Shape memory alloy expansion of single step

Abstract

To provide a Nitinol medical equipment formation method capable of overcoming defects of the prior art.SOLUTION: In a state where no strain is imparted or minimum strain is imparted, Nitinol is subjected to a shape fixation temperature. Then the shape of Nitinol is substantially deformed during a time when it has a high temperature. After the deformation, Nitinol is kept at the high temperature for a prescribed time so that the shape of the material is fixed. Then Nitinol is returned approximately to a room temperature 20°C by, for example, water-quenching or air cooling.SELECTED DRAWING: Figure 2

Description

[Background technology]

[0001] It is well known to employ a variety of percutaneously delivered intravascular endoprostheses to treat various body vascular diseases. These types of endoprostheses are commonly referred to as stents. Stents are generally tubular devices formed from biocompatible materials, such as Nitinol. It is commonly known to fabricate stents from Nitinol tubes cut by methods such as laser cutting, water jet cutting, electrochemical machining, and chemical polishing. Nitinol is considered a shape memory alloy (SMA). Nitinol also has a shape lock temperature. The shape lock temperature is defined as any temperature within a temperature range at which a shape memory alloy (SMA) article, when exposed to that temperature in a constrained shape for a predetermined period of time, will substantially retain that constrained shape when the article is subsequently released from the constraint.

[0002] Nitinol tubing is expensive to manufacture. The larger the diameter of the Nitinol tube, the more expensive it becomes. As a result of the cost constraints of large diameter Nitinol tubing, larger diameter Nitinol tubes (and / or Nitinol stents) are made by cutting patterns (e.g., stent patterns) into small diameter Nitinol tubes and then incrementally expanding and shape-setting these tubes.

[0003] One common method of Nitinol shape setting involves deforming and constraining Nitinol into a desired shape at or below room temperature (usually around 20°C). The Nitinol is then exposed to high temperatures (usually around 500°C), for example in a furnace, while being constrained in the desired shape for a predetermined time (usually around 5-20 minutes). The Nitinol is then cooled to room temperature by water quenching or allowing it to air cool. This shape setting process imparts a new shape to the Nitinol. The new shape is the result of specifically pre-deforming and constraining the cut tube.

[0004] When expanding pre-cut Nitinol tubes, a series of incremental expansion and shape-setting steps is typically used. Traditional Nitinol stent device manufacturing is described by Poncin et al. (SMST-2000 Conference Proceedings, pp 477-486), which states that "the device is expanded to its final size by a series of incremental shape-setting steps involving heat treatment." Using a series of incremental expansion steps reduces the occurrence of fracture or cracking of the pre-cut Nitinol tubes during shape-setting.

[0005] In one example, a stent pattern can be laser cut into a Nitinol tube with an outer diameter of approximately 4 mm. To expand the 4 mm cut tube into a 24 mm cut tube, a series of incremental expansion steps can be employed. For example, the cut tube can be expanded from a 4 mm diameter to an 8 mm diameter and then shape set. The cut tube can then be expanded from an 8 mm diameter to a 12 mm diameter and then shape set, and so on until the desired 24 mm diameter cut tube is obtained.

[0006] To avoid stent fracture during the shape setting process, it is common to use a series of expansion steps in forming the stent. The above example used five expansion steps to achieve the desired stent diameter of 24 mm. Omitting even one of these expansion steps, e.g., the expansion and shape setting step from 4 mm to 12 mm, can result in the stent fracturing during shape setting. This process of incrementally forming Nitinol through a series of shape setting steps is costly and time consuming.

[0007] It is also common practice in the art to cool Nitinol stents to form thermally induced martensite prior to expansion of the Nitinol tube. The Nitinol tube, which is primarily austenitic at room temperature, is easier to deform and expand diametrically if it is first cooled to form thermally induced martensite. Because martensitic Nitinol is easier to deform than austenitic Nitinol, it is believed that forming thermally induced martensite prior to expansion of the Nitinol tube minimizes crack formation in the stent. Despite this thermal induction of martensite prior to expansion of the Nitinol tube, crack formation during expansion of the Nitinol tube is a problem. Thermal induction of martensite prior to expansion of the Nitinol tube does not eliminate the need for incremental expansion steps to diametrically expand and shape set the Nitinol tube. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, there is a need to have a method for forming Nitinol medical devices that overcomes the shortcomings of the prior art. The present invention provides such a solution. [Means for solving the problem]

[0009] According to the present invention, a method of forming Nitinol is provided. In one embodiment, Nitinol is exposed to a shape setting temperature of at least 300°C to about 650°C while in an unstrained or minimally strained state. The shape of the Nitinol is then substantially deformed at this elevated temperature. After deformation, the Nitinol is held at this elevated temperature while constrained in the desired shape for a period of time to shape set the material. In another embodiment, the Nitinol may be deformed one or more times at this elevated temperature. The Nitinol is then returned to about room temperature (about 20°C) while still constrained, for example by water quenching or air cooling.

