition and adhesion tests were carried out using selected Staphylococcus aureus and Escherichia coli, two of the major pathogens associated with infections frequently found in hospital environments. The coating without doping presented a structure of columnar growth, which became densified with the increase in the Ag-Cu content and took on a glassy appearance, accompanied by an increased size of the Ag-Cu particles and consequently also in the surface roughness. TiAlN(Ag,Cu) with 17 and 20 at.% Ag-Cu exhibited a higher bactericidal effect than TiAlN, showing high inhibition and less adhesion to both bacteria strains. Another series of techniques that comprehensively describe the relationship between external factors and the bactericidal response of the material were made. Based on the results obtained, the developed nanostructured coating system can be considered very promising for potential applications in surgical and dental instrumentation.
Nanostructured implant is an emerging field that is finding enormous scope in the medical science and dental implant. Surface nanofeatures are providing considerable potential solutions to medical problems by the introduction of better biomaterials, improved implant design, and surface engineering techniques such as coating, patterning, functionalization and molecular grafting at the nanoscale. This review is of interdisciplinary nature, addressing the history and development of dental implant, and emerging area of nanotechnology in dental implant. After a brief introduction on nanotechnology in dental implant, the main classes of dental implants, an overview of different types of nanomaterials (i.e. metals, metal oxides, ceramics, polymers and hydrides) used in dental implant together with their unique properties, influence of elemental compositions and surface morphologies and possible applications are presented from a chemical point of view. In the core of this review, the dental implant materials, physical and chemical fabrication techniques, and the role of nanotechnology in achieving ideal dental implants are discussed. Finally, the critical parameters in dental implants design and available data on the current dental implant surfaces that use nanotopography in clinical dentistry are discussed.
This study focused on the study of the influence of nitrogen content on the microstructure, chemical composition, mechanical and tribological properties of TaN coatings deposited on 420 stainless steel and silicon samples (100) using the magnetron sputtering technique. For the deposition of the TaN coatings an argon/nitrogen atmosphere was used, varying the nitrogen flux between 12% and 25%. For the coating characterization, scanning electron microscopy, energydispersive X-ray spectroscopy, atomic force microscopy, X-ray diffraction (XRD), micro-Raman spectroscopy, a microhardness tester, and a ball on disc tribometer were used. A refining of the columnar structure of the coatings, accompanied by a decrease in their thickness with the increased nitrogen content was observed. Initially, fcc-TaN (111) cubic phase growth was observed; this phase was changed to the fcc-TaN (200) above N2 12%. For contents greater than N2 18%, another nitrogen-rich phase was formed and the system tended towards amorphicity, particularly for a coating with N2 25% content. The TaN-1sample deposited with N2 12% in the gas mixture presented the highest micro-hardness value with 21.3GPa and the lowest friction coefficient and wear rate with 0.02 and 1.82x10-7 (mm³/Nm), respectively. From the obtained results, an important relationship between the microstructural, mechanical and tribological properties of the coated samples and their nitrogen content was observed.
In this interview Prof. Eleonore Stump speaks about the causes of the emergence of Analytic Philosophical Theology within the analytic tradition; the advantages of maintaining the traditional picture of perfect being theology with regards to divine attributes; her conception about the importance of biblical narratives in facing the problem of suffering; and the importance of university involvement in research on philosophical theology.
En este trabajo se desarrolló el recubrimiento compuesto de TaN(Ag) con una variación del contenido de plata entre 2,26 y 28,51 %at, mediante la técnica de pulverización catódica asistida por campo magnético desbalanceado. Se eligió el recubrimiento que presentó el mejor balance entre propiedades mecánicas y tribológicas, y se sometió a un ciclo de tratamientos térmicos con temperaturas entre 175 °C y 275 °C para producir la nucleación, el crecimiento y difusión controlada de las nanopartículas de Ag hasta la superficie del recubrimiento. Se verificó el tamaño y densidad de distribución de las nanopartículas en la superficie del recubrimiento, y su influencia en las propiedades mecánicas y tribológicas. Posteriormente se estudió el efecto bactericida frente a la bacteria P. aeruginosa mediante las pruebas de inhibición al crecimiento y de adherencia, así como el comportamiento citotóxico del material frente a osteoblastos humanos utilizando el método MTT. El recubrimiento TaN(Ag)-3 tratado térmicamente a 200 °C durante 4 min, incrementó la microdureza del acero inoxidable AISI 316L de 2,6 GPa a 10,7 GPa, y disminuyó la tasa de desgaste de 1.11x10-3 mm3/N.m a 0.17x10-12 mm3/N.m.. Este recubrimiento presentó 100% de viabilidad celular de osteoblastos, y un excelente comportamiento a la inhibición del crecimiento y adherencia de la bacteria P. aeruginosa.
Treatment of implants with peri-implantitis is often unsuccessful, because an instrumented implant surface and residual microbial biofilm impedes re-osseointegration. The application of cold atmospheric plasma (CAP) could be a simple and effective strategy to overcome the inherent problems of peri-implantitis treatment. CAP is able to destroy and eliminate bacterial biofilms. Additionally, it increases the wettability of titanium, which supports cellular attachment. In this study, the behaviour of osteoblasts on titanium discs was analysed after treatment of bacterial biofilms with CAP, brushing, or a combination of both. A human plaque biofilm was cultured on titanium discs. Treatment with a brush (BR), 1% oxygen/argon CAP (PL), or brushing combined with CAP (BR + PL) was used to eliminate the biofilm. Discs without biofilm (C), autoclaved biofilm (AUTO) and untreated biofilm (BIO) served as controls. Subsequently, human osteoblastic cell growth (MG-63) was observed after 1 and 24 h. Biofilm remnants on BR and PL impaired osteoblastic cell development, whereas the BR + PL provided an increased area of osteoblastic cells. A five-day cell growth was only detectable on BR + PL treated discs. The combination of established brushing and CAP application may be a promising strategy to treat peri-implantitis.
