Search

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 interest in Nitinol (NiTi) as biomedical material is growing thanks to its unique properties, particularly shape memory and superelasticity. Recently, additive manufacturing (AM) has emerged as an alternative to fabricate superelastic NiTi biomedical parts. However, when using AM to fabricate NiTi parts, a proper heat treatment must follow, recommended not only to alleviate the AM-induced residual stresses, but also to develop a suitable microstructure to enhance the material superelasticity. This heat treatment is expected to modify also the NiTi corrosion behavior, which must be evaluated since corrosion may lead to the possible harmful release of nickel ions in the human environment. In this framework, the objective of the paper is to assess the mechanical and corrosion properties of a Ni-rich NiTi fabricated by laser powder bed fusion before and after heat treatment. To this aim, nano-indentation was used to evaluate superelasticity, whereas electro-chemical tests provided the corrosion potential and current density. The results of the analyses show that both the mechanical and corrosion characteristics were related to the peculiar microstructural features induced by the AM and heat treatment steps, nevertheless ageing at 600°C was the best in terms of superelasticity, while aging at 300°C assured the highest corrosion resistance. [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]

Fusion-based joining techniques such as TIG and Laser are used for the high-quality Nitinol welds. The joining of Nitinol is challenging due to the formation of intermetallic, which results in the loss of Superelastic and Shape Memory Effect behavior. The optimum heat input is necessary to produce high-quality welds especially in thin sheet joining. Autogenous TIG welding with optimum heat input creates the satisfactory Nitinol weld joints consisting narrower heat-affected zones, and prevents the extensive precipitate formation in weld region. In the paper, autogenous TIG and Laser Beam welding were used for the welding of Nitinol superelastic sheet. The SEM fractography and microhardness were studied to understand the weld zone behavior of Nitinol welds. The Deep Hole Drilling technique was implemented to quantify the residual stresses in TIG and Laser Nitinol welds. The weld longitudinal residual stresses are found to be higher than the transverse residual stresses in both, TIG and Laser welds. In the base material, the compressive residual stresses were present up to near yield strength of material. [ABSTRACT FROM AUTHOR]

Abstract Nitinol, a biocompatible material, is gradually becoming famous for its superelasticity, shape memory and corrosion resistance behaviours. However, the lower machinability due to the strain-hardening effect and lower thermal conductivity is contrary to its adventitious properties. Therefore, EDM is a preferable machining process for materials like Nitinol. EDM, thermal processing, raises the concern of processing Nitinol with minimal variation of its well-known properties and economical machining process. Therefore, this article deals with multi-objective optimization through GRG-assisted GA of µ-EDM drilling of Ni51.58Ti48.34 alloy using a copper electrode and distilled water. It was found that discharge current and servo voltage significantly influence the responses. The GA, with the assistance of GRG, optimized the multiple responses (viz. MRR, TWR and DoT) and yielded a discharge current of 12 A, gap voltage of 40 V, discharge time of 2 µs, charging time of 9 µs and flushing pressure of 50 kg/cm2. The confirmatory experiment yielded MRR of 0.0036 g/min, TWR of 0.0038 g/min and DoT of 0.0089 radians. There were variations of the predicted and experimentally validated responses by − 2.78, 26.32 and 35.96% for MRR, TWR and DoT, respectively.

This study investigates the greater coefficient of Performance (COP) exhibited by the Ni–Ti lattice geometry (LS) over the solid geometry (SS) for solid-state heating and cooling. The LS's advantageous COP can be attributed to factors including variations in phase transformation behavior, a larger surface area facilitating enhanced heat transfer, and a greater volume of water heated per cycle owing to the cavities. Moreover, the LS demands lower compression forces due to its lower mass and geometry, which contribute to its heightened energy efficiency. Remarkably, the LS achieved a maximum temperature span of 11.2 °C at 40 kN compression force, whereas the SS required 80 kN to attain a similar 12.9 °C span. Both the SS and LS showcased a non-linear correlation with compression force which was attributed to Lauder's transformation and pseudo-elastic behaviors. Additionally, the temperature span of the SS exhibited symmetrical behavior during heating-cooling cycles. Conversely, the LS displayed asymmetry, with a more substantial temperature change during the cooling phase than the heating phase.

