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This paper introduces a comprehensive computational framework, comprising a finite deformation crystal inelasticity constitutive model and phase field model, for modeling crack growth in superelastic nitinol polycrystalline microstructures. The crystal inelasticity model represents crystal stretching and lattice rotation from elastic mechanisms, as well as local inelastic deformation due to austenite-martensite phase transformation. The phase field formulation decomposes the Helmholtz free energy density into stored elastic energy, phase transformation energy, and crack surface energy components. The elastic energy accounts for tension-compression asymmetry with the formation of the crack through a spectral decomposition. Kinetic Monte Carlo simulations generate equilibrium area fractions of different surface orientations, which serve as weights for the surface energy. An adaptive wavelet-enhanced hierarchical finite element (FE) model is introduced to alleviate high computational overhead in phase field crack simulations. Simulations with the coupled inelasticity phase field model are conducted under various loading conditions including Mode-I tension, a quasi-static Kalthoff experiment, and cyclic loading of polycrystalline microstructures. Crack propagation is effectively predicted by this model, providing valuable insights into the material mechanical behavior with growing cracks. [ABSTRACT FROM AUTHOR]

The revision of ceramic inlays of acetabular cups is a challenging surgical procedure. The mechanical impact during the inlay extraction process can damage the ceramic or metal cup rim. To avoid these risks, a concept for a new revision procedure was developed. It is based on an actuator system, which allows a non-destructive release of the ceramic inlay. To integrate the actuator system, different design concepts of acetabular cup components were investigated, and an actuator based on shape-memory alloy (SMA) wires was developed. The process chain for the actuator, starting from nickel-titanium wires manufactured into the actuator geometry by laser welding and thermo-mechanical treatment for the shape setting process up to the functionality evaluation of the actuator system, was implemented on a laboratory scale. The new revision procedure is based on a phase transformation of the SMA wire actuator, which was obtained through two methods—applying an electrical current by an instrument and rinsing the wire with heated water. The phase transformation of the actuator resulted in a contraction between 3.2% and 4.3% compared to its length after pre-stretching and was able to release the ceramic inlay from the cup. Therefore, the developed actuator design and process chain is a proof of concept towards a new revision procedure for modular acetabular cups. [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]

OBJECTIVE Shape-memory polymers (SMPs) are smart materials suitable for modifying size, shape, stiffness, and strain in response to different external stimuli. Nitinol, used in the medical field, has increased in recent years and is the most important example of SMPs. In this study, we aimed to make the dosimetric evaluation of Nitinol to test its usability in Brachytherapy treatment. METHODS To achieve the aim of the study, we designed a tandem to be made of polyamide 12 for the straight part (4 and 6 centimeters on both sides) and Nitinol for the angled part (4 centimeters). Afterward, we placed the produced tandem into the bolus and measured the dose using different dosimetry methods such as the treatment planning system (TPS), GafChromic film dosimetry, and MOSFET dosimetry. Three different measurements were made with the same irradiation dose for each measurement method, and the average results were recorded. RESULTS The Euclidean distance between the source and the measuring point was 34.0 millimeters for the Polyamide 12 part, and 32.8 millimeters for the Nitinol part. The calculated irradiation time was 284.9 seconds for the Polyamide 12 part and 268.2 seconds for the Nitinol part. Considering the irradiation times and source distances, the calculated difference between Nitinol and Polyamide 12 was 1.15%. This difference was 1.0%, 1.87%, and 2.08% for TG43, MOSFET, and GafChromic film dosimetry, respectively. CONCLUSION In conclusion, Nitinol did not have a negative effect on the dose distribution. However, these results should be supported by further studies including other dosimetry measurements. [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]

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]

Standard laparoscopes, which are widely used in minimally invasive surgery, have significant handling limitations due to their rigid design. This paper presents an approach for a bending section for laparoscopes based on a standard semi-finished tube made of Nitinol with laser-cut flexure hinges. Flexure hinges simply created from a semi-finished product are a key element for realizing low-cost compliant structures with minimal design space. Superelastic materials such as Nitinol allow the reversible strain required for this purpose while maintaining sufficient strength in abuse load cases. This paper focuses on the development of a bending section for single use laparoscopic devices (OD 10 mm) with a bending angle of 100°, which enables the application of 100 µm diameter Nitinol actuator wires. For this purpose, constructive measures to realise a required bending curvature and Finite Element Analysis for determining the strain distribution in the flexural region are applied and described for the design of the flexure hinges. In parallel, the influence of the laser-based manufacturing process on the microstructure is investigated and evaluated using micrographs. The deformation behavior of the bending section is experimentally determined using Digital Image Correlation. The required actuation forces and the failure load of the monolithic bending section is measured and compared to a state of the art riveted bending section made of stainless steel. With the developed monolothic bending section the actuation force could be reduced by 50% and the available inner diameter could be increased by 10% while avoiding the need of any assembly step. [ABSTRACT FROM AUTHOR]

Hip implants have a modular structure which enables patient-specific adaptation but also revision of worn or damaged friction partners without compromising the implant-bone connection. To reduce complications during the extraction of ceramic inlays, this work presents a new approach of a shape-memory-alloy-actuator which enables the loosening of ceramic inlays from acetabular hip cups without ceramic chipping or damaging the metal cup. This technical in vitro study exam-ines two principles of heating currents and hot water for thermal activation of the shape-memory-alloy-actuator to generate a force between the metal cup and the ceramic inlay. Mechanical tests concerning push-in and push-out forces, deformation of the acetabular cup according to international test standards, and force generated by the actuator were generated to prove the feasibility of this new approach to ceramic inlay revision. The required disassembly force for a modular acetabular device achieved an average value of 602 N after static and 713 N after cyclic loading. The actuator can provide a push-out force up to 1951 N. In addition, it is shown that the necessary modifications to the implant modules for the implementation of the shape-memory-actuator-system do not result in any change in the mechanical properties compared to conventional systems. [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]

Changes in hydrogen states after dynamic interactions between hydrogen and a stress-induced martensite transformation have been investigated for Ni–Ti superelastic alloy. After homogenised hydrogen concentration by aging, the interactions change the hydrogen thermal desorption behaviour. Hydrogen in a solid solution probably changes to hydrogen trapped in damage regions induced by the interactions, as reported previously. With time after the interactions, the amount of hydrogen desorbed at low temperatures (200–400°C) markedly increases, clearly indicating that hydrogen states further change from the states immediately after the interactions. In cyclic tensile deformation in the stress plateau region caused by stress-induced martensite and reverse transformations, the number of cycles to fracture substantially increases with time after the interactions. The present results indicate that hydrogen states further change to a nominally interacting state after the interactions despite the absence of dynamic structural changes and a hydrogen concentration gradient, thereby suppressing hydrogen embrittlement related to the martensite transformation of the alloy. [ABSTRACT FROM AUTHOR]

