Nitinol is a nickel-titanium alloy widely used in medical devices for its unique pseudoelastic and shape-memory properties. However, nitinol can release potentially hazardous amounts of nickel, depending on surface manufacturing yielding different oxide thicknesses and compositions. Furthermore, nitinol medical devices can be implanted throughout the body and exposed to extremes in pH and reactive oxygen species (ROS), but few tools exist for evaluating nickel release under such physiological conditions.
View Article and Find Full Text PDFJ Biomed Mater Res B Appl Biomater
August 2021
Nitinol exhibits unique (thermo)mechanical properties that make it central to the design of many medical devices. However, nitinol nominally contains 50 atomic percent nickel, which if released in sufficient quantities, can lead to adverse health effects. While nickel release from nitinol devices is typically characterized using in vitro immersion tests, these evaluations require lengthy time periods.
View Article and Find Full Text PDFComputational modeling and simulation are commonly used during the development of cardiovascular implants to predict peak strains and strain amplitudes and to estimate the associated durability and fatigue life of these devices. However, simulation validation has historically relied on comparison with surrogate quantities like force and displacement due to barriers to direct strain measurement-most notably, the small spatial scale of these devices. We demonstrate the use of microscale two-dimensional digital image correlation (2D-DIC) to directly characterize full-field surface strains on a nitinol medical device coupon under emulated physiological and hyperphysiological loading.
View Article and Find Full Text PDFTranscatheter aortic valves (TAV) are symmetrically designed, but they are often not deployed inside cylindrical conduits with circular cross-sectional areas. Many TAV patients have heavily calcified aortic valves, which often result in deformed prosthesis geometries after deployment. We investigated the effects of deformed valve annulus configurations on a surgical bioprosthetic valve as a model for TAV.
View Article and Find Full Text PDFCrevice corrosion is one of the major mechanisms that drives implant failure in orthopedic devices that have modular interfaces. Despite the prevalence of crevice corrosion in modular interfaces, very little is known with regards to the susceptibility of different material combinations to participate in crevice corrosion. In this study, we compare two electrochemical methods, ASTM F2129, , and a modified version of ASTM F746, , in their ability to induce crevice corrosion.
View Article and Find Full Text PDFAfter implantation of a transcatheter bioprosthetic heart valve its original circular circumference may become distorted, which can lead to changes in leaflet coaptation and leaflets that are stretched or sagging. This may lead to early structural deterioration of the valve as seen in some explanted transcatheter heart valves. Our in vitro study evaluates the effect of leaflet deformations seen in elliptical configurations on the damage patterns of the leaflets, with circular valve deformation as the control.
View Article and Find Full Text PDFEvaluating risk of fatigue fractures in cardiovascular implants via nonclinical testing is essential to provide an indication of their durability. This is generally accomplished by experimental accelerated durability testing and often complemented with computational simulations to calculate fatigue safety factors (FSFs). While many methods exist to calculate FSFs, none have been validated against experimental data.
View Article and Find Full Text PDFShap Mem Superelasticity
September 2017
Nitinol is used as a metallic biomaterial in medical devices due to its shape memory and pseudoelastic properties. The clinical performance of nitinol depends on factors which include the surface finish, the local environment, and the mechanical loads to which the device is subjected. Preclinical evaluations of device durability are performed with fatigue tests while electrochemical characterization methods such as ASTM F2129 are employed to evaluate corrosion susceptibility by determining the rest potential and breakdown potential.
View Article and Find Full Text PDFJ Biomed Mater Res B Appl Biomater
November 2017
Metallic medical devices such as intravascular stents can undergo fretting damage in vivo that might increase their susceptibility to pitting corrosion. As a result, the US Food and Drug Administration has recommended that such devices be evaluated for corrosion resistance after the devices have been fatigue tested in situations where significant micromotion can lead to fretting damage. Three common alloys that cardiovascular implants are made from [MP35N cobalt chromium (MP35N), electropolished nitinol (EP NiTi), and 316LVM stainless steel (316LVM)] were selected for this study.
View Article and Find Full Text PDFJ Biomed Mater Res B Appl Biomater
October 2017
The effect of mechanical fatigue on the corrosion resistance of medical devices has been a concern for devices that experience significant fatigue during their lifespan and devices made from metallic alloys. The Food and Drug Administration had recommended in some instances for corrosion testing to be performed on post-fatigued devices [Non-clinical tests and recommended labeling for intravascular stents and associated delivery systems: guidance for industry and FDA staff. 2005: Food and Drug Administration, Center for Devices and Radiological Health], although the need for this has been debated [Nagaraja S, et al.
View Article and Find Full Text PDFAlthough generally manufactured as circular devices with symmetric leaflets, transcatheter heart valves can become non-circular post-implantation, the impact of which on the long-term durability of the device is unclear. We investigated the effects of five non-circular (EllipMajor, EllipMinor, D-Shape, TriVertex, TriSides) annular configurations on valve leaflet stresses and valve leaflet deformations through finite element analysis. The highest in-plane principal stresses and strains were observed under an elliptical configuration with an aspect ratio of 1.
View Article and Find Full Text PDFJ Mater Eng Perform
December 2015
Given its relatively simple setup and ability to produce results quickly, rotary bend fatigue testing is becoming commonplace in the medical device industry and is the subject of a new standard test method ASTM E2948-14. Although some research has been conducted to determine if results differ for different rotary bend fatigue test setups or test speeds, these parameters have not been extensively studied together. In this work, we investigate the effects of these two parameters on the fatigue life of three commonly used medical device alloys (ASTM F2063 nitinol, ASTM F138 stainless steel, and ASTM F1058 cobalt chromium).
View Article and Find Full Text PDFJ Mech Behav Biomed Mater
April 2015
Prior to implantation, Nitinol-based transcatheter endovascular devices are subject to a complex thermo-mechanical pre-strain associated with constraint onto a delivery catheter, device sterilization, and final deployment. Though such large thermo-mechanical excursions are known to impact the microstructural and mechanical properties of Nitinol, their effect on fatigue properties is still not well understood. The present study investigated the effects of large thermo-mechanical pre-strains on the fatigue of pseudoelastic Nitinol wire using fully reversed rotary bend fatigue (RBF) experiments.
View Article and Find Full Text PDFPolyvinyl alcohol (PVA) cryogel covered stents may reduce complications from thrombosis and restenosis by decreasing tissue prolapse. Finite element analysis was employed to evaluate the effects of PVA cryogel layers of varying thickness on tissue prolapse and artery wall stress for two common stent geometries and two vessel diameters. Additionally, several PVA cryogel covered stents were fabricated and imaged with an environmental scanning electron microscope.
View Article and Find Full Text PDFJ Biomed Mater Res B Appl Biomater
January 2012
Covered stents may be able to prevent both thrombosis and restenosis, but new mechanically suitable and biocompatible materials are needed before this treatment option can become a reality. Hydrophilic polyvinyl alcohol (PVA) cryogels have desirable mechanical properties for covered stent membranes and may be able to provide a physical barrier to restenosis with low thrombogenicity. An in vitro flow loop with porcine blood was used to compare thrombus formation on different blood-contacting biomaterials.
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