US20080091258A1 - Stent Fabrication Method - Google Patents

Abstract

A stent and a method for fabricating the stent are disclosed. The stent has an originally flat pattern and connection points where the sides of the flat pattern are joined. The method includes the steps of a) cutting a stent pattern into a flat piece of metal thereby to produce a metal pattern, b) deforming the metal pattern so as to cause two opposing sides to meet, and c) joining the two opposing sides at least at one point. Substantially no portion of the stent projects into the lumen of the stent when the stent is expanded against the internal wall of a blood vessel.

Description

FIELD OF THE INVENTION
• The present invention relates generally to methods of fabricating stents.
BACKGROUND OF THE INVENTION
• Stents are known in the art. They are typically formed of a cylindrical metal mesh which can expand when pressure is internally applied. Alternatively, they can be formed of wire wrapped into a cylindrical shape.
• As described in U.S. Pat. No. 4,776,337 to Palmaz, the cylindrical metal mesh shape is produced by laser cutting a thin walled metal tube. The laser cuts away all but the lines and curves of the mesh.
• The method of U.S. '337 is applicable for relatively large mesh shapes and for meshes whose lines are relatively wide. However, for more delicate and/or intricate shapes, the spot size of the laser is too large.
SUMMARY OF THE PRESENT INVENTION
• It is, therefore, an object of the present invention to provide a stent fabrication method which can produce stents with relatively intricate and/or delicate designs.
• The method involves first creating a flat version of the desired stent pattern from a piece of thin sheet metal. The flat pattern can be produced through any suitable technique, such as etching the design into the sheet metal, or by cutting with a very fine laser, should one become commercially available or by any other technique.
• Once the sheet metal has been cut, it is deformed so as to cause its edges to meet. To create a cylindrical stent from a flat, roughly rectangular metal pattern, the flat metal is rolled until the edges meet. The locations where edges meet are joined together, such as by spot welding. Afterwards, the stent is polished, either mechanically or electrochemically.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:
• FIG. 1 is a flow chart illustration of the stent fabrication method of the present invention;
• FIGS. 2A, 2B and2C are illustrations of three alternative stent patterns to be etched, in accordance with the method ofFIG. 1, into a flat sheet of metal;
• FIG. 3 is an isometric illustration of a stent being deformed, useful in understanding the method ofFIG. 1;
• FIG. 4 is an isometric illustration of a stent formed from the method ofFIG. 1;
• FIGS. 5A and 5B are side and top view illustrations, respectively, of one connection location of the stent ofFIG. 4;
• FIG. 6 is a side view illustration of one connection location of the stent ofFIG. 4 which is connected in a nail-like manner;
• FIG. 7 shows a piece of sheet metal with a plurality of patterns made in accordance with the invention;
• FIG. 8 shows a detailed view of one of the patterns shown inFIG. 7;
• FIG. 9 shows a detailed view of a pair of engagement troughs shown inFIG. 8;
• FIG. 10 shows a detailed view of a pair of engaging protrusions shown inFIG. 8;
• FIG. 11 shows the engagement troughs and engagement protrusions ofFIGS. 9 and 10 in the engaged position;
• FIG. 12 shows a welding run practiced in accordance with the invention;
• FIG. 13 is a detailed view of the welding run shown inFIG. 12;
• FIG. 14 is a detailed view of a cell of a stent made in accordance with this invention;
• FIG. 15 is a detailed view of a cell made in accordance with this invention;
• FIG. 16 shows a cell of a stent made in accordance with this invention;
• FIG. 17 is an enlarged view of the cell shown inFIG. 16;
• FIG. 18 is a cross-sectional view of a longitudinal member of a stent constructed in accordance with this invention;
• FIG. 19 is a cross-sectional view of a stent constructed in accordance with this invention;
• FIG. 20 is a perspective view of a stent constructed in accordance with this invention;
• FIG. 21 is a cross-sectional front view of an unexpanded stent made in accordance with the invention;
• FIG. 22 is a cross-sectional front view of the stent shown inFIG. 21 after it has been expanded;
• FIG. 23 is a cross-sectional front view of an unexpanded stent made by cutting a pattern in a tube; and
