CA2257750C

CA2257750C - An intravascular stent having curved bridges for connecting adjacent hoops

Info

Publication number: CA2257750C
Application number: CA002257750A
Authority: CA
Inventors: Mark Mathis; Thomas Duerig
Original assignee: Nitinol Development Corp
Current assignee: Nitinol Development Corp
Priority date: 1998-01-09
Filing date: 1999-01-04
Publication date: 2006-12-19
Anticipated expiration: 2019-01-04
Also published as: DE69942076D1; JP4675440B2; CA2257750A1; US6342067B1; JPH11276598A; EP0928606A1; JP2009022779A; AU1006499A; AU742914B2; JP5208641B2; EP0928606B1

Abstract

In accordance with the present invention, there is provided a stent for insertion into a vessel of a patient. The stent is a tubular member having front and back open ends and a longitudinal axis extending therebetween. The tubular member has a first smaller diameter for insertion into a patient and navigation through the vessels, and a second larger diameter for deployment into the target area of a vessel. The tubular member is made from a plurality of adjacent hoops extending between the front and back ends. The hoops include a plurality of longitudinal struts and a plurality of loops connecting adjacent struts. The stent further includes a plurality of bridges having loop to bridge connections which connect adjacent hoops to one another. The bridge to loop connection points are separated angularly with respect to the longitudinal axis. The bridges have one end attached to a loop, another end attached to a loop on an adjacent hoop. The bridges have a non-linear curved profile between their bridge to loop connection points.

