METHOD OF MASS REMOVAL AND ELECTROPOLISHING OF STENT ALLOYS CONTAINING NOBLE ELEMENTS

Abstract

A process for electrochemical mass removal and/or electropolishing a stent formed from a cobalt-chromium-tungsten-platinum alloy. The alloy may also comprise nickel (e.g., at about 10% by weight), where no other elements are present in an amount over 3% by weight. The process includes positioning the stent in an electrolyte solution in an electropolishing cell, wherein the electrolyte includes each of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, e.g., in a volumetric ratio (as prepared) of about 6:1:1, wherein the electrolyte further comprises ethylene glycol. The metallic body is electrochemically processed in the electrolyte solution in the electropolishing cell, wherein the mass removal and electropolishing includes application of an alternating current with a forward:reverse current ratio of at least 3:1 (e.g., from 3:1 to 5:1). Voltage may be allowed to float, e.g., within a range of 1 to 6 volts. Superficially similar processes using DC, other AC settings, or without ethylene glycol were ineffective.

Claims

1. A process for electrochemical mass removal and/or electropolishing a metallic body formed from a cobalt-chromium-tungsten-platinum alloy, the process comprising: positioning the metallic body in an electrolyte solution in an electropolishing cell, wherein the electrolyte solution includes each of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, in a volumetric ratio where at least 5 times more H.sub.2SO.sub.4 is provided, relative to HCl and/or relative to H.sub.3PO.sub.4, wherein the electropolishing electrolyte further comprises ethylene glycol; and electrochemically removing mass and/or electropolishing the metallic body in the electrolyte solution in the electropolishing cell, wherein the electrochemical mass removal and/or electropolishing includes an alternating current with a forward:reverse current ratio of at least 3:1.

2. The process of claim 1, wherein the volumetric ratio of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, of the as prepared electrolyte is about 6:1:1, and the ethylene glycol comprises about 25% to 75% by volume of the electrolyte solution.

3. The process of claim 1, wherein forward and reverse phases of the applied alternating current each having a duration in a range of about 3 ms to about 10 ms during an electropolishing portion of the process, and/or in a range of about 10 ms to 50 ms during an electrochemical mass removal portion of the process.

4. The process of claim 1, wherein the metallic body comprises at least a portion of at least one of a stent, a guidewire, an embolic protection filter, or a closure element.

5. The process of claim 1, wherein the alloy comprises no greater than 30% platinum by weight.

6. The process of claim 1, wherein the alloy comprises cobalt, chromium, tungsten, platinum and nickel.

7. The process of claim 6, wherein the alloy comprises cobalt in an amount from about 20% to about 40% by weight.

8. The process of claim 6, wherein the alloy comprises chromium in an amount of about 20% by weight.

9. The process of claim 6, wherein the alloy comprises nickel in an amount of about 10% by weight.

10. The process of claim 6, wherein the alloy is substantially or entirely free of molybdenum.

11. The process of claim 6, wherein the alloy is substantially or entirely free of carbon.

12. The process of claim 6, wherein the alloy comprises no more than 1% of each of silicon, phosphorus, and sulfur by weight.

13. The process of claim 6, wherein the alloy further comprises manganese in a amount of up to 5% by weight.

14. The process of claim 6, wherein the alloy further comprises iron in an amount of up to 5% by weight.

15. The process of claim 6, wherein the alloy further comprises both manganese and iron in a concentration of up to about 3% each, by weight.

16. The process of claim 6, wherein a sum of cobalt and platinum comprises from 45% to about 60% by weight of the alloy.

17. The process of claim 1, wherein said alloy includes precipitate inclusions, wherein the precipitate inclusions comprise tungsten (e.g., Co.sub.3W).

18. The process of claim 1, wherein the alloy comprises: about 20-37% cobalt; about 20-30% platinum; about 19-21% chromium; about 14-16% tungsten; about 9-11% nickel; and about 1-2% manganese.

19. The process of claim 18, wherein the alloy comprises one or more trace elements as follows: 0-3% iron; 0-0.03% sulfur; 0-0.04% phosphorus 0-0.04% silicon; or 0.05-0.15% carbon.

20. A process for electrochemical mass removal and electropolishing a stent formed from a cobalt-chromium-tungsten-platinum-nickel alloy, the alloy including no other elements in an amount over 3% by weight, the process comprising: positioning the stent in an electrolyte solution in an electropolishing cell, wherein the electrolyte solution includes each of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, in a volumetric ratio of about 6:1:1, wherein the electropolishing electrolyte further comprises ethylene glycol; and electrochemically removing mass and/or electropolishing the metallic body in the electrolyte solution in the electropolishing cell, wherein the electrochemical mass removal and/or electropolishing includes application of an alternating current with a forward:reverse current ratio of 3:1 to 5:1, wherein voltage is within a range of 1 to 6 volts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] To further clarify the above and other advantages and features of the present disclosure, a more particular description will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The present disclosure will be described and explained with additional specificity and detail through the use of the accompanying drawings.

[0052] FIG. 1 is an elevation view, partially in section, of a radiopaque stent that can be formed according to the present invention, mounted on a delivery catheter and disposed within a damaged lumen.

[0053] FIG. 2 is an isometric view of an exemplary stent.

[0054] FIG. 3 is an elevation view, partially in section, showing the radiopaque stent of FIG. 1 within a damaged lumen.

[0055] FIG. 4 is an elevation view, partially in section, showing the radiopaque stent of FIG. 1 expanded within the lumen after withdrawal of the delivery catheter.

[0056] FIG. 5 is a schematic illustration of an exemplary apparatus that could be used to practice mass removal and electropolishing as described herein.

[0057] FIGS. 5A-5B schematically illustrate another exemplary apparatus that could be used to practice mass removal and electropolishing as described herein.

[0058] FIGS. 6A-6B schematically illustrate the effect of electropolishing on a stent or similar surface.

[0059] FIG. 7 shows mass removal achieved using various electrolyte formulations, and electrical settings.

DETAILED DESCRIPTION

I. Introduction

[0060] Many alloys proposed for use in construction of stents or similar implantable medical devices must be subjected to electrochemical mass removal and electropolished before a structure with sufficient smoothness to be useful as a stent can be achieved. For example, mass removal reduces the wall and strut thickness of the stent or other structure. As to electropolishing, without such electropolishing, the resulting metal surfaces are too rough for implantation within a body lumen in a manner that would minimize later complication risks associated with stent placement. While existing CoCr stent materials (such as L-605) are routinely subjected to mass removal and then electropolished using an electrolyte solution including sulfuric acid, phosphoric acid, and hydrochloric acid in a volumetric ratio (as prepared) of 6:1:1 for mass removal, followed by electropolishing in an ethylene glycol electrolyte solution, it was found that attempts to perform mass removal and electropolish the present alloys, which are similar to L-605 CoCr alloy, except that a portion of the cobalt has been replaced with platinum, will not result in mass removal, or achieve the desired electropolished finish within such standard mass removal and electropolishing electrolyte solutions, with the normally applied DC current.