• FIG. 24 is a cross-sectional front view of the stent shown inFIG. 23 after expansion.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
• Reference is now made toFIG. 1 which illustrates the stent fabrication method of the present invention and toFIGS. 2A, 2B,2C,3 and4 which are useful in understanding the method ofFIG. 1.
• In the stent fabrication method of the present invention, a stent designer first prepares a drawing of the desired stent pattern in a flat format (step10).
• FIGS. 2A, 2B and2C illustrate three exemplary stent pattern designs. The pattern ofFIG. 2A has two types ofsections20 and22. Eachsection20 has two opposing periodic patterns and eachsection22 has a plurality of connectinglines24. The pattern ofFIG. 2A can be formed of any size; a preferable size is to have eachsection20 be between 1 and 6 mm wide and eachsection22 have connectinglines24 of 1-6 mm long. At such sizes, the pattern ofFIG. 2A cannot be cut using a laser cutting system.
• The pattern ofFIG. 2B is similar to that ofFIG. 2A in that it also hassections20 of opposing periodic patterns. The pattern ofFIG. 2B also has connecting sections, labeled30, which have a Z shape.
• The pattern ofFIG. 2C has no connecting sections. Instead, it has a series of alternating patterns, labeled32 and34.
• The patterns ofFIGS. 2A, 2B and2C optionally also have a plurality ofsmall protrusions38 which are useful in forming the stent, as described herein below.
• Returning toFIG. 1, in step12, the stent pattern is cut into a flat piece of metal (“sheet metal”). The metal can be any type of biocompatible material, such as stainless steel, or a material which is plated with a biocompatible material. The cutting operation can be implemented in any of a number of ways, such as by etching, or by cutting with a fine cutting tool, or by cutting with a very fine laser, should one become commercially available.
• If step12 is implemented with etching, then, the process is designed to cut through the sheet metal. This process is known; however, for the purposes of completeness, it will be briefly described herein below.
• The drawing of the pattern is reduced and printed onto a transparent film. Since it is desired to cut completely through the metal, the drawing is printed onto two films which are joined together in a few places along their edges. The sheet metal is covered, on both sides, with a layer of photoresist and placed between the two transparent, printed films. The structure is illuminated on both sides which causes the portions of the photoresist which receive the light (which are all the empty spaces in the pattern, such asspaces26 ofFIG. 2A) to change properties.
• The sheet metal is placed into acid which eats away those portions of the photoresist which changes properties. The sheet metal is then placed into an etching solution which etches away all material on which there is no photoresist-removing solution which removes the photoresist, leaving the metal having the desired stent pattern.
• In step14, the metal pattern is deformed so as to cause its long sides (labeled28 inFIGS. 2A, 2B and2C) to meet each other.FIG. 3 illustrates the deformation process. For cylindrical stents, the deformation process is a rolling process, as shown.
• If theprotrusions38 have been produced, after deformation of the metal pattern, theprotrusions38 protrude over theedge28 to which they are not attached. This is illustrated inFIG. 5A.
• In step16, theedges28 are joined together by any suitable process, such as spot welding. If theprotrusions38 were made, theprotrusions38 are joined to theopposite edge28, either by welding, adhesive or, as illustrated inFIG. 6, with a nail-like element40.FIG. 5B illustrates the connection of the protrusion to theopposite edge28. Sinceprotrusion38 is typically designed to extend the width of one loop39, the pattern in approximately preserved. This is seen inFIG. 5B.
• Alternatively, theedges28 can be brought together and joined in the appropriate places.
• FIG. 4 illustrates a stent31 formed by the process of steps10-16 for the pattern ofFIG. 2A. It is noted that such a stent has connection points32 formed by the joining of the points30.
• Finally, the stent31 is polished to remove any excess material not properly removed by the cutting process (step12). The polishing can be performed mechanically, by rubbing a polishing stick having diamond dust on its outside inside the stent31. Alternatively, an electropolishing unit can be utilized.