Nitinol belongs to the class of smart materials that have attracted the attention of researchers in recent decades due to their new promising industrial applications. Because of the austenite/martensite phase transformation, nitinol offers unique properties: superelasticity and shape memory effect. The former ability can be exploited for sensing, actuating, and damping applications. On the other hand, additive manufacturing of nitinol has started kicking off unimaginable applications exploiting the complexity-for-free characteristics offered by the 3D printing processes. Although stand-alone research on additive manufacturing of nitinol is available, the impact of different manufacturing steps, such as machining and heat treatment, on its superelasticity is severely lacking. This work used a powder bed fusion process using a laser beam to manufacture a Ni 50.4 Ti 49.6 austenitic alloy, which was subsequently heat-treated at different aging temperatures. Subsequently, turning operations were carried out at varying cutting speeds under cryogenic cooling conditions. An in-depth characterization of the surface integrity and SE alterations induced by manufacturing was conducted before and after machining. The outcome of the work provides the best combination of heat treatment and machining parameters that allow for maximum surface integrity and SE. [ABSTRACT FROM AUTHOR]

Background: Primary arthrodesis of Lisfranc fracture-dislocations is a reliable treatment option, yet concerns remain about nonunion. Nitinol staple use has recently proliferated in midfoot arthrodesis. The purpose of this study is to examine the union rate of primary arthrodesis of acute Lisfranc fracture-dislocations treated with nitinol staples compared with traditional plate-and-screw fixation. The secondary objective is to assess the difference in operative times and reoperation rates. Methods: Midfoot fracture-dislocations treated with primary arthrodesis by 7 foot and ankle orthopaedic surgeons were reviewed. Of 160 eligible patients, 121 patients (305 joints) met the required 4-month minimum radiographic follow-up. Radiographic outcomes were analyzed at the individual joint level. Each joint was classified as either staples alone (45 patients, 154 joints), staples plus plates and screws (hybrid) (45 patients, 40 joints), or plates and screws alone (31 patients, 111 joints). The primary outcome was arthrodesis union at each joint fused. Results: Nonunion was more common (9.0%, 10/111) among joints fixed with plate and screws than with hybrid (2.5%, 1/40) or staples only (1.3%, 2/154) (P =.0085). Multivariable regression demonstrated that autograft use was independent associated with union (P =.0035) and plate-and-screw only fixation was an independent risk factor for nonunion (P =.0407). Median operating room and tourniquet times were shorter for hybrid (92 and 83 minutes) and staple only (67 and 63 minutes) constructs compared to plate-and-screw only fixation (105 and 95 minutes) (P ≤.0001 and.0003). There was no difference in reoperation rates among patients with different fixation types. Conclusion: We found that use of nitinol compression staple and bone autograft in primary arthrodesis of Lisfranc and midfoot fracture-dislocations was associated with both improved union rates and shorter tourniquet and operative times compared to traditional plate-and-screw fixation techniques. Level of Evidence: Level III, therapeutic. [ABSTRACT FROM AUTHOR]

Is additive manufacturing (AM) a sustainable process? Can the process be optimised to produce sustainable AM parts and production techniques? Additive manufacturing offers the production of parts made of different types of materials in addition to the complex geometry that is difficult or impossible to produce by using the traditional subtractive methods. This study is focused on the optimisation of laser powder bed fusion (L-PBF), one of the most common technologies used in additive manufacturing and 3D printing. This research was carried out by modulating the build layer thickness of the deposited metal powder and the input volumetric energy density. The aim of the proposed strategy is to save the build time by maximizing the applied layer thickness of nitinol powder while retrieving the different AM part properties. The saving in the process time has a direct effect on the total cost of the produced part as a result of several components like electric energy, inert gas consumption, and labour. Nickel-rich nitinol (52.39 Ni at.%) was selected for investigation in this study due to its extremely high superplastic and shape memory properties in addition to the wide application in various industries like aerospace, biomedical, and automotive. The results obtained show that significant energy and material consumption can be found by producing near full dens AM parts with limited or no alteration in chemical and mechanical properties. [ABSTRACT FROM AUTHOR]

