Patent Application
20240229289
Intraluminal stents implanted with percutaneous methods have become a standard adjunct to procedures such as balloon angioplasty in the treatment of atherosclerotic disease of the arterial system. Stents, by preventing acute vessel recoil, improve long-term patient outcome and have other benefits such as securing vessel dissections.
Intraluminal stents comprise generally tubular-shaped devices that are constructed to hold open a segment of a blood vessel or other anatomical lumen. Intraluminal stents are used in treatment of diseases such as atherosclerotic stenosis as well as diseases of the stomach and esophagus, and for urinary tract applications. Adequate stent function requires a precise placement of the stent over a lesion or site of plaque or other lumen site in need of treatment. Typically, the stent is delivered to a treatment site by a delivery catheter that comprises an expandable portion for expanding the stent within the lumen.
The delivery catheter onto which the stent is mounted may be a balloon delivery catheter similar to those used for balloon angioplasty procedures. In order for the stent to remain in place on the balloon during delivery to the site of damage within a lumen, the stent may be compressed onto the balloon. The catheter and stent assembly are introduced within a patient's vasculature using a guide wire. The guide wire is disposed across the damaged arterial section and then the catheter-stent assembly is advanced over the guide wire within the artery until the stent is directly within the lesion or the damaged section.
The balloon of the catheter is expanded, expanding the stent against the artery wall. The artery is preferably slightly expanded by the expansion of the stent to seat or otherwise fix the stent to prevent movement. In some circumstances during treatment of stenotic portions of the artery, the artery may have to be expanded considerably in order to facilitate passage of blood or other fluid therethrough. In the case of a self-expanding stent, the stent is expanded by retraction of a sheath or actuation of a release mechanism. Self-expanding stents may expand to the vessel wall automatically without the aid of a dilation balloon, although such a dilation balloon may be used for another purpose.
These manipulations are performed within the body of a patient by a practitioner who may rely upon both placement markers on the stent catheter and/or on the radiopacity of the stent itself. The stent radiopacity arises from a combination of stent material and stent pattern, including stent strut or wall thickness. After deployment within the vessel, the stent radiopacity should allow adequate visibility of both the stent and the underlying vessel and/or lesion morphology under fluoroscopic visualization.
Stent radiopacity relies on the use of materials having high density, a high atomic number and/or a high electron density contrast compared to the stent's surroundings.
Stents may be precision cut from drawn metallic tubes by using a laser cutting machine. The drawn ID/OD surfaces of the metallic tubes are often rough and laser cutting a stent produces sharp edges on the stent struts. Typically, the tube wall thickness of such a prepared “raw” stent is greater than desired for the finished stent and the stent struts are cut wider than desired for the finished stent. Typically, the cut stent is subjected to electrochemical mass removal and electropolishing from such “raw” stent geometry to its finished/desired dimensions. Electrochemical mass removal brings the stent closer to the final desired weight, while final electropolishing smoothes the ID/OD surfaces of the stent and rounds the edges of the stent struts. Smooth ID/OD surfaces and rounded strut edges make the stent less traumatic to the vessel during stent positioning and deployment and also, minimizes possible damage to the catheter, balloon and/or sheath during construction and use.
Although various procedures exist for electrochemical mass removal and final electropolishing of typical stent materials, e.g., L-605, stainless steel, or the like, such procedures do not work when attempting to achieve mass removal and electropolishing for alloys that include a significant fraction of platinum, particularly where such alloy also includes tungsten, and/or nickel.
In addition, while US 2014/0277392 describes a process for electropolishing a particular Co—Cr—Pt alloy, the alloy for which such electropolishing process was developed includes a very high fraction of platinum (57% by weight), and includes no tungsten or nickel. The process developed as described in US 2014/0277392 did not work with the presently contemplated alloys. As such, there is a need in the art for mass removal and electropolishing processes that could be used to achieve target mass and electropolish Co—Cr—Pt alloys that also include significant fractions of tungsten and/or nickel, such as an alloy that is analogous to L-605, but in which some of the cobalt has been replaced with platinum (e.g., including 20-30% platinum).