[0010] Accordingly, one embodiment of the invention includes a method of forming a shape memory alloy (SMA) article, the method comprising providing an SMA article having an initial shape, wherein the SMA has a shape setting temperature, heating the SMA article to about the shape setting temperature, deforming the SMA article to a final shape while the SMA article is at about its shape setting temperature, and cooling the SMA article under restraint, thereby substantially retaining the final shape. In one embodiment, after deforming the SMA article while the SMA article is at about its shape setting temperature, the deformed SMA article is allowed to remain at about its shape setting temperature. In another embodiment, the shape setting temperature is between about 300°C and about 650°C. In another embodiment, the SMA is Nitinol. In another embodiment, deforming the SMA article to the final shape is achieved by application of an internal force. In another embodiment, deforming the SMA article to the final shape is achieved by application of an external force. In another embodiment, transforming the SMA article into the final shape is accomplished by using a tapered mandrel. In another embodiment, the SMA article is formed into a medical device. In another embodiment, the medical device is an implantable medical device. In another embodiment, the implantable medical device is selected from the group consisting of a stent, a cardiac occluder, a valve, and an intraluminal filter. In another embodiment, the SMA initial shape is formed by machining. In another embodiment, the machining includes laser cutting, water jet cutting, electrical discharge machining, and / or chemical etching.

[0011] Another embodiment of the invention includes a method of forming a stent comprising providing a machined shape memory alloy (SMA) tube, the machined SMA tube having a stent pattern, a first (small) diameter, and a shape-setting temperature, heating the machined SMA tube to about the shape-setting temperature, deforming the machined SMA tube to a second (large) diameter while the machined SMA tube is at about its shape-setting temperature, and cooling the SMA article under restraint, thereby substantially retaining the second diameter. In one embodiment, the machining comprises laser cutting, water jet cutting, electrical discharge machining, and / or chemical etching. In another embodiment, the stent pattern comprises a sinusoidal shape, a diamond shape, a U-shape, a V-shape, or an ovaloid shape. In another embodiment, the SMA tube has a circular cross-section. In another embodiment, after deforming the SMA tube while the SMA tube is at about the shape-setting temperature, the deformed SMA tube is maintained at about the shape-setting temperature. In another embodiment, the shape setting temperature is about 300°C to about 650°C. In another embodiment, deforming the SMA tube into the second shape is accomplished by applying an internal force. In another embodiment, deforming the SMA tube into the second shape is accomplished by applying an external force. In another embodiment, deforming the SMA tube into the second shape is accomplished by using a tapered mandrel. In another embodiment, the ratio of the second (large) diameter shape to the first (small) diameter shape is greater than about 1.25:1. In another embodiment, the ratio of the second (large) diameter shape to the first (small) diameter shape is greater than about 1.5:1. In another embodiment, the ratio of the second (large) diameter shape to the first (small) diameter shape is greater than about 2:1. In another embodiment, the ratio of the second (large) diameter shape to the first (small) diameter shape is greater than about 3:1.In another embodiment, the ratio of said second (larger) diameter shape to said first (smaller) diameter shape is greater than about 4:1.

[0012] In another embodiment, the invention includes a medical device including a shape memory alloy (SMA) article adapted to transition between a first state, a second state, and a third state, the SMA having a shape-set temperature, the article having a first circumferential perimeter in the first state, the article having a plurality of annular perimeters in the second state, the article having a third annular perimeter in the third state, each annular perimeter in the second state being larger than the annular perimeter in the first state and smaller than the annular perimeter in the third state, and the shape memory alloy (SMA) article being maintained at the shape-set temperature while transitioning between the first state, the second state, and the third state.

[0013] Another embodiment of the invention is an apparatus for deforming an SMA article, the apparatus comprising an elongated slotted tube, (i) the tube having a longitudinal axis and a first outer periphery, (ii) the tube having a length, a lumen therethrough and a wall, (iii) the lumen defining a first inner circumference, (iv) the tube having at least two slots therethrough, (v) the slots being oriented essentially parallel to the longitudinal axis of the tube, and (vi) the slots extending partially along the length of the tube, and an expandable mandrel. The apparatus includes a mandrel, (i) the mandrel includes a first portion having an essentially constant first circumference, (ii) the mandrel includes a second tapered portion, (iii) the second tapered portion has a varying circumference that transitions from the first circumference of the mandrel to a larger second circumference, and (iv) the circumference of the first portion of the mandrel is sized to be inserted within a first inner circumference of the lumen of the slotted elongated tube, and a shape memory alloy article surrounding at least a portion of the slotted elongated tube. In one embodiment, the SMA is Nitinol. In another embodiment, the SMA article is a medical device. In another embodiment, the medical device is selected from the group consisting of a stent, a cardiac occluder, a valve, and an intraluminal filter.

[0014] Another embodiment of the invention is an apparatus for deforming an SMA article, the apparatus comprising: an elongated slotted tube, (i) the tube having a longitudinal axis and a first outer circumference, (ii) the tube having a length, a lumen therethrough and a wall, (iii) the lumen defining a first inner circumference, (iv) the tube having at least two slots therethrough, (v) the slots being oriented essentially parallel to the longitudinal axis of the tube, and (vi) the slots extending partially along the length of the tube; the apparatus comprising: an expansion mandrel, (i) the mandrel being The present invention includes an apparatus comprising: (i) a first portion having an essentially constant first circumference, (ii) the mandrel includes a second tapered portion, (iii) the second tapered portion having a varying circumference transitioning from the first circumference of the mandrel to a larger second circumference, and (iv) a circumference of the first portion of the mandrel sized to be inserted within a first inner circumference of the lumen of the slotted elongated tube, the slotted elongated tube surrounding at least a portion of the expansion mandrel, the apparatus comprising a shape memory alloy article surrounding at least a portion of the slotted elongated tube. In one embodiment, the slotted elongated tube surrounding at least a portion of the first portion of the expansion mandrel. In another embodiment, the slotted elongated tube surrounding at least a portion of the second tapered portion of the expansion mandrel. In another embodiment, the expansion mandrel further includes a third portion having an essentially constant second circumference. In another embodiment, the slotted elongate tube surrounds at least a portion of the expansion mandrel third portion.