The process of argon arc welding of nickel onto titanium with a nonconsumable electrode with feeding of the nickel filler wire into the liquid metal pool is investigated. The influence of the welding modes on the geometrical parameters of the bead and on the susceptibility of the forming surface layer to crack formation is described. The effect of the welding modes on the chemical and phase compositions of the formed surface layer of titanium nickelide is determined. The chemical and phase compositions of the welded-on layer are shown to affect its hardness and wear resistance. [ABSTRACT FROM AUTHOR]

Experimental investigations are presented on the effect of fiber dosage in a high strength cementitious composite (HSCC) with superelastic fibers with an L-shape at both ends. Superelasticity is one of the smart properties of shape memory alloys, and another property is shape memory effect. Out of the superelasticity and shape memory effect, only superelasticity is exploited in this present application. The rheological properties of the fresh composite system are investigated first using the slump flow table test. The slump test shows that although the fibers with L-shaped ends adversely affect the rheological properties of fresh concrete, the consistency of the mix is hardly compromised. The three-point bending test is conducted thereafter to assess the flexural performance of several beam specimens in the hardened state. The results from the three-point bending test are employed to quantify the influence (of fiber dosage) on the post-peak behavior using alternative protocols for the quantifying measures. The increase in fiber content generally increases flexural toughness. However, a fiber content beyond 0.75% in volume is required to achieve post-peak hardening. Alternative standards for evaluating flexural toughness are assessed in reference to the post-peak behavior of the composite system under flexure. The recentering capability using the cyclic three-point bending test is also calculated. Finally, the failure modes of the fiber are assessed to show the combined effect of the anchorage offered by the L-shape of the fibers and the interfacial bond strength. It is observed that the anchorage of HSCC is sufficient to hold the fibers until rupture. The failure modes of the fibers are noted to be irrespective of the fiber content yet sensitive to the orientation and length of embedment. [ABSTRACT FROM AUTHOR]

In the present article, mesoporous SiO 2 /hydroxyapatite (HA) composite particles were produced via employing CTAB as a template, and then co-electrodeposited on Nitinol biomedical alloy with HA. Characterization results showed the formation of about 200 nm spheres with numerous plate-like particles and slit-shaped pores. The composite coatings were applied by using different concentrations of particles in the deposition electrolyte (500, 750, 1000, and 1250 mg/L). Morphological observations revealed that with an increase in particle concentration, the film exhibited greater compactness, leading to the formation of particle agglomerates in certain regions. This was further proved by the atomic force microscopy analysis where the porosity of the layers decreased, and the roughness diminished by raising particle concentration. This made composite coatings a little more hydrophobic than pure HA coating. Furthermore, the incorporation of these particles significantly enhanced the corrosion protection of the composite coatings. Specifically, the corrosion current density for the sample coated with a solution containing 1000 mg/L of particles decreased to nearly one-fifth of that observed in the pure HA coating. Last but not least, MG-63 osteoblasts were provided with a convenient environment on composite coatings since they fed on Si nutritious element to reproduce and proliferate more aggressively than on pure HA layer. [ABSTRACT FROM AUTHOR]

Delayed coronary obstruction is a rare complication occurring after transcatheter aortic valve replacement (TAVR). Although TAVR has become popular, in some cases, the therapeutic strategy should be carefully selected depending on the patient's anatomical and/or functional restrictions. We report a rare case of delayed coronary obstruction in which coronary obstruction was caused by thick endothelialization of the nitinol frame of the prosthetic valve. A 79-year-old female who had undergone TAVR 4 months before presented with mild chest pain and was admitted to our institution. Computed tomography and coronary angiography revealed that the space from the sinus of Valsalva to the nitinol frame was narrow and separated from the inside of the nitinol frame because of critical endothelialization. Therefore, an emergency surgical aortic valve replacement was performed. The patient had an uneventful postoperative course and was discharged 20 days postoperatively without any complications. [ABSTRACT FROM AUTHOR]

In this study, the effect of heat treatment parameters on the optimized performance of Ni-rich nickel–titanium wires (NiTi/Nitinol) were investigated that were intended for application as actuators across various industries. In this instance, the maximum recovery strain and actuation angle achievable by a nitinol wire were employed as indicators of optimal performance. Nitinol wires were heat treated at different temperatures, 400–500 °C, and times, 30–120 min, to study the effects of these heat treatment parameters on the actuation performance and properties of the nitinol wires. Assessment covered changes in density, hardness, phase transition temperatures, microstructure, and alloy composition resulting from these heat treatments. DSC analysis revealed a decrease in the austenite transformation temperature, which transitioned from 42.8 °C to 24.39 °C with an increase in heat treatment temperature from 400 °C to 500 °C and was attributed to the formation of Ni4Ti3 precipitates. Increasing the heat treatment time led to an increase in the austenite transformation temperature. A negative correlation between the hardness of the heat-treated samples and the heat treatment temperature was found. This trend can be attributed to the formation and growth of Ni4Ti3 precipitates, which in turn affect the matrix properties. A novel approach involving image analysis was utilized as a simple yet robust analysis method for measurement of recovery strain for the wires as they underwent actuation. It was found that increasing heat treatment temperature from 400 °C to 500 °C above 30 min raised recovery strain from 0.001 to 0.01, thereby maximizing the shape memory effect. [ABSTRACT FROM AUTHOR]

The Pivot Mandu is an innovative device featuring a leak-tight adjustable 3D balloon spacer, incorporating inner mesh support, an outer e-PTFE layer, and a compliant balloon in the middle layer with a specialized detachable system. To assess its feasibility, proof of concept was rigorously evaluated through bench testing and survival porcine animal experiments. The results demonstrated successful remote inflation of the balloon system, with the balloon spacer exhibiting sustained patent and functional integrity over an extended observation period of up to 6 months. A noteworthy feature of the newly designed 3D balloon spacer is its capability for easy size adjustment during procedures, enhancing its adaptability and practicality in clinical settings. This three-layered 3D balloon spacer, with its established long-term patency, exhibits highly encouraging outcomes that hold promise in overcoming the current limitations of spacer devices for heart valve diseases. Given the compelling results from preclinical investigations, the translation of the Pivot Mandu into human trials is strongly warranted. [ABSTRACT FROM AUTHOR]

