Nitinol Tubes Research Articles

Effect of heat treatments on the structure and properties of a small-diameter thin-walled tube of a medical nickel titanium alloy

The present study examines the effect of annealing at temperatures of 300-500°C on the structure and properties of a thin-walled nitinol tube of composition Ti49.1Ni50.9 used for the manufacture of intravascular stents. Annealing temperature dependences are obtained for the martensitic transformation temperatures, the size of the structural elements of the grain-subgrain structure, phase composition, pseudo-yield stress, and ultimate strength. The effect of the Ti3Ni4 particle precipitation in aging during annealing at different temperatures on the obtained dependences is analyzed.

Force Sensing With 1 mm Fiber Bragg Gratings for Flexible Endoscopic Surgical Robots

This article presents a novel force sensor to detect the distal force of tendon-sheath mechanisms (TSMs) in flexible endoscopic surgical robots. We propose to measure the compression force on the sheath at the distal end so that the tension force on the tendon, which equals the compression force on the sheath, can be obtained. With this approach, a new force sensor made up of a 1 mm fiber Bragg grating attached to a 3 mm long nitinol tube was developed to measure the compression force exerted on the sheath. Mechanics analysis and verification tests were conducted to characterize the relationship between tension and compression on a TSM. Force calibrations, hysteresis study, and temperature compensation verification tests on the sensor were carried out. The force sensor has a measurement error of 0.178 N and a sensitivity of 34.14 pm/N. Applications of the sensor in a TSM-driven robotic grasper and a tendon-driven continuum robot were demonstrated. This force sensor has salient advantages: it is small, structurally simple, electrically passive, temperature-compensated, easy to assemble and disassemble, flexible, and biocompatible. This proposed approach with the new force sensor can also be applied to both TSM-driven systems and tendon-driven systems such as robotic fingers/hands, wearable devices, surgical catheters, and rehabilitation devices.

A Needlescopic Wrist Mechanism With Articulated Motion and Kinematic Tractability for Micro Laparoscopic Surgery

Invasiveness of laparoscopic surgery can be further reduced by using needlescopic instruments which diameter approaches that of a hypodermic needle. However, such needlescopic instruments are limited by the lack of wrist mechanisms with precise and sharp articulating motion. In this article, we present a two-degree-of-freedom wrist mechanism with articulating motion and enhanced kinematic tractability for micro laparoscopic surgery. The mechanism consists of two highly curved nitinol tubes serially connected by rotary joints whose axes intersect at a remote center of motion (RCM). Its elasticity is only utilized for introducing through a trocar. Once introduced, the rigid body motions of each tube by the rotary joints generate pivoting motion of the attached end-effector about the RCM point. This allows large reorientation of the end-effector's direction with minimal displacement. The serial link structure of the mechanism leads to analytic solutions for tractable kinematics. The design, manufacturing, and the validation of the kinematics of the mechanism are presented, and the feasibility of the mechanism is demonstrated through the peg transfer test using a teleoperated robot system.

The Wall Apposition Evaluation for a Mechanical Embolus Retrieval Device.

A computational evaluation approach to the wall apposition of a cerebral mechanical emboli retrieval device (MERD) is presented. The typical enclosed multilattice structure, manufactured from the thin-walled Nitinol tube, consists of repeated “V”-shaped unit cells. During interventional thrombectomy, the MERD system is delivered inside an artery stenosis segment to capture emboli and restore cerebral blood flow. The wall apposition, which deteriorates during embolus capture, occurs during system migration along the tortuous intracranial vessel. The commercial finite element analysis (FEA) solver ABAQUS 6.10 Standard and user subroutine (UMAT/Nitinol) are utilized to study the ability to remain in close contact with the curved vessel wall during migration. In this numerical analysis, the influence of the contacting interference loadings on structure deformation and strain field distribution is obtained and analyzed. The results indicate that the middle segment of the MERD seriously contracts or collapses inside the curved vessel. In addition, the peak strain is in the apex flow-prone region and maintains at the safe range.

Development of a Novel Continuum Robotic System for Maxillary Sinus Surgery

Lesions in the maxillary sinus area are usually treated with endoscopic interventional surgery. However, target lesions are often hardly accessible with conventional surgical tools. A new continuum module is proposed with a bending manipulator to perform maxillary sinus surgery. The developed manipulator has a NiTiNol tube embedded in its continuum module. It has a diameter of 4 mm and can be bent up to 270° to reach the target position flexibly. In this paper, a kinematic model of the continuum module is presented. An external loading analysis of the robot was formulated to analyze payload capacity and tensions, by taking into account friction, actuation, elastic effects, and external loadings. Some experiments were carried out to validate the kinematics and to test the robot capabilities of scissoring, payload, and manipulation.

