Nitinol Plate Research Articles

Plasma Electrolytic Polishing of Nitinol: Investigation of Functional Properties.

A novel, environmentally friendly, fast, and flexible polishing process for Nitinol parts is presented in this study. Nitinol samples with both superelastic and shape memory properties at room temperature were investigated. The chemical contamination and surface roughness of superelastic Nitinol plates were examined before and after plasma electrolytic polishing. The shift in phase transformation temperature and tensile strength before and after the polishing process were analysed using Nitinol wire with shape memory properties. The obtained experimental results were compared to the data obtained on reference samples examined in the as-received condition. It was found that plasma electrolytic polishing, when the right process parameters are applied, is capable of delivering Nitinol parts with extremely high surface quality. Moreover, it was experimentally proven that plasma electrolytic polishing does not have a negative impact on functionality or mechanical properties of polished parts.

Clinical results of nitinol plate implentation for reconstruction of sternal dehiscence

Clinical results of nitinol plate implentation for reconstruction of sternal dehiscence

Physicochemical and biological characteristics of chitosan/κ-carrageenan thin layer-by-layer films for surface modification of nitinol

Thin films based on the natural polysaccharides κ-carrageenan (Carr) and chitosan (Chit) were formed by layer-by-layer deposition technique. Surface topography and mechanical characteristics (Young's modulus, adhesion strength) of the polymer films with different number of layers were determined using various modes of atomic force microscopy (AFM). Polymer films were used to deposit on the surface of nitinol (NiTi) plates. The creation of polysaccharide coatings on nitinol led to a change in surface properties, such as hydrophilicity and root mean square roughness. in vitro cytotoxicity assay for nitinol plates with and without polymer coating by the MG-63 osteoblast-like cell line was conducted and was shown that all the studied samples are not toxic. A decrease in cytotoxicity for samples with a polymer film consisting of 4 layers of chitosan and carrageenan was shown as compared to an uncoated nitinol plates.

Ultimate Venous Hemostasis Method

Porous nitinol plate germinated by nerve, connective tissue cells and capillaries is biomechanically and biophysically compatible with vein based on study above. It becomes a mechanical carcass to form a blood vessel wall in defect area, so designed technic provides fast and safe hemostasis with bloodstream recovery.

Nitinol laser cutting: microstructure and functional properties of femtosecond and continuous wave laser processing

Thermal processing can affect the properties of smart materials, and the correct selection of the best manufacturing technology is fundamental for producing high tech smart devices, containing embedded functional properties. In this work cutting of thin superelastic Nitinol plates using a femtosecond (fs) and continuous wave (CW) laser was studied. Diamond shaped elements were cut to characterize the kerf qualitative features; microstructural analysis of the cross sections allowed identification of thermal damage characteristics introduced into the material during the laser processes. A thermally undamaged microstructure was observed for fs laser cutting, while CW was seen to be characterized by a large heat-affected zone. Functional properties were investigated by differential scanning calorimetry and tensile testing of laser cut microelements and of the reference material. It was seen that the martensitic transformation behavior of Nitinol is not affected by fs regime, while cw cutting provokes an effect equivalent to a high temperature thermal treatment in the material surrounding the cutting kerf, degradating the material properties. Finally, tensile testing indicated that superelastic performances were guaranteed by fs regime, while strong reduction of the recoverable strain was detected in the CW processed sample.

Metallurgical Aspects and Optimisation of Yb: YAG Laser Welded NiTinol Shape Memory Alloy

This article presents a study on optimization of multi performance characteristics using grey relational analysis (GRA) in laser welding of NiTinol shape memory alloys. Bead on plate welding was done on NiTinol plates of 1 mm thickness using Ytterbium: Yttrium aluminium garnet (Yb: YAG) laser welding process. The experiment was carried out on the basis of Taguchi L9 Design with welding speed, Shielding gas blown distance, focal position and power as input parameters. Bead geometry (Depth of penetration, bead width) and microhardness were measured as performance characteristics. Analysis of variance (ANOVA) was utilized for calculating individual parameter percentage contribution on the multi performance characteristics. It was found that welding speed as the most influential parameter on the multi performance characteristics followed by shielding gas blown distance, power and focal position. The metallurgical aspects of the optimized weld are also discussed with help of microstructure.

Effect of welding speed on mechanical and fracture behavior of nitinol laser-joints

In this study, the effect of a pulsed Nd:YAG laser speed welding of Nitinol plates on the microstructure, mechanical properties and fracture behavior was investigated. The samples were double-sided butt welded in various welding speeds. Optical and Scanning Electron Microscopy, EDS analysis, XRD, microhardness and tensile test were used for the weldment characterization. Under the circumstances in which the heat input was low, the amount of Ti2Ni brittle intermetallic phase in the weld metal was reduced and this removed brittle grain boundaries from weld metal and consequently improved mechanical properties. Investigations on the fracture surfaces of the tensile test specimens showed that fracture mechanism was changed by increase of the welding speed.