Description

, CA 02257750 1999-O1-04 AN INTRAVASCULAR STENT HAVING CURVED
BRIDGES FOR CONNECTING ADJACENT HOOPS
Thomas Duerig Mark Mathis FIELD OF THE INVENTION
The present invention relates to an expandable intraluminal gaffs ("stents'~
for use within a body passageway or duct which are particularly useful for repairing blood vessels 1o narrowed or occluded by disease. The present invention relates even further to such stents which are self-expanding and made from a superelastic material such as Nitinol. The present invention also relates to delivery systems for such stents.
BACKGROUND OF THE INVENTION
Percutaneous transluminal coronary angioplasty (PTCA) is a therapeutic medical procedure used to inaease blood flow through the coronary artery and can often be used as an alternative to coronary by-pass surgery. In this procedure, the angioplasty balloon is inflated within the stenosed vessel, or body passageway, in order to shear and disrupt the wall components of the vessel to obtain an enlarged Lumen. With rat to arterial stenosed lesions, the rdati~r incompressible plaqut remains unaherod, whr~e the more elastic medial and adventitial layers of the body passageway stretch around the plaque. This process produces dissection, or a splitting and tearing, of the body passageway wall layers, wherein the intima, or intawal surface of the utery or body passageway, suffers fissuring.
This dissection forms a "flap" of underlying tissue which may reduce the blood Bow through the Iumen, or block the lumen. Typically, the distending intrsluminal pressure within the body passageway can hold the disrupted layer, or flap, in place. If the intimal flap cxeated by the balloon dilation procedure is not maintained in place against the expanded intima, the i~imal flap can fold down into the lumen and close off the lumen, or may even become detached and enter the body passageway. When the intimal flap closes off the body passageway, immediate surgery is 3o necessary to correct this problem.
Roceatly, translumirral prod have been widely used in the medical arts for implantation in blood vessels, biliary ducts, or other similar organs of the living body. These rmc-g t prostheses are commonly known as stems and are used to maintain, open, or dilate tubular structures. An example of a commonly used stmt is given in U.S. Patent 4,733,665 filed~by Palmaz on November 7, 1985. Such stems are often referred to as balloon expandable stems.
Typically the stmt is made from a solid tube of stainless steel. Thereafter, a series of cuts are S made in the wall of the stent. The stmt has a first smaller diameter which permits the stmt to be delivered through the human vasculature by being crimped onto a balloon catheter. The stmt also has a second, expanded diameter, upon the application, by the balloon catheter, from the interior of the tubular shaped member of a radially, outwardly extending.
to However, such stems are often irapractical for use in some vessels such as the carotid srtery. The carotid artery is easily acces~le from the exterior of the human body, and is often visible by looking at ones nook. A patient having a balloon expandable stent made from stainless steel or the like, placed in their carotid artery might be susceptible to sever injury through day to day activity. k su»cient force placed on the patients neck, such as by falling, 1s could cause the tent to collapse, resulting in injury to the patient. In order to prevent this, ~ ceding mss have been proposed for use in such vessels. Self expanding sterns act like springs and will recover to their expanded or implanted configuration after being cxushed:
One type of self-expanding stmt is disclosed in U.S. Patent 4,665,771, which stmt has a radiaUy and axis>!y 8ean'bk, elastic tubular body with a predetermined diameter that is 2o variable under axial movema<t of aids of the body relative to each other and which is composed of a plurality of individually rigid but flexible and elastic thread elements desning a ndially adff ocpandiog helix. This type of rtent is known in the art as a "braided stmt' and is so d~tod baaia. Plscdrumt of such darts in a body vessel can be achieved by a device which comprise an outer c~h~ for holding the stmt at its distal end, and an inner piston 2s which puss the forward once it is in position.
How~evn', braided ata~s have many disadvantages. Tlwy typically do not have the ~sarY radial to vdy hold opea a diaeaxd vessel. In addition, the plurality of wines or 56as wed to make such stavts could become dangerous if separated from the body of the stem, svlxre it could pierce through the vessel. 'Therefore, there has been a desire 3o to have a self-acpsnding alert, which ~ cut from a tube of metal, which is the common ' g method for' many commercially available balloon expandable stems. In order to msu~rl~ure a self-expanding stmt cut 5~om a tube,, tlar alloy used would preferably be superelastic or psuedoelastic characta~istics at body temperature, so that it is crush recoverable.
The prior art makes reference to the use of alloys such as Ntinol (Ni-Ti alloy) which have shape memory and/or superelastic characteristics in medical devices which are designed to be inserted into a patient's body. The shape memory characteristics allow the devices to be defonmed to facilitate their inse<tion into a body lumen or cavity and then be heated within the body so that the device returns to its original shape. Superelastic characteristics on the other hand generally allow the metal to be deformed and restrained in the deformed condition to fac~tate the 1o insertion of the medical device containing the metal into a patient's body, with such deformation causing the phase transformation. Once within the body lumen the restraint on the superelastic manber can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase.
Alloys having shape memory/superelastic characteristics generaDy have at least two phases. These phases are a martensite phase, which has a relatively low tensile strength and which is stable at relatively low tempa~ahrres, and an austenite phase, which has a relatively high tensile strength and which is stable at temperatures higher than the martensite phase.