This research aims to analyze the welding of 1 mm thick NiTinol sheets using an autogenous double pulse tungsten inert gas (DPTIG) welding process. The effect of heat input (HI) on bead geometry, microstructure, hardness, tensile strength, phase transformation temperature (PTT), and corrosion behavior was studied. The lower (111.25 J/mm), and higher (120.14 J/mm) HI produced an average grain size of 26 μm and 36 μm, respectively. The microstructure of the fusion zone (FZ) had coarser columnar grains with intermetallic phases such as Ni3Ti, and TiO2. The grain size in the FZ increased with the increase in HI. Sample P (111.25 J/mm) showed a higher hardness of 280.54 HV and tensile strength of 566 MPa due to a higher proportion of austenite phase (99.4%), the smaller grain size of 26 µm, a larger fraction of high angle grain boundary (HAGB) of 75.8%, and higher kernel average misorientation (KAM) value of 4.93. Compared to base metal (BM), sample P (111.25 J/mm), and sample S (120.14 J/mm) exhibited a reduction in tensile strength of 19.14% and 32.29%, respectively. The decline in hardness and tensile strength was attributed to the formation of intermetallic phases, a decrease in the Ti/Ni ratio, coarser grain formation, and a decrease in HAGB fraction and KAM values. The fractured tensile samples showed a mixed mode of fracture with dimples and cleavage facets. Compared to BM, Sample Q (118.05 J/mm) exhibited lesser variation in temperature hysteresis values for austenite and martensite temperatures, with a deviation of 0.4°C and 3.1°C, respectively. All the welded samples had better corrosion behavior than the BM due to a higher Ti/Ni ratio. [ABSTRACT FROM AUTHOR]

The binary nickel–titanium (NiTi) alloy, "Nitinol", has become a prominent name in the medical device industry among medical device manufacturers. The unique properties of the material, such as the shape‐memory effect and pseudoelasticity, have earned the material increasing popularity for new product innovations. Among the various manufacturing processes available for metal alloys, laser micromachining has taken the lead for processing Nitinol‐based products. This literature review provides an analysis of the history and applications of Nitinol, an overview of the microstructure of the material, and a review of the current manufacturing methods for laser cutting medical‐grade Nitinol. A more in‐depth focus is placed on the realm of laser processing and the challenges associated with the manufacturing process. Ultrafast femtosecond pulse processing delivers promising results and quality for manufacturing Nitinol medical devices. However, there exists a need to investigate potential approaches to increase the cutting speed of the process to enhance throughput and stay competitive in a growing market due to the cutting speed being over 4‐times slower than long pulse cutting. Many tactics to address the problem are discussed, ranging from laser selection, processing parameters, and nontraditional laser machining approaches. [ABSTRACT FROM AUTHOR]

Objectives: The present study reviews the current literature regarding the utilization of the extended finite element method (XFEM) in clinical and experimental endodontic studies and the suitability of XFEM in the assessment of cyclic fatigue in rotary endodontic nickel–titanium (NiTi) instruments. Material and Methods: An electronic literature search was conducted using the appropriate search terms, and the titles and abstracts were screened for relevance. The search yielded 13 hits after duplicates were removed, and four studies met the inclusion criteria for review. Results: No studies to date have utilized XFEM to study cyclic fatigue or crack propagation in rotary endodontic NiTi instruments. Challenges such as modelling material inputs and fatigue criteria could explain the lack of utilization of XFEM in the analysis of mechanical behavior in NiTi instruments. Conclusions: The review showed that XFEM was seldom employed in endodontic literature. Recent work suggests potential promise in using XFEM for modelling NiTi structures. [ABSTRACT FROM AUTHOR]