Modeling of steady-state crack growth in shape memory alloys using a stationary method

Shape memory alloys experience phase transformation from austenite to martensite around crack tip. When the crack advances, martensitic transformation occurs at the tip and the energy that goes into this transformation results in stable crack growth like in the case of plastic deformation. In literature, steady-state crack growth in elasto-plastic materials with small scale yielding at the crack tip has been successfully modeled using stationary methods. In this work, Mode I steady-state crack growth in an edge-cracked Nitinol plate is modeled using a non-local stationary method (Moumni, 1995). The Zaki–Moumni (ZM) constitutive model is utilized for this purpose. The model is implemented in ABAQUS by means of a user-defined material subroutine (UMAT) to determine transformation zones around the crack tip. Steady-state crack growth is first simulated without considering reverse transformation to calculate the effect of transformation on stress distribution in the wake region, then reverse transformation is taken into account. The effect of reorientation of martensite near the crack tip as a result of non-proportional loading is also studied. The stress distribution and the phase transformation region are compared to results obtained for the case of a static crack.

Electrochemical Investigation of Nitinol/Tantalum Hybrid Surfaces Modified with Phosphonic Acid Derivatives

Nitinol, a nickel and titanium alloy in quasi-equiatomic proportions, is used in numerous biomedical applications due to its remarkable mechanical characteristics, its resistance towards corrosion and good biocompatibility. Further research to reinforce osseointegrative abilities and barrier properties towards external aggressive agents are still needed.In this context, electrochemical methods can be used to generate protective and functional surface coatings on Nitinol substrates with a good level of control and versatility. Specifically here are considered the elaboration of a structured thin layer on Nitinol plates by electrodeposition of tantalum and its subsequent modification by the self-assembly of phosphonic acid derivatives to consolidate corrosion protection and bioactivity features. Electrochemical techniques are also used to assess and study the different deposited layers. Cyclic voltammetry, polarization curves, free potential measurements, and scanning electrochemical microscopy experiments are performed to qualitatively and quantitatively evaluate electron and mass transfers at the interface, as well as corrosion resistance properties. Spectroscopic (XPS) and microscopic (SEM) analyses complete the characterization process regarding chemical nature and morphology aspects.

Bioinspired and biocompatible adhesive coatings using poly(acrylic acid)‐grafted dopamine

AbstractPoly(acrylic acid) (PAA) was grafted with dopamine to increase its adhesion force to metal surface. Nitinol plate surfaces were then modified by coating with PAA‐g‐dopamine. To synthesize PAA‐g‐dopamine, PAA was first activated by dicyclohexylcarbodiimide and N‐hydroxysuccinimide (NHS) to form PAA–NHS. Dopamine was then copolymerized with PAA–NHS in an aqueous medium at pH 8.5. We propose to increase the adhesion of adhesive PAA‐g‐dopamine on nitinol to improve its durability. In this article, we studied wettability, surface elemental composition, and surface morphology. Biocompatibility was also assessed by L929 fibroblast cells in vitro. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Study of the formation process and the characteristics of tantalum layers electrodeposited on Nitinol plates in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid

Thanks to excellent mechanical and biochemical properties, the nickel–titanium shape memory alloy (Nitinol) constitutes an increasingly praised platform material in dental, cardiovascular and orthopedic biomedical devices. In order to strengthen their protective abilities toward corrosion, to reinforce their biocompatibility and to confer them specific osseointegrative capacities, Nitinol plates are covered with a thin tantalum layer by electrodeposition in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid. XPS and SEM/EDX analyses highlight the chemical and morphological characteristics of the deposits: notably, these present an intrinsic dimpled nanometric structuration which is particularly remarkable considering the “soft” experimental conditions and very interesting for fundamental and applied bioactive perspectives. The present study investigates the specific and synergic effects of the Ni occurrence on the surface of the Nitinol substrates, the presence of fluorine species in the working bath, and the electrodeposition duration on the resulting formation process, morphology and chemical composition of the tantalum coating. Finally, samples are submitted to electrochemical characterizations and in vitro hydroxyapatite growth tests for a primary assessment of their corrosion resistance and osseoinductive features.