[0061] Electrochemical mass removal and electropolishing are unpredictable chemical arts, and it was found that such CoPtCrNiW alloys could achieve electrochemical mass removal and be electropolished under a very specific process, where the electrolyte solution is the same for both portions of the process (e.g., including sulfuric acid, hydrochloric acid, and phosphoric acid in a volumetric ratio (as prepared) of 6:1:1), where an alternating current is applied, with a forward:reverse current ratio of at least 3:1. It was observed that lower forward:reverse current ratios (e.g., 2:1) were ineffective, and forward:reverse current ratios where the reverse current dominates (e.g., a ratio of less than 1:1) caused staining and/or burning, and achieved no significant mass removal. It is surprising and unpredictable that application of a direct current to the same electrolyte solution produces no significant removal of material from the raw stent surface, but when the current is applied as an alternating current, with the specific forward/reverse current ratio of 3:1 or greater, that excellent results can be achieved, both for the mass removal portion of the process, and the final electropolishing portion of the process.

[0062] While described in the context of CoPtCrNiW alloys that are similar to L-605 alloy (but in which some cobalt has been replaced with platinum), it will be apparent that the present electrochemical mass removal and electropolishing methods may have applicability to other alloys, e.g., particularly those where some fraction of cobalt has been replaced with a platinum group metal, refractory metal, or other precious or exotic metal having an atomic number and/or density greater than that of cobalt, so as to act as a radiopacifier. Examples of such alloys that may similarly benefit from processes as described herein are described in applicant's U.S. Pat. Nos. 9,566,147; 10,441,445, and application Ser. Nos. 16/601,259; 17/068,526 and 17/562,592, each of which is herein incorporated by reference in its entirety. A wide variety of radiopacifier metals may be possible, including metals other than those described in the above referenced patents.

[0063] An embodiment of the present disclosure includes a process for electrochemical mass removal and/or electropolishing a metallic body formed from a cobalt-chromium-tungsten-platinum alloy, the process including positioning the metallic body in an electrolyte solution in an electropolishing cell, wherein the electrolyte includes each of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, e.g., in a volumetric ratio (as prepared) of about 6:1:1, wherein the electrolyte further comprises ethylene glycol, and performing electrochemical mass removal and/or electropolishing the metallic body in the electrolyte solution in the electropolishing cell, wherein the electrochemical mass removal and electropolishing includes application of an alternating current with a forward:reverse current ratio of at least 3:1.

[0064] Another exemplary process is directed to electrochemical mass removal and/or electropolishing a stent formed from a cobalt-chromium-tungsten-platinum-nickel alloy, the alloy including no other elements in an amount over 3% by weight. The process includes positioning the stent in an electrolyte solution in an electropolishing cell, wherein the electrolyte includes each of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, e.g., in a volumetric ratio (as prepared) of about 6:1:1, wherein the electropolishing electrolyte further comprises ethylene glycol, and electropolishing the metallic body in the electropolishing electrolyte solution in the electropolishing cell, wherein the electropolishing includes application of an alternating current with a forward:reverse current ratio of 3:1 to 5:1, wherein voltage is within a range of 1 to 6 volts.

[0065] In an embodiment, the ethylene glycol (or another suitable viscosity modifier) may comprise at least 25%, at least 30%, or at least 35% by volume of the electropolishing electrolyte solution. For example, the ethylene glycol or other viscosity modifier may comprise up to 90%, up to 80%, up to 75%, or up to 70% by volume of the solution. Exemplary fractions for the ethylene glycol or other viscosity modifier may include 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% by volume of the electropolishing electrolyte solution.

[0066] As noted above, very similar processes (e.g., same or similar electrolyte, but application of DC voltage, rather than AC voltage) resulted in no significant mass removal and/or electropolishing at all. Even use of AC voltage, where the voltage ratio (rather than current ratio) is varied as taught in US20140277392 did not produce suitable results. The particularly described process thus includes characteristics that are important, perhaps even critical, to the ability to successfully achieve electrochemical mass removal and electropolish alloy compositions as contemplated herein.

II. Exemplary Processes and Alloys

[0067] The radiopaque stent of the present disclosure comprises a main body, one embodiment of which is illustrated generally at 10 in FIG. 1, which can be fabricated from an alloy comprising cobalt-chromium-tungsten (CoCrW), as well as an additional element providing radiopacity greater than that afforded by cobalt (e.g., addition of platinum). By way of example, the alloy may include at least 10%, at least 15%, or at least 20%, no more than 35%, or no more than 30%, such as from about 20% to about 30% by weight platinum. Nickel may also be present (e.g., in an amount of from 5-15%, such as about 10%). Additional features of such alloy are described in applicant's U.S. Patent Application No. 63/350,106 already incorporated by reference in its entirety. For example, such alloy can be processed as described therein so as to be free or substantially free of precipitate inclusions present within the alloy structure, so as to instead have a substantially single-phase microstructure, without (or substantially without) the presence of any such precipitates or inclusions. Such a structure allows the alloy from which the stent is formed to be capable of deforming in a ductile manner, rendering the radiopaque stent formed therefrom to be expandable. The substantial absence of such precipitates or inclusions also minimizes any tendency for microcracks or similar undesirable mechanical problems to form during expansion, or during manufacture (including during drawing, cutting, descaling, mass removal or electropolishing, etc.).

[0068] The radiopaque CoCrW alloy may be similar to L-605, but in which an amount of platinum is provided, e.g., reducing the amount of cobalt accordingly relative to L-605. Such an alloy may be referred to by applicant as P-605. The remaining weight fractions of other alloying elements in L-605 may remain unaltered (other than cobalt, which decreases). For example, alloy L-605 contains 14-16% by weight tungsten, 19-21% by weight chromium, 9-11% by weight nickel, 1-2% manganese, with a balance (other than trace elements) being cobalt. In the contemplated P-605 alloy, the cobalt may be present in an amount of from 20-40%, or 20-37%, where platinum is present at 20-30% by weight. By including a substantial fraction of platinum (by substituting some of the cobalt), while retaining the remaining weight fractions, the relative radiopacity of the resulting P-605 alloy is increased relative to L-605, and as described herein, it is possible to electropolish such an alloy, using the particular process as described herein.