[0015] Another embodiment of the invention is an apparatus for deforming a shape memory alloy (SMA) article, comprising an elongated slotted tube, (i) the tube having a longitudinal axis and a first outer periphery, (ii) the tube having a length, a lumen therethrough and a wall, (iii) the lumen defining a first inner circumference, (iv) the tube having at least two slots therethrough, (v) the slots being oriented essentially parallel to the longitudinal axis of the tube, (vi) the slots extending partially along the length of the tube, (vii) the tube having a first portion having an essentially constant first circumference, and (viii) the tube having a first portion having a first circumference that is substantially constant, and (viii) the tube having a second portion having a second circumference that is constant, and (viii) the tube having a second portion having a second circumference that is constant, and (viii) the tube having a second portion having a second circumference that is constant, and (viii) the tube having a second portion having a second circumference that is constant, and (viii) the tube having a second portion having a second circumference that is constant, and (viii) the tube having a third portion having a second circumference that is constant, and (viii) the tube having a fourth portion having a third circumference that is constant, and (viii) the tube having a fourth portion having a fourth ... fifth portion having a fourth circumference that is constant, and (viii) the the tube having a second tapered portion, (ix) the second tapered portion having a varying circumference transitioning from a first circumference of the tube to a larger second circumference; a translation instrument, (i) the translation instrument including a rod sized to extend and slide through a through lumen of the slotted elongate tube, and (ii) the rod having at least two fins sized to extend and slide through the slots through a wall of the slotted elongate tube; and a shape memory alloy article surrounding at least a portion of the slotted elongate tube. Effect of the Invention

[0016] Thus, the method of the present invention allows a Nitinol tube (eg, a stent) to be expanded to a significantly larger diameter (eg, six times or more) in a single processing step.

[0017] Exemplary embodiments of the invention are described in connection with the accompanying drawings, in which, where necessary, like numerals indicate like elements and are offset by 100. The accompanying drawings are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the specification, serve to explain the principles of the invention. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a time / temperature graph illustrating a multi-step thermoforming process currently known in the art.

[0019] [Diagram 2] FIG. 2 is a time / temperature graph illustrating a single step thermoforming process according to the present invention.

[0020] [Diagram 3] 3A and 3B are perspective views showing the cut patterned tube before and after expansion.

[0021] [Figure 4] FIG. 4 is a perspective view of the expansion fixture of the present invention showing the slotted mandrel, expansion die and pulling rod.

[0022] [Figure 5A] FIG. 5A is a side view of the stent expansion mandrel assembly of the present invention showing the slotted mandrel, expansion die, pulling rod and stent.

[0023] [Figure 5B] FIG. 5B is a side view of the stent expansion mandrel assembly of the present invention showing the slotted mandrel, expansion die, pulling rod and stent.

[0024] [Figure 5C] FIG. 5C is a side view of the stent expansion mandrel assembly of the present invention showing the slotted mandrel, expansion die, pulling rod and partially expanded stent.

[0025] [Figure 5D] FIG. 5D is a side view of the stent expansion mandrel assembly of the present invention showing the slotted mandrel, expansion die, pulling rod and fully expanded stent.

[0026] [Figure 5E] FIG. 5E is a side view of the stent expansion mandrel assembly of the present invention showing the slotted mandrel and fully expanded stent.

[0027] [Figure 6A] FIG. 6A is a perspective view of a slotted tube and an unexpanded stent of the present invention.

[0028] [Figure 6B] FIG. 6B is a perspective view of a tapered mandrel of the present invention.

[0029] [Figure 6C] FIG. 6C is a perspective view of the stent expansion mandrel assembly of the present invention showing the slotted tube, tapered mandrel and unexpanded stent.

[0030] [Figure 6D] FIG. 6D is a perspective view of the stent expansion mandrel assembly of the present invention showing the slotted tube, tapered mandrel and expanded stent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] As currently known in the art, Nitinol tubing of various diameters and wall thicknesses can be cut to form a desired pattern, e.g., a stent pattern. The cut tube can be placed on an expansion fixture and expanded approximately 20% while at ambient temperature. The cut tube and expansion fixture can then be heated to an elevated temperature, and after a suitable dwell time, the cut tube and fixture can be quenched to return the cut tube to ambient temperature. This process can be repeated, with each cycle expanding the tube an additional approximately 20% resulting in a diameter of the desired diameter (i.e., 100% expansion).

[0032] FIG. 1 shows a time / temperature graph illustrating a typical expansion process commonly known in the art. In this example, a five-step expansion process is shown, with each expansion occurring at approximately ambient temperature (about 20° C.). Each of the five expansion steps expands the cut tube by about 20% of its expanded diameter. After each expansion, the cut tube and expansion fixture are heated to about 500° C., and after a suitable dwell, the cut tube and expansion fixture are water quenched and the cut tube and expansion fixture are returned to ambient temperature. As shown, the process is repeated four more times, resulting in the desired diameter (total expansion of about 100%).