Abstract Due to the advantages of both the metallic and glass fiber qualities, glass fiber reinforced metal layers are one of the best impact resistant materials. Shape memory alloys have also been thought to be effective materials for equipping the traditional impact-exposed materials due to their high impact damping capabilities. The modal response (natural frequencies, damping, and vibration amplitude) of the laminate composite constructions that incorporate shape memory wires was experimentally investigated in this article. The goal of the current research is to ascertain how the modal responses are impacted by three production parameters: wire diameter, wire location, and wire number. Using an experimental design plan and a central composite design, hybrid specimens were planned. The results showed that the manufacturing variables influence all the modal responses in different proportions. Regarding the innovations in the construction of this type of hybrid composite, this study could be used in the design of mechanical and airspace structures. [ABSTRACT FROM AUTHOR]

Shape memory alloy (SMA) heat engines possess an inherent property of sensing a change in temperature, performing work, and rejecting heat through the shape memory effect resulting from a temperature-induced phase transformation. This work presents a framework for the design and implementation of an SMA-based Stirling heat engine for maximum torque or speed incorporating and combining mechanical, thermal, and material aspects. There is a growing need for such engines for reliable thermal management and energy recovery in both ground and space applications. Mechanical aspects were addressed from force balances in the SMA element and focused on the resulting stress distribution. Thermal aspects considered heat transfer between the SMA element and both the heat source and the heat sink. Materials aspects considered the chemical, elastic, and frictional contributions to the enthalpy of the transformation. The roles of nano- and microstructure through composition, precipitates, variant interfaces, training, cycling, texture, defects, nucleation sites (bulk vs. surface), and multi-step transformations (e.g., a trigonal R-phase transformation) in NiTi based-alloys are also emphasized. The aforementioned aspects were combined to present a figure of merit to aid in the design and implementation of a Nitinol Stirling heat engine operating to maximize torque or maximize speed. [ABSTRACT FROM AUTHOR]

Most relevant to predicting the behavior of shape-memory-alloy (SMA)-based actuator-sensor applications activated by Joule heating are the electro-mechanical characteristics of the material under consideration. For a comprehensive characterization, a single setup that is able to provide all relevant data and information is desirable. This work covers the design, implementation and validation of such a high-end test bench for the holistic characterization of SMA micro-wires. In addition, the setup provides the possibility of application simulation experiments. Key elements of the design are the clamping mechanism guided on air bearings, a linear direct drive, a high-resolution load cell, a high-precision constant current source and a stress-controlled in-line wire sample installation. All measurements take place inside an isolated, temperature-controlled chamber. With the presented setup, the electro-mechanical and thermal characteristics of SMA wire samples with diameters from 20 µm to 100 µm can be determined. Via hardware-in-the-loop (HiL) implementation, the outputs with different biasing mechanisms and additional end-stops can be simulated even at high ambient temperatures. The generated results facilitate the prediction of the exact characteristics of SMA-driven actuator-sensor systems in a variety of applications and lead to a better general understanding of the alloy's properties. All functionalities and features of the setup are presented by discussing the results of exemplary experiments. [ABSTRACT FROM AUTHOR]

The main objective of the work was to create a layer of carbon nanofibre on the surface of the NiTi shape memory alloy. The coating process was carried out in three stages. First, polyacrylonitrile was deposited by electrospinning. Then it was stabilized at temperatures up to 250°C. The last stage was the carbonization performed below 1000°C. The microstructure of the obtained coatings was observed using a scanning electron microscope. The X-ray diffraction techniques were applied to analyze the coating structure. After the polyacrylonitrile deposition, the fibers had an average diameter of about 280 nm, and the final fibers were almost twice as tiny. The applied steps also changed the phase and crystalline state of the fibers, finally leading to the formation of amorphous-nanocrystalline graphite. [ABSTRACT FROM AUTHOR]

In this study, corrosion and wear tests of NiTi alloy (Ni 55%–Ti 45%) samples, known as shape memory alloy, which offer a shape recovery memory effect between memory temperatures ranging from 25 to 35 °C, have been carried out. The standard metallographically prepared samples' microstructure images were obtained using an optical microscope device and SEM with an EDS analyzer. For the corrosion test, the samples are immersed with a net into the beaker of synthetic body fluid, whose contact with the standard air is cut off. Electrochemical corrosion analyses were performed after potentiodynamic testing in synthetic body fluid and at room temperature. The wear tests of the investigated NiTi superalloy were carried out by performing reciprocal wear tests under 20 N and 40 N loads in a dry environment and body fluid. During wear, a 100CR6-quality steel ball of the counter material was rubbed on the sample surface for a total of 300 m with a unit line length of 13 mm and a sliding speed of 0.04 m/s. As a result of both the potentiodynamic polarization and immersion corrosion tests in the body fluid, an average of 50% thickness reduction in the samples was observed in proportion to the change in the corrosion current values. In addition, the weight loss of the samples in corrosive wear is 20% less than that in dry wear. This can be attributed to the protective effect of the oxide film on the surface at high loads and the effect of reducing the friction coefficient of the body fluid. [ABSTRACT FROM AUTHOR]

NiTi (also called Nitinol) transforms from cubic (austenite) to monoclinic (martensite), and vice versa, owing to the shape memory effect and superelasticity. Nitinol has a large number of biomedical applications because of its low elastic modulus close to that of natural bone material and good resistance to corrosion and fatigue, in addition to the transformation temperatures of nitinol that are close to body temperature. It has many other important applications, such as in the aircraft industry. In all these important applications, especially medical applications, Nitinol stability is an important factor for safety. Our goal is to study the stability of NiTi by calculating the phonon dispersion relation to obtain an accurate understanding of the mechanically unstable phases of the NiTi alloy. The dispersion relation for the cubic and monoclinic phases was studied and coded using MATLAB to make a clear consideration of the dispersion relation and its optical and acoustic branches. Moreover, the density of the state and energy from the lattice vibrations were calculated. The crystal is found to be stable by the anharmonic part of the interactions. The austenite phase is stable up to (300 K). While it is not above (300 K). Any extra energy due to temperature changes caused the transformation to the martensite phase. The positive phonon modes indicate that the monoclinic phase is stable against energy perturbations. When the thermal vibration energy was calculated Fvib(T) = 54.8 meV for the cubic phase and Fvib(T) = 38meV in the case of the monoclinic phase at T= 300 K. In both cases, it was less than 5 eV. There are no broken bonds owing to the energy of vibration. [ABSTRACT FROM AUTHOR]

