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Utilizing molecular dynamics simulation, this study aims to explore the phase transformation behavior of porous nanocrystalline (NC) NiTi shape memory alloys (SMAs) when subjected to cyclic deformation. The influences of porosity and cyclic deformation on the phase transformation of NC NiTi SMAs are examined and discussed. The simulation results show that the increase in the porosity and number of cycles leads to a decrease in both the critical phase transformation stress and peak stress whereas an increase in the residual martensite, phase boundary, and interstitial atoms; the related results can be supported by previous experiments. After cyclic deformation, the reduction in the potential energy for the entire system during the tensile phase occurs at an earlier stage, indicating that the martensitic transformation occurs earlier as the number of cycles increases. Notably, the dissipated energy demonstrates a decrease with an increasing number of cycles, and the potential energy during the austenite elastic unloading stage undergoes a transition from a decreasing to an increasing trend due to the presence of residual martensite increasing with the number of cycles. [ABSTRACT FROM AUTHOR]

In this study, hydroxyapatite (HA) incorporated in mesoporous SiO 2 particles (SiO 2 /HA) was initially synthesized using a soft template method. The resulting structure owned a high surface area (796.62 m2 g-1) and a substantial pore volume (0.757 cm3 g-1). The TEM and FESEM images indicated that the synthesized mesoporous particles possessed a spherical morphology, with a diameter of approximately 200 nm, and pores of slit-shape. The mission was to improve the surface characteristics of NiTi implants by composite coatings. This investigation emphasized specifically the impact of different concentrations of mesoporous SiO 2 /HA particles within the electrolyte on the properties of HA/mesoporous composite coatings. The surface characteristics of the coatings were examined using ATR-FTIR, FESEM, EDS, AFM, and hydrophilicity measurements. Furthermore, the osteogenic activity of the coatings was evaluated by culturing the osteosarcoma cell line SAOS-2 on the coated samples. The introduction of mesoporous particles resulted in a decrease in the coatings' surface roughness along with an improvement in their wettability. Moreover, there was an enhancement in the cell viability (99% after 7 days), proliferation, adhesion, and growth of SAOS-2 cells at the optimized concentration of mesoporous SiO 2 /HA particles (1000 mg/L). DAPI images illustrated that the mesoporous particles did not cause any adverse impact on the cellular nuclei. Finally, in the apoptosis test, the composite coating displayed a reduced number of necrotic cells compared to the pure HA coating. [ABSTRACT FROM AUTHOR]

Introduction: Retrograde intrarenal surgery (RIRS) is associated with complications, many of which are related to the intrarenal pressure (IRP). We aim to describe the design of a novel isoprenaline-eluting guidewire ("IsoWire") and present the results from the first in vitro release studies and the first animal studies showing its effect on IRP. Materials and Methods: The IsoWire comprises a Nitinol core surrounded by a stainless-steel wire wound into a tight coil. The grooves created by this coil provided a reservoir for adding a hydrogel coating into which isoprenaline, a beta-agonist, was loaded. Animal studies were performed using a porcine model. For the control, IRP, heart rate (HR), and mean arterial pressure (MAP) were measured continuously for 6 minutes with a standard guidewire in place. For the experiment, the standard hydrophilic guidewire was removed, the IsoWire was inserted into the renal pelvis, and the same parameters were measured. Results:In vitro analysis of the isoprenaline release profile showed that most (63.9 ± 5.9%) of the loaded drug mass was released in the 1st minute, and almost all of the drug was released in the first 4 minutes exponentially. Porcine studies showed a 25.1% reduction in IRP in the IsoWire that released 10 μg in the 1st minute; however, there was a marked increase in HR. The average percentage reduction in IRP was 8.95% and 21.3% in the IsoWire that released 5 and 7.5 μg of isoprenaline, respectively, with no changes in HR or MAP. Conclusions: The IsoWire, which releases 5 and 7.5 μg of isoprenaline in the 1st minute, appears to be safe and effective in reducing the IRP. Further studies are needed to establish whether the isoprenaline-induced ureteral relaxation will render easier insertion of a ureteral access sheath, reduce IRP during sheathless RIRS, or even promote the practice of sheathless RIRS. [ABSTRACT FROM AUTHOR]

A three‐dimensional non‐isothermal phase field model of polycrystalline NiTi shape memory alloy (SMA) was established based on the Ginzburg–Landau's theory, which considered the interaction between crack growth and martensite transformation (MT). Then, the crack propagation of polycrystalline NiTi SMA and its dependence on the system's grain size and loading rate were studied by the phase field simulations. The results show that the proposed phase field model can characterize the MT behavior, temperature field changes, and stress‐displacement response of NiTi SMA during the crack growth with different grain sizes and loading rates. That is the higher the loading rate, the higher the fracture toughness is; the larger the grain size, the higher the fracture toughness is and the more significant the influence of grain boundary on the crack growth path becomes. Meanwhile, as the grain size increases, the fracture mode gradually changes from the transgranular fracture (for the fine‐grained alloy with a grain size ≈ 15 nm) to the intergranular one (for the coarse‐grained alloy with a grain size ≈ 100 nm). Highlights: The mechanisms for the rate dependence of crack propagation are clarified.The influence of the latent heat effect on crack propagation are clarified.The mechanisms for the toughening effects under different grain sizes are clarified.The mechanisms for the change in fracture mode are clarified. [ABSTRACT FROM AUTHOR]

In this research, titanium alloys including smart nitinol (NiTi) were studied. The (NiTi) alloy tends to emitting (Ni) toxic ions due to its low resistance to corrosion within the body conditions over time. For (NiTi) coating process, the magnetron plasma sputtering (DC) technique was used with Aragon gas ratio of (90%) and Oxygen of (10%) in order to coat the alloy with Tantalum and its Oxide (Ta2O 5) thin films. This is one of the methods used to improve the biocompatibility and better adhesion stability of the membrane on the (NiTi) surface, since Tantalum and its oxides are biocompatible and are not affected by the body fluids. Hardness, corrosion and biocompatibility were tested. The results showed improvement in the nominated properties using this coating technique. The hardness for the non-coated sample was (630 Kgf/mm 2) , meanwhile, the coated sample recorded (762 Kgf/mm 2) using sputtering power of (25 W) with a thickness of (226 nm). Tantalum and its precipitated oxides on a pillar of thickness (90.4–226 nm) also exhibited a biocorrosion enhancement, when it was immersed in a Simulated Body Fluid (SBF). The corrosion rate for the non-coated sample was (1.204 × 10 − 2) , meanwhile for the coated sample, its value was (3.453 × 10 − 5) at sputtering power of (15 W), considered as the lower corrosion rate. The scanning electron micrographs also showed an increase in the biocompatibility for the coated nitinol alloys (NiTi) in comparison with the non-coated, ones since it showed a clear formation of Hydroxyapatite (HA) on the sample surface after immersion in the SBF. This behavior was confirmed by the XRD measurements, which presented higher HA peaks on the coated samples surface in comparison with the non-coated samples. [ABSTRACT FROM AUTHOR]