One embodiment of the present disclosure includes a process for mass removal and/or electropolishing a metallic body (e.g., a stent) formed from a cobalt-chromium-tungsten-platinum alloy. The term “electropolish” may be used herein, in reference to both (i) the final electropolishing step, which achieves rounding of corners, removal of protrusions, sharp edges, and the like, as well as (ii) mass removal, where similar conditions may be applied, but where the result is more general mass removal from the part being treated, rather than rounding of corners, sharp edges and the like. Slight changes in the applied conditions may apply between the mass removal portion of the process, and the final electropolishing portion of the process, to achieve the principal desired result (mass removal vs. polishing). For example, the same or a similar electrolyte solution may be employed in both steps, and may simply be referred to as an “electropolishing electrolyte solution”. Similarly, the cell in which both such steps are performed may be referred to as an “electropolishing cell”, for simplicity. The present process may include positioning the metallic body in an electropolishing electrolyte solution in an electropolishing cell, wherein the electropolishing electrolyte includes each of H2SO4, HCl, and H3PO4. In an embodiment, such acids may be prepared in a volumetric ratio where the H2SO4 is present in an amount that is at least 5 times greater than the amount of HCl and/or H3PO4. For example, in an embodiment, the volumetric ratio of H2SO4 to HCl to H3PO4 may initially be prepared at 6:1:1. The composition further includes ethylene glycol or another compatible viscosity modifier (e.g., another glycol that is stable in the presence of such acids). In an embodiment, the electrolyte is free or substantially free of hydrofluoric acid. While hydrofluoric acid is used in processing some noble metals, hydrofluoric acid is particularly hazardous, and avoidance of such is beneficial. The process further includes performing electrochemical mass removal and/or electropolishing the metallic body in the electropolishing electrolyte solution in the electropolishing cell, where the mass removal and/or electropolishing includes application of an alternating current with a forward:reverse current ratio of at least 3:1. While US 2014/0277392 describes an electrolyte solution that may appear superficially similar (H2SO4:H3PO4:HCl in a ratio of 5:9:5), with application of an alternating current at a forward:reverse voltage ratio of about 2:1, such a process does not work with the particular Co—Cr—Pt—W—Ni alloy contemplated here. For example, being familiar with US 2014/0277392, Applicant did attempt to use the process described in that reference with the present alloys (using voltage control as described in US 2014/0277392), and the results were unsatisfactory. In particular, Applicant evaluated the procedure described in US2014/0277392 with forward:reverse voltage ratios of 2:1, 3:1 and 4:1. Even where the actual applied voltage was the same as the lower voltage level in US2014/0277392, or even lower values were used (with the same ratios), the results were poor, as summarized in Table 1 below.
As with many chemical processes, it can be difficult if not impossible as a practical matter to predict whether any particular process will work, due to changes in the composition from one alloy to the next, changes from one electrolyte to the next, and/or changes from one set of applied current conditions to the next. Interestingly, a 5:9:5 electrolyte solution as described in US2014/0277392 can work with the presently contemplated alloy, if the required forward:reverse current ratio (not voltage ratio) of at least 3:1 is employed.
What is apparent is that when performing electrochemical mass removal and electropolishing a Co—Cr—Pt alloy such as that contemplated herein (which also includes tungsten and nickel, so as to be analogous to L-605, but where some of cobalt has been replaced, so as to result in an alloy that includes 20-30% platinum by weight), successful mass removal and electropolishing can be achieved under the conditions described herein. Significant differences exist in the disclosed and claimed mass removal and electropolishing procedure as compared to that described in US2014/0277392. For example, in US2014/0277392, while an alternating current is employed, the phased settings differ significantly. In the present process, the alternating current is applied with a forward:reverse current ratio of at least 3:1 while in US2014/0277392 the alternating current is applied with a forward:reverse voltage ratio of 2:1. In the present process, it is important that the current (not the voltage) be applied higher in the forward direction as compared to the reverse direction. The voltage itself may simply be allowed to float, and such floating voltage is significantly lower than that taught in US2014/0277392, which teaches use of a forward voltage of 10 to 25 volts, and a reverse voltage of 5 to 12.5 volts. In the present process, the floating voltage may be less than 10 volts, less than 8 volts, less than 6 volts, less than 5 volts or less than 4 volts, such as 3-4 volts (e.g., 3.48 V).