Population explosion, industrialization, and urbanization have accelerated energy requirements across the globe. This has led to the human quest to find simple and cost-effective energy solutions. A promising solution is the revival of the Stirling engine with the addition of Shape Memory Alloy NiTiNOL in it. The experimental results reveal that the addition of a NiTiNOL spring at the base plate of the Stirling engine enhances the overall efficiency of the engine, demonstrating some impact of the shape memory alloy toward the performance output of the Stirling engine. The newly modified engine has been named the STIRNOL ENGINE. The comparative study of Stirling and Stirnol engines reveals a minuscule efficiency improvement, yet there is a furtherance that opens a window for future researchers to get a lead and venture into this new field. We are confident that with more complex designs and better Stirling and NiTiNOL combinations, more efficient engines can be invented in the future. This research focuses on changing the material of the base plate of the Stirnol engine and ascertaining its performance differential through the integration of the NiTiNOL spring. A minimum of four types of materials are utilized for experimentation. [ABSTRACT FROM AUTHOR]

Fetal aqueductal stenosis (AS) is one of the most common causes of congenital hydrocephalus, which increases intracranial pressure due to partial or complete obstruction of cerebrospinal fluid (CSF) flow within the ventricular system. Approximately 2–4 infants per 10,000 births develop AS, which leads to progressive hydrocephalus, which enlarges the head often necessitating delivery by cesarean section. Most babies born with AS are severely neurologically impaired and experience a lifetime of disability. Therefore, a new device technology for venticuloamniotic shunting is urgently needed and has been studied to ameliorate or prevent fetal hydrocephalus development, which can provide a significant impact on patients and their family's quality of life and on the decrease of the healthcare dollars spent for the treatment. This study has successfully validated the design of shunt devices and demonstrated the mechanical performance and valve functions. A functional prototype shunt has been fabricated and subsequently used in multiple in vitro tests to demonstrate the performance of this newly developed ventriculoamniotic shunt. The shunt contains a main silicone-nitinol composite tube, a superelastic 90° angled dual dumbbell anchor, and an ePTFE valve encased by a stainless-steel cage. The anchor will change its diameter from 1.15 mm (collapsed state) to 2.75 mm (deployed state) showing up to 1.4-fold diameter change in human body temperature. Flow rates in shunts were quantified to demonstrate the valve function in low flow rates mimicking the fetal hydrocephalus condition showing "no backflow" for the valved shunt while there is up to 15 mL/h flow through the shunt with pressure difference of 20 Pa. In vivo ovine study results show the initial successful device delivery and flow drainage with sheep model. [ABSTRACT FROM AUTHOR]

In the absence of any literature regarding the development of erosion resistance protective coatings on the aerospace engine parts using NiTi alloy, the current work has been focused on the detail investigation of the solid particle erosion resistance of the NiTi coating developed by atmospheric plasma spray technique. The coating has been prepared by considering an elemental mixture of equiatomic Ni and Ti powder as feedstock material with different plasma arc currents and primary gas flow rates. The quality of the coatings has been checked by different characterization techniques like x-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. The defects observed from the microstructural investigation sometimes lead to more erosion and sometimes resulted in less erosion rate. The investigation of the effect of the porosity percentage on the erosion rate revealed that as the porosity percentage increases, the erosion rate increases at both 45° and 90° erodent impingement angles due to the lack in strength at the edges of the pores. Furthermore, the surface area of the roughness peaks, the stress concentration at the gap between the roughness peaks and height of the surface profile are mainly responsible for the erosion performance at both the erodent impact angles. The erosion rate is inversely proportional to the microhardness of the coatings. In addition to the above, according to the results disclosed by the erosion performance at different impingement angles, the coating is brittle in nature. The surface morphological study of the eroded coatings indicated various erosion mechanisms like plastic deformation, plowing, microcutting, lip formation, scratches, groove formation on the coatings impinged at 45° impact angle and groove formation, splat fracture, splat fragmentation, splat delamination, pit formation on the coatings impinged at 90° impingement angle. [ABSTRACT FROM AUTHOR]

Nitinol (NiTi) alloy is a widely used material for the production of orthodontic archwires. Its corrosion behavior in conditions that exist in the oral cavity still remains a great characterization challenge. The motivation behind this work is to reveal the influence of commercially available mouthwashes on NiTi orthodontic archwires by performing non-electrochemical corrosion tests and quantifying the changes in the nanotopography of commercially available NiTi orthodontic wires. In this study, we examined the behavior of NiTi alloy archwires exposed for 21.5 days to different corrosive media: artificial saliva, Eludril®, Aquafresh®, and Listerine®. The corrosion was characterized by contact mode atomic force microscopy (AFM) before and after the corrosion tests. A novel analysis methodology was developed to obtain insight into locations of material gain or material loss based on standard surface roughness parameters Sa, Sdr, Ssk, and S10z. The developed methodology revealed that fluoride-containing mouthwashes (Aquafresh® and Listerine®) dominantly cause material loss, while chloride-containing mouthwash (Eludril®) can cause both material loss and material gain. The sample exposed to artificial saliva did not display significant changes in any parameter. [ABSTRACT FROM AUTHOR]

One of the key aspects of the biochemical compatibility of medical alloys is the surface corrosion resistance in living organisms. This study discusses the structure of the ceramic-metal surface layer of a porous nickel-titanium alloy (nitinol) and the corrosion resistance in simulated physiological liquids. The structure of the protective layer and glass-ceramic non-metallic inclusions in the surface of the porous alloy have been studied. The formation of the surface ceramic-metal layer and crystallization of various glass-metal-ceramic phases as a result of chemisorption from reaction gases and epitaxial growth from the gas phase during the self-propagating high-temperature synthesis are observed. [ABSTRACT FROM AUTHOR]

Pneumatic structures are recognized as promising thin-walled structures for their advantageous features such as lightness, portability, versatile design, and ease of installation. Although their bearing capacity under monotonic static loads can be formidable, their inherent dissipation capacity is low and thus entails significant limitations when counteracting dynamic loads. A novel tensairity structure is here proposed to overcome this drawback. The innovative design features a cylindrical inflatable element integrated with NiTiNOL cables wrapped around and affixed to a slender beam positioned along its generatrix. A laboratory-scale prototype is employed to assess how the structure behaves under cyclic loading in comparison to a standalone inflated beam and a conventional tensairity structure outfitted with steel cables. This experimental study delves into the influence of internal pressure and pretension levels of the metallic cables. Experimental results unfold a smooth softening-type hysteretic behavior under cyclic loading, which is accompanied by a slight stiffness degradation and a moderate pinching. The comparative analysis of the experimental results also demonstrates the substantially improved and consistent dissipation capacity of the presented novel concept of tensairity structure, which thus offers superior stability under cyclic loads. A parametric identification based on a modified Bouc–Wen model is finally performed to simulate the hysteretic response of the structure. A correlation is also established between the identified parameters of the phenomenological model and the internal pressure, type and cables pretension levels. The excellent agreement between numerical predictions and experimental force–displacement cycles other than those used for the parametric identification demonstrates the suitability of the adopted phenomenological modeling. • Tensairities are formidable for lightness, portability, easy installation, and load capacity. • Increasing structural damping in tensairities allows use under dynamic load conditions. • Shape memory cables enhance dissipation capacity of tensairity structures significantly. • Tensairities can be used for long-span roofs, bridges, aerostats, and space habitats. [ABSTRACT FROM AUTHOR]