[0069] In particular, applicant has found that mass removal and electropolishing can be achieved, by altering the process typically employed for mass removal and electropolishing an L-605 alloy, as such typical process does not work at all with the presently contemplated alloys. In particular, where the electrolyte solution includes each of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, in a volumetric ratio (as prepared) of 6:1:1, where the electrolyte further comprises ethylene glycol, and where an alternating current with a forward:reverse current ratio of at least 3:1 is applied, mass removal and electropolishing can be achieved. Surprisingly, little to no mass removal and/or electropolishing occurs even if the same electrolyte solution components are used, but a direct current is applied. Similarly surprising, if the same electrolyte solution is used, and an alternating current is applied, but the forward:reverse current ratio is only 2:1, little or no mass removal and/or electropolishing is achieved.

[0070] Thus in an embodiment, the applied current must be an alternating current, e.g., with a forward:reverse current ratio of at least 3:1, such as 3:1 to 5:1. The voltage of the applied current may be allowed to float, rather than setting such current to a specific value (i.e., the current is set to a specific value, and the voltage is allowed to float). For example, the voltage for forward and/or reverse may be less than 10 volts, less than 8 volts, less than 6 volts, or less than 5 volts, such as 3-4 volts.

[0071] One embodiment of the radiopaque CoPtCrNiW alloy of the present disclosure is comprised of chromium in a concentration of about 20% (e.g., 15% to 25%) by weight, tungsten in a concentration that is about 15% (e.g., at least 10%, such as 10-20% by weight, nickel in a concentration of 5-15% (e.g., about 10%) by weight, manganese in a concentration of 0-5% (e.g., 1-3%) by weight, and iron in a concentration of 0-5% (e.g., 0-3%, or 1-3%) by weight. Trace elements may be present, if at all, in concentrations of less than 1%, less than 0.5%, less than 0.4%, less than 0.3%, less than 0.2%, less than 0.1%, less than 0.05%, less than 0.04%, less than 0.03%, less than 0.02%, or less than 0.01% by weight. Platinum or another metal selected to provide greater radiopacity than cobalt may be present in an amount of about 25%, such as from 15% to 40%, or 20% to 35%, or 20% to 30% by weight. The balance of material may be cobalt, e.g., typically from about 20% to 40%, 20% to 35%, or 25% to 32% by weight. In an embodiment, the weight fractions for one or more of chromium, tungsten, manganese, iron, or nickel may be identical to those in L-605 (hence the applicant's reference to the alloy as P-605). In an embodiment, the fractions of cobalt and platinum may be the only significant difference in composition relative to L-605, although the sum of the cobalt+platinum weight fractions may be equal to that of cobalt in L-605 (e.g., about 50%, or about 55%, such as 45-57%, or 45-55% by weight). Because of the similarity in composition, it is surprising that electrochemical mass removal and electropolishing procedures that provide excellent results with L-605 provide no substantial mass removal and/or electropolishing of the present alloys.

[0072] According to a further embodiment, the radiopaque CoPtCrNiW alloy may be substantially or entirely free of molybdenum and/or carbon as deliberately added alloying elements. Substantially free as used herein may include less than 2%, less than 1.5%, less than 1%, less than 0.5%, less than 0.15%, less than 0.1%, less than 0.05%, less than 0.04%, less than 0.03%, less than 0.02%, or less than 0.01% weight. For example, an embodiment that is substantially free of carbon, but still includes a very small amount of carbon may include from 0.05% to 0.15% carbon. The alloy may also be free or substantially free of any other elements of the periodic table not specifically noted as present.

[0073] According to a further embodiment, the alloy comprises no more than 1%, no more than 0.5%, no more than 0.4%, no more than 0.3%, no more than 0.2%, no more than 0.1%, no more than 0.5%, or no more than 0.04% of silicon (e.g., 0-0.04% max, Si). In an embodiment, the alloy may be entirely free of silicon. The alloy may be substantially or entirely free of phosphorous and/or sulfur, as quantified above (e.g., no more than 0.04%, or no more than 0.04% max by weight of each). For example, as a trace element, if present, phosphorus may be at 0% to 0.04% max, while sulfur, if present, may be at 0% to 0.03% max. Iron may be absent, or present in small amounts (e.g., 0% to 3% max Fe).

[0074] The radiopaque stent of the present disclosure overcomes limitations of other stents, e.g., particularly L-605 stents, which exhibit less than ideal radiopacity, without increasing tungsten content, which can result in solubility problems, as tungsten normally separates into a second phase in CoCr at concentrations over about 18% by weight.

[0075] Such a stent imparts a more visible image when absorbing x-rays during fluoroscopy as compared to a dimensionally similar L-605 stent. With this more visible image, the entire stent is better observed by the practitioner placing the stent. The image observed by the practitioner is not washed out due to excessive brightness and is not too dim. Because of the improved image contrast, the stent is accurately positioned and manipulated within a lumen of a patient, with a radiopacity such that stent expansion during and after deployment may be assessed accurately by the practitioner. An additional advantage to the increased radiopacity is the visualization of the stent and the underlying vessel during follow-up examinations by the practitioner.

[0076] In an embodiment, the entirety of the stent is formed from such an alloy (e.g., no radiopaque coatings, radiopaque markers, etc.). Because the entire stent is radiopaque, the diameter and length of the stent are readily discerned by the practitioner. Also, because the stent itself is made of the radiopaque alloy, the stent does not have problems associated with radiopaque coatings or varying metallic layers (e.g., no core/shell structure), such as cracking or separation or corrosion at interfaces inherent in such configurations. Also, because the entire stent is radiopaque, the stent does not require attachment of such extra markers during manufacture with their attendant issues. It will be apparent that the presence of such different layers or portions can also interfere with electropolishing, as portions having different material compositions may be attacked at different rates during electropolishing, leading to formation of unwanted crevices, ledges, etc. While some embodiments as described herein may include no such coatings, varying composition layers, or markers, in another embodiment, it may be possible to provide a stent where at least a portion of the stent (e.g., the stent body, a core, a shell, or marker thereof) is formed from the alloy and processes described herein, and another portion of the stent (e.g., another of the core, shell, or markers) is formed from a different material.

