Nickel Titanium Shape Memory Research Articles

The corrosion resistance and biomineralization of the DCPD-PCL coating on the surface of the additively manufactured NiTi alloy

Selective laser melting (SLM)-manufactured shape memory Nickel-Titanium (NiTi) alloy has great potential to use as an implant because it can achieve sophisticated structures and possess excellent mechanical properties. However, poor corrosion performance, biological inertness, and toxic Ni ions release limit its wide application. This study reports a multifunctional composite coating which composed of polycaprolactone (PCL) and dicalcium phosphate dihydrate (DCPD) by dipping method and electrodeposition to improve biomineralization and corrosion resistance of SLM-NiTi alloy. The results revealed that PCL coating successfully sealed the pores and cracks of DCPD coating and significantly improved the corrosion resistance of the coating (the corrosion current density decreased from 2.6 × 10−7 to 1.4 × 10−8 A/cm2) and the binding force was also improved (from 2397 to 2910 mN). In long-term immersion tests, the composite coating exhibited good biomineralization properties which promoted the deposition of Ca and P in simulated body fluids to form hydroxyapatite (HA). Moreover, the in vitro cell experiment showed that the composite coating was beneficial to cell adhesion and proliferation. Therefore, the DCPD-PCL-coated SLM-NiTi alloy has enormous potential as a medical implant in clinical applications.

Orthodontic Diagnostic Tools and Material Usage in Saudi Arabia

Introduction: The evaluation of changes in orthodontic practice over the years, is essential for defining treatment efficacy. Accordingly, shedding light on the profile of orthodontic practice in Saudi Arabia is crucial. Aim: To investigate current trends in orthodontic practice in Saudi Arabia and the factors affecting choices regarding materials and techniques among orthodontists. Materials and Methods: This cross-sectional study was conducted from July 2019 to December 2019 at the College of Dentistry, King Saud University, Riyadh, Saudi Arabia. An electronic survey of 29 objective questions was sent to 1,500 orthodontic members of the Saudi Orthodontic Society. The survey collected demographic data, diagnostic records and information on the fixed orthodontic appliances used by the respondents. Frequency and percentages were calculated for all variables. Chi-square test was used to determine the effects of factors, including years of experience and place of work, on the choice of diagnosis protocol and fixed appliance material, with the significance set at p-value ≤0.05. Results: Two hundred and nine respondents completed the survey. The respondents reported a highly significant use of computers for digitising cephalometric analysis, with the traditional method of obtaining study models reported as highly significant (p<0.001). Orthodontists routinely used the MBT preadjusted bracket system (52.6%) and performed direct bonding of the bracket (91.4%). Bonding of the first molars was preferred by 36.4% of the clinicians. Glass ionomer cement was the most frequently used band cement (55.5%), and the most popular archwire material was nickel–titanium shape memory. Clinicians with less than five years of experience used significantly more postcephalometric radiographs (p=0.006) and postorthodontic treatment models (p=0.028). Senior orthodontists (10-15 years of experience) had a higher use of indirect bonding techniques (p=0.05). Conclusion: This study provides information on the relevant aspects of orthodontists in Saudi Arabia in terms of their individuality, training and techniques used. The findings can be used as a reference for future national surveys to evaluate changes in orthodontic practice in Saudi Arabia.

Effect of Coating Method on the Surface Characteristics of NiTi Shape Memory Alloy

Metallic materials including stainless steel, cobalt-chromium alloys, titanium and its alloys, and nickel-titanium (NiTi) shape memory alloys have been used in biomedical applications since the 1940s due to their favorable mechanical properties. Classified as a smart material, NiTi alloy has gained noticeable popularity in biomedical fields such as orthopedic, dental, and cardiovascular applications as it retains reasonable corrosion resistance and biocompatibility along with unique shape memory properties. However, several studies have shown their limits in medical applications due to the risk of Ni ions release from the NiTi implant surface. In order to prevent Ni release, ceramic-based surface coatings such as hydroxyapatite, alumina, and titanium dioxide have been proposed applied by various methods such as electrophoretic deposition, sol-gel, biomimetic and dip coating. In this work, HA coatings on NiTi wire samples were obtained by using biomimetic and dip-coating methods. The biomimetic coating consisted of immersing the NiTi wire samples into simulated body fluid for 24 and 48 h periods, whereas dip coating was accomplished by placing the NiTi wire samples into the HA suspension and retracting the sample with a controlled speed. The effects of the two coating methods on coating quality, surface characteristics and corrosion behavior of NiTi wire samples were investigated. Dip coating method was shown to be a more favorable technique for the NiTi wire samples used throughout this study.