Microstructural changes induced by a hydrogen permeation into the NiTi superelastic alloy were investigated in-situ using the X-ray synchrotron diffraction. A new design of an electrochemical cell enabled to uncover time and position dependent processes under a flat alloy surface exposed to the cathodic hydrogen. The diffraction data supported by thermo-elastic FEM calculations helped to quantify an evolution of compressive stresses in the B2 austenitic phase hosting hydrogen atoms. The compressive stress state initiates a formation of martensitic phases starting from the exposed surface layer and advancing into the alloy volume with increasing time of hydrogen charging. We have performed the ab-initio DFT study in order to rationalize volumetric changes associated with variations in the B2 austenite and B19′ martensite lattice parameters. The numerical results also contributed to the identification of a new hydride phase with orthorhombic crystal structure and lattice parameters a = 0.8505 nm, b = 0.7366 nm and c = 0.4722 nm. [Display omitted] [ABSTRACT FROM AUTHOR]

• Laser texturing improved the laser actuation performance of nitinol shape memory alloy. • Textured nitinol showed significant improvement in actuation performance due to enhanced optical absorbance. • Influence of single- and two-stage texturing on actuation performance of nitinol was explored. • Improvement in actuation performance was demonstrated for continuous wave fiber and CO 2 lasers. Laser surface texturing of nitinol was performed using a nanosecond fiber laser to modify the surface structure and enhance the laser actuation performance of nitinol. The influence of laser processing parameters on surface morphology and chemical composition was studied in detail. The influence of texturing on the laser actuation behavior was evaluated using a continuous wave fiber laser and a CO 2 laser. Compared to the pristine sample, the textured samples demonstrated better displacements and faster actuation. During laser actuation using a fiber laser, the textured sample showed maximum and minimum displacement enhancements of 65% and 15%, respectively. The actuation performance of the textured sample was approximately twice that of the pristine sample during the irradiation with CO 2 laser. This paper presents the viability of laser surface texturing to enhance the actuation performance of shape memory alloys, and the results indicate that the power required for actuation can be reduced to avoid the use of bulky power and control units. [ABSTRACT FROM AUTHOR]

Nitinol is an alloy of roughly equiatomic nickel and titanium, having shape memory and widely used in many applications, such as aerospace, automotive, biomedical and others. One of techniques for its treatment is plasma or ion beam irradiation. In the work we investigated surface composition and topography of the alloy formed by ion and cluster ion bombardment. A strong enrichment of the surface with nickel is detected, which does not agree with contemporary ideas about preferential sputtering. The results were compared with other known results in the area, and the processes occurring under ion irradiation of compound materials were discussed. The role of ambient oxygen in the steady state surface composition establishing is described. [ABSTRACT FROM AUTHOR]

The effectiveness of supragingival dental biofilm control during orthodontic treatment and changes in the bacterial profile were analyzed. Sixty-four participants aged 12–22 years (57% female) were included in the study. Participants underwent orthodontic treatment with fixed appliances and were randomly assigned to one of the three groups, which during a period of one month: (I) used chlorhexidine digluconate (CHX), (II) used high concentration of fluoride (F) gel and (III) performed standard oral hygiene. The plaque and gingivitis index, pH of biofilm and white spot lesions (WSL) were assessed. Changes of the bacteria in the biofilm were analyzed by the quantitative polymerase chain reaction Increase in the plaque index, pH of biofilm, and WSL was observed during orthodontic treatment with standard oral hygiene. Large interindividual variability was present, and the effects of one-month use of fluorides and CHX on clinical parameters were not significant. Despite standard hygiene the abundance of studied biofilm bacteria increased - the most Streptoccocus mutans (14.2x) and S. salivarius (3.3x), moderate Veillonella parvula (3x) and the least S. sobrinus (2.3x) and Agregatibacter actinomycetemcomitans (1.9x). The use of CHX reduced S. sobrinus (2.2x) and A. actinomycetemcomitans (1.9x). Fluoride use reduced A. actinomycetemcomitans (1.3x) and S. sobrinus (1.2x). Fluorides better controlled S. mutans than CHX. Bacterial biomass in supragingival biofilm increased during treatment with metal orthodontic appliances, with greater increase in cariogenic bacteria than periopathogens. Fluoride controlled S. mutans , while CHX S. sobrinus and A. actinomycetemcomitans. • The abundance of studied biofilm bacteria increased during treatment with fixed appliance despite standard oral hygiene. • Greater increase in cariogenic bacteria than periopathogens is related to orthodontic treatment with fixed metal appliance. • S. mutans was controlled better with fluorides than chlorhexidine. • S. sobrinus and A. actinomycetemcomitans were controlled better with chlorhexidine. [ABSTRACT FROM AUTHOR]

In the present study, the effect of alumina (Al2O3) nano-powder was investigated for the electrical discharge machining (EDM) of a Nitinol shape memory alloy (SMA). In addition to the nano-powder concentration, other parameters of pulse-on-time (Ton), pulse-off-time (Toff), and current were selected for the performance measures of the material removal rate (MRR), surface roughness (SR), and tool wear rate (TWR) of Nitinol SMA. The significance of the design variables on all the output measures was analyzed through an analysis of variance (ANOVA). The regression model term has significantly impacted the developed model terms for all the selected measures. In the case of individual variables, Al2O3 powder concentration (PC), Toff, and Ton had significantly impacted MRR, TWR, and SR measures, respectively. The influence of EDM variables were studied through main effect plots. The teaching–learning-based optimization (TLBO) technique was implemented to find an optimal parametric setting for attaining the desired levels of all the performance measures. Pursuant to this, the optimal parametric settings of current at 24 A, PC at 4 g/L, Toff at 10 µs, and Ton of 4 µs have shown optimal input parameters of 43.57 mg/min for MRR, 6.478 mg/min for TWR, and 3.73 µm for SR. These results from the TLBO technique were validated by performing the experiments at the optimal parametric settings of the EDM process. By considering the different user and application requirements, 40 Pareto points with unique solutions were generated. Lastly, scanning electron microscopy (SEM) performed the machined surface analysis. The authors consider this to be very beneficial in the nano-powder-mixed EDM process for appropriate manufacturing operations. [ABSTRACT FROM AUTHOR]