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S keletal tissue is exposed to mechanical forces throughout a vertebrate life span, and bone mass is adjusted in response, either absorbing existing skeletal material or synthesising new bone in a site-specific manner. The precise cellular signalling mechanisms by which bone synthesis is controlled within developing osteoblasts and progenitor cells remains undefined. The process is likely to include early electrophysiological responses, possibly mediated by integrins and stretch activated ion channels, followed by activation of intracellular signalling pathways. These mechanisms can then act to regulate the actions and transcription levels of various transcription factors involved in the regulation of the osteoblast phenotype, which in turn regulate the genes that code for bone matrix proteins. This review will briefly discuss role of the key genetic regulators of the osteoblast phenotype, starting with various transcription factors, moving on to some key matrix proteins.
Recibido para revisar 15 de Mayo de 2006, aceptado 8 de Agosto de 2006, versión final 7 de Marzo de 2007 RESUMEN: Empleando la técnica de Pulverización catódica con radiofrecuencia y magnetrón (Magnetron Sputtering RF), se prepararon películas de (Ti,Al)N sobre sustratos de acero AISI 4140. Se utilizó un blanco formado con polvos metálicos de Ti y Al, con composición nominal 60% Ti y 40% Al (porcentaje en átomos) y una razón de presiones parciales de nitrógeno-argón, PN 2 /PAr de 0,1 aproximadamente; la temperatura del sustrato se varió entre 260 y 330 ºC y el tiempo de deposición entre 2 y 4,5 horas para obtener películas con diferentes espesores. La composición química de las películas se determinó mediante la técnica de energía dispersada de rayos X (EDX), y su topografía mediante microscopía de fuerza atómica (AFM). Igualmente se midió micro dureza, y se determinó su comportamiento electroquímico mediante espectroscopia de impedancia electroquímica EIS y ensayos TAFEL. Las películas obtenidas presentaron granos globulares, uniformes y de pequeño diámetro, con características electroquímicas de protección al sustrato frente a procesos de corrosión. ABSTRACT: TiAlN films were deposited by rf magnetron sputtering onto AISI 4140 steel substrates. A mixed target of metallic Ti and Al with a nominal composition of 60 atom% Ti and 40 atom% Al was used. The substrate temperature was varied between 260 ºC and 330 ºC, at a PN 2 /PAr pressure ratio of about 0.1. Coatings of different thickness were obtained, varying the time deposition between 2 and 4,5 hours. The chemical composition of the films was determined by EDX, and the surface topography by AFM. The electrochemical behavior, determined by EIS and TAFEL, and the micro-hardness were analyzed; the coatings displayed mainly a granular structure with small and regular grains.
Surface morphology modification during in situ cleaning of physical vapor deposition (PVD) process is essential to strengthen and prevent unexpected adhesion failure during machining. Applying pulse direct current (PDC) on substrate bias is still uncommon compared to a conventional direct current (DC). This paper is to compare the effects of DC and PDC applied at substrate bias, to the surface roughness and homogeneity. Tungsten carbide (WC) cutting tool insert and argon were used as substrate and inert gas, respectively. The runs were conducted to compare the bias at DC (-500 V) and PDC (-200 V, -500 V, -800 V). The surface roughness and homogeneity were inspected using atomic forced microscopy (AFM) and Minitab version 16 exploited to analyze the data. The wettability based on water drop static contact angle on the substrate surface was measured by a digital 800k USB 2.0 CCD DCAM and VIS ver7 (Professional Edition) software. PDC on the substrate bias produced finer grain structures compared to DC. Further increase in PDC voltage resulted in homogenous surface with finer and more globular microstructure with higher surface energy. Hence PDC at optimum level provides better surface readiness prior to coating compared to DC and proven to be a critical factor for further enhancement of coating adhesion.
Ultrasound irradiation was used for anchoring silver nanoparticles with an average size from 10 to 50 nm onto the surface of acrylonitrile–butadiene–styrene (ABS) sheets 1 mm thick. The sonochemical reduction was carried out under argon at room temperature. Silver nanoparticles were obtained and deposited on the ABS surface by the irradiation of a mixture containing ABS plaques, silver nitrate (AgNO3), ethylene glycol and water. Reaction conditions such as temperature, AgNO3 concentration and irradiation time were controlled to achieve the deposition of silver nanoparticles onto the surface of ABS sheets. Nano silver coated ABS samples were characterized by X-ray diffraction, transmission and scanning electron microscopy, Raman spectroscopy and antimicrobial activity, specifically against the fungus, Aspergillius niger, and the bacterium, Escherichia coli. The observed results may be applied in the design of industrial ABS sheets with antimicrobial characteristics.