[0033] FIG. 2 is a graph (having the same axes as FIG. 1) illustrating the process of expanding a pre-cut tube to a desired diameter (i.e., about 100% expansion) in a single expansion step. As shown in FIG. 2, the pre-cut tube is placed in an expansion fixture. The pre-cut tube and expansion fixture can then be heated to an elevated temperature, and at this elevated temperature, the pre-cut tube can be expanded about 100% in a single expansion step by activating the expansion fixture. In another embodiment, the pre-cut tube can be expanded about 200%, about 300%, about 400%, and / or about 500% by activating the expansion fixture. By comparing FIG. 1 to FIG. 2, it is clear that the method taught herein reduces the number of steps, and therefore the time, to expand a Nitinol tube.

[0034] FIG. 3A is a partial perspective view of an exemplary pre-cut tube 300a having an initial small diameter 302. The pre-cut tube 300a has a wavy shape including peaks 304 and valleys 306, typical of an implantable stent. FIG. 3B is a partial perspective view of an expanded pre-cut tube 300b after it has been expanded to a large diameter 308. The large diameter 308 is approximately 100% larger than the initial small diameter 302. The tube 300a can be cut to have any desired pattern. For example, the tube 300a can be cut to form individual rings, interlocking rings, open and / or closed cells, or shapes such as sinusoidal, diamond, U-shaped, V-shaped, or ovoid, or any other pattern tailored to a given application. The tube 300a can include Nitinol or any other similar metal having a shape-locking temperature range. Nitinol refers to a family of alloys including binary nickel-titanium binary shape memory alloys, as well as nickel-titanium based alloys with ternary and quaternary additions of alloying elements (such as, but not limited to, iron, niobium, chromium, copper, cobalt, vanadium, platinum, and hafnium). Shape memory alloys include Nitinol alloys as well as other alloys capable of reversible crystalline phase change (such as, but not limited to, AgCd, AuCd, CuAlZn, CuAlNi, CuAlBe, CuSn, NiAl, FePt, FePd, MnCu, and FeMnSi alloy systems).

[0035] The tube 300a may have a diameter ranging from about 0.5 mm to about 100 mm, with a preferred range being from about 2 mm to about 40 mm. The tube 300a may have a wall thickness ranging from about 0.05 mm to about 10 mm, with a preferred range being from about 0.1 mm to about 0.5 mm. The length of the tube 300a may range from about 1 mm to about 250 mm. The length of the tube 300a may be formed according to any particular application.

[0036] 4 shows a perspective view of at least one expansion fixture 400. In this example, the expansion fixture 400 includes a tapered, slotted tubular mandrel 402 fabricated from a high temperature metal, such as Inconel, stainless steel, or other suitable material. The slotted mandrel 402 has a large diameter section 404, an intermediate tapered section 406, a small diameter section 408, and a series of longitudinal slots 410. The longitudinal slots 410 are cut through the mandrel wall and extend through the small diameter and tapered sections (408 and 406) of the slotted mandrel. The longitudinal slots 410 are cut through the mandrel wall and extend only partially along the large diameter section 404 as shown in FIG. 4. In any configuration, the longitudinal slots can form a helix. The intermediate tapered section can have a varying taper angle or a sharp section instead of a constant taper angle, if desired.

[0037] The expansion fixture 400 further includes an expansion die 412 having a series of fins 414 as shown in Figure 4. The fins 414 of the expansion die 412 engage with the slots 410 of the slotted mandrel 402 to allow the fins 414 of the expansion die to slide through the longitudinal slots 410 of the slotted mandrel 402 along a longitudinal axis indicated by directional arrow 416.

[0038] 4, the expansion die 412 is coupled to a pull rod 418. The pull rod 418 extends through a central bore of the tubular slotted mandrel 402 and out of a collar portion 422 of the slotted mandrel 402. As the pull rod 418 is pulled along a longitudinal axis indicated by directional arrows 416, 420, the expansion die 412 is forced to slide over the small diameter portion 408, intermediate tapered portion 406, and large diameter portion 404 of the slotted mandrel 402.

[0039] The collar portion 422 of the slotted mandrel 402 is configured to secure the slotted mandrel to a heat source (not shown). The slotted mandrel 402 and the expansion die 412 are positioned within the heat source. The heat source is a tension rod. of 418 End 424 (opposite side of the extension die) is configured to allow it to protrude from the heat source.

[0040] Books Another embodiment of the invention is an apparatus for deforming a shape memory alloy (SMA) article, the apparatus comprising: an elongated slotted tube, (i) the tube having a longitudinal axis and a first outer periphery, (ii) the tube having a length, a lumen therethrough and a wall, (iii) the lumen defining a first inner circumference, (iv) the tube having at least two slots therethrough, (v) the slots being oriented essentially parallel to the longitudinal axis of the tube, and (vi) the slots extending partially along the length of the tube; The apparatus includes an expansion mandrel, (i) the mandrel includes a first portion having an essentially constant first circumference, (ii) the mandrel includes a second tapered portion, (iii) the second tapered portion has a varying circumference that transitions from the first circumference of the mandrel to a larger second circumference, and (iv) the circumference of the first portion of the mandrel is sized to be inserted within a first inner circumference of the lumen of the slotted elongated tube, and a shape memory alloy article surrounding at least a portion of the slotted elongated tube. In one embodiment, the SMA is Nitinol. In another embodiment, the SMA article is a medical device. In another embodiment, the medical device is selected from the group consisting of a stent, a cardiac occluder, and an intraluminal filter.