• FIG. 7 shows an alternative embodiment of the invention in which a plurality ofpatterns120 are etched and cut into the sheet metal121 as previously discussed.FIG. 8 is an enlarged view of one of the plurality ofpatterns120 shown inFIG. 7.
• FIG. 9 is an enlarged view of onepair127 of the plurality ofengagement troughs128 and129 shown inFIG. 8.FIG. 10 is an enlarged view of onepair130 of the plurality ofengagement protrusions131 and132 shown inFIG. 8. The sheet metal121 and each of thepatterns120 is provided with a plurality ofalignment apertures122 and122′ adapted to receive sprockets (not shown) for precisely moving and maintaining the precise alignment of the sheet metal121 and thepatterns120 during the various stages of manufacturing. Eachpattern120 has a first long side123 and a second long side124, a firstshort side125, and a secondshort side126. The first long side123 is provided with a plurality ofpairs127,127′ and127″ ofengagement troughs128 and129 (shown in greater detail inFIG. 9). Eachpair127,127′ and127″ of engagement troughs has afirst engagement trough128 and asecond engagement trough129. The second long side124 is provided with a plurality ofpairs130,130′ and130″ of engagement protrusions (shown in greater detail inFIG. 10). Eachpair130,130′ and130″ of engagement protrusions is provided with afirst engagement protrusion131 and asecond engagement protrusion132. The pairs ofengagement protrusions130,130′ and130″ are disposed substantially opposite the pairs ofengagement troughs127,127′ and127″.
• Theengagement troughs128 and129 are disposed and adapted to receive and engage theengagement protrusions131 and132 so that the alignment of the stent is maintained when thepattern120 is deformed and the flat sheet metal is rolled so that the first long side123 and the second long side124 meet each other to form a tube as shown inFIGS. 19 and 20.
• Abridge133 of material is disposed between eachpair127,127′ and127″ ofengagement troughs128 and129. Thisbridge133 imparts additional stability and facilitates alignment during manufacturing and imparts additional strength to the welds of the finished stent as discussed below.
• After the sheet has been rolled into a tubular stent and theengagement troughs128 and129 have received theengagement protrusions131 and132, means (not shown) are utilized to maintain the alignment and thebridge133 is cut to leave two substantially equal parts. Thebridge133 may be cut in a variety of ways well known to those skilled in the art, however, in a preferred embodiment, a laser is utilized.Engagement trough128 is welded toengagement protrusion131 andengagement trough129 is welded toengagement protrusion132 as shown inFIGS. 12 and 13. This may be accomplished in a variety of ways well known to those skilled in the art, however, in a preferred embodiment a plurality of spot welds are utilized. In an especially preferred embodiment, about five spot welds are used in each weld run as shown inFIGS. 12 and 13. The heat produced by the welding melts thecut bridge133 material and the material is drawn towards theengagement trough128 or129 to which the material is attached and is drawn into the welded area between the engagement trough and the engagement protrusion where the additional bridge material becomes part of and imparts additional strength to the weld. The stent may then be finished as previously discussed.
• FIG. 13 is an enlarged view of the welded area shown inFIG. 12. In a preferred embodiment, the weld run is offset from the point where the engagement trough and the engagement protrusion contact each other. In an especially preferred embodiment, the weld run is offset about 0.01 mm.
• FIG. 14 is a detailed view of the pattern shown inFIG. 8. As shown inFIGS. 14 and 20, Applicants' invention can also be described as an expandable stent defining alongitudinal aperture80 having a longitudinal axis orextension79 and a circumferential axis orextension105, including a plurality of flexibleconnected cells50 with each of theflexible cells50 having a firstlongitudinal end77 and a secondlongitudinal end78. Eachcell50 also is provided with a first longitudinal apex100 disposed at the firstlongitudinal end77 and a secondlongitudinal apex104 disposed at the secondlongitudinal end78. Eachcell50 also includes afirst member51 having a longitudinal component having afirst end52 and asecond end53; asecond member54 having a longitudinal component having afirst end55 and asecond end56; a third member57 having a longitudinal component having a first end58 and asecond