Nitinol, a biocompatible material, is gradually becoming famous for its superelasticity, shape memory and corrosion resistance behaviours. However, the lower machinability due to the strain-hardening effect and lower thermal conductivity is contrary to its adventitious properties. Therefore, EDM is a preferable machining process for materials like Nitinol. EDM, thermal processing, raises the concern of processing Nitinol with minimal variation of its well-known properties and economical machining process. Therefore, this article deals with multi-objective optimization through GRG-assisted GA of µ-EDM drilling of Ni51.58Ti48.34 alloy using a copper electrode and distilled water. It was found that discharge current and servo voltage significantly influence the responses. The GA, with the assistance of GRG, optimized the multiple responses (viz. MRR, TWR and DoT) and yielded a discharge current of 12 A, gap voltage of 40 V, discharge time of 2 µs, charging time of 9 µs and flushing pressure of 50 kg/cm2. The confirmatory experiment yielded MRR of 0.0036 g/min, TWR of 0.0038 g/min and DoT of 0.0089 radians. There were variations of the predicted and experimentally validated responses by − 2.78, 26.32 and 35.96% for MRR, TWR and DoT, respectively. [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]

Thrombus formation in blood-contacting medical devices is a major concern in the medical device industry, limiting the clinical efficacy of these devices. Further, a locally formed clot within the device has the potential to detach from the surface, posing a risk of embolization. Clot embolization from blood-contacting cardiovascular devices can result in serious complications like acute ischemic stroke and myocardial infarction. Therefore, clot embolization associated with device-induced thrombosis can be life-threatening and requires an enhanced fundamental understanding of embolization characteristics to come up with advanced intervention strategies. Therefore, this work aims to investigate the adhesive characteristics of blood clots on common biocompatible materials used in various cardiovascular devices. This study focuses on characterizing the adhesion strength of blood clots on materials such as polytetrafluoroethylene (PTFE), polyurethane (PU), polyether ether ketone (PEEK), nitinol, and titanium, frequently used in medical devices. In addition, the effect of incubation time on clot adhesion is explored. Results from this work demonstrated strongest clot adhesion to titanium with 3 h of incubation resulting in 1.06 ± 0.20 kPa detachment stresses. The clot adhesion strength on titanium was 51.5% higher than PEEK, 35.9% higher than PTFE, 63.1% higher than PU, and 35.4% higher than nitinol. Further, adhesion strength increases with incubation time for all materials. The percentage increase in detachment stress over incubation time (ranging from 30 min to 3 h) for polymers ranged from at least 108.75% (PEEK), 140.74% (PU), to 151.61% (PTFE). Whereas, for metallic surfaces, the percentage rise ranged from 70.21% (nitinol) to 89.28% (titanium). Confocal fluorescence imaging of clot remnants on the material surfaces revealed a well-bounded platelet-fibrin network at the residual region, representing a comparatively higher adhesive region than the non-residual zone of the surface.

One of the long-standing mechanical challenges associated with shape memory alloys (SMAs) is achieving and stabilizing an evolving two-way shape memory effect (TWSME) through thermomechanical training/cycling. In most martensitic NiTi SMAs that exhibit zero TWSME at room temperature, the TWSMEs typically require hundreds of cycling repetitions to track trivial values. This demonstrates a promising solution to overcome this challenge. The surface of NiTi SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers on the NiTi surface using a laser beam. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 cycles when the optimum number of five Ti layers was deposited, which was much higher than that of the NiTi sheet (0.3% TWSME) and the sample with a single-time laser path irradiation (1.8%). This was attributed to the low coefficient of thermal expansion of the Ti vs. NiTi sheet, which prevented reverse bending during heating, and the formation of Ti-rich intergranular Ti2Ni(Ox) precipitates, which hindered dislocation movement. Meanwhile, in this sample, owing to the generation of a large residual tensile stress and a large heat-affected zone that led to a reduction in plastic zones, the one-way shape memory effect (OWSME) was retained at values above 90% with good stability over cycling. However, the introduction of additional Ti layers can cause problems in terms of oxygen accumulation within the NiTi sheet, which should be considered when designing a product.

Abstract 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.