What EBSD and TKD Tell Us about the Crystallography of the Martensitic B2-B19′ Transformation in NiTi Shape Memory Alloys

The complex and intricate microstructure of B19′ martensite in shape memory nickel titanium alloys is generally explained with the Phenomenological Theory of Martensitic Crystallography (PTMC). Over the last decade, we have developed an alternative approach that supposes the existence of a “natural” parent–daughter orientation relationship (OR). As the previous TEM studies could not capture the global crystallographic characteristics of the B2→B19′ transformation required to discriminate the models, we used Electron BackScatter Diffraction (EBSD) and Transmission Kikuchi Diffraction (TKD) to investigate a polycrystalline NiTi alloy composed of B19′ martensite. The EBSD maps show the large martensite plates and reveal the coexistence of different ORs. The TKD maps permit us to image the “twins” and confirm the continuum of orientations suspected from EBSD. The results are interpreted with the alternative approach. The predominant OR in EBSD is the “natural” OR for which the dense directions and dense planes of B2 and B19′ phases are parallel—i.e., (010)B19′//(110)B2 and [101]B19′//[ 1 ¯ 11]B2. The natural OR was used to automatically reconstruct the prior parent B2 grains in the EBSD and TKD maps. From the distortion matrix associated with this OR, we calculated that the habit plane could be (1 1 ¯ 2)B2//(10 1 ¯ )B19′. The traces of these planes are in good agreement with the EBSD maps. We interpret the other ORs as “closing-gap” ORs derived from the natural OR to allow the compatibility between the distortion variants. Each of them restores a parent symmetry element between the variants that was lost by distortion but preserved by correspondence.

Efficacy of Controlled Memory and Shape Memory Nickel Titanium Instruments in Removing Filling Material from Severely Curved Root Canals: An Ex Vivo Study.

The aim of the present study was to compare the efficacy of four NiTi instruments with different properties (shape memory and control memory), in both rotary and reciprocating motions, during retreatment procedures. Mesial canals of thirty-two mandibular molars were instrumented, obturated, and then scanned with" Cone-beam Computed Tomography" (CBCT). Teeth were randomly divided into 4 groups (n=8) according to each system: "Shape Memory" (SM) instruments including Reciproc (R25 file) and ProTaper Next (X3 and X2 file), "Controlled Memory" (CM) instruments including WaveOne Gold (Primary file) and Hyflex (30.06 and 25.06 file). The specimens were rescanned after retreatment procedures. The volume of the residual material left inside the canals, the operating time and the fractured files were analyzed. ANOVA and student t-tests were used for statistical analysis. There were no significant differences in the percentage of the residual filling material or requiring time amongst different groups of instruments (P>0.05). However, CM instruments presented the highest frequency of fractured files [2 SM instruments (12.5%) and 7 CM instruments (43.75%)] with a significant difference (P=0.023). This ex vivo study showed that CM and SM instruments can remove filling materials from mandibular mesial root canals during retreatment procedures; nonetheless the CM instruments had a higher frequency of fractured files. No system was able to completely remove the filling materials. Therefore, additional procedures and techniques are needed to improve root canal cleanliness.

Shape memory compression anastomosis clips in gastrointestinal surgery in dogs

This paper describes clinical experiences with the use of shape memory nickel-titanium (NiTi) clips in gastrointestinal surgery in dogs. Side-to-side small bowel anastomosis was performed in eight dogs where intestinal continuity had to be restored after bowel resection. Billroth’s operation I was performed in one case. Compression anastomosis clips with two-way shape memory were used in all surgical procedures. Intestinal and gastrointestinal anastomoses involving shape memory clips were effective in all patients. Anastomotic leaks were not observed, and all clips were expelled 5–7 days after surgery. The outcomes of surgical procedures performed on canine patients with the use of shape memory NiTi clips indicate that sutureless compression anastomosis is a safe, effective and simple method of restoring gastrointestinal continuity, which can be widely applied in veterinary practice.