end59; and afourth member60 having a longitudinal component having a first end61 and asecond end62. The stent also includes afirst loop63 defining a first angle64 disposed between thefirst end52 of thefirst member51 and thefirst end55 of thesecond member54. Asecond loop65 defining a second angle66 is disposed between thesecond end59 of the third member57 and thesecond end62 of thefourth member60 and is disposed generally opposite to thefirst loop63. A first flexible compensating member orflexible link67 having afirst end68 and a second end69 is disposed between thefirst member51 and the third member57 with thefirst end68 of the first flexible compensating member orflexible link67 communicating with thesecond end53 of thefirst member51 and the second end69 of the first flexible compensating member orflexible link67 communicating with the first end58 of the third member57. Thefirst end68 and the second end69 are disposed a variablelongitudinal distance70 from each other. A second flexible compensating member71 having afirst end72 and asecond end73 is disposed between thesecond member54 and thefourth member60. Thefirst end72 of the second flexible compensating member or flexible link71 communicates with thesecond end56 of thesecond member54 and thesecond end73 of the second flexible compensating member or flexible link71 communicates with the first end61 of thefourth member60. Thefirst end72 and thesecond end73 are disposed a variable longitudinal distance74 from each other. In a preferred embodiment, the first and second flexible compensating member orflexible links67 and71 are accurate. The first and second flexible compensating member orflexible links67 and71 are differentially extendable or compressible when the stent is bent in a curved direction away from thelongitudinal axis79 of theaperture80. (Shown inFIG. 20.) Thefirst member51,second member54, third member57, andfourth member60 and thefirst loop63 and thesecond loop65 and the first flexible compensating member orflexible link67 and the second flexible compensating member or flexible link71 are disposed so that as the stent is expanded the distance between the first flexible compensating member orflexible link67 and the second flexible compensating member or flexible link71 increases and the longitudinal component of thefirst member51,second member54, third member57 andfourth member60 decreases while thefirst loop63 and thesecond loop65 remain generally opposite to one another, the ends68 and69 of the first flexible compensating member orflexible link67 and theends72 and73 of the second flexible compensating member or flexible link71 open so as to increase the variablelongitudinal distance70 between thefirst end68 and the second end69 of the first flexible compensating member orflexible link67 and so as to increase the variable longitudinal distance74 between thefirst end72 and thesecond end73 of the second flexible compensating member or flexible link71. This compensates for the decreasing of the longitudinal component of thefirst member51,second member54, third member57, andfourth member60 and substantially lessens the foreshortening of the stent upon its expansion. Upon expansion, the first flexible compensatingmember67 and the second flexible compensating member71 impart support to the lumen being treated.
• FIG. 15 shows the dimensions of an especially preferred embodiment of this invention. The deflection points, i.e., the first andsecond loops63 and65 and the first and second compensatingmembers67 and71, are made wider than the first, second, third, andfourth members51,54,57 and60 so that the force of the deflection is distributed over a wider area upon the expansion of the stent. The deflection points can be made wider than the first, second, third and fourth members in differing amounts so that the deflection will occur in the narrower areas first due to the decreased resistance. In a preferred embodiment, the first and second compensating members are wider than the first, second, third and fourth members and the first and second loops are wider than the first and second compensating members. One of the advantages of sizing the first and second loops so that they are wider than the first and second compensating members is that the stent will substantially compensate for foreshortening as the stent is expanded. In the embodiment shown inFIG. 15, the first, second, third andfourth members51,54,57 and60 have a width of about 0.1 mm. The first andsecond loops63 and65 have a width of about 0.14 mm. The first and second compensatingmembers67 and71 are provided with a thickenedportion75 and76 having a width of about 0.12 mm. Thus, in this especially preferred embodiment, the first and second loops have a width that is about 40% greater and the first and second compensating members have a width that is about 20% greater than the width of the first, second, third and fourth members.