Differences also exist between the preferred electrolyte solution employed in the present process, which includes significantly more H2SO4 than the other employed acids, which is contrary to the H3PO4 rich electrolyte described in US2014/0277392. While a 6:1:1 plus ethylene glycol solution may be preferred, a solution more similar to that used in US2014/0277392 can work (e.g., 9 parts H3PO4 to 5 parts of each of the other 2 acids, plus ethylene glycol), as shown below in Table 2, so long as the appropriate alternating current is applied with a forward:reverse current ratio of at least 3:1 (not the voltage ratio settings described in US2014/0277392, as such do not work, as shown above in Table 1).
Another exemplary process for mass removal and electropolishing a metallic body (e.g., a stent) formed from a cobalt-chromium-tungsten-platinum-nickel alloy, includes positioning the stent or other metallic body in an electropolishing electrolyte solution in an electropolishing cell, wherein the electropolishing electrolyte includes each of H2SO4, HCl, and H3PO4, in a volumetric ratio of about 6:1:1. The composition further includes ethylene glycol. In an embodiment, the electropolishing electrolyte may comprise at least 25%, or at least 30% ethylene glycol (e.g., 30-90%, 30-80%, or 25-75% ethylene glycol) by volume. It is noted that the acid solution may be prepared at a 6:1:1 (or other ratio), but that a significant portion of the HCl in particular may volatize away, shortly after preparation. For example, a typical 6:1:1 electrolyte solution, after such volatization, may include no more than 130 ppm, or even no more than about 70 ppm HCl. The electropolishing electrolyte may consist or consist essentially of the 3 acids, and the ethylene glycol. The process further includes performing electrochemical mass removal and/or electropolishing the stent or other metallic body in the electropolishing electrolyte solution in the electropolishing cell, where the mass removal and/or electropolishing includes application of an alternating current with a forward:reverse current ratio of 3:1 to 5:1, where voltage is within a range of 1 to 6 volts (e.g., 3-4 volts).
In an embodiment, the forward and reverse phases of the applied alternating current during the polishing portion of the process each have a duration in a range of about 3 ms to about 10 ms (e.g., about 5 ms).
The polishing portion of the process is preceded by the mass removal portion of such an overall electrochemical process, where similar settings may be employed, but duration of the forward and reverse phases of the applied alternating current may be longer. For example, an exemplary mass removal portion of the process may include a forward duration of 10 ms to 50 ms, or 15 ms to 40 ms, or 20-30 ms. The reverse duration may be from 1 to 20 ms, from 5 to 20 ms, from 1 to 10 ms, from 2 to 8 ms, or from 3 to 7 ms. By way of example. The same forward:reverse current ratio of at least 3:1 as described herein for polishing may be used during the mass removal portion of the process, that precedes final electropolishing. Table 3 below provides non-limiting, exemplary parameters for both the mass removal portion of the process, and the polishing portion of the process.
While Table 3 notes 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.
In an embodiment, 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.
In an embodiment, the alloy comprises cobalt, chromium, tungsten, platinum and nickel.
In an embodiment, the alloy may include cobalt in an amount from about 20% to 40% by weight.
In an embodiment, the alloy may include chromium in an amount of about 20% by weight.
In an embodiment, the alloy may include nickel in an amount of about 10% by weight.
In an embodiment, the alloy may be substantially or entirely free of molybdenum (and/or other elements of the periodic table not mentioned herein).
In an embodiment, the alloy may be substantially or entirely free of carbon (e.g., carbon may be included from 0.05% to 0.15% by weight).
In an embodiment, the alloy may include no more than 1%, no more than 0.5%, no more than 0.1%, or no more than 0.05% by weight of one or more of silicon, phosphorus, or sulfur.
In an embodiment, the alloy may further include manganese in an amount of up to 5%, up to 3%, or up to 2% (e.g., 1-2%) by weight.