[0077] The low profile of the CoPtCrNiW stent, coupled with its enhanced radiopacity renders the stent more easily deliverable with easier observation and detection throughout its therapeutic use than stents heretofore available. A stent constructed of a CoPtCrNiW alloy as contemplated herein can be made thinner than one of stainless steel, or L-605 without sacrificing fluoroscopic visibility. The low profile of the CoPtCrNiW stent renders the stent more deliverable with greater flexibility. Additionally or alternatively, the P-605 stent may provide greater radial strength as compared to a similarly sized (or even larger L-605).

[0078] The composition of L-605 is as follows. Values may vary somewhat (e.g., ?1 percentage point).

TABLE-US-00004 TABLE 4 ASTM F90 L-605 Alloy Element Weight Percent Atomic Percent Cobalt 53.4 53.9 Chromium 20 24.4 Tungsten 15 5.2 Nickel 10 10.8 Manganese (maximum) 1.5 2.3 Iron (maximum) 0.1 3.4

[0079] L-605 is reported to have a melting range of 1602 to 1683K (e.g., 1329? C. to 1410? C.) a maximum hardness of 277 HB and a density of 9.13 g/cm.sup.3. This alloy in annealed bar form has a minimum ultimate tensile strength of 125 ksi, a minimum yield strength of 45 ksi and a minimum total elongation of 30%. In an embodiment, the contemplated alloys may have similar tensile strength, yield strength, and elongation properties, as such properties are desirable. That said, the relative radiopacity of L-605 is lacking, e.g., being only 3.6 barnes/cc. While this is better than stainless steel (with a relative radiopacity of only about 2.5 barnes/cc), it is far below a more suitable range, such as greater than 4 barnes/cc, greater than 4.5 barnes/cc, or from 4 barnes/cc to 10 barnes/cc, 4 barnes/cc to 8 barnes/cc, or 4 barnes/cc to 7 barnes/cc.

[0080] Alloys based on L-605, but in which some of the cobalt is replaced with platinum, to result in an alloy having 20-30% (e.g., about 25%) platinum by weight (with the other percentages and relative ratios of one element to another remaining substantially unchanged) provide for far better radiopacity. Applicant's Application No. Application No. 63/350,106, already incorporated by reference, describes how to address problems related to the microstructure of such alloys that can occur during drawing, etc. An exemplary manufacturing process may include a process of alloy formation melting in specialized furnaces to fuse the elements involved. The material then undergoes extrusion to form bars, normalization heat treatments, forging and machining to form rods suitable for tube draw. The tube draw process can involve several stages of draw through dies that reduce the tube diameter, as well as cleaning and annealing heat treatments. The annealing heat treatment re-creates the crystalline structure of the alloy and softens the material in preparation for the next stage of tube draw. U.S. Application No. 63/350,106 describes particular heat treatments that may be used to minimize, dissolve or dissipate the presence of precipitates or inclusions that form during such processing.

[0081] Exemplary alloy compositions that may be electrochemically processed using the methods as described herein are shown below.

Example 1

[0082]

TABLE-US-00005 Symbol Name Weight % Si Silicon 0-0.04 P Phosphorous 0-0.04 Si Sulfur 0-0.03 Cr Chromium 19-21 Mn Manganese 1-2 Fe Iron 0-3 Co Cobalt 20-37 Ni Nickel 9-11 W Tungsten 14-16 Pt Platinum 20-30 Total 100.00

Example 2

[0083]

TABLE-US-00006 Symbol Name Weight % Si Silicon 0-0.04 P Phosphorous 0-0.04 Si Sulfur 0-0.03 Cr Chromium 20 Mn Manganese 1.5 Fe Iron 0-3 Co Cobalt 33.5 Ni Nickel 10 W Tungsten 15 Pt Platinum 20 Total 100.00

Example 3

[0084]

TABLE-US-00007 Symbol Name Weight % Si Silicon 0-0.04 P Phosphorous 0-0.04 Si Sulfur 0-0.03 Cr Chromium 20 Mn Manganese 1.5 Fe Iron 0-3 Co Cobalt 28.5 Ni Nickel 10 W Tungsten 15 Pt Platinum 25 Total 100.00

Example 4

[0085]

TABLE-US-00008 Symbol Name Weight % Si Silicon 0-0.04 P Phosphorous 0-0.04 Si Sulfur 0-0.03 Cr Chromium 20 Mn Manganese 1.5 Fe Iron 0-3 Co Cobalt 23.5 Ni Nickel 10 W Tungsten 15 Pt Platinum 30 Total 100.00

[0086] As shown above, in an example, the alloy may consist essentially of Co, Cr, Ni, W, and Pt, where any additional elements that may be present, may be present at less than 2% by weight (e.g., particularly in the case of Mn and/or Fe), less than 1%, or less than 0.5%, or less than 0.25% (e.g., particularly in the case of Si, P, and/or S), if at all.

[0087] The radiopaque stent of the present disclosure may be fabricated according to any number of configurations. Non-limiting exemplary configurations include a solid cylinder, a coiled stent, a ratcheting stent, a stent embodiment with a backbone, or a stent embodiment with a staggered backbone. FIG. 2 illustrates one exemplary stent structure. In an embodiment, the entirety of the stent body may be formed from the radiopaque CoCr alloy described herein (e.g., without various metallic layers, markers, or the like).

[0088] One type of radiopaque stent design embodiment is a high precision patterned cylindrical device. An example of such is illustrated generally at 10 in FIG. 1. The stent 10 typically comprises a plurality of radially expanded cylindrical elements 12 disposed generally coaxially and interconnected by elements 13 disposed between adjacent cylindrical elements.

[0089] For some embodiments, the stent 10 is expanded by a delivery catheter 11. The delivery catheter 11 has an expandable portion or a balloon 14 for expanding of the stent 10 within an artery 15. The delivery catheter 11 onto which the stent 10 is mounted is similar to a conventional balloon dilation catheter used for angioplasty procedures. The artery 15, as shown in FIG. 1, has a dissected lining 16 which has occluded a portion of the arterial passageway.

[0090] Each radially expandable cylindrical element 12 of the radiopaque stent 10 is independently expandable. Therefore, the balloon 14 may be provided with an inflated shape other than cylindrical, e.g., tapered, to facilitate implantation of the stent 10 in a variety of body lumen shapes.