Ag-TiCN coatings were deposited by dc reactive magnetron sputtering and their structural and morphological properties were evaluated. Compositional analysis showed the existence of Ag-TiCN coatings with different Ag/Ti atomic ratios (ranging from 0 to 1.49). The structural and morphological properties are well correlated with the evolution of Ag/Ti atomic ratio. For the samples with low Ag/Ti atomic ratio (below 0.20) the coatings crystallize in a B1-NaCl crystal structure typical of TiC0.3N0.7. The increase in Ag/Ti atomic ratio promoted the formation of Ag crystalline phases as well as amorphous CNx phases detected in both x-ray photoelectron spectroscopy and Raman spectroscopy analysis. Simultaneously to the formation of Ag crystalline phases and amorphous carbon-based phases, a decrease in TiC0.3N0.7 grain size was observed as well as the densification of coatings.
Studies on biomedical applications of nanoparticles are growing with a rapid pace. In medicine, nanoparticles may be the solution for multi-drug-resistance which is still a major drawback in chemotherapy of cancer. In the present study, we investigated the potential cytotoxic effect of silver nanoparticles (Ag NPs) and silver ions (Ag(+)) in both parent and tamoxifen-resistant T47D cells in presence and absence of tamoxifen. Ag NPs were synthesized (< 28 nm) and MTT assay was carried out. The associated IC(50) values were found to be: 6.31 µg/ml for Ag NPs/parent cells, 37.06 µg/ml for Ag NPs/tamoxifen-resistant cells, 33.06 µg/ml for Ag(+)/parent cells and 10.10 µg/ml for Ag(+)/resistant cells. As a separate experiment, the effect of subinhibitory concentrations of Ag NPs and Ag(+) on the proliferation of tamoxifen-resistant cells was evaluated at non-toxic concentrations of tamoxifen. Our results suggested that in non-cytotoxic concentrations of silver nanomaterials and tamoxifen, the combinations of Ag(+)-tamoxifen and Ag NPs-tamoxifen are still cytotoxic. This finding may be of great potential benefit in chemotherapy of breast cancer; since much lower doses of tamoxifen may be needed to produce the same cytotoxic effect and side effects will be reduced.
Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth. © 2003 American Vacuum Society.
The corrosion behaviors of single layer TiN, CrN, TiAlN and multilayer TiAlN/CrN coatings, deposited on steel substrate using a multi-target reactive direct current magnetron sputtering process, were studied in 3.5% NaCl solution by potentiodynamic polarization and electrochemical
impedance spectroscopy (EIS). The total thickness of the coatings was about 1.5 μm. About 0.5 μm thick chromium interlayer was used for improved adhesion of the coatings. The potentiodynamic polarization measurements showed that for all the coatings the corrosion potential shifted
to higher values as compared to the uncoated substrate. Similarly, the corrosion current density decreased for coated samples, indicating better corrosion resistance of the coated samples. The multilayer coatings of TiAlN/CrN exhibited superior corrosion behavior as compared to the single layer coatings. The Nyquist and the Bode plots obtained from the EIS measurements were fitted by appropriate equivalent circuits to calculate the
pore resistance, the charge transfer resistance and the capacitance. These studies revealed that the pore resistance was lowest for TiN coatings, which increased for TiAlN coatings. TiAlN/CrN multilayer coatings exhibited highest pore resistance. No significant change in the capacitive
behavior of the coatings was observed, suggesting minimal morphological changes as a result of immersion in the electrolyte. This could be attributed to shorter immersion durations. These studies were confirmed by examining the corroded samples under scanning electron microscope.
Preliminary experiments conducted with additional interlayer of electroless nickel (5.0 μm thick) have shown significant improvement in the corrosion resistance of the coatings.
© 2006 Elsevier B.V. All rights reserved.
This article reviews the mechanisms of bacterial adhesion to biomaterial surfaces and the factors affecting the adhesion. The process of bacterial adhesion includes an initial physicochemical interaction phase (phase one) and a late molecular and cellular interaction phase (phase two), which is a complicated process affected by many factors, including the characteristics of the bacteria themselves, the target material surface, and the environmental factors, such as the presence of serum proteins or bactericidal substances. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 43: 338–348, 1998
We quantitatively evaluated the adhesion of human osteoblasts on orthopedic metallic substrates (Ti6Al4V alloy) with various surface roughnesses at several times after inoculation and studied its correlation with qualitative changes in the expression of adhesion proteins and with parameters extensively describing the surface topographies. Cells were orientated in a parallel order on polished surfaces. This orientation was not affected by residual grooves after polishing. On sandblasted surfaces the cells never attained confluence and had a stellate shape, and the cell layer had no particular organization. Extracellular matrix (fibronectin, type I collagen, osteopontin) and cytoskeletal protein (actin, vinculin) orientation reflected the cell layer organization. In our experiment human osteoblasts expressed α3β1 integrin but not α2β1 integrin. In addition to currently analyzed roughness magnitude parameters, we calculated roughness organization parameters (fractal dimension parameters) of the substrates. We observed lower adhesion and proliferation on less organized surfaces (i.e., sandblasted ones). The significant statistical correlation observed between fractal dimension parameters (describing surface roughness organization) and cell parameters adds a new concept to the studies of substratum roughness influence on cell behavior. An attempt at modelization of the cell–surface interaction was made that includes the influence of fractal dimensions parameters. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 49, 155–166, 2000.