Shape memory characteristics are imparted to the alloy by heating the metal at a tanpe'rature above which the transfonm:von from the marte~~site phase to the austarite phase is complete, i.e. a temperature above which the austenite phase is stable (the Af temperature).
The shape of the metal during this heat treatment is the shape "remembered".
The best treated metal is cooled to a tanperature at which the martensite phase is stable, causing the austenite phase to transform to the martensite phase. The metal in the martensite phsae is then 2s plastically deformed, e.g. to facilitate the a~try thereof into a patient's body. S~sequent heating of the deformed martensite phase to a temperature above the martensite to austenite transformation tempasture causes the deformed martensite phase to transform to the austenite phase and during this phase transformation the metal reverts back to its origins! shape if unr~rained. If restrained, the metal will remain martensitic until the restraint is removed.
3o Methods of using the shape manory characteristics of these alloys in medial devices intended to be placed within s patient's body present operational di~culties.
For example, with shape memory alloys 'having a stable martensite temperature below body tetnpaatirre, it , . CA 02257750 1999-O1-04 is frequently difficult to maintain the temperature of the medical device containing such an alloy sufficiently below body temperature to prevent the transformation of the martensite phase to the austenite phase when the device was being inserted into a patient's body. With intravascular devices formed of shape memory alloys having martensite-to-austenite transformation temperatures well above body temperature, the devices can be introduced into a patient's body with little or no problem, but they must be heated to the nrartenste-to-austenite transformation temperature which is frequently high enough to cause tissue damage and very high levels of pain.
When stress is applied to a spocimen of a metal such as Ntinol exhibiting superelastic 1o characteristics at a tanperature above which the austenite is stable (i.e.
the temperature at which the transformation of martensite phase to the austenite phase is complete), the specimen deforms elastically until it reaches a particular stress level where the alloy then undergoes a stress-induced phase transformation from the austenite phase to the martensite phase. As the phase transformation proceeds, the aDoy undergoes significant increases in strain but with little 1s or no corresponding increases in stress. The strain increases while the stress remains essentially constant until the transformation of the austenite phase to the martensite phase is complete. Thereafter, further increase in stress are necessary to cause further deformation. The martensitic metal first deforms elastically upon the application of additional stress and then plastically with permanart residual deformation.
2o If the load on the is removed before amr permanent deformation has occaured, the martensitic spocirnen will elastically recover and transform back to the austenite phase. The reduction in stress first causes a decrease in strain. As stress reduction reaches the level st which the matteosite phase trant~forms back into the sustenite phase, the level in the will 2s remain essentially oon~taru (but substantially less than the constant stress level at which the austenite transforms to the martensite) until the transformation back to the sustenite phase is complete, i.e. there is sib recovery in strain with only negligible oonesponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction. This ability to incur significant strain at relatively constant 3o stress upon the applic~On of a load and to recover from the deformation upon the removal of the load is commonly referred to as supa~dasticity or pswdodasricity. ~ It is this property of the tr~ataial which makes it useful in manufacx~uing tube cut self-expanding stems. The prior art makes reference to the use of metal alloys having superelastic characteristics in medical devices which are intended to be inserted or otherwise used within a patient's body. See for example, U.S. Pat. No. 4,665,905 (Jervis) and U.S. Pat. No. 4,925,445 (Sakamoto et al.).
However, the prior art has yet to disclose any suitable tube cut self expanding stents.
s In addition, many of the prior art stems lacked the necessary rigidity or hoop strength to keep the body vessel open. In addition, many of the prior art stents have large openings at their expended diameter. The srnaUer the openings are on an expanded stent, the more plaque or other deposits it can trap between the stmt and the vessel wall. Trapping these deposits is important to the continuing health of the patient in that it helps prevent stokes as well as helps 1o prevents restenosis of the vessel it is implanted into. The present invention provides for a self expanding tube cut stent which overcomes many of the disadvantages associated with the prior art stems.
SLfMMARY OF THE IIWENTION
15 In accordance with the present inv~tion, there is provided a stent for insertion into a vessel of a patient. The stmt is a tubular member having front and back open ends and a longitudinal axis extending therebetween. The tubular member has a first smaller diameter for insertion into a patient and navigation through the vessels, and a second larger diameter for deploymait into the target area of a vessel. The tubular member is made from a plurality of 2o adjacefit hoops e~cta~ding between the frost and back ends. The hoops include a phuaftty of longitudinal struts and a plurality of loops connecting adjacent struts. The stent further includes a plurality of bridges having loop to bridge connections which connect adjacent hoops to one another. The bridge to loop connection points are separated angularly with to the longbrdinal axis. The bridges have one aid attached to a loop, another end attached to a 25 loop on an sdjacent hoop. The bridges have a non-linear curved profile between their bridge to loop connection points.
BRIEF DESCRIPTION OF DRAWITTGS
The foregoing and other aspects of the present invention will best be appreciated with 3o reference to the detailed description of the invention in conjunction with the accompanying drawings, wherein:

Figure 1 is a simplified partial cross-sectional view of a stent delivery apparatus having a stent loaded therein, which can be used with a stent made in accordance with the present invention.
Figure 2 is a view similar to that of figure 1 but showing an enlarged view of the distal end of the apparatus.
Figure 3 is a perspective view of a stern made in accordance with the present invention, showing the stent in its compressed state.
Figure 4 is a secxional, flat view of the scent shown in Figure 1.
Figure 4A is an enlarged view of saxion of the stent shown in Figure 4.
1o Figure 5 is a perspective view of the stent shown in Figure 1 but showing it in its expanded state.
Figure 6 is an enlarged sectional view of the stent shown in Figure S.
Figure ? is a view similar to that of Figure 4 but showing an alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVIENTION
Referring now to the figures wherein like numerals indicate the same element throughout the views, there is shown in Figures 3 and 4, a stent 50 made in accordance with the present invention. Figures 3 and 4 show stmt 50 in its un-expanded or compressed state.
Start 50 is preferably made from a superclastic alloy such as Ntinol. Most preferably, stent 50 is made from an alloy comprising from about 50.5% (as used herein these percentages refer to atomic percentages) N to about GO'/e N~, and most preferably about 55% Nl, with the raasi~nda of the alloy Ti. Preferably, the stmt is such that it is supa~dasbc at body tanpa~ature, and preferably has an Af in the range from about 24° C to about 37° C. The 2s supadasac design of the start makes it cxush recoverable which, as discussed above, can be used as a start or frame for arty number of vascular devices for different appGc~tions.
Start 50 is a t<rbular member having front and back open ends 81 and 82 and a longitudinal axis 83 extending therebetween. The tubular member has a first smaller diameter, figures 3 and 4, for insertion into a patia>t and navigation through the vessels, and a second larger diameter, figures 5 and 6, for dcployment into the target area of a vessel. The tubular nurmb~a is made from a phrrality of adjacait hoops 52, figure 1 showing hoops 52(a) - 52(b), exta~ding betwxn the front and back aids 81 and 82. The hoops 52 include a plurality of longitudinal struts 60 and a plurality of loops 62 connecting adjacent struts, wherein adjacent struts are connected at opposite ends so as to form an S or Z shape pattern.
The loops 62 are curved substantially semi-circular and symmetrical sections having centers 64.
Stent 50 further includes a plurality of bridges 70 which connect adjacent hoops 52 s which can best be described by referring to Figure 4. Each bridge has two ends 56 and 58.
The bridges have one end attached to one strut and/or loop, another end attached to a strut and/or loop on an adjacent hoop. Bridges 70 connect adjacent struts together at bridge to loop connection points 72 and 74. For example, end 56 is connected to loop 64(a) at bridge to loop connection point 72, and end 58 is connected to loop 64(b) at bridge to loop 1o connection point 74. Each bridge to loop connection points have centers 76.
The bridge to loop connection points are separated angularly with respect to the longitudinal axis. That is the connection points are not immediately opposite each other. One could not draw a straight line between the connection points, wherein such line would be parallel to the longitudinal axis of the stent.
15 The above described geometry helps to better distribute strain throughout the slant, prevents metal to metal contact when the slant is bent, and minimizes the opening size betweeri the features, struts loops and bridges. The number of and nature of the design of the struts, loops and bridges are important factors when determining the working properties and fatigue life properties of the slant. Preferably, each hoop has between 24 to 36 or more struts.
2o Preferably the start has a ratio of numbs of struts per hoop to strut length L (in inches) which is greater than 200. The length of a strut is measured in its compressed state parallel to the longitudinal axis 83 of the slant.
Aa sear from Figures 4 and 5, the geometry of the stem changes quite significamlyr as a slant is deployed from its un-expanded state to its expanded state. As a stmt undergoes 2s diametric change, the strut angle and strain levels in the loops and bridges are effected.
Preferably, all of the slant features will strain in a predictable manor so that the slant is reliable and un~n in strength. In addition, it is preferable to minimize the maximum strain experienced by struts loops and bridges, since Ntinol properties are more generally limited by strain rather than by stress as most materials are. As will be discussed in greater detail below, 3o the slant sits in the delivery system in its un-expanded state as shown in Figure 4. As the slant is deployed, it is allowed to expand towards it's expanded state, as shown in Figure 5, which pre~asbty has a diemaer which is the same or larger than the dian~tter of the target vessel.
Nnc-s Ntinol stents made from wire deploy in much the same manor and are dependent upon the same design constraints as laser cut stents. Stainless steel stents deploy similarly in terms of geometric changes as they are assisted with forces from balloons or other devices.