Single-phase Mn50Ni40In10−xCux (x = 0, 1, 2, 4, 6, 8, and 10) Heusler alloys were synthesized by melt-spinning method. Martensitic transformation is retained within the whole composition range studied. The substitution of Cu for In leads to a drastic increase in the martensitic transformation temperature TM from below room temperature to above 750 K, and enhances the antiferromagnetic character of the martensite. The increase in TM is related to the increasing electron concentration e/a and decreasing cell volume V with Cu doping. The energy difference between martensite and austenite also increases with Cu doping, which tends to elevate the TM. Cu doping can enhance the metallic bonding character in NiMn-based magnetic shape memory alloys (MSMAs) and is a grain refining strategy of their ribbons. The oriented columnar grains in In-rich samples change to fine equiaxial grains in Cu-rich samples. All this has a positive effect on the strength and ductility. The tensile strength of the Mn50Ni40Cu10 ribbon is 3.6 times higher than that of Mn50Ni40In6Cu4. So, Mn–Ni–Cu can be a promising all-d-metal Heusler alloy platform for developing MSMAs with interesting properties. [ABSTRACT FROM AUTHOR]

In this article, the results of research on a NiTi alloy with a high nickel content (51.7 at.%), produced using the additive technology SLM method and subjected to isothermal ageing after solution annealing, are presented. The study involved the determination of the sequence of phase transformations occurring using differential scanning calorimetry (DSC) and the determination of the temperature range of these transformations. In parallel, the phase composition was determined using the XRD method; the hardness and the Young's modulus were also determined. The analysis of the DSC results obtained indicates the following characteristic features of the NiTi alloy, which change with ageing time: (1) During cooling (from +150 °C to −50 °C), the type of transformation changes from a one-step transformation after solution annealing to a two-step transformation after the ageing process over 1, 20, and 100 h at 500 °C; (2) during heating (from −50 °C to +150 °C) for all the samples, regardless of the ageing time, only a one-step transformation from martensite M(B19′) to austenite A(B2) is observed; (3) the temperature at which the transformation starts increases with the ageing time; (4) the width of the total temperature range of the transformation M(B19′) → A(B2) during heating changes from large (ΔT = 49.7 °C), after solution annealing, to narrow (ΔT = 19.3 °C and ΔT = 17.9 °C after 20 h and 100 h of ageing); and, most importantly, (5) a comparison with the literature data shows that, irrespective of the composition of the NiTi alloy and the manufacturing technology of the alloy samples (regardless of whether this was traditional or additive technology), a sufficiently long ageing process period leads to the occurrence of the martensite → austenite transformation in the same temperature range. [ABSTRACT FROM AUTHOR]

The resistance of nickel–titanium endodontic instruments against cyclic fatigue failure remains a significant concern in clinical settings. This study aimed to assess the cyclic fatigue strength of five nickel–titanium rotary systems, while correlating the results with the instruments' geometric and metallurgical characteristics. A total of 250 new instruments (sizes S1/A1, S2/A2, F1/B1, F2/B2, F3/B3) from ProTaper Gold, ProTaper Universal, Premium Taper Gold, Go-Taper Flex, and U-Files systems underwent mechanical testing. Prior to experimental procedures, all instruments were meticulously inspected to identify irregularities that could affect the investigation. Using a stereomicroscope, design characteristics such as the number of spirals, length, spirals per millimeter, and average helical angle of the active blade were determined. The surface finishing characteristics of the instruments were examined using a scanning electron microscope. Differential scanning calorimetry was employed to establish the instruments' phase transformation temperatures, while energy-dispersive X-ray spectroscopy was utilized to analyze the elemental composition of the alloy. The instruments were subjected to cyclic fatigue testing within a stainless steel non-tapered artificial canal featuring a 6 mm radius and 86 degrees of curvature. Appropriate statistical tests were applied to compare groups, considering a significance level of 0.05. The assessed design characteristics varied depending on the instrument type. The least irregular surface finishing was observed in U-Files and Premium Taper Gold files, while the most irregular surface was noted in Go-Taper Flex. All instruments exhibited near-equiatomic proportions of nickel and titanium elements, whereas ProTaper Universal and U-Files instruments demonstrated lower phase transformation temperatures compared to their counterparts. Larger-sized instruments, as well as ProTaper Universal and U-Files, tended to display lower cyclic fatigue strength results. Overall, the design, metallurgical, and cyclic fatigue outcomes varied among instruments and systems. Understanding these outcomes may assist clinicians in making more informed decisions regarding instrument selection. [ABSTRACT FROM AUTHOR]

The review summarizes the progress achieved in the surface modification of NiTi shape memory alloys (SMAs) with laser and electron beams in terms of their compliance with the requirements for biomedical devices and implants. The main provisions of the standards regulating this area of activity are aggregated. The production routes for manufacturing bulk items from NiTi SMAs are described. Since the formation of surface alloys on NiTi SMAs is now an intensively growing area of research, the influence of additional alloying elements on their functional properties is also discussed. The common patterns of interaction of laser and electron radiation with NiTi SMAs are specified. The typical requirements for surface layer conditions and conventional methods for their modification are reported. The results of various laser processing methods, differing in energy parameters, atmospheres and beam scanning algorithms, are summarized. They include remelting, annealing, nitriding, shock peening, alloying and texturing. In addition, some data on the modification and alloying of the surface layers with high-current pulsed electron beams are integrated. Finally, the aggregated information is compared and analyzed from the point of view of its prospects in these research areas. [ABSTRACT FROM AUTHOR]

Introduction: Modern endodontics aims to decrease the bacterial load from the complex endodontic space. Over the years, improvements in the operative phases have led to a considerable increase in the success rate of endodontic treatments. The shaping phase has seen the development of new techniques supported by technological innovations that have led to higher treatment predictability. Endodontic instruments have experienced a series of changes that have led to modifications in their design, surface treatments, and heat treatments. The clinical use of rotating nickel–titanium instruments has become widespread and consolidated, a success due primarily to the alloy's mechanical characteristics, which are superior to steel ones, but also to innovations in instrument design. The advent of the Ni-Ti alloy has kept the concepts and requirements of shaping the same but has modified its implementation in endodontics. Aim: The following review followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) protocol. The research question focused on Ni-Ti endodontic instruments whose cyclic fatigue was evaluated by analyzing cyclic fatigue strength and the incidence of fracture. Results: At the end of the research, 10 systematic reviews and 1 randomized controlled trial were included in this comprehensive review. The most frequently analysed alloys were M-wire, conventional Ni-Ti, and CM-wire. In seven articles, instruments made of M-wire alloy were used; in eight articles, instruments made of conventional Ni-Ti; and in seven articles, instruments made of CM-wire alloy. Conclusions: The technological evolution of Ni-Ti alloys has led to the development of increasingly high-performance endodontic files that are resistant to cyclic fatigue during clinical practice and have greater resistance to sterilisation practices, making treatment easier and more predictable over time. In particular, heat-treated nickel-titanium root canal instruments present greater resistance to cyclic fatigue than untreated ones and those used with reciprocating kinematics concerning continuous rotation. [ABSTRACT FROM AUTHOR]

Vacuum induction melting is a more energy-efficient process for the preparation of a titanium alloy with good homogeneity and low cost. But the crucial problem for this technology is in developing a crucible refractory with high stability. In the present work, a novel (Ca,Sr,Ba)ZrO3 crucible was prepared by slip casting and its performance in melting NiTi alloy was studied. The results showed that a single solid solution was formed with a homogeneous distribution of metal elements after sintering at 1500 °C. It was found that the total content of oxygen and nitrogen remaining in the TiNi alloy after melting in the (Ca,Sr,Ba)ZrO3 crucible was 0.0173 wt.%, which fulfills the ASTM standard on biomedical TiNi alloys. The good resistance of the (Ca,Sr,Ba)ZrO3 crucible to molten NiTi has a relationship with the sluggish diffusion effect of high-entropy ceramics. This study provides insights into the process of designing highly suitable crucible material for melting a NiTi alloy. [ABSTRACT FROM AUTHOR]