The electrochemical behavior of single layer TiN, CrN, TiAlN and multilayer TiAlN/CrN coatings, deposited on steel substrates using a multi-target reactive direct current (dc) magnetron sputtering process, was studied in 3.5% NaCl solution. The total thickness of the coatings was about 1.5 μm. About 0.5 μm thick chromium interlayer was used to improve adhesion of the coatings. With an aim to improve the corrosion resistance, an additional interlayer of approximately 5 μm thick electroless nickel (EN) was deposited on the substrate. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to study the corrosion behavior of the coatings. Scanning electron microscopy and energy dispersive X-ray analysis were used to characterize the corroded samples. The potentiodynamic polarization tests showed lower corrosion current density and higher polarization resistance (Rp) for the coatings with EN interlayer. For example, the corrosion current density of TiN coated steel was decreased by a factor of 10 by incorporating 5 μm thick EN interlayer. Similarly, multilayer coatings of TiAlN/CrN with EN interlayer showed about 30 times improved corrosion resistance as compared to the multilayers without EN interlayer. The porosity values were calculated from the potentiodynamic polarization data. The Nyquist and the Bode plots obtained from the EIS data were fitted by appropriate equivalent circuits. The pore resistance (Rpore), the charge transfer resistance (Rct), the coating capacitance (Qcoat) and the double layer capacitance (Qdl) of the coatings were obtained from the equivalent circuit. Multilayer coatings showed higher Rpore and Rct values as compared to the single layer coatings. Similarly, the Qcoat and Qdl values decreased from uncoated substrate to the multilayer coatings, indicating a decrease in the defect density by the addition of EN interlayer. These studies were confirmed by examining the corroded samples under scanning electron microscopy.
To investigate the mechanism of inhibition of silver ions on microorganisms, two strains of bacteria, namely Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), were treated with AgNO3 and studied using combined electron microscopy and X-ray microanalysis. Similar morphological changes occurred in both E. coli and S. aureus cells after Ag⁺ treatment. The cytoplasm membrane detached from the cell wall. A remarkable electron-light region appeared in the center of the cells, which contained condensed deoxyribonucleic acid (DNA) molecules. There are many small electron-dense granules either surrounding the cell wall or depositing inside the cells. The existence of elements of silver and sulfur in the electron-dense granules and cytoplasm detected by X-ray microanalysis suggested the antibacterial mechanism of silver: DNA lost its replication ability and the protein became inactivated after Ag⁺ treatment. The slighter morphological changes of S. aureus compared with E. coli recommended a defense system of S. aureus against the inhibitory effects of Ag⁺ ions. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 52, 662–668, 2000.
In the sensors field, titanium based coatings are being used for the acquisition/application of electrical signals from/to piezoelectric materials. In this particular case, sensors are used to detect dynamic mechanical loads at early stages after intervention of problems associated with prostheses implantation. The aim of this work is to select an adequate electrode for sensor applications capable, in an initial stage to avoid bone cell adhesion, but at a long stage, permit osteointegration and osteoinduction. This work reports on the evaluation of osteoblast MC3T3-E1 cells behavior in terms of proliferation, adhesion and long-term differentiation of two different systems used as sensor electrodes: Ti1-xAgx and Ag-TiNx deposited by d.c. and pulsed magnetron sputtering at room temperature on poly(vinylidene fluoride) (PVDF). The results indicated an improved effect of Ag-TiNx electrodes compared with Ti1-xAgx and TiN, in terms of diminished cell adhesion and proliferation at an initial cell culture stage. Nevertheless, when cell culture time is longer, cells grown onto Ag-TiNx electrodes are capable to proliferate and also differentiate at proper rates, indicating the suitability of this coating for sensor application in prostheses devices. Thus, the Ag-TiNx system was considered the most promising electrode for tissue engineering applications in the design of sensors for prostheses to detect dynamic mechanical loads.
In general terms, there are four elements which influence on bacterial adhesion: the material, the micro organisms, antimicrobials and defence mechanisms. The influence of the material is more relevant at the initial states of adhesion where the proper material, its roughness or its superficial energy can have some influence. If there is some influence of the material in the bacterial adhesion, it relies on the features of the acquired film and on the specificity of the adsorved salivary proteins (receptors), which can be influenced by the composition of the material or the characteristics of its surface.
A new bis((2-(dimethylamino)ethyl)(methyl)amido)methyl(tert-butylimido)tantalum complex was synthesized for plasma-enhanced atomic layer deposition (PEALD) of tantalum nitride (TaN) film. Using the synthesized Ta compound, PEALD of TaN was conducted at growth temperatures of 150–250 °C in combination with NH3 plasma. The TaN PEALD showed a saturated growth rate of 0.062 nm/cycle and a high film density of 9.1–10.3 g/cm3 at 200–250 °C. Auger depth profiling revealed that the deposited TaN film contained low carbon and oxygen impurity levels of approximately 3–4%. N-rich amorphous TaN films were grown at all growth temperatures and showed highly resistive characteristic. The Cu barrier performance of the TaN film was evaluated by annealing of Cu/TaN (0–6 nm)/Si stacks at 400–800 °C, and excellent Cu diffusion barrier properties were observed even with ultrathin 2 nm-thick TaN film.
tPiezoelectric materials are interesting for the development of sensors and actuators for biomedical appli-cations in areas such as smart prosthesis, implantable biosensors and biomechanical signal monitoring,among others. For acquiring or applying the electrical signal from/to the piezoelectric material, suitableelectrodes can be produced from Ti based coatings with tailored multifunctional properties: conductiv-ity and antibacterial characteristics through Ag inclusions. This work reports on Ti1−xAgxelectrodes withdifferent Ag/Ti atomic ratios deposited by dc and pulsed magnetron sputtering at room temperature onpoly(vinylidene fluoride), PVDF. The X-ray diffraction (XRD) results revealed that the deposition condi-tions preserve the polymer structure and suggested the presence of crystalline Ti� phase in pure titaniumcoating and fcc-Ag phase in pure silver coating. According to the results obtained from scanning electronmicroscopy (SEM) analysis, the coatings are homogeneous and no clusters were found; since �-PVDFis anisotropic, the deposited coatings replicate the underlying substrate surface. Sheet resistivity valuesshow a typical behavior of a binary alloy system, with low resistivity values for coatings of zone 1 (Ti rich)and zone 3 (Ag rich) and a slightly higher resistivity values in zone 2. The piezoelectricity of the differentsamples show similar values.