Laser Powder Bed Fusion (LPBF) technology is a new trend in manufacturing complex geometric structures from metals. This technology allows producing topologically optimized parts for aerospace, medical and industrial sectors where a high performance-to-weight ratio is required. Commonly the feature size for such applications is higher than 300–400 microns. However, for several possible applications of LPBF technology, for example, microfluidic devices, stents for coronary vessels, porous filters, dentistry, etc., a significant increase in the resolution is required. This work is aimed to study the resolution factors of LPBF technology for the manufacturing of superelastic instruments for endodontic treatment, namely Self-Adjusting Files (SAF). Samples of thin walls with different incline angles and SAF samples were manufactured from Nickel-Titanium pre-alloyed powder with a 15–45 μm fraction. The printing procedure was done using an LPBF set-up equipped with a conventional ytterbium fiber laser with a nominal laser spot diameter of 55 microns. The results reveal physical, apparatus, and software factors limiting the resolution of the LPBF technology. Additionally, XRD and DSC tests were done to study the effect of single track based scanning mode manufacturing on the phase composition and phase transformation temperatures. Found combination of optimal process parameters including laser power of 100 W, scanning speed of 850 mm/s, and layer thickness of 20 μm was suitable for manufacturing SAF files with the required resolution. The results will be helpful for the production of NiTi micro objects based on periodic structures both by the LPBF and μLPBF methods. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to investigate the effect of remelting each layer on the homogeneity of nickel-titanium (NiTi) parts fabricated from elemental nickel and titanium powders using laser powder bed fusion (LPBF). In addition, the influence of manufacturing parameters and different melting strategies, including multiple cycles of remelting, on printability and macro defects, such as pore and crack formation, have been investigated. Design/methodology/approach: An LPBF process was used to manufacture NiTi alloy from elementally blended powders and was evaluated with the use of a remelting scanning strategy to improve the homogeneity of fabricated specimens. Furthermore, both single melt and up to two remeltings were used. Findings: The results indicate that remelting can be beneficial for density improvement as well as chemical and phase composition homogenization. Backscattered electron mode in scanning electron microscope showed a reduction in the presence of unmixed Ni and Ti elemental powders in response to increasing the number of remelts. The microhardness values of NiTi parts for the different numbers of melts studied were similar and ranged from 487 to 495 HV. Nevertheless, it was observed that measurement error decreases as the number of remelts increases, suggesting an increase in chemical and phase composition homogeneity. However, X-ray diffraction analysis revealed the presence of multiple phases regardless of the number of melt runs. Originality/value: For the first time, to the best of the authors' knowledge, elementally blended NiTi powders were fabricated via LPBF using remelting scanning strategies. [ABSTRACT FROM AUTHOR]

Titanium oxynitride coatings deposited by reactive magnetron sputtering improve biocompatibility of vascular stents by increasing NO production, viability, and adhesion of EA.hy926 cells. Thus, the application of titanium oxynitride coatings is a promising strategy for increasing the biocompatibility of nitinol stents. [ABSTRACT FROM AUTHOR]

Shortage of healthy donors' organs has appeared as one of the main challenges for organ transplantation. This study focuses on the novel endovascular device development to increase the number of available organs from cardiac death donors. The primary objective of this study is the design validation of a newly developed stent graft for the abdominal organ perfusion with cardiac blood flow isolation. In this paper, the effectiveness of the device design has been validated via the assessment of the device performance both in vitro and in vivo. The radial force of stent structure was first numerically analyzed using finite element method, then was quantified experimentally. The blood perfusion parameters were investigated to demonstrate their effect on the blood delivered to the abdominal organs, maintaining the organs healthy for donation. In vitro flow leakage was measured using a 3-D printing-based silicone aortic model to evaluate the isolation between cardiac flow and perfusion flow with minimum values. Following the design validation process, a functional prototype stent graft has been successfully fabricated using optimized laser welding conditions and subsequent joining processes. In vivo porcine study results have demonstrated smooth delivery and successful placement of the device showing complete cardiac flow separation isolating abdominal regions only with the oxygenated blood flow. [ABSTRACT FROM AUTHOR]

Background: The spinal hybrid elastic (SHE) rod dynamic stabilization system can provide sufficient spine support and less adjacent segment stress. This study aimed to investigate the biomechanical effects after the internal fracture of SHE rods using finite element analysis. Methods: A three-dimensional nonlinear finite element model was developed. The SHE rod comprises an inner nitinol stick (NS) and an outer polycarbonate urethane (PCU) shell (PS). The fracture was set at the caudal third portion of the NS, where the maximum stress occurred. The resultant intervertebral range of motion (ROM), intervertebral disc stress, facet joint contact force, screw stress, NS stress, and PCU stress were analyzed. Results: When compared with the intact spine model, the overall trend was that the ROM, intervertebral disc stress, and facet joint force decreased in the implanted level and increased in the adjacent level. When compared with the Ns-I, the trend in the Ns-F decreased and remained nearly half effect. Except for torsion, the PS stress of the Ns-F increased because of the sharing of NS stress after the NS fracture. Conclusions: The study concluded the biomechanical effects still afford nearly sufficient spine support and gentle adjacent segment stress after rod fracture in a worst-case scenario of the thinnest PS of the SHE rod system. [ABSTRACT FROM AUTHOR]

Background: The spinal hybrid elastic (SHE) rod dynamic stabilization system can provide sufficient spine support and less adjacent segment stress. This study aimed to investigate the biomechanical effects after the internal fracture of SHE rods using finite element analysis.Methods: A three-dimensional nonlinear finite element model was developed. The SHE rod comprises an inner nitinol stick (NS) and an outer polycarbonate urethane (PCU) shell (PS). The fracture was set at the caudal third portion of the NS, where the maximum stress occurred. The resultant intervertebral range of motion (ROM), intervertebral disc stress, facet joint contact force, screw stress, NS stress, and PCU stress were analyzed.Results: When compared with the intact spine model, the overall trend was that the ROM, intervertebral disc stress, and facet joint force decreased in the implanted level and increased in the adjacent level. When compared with the Ns-I, the trend in the Ns-F decreased and remained nearly half effect. Except for torsion, the PS stress of the Ns-F increased because of the sharing of NS stress after the NS fracture.Conclusions: The study concluded the biomechanical effects still afford nearly sufficient spine support and gentle adjacent segment stress after rod fracture in a worst-case scenario of the thinnest PS of the SHE rod system. [ABSTRACT FROM AUTHOR]