[0091] The delivery of the radiopaque stent 10 is accomplished by mounting the stent 10 onto the inflatable balloon 14 on the distal extremity of the delivery catheter 11. The catheter-stent assembly is introduced within the patient's vasculature using conventional techniques through a guiding catheter which is not shown. A guidewire 18 is disposed across the damaged arterial section and then the catheter-stent assembly is advanced over a guidewire 18 within the artery 15 until the stent 10 is directly under detached lining 16 of the damaged arterial section. The balloon 14 of the catheter is expanded, expanding the stent 10 against the artery 15, which is illustrated in FIG. 3. While not shown in the drawing, the artery 15 is preferably expanded slightly by the expansion of the stent 10 to seat or otherwise fix the stent 10 to prevent movement. In some circumstances during the treatment of a stenotic portion of an artery, the artery may have to be expanded considerably in order to facilitate passage of blood or other fluid therethrough. This expansion is easily observable by the interventionalist with the radiopaque stent of the present disclosure. While balloon expandable stents are described, it will be appreciated that the alloys and configurations described herein may, in at least some embodiments, be self-expanding.

[0092] The stent 10 serves to hold open the artery 15 after the catheter 11 is withdrawn, as illustrated in FIG. 4. Due to the formation of the stent 10 from the elongated tubular member, the undulating component of the cylindrical elements of the stent 10 is relatively flat in transverse cross section so that when the stent is expanded, the cylindrical elements are pressed into the wall of the artery 15 and as a result do not interfere with the blood flow through the artery 15. The cylindrical elements 12 of the stent 10 which are pressed into the wall of the artery 15 are eventually covered with endothelial cell growth which further minimizes blood flow interference. The undulating pattern of the cylindrical sections 12 provides good characteristics to prevent stent movement within the artery. Furthermore, the closely spaced cylindrical elements at regular intervals provide uniform support for the wall of the artery 15, and consequently are well adapted to tack up and hold in place small flaps or dissections in the wall of the artery 15 as illustrated in FIG. 3 and FIG. 4. The undulating pattern of the radiopaque stent is readily discernable to the interventionalist performing the procedure.

[0093] The illustrative stent 10 and other stent structures can be made using several techniques, including laser machining, followed by electrochemical mass removal and electropolishing as described herein. One method of making the radiopaque stent is to cut a thin walled tubular member made of the radiopaque CoPtCrNiW alloy described herein, to remove portions of the tubing in a desired pattern for the stent, leaving relatively untouched the portions of the radiopaque CoPtCrNiW alloy tubing which are to form the stent. In accordance with one method of making the device of the present disclosure, the tubing is cut in a desired pattern using a machine-controlled laser.

[0094] Typically, before crimping, the stent has an outer diameter on the order of about 0.04 to 0.10 inches in the unexpanded condition, approximately the same outer diameter of the tubing from which it is made, and may be expanded to an outer diameter in a range of about 1 to 15 millimeters. Stents for peripheral and other larger vessels may be constructed from larger diameter tubing. By way of example, the strut thickness in a radial direction may be in a range of 0.00157 to 0.0039 inches (e.g., 40 to 100 ?m). After electropolishing, the finished stent may have an outer diameter on the order of about 0.059 to about 0.276 inches (1.5 mm to 7 mm) in the unexpanded condition.

[0095] An important objective of the P-605 alloy is to open the stent pattern design window, providing greater ability to adjust thickness, geometry, etc. while providing sufficient strength, radiopacity, and other characteristics.

[0096] The tubes are made of a CoPtCrNiW allow as described herein that includes significant platinum content (e.g., 20-30% platinum by weight), while maintaining primarily single-phase characteristics within the alloy. In one embodiment, the tubes are fixed under a laser and are positioned using a CNC to generate a very intricate and precise pattern. Due to the thin wall and the small geometry of the stent pattern, it is necessary to have very precise control of the laser, its power level, the focus spot size and the precise positioning of the laser cutting path.

[0097] In other embodiments, the radiopaque CoPtCrNiW alloy stent of the present disclosure is fabricated of radiopaque CoPtCrNiW alloy wire elements. In another embodiment, the stent is made of a radiopaque CoPtCrNiW alloy flat stock. In another embodiment, the stent is made of radiopaque CoPtCrNiW alloy materials using near-net shape processing such as metal injection molding.

[0098] When expanded, the stent may cover about 10-45% of an arterial wall surface area. The radiopaque CoPtCrNiW alloy stent of the present disclosure can withstand at least about 35% tensile deformation before failure.

[0099] Once a suitable tube structure has been formed through such manufacturing techniques, and such tube has been cut (e.g., laser cut) to achieve the desired raw stent structure, it is necessary to remove some of the mass of such raw structure, and finally, to polish the rough raw stent structure, before it can be suitably used as a stent. For example, the surfaces are too rough and struts and wall thickness are somewhat oversized, and must be thinned, smoothed and edges and corners rounded.

[0100] A schematic of an exemplary electrochemical mass removal and electropolishing apparatus 100 suitable for practicing the embodiments described herein is illustrated in FIG. 5. The typical apparatus 100 includes an electrolyte reservoir 102 that is configured to hold an electrolyte solution 104. The typical apparatus 100 further includes one or more conductors 106a, 106b, and 107, and a power supply 108 capable of delivering an alternating current in short pulses.

[0101] In the apparatus 100, a number of metal work pieces 110 (e.g., stents) are electrically connected to a first terminal 112a of the power supply 108 via conductor 107, while the second terminal 112b of the power supply 108 is connected to conductors 106a and 106b. For convenience, the terminal 112a may be referred to as the anode and terminal 112b may be referred to as the cathode, although it will be apparent that when operated under an alternating current the polarity of terminals 112a and 112b may change with each cycle.

[0102] The conductors 106a, 106b, and 107 are connected to the power supply 108 and suspended in the reservoir 102 in the electrolyte solution 104. The conductors 106a, 106b, and 107 are submerged in the solution, forming a complete electrical circuit with the electrolyte solution 104. An alternating current is applied to the conductors 106a, 106b, and 107 to initiate the electrochemical mass removal and/or electropolishing portions of the process.

[0103] In the methods described herein, for example, mass removal and electropolishing is carried out with the electrolyte solution 104 at about room temperature (e.g., about 20-25? C.). Where it is desired to conduct such mass removal or electropolishing under cooled conditions, the apparatus 100 may also include a combined temperature probe/heating and cooling unit 114, which is attached to a control unit 116. In the illustrated embodiment, the combined temperature probe/heating and cooling unit 114 is submerged in the electrolyte solution 104. The control unit 116 may be programmed to monitor and control the temperature of the electrolyte solution 104. Other configurations for monitoring/controlling the temperature of the electrolyte solution 104 may be used in other embodiments.