In trying to minimize the maximum strain experienced by features, the present invention utilizes structural geometry's which distribute strain to areas of the stent which are less susceptible to failure than others. For example, one of the most vulnerable areas of the scent is the inside radius of the cotuiecting loops. The connecting loops undergo the most defornrstion of all the stem features. The inside radius of the loop would norn~ally be the area with the highest level of strain on the stmt. This area is also critical in that it is usually the 1o smallest radius on the stent. Stress concentrations are generally controlled or minimized by maintaining the largest radii possible. Similarly, we want to minimize local strain concentrations on the bridge and bridge connection points. One way to accomplish this is to utilize the largest possible radii while maintaining feature widths which are consistent with applied forces. Another consideration is to minimize the maximum open area of the slant.
E~cient utilizatipn of the original tube from which the slant is cut increases slant strength and it's ability to trap embolic material.
Many of these objectives have been accomplished by a preferred embodiment of the present invention, shown in Figures 3 and 4. As seen from these figures, the most compact designs which maintain the largest radii at the loop to bridge connections are non-symmetric 2o with reject to the centerline of the strut conna~ing loop. That is, loop to bridge connection point centers 76 are off set from the center 64 of the loops 62 to which they are attached.
The faaure is particularly advantageous for sterns having large expansion ratios, which in turn requires tbem to have extreme bending requiranarts where large elastic strains are required.
Ntinol can witi>Stand actrandy large amounts of elastic strain defonmation, so the above festeu~ are well suited to slants made from this alloy. This feature allows for maacimum utivzation of N-Ti or other material capabilities to enhance radial strength, improve stem atraq;th uniformity, improves fatigue life by miimmizing local strain levels, allows for smaller open areas which enhance entrapment of embolic material, and improves slant apposition in irregular vessel wall shapes and curves.
3o As seen in figure 4A, slant 50 has strut connecting loops 62 having a width W4, as rrreaarred st the center 64 parallel to axis 83, which are greater than the strut widths W2, as measured papaidicular to axis 83 itself. In fact it is preferable that the thicla>ess of the loops NDC-s g vary so that they are thickest near their centers This increases strain deformation at the strut and reduces the maximum strain levels at the extreme radii of the loop. This reduces the risk of stmt failure and allows us to maximize radial strength properties. Tire feature is particularly advantageous for stents having large expansion ratios, which in turn requires them to have extreme bending requirements where large elastic strains are required. Ntinol can withstand act<arrely large amounts of elastic strain deformation, so the above features are well suited to steMs mtde from this alloy. This feature allows for maximum utilization of Nl-Ti or other material capabilities to aihance radial stra>gth, improve stmt strength uniformity, improves fatigue life by minimizing local strain levels, allows for smaller open areas which enhance to entrapment of embolic material, and improves slant apposition in irregular vessel wall shapes and curves.
As mentioned above bridge geometry changes as a slant is deployed from its compressed state to its expanded state and vise-versa. As a slant undergoes diametric change, strut angle and loop strain is effected. Since the bridges are conrto either the loops, struts or both, they are effected. twisting of one end of the slant with respect to the other, while loaded in the stent~ delivery system, should be avoided. Local torque delivered to the bridge ends displaces the bridge geometry. If the bridge design is duplicated around the slant perimeter, this displacement causes rotational shifting of the two loops being connected by the bridges. If the bridge design is duplicated throughout the slant, as in the present invention, this shift will occur down the length of the start. This is a cunw>abve effect as one considers rotation of one end with respect to the other upon deployment. A scent delivery system, such as the one described below, will deploy the distal end first, then allow the proximal end to expand. It would be undesirable to allow the distal end to anchor into the vessel wall while holding the stmt fixed in rotation, then release the proximal end. this could cause the slant to 2s twist or whip in rotation to equilibrium after it is at least partially deployed within the vessel.
Such whipping action could cause damage to the vessel.
However, one embodima~t of the print invention, as shown in Figures 3 and 4, reduces the chance of such events from happening when deploying the slant. By mirroring the bridge geometry longidrdinally down the stem, the rotational shift of the Z-sections can be 3o made to alternate and will minimize large rotational changes betwear any two points on a given start during deployment or constrsirn. That is the bridges connecting loop 52(b) to loop 52(c) are angled upwardly from left to right, while the bridges conracting loop 52(c) to loop NDC,B 9 52(d) are angled downwardly from left to right. This alternating pattern is repeated down the length of the stent. This alternating pattern of bridge slopes improves the torsional characteristics of the stent so as to minimize any twisting or rotation of the stent with respect to any two hoops. This ahernating bridge slope is particularly beneficial if the stent starts to s twist in vivo. As the stent twists, the diameter of the stent will change.