[0041] Another embodiment of the invention is an apparatus for deforming a shape memory alloy (SMA) article, the apparatus comprising: an elongated slotted tube, (i) the tube having a longitudinal axis and a first outer periphery, (ii) the tube having a length, a lumen therethrough and a wall, (iii) the lumen defining a first inner circumference, (iv) the tube having at least two slots therethrough, (v) the slots being oriented essentially parallel to the longitudinal axis of the tube, and (vi) the slots extending partially along the length of the tube; the apparatus comprising an expansion mandrel, (i) a slotted tube having a first outer periphery and a second outer periphery; (ii) a slotted tube having a first inner periphery and a second outer periphery; (iii) a slotted tube having a first inner periphery and a second outer periphery; (iv) a slotted tube having at least two slots therethrough; (v) the slots being oriented essentially parallel to the longitudinal axis of the tube; and (vi) the slots extending partially along the length of the tube; The present invention also includes an apparatus comprising: (i) a mandrel including a first portion having an essentially constant first circumference; (ii) the mandrel including a second tapered portion; (iii) the second tapered portion having a varying circumference transitioning from the first circumference of the mandrel to a larger second circumference; and (iv) a circumference of the first portion of the mandrel sized to be inserted within a first inner circumference of the lumen of the slotted elongated tube, the slotted elongated tube surrounding at least a portion of the expansion mandrel; and the apparatus comprising a shape memory alloy article surrounding at least a portion of the slotted elongated tube. In one embodiment, the slotted elongated tube surrounding at least a portion of the first portion of the expansion mandrel. In another embodiment, the slotted elongated tube surrounding at least a portion of the second tapered portion of the expansion mandrel. In another embodiment, the expansion mandrel further includes a third portion having an essentially constant second circumference. In another embodiment, the slotted elongate tube surrounds at least a portion of the expansion mandrel third portion.

[0042] Another embodiment of the invention is an apparatus for deforming a shape memory alloy (SMA) article, the apparatus comprising an elongated slotted tube, (i) the tube having a longitudinal axis and a first outer periphery, (ii) the tube having a length, a lumen therethrough and a wall, (iii) the lumen defining a first inner circumference, (iv) the tube having at least two slots therethrough, (v) the slots being oriented essentially parallel to the longitudinal axis of the tube, (vi) the slots extending partially along the length of the tube, (vii) the tube having a first portion having an essentially constant first circumference, and (viii) the first portion having a first circumference. The device includes: the tube having a second tapered portion, (ix) the second tapered portion having a varying circumference transitioning from a first circumference of the tube to a larger second circumference; a translation instrument, (i) the translation instrument including a rod sized to extend and slide through a through lumen of the slotted elongate tube, and (ii) the rod having at least two fins sized to extend and slide through the slots through a wall of the slotted elongate tube; and a SMA article surrounding at least a portion of the slotted elongate tube.

[0043] Any suitable heat source can be used to heat the extension fixture 400, including a flowing bath, a salt bath, a hot liquid, a hot gas, radiative heating, induction heating, convection heating, electrical resistance heating, radio frequency heating, conductive heating, or a combination of different energy sources.

[0044] Accordingly, one embodiment of the present invention is a method of expanding cut tubes comprising the steps of: cutting a metal tube to form a desired cut pattern; placing the cut metal tube over a smaller diameter portion of a slotted tapered mandrel; inserting a pulling rod having an expansion die attached thereto into a central bore of the slotted tapered mandrel; engaging a series of fins (integral with the expansion die) within the slots of the slotted tapered mandrel; placing the cut tubes, the slotted tapered mandrel and the expansion die into a heat source such that an end of the pulling rod extends outside of the heat source; and the method includes the steps of heating a slotted tapered mandrel and the expansion die to an elevated temperature (a shape-setting temperature); and translating the pulling rod (while maintaining the shape-setting temperatures of the cut tube, the slotted tapered mandrel, and the expansion die) to force the expansion die to slide over the smaller, tapered, and larger diameter sections of the slotted tapered mandrel, where as the pulling rod is translated, fins of the expansion die engage the cut SMA tube and force the cut SMA tube to slide over the smaller, tapered, and larger diameter sections of the slotted tapered mandrel.

[0045] One expansion process of a cut SMA tube according to the present invention is shown in Figures 5A-5E. In Figure 5A, an expansion fixture 500 is shown. Expansion fixture 500 includes a tapered, slotted tubular mandrel 502. Slotted mandrel 502 has a large diameter section 504, an intermediate tapered section 506, a small diameter section 508, and a series of longitudinal slots 510. The longitudinal slots 510 are cut through the mandrel wall and extend through the small diameter and tapered sections (508 and 506) of the slotted mandrel. The longitudinal slots 510 are cut through the mandrel wall and extend only partially along the large diameter section 504 as shown in Figure 5A.

[0046] The cut tube 524 a having an initial smaller diameter is placed over the smaller diameter portion 508 of the slotted mandrel 502 .

[0047] An expansion die 512 having a series of fins (414 in FIG. 4) formed to engage slots 510 in the slotted mandrel 502 is coupled to a pull rod 518. The pull rod 518 extends through a central bore of the tubular slotted mandrel 502 and out the end of the slotted mandrel opposite the expansion die.

[0048] As shown in FIG. 5B, the pull rod 518 is translated in the direction indicated by arrow 520 to advance the expansion die 512 and allow the fins (414 in FIG. 4) of the expansion die to engage with the slots 510 of the slotted mandrel 502.