In this paper, a CatBoost model for predicting superelastic strains of alloys was established by utilizing features construction and selection as well as model filtering and evaluation based on 125 existing data points of superelastic titanium alloys. The alloy compositions of a TiNbMoZrSnTa system were optimized and three nickel-free titanium alloys with potentially excellent superelastic properties were designed using the Bayesian optimization algorithm using a superelastic strain as the optimization target. The experimental results indicated that only Ti-12Nb-18Zr-2Sn and Ti-12Nb-16Zr-3Sn exhibited clear superelasticity due to the absence of relevant information about the alloys' β stability in the machine learning model. Through experimental optimization of the heat treatment regimens, Ti-12Nb-18Zr-2Sn and Ti-12Nb-16Zr-3Sn ultimately achieved recovery strains of 4.65% after being heat treated at 853 K for 10 min and 3.01% after being heat treated at 1073 K for 30 min, respectively. The CatBoost model in this paper possessed a certain ability to design nickel-free superelastic titanium alloys but it was still necessary to combine it with existing knowledge of material theory for effective utilization. [ABSTRACT FROM AUTHOR]

Nickel‐titanium alloys are produced via laser metal deposition using titanium carbide and titanium diboride as nucleating agents to refine the grain structure. The optimal process parameters are determined by analyzing the quality of the alloy formation. X‐ray diffraction confirms the simultaneous presence of the B19′ martensitic phase and B2 austenitic phase in the nickel‐titanium alloy fabricated by laser metal deposition. Tensile testing is performed on the samples at room temperature. The results show that adding mass fractions 0.9 % titanium carbide and titanium diboride effectively refines the grain size of the nickel‐titanium alloy fabricated by laser metal deposition, leading to improved tensile properties. Specifically, the addition increases the tensile strength by 40 % and 70 %, and the elongation by 50 % and 60 %. [ABSTRACT FROM AUTHOR]

This work explores the influence of a pre-engineered notch on the electromagnetic radiation (EMR) parameters in NiTi shape memory alloy (SMA) during tensile tests. The test data showed that the EMR signal fluctuated between oscillatory and exponential, signifying that the specimen's viscosity damping coefficient changes during strain hardening. The EMR parameters, maximum EMR amplitude, and average EMR energy release rate remained constant initially but rose sharply with the plastic zone radius with progressive loading. It was postulated that new Frank–Read sources permit dislocation multiplication and increase the number of edge dislocations participating in EMR emissions, leading to a rise in the value of EMR parameters. The study of the correlation between EMR emission parameters and the plastic zone radius before the crack tip is a vital crack growth monitoring tool. An analysis of the interrelationship of the EMR energy release rate at fracture with the elastic strain energy release rate would help develop an innovative approach to assess fracture toughness, a critical parameter for the design and safety of metals. The microstructural analysis of tensile fractures and the interrelation between deformation behaviours concerning the EMR parameters offers a novel and real-time approach to improve the extant understanding of the behaviour of metallic materials. [ABSTRACT FROM AUTHOR]

The objective was to evaluate the effect of glide path and coronal flaring on the dentin volume removal and percentage of touched walls in curved canals using two heat-treated rotary files. The mesiobuccal canal of forty-eight, randomly selected, extracted mandibular molars was divided into two groups of 24 each, according to the type of instrument used (RACE EVO and EdgeSequel rotary files). Each group was further divided into three subgroups; Group (A): Control using one file shaped to 04/30, Group (B) with a glide path (EdgeGlidePath (EGP)), and Group (C): with a glide path and coronal flaring (EGP and EdgeTaper Platinum (ETP) SX file respectively). The root canals were then instrumented using the assigned instruments. The assessment was carried out using micro-CT. The comparison of the mean values of the tested groups about dentin volume removal and percentage of untouched walls did not reach statistical significance (p<0.05). Glide path and coronal flaring had an insignificant effect on the dentin volume removal and percentage of untouched walls in curved canals. [ABSTRACT FROM AUTHOR]

Background: Comprehensive datasets quantifying the coupled thermo-mechanical and electrical properties of shape memory alloys (SMAs) are lacking, as are standardized techniques for robust characterization. This hampers accurate modeling and design of SMA-based components. Objective: This work develops an automated experimental system to enable simultaneous measurement of stress-strain-temperature behavior and electrical resistivity evolution in NiTi SMA wires under controlled stress conditions. Methods: Customized test frames apply precise mechanical stresses while allowing for in situ electrical measurements and infrared imaging during complete thermal cycling protocols. Specialized instrumentation including a Keithley 2002 multimeter, Agilent E3631A programmable power supply, and FLIR A615 thermal camera are integrated with LabVIEW-based software routines for complete automation of the characterization process. Rigorous metrology principles are implemented throughout the measurement procedure to improve accuracy, repeatability, and consistency compared to prior manual techniques. Results: Extensive datasets are generated which reveal pronounced stress-dependencies in key SMA material parameters including transformation temperatures, recoverable strain, and electrical resistivity. A 3D regression model describes the comprehensive relationship between resistivity, temperature, and applied stress across the entire characterization domain. Conclusions: The automated measurement framework and methodology establishes a foundation for high-fidelity, reliable acquisition of coupled SMA property data. This will enable more accurate modeling and design of components and systems incorporating SMA actuation or sensing functions. [ABSTRACT FROM AUTHOR]

The stress-induced martensitic transformations and superelasticity behavior in the NiTi alloy with a single crystal model and a twist grain boundary bicrystal model at different temperatures are studied using molecular dynamics simulations. An atomic tracing method is proposed to identify specific numbers of B19′ martensite variants. Under uniaxial compressive loading, the stress-induced martensitic transformation takes place accompanied by the formation of <011>M type II twins, and the deformation process can be divided into three distinct stages based on microstructure evolution and average atomic total energy. It is found that the twist grain boundary induces an increase in the martensite start temperature, which is consistent with the experimental results. There is no residual B19′ martensite at the end of the unloading process, and the irrecoverable strain mainly results from plastic deformation at the grain boundary through the analysis of atomic local shear strains and has hardly changed with increasing deformation temperature. Remarkably, the grain boundary brings about the acceleration of martensite nucleation and an earlier occurrence of stress plateau. Further simulation results manifest that the presence of the twist grain boundary leads to weakened temperature dependence of martensitic transformation stress and a reduction in the hysteresis loop area. [ABSTRACT FROM AUTHOR]

