High hardness in the biocompatible intermetallic compound β-Ti3Au

Nanomechanical and Microstructural Characterization of Biocompatible TiAu Thin Films Grown on Glass and Ti6Al4V Substrates

Ti-Au intermetallic-based material systems are being extensively studied as next-generation thin film coatings to extend the lifetime of implant devices. These coatings are being developed for application to the articulating surfaces of total joint implants and, therefore, must have excellent biocompatibility combined with superior mechanical hardness and wear resistance. However, these key characteristics of Ti-Au coatings are heavily dependent upon factors such as the surface properties and temperature of the underlying substrate during thin film deposition. In this work, Ti3Au thin films were deposited by magnetron sputtering on both glass and Ti6Al4V substrates at an ambient and elevated substrate temperature of 275 °C. These films were studied for their mechanical properties by the nanoindentation technique in both variable load and fixed load mode using a Berkovich tip. XRD patterns and cross-sectional SEM images detail the microstructure, while AFM images present the surface morphologies of these Ti3Au thin films. The biocompatibility potential of the films is assessed by cytotoxicity tests in L929 mouse fibroblast cells using Alamar blue assay, while leached ion concentrations in the film extracts are quantified using ICPOEMS. The standard deviation for hardness of films deposited on glass substrates is ∼4 times lower than that on Ti6Al4V substrates and is correlated with a corresponding increase in surface roughness from 2 nm for glass to 40 nm for Ti6Al4V substrates. Elevating substrate temperature leads to an increase in film hardness from 5.1 to 8.9 GPa and is related to the development of a superhard β phase of the Ti3Au intermetallic. The standard deviation of this peak mechanical hardness value is reduced by ∼3 times when measured in fixed load mode compared to the variable load mode due to the effect of nanoindentation tip penetration depth. All tested Ti-Au thin films also exhibit excellent biocompatibility against L929 fibroblast cells, as viability levels are above 95% and leached Ti, Al, V, and Au ion concentrations are below 0.1 ppm. Overall, this work demonstrates a novel Ti3Au thin film system with a unique combination of high hardness and excellent biocompatibility with potential to be developed into a new wear-resistant coating to extend the lifetime of articulating total joint implants.

Biocompatible Ti3Au-Ag/Cu thin film coatings with enhanced mechanical and antimicrobial functionality

BACKGROUND

Biofilm formation on medical device surfaces is a persistent problem that shelters bacteria and encourages infections and implant rejection. One promising approach to tackle this problem is to coat the medical device with an antimicrobial material. In this work, for the first time, we impart antimicrobial functionality to Ti3Au intermetallic alloy thin film coatings, while maintaining their superior mechanical hardness and biocompatibility.

METHODS

A mosaic Ti sputtering target is developed to dope controlled amounts of antimicrobial elements of Ag and Cu into a Ti3Au coating matrix by precise control of individual target power levels. The resulting Ti3Au-Ag/Cu thin film coatings are then systematically characterised for their structural, chemical, morphological, mechanical, corrosion, biocompatibility-cytotoxicity and antimicrobial properties.

RESULTS

X-ray diffraction patterns reveal the formation of a super hard β-Ti3Au phase, but the thin films undergo a transition in crystal orientation from (200) to (211) with increasing Ag concentration, whereas introduction of Cu brings no observable changes in crystal orientation. Scanning and transmission electron microscopy analysis show the polyhedral shape of the Ti3Au crystal but agglomeration of Ag particles between crystal grains begins at 1.2 at% Ag and develops into large granules with increasing Ag concentration up to 4.1 at%. The smallest doping concentration of 0.2 at% Ag raises the hardness of the thin film to 14.7 GPa, a 360% improvement compared to the ∼4 GPa hardness of the standard Ti6Al4V base alloy. On the other hand, addition of Cu brings a 315-330% improvement in mechanical hardness of films throughout the entire concentration range of 0.5-7.1 at%. The thin films also show good electrochemical corrosion resistance and a > tenfold reduction in wear rate compared to Ti6Al4V alloy. All thin film samples exhibit very safe cytotoxic profiles towards L929 mouse fibroblast cells when analysed with Alamar blue assay, with ion leaching concentrations lower than 0.2 ppm for Ag and 0.08 ppm for Cu and conductivity tests reveal the positive effect of increased conductivity on myogenic differentiation. Antimicrobial tests show a drastic reduction in microbial survival over a short test period of < 20 min for Ti3Au films doped with Ag or Cu concentrations as low as 0.2-0.5 at%.

CONCLUSION

Therefore, according to these results, this work presents a new antimicrobial Ti3Au-Ag/Cu coating material with excellent mechanical performance with the potential to develop wear resistant medical implant devices with resistance to biofilm formation and bacterial infection.