Mechanical behavior of deep cryogenically treated martensitic shape memory nickel-titanium rotary endodontic instruments.

Objectives:The aim of this study was to investigate the role of deep cryogenic treatment (DCT) on the cyclic fatigue resistance and cutting efficiency of martensitic shape memory (SM) nickel–titanium (NiTi) rotary endodontic instruments.Materials and Methods:Seventy-five HyFlex® CM instruments were randomly divided into three groups of 25 each and subjected to different DCT (–185° C) conditions based on soaking time: DCT 24 group: 24 h, DCT 6 group: 6 h, and control group. Each group was randomly subdivided for evaluation of cyclic fatigue resistance in custom-made artificial canals (n = 15) and cutting efficiency in plexiglass simulators (n = 10). The cyclic fatigue resistance was measured by calculating the number of cycles to failure (NCF) and cutting efficiency was measured using the loss of weight method.Results:Increase in NCF of instruments in DCT 24 group was highly significant (P < 0.01; Tukey's honest significant difference). There was no difference in weight loss of plexiglass simulators in all the groups (P > 0.05; one-way analysis of variance). In conclusion, deep dry cryogenic treatment with 24 h soaking time significantly increases the cyclic fatigue resistance without affecting the cutting efficiency of SM NiTi endodontic instruments.Materials and Methods:Seventy-five HyFlex® CM instruments were randomly divided into three groups of 25 each and subjected to different DCT (–185° C) conditions based on soaking time: DCT 24 group: 24 h, DCT 6 group: 6 h, and control group. Each group was randomly subdivided for evaluation of cyclic fatigue resistance in custom-made artificial canals (n = 15) and cutting efficiency in plexiglass simulators (n = 10). The cyclic fatigue resistance was measured by calculating the number of cycles to failure (NCF) and cutting efficiency was measured using the loss of weight method.Results:Increase in NCF of instruments in DCT 24 group was highly significant (P < 0.01; Tukey's honest significant difference). There was no difference in weight loss of plexiglass simulators in all the groups (P > 0.05; one-way analysis of variance). In conclusion, deep dry cryogenic treatment with 24 h soaking time significantly increases the cyclic fatigue resistance without affecting the cutting efficiency of SM NiTi endodontic instruments.

Effect of dry cryogenic treatment on Vickers hardness and wear resistance of new martensitic shape memory nickel-titanium alloy.

Objectives:The aim of this study is to investigate the role of dry cryogenic treatment (CT) temperature and time on the Vickers hardness and wear resistance of new martensitic shape memory (SM) nickel-titanium (NiTi) alloy. The null hypothesis tested was that there is no difference in Vickers hardness and wear resistance between SM NiTi alloys following CT under two soaking temperatures and times.Materials and Methods:The composition and the phase transformation behavior of the alloy were examined by X-ray energy dispersive spectroscopy and differential scanning calorimetry, respectively. Fifteen cylindrical specimens and 50 sheet specimens were subjected to different CT conditions: Deep cryogenic treatment (DCT) 24 group: −185°C, 24 h; DCT six group: −185°C, 6 h; shallow cryogenic treatment (SCT) 24 group: −80°C, 24 h; SCT six group: −80°C, 6 h; and control group. Wear resistance was assessed from weight loss before and after reciprocatory wet sliding wear.Results:The as-received SM NiTi alloy contained 50.8 wt% nickel and possessed austenite finish temperature (Af) of 45.76°C. Reduction in Vickers hardness of specimens in DCT 24 group was highly significant (P < 0.01; Tukey's honest significant difference [HSD]). The weight loss was significantly higher in DCT 24 group (P < 0.05; Tukey's HSD).Conclusion:Deep dry CT with 24 h soaking period significantly reduces the hardness and wear resistance of SM NiTi alloy.

The effect of cobalt additives on martensitic transformations and deformation in sintered porous nickel titanium alloys

Porous nickel titanium (TiNi) shape memory alloys with cobalt additives have been obtained by reaction and diffusion sintering. Analysis of the experimental temperature dependence of the electric resistance and multiple shape memory effect leads to a conclusion that Co additives below 1 at % in reaction-sintered, and even more so in diffusion-sintered, alloys lead to a reduction in intrinsic internal stresses in the TiNi phase. Additives above 1 at % induce dispersion hardening of the alloy. At all concentrations, cobalt additives lead to obstacles for the martensitic phase transformations.