Mechanical properties of nanocrystalline NiTi shape memory alloys (SMAs) change drastically with grain size. The present contribution develops a constitutive model to reproduce the grain size dependent superelastic behavior and tensile–compressive asymmetry observed in the experiments of nanocrystalline NiTi SMAs. Effects of grain size are incorporated in the developed model by introducing the intrinsic length scale accounting for the transformation hardening as well as the grain-core and grain-boundary phase. In this work, nanocrystalline NiTi SMA is regarded as a two-phase composite material made of inclusions of the grain-core phase dispersed in the grain-boundary phase acting as a matrix. A transformation function allowing for the description of fine-grain strengthening mechanism and tensile–compressive asymmetry is proposed. In the grain-core phase, the evolution law for transformation strain during the forward and reverse transformation is determined. Besides, the constitutive relation of the grain-boundary phase is assumed to be linearly elastic. Based on the equivalent secant bulk and shear modulus of the grain-core and grain-boundary phase, the stress–strain relationship of nanocrystalline NiTi SMAs is derived by using the extended Mori–Tanaka method. Comparisons between experimental and predicted results demonstrate that the proposed model has the ability to reproduce the grain size dependent deformation and asymmetric stress–strain behavior under tension and compression of nanocrystalline NiTi SMAs. In detail, it is found that critical transformation stresses for forward and reverse transformations, dissipation energy density, transformation strain hardening, and maximum transformation strain are sensitive to the grain size and stress states. [ABSTRACT FROM AUTHOR]

The NiTi alloy, known as Nitinol, represents one of the most investigated smart alloys, exhibiting a shape memory effect and superelasticity. These, among many other remarkable attributes, enable its utilization in various applications, encompassing the automotive industry, aviation, space exploration, and, notably, medicine. Conventionally, Nitinol is predominantly produced in the form of wire or thin sheets that allow producing many required components. However, the manufacturing of complex shapes poses challenges due to the tenacity of the NiTi alloy, and different processing routes at elevated temperatures have to be applied. Overcoming this obstacle may be facilitated by additive manufacturing methods. This article provides an overview of the employment of additive manufacturing methods, allowing the preparation of the required shapes of Nitinol products while retaining their exceptional properties and potential applications. [ABSTRACT FROM AUTHOR]

A novel transient liquid phase bonding (TLP) method for obtaining high-temperature resistant diamond/Cu joint was designed. The joint was achieved through the isothermal solidification of Au–Si interlayer assisted by the diamond active modified layer and NiTi particles. The interfacial reaction mechanisms in the TLP process were systematically investigated in this study. The results shown that Ti 5 Si 3 C, CuTiSi and NiTiSi precipitated from the seam. Due to the precipitation of Si and the interdiffusion of Au–Cu, a ductile Au–Cu solid solution ((Au, Cu)ss) matrix formed. The shear strength of the diamond/Cu joint was notably affected by the holding time. The maximum room-temperature shear strength of 108 MPa was achieved when the joints were held at 600 °C for 60 min, and the high-temperature strength was still up to 22 MPa at 600 °C. The high strength of the joints was achieved because of (i) the elimination of the Cu(Au)–Si brittle phases, (ii) the NiTiSi whiskers pulling-out mechanism, and (iii) the moderate distribution of compounds at the diamond/seam interface. [ABSTRACT FROM AUTHOR]

Development of efficient photothermal catalysts made of earth-abundant elements is of prime importance for heterogeneous photocatalysis driven by solar light. Herein, we report for the first time the synthesis of NiTi@TiO 2 /Ni core-shell-satellite nanoparticles from pristine nitinol nanopowder (NiTi) by simple and easily scalable ultrasonically assisted hydrothermal treatment in pure water (T = 200 °C, P = 14 bar, f = 20 kHz, P ac = 17 W, τ = 3 h). Prepared material exhibits unique set of properties, such as strong capability of light-to-heat conversion, good magnetization, high stability, and remarkable thermally assisted photocatalytic hydrogen production (5.5 mmol h−1 g−1 at T = 90 °C). The core-shell-satellite morphology of NiTi@TiO 2 /Ni particles maximizes the contact area between the heat generating metallic core and photocatalytically active TiO 2 /Ni nanocrystalline shell providing the most efficient photothermal effect in the processes of H 2 production and CO 2 methanation without CO emission. In addition, significant magnetic susceptibility of the NiTi@TiO 2 /Ni nanoparticles allows their easy recovery from solution with an external magnetic field. Noncongruent surface oxidation of nanoalloys reported in this work paves the way to the preparation of new generation of catalysts with advanced photothermal properties. [Display omitted] • NiTi@TiO 2 /Ni photocatalyst was prepared from NiTi nanopowder by ultrasonically assisted hydrothermal treatment in water. • Obtained material exhibits strong capability of light-to-heat conversion, good magnetization, and high stability. • NiTi@TiO 2 /Ni nanoparticles exhibit remarkable activity for thermally assisted photocatalytic hydrogen production. • This material enables CO 2 methanation by in situ generated hydrogen in aqueous solutions. [ABSTRACT FROM AUTHOR]

This study endeavors to comprehensively explore and elucidate the seamless integration of NiTi shape memory alloys (SMAs) into multifaceted applications through the utilization of novel joining techniques. The primary focus lies in the utilization of wire arc additive manufacturing (WAAM) to deposit Nitinol (NiTi) onto Copper (Cu), thereby introducing a transformative approach for their integration into electro-mechanical systems and beyond. Through a detailed examination of the NiTi/Cu bimetallic junction, using advanced analytical techniques including SEM, XRD, and DSC analyses, this research aims to unravel the intricate complexities inherent within the interface. The SEM images and X-ray patterns obtained reveal a complex and nuanced interface characterized by a broad mixed zone comprising various constituents, including Ti(Ni,Cu)2, pure Cu, Ti2(Ni,Cu)3 precipitates, and Ni-rich NiTi precipitates. The DSC results, showcasing low-intensity broad peaks during thermal cycling, underscore the inherent challenges in demonstrating functional properties within the NiTi/Cu system. Recognizing the critical importance of an enhanced martensitic transformation, this study delves into the effects of heat treatment. Calorimetric curves post-annealing at 500 °C exhibit distinct transformation peaks, shedding light on the intricate influence of NiTi layer distribution within the junction. The optimal heat treatment parameters for NiTi/Cu junction restoration are meticulously explored and determined at 500 °C for a duration of 12 h. Furthermore, the study offers valuable insights into optimizing NiTi–Cu joints, with micro-hardness values reaching 485 HV and compressive strength scaling up to 650 MPa. These significant findings not only hold promise for diverse applications across various industries but also pave the way for further research directions and explorations into the realm of SMA integration and advanced joining methodologies. [ABSTRACT FROM AUTHOR]

This document is a special issue of the journal "Materials" that focuses on the recent progress in the structure transition, processing, characterization, and applications of metallic materials. The issue includes research papers on various topics such as the development of dispersion-strengthened copper alloys, the characterization of carbide precipitation in steel, the effect of magnetic fields on aluminum bronze, and the enhancement of impact toughness in cast iron through heat treatment. The issue aims to provide comprehensive and up-to-date information for researchers, engineers, and industry experts in the field of metallic materials. [Extracted from the article]

Significant attention has been directed to the need for a strong and lightweight welding technology for joining the NiTi shape memory alloys (SMAs) to stainless steel (SS). Dissimilar NiTi/SS joints suffer from the brittle and inevitable intermetallic compounds (IMCs) like TiFe, TiFe2, and FeNi that are formed during the welding process. To tackle this challenge, this study explores the use of an engineered magnetic field during the dissimilar laser welding of NiTi to SS. The presence of a magnetic field delivered a remarkable improvement in the tensile strength (over 452 MPa) of the joint, with a notable difference in the microstructure. The effect of the magnetic field on microstructure was investigated; material characterizations showed brittle IMC-free microstructure and a change in grain growth mechanism from columnar to cellular growth during the solidification. Further, fractography analysis proved a ductile failure mode at the joint. [ABSTRACT FROM AUTHOR]