Effects of Tube Processing on the Fatigue Life of Nitinol

Nitinol tubes were manufactured from Standard Grade VIM-VAR ingots using Tube Manufacturing method “TM-1.” Diamond-shaped samples were laser cut, shape set, then fatigued at 37 °C to 107 cycles. The 50, 5, and 1% probabilities of fracture were calculated as a function of number of cycles to fracture and compared with probabilities determined for fatigue data published by Robertson et al. (J Mech Behav Biomater 51:119–131, 2015). Robertson tested similar diamonds made from the same standard grade of Nitinol as in the current study, two other standard grades of Nitinol, and two high-purity grades of Nitinol expressly designed to improve fatigue life. Robertson’s tubes were manufactured using Tube Manufacturing method “TM-2.” Fatigue performance of TM-1 and TM-2 diamonds were compared: At 107 cycles, strain amplitudes corresponding to the three probabilities of fracture of the TM-1 diamonds were 2–3 times those of the TM-2 diamonds made from the same grade of Nitinol, and comparable to TM-2 diamonds made from the higher-purity materials. This difference is likely a result of the differences in tube manufacturing techniques and effects on resulting microstructures. Microstructural analyses of samples revealed a correlation between the median probability of fracture and median inclusion diameter that follows an inverse power-law function of the form y ≈ x−1.

023 Moving Beyond Hydraulics: Safety and Efficacy of Magnetic Induction for a New Penile Prosthesis in Human Cadavers and Animal Tissue

We previously developed a novel shape memory alloy prosthesis using a lasercut Nitinol extruded tube that expands and becomes rigid when activated to simulate an erection. We also described how it is possible to activate it using magnetic induction (MI) in vitro without the use of pumps or reservoirs. To better understand the thermal safety and efficacy of this approach in tissue, we tested MI activation using an in vitro animal tissue model and human cadavers. We used a commercially available magnetic inductor with a power of 1000W and a custom made 2mm copper coil of 3 turns of 4cm diameter. The prosthesis or nitinol tube was inserted down the length of a pork-product sausage or implanted in the corpora cavernosa of a human cadver. Two thermocouples were placed to measure temperature changes: (1) on the exoskeleton, and (2) 2 mm away in the tissue. The miniductor was waved over the embedded prosthesis and activated. Temperature tracings were recorded over time. As a control, the same setup was placed on a laboratory hot plate with temperature set at 43C.

Design of a Contact-Aided Compliant Notched-Tube Joint for Surgical Manipulation in Confined Workspaces

This work presents a novel miniature contact-aided compliant joint mechanism that can be integrated into millimeter-sized manual or robotic surgical instruments. The design aims to address the trade-off between notched-tube compliant joints' range of motion and stiffness, while also ensuring a compact form factor. The mechanism is constructed from a nitinol tube with asymmetric cutouts and is actuated in bending by a cable. The innovative feature of this design is the incorporation of a contact aid into the notched-tube topology, which acts to both increase the stiffness of the joint and change the shape that it undertakes during bending. Using finite element modeling (FEM) techniques, we present a sensitivity analysis investigating how the performance of this contact-aided compliant mechanism (CCM) is affected by its geometry, and derive a kinematics and statics model for the joint. The FEM simulations and the kinematic and static models are compared to experimental results. The design and modeling presented in this study can be used to develop new miniature dexterous instruments, with a particular emphasis on applications in minimally invasive neurosurgery.

Innovative Technology for Preparation of Seamless Nitinol Tubes Using SHS Without Forming

This paper presents innovative technology for the production of seamless Ni-Ti tubes using self-propagating high-temperature synthesis (SHS). The proposed production technology is a unique method which removes the need of forming operations, reduces machining processes, and at the same time it eliminates the negatives of production Ni-Ti alloys by conventional melting methods. The proposed process consists in SHS reaction in evacuated silica tube with the use of extremely high heating rate (over 300 K min−1).

Effect of heat treatment and mandrel material on precision tube drawing of Ni-Ti shape memory alloy