[0049] The cut tubing extension fixture is then placed over the heating chamber so that the collar portion 522 and protruding pull rod 518 are outside the heated chamber (directional arrow 526 5), while the remainder of the slotted mandrel 502, the expansion die 512, and the cut tubes 524a are positioned in the heated region of the heating chamber (indicated by directional arrow 525 The temperature of the heating chamber is then raised to the desired temperature. If a salt bath or similar heat transfer medium is used, the medium can be preheated or fully heated to the desired elevated temperature.

[0050] As shown in FIG. 5C, after proper residence within the heated chamber, the pulling rod 518 is further advanced along direction 520 such that the expansion die 512 forces the cut tube 524b over the tapered portion 506 of the slotted mandrel 502.

[0051] 5D, the pulling rod 518 is further advanced along direction 520 such that the expansion die 512 forces the cut tube 524c over the large diameter portion 504 of the slotted mandrel 502. The translational motion of the pulling rod 518 can include continuous, intermittent, or variable speed motion.

[0052] The expansion fixture 500 with the fully expanded cut tube 524c is then removed from the heating chamber. The pulling rod 518 and expansion die 512 are then attached to a slotted mandrel. 502 The slotted mandrel 502 and fully expanded cut tubes 524c are then quenched in a several temperature water bath. After reaching ambient temperature, the fully expanded cut tubes 524c can be removed from the slotted mandrel 502.

[0053] 5A-5E depict short lengths of tubing, any length of tubing can be expanded using the above process. The large diameter portions 404, 504 of the slotted mandrels 402, 502 can be any size to accommodate any length of tubing.

[0054] 5A-5E is one method of using an internal force (a force inward relative to the tube being expanded) to expand the SMA tube, but other methods can be used. These include an expansion mandrel that expands the tube over the mandrel.

[0055] In another embodiment, expansion of the cut SMA tubing is accomplished by applying an external force that pulls the tube apart. Hooks or clamps that grip specific areas of the tube can pull the tube apart, thereby expanding the tube.

[0056] While specific embodiments of the present invention have been shown and described herein, the present invention should not be limited to such illustrations and descriptions. Changes and modifications may be incorporated and embodied as part of the present invention within the scope of the following claims. The following examples are provided to further illustrate the present invention.

[0057] example Example 1: Loading and expansion of pre-cut Nitinol tubing on a slotted mandrel The nitinol stent ring 524a shown in Figures 5A and 5B was obtained. The stent ring 524a was laser cut from a nitinol tube with an inner diameter (ID) of about 4 mm and a wall thickness of about 0.5 mm. The length of the stent ring 524a was about 10 mm.

[0058] A tapered slotted mandrel 402 was custom fabricated from a suitable high temperature steel as shown in Figure 4. Slotted Mandrel 402 Large diameter portion 404 was about 26 mm. The minor diameter of the slotted mandrel 402 was about 8 mm. The length of the slotted mandrel 402 was about 11 cm. An expansion die 412 was custom fabricated from a suitable high temperature steel.

[0059] The expansion die 412 was designed such that the fins 414 of the die engage with the slots 410 of the slotted mandrel 402 allowing the expansion die 412 to slide through the slotted mandrel 402 .

[0060] The expansion die 142 is attached, for example, by laser welding, to a pulling rod 418. The pulling rod 418 is approximately 2 mm in diameter, approximately 60 cm in length, and is fabricated from a suitable high temperature steel. A fluidized bath (Techne Fluidized Bath Model FB-08) was obtained to be used for the heat treatment section.

[0061] As shown in FIG. 5A, the stent ring 524a is inserted into the small diameter slotted mandrel 502. portion508. To load the stent ring 524a with an ID of about 4 mm onto the smaller diameter end 508 of the slotted mandrel 502, the stent ring 524a was first expanded to about 8 mm (at room temperature) using a tapered mandrel with a diameter of about 4 mm on one end and a diameter of about 8 mm on the opposite end. At this point, the stent is minimally constrained (or substantially unconstrained). The about 8 mm end of the tapered mandrel was then abutted against the smaller diameter end 508 of the slotted mandrel 502, and the stent ring 524a was transferred from the tapered mandrel to the slotted mandrel 502 at room temperature. A pulling rod 518 with an expansion die 512 attached was inserted into the slotted mandrel, as shown in FIG. 5A. The fins 414 (FIG. 4) of the expansion die 512 were engaged with the slots 510 of the slotted mandrel 502, as shown in FIG. 5B.

[0062] The assembly consisting of slotted mandrel 502, stent ring 524a, expansion die 512, and pulling rod 518 was then immersed in a fluidized bath preheated to a temperature of about 550° C. and allowed to dwell for about 3 minutes. After about 3 minutes, pulling rod 518 was raised from the position shown in FIG. 5B to the position shown in FIG. 5D. It took about 2 seconds to raise pulling rod 518 from the position shown in FIG. 5B to the position shown in FIG. 5D. As an upward force is applied to pulling rod 518, fins 414 (FIG. 4) of attached expansion die 512 exert a force on stent ring 524b, pulling it up along slotted mandrel 502 as shown in FIG. 5C. The orientation of slots 510 and fins 414 (FIG. 4) also helps maintain a uniform diametric expansion of stent ring 524c as shown in FIG. 5D. After a residence time of about 15 minutes in the preheated fluidized bath, the assembly consisting of slotted mandrel 502, expanded stent ring 524c, expansion die 512, and pulling rod 518 was then removed from the fluidized bath and water quenched. The pulling rod 518 and attached expansion die 512 were then removed from the slotted mandrel 502. The expanded nitinol stent ring 524c and slotted mandrel 502 following heat treatment and shape setting in the fluidized bath are shown in FIG. 5E. The resulting nitinol stent ring 524c was expanded and shape set to about 26 mm in diameter.