TaN0.43 nanowires have been prepared via a controlled thermal process using spongiform Ta as precursor. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the compositions, morphology, and structures of the samples. The results show that the sample consisted of single-crystalline nanorods with the diameter of 100–500 nm. The X-ray diffraction pattern of the product was indexed as the hexagonal TaN0.43. TEM and selected area electron diffraction (SAED) patterns identify that the TaN0.43 nanowires are single-crystalline in nature. The TaN0.43 nanowires display an intensive violet PL emission at around 432 nm. A growth mechanism is proposed for the formation of nanowires.
Silver nanoparticles were deposited on the surface of the external polyamide 6 (PA6) layer of a multilayer film, by spraying and ultrasound-assisted methods. The effect of silver nanoparticles content and deposition method on the mechanical and optical properties of the multilayered films as well as the efficiency of silver ion release and their fungicidal characteristics were evaluated. Itaconic (IA) and Maleic anhydride (MA) were used as adhesion promoter agents for preventing the agglomeration of the silver nanoparticles and for improving the adhesion to the PA6 polymer surface. With IA, a homogeneous distribution of silver nanoparticles on the PA6 surface was achieved. The silver ion release and biocide effect of the multilayered films was found to be dependent on the anhydride type and on the deposition method used. The multilayer films with a layer of PA6-silver nanocomposite demonstrated good fungicidal activity, specifically against fungus Aspergillius niger. The observed results could be applied in the design of industrial films for packaging. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Properties of materials -- Classes of materials used in medicine -- Some background concepts -- Host reactions to biomaterials and their evaluation -- Biological testing of biomaterials -- Degradation of materials in the biological environment -- Application of materials in medicine, biology, and artificial organs -- Tissue engineering -- Implants, devices, and biomaterials: issues unique to this field -- New products and standards -- Perspectives and possibilities in biomaterials science
Tantalum (Ta) and tantalum nitride thin films are highly important as diffusion barriers and adhesion layers in microelectronics and hard coatings for cutting tools. In this study, the effect of the underlying substrate on the phase formation of Ta and the influence of a changing N-2/Ar flow ratio on hardness, phase and composition of reactively formed tantalum nitride have been investigated. Ta is DC sputter deposited and forms beta-Ta on amorphous diamond-like carbon and on the amorphous natural oxide layers of Ti and Si(100) while a 15 nm TaN seed layer results in the formation of alpha-Ta. The chemical composition of the topmost layers of a substrate influences the formation of a-and alpha-Ta. With increasing N-2/Ar flow ratios a transition from amorphous Ta-rich tantalum nitride over face-centered cubic tantalum nitride (fcc-TaN) to (100) textured fcc-TaN at flow ratios above 45% is observed. The hardness of the tantalum nitride thin film reaches a maximum at a flow ratio of 45%, followed by a decrease in hardness for higher N-2/Ar flow ratios. The increase in hardness is associated with a decrease in grain size and shows a stronger correlation for a Meyers and Ashworth relationship than for a Hall-Petch relationship.
The Ti6Al4V surface, commonly employed in biomedical prostheses, has been chemically functionalized by non-covalent binding to obtain improved antibacterial responses. The methodology combines the well-known antibacterial activity of silver(I) ions with those of other common antimicrobials such as carboxylic acids, trans-cinnamaldehyde, farnesol, and the broad-range antibiotic chloramphenicol. To this end, on previously aminosilanizated Ti6Al4V surfaces (Material A) were attached via saline bonds (involving both ionic and dipole interactions) acetic, propanoic, benzoic, and sorbic acids (Materials B). Likewise silver(I) acetate undergoes non-covalent cross-linking with the aminosiloxane-coated surface (Material C) after incubation at 60 ºC for 48 h, thus resulting in a density of ca. 4.11 x 10- 8 mol cm- 2. The coordinating ability of Ag(I) ions enables further attachment of the above-mentioned carboxylic acids onto the surface (Material D) and other neutral antimicrobials (Materials E). Surface characterization has been accomplished using infrared spectroscopy and X-ray photoelectron spectroscopy, which support non-covalent binding. In particular, the existence of ammonium and carboxylate groups together with other intact functional groups (carbonyl, hydroxyl and amino) reveals that aminosiloxane-coated surfaces adhere via both ionic and weak interactions. As a proof of concept, adhesion and viability tests of Staphylococcus aureus on the functionalized surfaces show the adequate performance of the coverage at short and medium contact times with the surrounding cells.