Abstract The Ni-Ti shape memory alloy (NITINOL) was known as one of difficult materials to meet the dimensional accuracy because of the complex phase transformation and the shape recovery characteristics. In this study, a tube drawing process with mandrel was numerically and experimentally investigated for manufacturing precision NITINOL tube to identify the stable phase transformation condition to remove the R-phase by differential scanning calorimeter. To study the non-linear material and shape recovery behavior of the NITINOL, tension and loading-unloading tests were conducted with three test velocities of 1, 5, and 10 mm/min. The three dimensional finite element (FE) analyses were carried out using the ABAQUS with hyperelastic and Mullins effect model. The amount of the shape recovery was checked for the drawn tubes compared to the numerical results. According to the present investigation, it was found out that the stable phase transformation which improved the ductility and reduced the effect of shape recovery was occurred under the condition of the heat treatment at 700˚C for 30 min and the tensile test velocity of 10 mm/min. The FE results showed similar tendency of the stress-strain curves obtained from the experiments. Moreover, the amount of the shape recovery of the NITINOL could be predicted by the FE analysis. From the results of the FE analysis and the tube drawing with red copper and brass mandrel, the dimensional accuracy was found to be improved by using the brass mandrel, but the drawing stress was somewhat higher for the brass mandrel than the case using the red copper mandrel. In conclusion, the shape recovery effect of the NITINOL could be predicted by the FE analysis and the process condition determined by the current experiments could be helpful for the precision tube drawing of the NITINOL shape memory alloy tube.

Design, Fabrication, and Testing of a Needle-Sized Wrist for Surgical Instruments.

This paper presents a miniature wrist that can be integrated into needle-sized surgical instruments. The wrist consists of a nitinol tube with asymmetric cutouts that is actuated by a single tendon to provide high distal curvature. We derive and experimentally validate kinematic and static models for the wrist and describe several prototype wrists, illustrating the straightforward fabrication and scalability of the design. We experimentally investigate fatigue life, the concept of tip-first bending, and practical use of the wrist with a concentric tube robot in an endonasal surgical scenario.

Curve micromachining on the edges of nitinol biliary stent by ultrashort pulses laser

In this study, a curve micromaching process on the edges of nitinol biliary stent was proposed by a femtosecond laser system with a galvano-mirror scanner. Furthermore, the outer diameter of nitinol tube was 5.116mm, its inner diameter was 4.648mm, and its length was 100mm. The initial fabricated results of nitinol biliary stent represented that the edges of nitinol biliary stent were steep and squared by femtosecond laser. However, the results also indicated that if the laser movement path was precisely programmed by utilizing the unique characteristic of Gaussian beam of femtosecond laser with aligning the edges of stent, the radius of edges enhanced significantly from 9µm to 42.5µm. As a result, the edges of nitinol biliary stent can be successfully fabricated from squared edges to rounded-shaped edges with precise dimension, clean surface morphology, and minimal heat-affected zone remained. Hence, the nitinol biliary stent, after femtosecond laser micromachining, would not need any further post-process to remove heat-affected zone and the squared edges.

Analysis and Validation of a Teleoperated Surgical Parallel Continuum Manipulator

In this letter, we present the design, kinematic analysis, model validation, and teleoperation of a miniature eight-degree-of-freedom (8-DOF) parallel continuum manipulator with a cable-driven grasper. Our motivation is to provide increased dexterity and stability in confined-space surgical applications, particularly for intraluminal endoscopic procedures. The system design uses six superelastic NiTi (Nitinol) tubes in a standard Stewart-Gough configuration and an integrated end effector that provides 180° articulation of two jaws actuated by Kevlar cables that pass through the tube legs. A computationally efficient inverse kinematics model provides real-time, low-level actuator commands to enable teleoperation. We provide a kinematic workspace analysis of this design, which depicts how mechanical strain, dexterity, and the effect of force application vary over the reachable workspace. We also experimentally characterize the open-loop model accuracy and repeatability of our physical prototype, obtaining mean errors of approximately 1.19 mm and 3.81° and a repeatability RMS error of 0.88 mm and 1.96°. Finally, we demonstrate the feasibility of minimally invasive surgical applications by conducting user trials for a pick-and-place task under unilateral model-based teleoperation.

Curvature, Torsion, and Force Sensing in Continuum Robots Using Helically Wrapped FBG Sensors

Due to their small size and flexibility, fiber Bragg grating (FBG) sensors have been integrated into needle-sized continuum robots for shape estimation and force measurement. The challenge in extending previous shape and force sensing technologies to pre-curved continuum robots, such as concentric-tube robots, is that torsion information is essential for accurate shape estimation, and the force-strain relationship is nonlinear. In this letter, a novel helically wrapped FBG sensor design and corresponding force-curvature-strain model are developed to provide simultaneous curvature, torsion, and force measurement. To validate this design and modeling technique, two sensorized Nitinol tubes were fabricated and tested in an experimental setup. The results showed that accurate and sensitive curvature, torsion, and force measurements can be obtained at a 100 Hz sampling rate.

Biocompatibility and Systemic Safety of a Novel Implantable Annuloplasty Ring for the Treatment of Mitral Regurgitation in a Minipig Model.