Influence of SLM on shape memory and compression behaviour of NiTi scaffolds

Octahedron-shaped porous scaffolds made from shape memory nickel–titanium (NiTi) were manufactured with different solid volume fractions using selective laser melting (SLM). Various SLM parameters were selected to affect the mechanical behaviour and shape memory response. It was shown that high laser power with high scanning speed (HP) parameters reduced the martensitic transformation temperatures as compared to low laser power low scanning speed (LP) parameters, resulting in an increased pseudoelastic behaviour (due to presence of austenite at room temperature). HP parameters, however, led to a larger geometrical mismatch with the original design and a higher solid volume fraction. The compression behaviours were also analysed and exhibited in correlation with the volume fractions.

Microstructure of cryogenically treated martensitic shape memory nickel-titanium alloy.

Context:Recent introduction of shape memory (SM) nickel-titanium (NiTi) alloy into endodontics is a major breakthrough. Although the flexibility of these instruments was enhanced, fracture of rotary endodontic instruments during instrumentation is an important challenge for the operator. Implementation of supplementary manufacturing methods that would improve the fatigue life of the instrument is desirable.Aim:The purpose of this study was to investigate the role of dry cryogenic treatment (CT) conditions on the microstructure of martensitic SM NiTi alloy.Materials and Methods:Experiments were conducted on Ni-51 wt% Ti-49 wt% SM alloy. Five cylindrical specimens and five sheet specimens were subjected to different CT conditions: Deep CT (DCT) 24 group: −185°C; 24 h, DCT 6 group: −185°C; 6 h, shallow CT (SCT) 24 group: −80°C, 24 h, SCT 6 group: −80°C, 6 h and control group. Microstructure of surface was observed on cylindrical specimens with an optical microscope and scanning electron microscope at different magnifications. Subsurface structure was analyzed on sheet specimens using X-ray diffraction (XRD).Results:Microstructures of all SM NiTi specimens had equiaxed grains (approximately 25 μm) with well-defined boundaries and precipitates. XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks. The volume of martensite and its crystallite size was relatively more in DCT 24 specimen.Conclusions:DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size.

Optimization of Electrical Discharge Machining Parameters for Niti Shape Memory Alloy by Using the Taguchi Method

Electrical discharge machining (EDM) is among the most essential nontraditional machining processes. Material removal rate (MRR) and surface roughness are the two main parameters applied in this method. A desired surface roughness can be achieved at the maximal MRR by selecting the optimal input parameters. Because of the mechanical properties and hardness of shape-memory nickel titanium (NiTi) alloy, material can be removed using an EDM method. NiTi alloy is widely used in marine science and aerospace industries. Surface roughness is a critical parameter affecting the machining of this alloy. This study examined the effect the input parameters (pulse current, gap voltage, pulse on time, and pulse off time) on the output parameters (surface roughness and MRR) to determine the minimal surface roughness and maximal MRR for NiTi alloy. Accordingly, the Taguchi method and analysis of variance were employed to optimize the machining parameters. The modeling and experimental results indicate that pulse current and pulse-on time are the most critical parameters affecting MRR and surface roughness.

Experimental Study on Variable Deflection Control of SMA Actuated Composite Plate

This paper presents a variable deflection control of a fiber glass composite plate system using shape memory alloy (SMA) actuators. The technique on changing the camber of plate needs to be developed as it is the most investigated approach of shape morphing. Gradual changes of the camber along the span can create controllable twisting of the composite plate. The necessary camber change is pursued either by reconfiguration of the underlying structure or the shape changing of the composite plate or smart composite. In this proposed platform, strain gauges are used to measure the strain of the plate in a single cantilever mode while nickel titanium (NiTi) Shape Memory Alloy (SMA) wires are used as actuators to actuate the composite plate, which are controlled using Proportional-Integral-Derivative (PID) controller. In this research six strain gauges were placed at different location of the plate: tip, mid and root part of the plate. From the experimental result, it was found that the mid part of the plate had the highest change in strain value and the control system using input from the strain gauge located there produced the best performance compared to those located at the tip and root of the plate.