[0104] The apparatus 100 may also include any of a wide variety of mechanisms for providing agitation to the electrolyte 104, such as a magnetic stir bar plate. For example, in an embodiment, a magnetic stir plate 118 and a magnetic stir bar 120 may be provided for mixing the electrolyte solution 104 and ensuring even distribution of the electrolyte 104 around the workpieces 110 and the electrodes 106a, 106b, and 107. A wide variety of other configurations for providing agitation of the electropolishing electrolyte 104 may be used, as will be apparent.

[0105] FIGS. 5A-5B illustrate another exemplary apparatus 100 for performing mass removal and/or electropolishing as described herein. As shown, apparatus 100 includes an electrolyte reservoir 102 that is configured to hold an electrolyte solution 104. One or more metal work pieces 110 (e.g., stents) are electrically connected to anode 106a which is connected to a terminal of the power supply as shown, while cathode 106b is connected to the other terminal of the power supply. As already noted, it will be apparent that when operated under an alternating current the polarity of the terminals (and thus the anode and cathode in the electrolyte solution 104) changes with each cycle. In an embodiment, the anode 106a may comprise a spiral mandrel, while the cathode 106b may comprise a platinum coated niobium mesh. The anode and cathode 106a, 106b are connected to the power supply and suspended in the reservoir 102 in the electrolyte solution 104. The anode and cathode 106a, 106b, are submerged in the solution, forming a complete electrical circuit with the electrolyte solution 104. An alternating current is applied to the electrodes 106a, 106b, to initiate the electrochemical mass removal and/or electropolishing portions of the process. A heating element 114 may be provided, as may an agitation element 120 (e.g., a magnetic stir bar or any other mechanism for providing agitation).

[0106] For a given electrolyte solution, the quantity of metal removed from the work piece is proportional to the amount of current applied and the time. Other factors, such as the geometry of the work piece, affect the distribution of the current and, consequently, have an important bearing upon the amount of metal removed in local areas. For example, FIGS. 6A and 6B illustrate a surface 200 and 230 before and after electropolishing. Sharp regions, such as burrs and sharp edges, illustrated at 210 in FIG. 6A have higher current density than smoother areas illustrated at 220, which leads to the preferential removal of material from the sharp regions 210 and relatively little material removal from the smoother regions. The principle of differential rates of metal removal is important to the concept of smoothing accomplished by the electropolishing portion of the present process. Fine burrs have very high current density and are, as a result, rapidly dissolved. Smoother areas have lower current density and, as a result, less material is removed from these areas. The result of electropolishing is illustrated in FIG. 6B. As can be seen, the sharp regions illustrated at 210 in FIG. 6A are eroded away leaving a substantially flat, defect free surface 230.

[0107] In the course of both the electrochemical mass removal and electropolishing portions of the process, the work piece is manipulated to control the amount of metal removal so that mass removal and/or polishing is accomplished and, at the same time, dimensional tolerances are maintained. Electropolishing literally dissects the metal crystalline structure atom by atom, with rapid attack on the high current density areas and lesser attack on the low current density areas. The result is an overall reduction of the surface profile with a simultaneous smoothing and brightening of the metal surface.

[0108] While the P-605 alloy may be quite similar in composition to standard L-605, the same settings for mass removal and electropolishing were found to be completely ineffective. In particular, when using mass removal and electropolishing procedures that work with L-605 with the P-605 alloy, substantially no metal mass could be removed at all, and no polishing or rounding of stent edges/corners occurred. This continued to be the case, even where processing time was greatly extended (e.g., up to 40 minutes)no metal mass could be removed. Normal L-605 is fully electropolished within a time period of about 4 minutes.

[0109] Because of such results, and the unpredictability of the art, it became clear that a different process, involving changing electrolyte solutions and physical conditions and settings would be required, if mass removal and electropolishing could even be achieved at all. One aspect of the challenge was to develop a suitable process for electrochemical mass removal and electropolishing the P-605 alloy that would use current electropolishing equipment, as much as possible, to reduce health and safety risks, and minimize costs associated with mass removal and electropolishing such a material.

[0110] While applicant has prior experience in electropolishing a platinum containing alloy known as MP-23 as described in US20140277392, this alloy had a composition that differed greatly from the new P-605 alloy. Table 5 below illustrates the differences in composition between the alloy for which the present process was developed (P-605), existing alloy L-605, and the alloy (MP-23) for which the previous process was developed.

TABLE-US-00009 TABLE 5 L-605 P-605 MP-23 Element Wt % Element Wt % Element Wt % Cobalt 46-56% Platinum .sup.25% Platinum 57% Chromium 19-21% Cobalt .sup.25% Cobalt 23% Tungsten 14-16% Chromium 19-21% Chromium 14% Nickel 9-11% Tungsten 14-16% Iron 7% Manganese 1-2% Nickel 9-11% Iron 0-3% Manganese 1-2% Carbon 0.05-0.15% Iron 0-3% Carbon 0.05-0.15% Trace Elements Trace Elements Trace Elements Phosphorus 0.040% max Phosphorus 0.040% max N/A Silicon 0.040% max Silicon 0.040% max Sulphur 0.030% max Sulphur 0.030% max

[0111] Given the far greater similarities in the new alloy P-605 to L-605, one would expect that a mass removal and electropolishing process that works for L-605 would be more relevant to mass removal and electropolishing P-605, than any process that may have been developed for MP-23. That said, as noted above, the process that provides excellent results when performing mass removal and electropolishing L-605 alloys provided no smoothing, no polishing, and no removal of metal material at all, when used with the P-605 alloy.

[0112] Furthermore, there are significant differences in the P-605 alloy as compared to the MP-23 alloy that was actually used in US2014/0277392, that would lead one of ordinary skill in the art to question the applicability of any process parameters used to electropolish MP-23 alloy, for use in mass removal or electropolishing P-605. Furthermore, as noted, use of the process described in US2014/0277392 did not provide satisfactory results when used with P-605 alloy.

[0113] For example, the fraction of platinum in P-605 is very different from that in MP-23. Platinum is a noble metal that shows outstanding resistance to chemical attack, even at elevated temperatures. Electropolishing electrolytes are a combination of acids to liberate metallic ions. The variation from 20-30% (e.g., 25%) platinum in P-605 to 57% platinum in MP-23 is a very significant change in relation to electrochemical mass removal or electropolishing, where the alloy containing 57% platinum would be much more resistant to acid induced ion formation.

[0114] In addition, the fraction of chromium in P-605 is significantly different from that in MP-23. Chromium forms a stable tenacious oxide on the surface of the alloy stent. This creates a non-reactive passive layer on the stent surface. The change from 14% chromium (in MP-23) to 19-21% chromium (in P-605) would result in a change to the extent of this layer, making chemical attack more difficult (because of the higher chromium content).