Nickel-titanium alloy (Nitinol) is an excellent shape memory alloy (SMA) for microelectro-mechanical systems (MEMS) particularly in biomedical applications owing to its three excellent features shape memory effect (SME), superelasticity, and biocompatibility. The temperature-dependent material transformation properties of Nitinol SMAs make conventional machining difficult. Micro-ECM, a non-conventional machining process for conductive materials regardless of their strength and hardness, has the potential to fabricate microfeatures on Nitinol. This study presents the investigation on the electrochemical dissolution behavior of Nitinol in different electrolytes for micro-ECM. The influence of electrolytes on the nature of dissolution of Nitinol was studied by fabricating microchannels in three levels of parameters containing applied voltage and electrolyte concentration. The first three electrolytes were all aqueous neutral electrolytes, i.e., NaCl, NaNO3, and NaBr. The aqueous NaNO3 was successful in fabricating microchannels at all levels of process parameters. However, aqueous electrolytes form relatively a huge amount of sludge on the machined surface reducing both dissolution efficiency and machining accuracy. Thus, ethylene glycol-based NaNO3 was used to fabricate microchannels with lower depth overcut (DOC), width overcut (WOC), and length overcut (LOC) with respect to aqueous NaNO3 electrolyte. The potentiodynamic polarization (PDP) tests of Nitinol through cyclic voltammetry (CV) shows passive dissolution in aqueous electrolyte and active dissolution in non-aqueous electrolyte. [ABSTRACT FROM AUTHOR]

A model is presented to analyze the evolution of mechanical stresses in the vicinity of the coating–substrate interface under processing conditions. The model takes into account different mechanisms of stress formation, including the temperature and phase composition changes. It is shown that the coating stresses significantly exceed the strength limit of the material, with the main contribution coming from the changes in the composition. [ABSTRACT FROM AUTHOR]

Nitinol (NiTi) alloys are gaining extensive attention due to their excellent mechanical, superelasticity, and biocompatibility properties. It is difficult to model the complex mechanical behavior of NiTi alloys due to the solid-state diffusionless phase transformations, and the differing elasticity and plasticity presenting from these two phases. In this work, an Auricchio finite element (FE) model was used to model the mechanical behavior of superelastic NiTi and was validated with experimental data from literature. A Representative Volume Element (RVE) was used to simulate the NiTi microstructure, and a microscale study was performed to understand how the evolution of martensite phase from austenite affects the response of the material upon loading. Laser Powder Bed Fusion (L-PBF) is an effective way to build complex NiTi components. Porosity being one of the major defects in Laser Powder Bed Fusion (L-PBF) processes, the model was used to correlate the macroscale effect of porosity (1.4–83.4%) with structural stiffness, dissipated energy during phase transformations, and damping properties. The results collectively summarize the effectiveness of the Auricchio model and show that this model can aid engineers to plan NiTi processing and operational parameters, for example for heat pump, medical implant, actuator, and shock absorption applications. [ABSTRACT FROM AUTHOR]

Over the last decade, pedicle fixation systems have evolved and modifications in spinal fusion techniques have been developed to increase fusion rates and improve clinical outcomes after lumbar interbody fusion (LIF). Regarding materials used for screw and rod manufacturing, metals, especially titanium alloys, are the most popular resources. In the case of pedicle screws, that biomaterial can be also doped with hydroxyapatite, CaP, ECM, or tantalum. Other materials used for rod fabrication include cobalt–chromium alloys and nitinol (nickel–titanium alloy). In terms of mechanical properties, the ideal implant used in LIF should have high tensile and fatigue strength, Young's modulus similar to that of the bone, and should be 100% resistant to corrosion to avoid mechanical failures. On the other hand, a comprehensive understanding of cellular and molecular pathways is essential to identify preferable characteristics of implanted biomaterial to obtain fusion and avoid implant loosening. Implanted material elicits a biological response driven by immune cells at the site of insertion. These reactions are subdivided into innate (primary cellular response with no previous exposure) and adaptive (a specific type of reaction induced after earlier exposure to the antigen) and are responsible for wound healing, fusion, and also adverse reactions, i.e., hypersensitivity. The main purposes of this literature review are to summarize the physical and mechanical properties of metal alloys used for spinal instrumentation in LIF which include fatigue strength, Young's modulus, and corrosion resistance. Moreover, we also focused on describing biological response after their implantation into the human body. Our review paper is mainly focused on titanium, cobalt–chromium, nickel–titanium (nitinol), and stainless steel alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomic layer deposition of ZnO-TiO 2 oxide (ZTO) nanocoatings on nitinol surface. • Supercycle approach permits a wide range of adjustments to the coating composition. • ZTO coatings exhibit high biocompatibility, bactericidal and anticorrosion properties. In order to enhance the corrosion resistance and bioactivity of the additively manufactured nitinol alloy, ZnO-TiO 2 (ZTO) nanocoatings have been synthesised by atomic layer deposition. The supercycle approach was employed to deposit 40 nm coatings with varying ZnO/TiO 2 ratios: 5/1, 1/1, 1/5 and 1/20. The results demonstrated that this approach permitted the coating composition to be varied over a wide range. The study of anticorrosion properties in physiological Ringer's solution revealed that the coatings, depending on their composition, are capable of reducing the corrosion rate of nitinol by a value ranging from 4 to 58 times. In vitro studies have demonstrated high viability, good adhesion and spreading of human osteoblast-like MG-63 and mesenchymal stem FetMSC cells on the surface of all samples except those with high zinc content (ZnO and ZTO-5/1). All coatings induced differentiation of both cell lines in the osteogenic direction and demonstrated antibacterial activity against multi-drug resistant A. baumannii (>96 %) and P. aeruginosa (>90 %) strains. The results indicate the considerable potential of the developed methodology for the ALD of ZTO that combine the biocompatibility of titanium oxide, the antibacterial properties of zinc oxide and their overall stability and effectiveness for the protection of nitinol against biocorrosion. [ABSTRACT FROM AUTHOR]

The Langevin transducer is widely used in medical and industrial ultrasonics, typically comprising a piezoelectric ceramic stack preloaded between two end-masses. A principal operational challenge is that, depending on the target application or operational environment, piezoelectric ceramics commonly experience elevated temperatures promoting nonlinear dynamic behaviours, often reducing operational performance. Transducers can be operated via burst excitation to mitigate this, but such methods can have limited efficacy, particularly at elevated temperatures. A novel emergent approach is the incorporation of shape memory Nitinol into the transducer, where its temperature-dependent microstructural phase transformations can compensate for changes in the mechanical properties of the piezoelectric ceramics. However, the ability to maintain dynamic stability under power and current tracking, common methods used to ensure stability of Langevin transducers in practical applications, remains unknown. In this research, a cascaded Nitinol Langevin transducer is used to demonstrate its practical application potential. Dynamic stability is assessed whilst power and current levels are tracked in operation. Stable operating frequency, electrical impedance, and vibration amplitude are shown, using a combination of methods including electrical impedance analysis and laser Doppler vibrometry. This research demonstrates the practical application of Langevin transducers incorporating shape memory materials, including with dynamic stability at elevated temperatures. • Manufacturing approach for a Nitinol Langevin transducer. • Frequency responses of a hard piezoelectric ring at elevated temperatures. • In-situ frequency variations of the transducer at constant voltages. • In-situ dynamic stability of the transducer under power and current tracking conditions. [ABSTRACT FROM AUTHOR]