Due to the poor machinability and weldability of nickel-titanium (NiTi) shape memory alloy, application of NiTi alloy components prepared by smelting technology has been limited in aerospace and other fields. Laser metal deposition (LMD) technology opens a new way for the fabrication of NiTi alloy components. However, deposition quality and deposition rate are significantly influenced by the employed LMD process parameters. In this work, a small-sample prediction and optimization model based on BP-GA neural network for LMD process parameters selection was developed to improve the deposition quality and deposition rate of NiTi alloy components. The initial step involved the design of a central composite experiments consisted of thirty small-sample single-track experiments and building of the prediction model for deposition quality and deposition rate, wherein the inputs were consisted of the process parameters such as the laser power, scanning speed, and powder feeding rate. The responses, on the other hand, included the microhardness, roughness, and deposition rate. Prediction of the single-track cladding results by regression models of the response surface methodology, the ML models of back propagation neural network and random forest algorithms were comparatively analyzed and the prediction model was established. Then, based on the prediction model, non-dominated sorting genetic algorithm-II algorithm was applied to optimize the three input process parameters with the multi-objective of maximizing microhardness and deposition rate, and minimizing roughness. And the optimal combination of process parameters was obtained as a laser power of 1292.14 W, a scanning speed of 8.79 mm/s and a powder feeding rate of 16.78 g/min. Finally, single-track deposition experiments under the optimal combination of process parameters were carried out. The results showed that microhardness of 267.01 (5.23% improvement) and roughness of 7.86 µm (20.04% improvement) was achieved while maintaining a high deposition rate of 36.45 mm3/s. Objective of this study was to improve the deposition quality of NiTi alloy components with high deposition rate. [ABSTRACT FROM AUTHOR]

In the realm of biomaterials engineering, Functionally Graded Materials (FGMs) have emerged as a novel class of composites, characterized by spatial variations in composition that yield a gradient in properties tailor-made for specific applications. This investigation delineates the development of a multi-layered FGM composed of titanium, nickel, and hydroxyapatite (NiTi/HA), designed to address the challenges associated with bone implant integration. Porous NiTi, renowned for its mechanical compatibility with bone tissue, is coupled with hydroxyapatite, a material celebrated for its osteoconductive properties, to enhance bioactivity and promote bone ingrowth. The fabrication of this NiTi/HA FGM was realized through a powder metallurgy approach, culminating in the production of specimens with either three or five stratified layers that progressively transition from NiTi-rich at one extremity to HA-rich at the other. The compaction of these powders was executed under a pressure of 450 MPa, followed by a sintering process at 1000°C sustained for a duration of three hours--parameters meticulously chosen to optimize material integrity without compromising the functional gradient. Mechanical characterization was systematically conducted, revealing that the microhardness of the FGMs ranged from 269.6 to 458.11 kg/mm² and 365.5 to 436.5 kg/mm² for the three-layered and five-layered specimens, respectively. The density and porosity of these materials were also quantified, with the three-layered FGM (FGM1) exhibiting an apparent density of 2.665 g/cm³ and a porosity of 33.5%, while the five-layered FGM (FGM2) displayed an increased density of 3.754 g/cm³ and a reduced porosity of 24.6%. X-ray diffraction analysis verified the phase composition of the graded specimens, confirming the presence of the anticipated monoclinic NiTi, cubic NiTi, and hexagonal Ni3Ti phases, integral to the material's function. The synergistic combination of the robust mechanical properties of the NiTi alloy with the superior bioactivity of hydroxyapatite underscores the potential of this FGM NiTi/HA for hard tissue implant applications, offering a promising avenue for the advancement of orthopedic treatments. [ABSTRACT FROM AUTHOR]

To investigate the effect of the sintering temperature on the microstructure characteristics of porous NiTi alloys, two types of porous NiTi alloys with equal atomic ratios were fabricated via elemental powder sintering at 950 °C and 1000 °C. Afterwards, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were collectively applied to investigate the pore characteristics and microstructure of the fabricated porous NiTi alloy. The results show that when the sintering temperature increases from 950 °C to 1000 °C, the average pore size increases from 36.00 μm to 181.65 μm, owing to the integration of these newly formed small pores into these pre-existing large-sized pores. The measured density increases from 2.556 g/cm3 to 3.030 g/cm3, while the porosity decreases from 60.4% to 51.8%. This is due to the occurrence of shrinkage after the sufficient diffusion of atoms. Furthermore, the characterization results confirm that a change in the sintering temperature would not change the phase types within a porous NiTi alloy; namely, the matrix consists primarily of B2 NiTi, with a significant amount of Ni4Ti3 precipitates and a small amount of Ni3Ti precipitates and Ti2Ni precipitates. However, as the sintering temperature increases, the number of Ni4Ti3 precipitates decreases significantly. The formation of a Ni4Ti3 phase in the present study is closely related to the enrichment of Ni content in the matrix owing to the diffusion rate difference between Ni atoms and Ti atoms and the absence of a transient liquid phase (TLP) during the sintering process owing to the relatively low sintering temperature (lower than the eutectic temperature). Moreover, the increasing sintering temperature speeds up the atom diffusion, which contributes to a reduction in the enrichment of Ni as well as the number of formed Ni4Ti3 precipitates. [ABSTRACT FROM AUTHOR]

The deposition of multilayer coating of NiTi is carried out by a thermal plasma spraying process on a stainless steel substrate. The deposition of melted NiTi particles creates an adhesion layer on the substrate with the subsequent formation of multilayer coating with a certain thickness. Six layers of coating are created to achieve a certain thickness in terms of the sprayed sample. This paper aims to investigate multilayer NiTi coatings created through a thermal plasma process. The key variable feed rate was considered, as well as its effect on the microstructure characteristics. The shape memory effect associated with the coating properties was analyzed in detail. The variable feed rate was considered one of the most important parameters in the thermal plasma spraying process due to its ability to control the quality and compactness of the coating structure. The coatings were characterized by examining their microstructure, thermal, chemical, and microhardness. The indent marks were made/realized along the cross-section surface for the analysis of crack propagation resistance and wear properties. The coating's surface did not display segmentation crack lines. Nevertheless, the cross-sectional surfaces showed evidence of crack lines. There were eutectic zones of the interlamellar structure observed in the structure of the coating. The plasma-sprayed samples from thermo-mechanical analysis of the hysteresis curve provide strong confirmation of the shape memory effect. [ABSTRACT FROM AUTHOR]