Alternating bridge slopes tend to muwnize this effect. The diameter of a stent having bridges which are all sloped in the same direction will tend grow if twisted in one direction and shrink if twisted in the other direction. With alternating bridge slopes this effect is minimized and localized.
The feature is particx~larly advanugeous for stents having large expansion ratios, which to in turn requires them to have extreme bending requirements where large elastic strains are required. Ntinol can withstand extremely large amounts of elastic strain deformation, so the above features are well suited to stents made from this alloy. This feature allows for maximum utilization of N-Ti or other material capabilities to enhance radial strength, improve stent unifonmity, improves fatigue life by minimizing local strain levels, allows for smaller 15 open areas which azhar~ce entrapment of embolic material, and improves stent apposition in irregular vessel wall shapes and curves.
Preferably, stents are laser cut from small diameter tubing. For prior art slants, this manufacturing process lead to designs with geometric features, such as struts, loops and bridges, having axial widths W2, W4 and W3 (respectively) which are larger than the tube wall 20 thiclcnas T (showA in Hgure 5). When the stets is compressed, most of the bending occurs the plane that is created if one were to cut longitudinally down the slant and Batten it out.
However, for the individual bridges, loops and struts, which have widths greater than their thick~s, they have a greater resistance to this in-plarnr bending than they do to out of plane balding. Because of this, the bridges and struts tend to twist, so that the stets as a whole can 25 bald more easily. This twisting is a buckling condition which is unpredictable and can cause pote~ially high strain.
However, this problem has been solved in a preferred embodiment of the presort invention, shown in Figures 3 and 4. As seen from these figures, the widths of the stntts, hoops and bridges are equal to or less than the wall thickness of the tube.
Therefore, 3o substantially all banding and, therefore, all strains are "out of plane".
This minimizes twisting of the slant which minimizes or eliminates buckling and unpredictable strain conditions. The feature is particularly advantageous for stems having large expansion ratios, which in turn NDC-8 to requires them to have extreme bending requirements where large elastic strains are required.
Nitinol can withstand extremely large amounts of elastic strain deformation, so the above features are well suited to :tents made from this alloy. This feature allows for maximum utilization of N-Ti or other material capabilities to enhance radial strength, improve stent s strength uniformity, improves fatigue life by minimizing local strain levels, allows for smaller open areas which enhance entrapment of embolic material, and improves :tent apposition in irregular vessel wall shapes and curves.
An ahecnative wt~bodirnent of the present invention is shown in Figure 7.
Figure 7 shows stmt 150 which is similar to step 50 shown in the previous drawings.
Stmt 150 is 1o made from a plurality of adjacent hoops 152, figure 7 showing hoops 152(a) -152(d). The hoops 152 include a plurality of longitudinal struts 160 and a plurality of loops 162 connecting adjacent struts, wherein adjacent struts are connected at opposite ends so as to form an S or Z
shape pattern. Stent 150 further includes a phrrality of bridges 170 which connect adjacent hoops 152. As seen from the figure, bridges 170 are non-linear and curve between adjacent 15 hoops. Having curved bridges allows the bridges to cwve around the loops and struts so that the hoops to be placed closer together which in turn, minimizes the maximum open area of the stmt and increases its radial strength as well. This can best be explained by referring to Figure 6. The above described stent geometry attempts to minimize the largest circle which could be inscribed between the bridges, loops and struts, when the start is expanded.
ll~~nimizing the 2o size of this tlreoredcal c~rrcle, greatly improves the :tent because it is then better suited to trap embolic material once it is inserted into the patient.
It has also been discovered that stems with curved bridges resist bending much less, and tend to bend uniformly and progressively with ever increasing loads. This is because the bridges hsve an inainsic moment buih into their geometry, when any load is applied. Prior art 25 articulated stems having straight bridges bend locally only after overcoming a threshold force which causes the bridge to buckle. Until this tlueshold is reached, the high column str~gth of the bridge resists compressive de8a~ion w~' causes the stets to bend in 5nite and x steps. This effect is particularly noticed when using Ntinol, since its elastic range extends through a highly nonlinear region. This 5nite and distinct bending effect is undesirable. The 3o stern should have smooth and gradual bends, as loads are applied thereto, to maintain laminar Bow through the hm>en of the implanted :fait.