A key property of multicomponent bioactive nanostructured Ti(C,N)-based films doped with Ca, P, and O (TiCaPCON) that can be improved further is their antibacterial effect that should be achieved without compromising the implant bioactivity and biocompatibility. The present work is focused on the study of structure, chemical, mechanical, tribological, and biological properties of Ag- and Cu-doped TiCaPCON films. The films with Ag (0.4–4 at.%) and Cu (13 at.%) contents were obtained by simultaneous sputtering of a TiC0.5–Ca3(PO4)2 target and either an Ag or a Cu target. The film structure was studied using X-ray diffraction, transmission and scanning electron microscopy, energy dispersive X-ray spectroscopy, glow discharge optical emission spectroscopy, and Raman-shift and IR spectroscopy. The films were characterized in terms of their hardness, elastic modulus, dynamic impact resistance, friction coefficient and wear rate (both in air and normal saline), surface wettability, electrochemical behavior and Ag or Cu ion release in normal saline. Particular attention was paid to the influence of inorganic bactericides (Ag and Cu ions) on the bactericidal activity against unicellular yeast fungus Saccharomyces cerevisiae and gram-positive bacteria Lactobacillus acidophilus, as well as on the attachment, spreading, actin cytoskeleton organization, focal adhesions, and early stages of osteoblastic cell differentiation. The obtained results show that the Ag-doped films are more suitable for the protection of metallic surfaces against bacterial infection compared with their Cu-doped counterpart. In particular, an excellent combination of mechanical, tribological, and biological properties makes Ag-doped TiCaPCON film with 1.2 at.% of Ag very attractive material for bioengineering and modification of load-bearing metal implant surfaces.
Cu-doped TaN films were known to have good anti-bacterial and anti-wear behaviors. However, in some of the practical applications, the depletion of surfaced Cu might eventually cause the films to lose their effectiveness against wear and bacteria. This study hence was aimed at understanding the rejuvenation process for these films. The structures, morphologies, antibacterial and mechanical properties of TaN–Cu nanocomposite thin films after multi-rejuvenating processes were the focus of this study. The results revealed that the Cu particles would re-appear on the film surface after each rejuvenation cycle, which can recover the anti-wear and anti-bacterial properties. The particle size and density appeared to decrease with the increase of rejuvenation cycle. The hardness of the samples would also decrease with the number of cycles. This was due to the slow depletion of Cu atoms, which might cause the increase of porosity and the decrease of hardness. The wear rates and friction coefficients of these rejuvenated samples depend mainly on the possibility of forming lubricious Cu films, although film hardness also played a certain role. In sum, the present study confirms that the anti-bacterial and anti-wear behaviors can be rejuvenated twice or more, under the experimental conditions adopted.
TaN–(Ag,Cu) nanocomposite films were deposited by reactive co-sputtering on Si(001). The films were then annealed using RTA (Rapid Thermal Annealing) at 200–400 °C to induce the nucleation and growth of metal particles in TaN matrix and on film surface. After the surface morphologies were analyzed, the samples were tested for their antibacterial behaviors against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. It is found that the antibacterial efficiency against either E. coli or S. aureus can be much improved for TaN–(Ag,Cu), comparing with TaN–Ag or TaN–Cu films. The annealing temperature for TaN–(Ag,Cu) can be as low as 250 °C. Being annealed at this temperature, the film still shows good antibacterial behaviors against either bacterium. The synergistic effect due to the co-existence of Ag and Cu is obvious, while the films still shows good tribological behaviors.
This paper concentrates on the deposition of Ta, TaN and TaNO thin films by r.f. magnetron sputtering in Ar/N2/O2 gas mixtures. The film properties and their suitability as diffusion barriers and protective coatings in silicon devices were characterized using four-point probe measurements, Auger electron spectroscopy, Rutherford backscattering, glancing angle X-ray diffractometry, atomic force microscopy and scanning electron microscopy. With the addition of N2 to the gas mixture a transition from tetragonal Ta to b.c.c.-Ta(N) was detected, leading to the nanocrystalline metastable b.c.c.-Ta(N) phase with approximately 20 at.% interstitially incorporated nitrogen. Increasing the nitrogen flow above a critical value, an abrupt transition between metal-sputtering to nitride-sputtering mode was observed, resulting in a sharp increase in the N:Ta atomic ratio slightly above the stoichiometric value for the TaN phase, which was found to exhibit f.c.c. structure. With the addition of oxygen at fixed nitrogen flow the films tend to grow in an amorphous state. Due to the lack of short-circuit diffusion paths, the as-deposited amorphous Ta(N,O) films are considered as excellent candidates for ultra-thin diffusion barriers and protection layers in future Cu-metallized ULSI devices.
Surface engineering using plasma, grafting, and related techniques is an important area in biomaterials research and biomedical engineering. The burgeoning technology enables the modification of selected surface characteristics while the favorable bulk materials properties can be retained. In this invited mini-review, recent work related to surface modification of biomaterials by plasma-based and related techniques conducted in the Plasma Laboratory at City University of Hong Kong is described. Examples of new applications include enhancement of antimicrobial properties and cytocompatibility of plasma and surface-treated and nanostructured biomaterials, corrosion resistance of plasma-treated biodegradable metals, as well as targeted drug delivery capability and magnetic properties of surface-modified silica nanospheres and polymeric micelles.