The antibacterial ability of an implant is governed by the interaction between the surface of the material and the cells. Nanosized features that promote bacterial killing were achieved through synthesizing a Zn/graphene/chitosan surface on a NiTi alloy. The surface morphology and microstructure of the Zn/graphene/chitosan surfaces were observed, and their antibacterial behavior was investigated. The Zn/graphene/chitosan surface exhibited 93 % antibacterial activity against Staphylococcus aureus (S. aureus), which was higher than the Zn/chitosan surface (67 %), and it inhibited bacterial adhesion. This was attributed to the fast release of Zn ions from the Zn/graphene/chitosan surfaces and the sharp morphology of graphene on the surface. In addition, the adhesion of the Zn/graphene/chitosan coating increased with the amount of graphene content. This finding suggests that the synergy of graphene improves the antibacterial ability, bioactivity, and adhesion of Zn-containing coatings. [Display omitted] • Zn/Gr/chitosan has higher antibacterial activity than Zn/chitosan. • Nanosized features of graphene promote killing bacteria. • Zn/Gr/chitosan exhibits a fast release of Zn-ion. • Adhesion of Zn/Gr/chitosan coating increased with graphene amounts. • NiTi with coatings still have superelasticity and shape memory ability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hybrid fatigue and fracture mechanics study of superelastic Nitinol material. • Starter cracks milled into axial tension–tension specimens using focused-ion-beam. • Loading conditions suited for proper fracture mechanics-based properties. • New experimentally defined strain and stress fatigue limits for Nitinol. • New experimentally defined small crack growth threshold for Nitinol. The present study develops a hybrid total life and damage-tolerant fatigue methodology for the determination of a small crack growth threshold in Nitinol. Axial tension–tension/Mode I fatigue testing was performed on superelastic Nitinol wire specimens with starter cracks milled into the specimens using focused ion beam (FIB). Fatigue testing was performed in displacement control at various strain amplitudes, typical for Nitinol fatigue characterization given its superelastic behavior. The simplistic geometry of the test specimen and axial loading conditions also allowed for the calculation of stress amplitude and initial stress intensity factor range. A logistic regression analysis was used to determine strain/stress-based fatigue limits. The small crack growth threshold for superelastic Nitinol was obtained for the first time from physically small cracks with sizes comparable to native inclusions. Lastly, a fractographic analysis was performed to examine crack initiation and propagation from the FIB-milled starter cracks and to identify relevant fractographic features. While the proposed methodology is centered around the use case of Nitinol medical devices, it could be adapted for other materials and applications where small crack initiation and propagation play an important role in fatigue lifetime prediction. [ABSTRACT FROM AUTHOR]

Nitinol shape memory alloy (SMA) is one of the toughest and difficult to cut advanced smart material. Also, the properties of the material should not be affected during machining operations. Wire electrochemical machining (WECM) was created to address these issues as a result of technological innovation and the necessity for high aspect ratio products. This paper explains the effect of different aqueous solution of electrolytes, i.e., NaBr, NaCl, and NaNO3 on nitinol dimensional and surface characteristics by microgroove fabrications during WECM. Further, in order to improve machining performance, the machining has been carried out with mixed and ozonated mixed conditions of NaCl + NaNO3 electrolytes, and the quality of machined microgrooves is examined for surface topography, dimensional precision, and homogeneity. The best electrolyte, i.e., NaCl + NaNO3 has been further used in combination with EDTA (ethylenedinitrilotetraacetic acid disodium salt dehydrate) complexing agent under non-ozonated and ozonated conditions and resulted in improved surface finish and dimensional features of the microfeatures by expeditiously removing sludge and dissolved products and increasing the efficacy of dissolution than other electrolytic conditions. The average groove width of 105.86 µm, mean depth of 264.6 µm, average surface roughness of 0.1346 µm, homogeneous microslit of average width of 106.40 µm, and average surface roughness (Ra) of 0.1261 µm have been obtained at 5 V pulse voltage and 1.4 µm/s wire feed rate with ozonated aqueous 0.2 M NaCl + 0.2 M NaNO3 mixed with 0.2 M EDTA. [ABSTRACT FROM AUTHOR]

Shape memory alloy (SMA), a distinctive class of material, can possess its preceding form when subjected to definite thermo-mechanical energy. Nitinol, an SMA, having an admirable shape memory effect, super elastic, and biomechanical properties, has developed a vast application in the field of biomedical, automobile, robotics, aerospace, etc. Wire electrical discharge machining (WEDM) technique is employed for machining of electrically conductive materials like SMAs, high tech ceramics, smart materials, etc. This paper is focused on analyzing the effect of different significant input parameters on the vital machinability aspects of SMA nitinol during WEDM. Independent input variables like pulse-on time ( T ON ) , discharge current (I) , wire-speed (WS), wire tension (WT) and flushing pressure (FP) were considered to find out their influence on the kerf width (KW), material removal rate (MRR), arithmetic mean roughness ( R a) , and microhardness (μ h). 3D optical profile, X-ray diffraction analysis, and scanning electron microscopy were also executed on the WEDMed surface to inspect the surface, microstructure, and phase changes in the machined surface. It was detected that I , T ON and FP were more influential than WT and WS for most of the responses. [ABSTRACT FROM AUTHOR]

The role of damage in the degradation of tensile properties related to a stress-induced martensite transformation in a hydrogen-charged Ni–Ti superelastic alloy has been investigated. By damage, we mean vacancy clusters and dislocation structures induced in advance by a dynamic interplay between hydrogen and the martensite transformation. To homogenise the hydrogen concentration, the specimen was aged at room temperature after charging with a small amount of hydrogen (approximately 30 mass ppm). In this case, no fracture occurs within 2000 cycles during a cyclic tensile deformation test in the stress plateau region generated by stress-induced martensite and reverse transformations. With this hydrogen concentration, cyclic interplay between hydrogen and the martensite transformation scarcely leads to the degradation of tensile properties. Nevertheless, following cyclic martensite transformations before aging that induces pre-damage, fracture occurs after around 1000 cycles under a cyclic tensile deformation test despite the hydrogen concentration being the same. The present results clearly indicate that pre-damage induced by hydrogen affects the subsequent transformations, thereby causing the self-multiplication of damage, which degrades the tensile properties. [ABSTRACT FROM AUTHOR]