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]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using the example of a welded wire connection made of an alloy Ti–Ni (Ti–55.42% Ni)—nitinol, the shape memory effect is considered. In particular, with the help of nonconsumable electrode welding technology, welded joints of wire with a diameter of 2 mm were produced, the macro- and microstructure of the joints were studied, bending tests were carried out, and the shape memory effect of the obtained welded joints was evaluated. [ABSTRACT FROM AUTHOR]

Background/Purpose: Endoscopic treatment of common bile duct (CBD) stones involves the use of basket or balloon catheters; however, what is the appropriate device remains controversial. In this study we aimed to prospectively evaluate the usefulness of a novel 8‐wire helical basket (8WB) catheter made of Nitinol for the removal of CBD stones ≤10 mm. Methods: We conducted a multicenter prospective trial. Patients with CBD stones ≤10 mm were enrolled. The primary endpoint was the rate of complete stone removal within 10 min using the 8WB. The number of cases was determined using a previous study of stone removal by a conventional basket catheter as a historical control. Results: A total of 155 patients were enrolled and 139 were ultimately included in the analysis. Patients with a single stone were the most common (84 cases, 60.4%), with a median maximum stone diameter of 5 mm. The median stone removal time using the 8WB was 6 min. The complete stone removal rate was 95.0% (132/139). Adverse events were observed in 14 patients (10.1%). Conclusions: The novel 8WB catheter is useful in the treatment of CBD stones ≤10 mm, presenting a high complete stone removal rate in this study. Trial registration number: jRCT1032200324. [ABSTRACT FROM AUTHOR]

Currently, scientists from various fields are trying to find new ways of activating devices, considering the renewability of the used resources. The way to this goal can also be the search for the usability of various advanced materials in hitherto unexplored areas of technology. This article delves into the application of a non-contact infrared sensor MLX90614 to track dynamic temperature changes in a nitinol spring. By utilizing a controllable external power source, the material's temperature is manipulated through current modulation. This fluctuation is then captured and logged by a system that includes a microcontroller and a temperature sensor. The study's results provide vital information on the correlation between temperature and electrical properties, providing significant insights into the thermal behavior of nitinol springs for future research in this specialized field. [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]

Stent retrievers are medical devices that are designed to physically remove blood clots from within the blood vessels of the brain. This paper focuses on microfabricated nitinol (nickel–titanium alloy) stent retrievers, which feature micro-patterns on their surface to enhance the effectiveness of mechanical thrombectomy. A thick film of nitinol, which was 20 µm in thickness, was sputtered onto a substrate with a micro-patterned surface, using electroplated copper as the sacrificial layer. The nitinol film was released from the substrate and then thermally treated while folded into a cylindrical shape. In vitro experiments with pig blood clots demonstrated that the micro-patterns on the surface improved the efficacy of blood clot retrieval. [ABSTRACT FROM AUTHOR]

Abstract Objectives The present study reviews the current literature regarding the utilization of the extended finite element method (XFEM) in clinical and experimental endodontic studies and the suitability of XFEM in the assessment of cyclic fatigue in rotary endodontic nickel–titanium (NiTi) instruments. Material and Methods An electronic literature search was conducted using the appropriate search terms, and the titles and abstracts were screened for relevance. The search yielded 13 hits after duplicates were removed, and four studies met the inclusion criteria for review. Results No studies to date have utilized XFEM to study cyclic fatigue or crack propagation in rotary endodontic NiTi instruments. Challenges such as modelling material inputs and fatigue criteria could explain the lack of utilization of XFEM in the analysis of mechanical behavior in NiTi instruments. Conclusions The review showed that XFEM was seldom employed in endodontic literature. Recent work suggests potential promise in using XFEM for modelling NiTi structures.