In this study, the effects of N content, grain size, and growth texture on the hardness and Young's modulus of nanocrystalline Ta and Ta(N) thin films deposited using reactive DC magnetron sputtering are examined. The structure of the films was determined by X-ray diffraction and the hardness and modulus by nanoindentation. Pure Ta films typically exhibit a dominant (2 0 0) growth mode of the β-tetragonal phase. However, under certain conditions significant (2 0 2) growth is noted which is correlated with a marked decrease in hardness (from 18 to 11 GPa). Addition of N (pN2 = 0.026, 0.052, and 0.100 mTorr) increases the hardness of the Ta films with the maximum hardness (32 GPa) obtained for the films with pN2 = 0.100 mTorr. In the case of low Ta(N) films (pN2 = 0.026 mTorr), the hardness exhibits a clear microstructural dependence. A decrease in the grain size causes the hardness to increase from 16 to 24 GPa. The Young's modulus values, however, do not exhibit any systematic variation with either growth texture or grain size.
Contact angles of diiodomethane, bromoform, water, formamide, and glycerol were measured on cholesterol surfaces both bare and precontacted with bile salts (sodium cholate, sodium deoxycholate, and sodium chenodeoxycholate). Ten different sets of the measured contact angles were used for the calculation of the surface free energy components, Lifshitz-van der Waals, γLWs, electron acceptor, γ+s, and electron donor, γ-s. Additionally, contact angles of the same liquids were measured on the pellets of the bile salts. From the calculated values of the components it results that in the case of a bare surface, almost any of the liquid triplets can be used for determination of the surface free energy components. The lowest confidence level can be put to the values obtained from contact angles of the liquid set, including two weakly monopolar liquids (diiodomethane and bromoform), and also that including two liquids with similar strong electron donor and relatively weak electron acceptor interactions (glycerol and formamide). The situation is much more complicated in the case of precontacted surfaces, especially when micelles of bile salts were formed in the solutions in which the cholesterol surface was dipped. The results were very scattered and dependent on the triplet used for the calculations. However, an explanation can be found for such scattered values, based on calculations of the surface free energy of bile salt surface, and on the assumption of the presence of hydrating water molecules around bile salt ones.
Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn+. This study evaluates the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series platinum is more active than silver and therefore Pt enhances Ag+ ion formation through galvanic action. In order to evaluate this, potential step (chronoamperometric) experiments were performed on silver/platinum alloys containing 0.5 and 3.0% Pt. The resulting current–time curves demonstrated that Ag+ formation increased with platinum addition by up to 100%. A magnetron sputtering target was fabricated consisting of 1% Pt in a Ag matrix. This was used to sputter Pt/Ag coatings with thicknesses in the range 5–12 nm onto silicone and polyurethane substrates. The bacterial adhesion and bactericidal effects of the coated polymers was assessed using Straphylococcus epidermidis and the cytotoxicity using fibroblast cells. The addition of 1% Pt was found to significantly enhance the anti-bacterial effectiveness of the Ag coatings. Up to a 2 log reduction in bacterial adhesion was achieved for 5 nm thick Ag/1% Pt coatings on silicone, which did not exhibit cytotoxicity.
The article reports on the present status of knowledge in the field of hard and superhard nanocomposite coatings prepared by magnetron sputtering. Special attention is devoted to the two-phase nanocomposites composed of one hard and one soft phase. Trends of the next development are outlined.
The present work deals with the influence of coating thickness on the tribological response of bi-layer model coatings consisting of CrN with Cr interlayer with varying Cr/CrN thickness ratios on high-speed steel. Ball-on-disc experiments were carried out in ambient air at room temperature and alumina balls as counterbodies. The mechanical stresses in both layers generated during the tests were calculated with the software package Elastica. Wear tracks on the samples were characterised using both scanning electron microscopy and optical profilometry. The results show that the interlayer thickness plays a determinant role in the tribological response of the coatings provided that the CrN layer thickness exceeds a critical value to withstand mechanical wear.
The barrier performance and properties (resistivity, crystalline phase and surface microroughness) of tantalum nitride films, as well as the relationship between grain size and diffusivity of copper films, are reported. The resistivity and Ra roughness of Ta2N film formed by reactive sputtering using argon and nitrogen plasma are ˜200 µOmega·cm and ˜0.35 nm, respectively. The Ta2N diffusion barrier exhibits better barrier performance than Ta4N and bcc-Ta diffusion barriers. Giant-grain copper interconnects formed by sputtering in low-energy ion bombardment process show lower diffusivity than small-grain copper interconnects. The barrier performance of tantalum nitride film was evaluated by electrical measurement. An n+p junctions having 20 µm×20 µm contact holes filled with 10-nm-thick Ta2N diffusion barriers and giant-grain copper interconnects exhibit no increase in reverse-bias current after annealing at 700°C for 30 min in argon ambient.
In this paper, diamond like carbon (DLC) films were coated on polyethylene terephthalate (PET) film substrate as a function of biasing voltage using plasma enhanced chemical vapour deposition. The surface morphology of the DLC films was analyzed by scanning electron microscopy and atomic force microscopy. The chemical state and structure of the films were analyzed by X-ray photoelectrons spectroscopy and Raman spectroscopy. The micro hardness of the DLC films was also studied. The surface energy of interfacial tension between the DLC and blood protein was investigated using contact angle measurements. In addition, the blood compatibility of the films was examined by in vitro tests. For a higher fraction of sp3 content, maximum hardness and surface smoothness of the DLC films were obtained at an optimized biasing potential of −300V. The in vitro results showed that the blood compatibility of the DLC coated PET film surfaces got enhanced significantly.