In an embodiment, the alloy may further include iron in an amount of up to 5%, up to 3%, or up to 2% (e.g., 0-3%) by weight.
In an embodiment, the alloy may further include both manganese and iron in an amount of up to about 3% each, by weight.
In an embodiment, the sum of the percentage of cobalt and platinum in the alloy may be from 45% to 65%, from 45% to about 60%, or 45% to 55% (e.g., about 50%) by weight.
In an embodiment, the alloy may include by weight:
In an embodiment, the alloy may include one or more trace elements as follows:
In an embodiment, the alloy may not include any other elements in amounts greater than 3%, no greater than 2%, or no greater than 1% by weight.
The alloy may include chromium (e.g., in a concentration of about 20% by weight), and nickel in a concentration of 5-15% by weight (e.g., about 10% by weight), as well as small quantities of manganese (e.g., in a concentration of 0-5% by weight), iron (e.g., in a concentration of 0-5% by weight), as well as other trace elements as noted, e.g., in a concentration of 1% maximum, 0.5% maximum, 0.3% maximum, 0.2% maximum, 0.1% maximum, 0.05% maximum, or 0.01% maximum. Exemplary trace elements may include silicon (e.g., up to about 0.04%), phosphorus (up to about 0.04%), sulfur (up to about 0.03%) and carbon (e.g. 0.05 to 0.15% by weight). Other trace elements typically present in an L-605 alloy (e.g., beryllium, boron) may be absent, or at least present at lower concentration than the L-605 standard permits.
In an embodiment, the alloy may include a small amount (e.g., less than 0.5%, or less than 0.1% volume fraction) of residual precipitate inclusions, where such inclusions may include tungsten (e.g., Co3W). The occurrence of such inclusions is described in applicant's U.S. Patent Application No. 63/350,106, filed Jun. 8, 2022 and entitled PROCESSING OF COBALT-TUNGSTEN ALLOYS, which is herein incorporated by reference in its entirety.
The particles of any such secondary precipitate inclusion phase may have a maximum or even average particle size of less than 5 μm, less than 4 μm, less than 3 μm, less than 2 μm, or less than 1 μm. Any such secondary precipitate inclusion phase may be finely dispersed, e.g., with a maximum or average particle size that may be less than 10%, less than 5%, less than 3%, less than 2%, or less than 1% of the wall thickness of a stent wall (e.g., about 100 μm). For example, where wall thickness may be from 50 to 100 μm, or from 75 to 100 μm, maximum or even average particle size of any finely dispersed secondary precipitate inclusion phase may be less than 10%, less than 5%, less than 3%, less than 2%, or less than 1% that of the wall thickness (e.g., 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or even 1 μm or less) so that the presence of any such precipitate inclusion has a minimal impact on desired mechanical properties. As described in applicant's U.S. Patent Application No. 63/350,106, the presence of such precipitate inclusions can be minimized if not entirely eliminated by heating the solid alloy to about 1250° C., for about 30 minutes followed by rapid quenching. Such may occur prior to electropolishing.
It is possible that the present methods may prove useful in electrochemical mass removal and electropolishing of similar alloys, e.g., including those 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. For example, in addition to or alternative to the presence of platinum in the contemplated alloys, other noble metal elements that may behave similarly include platinum group metals other than platinum, such as palladium, rhodium, ruthenium, iridium and/or osmium. The methods described herein may prove useful in electrochemical mass removal and electropolishing of such similar alloys including a platinum group metal, and such is within the contemplated scope of the present disclosure. In any case, the presently described methods have been found to surprisingly result in effective mass removal and electropolishing of particular cobalt-chromium-platinum-tungsten-nickel alloys, even where methods for mass removal and electropolishing of similar appearing alloys (e.g., L-605) were unsuccessful.
The phrase “substantially free” as used herein may mean that if present, such a constituent is present in the alloy in an amount of 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%, less than 0.01%, less than 0.001%, or in some embodiments, 0% by weight.
Features from any of the disclosed embodiments may be used in combination with one another, without limitation. For example, any of the compositional limitations described with respect to one embodiment may be present in any of the other described embodiments. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.