The challenges facing metallic implants for reconstructive surgery include the leaching of toxic metal ions, a mismatch in elastic modulus between the implant and the treated tissue, and the risk of infection. These problems can be addressed by passivating the metal surface with an organic substrate and incorporating antibiotic molecules. Nitinol (NiTi), a nickel-titanium alloy, is used in devices for biomedical applications due to its shape memory and superelasticity. However, unmodified NiTi carries a risk of localized nickel toxicity and inadequately supports angiogenesis or neuroregeneration due to limited cell adhesion, poor biomineralization, and little antibacterial activity. To address these challenges, NiTi nanoparticles were modified using self-assembled phosphonic acid monolayers and functionalized with the antibiotics ceftriaxone and vancomycin via the formation of an amide. Surface modifications were monitored to confirm that phosphonic acid modifications were present on NiTi nanoparticles and 100% of the samples formed ordered films. Modifications were stable for more than a year. Elemental composition showed the presence of nickel, titanium, and phosphorus (1.9% for each sample) after surface modifications. Dynamic light scattering analysis suggested some agglomeration in solution. However, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed a particle size distribution of

This study examined the effect of variations in the laser power and scan speed for 52.39 at.%Ni-47.61 at.%Ti samples produced via laser powder bed fusion (L-PBF). The laser power was varied between 150W and 180 W, the scanning speeds were varied between 500 mm/s and 1000 mm/s, and other process parameters were kept constant. The resulting microstructures and physical properties of the produced samples were evaluated. In particular, the phase type and phase transformation characteristics, composition, Vickers microhardness, and microstructures were examined. It was observed that variation in the mean microhardness and relative density were not significant at a constant scan speed of 1000 mm/s, regardless of the laser power value. Samples processed at a laser power of 180W (with all other parameters kept constant) exhibited a bimodal micro- and nano structures. It was found that the samples with bimodal microstructure had a higher lattice strain, extent of B2 phase, and higher phase transformation temperatures.

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]

In a previous study (part I), the deposition of functional single-track and multi-layer Ni-rich NiTi using the electron beam freeform fabrication (EBF3) technique was demonstrated. The processed microstructure consists of columnar millimetre range grains that grow parallel to the build direction. Based on the same parameters of part I, this work successfully deposited a stable multi-track and multi-layer NiTi block. Different heat treatments were applied to modify the superelastic properties of the deposited material. Initially, the solution treatment reduces the chemical inhomogeneity and the thermal stresses that originated during the deposition and cooling. Subsequently, due to ageing, Ni4Ti3 particles precipitate at 350 °C and 450 °C for 1, 6 and 12 h, modified the superelastic behaviour of the deposited NiTi. The differential scanning calorimetry results did not reveal any difference in the martensitic starting temperature between as-built and solution-treated samples. However, a remarkable influence of the ageing temperature was detected: while ageing at 350 °C impacted R-phase starting temperatures, 450 °C altered the martensitic starting one. The superelastic behaviour was evaluated by cycling compression. As-built and solution heat-treated samples presented poor mechanical performance, with about 40% of strain recovered after 10 cycles. The ageing at 350 °C for 1 h led to a maximum measured strain recovery of 72.5% after 10 uniaxial compression cycles up to 860 MPa. This condition also resulted in 3.3% permanent deformation out of 11.3% of the total. This study addressed for the first time the fabrication by the EBF3 technique of a stable multi-track and multi-layer NiTi block besides the importance of heat treating it, demonstrating that this post-treatment improves the superelastic performance of EBF3 fabricated parts. [ABSTRACT FROM AUTHOR]

Biomedical alloys, like many engineering alloys, have chemical or physical heterogeneities at the surface, and such heterogeneities can potentially act as sites for pit initiation. Alloys of particular interest are 316/316L (and 316LVM) stainless steel, nitinol, and CoCr alloys. This review focuses on the sites—generally inclusions—that have been associated with pitting in various studies of biomedical alloys in simulated physiological solutions. The effect of these sites is discussed in relation to factors such as type and size. For both 316/316L stainless steel and nitinol, pitting has been found to initiate at two different types of inclusions: sulfide and oxide inclusions in stainless steel, and carbide and oxide inclusions in nitinol. Sulfide inclusions tend to be the predominant sites for pitting on 316/316L stainless steel, while there is some evidence to suggest that carbide inclusions may be more effective than oxide inclusions for pitting on nitinol. CoCrMo alloys differ from the other two alloys in that, although particles can be present in the form of carbides, the carbides typically do not provide sites for pit initiation except possibly for alloys with a high‐C content, certain heat treatments, and when anodically polarized to high potentials. CoNiCrMo differs further in that TiN inclusions can be present in the vicinity of pits and might be associated with them, but irrespective of the initiation site, any pits are unlikely to grow because of repassivation. [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]