Prosthetic annuloplasty rings are a common treatment modality for mitral regurgitation, and recently, percutaneous implantation techniques have gained popularity due to their favorable safety profile. Although in common use, biocompatibility of annuloplasty rings has been reported only sparsely in the literature, and none of these reports used the percutaneous technique of implantation. We report on the biocompatibility and the systemic safety of a novel transcatheter mitral valve annuloplasty ring (AMEND™) in 6 minipigs. This device is composed of a nitinol tube surrounded by a braided polyethylene terephthalate fabric tube. The device produced no adverse inflammatory response, showing gradual integration between the metal ring and the fabric by normal host fibrocellular response, leading to complete neoendocardium coverage. There was no evidence for adverse reactions, rejection, or intolerance in the valvular structure. In 2 animals, hemopericardium resulted from the implantation procedure, leading to right-sided cardiac insufficiency with pulmonary edema and liver congestion. The findings reported herein can serve as a case study for the expected healing pathology reactions after implantation of transcatheter mitral valve annuloplasty rings.

Rapid, Reliable Shape Setting of Superelastic Nitinol for Prototyping Robots.

Shape setting Nitinol tubes and wires in a typical laboratory setting for use in superelastic robots is challenging. Obtaining samples that remain superelastic and exhibit desired precurvatures currently requires many iterations, which is time consuming and consumes a substantial amount of Nitinol. To provide a more accurate and reliable method of shape setting, in this paper we propose an electrical technique that uses Joule heating to attain the necessary shape setting temperatures. The resulting high power heating prevents unintended aging of the material and yields consistent and accurate results for the rapid creation of prototypes. We present a complete algorithm and system together with an experimental analysis of temperature regulation. We experimentally validate the approach on Nitinol tubes that are shape set into planar curves. We also demonstrate the feasibility of creating general space curves by shape setting a helical tube. The system demonstrates a mean absolute temperature error of 10°C.

A new flow diverter stent for direct treatment of intracranial aneurysm

The use of a stand-alone flow diverter (FD) stent has demonstrated itself as an efficacious endovascular approach to intracranial aneurysm treatment. FD stents that are currently available adopt an interwoven braided design. The relatively low radial stiffness intrinsic to this design could cause difficulty in deployment and poor stent–wall apposition, leading to high complication rates. A new FD stent is proposed to overcome the problems of the interwoven FD stents. The new device is manufactured from a Nitinol tube through a laser-cutting technique, and its unique structure allows for both low porosity and high packaging efficiency. Computational simulation using Abaqus has been conducted to investigate the radial stiffness and longitudinal flexibility of the new device. The new device exhibits high radial stiffness when compared to interwoven FD stents and superior longitudinal flexibility. Results from on-going in-vivo experiments and CFD simulations have also demonstrated the efficacy of the new device as a FD stent.

A Bronchial Puncture Mechanism for Transoral Access to the Lung Parenchyma1

A Bronchial Puncture Mechanism for Transoral Access to the Lung Parenchyma1

Augmented reality visualization of deformable tubular structures for surgical simulation.

Surgical simulation based on augmented reality (AR), mixing the benefits of physical and virtual simulation, represents a step forward in surgical training. However, available systems are unable to update the virtual anatomy following deformations impressed on actual anatomy. A proof-of-concept solution is described providing AR visualization of hidden deformable tubular structures using nitinol tubes sensorized with electromagnetic sensors. This system was tested in vitro on a setup comprised of sensorized cystic, left and right hepatic, and proper hepatic arteries. In the trial session, the surgeon deformed the tubular structures with surgical forceps in 10 positions. The mean, standard deviation, and maximum misalignment between virtual and real arteries were 0.35, 0.22, and 0.99 mm, respectively. The alignment accuracy obtained demonstrates the feasibility of the approach, which can be adopted in advanced AR simulations, in particular as an aid to the identification and isolation of tubular structures. Copyright © 2015 John Wiley & Sons, Ltd.

A Wrist for Needle-Sized Surgical Robots.

The needle-sized surgical tools used in arthroscopy, otolaryngology, and other surgical fields could become even more valuable to surgeons if endowed with the ability to navigate around sharp corners to manipulate or visualize tissue. We present a needle-sized wrist design that grants this ability. It can be easily interfaced with manual tools or concentric tube robots and is straightforward and inexpensive to manufacture. The wrist consists of a nitinol tube with several asymmetric cutouts, actuated by a tendon. Perhaps counter-intuitively, within this seemingly simple design concept, design optimization is challenging due to the number of parameters available and nonlinearities in material properties. In this paper, we examine a subset of possible geometries and derive kinematic and static models. Experimental results with a 1.16 mm diameter prototype validate the models. Lastly, we provide a discussion summarizing the lessons learned in our early experience designing and fabricating wrists of this type.