As mentioned above, it is preferred that the stent of the present invention be made from a superelastic alloy and most preferably made of an alloy material having greater than 50.5 atomic % Nckel and the balance titsrtium. Greater than 50.5 atomic %
Nckel allows for an alloy in which the temperature at which the martensite phase transforms completely to the austenite phase (the Af temperature) is below human body temperature and preferably is about 24° C to about 37°C ao that sustenite is the only stable phase at body temperature.
In manuta~ring the Ntinol stmt, the material is first in the form of a tube.
Ntinol tubing is commercially available from a of suppliers including Ntinol Devices and Components, Fremont CA The tubular member is then loaded into a machine which will cut 1o the predetermined pattern of the slant, which was discussed above and is shown in the Sgures, into the tube. Machines for cutting patterns in tubular devices to make slants or the like are well known to those of ordinary skill in the art and are commercially available. Such machines typically hold the metal tube between the open ends while a cutting laser, preferably under microprocessor control, cuts the pattern. The pattern dimensions and styles, laser positioning requirements, and other information are programmed into a microprocessor which controls all aspects of the process. After the slant pattern is cut, the slant is treated and polished using any number of methods well known to those skilled in the art. Lastly, the slant is then cooled until it is completely martensitic, crimped down to its un-expanded diameter and then loaded into the sheath of the delivery apparatus.
2o It is betievved that many of the advantages of the presets imraition can be better understood through a brief description of a delivery apparatus for the stem, as shown in Figures 1 and 2. Figures 1 and 2 show a self-expanding slant delivery apparatus 1 for a slant made in accordance with the presart ion. Apparatus 1 comprises inner and outer coaxial tubes. The inner tube is called the shaft 10 and the outer tube is called the sheath 40.
Shaft 10 has proximal and distal aids 12 and 14 rvely. the distal end 14 of the shaft terminates at a luer lock hub 5. Preferably, shaft 10 has a proximal portion 16 which is made from a rdativdy stiff material such as a<amlas steel, Nrtinol, or any other suitable material, and an distal portion 18 which is made from a polyethylene, polyimide, pellethane, Pebax, Vestamid, Cristamid, Grillamid or arty other suitable material known to those of ordinary skill 3o in the art.. The two portions are joined together by any number of means known to those of ordinary skill in the art. The stainless sled proximal end gives the shaft the necessary rigidity or stirs it needs to effectively push out the stent, while the polymeric distal portion provides the necessary flexibility to navigate tortuous vessels.
The distal portion 18 of the shaft has a distal tip 20 attached thereto. The distal tip 20 has a proximal end 34 whose diameter is substantially the same as the outer diameter of the sheath 40. The distal tip tapers to a smaller diameter from its proximal end to its distal end, wherein the distal end 36 of the distal dp has a diameter smaller than the inner diameter of the sheath. Also attached to distal portion 18 of shaft 10 is a stop 22 which is proximal to the distal tip 20. Stop 22 can be made from any rwmbet of materials known in the art, including stainless steel, and is even more preferably made from a highly radiopaque material such as 1o platinum, gold tantalum. The diameter of stop . 22 is substantially the same as the inner diameter of sheath 40, and would actually make frictional contact with the inner surface of the sheath. Stop 22 helps to push the stent out of the sheath during deployment, and helps the stent from migrating proximally into the sheath 40.
A stmt bed 24 is defined as being that portion of the shaft between the distal tip 20 and 1s the stop 22. The stent bed 24 and the slant 50 are coaxial so that the portion of shaft 18 comprising the slant bed 24 is located within the lumen of the slant 50.
However, the slant hod 24 does not make any contact with slant 50 itself. Lastly, shaft 10 has a guidewire lumen 28 extending along its length from its proximal end 12 and exiting through its distal tip 20.
This sllows the shaft 10 to receive a guidevvire much in the same way that an ordinary balloon 20 angioplsatly catheter receives a guidewire. Such guidewvires are weU known in art and help guide catheters and other medical devices through the vasculature of the body.
Sheath 40 is preferably a polymeric catheter and has a proximal end 42 terminating at a hub 52. Sheath 40 also has a distal end 44 which terminates at the proximal end 34 of distal tip 20 of the shaft 18, when the slant is in its fully un-deployed position as shown in the 2s figures. The distal end 44 of sheath 40 includes a radiopaque marker band 46 disposed along its outer . As will be explained below, the stmt is fully deployed when the marker band 46 is lined up with radiopaque stop 22, thus mdic~ting to the physician that it is now safe to remove the apparatus 1 from the body. Sheath 40 preferably comprises an outer polymeric layer and an inner polymeric layer. Positioned between outer and inner layers a braided 3o rdnforcing lays. Braided reinforcing lays is preferably made from stainless steel. The use of braided reinforcing layers in other types of medical devices can be found in U.S. patents 3,585,707 issued to Stevens on June 22, 1971, 5,045,072 issued to Castivo et al. on September 3, 1991, and 5,254,107 issued to Soltesz on October 19, 1993.
Figures 1 and 2 show the stent 50 as being in its fully un-deployed position.
This is the position the stent is in when the apparatus 1 is inserted into the vasatlature and its distal end is navigated to a target site. Stent 50 is disposed around stent bed 24 and at the distal end 44 of stleath 40. The distal tip 20 of the shaft 10 is distal to the distal end 44 of the sheath 40, and the proximst end 12 of the shaft 10 is proximal to the proximal end 42 of the sheath 40. The stmt 50 is in a compressed state snd makes frictional contact with the inner surface 48 of the sW th 40.
to When being inserted into a patient, sheath 40 and shaft 10 are locked together at their proximal ends by a Touhy Borst valve 8. This prevents any sliding movement between the shaft and si~eath which could result in a premature deployment or partial deployment of the stmt. When the stmt 50 reachGS its target ate snd is ready for deployment, the Touhy Borst valve 8 is opened so that that the shesth 40 and shaft 10 are no longer locked together.
The anethod under which apparatus 1 deploys stent 50 should be readily apparent. The appsratua 1 is first inserted into a vessel so that the slant bed 24 is at a target diseased site.
Once this has occurrad~ the physician would open the Touhy Borst valve 8. The physician would then grasp the proximal end lZ.of shaft 10 so as to hold it in place.
Thereafter, the physician would grasp the proximal end 42 of sheath 40 and slide it proximal, relative to the . shaft 40. Stop 22 prmrans the start 50 from sliding back with the sheath 40, so that as the sheath 40 is moved back, the stmt 50 is pushed out of the distal end 44 of the sheath 40.
Stan deployment is complete when the radiopaque band 46 on the sheath 40 is proximal to ~radiopsque stop 22. The apparatus 1 can now be withdrawn through slant 50 and removed from the psua~t.
2s Although particular anbodima~ts of the presa~t invention have been slwwn and described, modification may be made to the device and/or method without departing from the spirit and scope of the preseat imrention. The terms used in descn'bing the invention are used in then d~aipwe sense and not as terms of limitations.