• FIGS. 16 through 20 show details of a stent constructed in accordance with this invention.
• Yet another advantage of Applicants' invention is shown in FIGS.21 to24. For the sake of clarity, the dimensions and the degree of displacement of the components of the stents shown in FIGS.21 to24 has been intentionally exaggerated.
• FIG. 21 is a cross-sectional front view taken along line A-A of the unexpanded stent made in accordance with applicants invention shown inFIG. 20. Theunexpanded stent200 ofFIG. 21 is shown disposed in thelumen202 of ablood vessel201 prior to expansion. As previously discussed, this stent is made by first cutting the stent pattern into a flat piece of sheet metal and then rolling the sheet metal into a tube to form the tubular stent. As shown inFIG. 21 after rolling, the first and second flexible compensatingmembers67 and71 of the unexpanded stent tend to “flare out” in a direction away from the longitudinal axis or lumen of the stent. Thus, the flexible compensatingmembers67 and71 define outer diameters which are larger than the outer diameters defined by the remaining portions of the stent.FIG. 22 shows the stent ofFIG. 21 after it has been expanded in the lumen and against the internal wall of the blood vessel. As shown inFIG. 22, upon expansion of the unexpanded stent toward the wall of the blood vessels, the walls of the blood vessel imparts a mechanical force to the first and second flexible compensatingmembers67 and71 and the compensating members move toward the longitudinal axis or lumen of the stent until they are substantially in registry with the remaining portion of the stent. Thus, the lumen of the expanded stent is substantially circular when viewed in cross section with substantially no portion of the expanded stent projecting into the lumen or towards the longitudinal axis of the expanded stent.
• FIG. 23 is similar toFIG. 21 except that the pattern has been cut into a tubular member using conventional methods of making stents. As shown inFIG. 23, the flexible compensating members do not flare out away from the longitudinal axis of theunexpanded stent203. Upon the expansion of the stent shown inFIG. 23 toward the walls of theblood vessel201, the flexible compensatingmembers67′ and71′ tend to “flare in” and project into thelumen204 of the expandedstent203.
• FIG. 24 shows thestent203 ofFIG. 23 after it has been expanded in alumen204 of ablood vessel201. The flexible compensatingmembers67′ and71′ are not in registry with the remaining portions of the stent and define a diameter smaller than the diameter of remaining portions of the stent. These projections into the lumen of the stent create turbulence in a fluid flowing through the longitudinal axis of the expanded stent and could result in clot formation.
• It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow.

Claims (5)

1-63. (canceled)

64. An expandable stent, comprising:

a plurality of portions connected, after removal of a plurality of temporary bridges, by a plurality of flexible compensating members, the flexible compensating members projecting from an external surface of the stent when the stent is in an unexpanded condition and configured to be in circumferential registry with remaining portions of the stent when the stent is in an expanded condition.

65. The stent ofclaim 64, wherein the stent is expandable from a first diacter to a second diameter so the flexible compensating members project from the external surface of the stent when the stent is at the first diameter and are configured to be in circumferential registry with remaining portions of the stent when the stent is at the second diameter.

66. An expandable stent, comprising:

a plurality of portions connected, after removal of a plurality of temporary bridges, by a plurality of flexible compensating members, wherein substantially no portion of the stent projects into a longitudinal lumen of the stent when the stent is expanded from a first diameter to a second diameter.

67. The stent ofclaim 66, wherein the second diameter is greater than the first diameter.

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