[0063] 4, it will be apparent to one skilled in the art that additional fixtures can be used to interface the slotted mandrel 402, which expands the stent, with the fluid bath. To accommodate such fixtures, a collar 422 can be formed by cutting the slotted mandrel 402. The collar 422 can be used to attach additional fixtures that allow the mandrel to be safely immersed in the heated medium of the fluid bath.

[0064] As will be apparent to one skilled in the art, various modifications can be made to the present invention. For example, the slotted mandrel 402 as shown in FIG. 4 can have four slots 410 instead of eight slots 410. Additionally, the expansion die 412 can have four fins 414 instead of eight fins 414. Additionally, the length of the slotted mandrel and the resulting taper angle can be modified. For example, the length of the slotted mandrel 402 can be increased to 20 cm instead of about 11 cm. This may reduce the force required during stent expansion.

[0065] Example 2: Expansion of pre-cut Nitinol tubing without heating 5A-5E, a nitinol stent ring 524a was loaded onto a slotted mandrel 502 using the methods and materials of Example 1. The stent ring 524a was then expanded at about room temperature (about 20° C.) by pulling the pulling rod 518 from the position shown in FIG 5B to the position shown in FIG 5D. The assembly of the slotted mandrel 502, stent ring 524c, expansion die 512, and pulling rod 518 as shown in FIG 5D was then immersed in a fluidized bath preheated to a temperature of about 550° C. and allowed to dwell for about 15 minutes.

[0066] The assembly consisting of slotted mandrel 502, stent ring 524c, expansion die 512, and pulling rod 518 was then removed from the fluidized bath and water quenched. The resulting nitinol stent ring was fractured and had complete discontinuities within the stent ring.

[0067] Example 3: Expanding pre-cut Nitinol tubing using an expandable mandrel Another extension fixture is shown in Figures 6A-6D. The slotted tube 610 shown in Figures 6A and 6C was formed from a suitable high temperature steel and was approximately 15 cm in length. The slotted tube had an inner diameter of 4.2 mm and a wall thickness of approximately 0.25 mm. The slots 604 cut in the tube and the resulting tube segments 606 were each approximately 12 cm in length.

[0068] As shown in Figure 6B, a tapered mandrel 618 was formed from a suitable high temperature steel and was approximately 40 cm in length. The large diameter section 612 was approximately 8 mm in diameter and approximately 8 cm in length. The small diameter section 616 was approximately 4 mm in diameter and approximately 28 cm in length. The tapered section 614 of the tapered mandrel 618 transitioned from approximately 8 mm in diameter to approximately 4 mm in diameter and was approximately 4 cm in length.

[0069] The Nitinol stent 624 shown in Figure 6A was obtained. The stent rings 624 were laser cut from Nitinol tubing with an inner diameter (ID) of about 4.1 mm and a wall thickness of about 0.25 mm. The length of the stent was about 60 mm. The stent 624 was loaded onto the slotted tube 610 close to the slotted end 602 of the slotted tube 610. The smaller diameter end 616 of the tapered mandrel 618 was then inserted into the slotted end 602 of the slotted tube 610.

[0070] A fluidized bath (Techne Fluidized Bath Model FB-08) was obtained for use in heat treating sections.

[0071] FIG. 6C shows an extended fixture 600. The slotted tube 610, stent 624, and tapered mandrel 618 assembly, as shown in Figure 6C, was then immersed in a fluidized bath heated to a temperature of about 550°C and allowed to dwell for about three minutes. After about three minutes, tapered mandrel 618 was pulled in the direction 620 shown in Figure 6C to the position shown in Figure 6D. It took about three seconds to pull tapered mandrel 618 from the position shown in Figure 6C to the position shown in Figure 6D.

[0072] After about 15 minutes residence in the preheated fluidized bath, the assembly consisting of the expanded slotted tube 628, expanded stent 626, and tapered mandrel 618, shown in FIG. 6D, was then removed from the fluidized bath and water quenched. Following heat treatment and shape setting, the expanded stent 626 was then removed from the expanded slotted tube 628. The resulting Nitinol stent was expanded and shape set to about 8.5 mm in diameter.

[0073] It will be apparent to one skilled in the art that additional fixtures can be used to interface the stent expansion hardware shown in Figures 6A and 6B with the fluid bath. In addition, it will be apparent to one skilled in the art that the dimensions of the hardware shown in Figures 6A and 6B can be modified to improve the interface of the stent expansion hardware with the fluid bath. For example, the length of the small diameter end 616 of the tapered mandrel 618 can be further extended, if necessary, so that it extends well above the level of the heated medium of the fluid bath. In addition, the length of the unslit end 608 of the slotted tube 610 can be further extended so that it extends well above the level of the heated medium of the fluid bath.

[0074] As will be apparent to those skilled in the art, various modifications may be made to the present invention. For example, the slotted tube 610 as shown in FIG. 6A may have eight slots 604 instead of four. Additionally, the tapered mandrel 618 may have longitudinal grooves that allow for interlocking with the segments 606 of the slotted tube 610. These grooves allow the segments to move in parallel with the tapered mandrel 618. classification As it moves to 614, it will control the expansion of segment 606.

