A new patent-pending technology to enhance the radiopacity (x-ray visibility) of wires is under development in Fort Wayne Metals R&D. Building upon our DFT® wire platform, this technique replaces the typically metallic core material with a radiopaque powder.
Fort Wayne Metals has developed a group of NiTi based super-elastic (SE) alloys that have upper plateau strengths above 1.0 GPa (1000-1500 MPa) and lower plateau strengths above 600 MPa.
Fort Wayne Metals has developed a Ni-free ß-Ti alloy showing large and stable superelastic properties at room temperatures. Mechanical properties and fatigue performance of this alloy are within the neighborhood of superelastic NiTi alloys.
Several Ultra-High-Strength (UHS) wires are produced that may be well suited to high strength wire, strands, cables and ropes used in robotics force transmission and other high-performance mono- and multifilament wire applications where high strength, low stretch and fatigue durability are important. The breadth of UHS materials processed to this condition included two binary molybdenum-rhenium alloys with between 30 and 50 wt.% rhenium and one tungsten-rhenium alloy with 26 wt.% rhenium. These three alloys are processed from a moderate strength (< 2 GPa) warm-drawn rod to bright drawn monofilament wire with extreme nanocrystalline grain refinement, high apparent fatigue durability, and ultimate strength levels exceeding 5 GPa in all cases, and in excess of 6.8 GPa in one exemplary case at monofilament diameters ranging from 7 to 100 µm.
Fort Wayne Metals has developed a composite wire technology with integrated proximal-to-tip guidewire performance in mind. One critical area in medical device practice is in vascular access guidewires. Many workhorse guidewires, 0.3302 mm to 0.3556 mm [0.013 in to 0.014 in], use a stiff material body (often stainless steel or CoNiCr) for control and a superelastic Nitinol tip for flexible navigation. The combination of properties for these hybrid wires is often used for effective navigation to areas of the heart, brain, and vessels of appendages.
In today's update, we've proposed a few applications where grooved wire could enable additional functionality in your next generation of devices.
Fort Wayne Metals Research and Development Engineers have co-authored an article for the Royal Society of Chemistry’s journal Chemical Communications. Titled “Innate glycosidic activity in metallic implants for localized synthesis of antibacterial drugs”, the article describes that iron-containing metallic implants are shown to mediate hydrolysis of glycosidic linkages. This behavior can be leveraged using glucuronide prodrugs for broad-spectrum fluoroquinolone antibacterial agents, to perform localized synthesis of antimicrobials which affords a significant zone of inhibition of bacterial growth around the metallic material.
Beta titanium alloys can be used in place of Nitinol as a nickel-free alternative in certain medical device allergy-sensitive applications, particularly in wear environments where particles of base metal can permeate tissue . Fort Wayne Metals began this work to provide improved care in such devices where Nitinol’s superelastic properties are desired but the chemistry is contraindicated.
Commercially available nanocrystalline Nitinol wire is capable of well over 8% total recoverable strain , whereas conventional beta titanium alloys including the venerable beta III systems and gum metal variants max out at about 2-3% total recoverable strain in uniaxial tension [1-3]. Thus, while useful, conventional beta alloys cannot directly “stand-in” for Nitinol in medical device design.
Wire cables are increasingly used in surgical procedures to provide mechanical fixation in applications like sternotomy repair and femoral cerclage. Current materials, including 316LVM, L605 and Titanium alloys, are stable in the body and are typically left behind indefinitely after healing. These implants deliver critical acute care and concurrently can lead to long-term complications such as bone stress shielding and imaging artifacts in later therapy. An emerging and more ideal solution may make use of implants which dissolve harmlessly and even beneficially after they are no longer needed. Recent efforts to develop these absorbable metals (Mg, Fe, or Zn) for medical implants have already resulted in two devices with promising outcomes and CE mark approval [1,2].
The Amplatzer™ self-centering septal occluder revolutionized minimally invasive closure of atrial septal defects (ASDs) in children in the late 1990’s, and has served the role well from that time on . Since the 1990s, Nitinol shape memory alloys (SMAs) have enabled high performance and less invasive treatment of aortic aneurysms, biliary ducts and cerebrovascular aneurysms. All such devices have relied on the remarkable combination of shape memory, superelasticity, corrosion and fatigue durability found in well-processed Nitinol wires and tubes.
Shape memory alloy (SMA) wires, such as nitinol, with diameters less than 8µm (~.0003”) can be produced by the accumulative drawing/rolling and bonding technique, which has been used to make other microscale metallics [1-2]. Further, Nitinol wire or fiber forms have already been explored for use in complex textile production for advanced function . In this working example, as shown in Figure 1 (a,b), over 2,000 NiTi wires with a diameter of 2.5 µm (approx. 0.0001 in) were produced by drawing inside a specially tuned and sacrificial, deformable matrix.
With the recent approval of two magnesium-based implants in Europe, we may be at the beginning of a paradigm shift in medical intervention. In the near future, devices whose structural support is only needed temporarily, such as stents, staples, and screws, may be predominantly made of absorbable metals which dissolve harmlessly and even beneficially over time. Of the three nutrient metal classes (Mg, Fe, Zn), magnesium has, of late, received the most attention.
At Fort Wayne Metals, we are applying our knowledge of Nitinol alloys and processing to decrease the stress-temperature sensitivity of Nitinol and increase the temperature range where superelasticity is possible. The superelastic (SE) properties of Nitinol are generally used in moderate temperature environments. Room temperature and body temperature are the most common.
Fort Wayne Metals is engaged in alloy design, process development, and thermomechanical conditioning and test development of low through high temperature nitinol and NiTi ternary alloys for actuator applications. Custom product forms range from ultrafine filament (e.g. 50 µm) through larger wire (e.g. 2-5 mm), cables, strip and other custom product forms. The present work on low temperature actuation using superelastic grade NiTi is adapted from a talk given by the authors at SMST 2015 .
Unique microstructures and properties of a ternary Ni46.7Ti42.8Nb10.5 alloy reported in one of our recent studies  shows great potential of this alloy system in applications that require high stiffness and large mechanical energy dissipation.
In August of 2015 progress towards making wire with microgrooves in the guidewire size range was summarized in A New Take on Wire Geometry – Functional Grooves. Now the focus has shifted to comparing the mechanical performance to that of solid round wire.
In our July 2015 installment , we discussed Fort Wayne Metals’ recent development of a beta titanium, nickel-free superelastic alloy. At the time, as shown in Figure 1 below, we were able to design excellent shape setting response in linear wire segments, e.g. for applications such as kink-resistant guidewire and stylets. Straight shapeset geometries were achieved through conventional stress-annealing of a suspended wire segment as well as continuous reel-to-reel wire lengths.
Medical device design with absorbable metals has the potential to revolutionize patient care by providing effective short-term therapy and then harmlessly dissolving away. One of the primary hurdles to overcome is that of premature material fracture which could potentially lead to improper device function. One potential avenue to solve this problem is to harness and use a natural property of metals to our advantage, namely galvanic activity. When two differing metals are in proximity to one another in a conductive solution, one material will be electrochemically dissolved and the other protected from dissolving. This is the same principle by which a potato battery or galvanized steel works
You may know that Fort Wayne Metals has been in the business of providing effective DFT® composite wire solutions for more than 30 years into industries such as cardiac pacing and neurovascular stenting. DFT wires are commonly ordered with a specific area fraction (%) of another metal, like silver for conductivity (e.g. 35N LT-DFT-28%Ag), or platinum for x-ray-opacity (e.g. NiTi-DFT-10%Pt) – these DFT wires with less than 50% area core fractions are known as thick wall composites.
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