The objective of this research was to develop a surface modification for the NiTi shape memory alloy, thereby enabling its long-term application in implant medicine. This was achieved through the creation of innovative multifunctional hybrid layers comprising a nanometric molecular system of silver-rutile (Ag-TiO2), known for its antibacterial properties, in conjunction with bioactive submicro- and nanosized hydroxyapatite (HAp). The multifunctional, continuous, crack-free coatings were produced using the electrophoretic deposition method (EPD) at 20 V/1 min. Structural and morphological analyses through Raman spectrometry and scanning electron microscopy (SEM) provided comprehensive insights into the obtained coating. The silver within the layer existed in the form of nanometric silver carbonates (Ag2CO3) and metallic nanosilver. Based on DTA/TG results, dilatometric measurements, and high-temperature microscopy, the heat treatment temperature for the deposited layers was set at 800 °C for 2 h. The procedures applied resulted in the creation of a new generation of materials with a distinct structure compared with the initial nanopowders. The resulting composite layer, measuring 2 μm in thickness, comprised hydroxyapatite (HAp), apatite carbonate (CHAp), metallic silver, silver oxides, Ag@C, and rutile exhibiting a defective structure. This structural characteristic contributes significantly to its heightened activity, influencing both bioactivity and biocompatibility properties. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the effect of body temperature (37 °C) on the cyclic fatigue resistance of three endodontic single-file systems using a new testing setup. One Shape® new generation (OS), WaveOne™ (WO) and WaveOne® GOLD (WOG), which are made from different NiTi alloys and operated in different motions (rotation/reciprocation), were evaluated. The study design included four groups. Each group comprised 30 files, 10 files of each of the three file systems, tested at 20 ± 2 °C (group 1 and 3) and at 37 ± 1 °C (group 2 and 4). All files were tested in a custom-made metal block with artificial canals of 60° angle, and a 5 mm and 3 mm radius of curvature, respectively. A heating element was attached to replicate a temperature of 37 °C. Files were introduced 18 mm into the canals and operated until failure. Transformation temperatures of five samples of each of the tested file systems were determined via the bend and free recovery (BFR) method. With the exception of WOG in canals with a 3 mm radius of curvature (p = 0.075), all the tested file systems showed statistically significantly less time needed to fracture when operated at 37 ± 1 °C compared to at 20 ± 2 °C in canals with a 5 mm and 3 mm radius of curvature using Mann–Whitney U test (p < 0.05). All file systems showed transformation temperatures below the body temperature. We concluded that body temperature directly affects the cyclic fatigue resistance of all tested file systems. Bend and free recovery can be suitable for the determination of austenite finish temperatures (Af) of endodontic instruments as it allows testing a longer portion of the instrument. [ABSTRACT FROM AUTHOR]

Aim: This study aimed to evaluate the effect of 5.25% sodium hypochlorite (NaOCl) and 17% ethylenediaminetetraacetic acid (EDTA) and sterilization on the nanostructural alteration of nickel titanium (Ni-Ti) rotary file systems in endodontics using the atomic force microscopy (AFM). Materials and Methods: The study was performed on four commercially available rotary Ni-Ti files: group I—Vortex Blue (Dentsply), group II—ProTaper Next (Dentsply), group III—Mtwo (VDW), and group IV—iRaCe (FKG). Each group was divided into four subgroups (n = 4), that is, subgroup A—control (new rotary file), subgroup B—subjected for five cycles of autoclave, subgroup C—immersed in 5.25% NaOCl for 5 minutes, and subgroup D—immersed in 17% EDTA solutions for 5 minutes. All the specimens were evaluated with AFM using roughness average (RA) and root-mean-square (RMS) values for surface roughness. Results: Among control groups, Vortex Blue showed the least RA and RMS values; the highest surface roughness was seen with Mtwo files. All the Ni-Ti rotary files showed a statistically significant (P <0.05) increase in surface hardness when subjected to autoclave and treatment with different irrigating solutions. In particular, 17% EDTA caused the highest surface deterioration in all the groups. Conclusion: AFM analysis revealed increased surface roughness values recorded for all the rotary files when treated with irrigating solutions and autoclave cycles. [ABSTRACT FROM AUTHOR]

Objective: The purpose of this study was to determine the effect of common methods of sterilization on the tensile strength of Beta titanium, Stainless steel, Australian Stainless steel, Copper Nickel-Titanium, and Nickel-Titanium wires. It also aimed to evaluate the changes in tensile strength values caused by repeated cycles of sterilization. Materials and Methods: A sample of 225 orthodontic wires, i.e., beta-titanium, stainless steel, Australian stainless steel, copper nickel-titanium, and nickel-titanium wires, were collected from different manufacturers. These wires were divided into three groups, which consists of Groups 1, 2, and 3. Four methods of sterilization used in this study were as follows: (i) autoclave (250°F for 20 min), (ii) dry heat sterilization (375°F for 20 min), (iii) ethylene oxide sterilization (54°C for 4 hrs), and (iv) 2.45% acidic glutaraldehyde (10 hrs). Results: The results of this study showed that there was increase in tensile strength of beta-titanium and nickel-titanium wires using autoclave and dry heat sterilization. No statistically significant difference in tensile strength of stainless steel and Australian stainless steel archwires. The tensile strength of copper nickel-titanium wires decreased following 0, 1, and 5 cycles of sterilization. Conclusion: The lack of statistically significant differences established in the study of new and sterilized orthodontic archwires gives us reason to conclude that the orthodontic arch wires can be sterilized because the sterilizing processes do not affect their tensile strength and the orthodontists could thus ensure the maximum safety of their patients. [ABSTRACT FROM AUTHOR]

Hydroxyapatite, a bio-ceramic material widely utilized in bioengineering, holds significant promise for bone implant applications due to its biocompatibility and nontoxic nature. This study focuses on the organic synthesis of hydroxyapatite with tailored nanoscale properties suitable for integration into functionally graded materials like NiTi/HA, intended for bone implants. Porous NiTi possesses desirable mechanical properties for such applications; however, its limited bioactivity poses a challenge for therapeutic use. Composite structures comprising porous NiTi and hydroxyapatite (HA) offer a viable solution to promote bone ingrowth and implant integration with surrounding tissue. Eggshells serve as the raw material in this research, subjected to calcination at 1000° for three hours to yield calcium oxide. Subsequent crushing and mixing with phosphoric acid, followed by milling using a planetary ball mill for twentytwo hours at 45 rpm, produces a homogeneous hydroxyapatite powder (HA). Comprehensive characterization using particle analysis, FTIR, SEM, and XRD confirms the desired properties of the synthesized powder. FTIR analysis verifies the presence of fundamental HA components, while XRD reveals a structure akin to traditional hydroxyapatite powder, featuring characteristic peaks corresponding to (PO43-), (CO32-), and bending OH-. Particle size analysis indicates a range of (0.301) μm to (4.759) μm, with a mean size of (1.088) μm. The findings of this study highlight that hydroxyapatite powder derived from eggshells exhibits favorable particle size, bioactivity, and porous nature, rendering it well-suited for incorporation into bone implant materials. [ABSTRACT FROM AUTHOR]

In this work, surface morphology, corrosion resistance, and mechanical properties of tantalum sputtered NiTi in Ar and Ar–N 2 atmospheres as well as room and 200 °C temperatures have been investigated. FESEM studies showed the positive effect of heat on forming a uniform and dense Ta layer under the Ar atmosphere whereas it left an adverse mark on coatings in the Ar–N 2 atmosphere. XRD patterns depicted amorphous coatings in all samples meaning 200 °C was not sufficient for the formation of crystallized Ta. AFM 3D images of surface topographies suggested that smooth and compact layers were produced in the Ar-injected chamber while the coatings containing N in their chemical composition owned irregular ups and downs with a higher porosity degree. Electrochemical measurements indicated that despite nonuniformity, Ar–N 2 coatings were more resistive whereas polarization resistance was at least three times greater than that of Ar coatings. Finally, nanoindentation results showed that the coating formed at 200 °C and Ar condition had the highest nano-hardness, Young's modulus, and elastic recovery. The sample coated in Ar–N 2 condition and the same temperature, however, expressed the least mechanically-favorable character. [ABSTRACT FROM AUTHOR]