[0075] Example 4: Expansion of pre-cut Nitinol tubing using an expandable mandrel without heat treatment A Nitinol stent 624 was loaded onto the slotted mandrel 610 using the method and materials of Example 3. The stent 624 was then expanded at about room temperature (about 20° C.) by pulling the tapered mandrel 618 in the direction shown in FIG. 6C to the position shown in FIG. 6D. The slotted tube 610, stent 624, and tapered mandrel 618 assembly as shown in FIG. 6C was then immersed in a fluidized bath preheated to a temperature of about 550° C. and allowed to dwell for about 15 minutes. The expanded slotted tube 628, expanded stent 626, and tapered mandrel 618 assembly was then removed from the fluidized bath and water quenched. The resulting Nitinol stent 626 had numerous fractures.

[0076] In addition to being directed to the above embodiments and claims below, the present invention further relates to embodiments having different combinations of the above patents and claims below. As such, the present invention also relates to other embodiments having any other possible combination of the independent features recited in the following claims.

[0077] Numerous features and advantages of the present invention, including preferred and alternative embodiments, as well as details of the structure and function of the present invention, are set forth in the above description. The present disclosure is intended to be illustrative only and is not intended to be comprehensive as such. As will be apparent to those skilled in the art, various modifications may be made within the principles of the present disclosure, particularly with respect to the structure, materials, elements, components, shapes, sizes, and arrangements of parts, to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. These various modifications are intended to be included in the present disclosure to the extent that they do not depart from the spirit and scope of the appended claims.

Claims

1. A medical device, A shape memory alloy (SMA) article capable of transitioning between an initial first state, an intermediate second state, and an extended third state. The SMA article, in the initial first state, has a first annular circumference length, The SMA article, in the intermediate second state, has a second annular circumference length, The SMA article, in the expanded third state, has a length around the third annular circumference. The circumference of the second annular ring is greater than the circumference of the first annular ring and less than the circumference of the third annular ring. The transition from the initial first state to the extended third state occurs within 3 seconds. The aforementioned medical device.

2. The medical device according to claim 1, wherein the third annular periphery is larger than the first annular periphery.

3. The medical device according to claim 2, wherein the ratio of the third annular periphery to the first annular periphery is 2:

1.

4. The medical device according to claim 2, wherein the ratio of the third annular periphery to the first annular periphery is 3:

1.

5. The medical device according to claim 2, wherein the ratio of the third annular periphery to the first annular periphery is 4:

1.

6. The medical device according to any one of claims 1 to 5, wherein the shape memory alloy (SMA) article can transition between a first state, a second state, and a third state in a single extension step.

7. The medical device according to any one of claims 1 to 6, wherein the SMA has a shape-fixing temperature, and the SMA article is maintained at the shape-fixing temperature while transitioning between the initial first state, the intermediate second state, and the extended third state.

8. The medical device according to any one of claims 1 to 7, wherein the SMA article contains nitinol.

9. The medical device according to any one of claims 1 to 8, wherein the medical device is a stent, a cardiac occluder, a valve, or an intraluminal filter.

10. It is a medical device, Includes shape memory alloy (SMA) articles, The SMA article is adjusted to transition between the first, second, and third states to 100% of its initial shape within 3 seconds. The aforementioned SMA article has a shape-fixing temperature, The aforementioned article is In the first state, it has a first annular periphery, In the second state, it has multiple annular peripheries, In the third state, it has a third annular periphery, Each annular periphery in the second state is larger than the annular periphery in the first state and smaller than the annular periphery in the third state. The SMA article is maintained at the shape-fixing temperature while transitioning between the first, second, and third states. Medical devices.

11. The medical device according to claim 10, wherein the shape-fixing temperature is approximately 300°C to approximately 650°C.

12. The medical device according to claim 10, wherein the value of the third annular periphery is at least twice the value of the first annular periphery.

13. A method for forming a shape memory alloy (SMA) article, A step of forming an assembly by placing the SMA article within an expansion fixture, wherein the SMA article has initial dimensions, A step of heating the assembly to a high temperature, A step of operating the expansion fixture to expand the SMA article to a first expanded dimension, wherein the first expanded dimension is 100% larger than the initial dimension, A step of cooling the assembly so that the first expanded dimension is maintained. A method that includes this.

14. The method according to claim 13, further comprising the step of operating the expansion fixture to expand the SMA article from a first expanded dimension to a second expanded dimension, wherein the second expanded dimension is 200% larger than the initial dimension.

15. The method according to claim 14, further comprising the step of operating the expansion fixture to expand the SMA article from a second expanded dimension to a third expanded dimension, wherein the third expanded dimension is 300% larger than the initial dimension.

16. The method according to claim 15, further comprising the step of operating the expansion fixture to expand the SMA article from a third expanded dimension to a fourth expanded dimension, wherein the fourth expanded dimension is 400% larger than the initial dimension.

17. The method according to claim 16, further comprising the step of operating the expansion fixture to expand the SMA article from the fourth expanded dimension to a fifth expanded dimension, wherein the fifth expanded dimension is 500% larger than the initial dimension.

18. The method according to any one of claims 13 to 17, further comprising the step of expanding the SMA article to the first expanded dimension within three seconds.

19. A medical device formed by the method described in any one of claims 13 to 18.

20. The medical device according to claim 19, wherein the medical device is a stent, a cardiac occluder, a valve, or an intraluminal filter.

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