[0115] Alloy P-605 includes 9-11% nickel, while MP-23 includes no nickel content. This is important as nickel stabilizes the alloy structure. Such a difference may result in a significantly different alloy structure in P-605 as compared to MP-23, with significantly different mass removal and electropolishing characteristics.

[0116] Finally, P-605 is designed to maintain the desirable properties of L-605 alloy as much as possible by adding platinum and reducing cobalt accordingly. One result of this design path is that the ratio of the other elements within the alloy relative to one another remain constant, from L-605 to P-605. MP-23 does not follow this design path, and would therefore be expected to exhibit significantly different properties (including different electrochemical mass removal and/or electropolishing properties).

[0117] For each of the above reasons, the process outlined in US2014/0277392 is not particularly relevant to the new P-605 alloy, and as noted, the mass removal and electropolishing process employed for L-605 alloy is wholly inadequate to achieve mass removal and electropolish P-605. As such, a new mass removal and electropolishing process needed to be developed through extensive trial and error, specific to P-605.

[0118] Production of L-605 stents involves laser cutting of the stent pattern from tube raw material, followed by oxide de-burring and removal of sections of the tube that are not part of the stent pattern. Next, the raw laser cut stent is fitted onto a spiral stainless steel mandrel. A similar process can be used to prepare P-605 alloy stents for mass removal and electropolishing. Mass removal and electropolishing L-605 stents includes the preparatory steps of descaling and mass removal (e.g., in an acid solution including H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, in a volumetric ratio (as prepared) of 6:1:1). The acidic electrolyte solution includes no ethylene glycol. This is followed by electropolishing in an electrolyte solution of ethylene glycol, followed by a nitric acid soak, and finally, cleaning with isopropyl alcohol. Water rinses can be employed between each phase to prevent carry over of solutions from one phase to the next.

[0119] When electropolishing L-605, the electrical current is applied at 1 amp, direct current during the mass removal phase (in acid), and at 4 amps direct current for the final electropolish (in ethylene glycol) phase. The stent and the spiral mandrel can be mounted within a fixture that aligns the stent position relative to the cathode, which is formed from a platinum coated niobium mesh. Processing times vary according to stent size, but are generally in the range of 4 minutes for the mass removal phase and 20 seconds for the final electropolishing phase.

[0120] As this process did not work with the P-605 alloy (even though the compositions between L-605 and P-605 are so similar), it was decided to apply a phased electrical current (alternating current), which switches polarity very rapidly from positive to negative, and includes periods of no current flow to the anode (stent and spiral mandrel) from the cathode (platinum coated niobium mesh). All other conditions of the process remained unchanged, relative to as described above, and employed in L-605 mass removal and electropolishing.

[0121] Such a system was evaluated using two levels of electrical current, at from 1-3 amps, and at from 3 to 6 amps. It was observed during such testing that mass could be removed from the raw stent, and the final stent mass target value achieved, but that such a process did not polish or round the sharp, angular edges of the stent, even though mass was being removed. The resulting stent was reduced in mass, but still exhibited a rough surface, with sharp angular edges.

[0122] The available phased electrical equipment could be set to many variations of current, positive and negative on and off times, as well as various amperage levels, e.g., from 100 milliamps to 6 amps. As noted herein, durations of applied Fwd or Rev amperage levels may range from time periods in the millisecond range, to significantly longer, e.g., up to 10 seconds.

[0123] While various settings were tried, and mass could be removed, it was found that no set of settings resulted in the desired polished and rounded surfaces required of an electropolished stent. It was observed that mass removal rate was dependent on applied amperage, with increased amperage providing increased rate of removal of metal.

[0124] It was further observed that mass removal could be achieved in the acid mass removal electrolyte solution, but not within the ethylene glycol electrolyte solution.

[0125] The next stage of evaluation was to alter the mass removal electrolyte. For example, based on a reference review, it was thought that lowering the HCl levels in the acid electrolyte solution (i.e., a relative increase in H.sub.3PO.sub.4 and/or H.sub.2SO.sub.4) might offer improvement. This is consistent with what would be suggested in US2014/0277392, which teaches a ratio of H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, where the H.sub.3PO.sub.4 concentration is highest, compared to the other 2 acid components. Additional formulas, with altered HCl concentrations (deviating from the 6:1:1 ratio) were evaluated. As noted herein, while the 6:1:1 electrolyte is prepared with 6 parts H.sub.2SO.sub.4, 1 part H.sub.3PO.sub.4, and 1 part HCl, most of the HCl volalizes, leaving a concentration of only about 70 ppm HCl in the 6:1:1 electrolyte. The altered electrolytes (otherwise like the normal 6:1:1 electrolyte) had levels of 130 ppm HCl, and 40 ppm HCl. Each showed no improvement.

[0126] It was also observed that attempts at electrochemical mass removal and/or electropolishing the P-605 alloy in the ethylene glycol solution showed no mass removal, and no polishing or rounding of edge surfaces, at any of the various tested phased current settings.

[0127] In theory, electropolishing as a process are believed to be controlled by the formation of a boundary layer in the electrolyte adjacent to the metallic stent surface. This boundary layer is formed of metal ions released from the stent surface by the acids employed in the electrolyte solution. This boundary layer acts as an insulator, preventing transmission of electrical current. Any prominences on the raw stent surface effectively reduce the thickness of the boundary layer in that location, so that more electrical current can be transmitted at that location, accelerating metallic ion release. This is the process of surface smoothing that occurs during an electropolishing process.

[0128] It is believed that the reason the standard L-605 process does not work for P-605 alloy is that either no boundary layer is formed, e.g., due to the nobility of platinum, or an initial layer is formed, but is so thick that electrical conduction sufficient to remove prominences associated with roughness and sharp edges is prevented.

[0129] Use of the same acid electrolyte as used in standard L-605 mass removal shows that boundary layer formation does not occurthe standard 6:1:1 electrolyte needs to have added glycol to function under AC, and the rapid switching of polarity prevents this layer from becoming too thick to prevent electrical conduction. The rapid switching creates a boundary layer of metallic ions, that is rapidly dissipated and then rapidly reforms, releasing more metallic ions and thereby reducing mass.

[0130] This was achieved through realizing that changing the viscosity of the acid electrolyte (through glycol addition) could slow the formation and dissipation of the boundary layer. Creating a thinner layer that would not be as aggressive as the less viscous, more reactive electrolyte was thought to possibly offer a solution to the problems observed.