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.
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 Co—Cr 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 Co—Cr 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.
Electrochemical mass removal and electropolishing are unpredictable chemical arts, and it was found that such Co—Pt—Cr—Ni—W 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.
While described in the context of Co—Pt—Cr—Ni—W 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.
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 H2SO4, HCl, and H3PO4, 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.
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 H2SO4, HCl, and H3PO4, 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.
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.
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.
The radiopaque stent of the present disclosure comprises a main body, one embodiment of which is illustrated generally at 10 in
The radiopaque Co—Cr—W 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.
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 H2SO4, HCl, and H3PO4, 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.
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.
One embodiment of the radiopaque Co—Pt—Cr—Ni—W 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.
According to a further embodiment, the radiopaque Co—Pt—Cr—Ni—W 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.
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).
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 Co—Cr at concentrations over about 18% by weight.
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.
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.
The low profile of the Co—Pt—Cr—Ni—W 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 Co—Pt—Cr—Ni—W 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 Co—Pt—Cr—Ni—W 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).
The composition of L-605 is as follows. Values may vary somewhat (e.g., ±1 percentage point).
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/cm3. 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.
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.
Exemplary alloy compositions that may be electrochemically processed using the methods as described herein are shown below.
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.
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.
One type of radiopaque stent design embodiment is a high precision patterned cylindrical device. An example of such is illustrated generally at 10 in
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
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.
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
The stent 10 serves to hold open the artery 15 after the catheter 11 is withdrawn, as illustrated in
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 Co—Pt—Cr—Ni—W alloy described herein, to remove portions of the tubing in a desired pattern for the stent, leaving relatively untouched the portions of the radiopaque Co—Pt—Cr—Ni—W 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.
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 μm). 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.
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.
The tubes are made of a Co—Pt—Cr—Ni—W 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.
In other embodiments, the radiopaque Co—Pt—Cr—Ni—W alloy stent of the present disclosure is fabricated of radiopaque Co—Pt—Cr—Ni—W alloy wire elements. In another embodiment, the stent is made of a radiopaque Co—Pt—Cr—Ni—W alloy flat stock. In another embodiment, the stent is made of radiopaque Co—Pt—Cr—Ni—W alloy materials using near-net shape processing such as metal injection molding.
When expanded, the stent may cover about 10-45% of an arterial wall surface area. The radiopaque Co—Pt—Cr—Ni—W alloy stent of the present disclosure can withstand at least about 35% tensile deformation before failure.
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.
A schematic of an exemplary electrochemical mass removal and electropolishing apparatus 100 suitable for practicing the embodiments described herein is illustrated in
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.
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.
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.
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.
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,
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.
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.
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.
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.
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.
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.
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.
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).
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.
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).
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.
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 H2SO4, HCl, and H3PO4, 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.
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.
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.
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.
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.
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.
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.
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 H3PO4 and/or H2SO4) might offer improvement. This is consistent with what would be suggested in US2014/0277392, which teaches a ratio of H2SO4, HCl, and H3PO4, where the H3PO4 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 H2SO4, 1 part H3PO4, 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.
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.
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.
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.
Use of the same acid electrolyte as used in standard L-605 mass removal shows that boundary layer formation does not occur—the 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.
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.
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 H2SO4, HCl, and H3PO4, in a volumetric ratio of 6:1:1, respectively, with differing volumes of ethylene glycol, to change the viscosity of the resulting electrolyte solution.
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.
The phased settings that achieved the best finish were as shown below in Tables 7-8.
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.
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.
In each case, the voltage was allowed to float. The voltage control settings on the available equipment were attempted but did not function.
Additional testing was performed using electrolyte solutions having a 5:9:5 volumetric ratio (as prepared) of H2SO4:H3PO4:HCl, with differing amounts of ethylene glycol. The electrolytes tested included the below formulations.
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.
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.
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.
As used herein, the term “between” includes any referenced endpoints. For example, “between 2 and 10” includes both 2 and 10.
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.
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.
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.
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63/479,307 (WN 17066.147) filed Jan. 10, 2023, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63479307 | Jan 2023 | US |