Claims

1. A stent for insertion into a vessel of a patient, said stent comprising:
a) a tubular member having a thickness and having front and back open ends and a longitudinal axis extending therebetween, said member having a first smaller diameter for insertion into said vessel, and a second larger diameter for deployment into said vessel;
b) said tubular member comprising a plurality of adjacent hoops extending between said front and back ends, said hoops comprising a plurality of longitudinal struts and a plurality of loops connecting adjacent struts; and c) a plurality of bridges connecting adjacent hoops to one another at bridge to loop connection points wherein said stent has end hoops at the front and back ends thereof wherein said end hoops have bridges connecting every other loop on said end hoops to its adjacent hoop, the number of bridge to loop connection points being less than the total number of loops on a hoop, wherein said connection points are separated angularly with respect to said longitudinal axis, said bridges having a non-linear curved profile between said bridge to loop connection points.

2. The stent according to claim 1 wherein said loops comprise curved substantially semicircular sections having centers, said bridges being connected to said loops at loop to bridge connection points having centers, said centers of said points are offset from said centers of said loops.

3. The stent according to claim 1 wherein said stent is made from a superelastic alloy.

4. The stent according to claim 3 wherein said alloy comprises from about 50.5 percent to about 60 percent Nickel and the remainder comprising Titanium.

5. The stent according to claim 1 wherein said bridges, loops and struts have widths which are less than said thickness of said tubular member.

6. A stent for insertion into a vessel of a patient, said stent comprising;
a) a tubular member made from a superelastic Nickel Titanium alloy, said member having a thickness and having front and back open ends and a longitudinal axis extending therebetween, said member having a first smaller diameter for insertion into said vessel, and a second larger diameter for deployment into said vessel;
b) said tubular member comprising a plurality of adjacent hoops extending between said front and back ends, said hoops comprising a plurality of longitudinal struts and a plurality of loops connecting adjacent struts; and c) a plurality of bridges connecting adjacent hoops to one another at bridge to loop connection points wherein said stent has end hoops at the front and back ends thereof wherein said end hoops have bridges connecting every other loop on said end hoops to its adjacent hoop, the number of bridge to loop connection points being less than the total number of loops on a hoop, wherein said connection points are separated angularly with respect to said longitudinal axis, said bridges having a non-linear curved profile between said bridge to loop connection points.

7. The stent according to claim 6 wherein said loops comprise curved substantially semicircular sections having centers, said bridges being connected to said loops to bridge connection points having centers, said centers of said points are offset from said centers of said loops.

8. The stent according to claim 6 wherein said alloy comprises from about 50.5 percent to about 60 percent Nickel and the remainder comprising Titanium.

9. The stent according to claim 8 wherein the stent has an Af temperature between about 24 to about 37 degrees Celsius.

10. The stent according to claim 6, wherein said bridges, loops and struts have widths which are less than said thickness of said tubular member.

11. A stent for insertion into a vessel of a patient, said stent comprising:
a) a tubular member made from a superelastic alloy comprising from about 50.5 percent to about 60 percent Nickel and the remainder comprising Titanium and having an Af temperature between about 24 to about 37 degrees Celsius;
b) said member having a thickness and having front and back open ends and a longitudinal axis extending therebetween, said member having a first smaller diameter for insertion into said vessel, and a second larger diameter for deployment into said vessel;
c) said tubular member comprising a plurality of adjacent hoops extending between said front and back ends, said hoops comprising a plurality of longitudinal struts and a plurality of loops connecting adjacent struts; and d) a plurality of bridges connecting adjacent hoops to one another at bridge to loop connection points wherein said stent has end hoops at the front and back ends thereof wherein said end hoops have bridges connecting every other loop on said end hoops to its adjacent hoop, the number of bridge to loop connection points being less than the total number of loops on a hoop, wherein said connection points are separated angularly with respect to said longitudinal axis, said bridges having a non-linear curved profile between said bridge to loop connection points.

12. The stent according to claim 11 wherein said loops comprise curved substantially semicircular sections having centers, said bridges being connected to said loops at loop to bridge connection points having centers, said centers of said points are offset from said centers of said loops.

13. The stent according to claim 11 wherein said bridges, loops and struts have widths which are less than said thickness of said tubular member.