TaN–Ag nanocomposite films were deposited by reactive cosputtering on Si. The films were then annealed using RTA (rapid thermal annealing) at 350 °C for 2, 4 and 8 min respectively to induce the nucleation and growth of Ag particles in TaN matrix and on film surface. FESEM (field emission scanning electron microscopy) were applied to characterize Ag nanoparticles emerged on the surface of TaN–Ag thin films. The effect of annealing on the antibacterial properties of these films was studied. The results first confirm that annealing by RTA can cause Ag nanoparticles with various sizes to emerge on the TaN surface. Consequently, the antibacterial behavior will vary, depending on the amount and size of the surfaced Ag particles.
Tantalum nitride (TaxN1−x) coatings were deposited onto high-speed steel using reactive DC magnetron sputtering. Five different combinations of magnetron power and nitrogen flow were used. Phase analysis (XRD) revealed that the phase composition changes with increasing N2 flow from a mixture of Ta and Ta2N to single phase Ta2N. This result was supported by GDOES analysis of the chemical composition. The coating hardness and residual stress were both found to increase with the amount of Ta2N in the coatings. In scratch testing, it was not possible to provoke adhesive failures at loads up to 100N. Finally, the coating abrasion resistance was very high for all specimens and found to increase with the amount of Ta2N in the coatings.
To review the literature on the prevalence and incidence of peri-implantitis.
Out of 322 potentially relevant publications we identified 29 articles concerning 23 studies, with information on the presence of signs of peri-implantitis in populations of at least 20 cases.
All studies provided data from convenience samples, typically from patients who were treated in a clinical center during a certain period, and most data were cross-sectional or collected retrospectively. Based on the reviewed papers one may state that the prevalence of peri-implantitis seems to be in the order of 10% implants and 20% patients during 5-10 years after implant placement but the individual reported figures are rather variable, not easily comparable and not suitable for meta-analysis. Factors that should be considered to affect prevalence figures are the disease definition, the differential diagnosis, the chosen thresholds for probing depths and bone loss, differences in treatment methods and aftercare of patients, and dissimilarities in the composition of study populations. Smoking and a history of periodontitis have been associated with a higher prevalence of peri-implantitis.
A comparison was made between the electrochemical corrosion behavior of chromium carbonitride (Cr-(C,N)) and chromium nitride (Cr-N) coatings produced by evaporation in a thermionic-arc ion-plating apparatus at 450 °C. These coatings were deposited on substrates in the form of discs of mild-steel (CK 45) and stainless-steel (SS 304). Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) were the techniques used to characterize the corrosion behavior. The potentiodynamic tests revealed the current density versus potential for the coated and uncoated substrates and the difference in their corrosion potentials (Ecorr). In all cases the Ecorr shifted to a more positive potential after the coatings were applied. The electrochemical impedance spectroscopy measurements as a function of immersion time were carried out in a 0.5 M NaCl solution at the Ecorr. The corrosion properties, lower current density, and higher polarization resistance were found to be two to six times better than the uncoated substrate for the Cr-(C,N) coatings and two orders of magnitude better for the Cr-N coatings.
The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
This paper attempts to reduce some of the confusion that exists over the nature of the nitrogen-rich layer produced by nitriding austenitic stainless steel at temperatures below 500°C. Cross-sectional transmission electron microscopy shows that the modified layer is dominated by a cubic phase with considerable expansion of the austenite lattice. In some cases, a thin (<0.1 μm) layer of CrN and α-Fe precipitates occurs right at the surface. There is an increase in dislocation density near the interface with the underlying material. These sublayers are not observed in X-ray diffraction, which confirms the dominant phase as an expansion of the austenite lattice and indicates a slight triclinic distortion, although a tetragonal lattice is not completely ruled out. Magnetic-force microscopy shows that the expanded austenite is ferromagnetic over most of the layer but becomes paramagnetic as the nitrogen concentration drops towards the interface with the underlying material. These features are common to austenitic stainless steel nitrided by low-pressure rf plasmas, plasma-immersion ion implantation and pulsed dc-glow discharges.
Many of the chemical and biological effects of silver nanoparticles (Ag NPs) are attributed to the generation of reactive oxygen species (ROS). ESR spectroscopy was used to provide direct evidence for generating ROS during decomposition of H(2)O(2) assisted by Ag NPs. Hydroxyl radical formation was observed under acidic conditions and was accompanied by dissolution of Ag NPs. In contrast, evolution of O(2) was observed in alkaline solutions containing H(2)O(2) and Ag NPs; however, no net dissolution of Ag NPs was observed due to re-reduction of Ag(+) as evidenced by a cyclic reaction. Since H(2)O(2) is a biologically relevant product being continuously generated in cells, these results obtained under conditions mimicking different biological microenvironments may provide insights for finding new biomedical applications for Ag NPs and for risk assessment.
Silver-doped organic–inorganic hybrid coating solutions were prepared by incorporating AgNO3 into organic–inorganic hybrid sols derived from methacryloxypropyl trimethoxysilane (MEMO) and vinyltriethoxysilane (VTES) using the sol–gel method. They were applied on the soda-lime slide glass, and crack-free and transparent coatings were obtained by a low temperature heat treatment at 150 °C for 3 h. The formation of Ag colloids in the coating films was confirmed by UV–vis spectroscopy and scanning electron microscopy. The size control of Ag colloids in the coating films was possible by adjusting initial AgNO3 concentrations in the coating solutions. The antibacterial activity of the coating films was tested against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria by film contact method. The coating films exhibited an excellent antibacterial activity against both S. aureus and E. coli.