NiTinol, because of its several superior properties like shape memory effect, pseudoelasticity, corrosion resistance and biocompatibility, has become a promising member for various application areas including biomedical, micro-electro-mechanical system and aerospace. Poor machinability, lack of joining techniques and high cost of the material are presently restricting the use of the material in practical applications to its full potential. Laser welding is the majorly used fabrication technique for this material. The effects of welding on the bead geometry, microstructure, new phase formation, phase transformation temperature for laser welding of 2-mm thick NiTinol sheet in bead-on-plate configuration were investigated through this study using Yb-fiber laser in continuous mode of operation. Moreover, the mechanical properties of the joint were assessed by means of tensile tests and cyclic loading–unloading test. The functionality of the cyclic loading–unloading was tested by analysis of the mechanical hysteresis response up to 6% strain levels. Furthermore, the fractured surface was analyzed by scanning electron microscopy. Results revealed that the microstructure varied across the different zones of welding depending on temperature gradient and solidification rate. The microhardness value of the weld-bead was reduced considerably from that of the parent material. Brittle intermetallic compounds of Ti and Ni were formed during welding. It was also found that the welding greatly influenced the phase transformation temperature, overall mechanical behavior and the mode of failure in comparison with parent material. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases, particularly coronary artery disease, pose big challenges to human life. Deployment of the stent is a preferable treatment for the above-mentioned disease. However, stents are usually made up of shape memory alloy called Nitinol. The poorer surface finish on the machined nitinol stents accelerates the migration of Nickel ions from the implanted nitinol stent, which is considered toxic and can lead to stenosis. The current study deals with controlling surface quality by minimising surface roughness and improving corrosion resistance. Femtosecond laser (fs-laser 10−15 s) micromachining was employed to machine the Nitinol surface to achieve sub-micron surface roughness. The Grey relational analysis (GRA)-coupled design of the experimental technique was implemented to determine optimal levels of four micromachining parameters (laser power, pulse frequency, scanning speed, and scanning pattern) varied at three levels to achieve minimum surface roughness and to maximise the volume ablation. The results show that to yield minimum surface roughness and maximum volume ablation, laser power and scanning speed are in a higher range. In contrast, the pulse frequency is lower, and the scanning pattern is in a zig-zag manner. ANOVA results manifest that scanning speed is the predominant factor in minimising surface roughness, followed by pulse frequency. Furthermore, the corrosion behaviour of the machined nitinol specimens was evaluated, and the results show that specimens with lower surface roughness had lower corrosion rates.

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.

NiTi is one the metal alloys exhibiting shape memory and superelasticity which makes it suitable for a wide range of engineering and biomedical applications. Nickel-rich NiTi requires heat treatment and cold work as post-processing steps to enable appropriate phase production for final applications. In the current work, NiTi tubes (50.8%Ni-49.2%Ti) produced using Laser Powder Bed Fusion (PBF-LB) and conventional drawing were heat treated at a constant temperature of 500 °C for 10, 30, and 60 min. Differential scanning calorimetry results indicate that the austenite finish temperatures for the tubes were set at 25.4 °C and 26.62 °C after 60 min of heat treatment for the PBF-LB and conventionally drawn tubes respectively. The enthalpy of phase transformation for PBF-LB tubes increased from 2.89 J/g to 17.14 J/g while for conventionally drawn tubes it increased from 5.41 J/g to 16.08 J/g. The EDX measurements on as-built and heat-treated tubes indicated no loss of nickel during the heat-treatment process. The thermal expansion results show an unstable evolution of CTEs in as-built NiTi tubes which were stabilized via heat-treated with resulting CTE ≈11.4 × 10−6/ºC. The hardness decreased in the heat-treated tubes as compared to the as-built tubes. The hardness decreased by 12.6% for PBF-LB and 12.4% for the conventionally drawn tubes respectively.