A Preliminary Study of Bending Stiffness Alteration in Shape Changing Nitinol Plates for Fracture Fixation

Nitinol is a promising biomaterial based on its remarkable shape changing capacity, biocompatibility, and resilient mechanical properties. Until now, very limited applications have been tested for the use of Nitinol plates for fracture fixation in orthopaedics. Newly designed fracture-fixation plates are tested by four-point bending to examine a change in equivalent bending stiffness before and after shape transformation. The goal of stiffness alterable bone plates is to optimize the healing process during osteosynthesis in situ that is customized in time of onset, percent change as well as being performed non-invasively for the patient. The equivalent bending stiffness in plates of varying thicknesses changed before and after shape transformation in the range of 24-73% (p values <0.05 for all tests). Tests on a Nitinol plate of 3.0 mm increased in stiffness from 0.81 to 0.98 Nm² (corresponding standard deviation 0.08 and 0.05) and shared a good correlation to results from numerical calculation. The stiffness of the tested fracture-fixation plates can be altered in a consistent matter that would be predicted by determining the change of the cross-sectional area moment of inertia.

Artificial urethral valve driven by SMA actuators with transcutaneous energy transmission system

Abstract. This paper presents the development of a mechanical SMA urethral valve driven by a portable transcutaneous energytransmission system, which is powered by batteries. Structure of the valve was improved by introducing a bite mechanism inorder to prevent the pinch of urethra by the valve. The cycling characteristics and energy transmission efficiency were examinedby laboratory tests. Experimental results show that the stable operation can be obtained by introducing a voltage regulatingcircuit to the energy transmission system and utilizing the sinusoidal oscillation in the energy transmission system can enhancethe transmission efficiency. Furthermore, the function of the valve system was tested by the vitro and vivo animal experiments. 1. IntroductionUrinary incontinence is the involuntary discharge of urine caused by trauma to the urethral sphincteror the weakness of the sphincter due to aging and the expansion of the prostate gland. The early andappropriate treatment of urinary incontinence is of great importance since the incontinence might causeurinary canal infection and bedsoreif it is not treated. However, the difference in ages, sexof the patientsandthe variouscausesof thedisorder makeit difficult to treat the diseasesimplyby medicinesor surgery.On the other hand, shape memory alloys (SMAs), especially nickel-titanium alloys (nitinol, NiTi),show many unique characteristics, among them the most important two are the ability of shape recoveryand the excellent biocompatibility. For this reason, their applications to the medical field are widelystudied. Using an SMA nitinol plate as the actuator, the authors developed an artificial urethral valve forthe treatment of urinary incontinence [1]. Thevalveis closedto clogthe involuntary dischargeof urineatthe body temperature and is opened to allow the micturition when the SMA plate is heated by runningelectric current through the nichrome wire attached to it. It is verified by the animal experiments usingcanine urethras that the valve functions well as artificial urethral sphincter in controlling the dischargeof urine.

Development of artificial urethral valve with transcutaneous energy transformer

This paper is concerned with the development of an artificial urethral valve for treating urinary incontinence, which is driven by shape memory alloy actuators. The latest valve has been modified by adding the SMA for the closing, which has the effect of preventing incorrect actions. Further, a compact, non-contact induction heating system using power transmission coils is introduced, which is improved by using an oscillation and amplifier circuit. It is found that the valve shows good opening and closing functions experimentally by using the urethrae of male dog through the induction-heating system. Urinary incontinence is the involuntary discharge of urine caused by the weakness of the urinary canal sphincter muscles due to aging and the expansion of the prostate gland. The difference in ages, sex of the patients and the various causes of the disorder make it difficult to treat the disease simply by drugs or surgery. Shape memory alloys (SMAs), especially nickel-titanium alloys (nitinol, NiTi), show many unique metallurgical and mechanical characteristics. One of the important features is the large change in the Young's modulus when the alloy experiences a martensitic transformation. The other is the significant shape recovery performance associated with reverse transformation of the deformed martensitic phase to the austenite phase at higher temperature. Because of its unique properties and characteristics, a great deal has been done on the metallurgical information and the applications of shape memory alloys as force and displacement actuators (1,2). For the treatment of urinary incontinence, Chonan et al. developed artificial urethral valve driven by SMA, nitinol plates. The SMA plate is designed to be cylindrical at the body temperature and to be flatten when heated. Heating can be done by running electric current through the copper wire attached on the surface of the plate. The plate is fixed with two semi-circular stainless steel shells to be cylindrical as a assembly. It was verified in the animal experiment using canine urethrae that the prototype valves work

Development of a Shape Memory Alloy Damper for Intelligent Bridge Systems

The application of intelligent materials with self-repairable and self-diagnosis functions will provide more efficient and effective earthquake protective system to bridge structures. Shape memory alloys are possible candidates of intelligent materials that are applicable to bridge structures. The damping device made of shape memory alloys was proposed in this paper. The damping device that was simple Nitinol plate can absorb seismic energy and reduce the seismic force by its pseudo yield effect. This study focuses on the damping enhancement effect of the device to bridge structures. A series of shaking table test was carried out in order to verify the damping enhancement effect under earthquake type excitations. As a result of this study, it is found that the Nitinol plate damping enhancement device can reduce the seismic response of the bridge structures and can perform its function more efficient and effective when in shape memory phase.