Thermal activation of Ti(1-x)Au(x) thin films with enhanced hardness and biocompatibility

The lifetime of orthopaedic implants can be extended by coating the softer Ti₆Al₄V alloy with harder biocompatible thin films. In this work, thin films of Ti_(1-x)Au_(x) are grown on Ti₆Al₄V and glass substrates by magnetron sputtering in the entire x = 0–1 range, before their key biomechanical properties are performance tuned by thermal activation. For the first time, we explore the effect of in-situ substrate heating versus ex-situ post-deposition heat-treatment, on development of mechanical and biocompatibility performance in Ti–Au films. A ∼250% increase in hardness is achieved for Ti–Au films compared to bulk Ti₆Al₄V and a ∼40% improvement from 8.8 GPa as-grown to 11.9 and 12.3 GPa with in-situ and ex-situ heat-treatment respectively, is corelated to changes in structural, morphological and chemical properties, providing insights into the origins of super-hardness in the Ti rich regions of these materials. X-ray diffraction reveals that as-grown films are in nanocrystalline states of Ti–Au intermetallic phases and thermal activation leads to emergence of mechanically hard Ti–Au intermetallics, with films prepared by in-situ substrate heating having enhanced crystalline quality. Surface morphology images show clear changes in grain size, shape and surface roughness following thermal activation, while elemental analysis reveals that in-situ substrate heating is better for development of oxide free Ti₃Au β-phases. All tested Ti–Au films are non-cytotoxic against L929 mouse fibroblast cells, while extremely low leached ion concentrations confirm their biocompatibility. With peak hardness performance tuned to >12 GPa and excellent biocompatibility, Ti–Au films have potential as a future coating technology for load bearing medical implants.

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Combined study on biocompatibility and mechanical performance of Ti–Au films.

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Reports on effect of varying of thermal activation on quality of Ti–Au film structure.

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Clear development of super-hard β-Ti₃Au phase with in-situ thermal activation.

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Peak hardness value > 12 GPa attained for Ti rich films with ex-situ thermal activation.

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All Ti–Au films highly biocompatible with safe cytotoxic profile against L929 cells.

A Programmable Dual-Regime Spray for Large-Scale and Custom-Designed Electronic Textiles

Increasing demand for wearable healthcare synergistically advances the field of electronic textiles, or e-textiles, allowing for ambulatory monitoring of vital health signals. Despite great promise, the pragmatic deployment of e-textiles in clinical practice remains challenged due to the lack of a method in producing custom-designed e-textiles at high spatial resolution across a large area. To this end, a programmable dual-regime spray that enables the direct custom writing of functional nanoparticles into arbitrary fabrics at sub-millimeter resolution over meter scale is employed. The resulting e-textiles retain the intrinsic fabric properties in terms of mechanical flexibility, water-vapor permeability, and comfort against multiple uses and laundry cycles. The e-textiles tightly fit various body sizes and shapes to support the high-fidelity recording of physiological and electrophysiological signals on the skin under ambulatory conditions. Pilot field tests in a remote health-monitoring setting with a large animal, such as a horse, demonstrate the scalability and utility of the e-textiles beyond conventional devices. This approach will be suitable for the rapid prototyping of custom e-textiles tailored to meet various clinical needs.

Me-Doped Ti-Me Intermetallic Thin Films Used for Dry Biopotential Electrodes: A Comparative Case Study

In a new era for digital health, dry electrodes for biopotential measurement enable the monitoring of essential vital functions outside of specialized healthcare centers. In this paper, a new type of nanostructured titanium-based thin film is proposed, revealing improved biopotential sensing performance and overcoming several of the limitations of conventional gel-based electrodes such as reusability, durability, biocompatibility, and comfort. The thin films were deposited on stainless steel (SS) discs and polyurethane (PU) substrates to be used as dry electrodes, for non-invasive monitoring of body surface biopotentials. Four different Ti–Me (Me = Al, Cu, Ag, or Au) metallic binary systems were prepared by magnetron sputtering. The morphology of the resulting Ti–Me systems was found to be dependent on the chemical composition of the films, specifically on the type and amount of Me. The existence of crystalline intermetallic phases or glassy amorphous structures also revealed a strong influence on the morphological features developed by the different systems. The electrodes were tested in an in-vivo study on 20 volunteers during sports activity, allowing study of the application-specific characteristics of the dry electrodes, based on Ti–Me intermetallic thin films, and evaluation of the impact of the electrode–skin impedance on biopotential sensing. The electrode–skin impedance results support the reusability and the high degree of reliability of the Ti–Me dry electrodes. The Ti–Al films revealed the least performance as biopotential electrodes, while the Ti–Au system provided excellent results very close to the Ag/AgCl reference electrodes.