[0131] Additional testing resulted in the electrolytes shown in Table 6, which shows volumetric fractions that were tested, for the various acids and ethylene glycol. Each tested solution included H.sub.2SO.sub.4, HCl, and H.sub.3PO.sub.4, in a volumetric ratio of 6:1:1, respectively, with differing volumes of ethylene glycol, to change the viscosity of the resulting electrolyte solution.

TABLE-US-00010 TABLE 6 H.sub.2SO.sub.4 H.sub.3PO.sub.4 HCl Glycol 6 1 1 5 6 1 1 10 6 1 1 15 6 1 1 20

[0132] Various AC phased current settings were evaluated, and it was found that mass removal, as well as polishing and rounding could be achieved with varying degrees of finish, with each of the 4 tested electrolyte solutions, with proper selection of phased settings.

[0133] The phased settings that achieved the best finish were as shown below in Tables 7-8.

TABLE-US-00011 TABLE 7 Mass Removal Process Settings Milli- Effective Floating Phased Current Settings seconds Current Amp. Voltage Stage 1 FWD on time 25 3 amp FWD 2.0-2.5 4.0-7.0 V amps Stage 2 FWD off time 0 none none None Stage 3 FWD duration 25 3 amp FWD 2.0-2.5 4.0-7.0 V amps Stage 4 REV duration 5 3 amp FWD 2.0-2.5 4.0-7.0 V amps Stage 5 REV on time 5 1 amp REV 2.0-2.5 4.0-7.0 V amps Stage 6 REV off time 0 none none none

TABLE-US-00012 TABLE 8 Polish Process Settings Phased Current Milli- Effective Floating Settings seconds Current Amp. Voltage Stage 1 FWD on time 5 3 amp FWD 0.5-2.0 1.86-4.26 V amps Stage 2 FWD off time 0 none none None Stage 3 FWD duration 5 3 amp FWD 0.5-2.0 1.86-4.26 V amps Stage 4 REV duration 5 3 amp FWD 0.5-2.0 1.86-4.26 V amps Stage 5 REV on time 5 1 amp REV 0.5-2.0 .sup.3.48 V amps Stage 6 REV off time 0 none none none

[0134] The various on time, off time and duration controls are control settings available within the employed system. The forward on time refers to the amount of time that the stent mandrel is the anode, and the mesh is the cathode. Forward off time refers to the amount of time where no current is applied during the forward phase. The reverse on time refers to the amount of time that the stent mandrel is the cathode and the mesh is the anode. The reverse off time refers to the amount of time where no current is applied, during the reverse phase. The duration refers to the total of a given set of forward (or reverse) on and off times. The duration setting allows for application of repeated forward or reverse cycles, before switching to the opposite cycle type. For example, where a forward duration is 100 ms, and the forward on and off times are each 25 ms, this would mean that 2 complete forward on and off cycles are applied before switching to reverse. While Tables 7 and 8 note duration values for both Fwd and Rev that are in the range of milliseconds, Applicant has further discovered that the phased switching may be performed in significantly longer durations, e.g., up to 10 seconds. Such increased durations are within the scope of the present disclosure.

[0135] Other tested phased settings resulted in differing degrees of finish, while some phased settings did not polish or round at all. For example, a 2:1 forward:reverse current ratio was found to not polish or round, while the best outcomes were achieved with 3:1 or 5:1 forward:reverse ratios. Thus, in an embodiment, the forward:reverse current ratio is greater than 2:1, such as at least 3:1, or from 3:1 to 5:1.

[0136] In each case, the voltage was allowed to float. The voltage control settings on the available equipment were attempted but did not function.

[0137] Additional testing was performed using electrolyte solutions having a 5:9:5 volumetric ratio (as prepared) of H.sub.2SO.sub.4:H.sub.3PO.sub.4:HCl, with differing amounts of ethylene glycol. The electrolytes tested included the below formulations. [0138] (1) 25% glycol and 75% 5:9:5 acids [0139] (2) 45% glycol and 55% 5:9:5 acids [0140] (3) 65% glycol and 35% 5:9:5 acids
The results of such testing are shown in FIG. 7, which shows mass removal for various tested formulations (1)-(3), at various forward and reverse duration values. The horizontal black line at 40% mass removal represents an exemplary desired target mass removal fraction. The results show mass removal can be achieved with all such formulations, and at the various tested duration values, so long as the forward:reverse current ratio is at least 3:1. Formula (3) provided the highest mass removal rate, with a forward on time and duration of 20 ms, and a reverse on time and duration of 8 ms.

[0141] Another additional example was developed as a combination of two differing groups of mass removal and polishing settings, with an AC process where the forward:reverse current ratio was 3:1 during both mass removal and polishing. The mass removal portion of the process included a forward on time and duration of 20 ms, and a reverse on time and duration of 8 ms. The polishing portion of the process included a forward on time and duration of 5 ms, and a reverse on time and duration of 5 ms.

[0142] In addition, unless otherwise indicated, numbers expressing quantities, constituents, distances, or other measurements used in the specification and claims are to be understood as optionally being modified by the term about or its synonyms. When the terms about, approximately, substantially, or the like are used in conjunction with a stated amount, value, or condition, it may be taken to mean an amount, value or condition that deviates by less than 20%, less than 10%, less than 5%, less than 1%, less than 0.1%, or less than 0.01% of the stated amount, value, or condition. Unless otherwise stated, percentages or fractions are by weight.

[0143] Some ranges may be disclosed herein. Additional ranges may be defined between any values disclosed herein as being exemplary of a particular parameter. All such ranges are contemplated and within the scope of the present disclosure.

[0144] As used herein, the term between includes any referenced endpoints. For example, between 2 and 10 includes both 2 and 10.

[0145] Although described principally for use in manufacturing stents, it will be understood that any of the disclosed alloys and electrochemical mass removal and electropolishing processes as described herein may also be used in the manufacture of a wide range of medical devices such as, but not limited to, guide wires, guide wire tip coils, balloon markers, or other structures associated with catheter or non-catheter use, and other implantable structures such as heart valves in which improved radiopacity or improved electrochemical mass removal or electropolishing would be desirable.

[0146] All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference. For example, US Publication No. 2014/0277392, referenced herein, is incorporated by reference in its entirety. Various features described therein (e.g., temperature control, use of methanolic HCl) may be employed in the present processes, insofar as they are compatible with the principles described herein.

[0147] The present invention can be embodied in other specific forms without departing from its spirit or essential characteristics. Thus, the described implementations are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.