Design of a Mechanical Exoskeleton System for Improving Hand-Gripping Force

Patients may lose part of the hand-gripping force, because of the diseases of stroke, carpal tunnel syndrome, nerve damage etc, which lead to greatly inconvenience during their daily life. The research work in this area has been really investigated in the world, and is with significant importance in medical and military areas. A mechanical exoskeleton system is designed in this project for improving hand-gripping force of these patients. The designed mechanical exoskeleton system in this project includes five parts: exoskeleton framework, finger motion intention detecting system, extra force output system, joints’ angle holding system and central construe system. In this study, titanium alloy are eventually adopted as the material of the exoskeleton framework after the mechanical analysis. A contact type sensor system for detecting finger motion intention, gripping or releasing object is also adopted in this project. Titanium-Nickel (Ti-Ni) shape memory alloy (SMA) plates are used here to provide extra 2N force for helping patients grip an object under 140g. A Ti-Ni plate based joint lock system has also been designed here for holding the angles of fingers’ joints.

Development of Nitinol Stents: Etching Experiments

The present study focus on the chemical etching of shape memory nickel-titanium (nitinol) alloy stents made by laser cutting. Application of nitinol stents widely spread in case of atherosclerosis of peripheral vessels. This type of stent has to have appropriate surface quality, flexibility and strength. The aim of chemical etching is removing the burr, which arises during the laser cutting. Etching is one step of the production of stents. The appropriate parameters allow the laser burned surface and most of protruding material removing without significant damage of stent shape. During these experiments etching time was changed. After etching the cross section area was determined by metallographic examinations. The results of the examinations show the relationship between the etching time and the cross-section area. The analysis of measurement data revealed the change of etching velocity. Before and after etching the samples was examined by scanning electron microscopy (SEM). The different surfaces also were compared and the findings were discussed.

Trans-Sutural Distraction Osteogenesis for Alveolar Cleft Repair: An Experimental Canine Study

To explore a new method of repair of alveolar cleft by trans-sutural distraction osteogenesis. Nine 8-week-old mongrel dogs were assigned randomly to two groups with three in the control group and six in the experimental group. First, an alveolar cleft model was created surgically in all animals. After 2 weeks, a U-shaped distractor, made of nickel-titanium (NiTi) shape memory alloy wire with 200 g tensile force, was inserted into the premaxilla of the experimental dogs to distract the mid-premaxillary suture for 3 weeks. Periosteoplasty of the alveolar cleft was performed when the premaxilla at the side of cleft approached the maxilla at the same side. The distractor was removed 2 weeks post periosteoplasty. The results were evaluated clinically, radiographically, and morphologically. The cleft model was stable and similar to the human alveolar cleft. No spontaneous bone union occurred in the control. In experimental dogs, the premaxilla was moved slowly toward the maxilla, and the cleft became gradually narrower and closed in the third week. Radiographically, the distracted mid-premaxillary suture showed a gradually widened triangle, with the tip of the triangle pointed posteriorly. The density of the distracted triangle suture was increased gradually. The alveolar cleft was completely bony 3 months post periosteoplasty. The morphology of the mid-premaxillary suture was also restored. The alveolar cleft could be repaired by the technique of mid-premaxillary suture distraction using the elastic device of NiTi shape memory alloy.

Fusion welding of nickel–titanium and 304 stainless steel tubes: Part II: tungsten inert gas welding

Shape memory nickel–titanium is attractive for lightweight actuators as it can generate large blocking stresses and high recovery strains through solid-state operation. A key challenge is the integration of the nickel–titanium components into systems; this alloy is difficult and expensive to machine and challenging to weld to itself and other materials. In this research, we join nickel–titanium and 304 stainless steel tubes of 9.53 mm (0.375 in) in diameter through tungsten inert gas welding. By joining nickel–titanium to a common structural material that is easily machined and readily welded to other materials, the system integration challenges are greatly reduced. The joints prepared in this study were subjected to optical microscopic inspection, hardness mapping, energy dispersive X-ray spectroscopy, mechanical testing, and failure surface analysis via scanning electron microscopy. The affected zone from welding is approximately 125 µm (0.005 in) wide including partially mixed zones with a maximum hardness of 817 HV and a possible heat-affected zone of 1–2 µm (39–79 µin) wide. The maximum average ultimate torsional strength is 415 MPa (60.2 x 103 lbf/in2). Implementation of this joining method is demonstrated in the construction of a solid-state torsional actuator that can lift a weight of 2.3 kg (5 lb) to a distance of 610 mm (24 in). The laser and TIG welding processes are compared.