A Review on Laser-Assisted Joining of Aluminium Alloys to Other Metals

Modern industry requires different advanced metallic alloys with specific properties since conventional steels cannot cover all requirements. Aluminium alloys are becoming more popular, due to their low weight, high corrosion resistance, and relatively high strength. They possess respectable electrical conductivity, and their application extends to the energy sector. There is a high demand in joining aluminium alloys with other metals, such as steels, copper, and titanium. The joining of two or more metals is challenging, due to formation of the intermetallic compound (IMC) layer with excessive brittleness. High differences in the thermophysical properties cause distortions, cracking, improper dilution, and numerous weld imperfections, having an adverse effect on strength. Laser beam as a high concentration energy source is an alternative welding method for highly conductive metals, with significant improvement in productivity, compared to conventional joining processes. It may provide lower heat input and reduce the thickness of the IMC layer. The laser beam can be combined with arc-forming hybrid processes for wider control over thermal cycle. Apart from the IMC layer thickness, there are many other factors that have a strong effect on the weld integrity; their optimisation and innovation is a key to successfully delivering high-quality joints.

Study of Ag precipitation and mechanical properties of Ti-Ta-Ag ternary alloy

Ti–25Ta–xAg alloy samples with different content of Ag were prepared by spark plasma sintering method. X-ray diffraction, microscopic metallographic, scanning electron microscopy, and transmission electron microscopy were used to analyze the phase structure and morphology of the alloy samples. Ti–Ta–Ag can form a stable ternary alloy system. Furthermore, with the increase of Ag content and sintering temperature, Ag will be precipitated at the grain boundary. In order to explore the precipitation mechanism of Ag in the alloy and its influence on the mechanical properties, the crystal structure, electronic structure, and elastic constant under different Ag solid solubility were calculated systematically by using first-principles calculations. The results show that the critical temperature of Ag in Ti–Ta–Ag ternary alloy is about 2200 K, and the high temperature is favorable for the aging precipitation of Ag. The lattice constants and mechanical properties of (Ti_1−xAg_x)₃Ta solid solution suddenly change when the Ag solid solubility x value is equal to 0.8, and their changes will follow different rules. The internal mechanism of this phenomenon is that the 4d¹⁰ electronic states of Ag have changed from obvious local electronic states to mixed local and non-local electronic states. These results provide theoretical guidance for the application of Ti–Ta–Ag ternary alloys in biomedicine.

Precipitation of columnar Ag particles from Ti–Ta–Ag ternary alloys improves mechanical properties.

Ultrastable Au nanoparticles on titania through an encapsulation strategy under oxidative atmosphere

Supported gold catalysts play a crucial role in the chemical industry; however, their poor on-stream stability because of the sintering of the gold nanoparticles restricts their practical application. The strong metal-support interaction (SMSI), an important concept in heterogeneous catalysis, may be applied to construct the structure of catalysts and, hence, improve their reactivity and stability. Here we report an ultrastable Au nanocatalyst after calcination at 800 °C, in which Au nanoparticles are encapsulated by a permeable TiO_x thin layer induced by melamine under oxidative atmosphere. Owning to the formed TiO_x overlayer, the resulting Au catalyst is resistant to sintering and exhibits excellent activity and stability for catalytic CO oxidation. Furthermore, this special strategy can be extended to colloidal Au nanoparticles supported on TiO₂ and commercial gold catalyst denoted as RR2Ti, providing a universal way to engineer and develop highly stable supported Au catalysts with tunable activity.

Sintering-resistant Au nanoparticles are highly desirable due to their low Tammann temperature. Here, the authors report an ultrastable titania-supported Au nanocatalyst through an encapsulation strategy under oxidative atmosphere.

Development of Vitroceramic Coatings and Analysis of Their Suitability for Biomedical Applications

Within the field of tissue engineering, thin films have been studied to improve implant fixation of metallic or ceramic materials in bone, connective tissue, oral mucosa or skin. In this context, to enhance their suitability as implantable devices, titanium-based substrates received a superficial vitroceramic coating by means of laser ablation. Further, this study describes the details of fabrication and corresponding tests in order to demonstrate the bioactivity and biocompatibility of the newly engineered surfaces. Thus, the metallic supports were covered with a complex material composed of SiO2, P2O5, CaO, MgO, ZnO and CaF2, in the form of thin layers via a physical deposition techniques, namely pulsed laser deposition. The resulting products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, selected area electron diffraction, and electron energy loss spectroscopy. It was found that a higher substrate temperature and a lower working pressure lead to the highest quality film. Finally, the samples biocompatibility was assessed and they were found to be bioactive after simulated body fluid soaking and biocompatible through the MTT cell viability test.