In this paper, Fe10Co25Ni34Cu23Al8 high-entropy-alloy nanoparticles have been synthesized by the in situ instantaneous electrical wire explosion method. Based on the thermodynamic parameters of the face-centered cubic phase of high-entropy-alloy, the parameters of the five kinds of wires were calculated and controlled, and the stable face-centered cubic structure with good crystallinity was synthesized in one step. The influence of the energy deposition during the electrical explosion on the nanoparticles and their electromagnetic absorption performance was explored. The results show that the face-centered cubic structure high-entropy-alloy with high crystallinity has better electromagnetic wave absorption performance when the energy deposition of the wires is increased. The minimum reflection loss can reach −39.37 dB at 15.34 GHz when the thickness is 1.9 mm and the effective absorption bandwidth is 6.63 GHz. It can provide a strategy for the microstructure and morphology design of high-entropy-alloy nanoparticles in electromagnetic wave absorption and magnetism in the electronics industry. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the load deflection characteristics of Gummetal® wires in comparison to nickel–titanium (NiTi) wires. Four different NiTi wires and one Gummetal® archwire were analyzed in two dimensions (0.014″ (0.36 mm) and 0.016″ × 0.022″ (0.41 mm × 0.56 mm)) and in two different orientations (edgewise and ribbonwise) using three-point bending tests at T = 37 °C. Force–displacement curves were recorded and analyzed. The Gummetal® 0.014″ wires exhibited higher forces compared to the NiTi wires at 2.0 mm deflection. At 1.0 mm deflection, the opposite pattern was observed. For the 0.016″ × 0.022″ Gummetal® wires, the forces were within the force interval of the NiTi wires at 2.0 mm deflection. At a deflection of 1.0 mm, no residual force was measurable for the Gummetal® wires. All the NiTi wires investigated showed hysteresis and a superelastic plateau. However, the Gummetal® did not form a plateau, but hysteresis was present. An easier plastic deformability compared to the NiTi wires was observed for all the tested geometries. [ABSTRACT FROM AUTHOR]

This paper presents a study of the total cutting force used and selected parameters of the geometric structure of the surface (e.g., Sa, Sz) during the end milling process of NiTi alloy. The input parameters included are cutting speed (vc), feed per tooth (fz), and radial depth of cut (ae). A Box–Behnken experimental design was employed to conduct the research. The obtained experimental results were utilized within the framework of a response surface methodology (RSM) to develop mathematical and statistical models capable of predicting cutting force components and selected 3D surface parameters. These models provide valuable insights into the relationships between the cutting parameters and the output variables, facilitating the optimization of the NiTi alloy milling process. The findings of this study contribute to a better understanding of the behavior of NiTi alloy during the milling process and offer information for process optimization. By employing a Box–Behnken experimental design, it was possible to investigate the effects of different parameter combinations on the components of total cutting force and selected 3D surface parameters according to ISO 25178, thus aiding in the identification of optimal milling conditions to achieve desired outcomes in the machining of NiTi alloy. [ABSTRACT FROM AUTHOR]

A study was made of the machinability of NiTi alloy in turning, under conditions resulting in a small cutting layer. The experiment involved cutting with variable feeds ranging from 0.01 to 0.1 mm/rev. The cutting conditions were carefully chosen, considering the rounding radius of the cutting edge. The machined surface was examined and measured in 3D using a confocal microscope and in 2D with a contact profilometer. These measurements were used to estimate hmin, leading to the development of a surface formation model that considers both the lateral material flow due to hmin and the lateral material flow due to altered thermodynamic conditions from the previous blade pass. A method for evaluating the surface and selecting its characteristics was proposed based on analyses derived directly from surface features: PCA (Principal Component Analysis) and EMD (Empirical Mode Decomposition) with the Hilbert transform (Hilbert–Huang transform). PCA analysis facilitated the examination of individual surface component variances, while analysis of the IMF components enabled the assessment of surface component energy combined with instantaneous frequencies. [ABSTRACT FROM AUTHOR]

This research explores discrete element method analysis to investigate the wear of NiTi Sand Screens in comparison to traditional materials. The study utilized Altair EDEM v2022.2 software and employed Oka and Archard models to simulate the wear behavior of Nitinol, a well-established Shape Memory Alloy (SMA). The mechanical properties considered include Poisson's ratio, solid density, shear modulus, and Young modulus. Results indicate significantly higher wear values and deformations with the Oka model compared to negligible wear with the Archard model. The Oka model's emphasis on impact as the primary wear mechanism, supported by high normal cumulative energy, better represents sand screen wear phenomena. Additionally, this study indicates that factors such as particle size distribution and normal and tangential cumulative contact energy hold potential as predictors of wear response and characteristics. The Oka model demonstrated that NiTi exhibited reduced wear losses compared to SUS630 and Cr–Mn white cast iron, both of which are recognized for their high toughness when subjected to an impact load. Experimental analysis validated the simulation findings with morphological and graphical erosion plots. The limitation of observing the shape memory effect through DEM (discrete element method) simulation was acknowledged. Recommendations include characterizing post-wear microstructural changes, exploring the influence of temperature on wear behavior, and further research to refine wear models and understand SMA sand screen responses. [ABSTRACT FROM AUTHOR]

Objective: Until now, giant intracranial aneurysms (GIAs) have in many cases been a vascular disease that was difficult or impossible to treat, not least due to the lack of availability of a large-format stent. In this multicentre study, we report on the first five clinical applications of the Accero®-Rex-Stents (Acandis, Pforzheim, Germany) in the successful treatment of fusiform cerebral giant aneurysms. Material and Methods: The Accero®-Rex-Stents are self-expanding, braided, fully radiopaque Nitinol stents designed for aneurysm treatment. The stent is available in three different sizes (diameter 7–10 mm, length 30–60 mm) and intended for endovascular implantation in vessels with diameters of 5.5–10 mm. Results: Five patients (all male, age 54.4 ± 8.1 years) with large fusiform aneurysms of the posterior circulation were treated endovascularly using the Accero®-Rex-Stents. There were no technical complications. One major ischemic complication occurred. A significant remodeling and reduction in the size of the stent-covered aneurysms was already seen in the short-term post-interventional course. Conclusions: The Accero®-Rex-Stents were successfully and safely implanted in all five patients with fusiform giant aneurysms, showing technical feasibility with promising initial results and significant aneurysm size reduction in already available follow-up imaging. Key point: With the Accero-Rex-Stents, a new device is available that offers another treatment option for rare cerebral fusiform giant aneurysms with very large parent vessels. [ABSTRACT FROM AUTHOR]

The actualization of high strength and ductility in alloys, in addition to providing strong, formable materials, can lead to reduced weights in practical applications. However, increasing strength typically comes at the cost of lowering the ductility and vice-versa, referred to as the strength–ductility trade-off. In this work, we investigate the thermo-mechanical response of a 3-element multifunctional NiTi–Nb nanocomposite material that overcomes this trade-off, as it exhibits a high strength of 980 MPa and an ultrahigh ductility of 58% at fracture. The remarkable properties are attributed to the underlying microstructure of Nb nanofibers dispersed in an NiTi matrix. Deformation is accommodated via the shape memory transformation of the active NiTi matrix in concert with elastoplastic deformation of Nb nanofibers embedded within the matrix. Consequently, the material exhibits multifunctionality and recovers deformation during heating via the reversion of the stress-induced martensitic transformation in the NiTi matrix. The high strength and high ductility of this 3-element nanocomposite material puts it amongst the best performing high-entropy alloys (HEAs) that are typically made up of five or more elements. [ABSTRACT FROM AUTHOR]