Torsion and Bending Properties of Shape Memory and Superelastic Nickel-Titanium Rotary Instruments

IntroductionRecently introduced into the market are shape memory nickel-titanium (NiTi) rotary files. The objective of this study was to investigate the torsion and bending properties of shape memory files (CM Wire, HyFlex CM, and Phoenix Flex) and compare them with conventional (ProFile ISO and K3) and M-Wire (GT Series X and ProFile Vortex) NiTi files. MethodsSizes 20, 30, and 40 (n = 12/size/taper) of 0.02 taper CM Wire, Phoenix Flex, K3, and ProFile ISO and 0.04 taper HyFlex CM, ProFile ISO, GT Series X, and Vortex were tested in torsion and bending per ISO 3630-1 guidelines by using a torsiometer. All data were statistically analyzed by analysis of variance and the Tukey-Kramer test (P = .05) to determine any significant differences between the files. ResultsSignificant interactions were present among factors of size and file. Variability in maximum torque values was noted among the shape memory files brands, sometimes exhibiting the greatest or least torque depending on brand, size, and taper. In general, the shape memory files showed a high angle of rotation before fracture but were not statistically different from some of the other files. However, the shape memory files were more flexible, as evidenced by significantly lower bending moments (P < .008). ConclusionsShape memory files show greater flexibility compared with several other NiTi rotary file brands.

Smart Switch Metamaterials for Multiband Radio Frequency Antennas

We investigate metal–matrix composite metamaterials with embedded electrical switches made of shape memory nickel–titanium (Ni–Ti) for use in broadband radio frequency (RF) antennas. Experiments show that a Ni–Ti ribbon can form an electrical contact that opens and closes depending on the Ni–Ti phase being austenite or martensite. Finite element modeling of thermal gradients illustrates the phase change within the ribbon. Ultrasonic additive manufacturing (UAM), a solid-state additive manufacturing process, was utilized for embedding a Ni–Ti switch in an aluminum matrix. The aluminum matrix must have structural-grade strength for use in load-carrying antennas; thus, mechanical testing was conducted to quantify the longitudinal tensile, transverse tensile, and shear strength of the UAM matrix. Reconfiguration using a Ni–Ti switch was proven using a shape memory switch on a monopole RF antenna producing an operating frequency shift from 270 to 185 MHz when the switch is connected. A planar microstrip line was used to demonstrate signal transmission and reflection efficiency in a smaller, second switch. Transmission tests yielded less than −10 dB signal reflection proving the feasibility of reconfigurable planar antenna arrays using smart switches.

Metal Ureteral Stent for Benign and Malignant Ureteral Obstruction

Metal ureteral stents are a relatively new version of a device with a long history of relieving ureteral obstruction. Metal stents are effective for relieving ureteral obstruction but success regarding patient tolerability has been variable. We present our single institution experience with long-term metal ureteral stent placement. The charts of patients undergoing metal ureteral stent placement for chronic ureteral obstruction were reviewed. Data collected included patient age, gender, diagnosis/cause of obstruction, laterality, duration of indwelling metal stent, number of routine metal stent changes, complications and early discontinuations or stent changes. A total of 23 patients underwent placement of metal ureteral stents between February 2008 and September 2010. Bilateral stents were placed in 5 patients and 9 underwent a yearly metal stent exchange for a total of 42 ureteral units treated with metal ureteral stents. All metal stents were placed to relieve ureteral obstruction due to ureteral stricture, ureteropelvic junction obstruction, retroperitoneal fibrosis or extrinsic malignant obstruction. There were 3 metal stent failures in 2 patients with malignant ureteral obstruction. There were no complications, or early discontinuations or changes due to adverse symptoms, patient dissatisfaction, worsening renal function or progressive hydronephrosis. Metal ureteral stents are effective for benign and malignant ureteral obstruction in the absence of urolithiasis. Good tolerability and annual stent exchange make metal stents an appealing alternative for patients with chronic ureteral obstruction treated with indwelling ureteral stents.