Effects of chemical disorder in the itinerant antiferromagnet Ti1-x V x Au

The fragile nature of itinerant magnetism can be exploited using non-thermal parameters to study quantum criticality. The recently discovered quantum critical point (QCP) in the Sc-doped (hole-like doping) itinerant antiferromagnet TiAu (Ti_1-x Sc _x Au) raised questions about the effects of the crystal and electronic structures on the overall magnetic behavior. In this study, doping with V (electron-like doping) in Ti_1-x V _x Au introduces chemical disorder which suppresses antiferromagnetic order from [Formula: see text] 36 K for x  =  0 down to 10 K for x  =  0.15, whereupon a solubility limit is reached. Signatures of non-Fermi-liquid behavior are observed in transport and specific heat measurements similar to Ti_1-x Sc _x Au, even though Ti_1-x V _x Au is far from a QCP for the accessible compositions [Formula: see text].

Strong Influence of Ti Adhesion Layer on Electron-Phonon Relaxation in Thin Gold Films: Ab Initio Nonadiabatic Molecular Dynamics

Electron-phonon relaxation in thin metal films is an important consideration for many ultrasmall devices and ultrafast applications. Recent time-resolved experiments demonstrate a significant, more than a factor of five, increase in the electron-phonon coupling and acceleration in the electron-phonon relaxation rate when a narrow Ti adhesion layer is introduced between an Au film and a nonmetal substrate. Using nonadiabatic molecular dynamics combined with real-time time-dependent density functional theory, we identify the reasons that give rise to this strong effect. First, the Ti layer greatly enhances the density of states (DOS) in the energy region starting at 1 eV below the Fermi level and extending several electronvolts above it. Second, Ti atoms are four times lighter than Au atoms and therefore generate larger nonadiabatic (NA) electron-phonon coupling. Because the transition rates depend on coupling and DOS, both the factors accelerate the dynamics. Showing good agreement with the experiments, the time-domain atomistic simulations provide a detailed mechanistic understanding of the electron-phonon relaxation dynamics in thin gold films and related nanomaterials.

Itinerant magnetic metals

In this review, an overview of itinerant magnets without magnetic elements is presented, beginning with a comparison of the local and itinerant moment pictures, the two extremes of magnetism. Then, the theoretical developments leading up to the self-consistent renormalization theory of spin fluctuations will be discussed, followed by an introduction to quantum criticality and the experimental signatures associated with systems near a quantum critical point. Three itinerant magnets without magnetic elements, ZrZn₂, Sc_3.1In, and TiAu are the focus of this review, as their empty d shells set them apart in their purely itinerant character, while several enhanced Pauli paramagnets and intermediate moment magnets are also discussed to put the overall comparison into perspective.

Structural damage of Bacillus subtilis biofilms using pulsed laser interaction with gold thin films

There is a huge interest in developing strategies to effectively eliminate biofilms due to their negative impact in both industrial and clinical settings. In this study, structural damage was induced on two day-old B. subtilis biofilms using the interaction of 532 nm pulsed laser with gold thin films. Radiant exposure of 225 mJ/cm² induced distinct changes on the surface structure and overall morphology of the matured biofilms after laser irradiation. Moreover, at the radiant exposure used, changes in the colour and viscosity of the biofilm were observed which may indicate a compromised extracellular matrix. Irradiated biofilms in the presence of gold film also showed strong propidium iodide signal which implies an increase in the number of dead bacterial cells after laser treatment. Thus, this laser-based technique is a promising approach in targeting and eradicating matured biofilms attached on surfaces such as medical implants.

Rediscovering the Crystal Chemistry of Borides

For decades, borides have been primarily studied as crystallographic oddities. With such a wide variety of structures (a quick survey of the Inorganic Crystal Structure Database counts 1253 entries for binary boron compounds!), it is surprising that the applications of borides have been quite limited despite a great deal of fundamental research. If anything, the rich crystal chemistry found in borides could well provide the right tool for almost any application. The interplay between metals and the boron results in even more varied material's properties, many of which can be tuned via chemistry. Thus, the aim of this review is to reintroduce to the scientific community the developments in boride crystal chemistry over the past 60 years. We tie structures to material properties, and furthermore, elaborate on convenient synthetic routes toward preparing borides.

Hardness of cubic solid solutions

We demonstrate that a hardening rule exists in cubic solid solutions with various combinations of ionic, covalent and metallic bonding. It is revealed that the hardening stress ∆τFcg is determined by three factors: shear modulus G, the volume fraction of solute atoms fv, and the size misfit degree δb. A simple hardening correlation in KCl-KBr solid-solution is proposed as ∆τFcg = 0.27 G. It is applied to calculate the hardening behavior of the Ag-Au, KCl-KBr, InP-GaP, TiN-TiC, HfN-HfC, TiC-NbC and ZrC-NbC solid-solution systems. The composition dependence of hardness is elucidated quantitatively. The BN-BP solid-solution system is quantitatively predicted. We find a hardening plateau region around the x = 0.55-0.85 in BNxP1-x, where BNxP1-x solid solutions are far harder than cubic BN. Because the prediction is quantitative, it sets the stage for a broad range of applications.