In recent years, additive manufacturing of nickel-titanium (NiTi) alloys as medical implant materials have attracted a lot of interest due to their precise, rapid, and integrated molding. However, the NiTi alloy as a bioinert material exhibits poor osteogenic activity and biomineralization properties. In this work, a graphene oxide (GO) coating containing nano-hydroxyapatite (HA) is fabricated on the NiTi alloys by a one-step DC electrodeposition method. The effects of HA (0.1 g/L) on the corrosion resistance, biomineralization properties and long-term stability of GO composite coating were investigated by electrochemical tests and immersion experiments. The result shows that the corrosion current density of GO coating reduces by one order of magnitude due to the introduction of nano-HA (from 2.24 × 10−8 A/cm2 to 3.18 × 10−9 A/cm2), the surface remains dense after 15 days of immersion, and a dense apatite layer is mineralized on the surface. In addition, in vitro MC3T3-E1 cell viability and cell morphology results showed that the coating can effectively enhance the biocompatibility of additively manufactured NiTi alloy because it provides a better microenvironment and interface for cell growth and adhesion. Taken together, the additively manufactured NiTi alloys with GO/HA coating present great potential for biological application, especially as orthopedic implants. [ABSTRACT FROM AUTHOR]

The cuttlebone is known for its ability to possess high specific stiffness, progressive failure and lightweight from the porous chambered structure. Inspired by the microstructural characteristics of cuttlebone and incorporating the wall gradient design, a series of double-asymmetric honeycombs were designed and processed by LPBF. Results indicated that bionic structural units with the junction design can maintain the integrity of the residual parts after local buckling and failure, improving the load-bearing capacity. The double-asymmetric honeycomb with gradation parameter a = 2/3 achieved a maximum specific compressive strength of 70.64 MPa cm3/g. As a decreases, there is an increase in specific energy absorption and a narrowing of the hysteresis loop. The as-build honeycomb had undergone stress-induced martensite transformation during compression. The dissipated mechanical energy (ME) decreased with the increasing cycle number and the decreasing a. The results provide design guidelines and process strategies for developing high-performance honeycombs. [ABSTRACT FROM AUTHOR]

Achieving grain refinement in the wire-arc directed energy deposition (DED) process of NiTi alloy is highly challenging. We have successfully obtained NiTi alloy with a fine microstructure and observed an improvement in superelastic recoverability by introducing an ultrasound-assisted field during the deposition process. The results show that the average grain size of the NiTi alloy samples decreased from 147.3 to 72.2 µm. Additionally, the recoverable strain of the samples increased significantly from 3.7% to 4.4%. This is attributed to the ultrasonic cavitation and acoustic streaming phenomena during the ultrasound-assisted process, which promotes the columnar-to-equiaxed transition (CET) during the solidification process. Fundamentally, the key to the enhancement of recoverable strain after ultrasound-assisted is that the formation of equiaxial grains provides more strain compatibility to the grain boundaries, which reduces the formation of dislocations during deformation. [ABSTRACT FROM AUTHOR]

There are various techniques and designs for springs used in orthodontic treatment, including frictionless methods for closing spaces. However, there is limited explicit evidence to support the superiority of one method over another. This review aims to investigate the available evidence and highlight the advantages of these different methods. This review contained six papers, and information such as study design, spring design, applied force systems, variables studied, follow-up period, and records were extracted. All of the studies focused on canine retraction with the Ladanyi spring showing the highest rate of movement (1.8 mm per month) among all springs for upper canine retraction. The Gjessing and T-loop springs outperformed the Reverse Closing Loop and Ricketts spring, respectively, substantially. In terms of tip control, the T-loop spring showed a clear advantage over the modified Marcotte spring with a difference of 1.2° vs. 6.6° per 3 months. Additionally, it was observed that the Reverse Closing Loop caused a significant loss of anchorage during canine retraction with a medial movement of 2.4 mm. When comparing wire types, no significant differences were found between TMA and Nitinol, while stainless steel was found to be less effective in terms of movement rate and tip control. However, the results indicated that there was no clear evidence that one specific technique was definitively preferable to another; therefore, there is an urgent need for more studies with proper study designs to produce more robust conclusions. [ABSTRACT FROM AUTHOR]

In recent years, additive manufacturing of nickel-titanium (NiTi) alloys as medical implant materials have attracted a lot of interest due to their precise, rapid, and integrated molding. However, the NiTi alloy as a bioinert material exhibits poor osteogenic activity and biomineralization properties. In this work, a graphene oxide (GO) coating containing nano-hydroxyapatite (HA) is fabricated on the NiTi alloys by a one-step DC electrodeposition method. The effects of HA (0.1 g/L) on the corrosion resistance, biomineralization properties and long-term stability of GO composite coating were investigated by electrochemical tests and immersion experiments. The result shows that the corrosion current density of GO coating reduces by one order of magnitude due to the introduction of nano-HA (from 2.24 × 10−8 A/cm2 to 3.18 × 10−9 A/cm2), the surface remains dense after 15 days of immersion, and a dense apatite layer is mineralized on the surface. In addition, in vitro MC3T3-E1 cell viability and cell morphology results showed that the coating can effectively enhance the biocompatibility of additively manufactured NiTi alloy because it provides a better microenvironment and interface for cell growth and adhesion. Taken together, the additively manufactured NiTi alloys with GO/HA coating present great potential for biological application, especially as orthopedic implants. [ABSTRACT FROM AUTHOR]

A flow diverter (FD) is an effective method for treating wide-necked intracranial aneurysms by inducing hemodynamic changes in aneurysms. However, the procedural technique remains challenging, and it is often not performed properly in many cases of deployment or placements. In this study, three types of FDs that changed the material of the wire were prepared within the same structure. Differences in physical properties, such as before and after delivery loading stent size, radial force, and radiopacity, were evaluated. The performances in terms of deployment and trackability force were also evaluated in a simulated model using these FDs. Furthermore, changes of deployment patterns when these FDs were applied to a 3D-printed aneurysm model were determined. The NiTi FD using only nitinol (NiTi) wire showed 100% size recovery and 42% to 45% metal coverage after loading. The low trackability force (10.9 to 22.9 gf) allows smooth movement within the delivery system. However, NiTi FD cannot be used in actual surgeries due to difficulties in X-ray identification. NiTi-Pt/W FD, a combination of NiTi wire and platinum/tungsten (Pt/W) wire, had the highest radiopacity and compression force (6.03 ± 0.29 gf) among the three FDs. However, it suffered from high trackability force (22.4 to 39.9 gf) and the end part braiding mesh tended to loosen easily, so the procedure became more challenging. The NiTi(Pt) FD using a platinum core nitinol (NiTi(Pt)) wire had similar trackability force (11.3 to 22.1 gf) to NiTi FD and uniform deployment, enhancing procedural convenience. However, concerns about low expansion force (1.79 ± 0.30 gf) and the potential for migration remained. This comparative analysis contributes to a comprehensive understanding of how different wire materials influence the performance of FDs. While this study is still in its early stages and requires further research, its development has the potential to guide clinicians and researchers in optimizing the selection and development of FDs for the effective treatment of intracranial aneurysms. [ABSTRACT FROM AUTHOR]