Abstract:
side and a pair of pins for insertion into the sleeve. In another embodiment, the device has an expanding mandrel having a side, two open ends and a plurality of longitudinal slots along the side. An expansion pin is included, and has a cylindrical body with a tapered tip. In another embodiment, the device expands a stent into a tapered stent. The tapered stent expanding device includes a slotted expansion mandrel and a tapered pin having an expansion crown. In another aspect, the device includes a threaded mandrel for the uniform expansion of the diameter of a stent.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates generally to minimum stress expansion devices for stents that limit the stresses applied to stent struts in the expansion process of stents. 
         [0002]    The term stent generally refers to a prosthesis, which can be introduced into a corporeal lumen and expanded to support that lumen or attach a conduit to the inner surface of that lumen. Stents made of shape settable material are generally known in the art. Stents are generally either balloon expandable or self-expanding devices. A balloon expandable stent is delivered within vasculature mounted on a balloon catheter and expanded at an interventional site to accomplish implantation. The self-expanding stent is compressed into a reduced size having an outer diameter substantially smaller than the stent in its expanded shape. The stent is held in its compressed state during its passage through the patient&#39;s vascular system until reaching the target treatment site, whereupon the compressed self-expanding stent may be deployed. While in its compressed state, stress is stored in the bends of the stent limbs. During deployment, the stresses in the stent limbs cause the stent to expand radially from its initially compressed state. Once in place, the radial extremities of the stent bear against the inside walls of the passageway, thereby allowing normal blood flow. 
         [0003]    One particular type class of shape settable materials that are practical for stents include Nickel-Titanium alloys (Nitinol). Previous methods to set a desired expanded Nitinol stent configuration involved forcing the stent over a cylindrical mandrel matching the desired inner diameter of the stent. The stent is then heat treated until the shape memory of the stent in its austenite phase has a diameter matching that of the mandrel. This process results in producing a stent that does not store stress in an optimal manner. Certain current approaches to stent expansion processes utilize the superelastic properties of Nitinol by creating a phase transformation in the stent as its diameter is enlarged. Alternatively, the stent may be tapered and, for example, transition from a seven millimeter (mm) diameter to a ten mm diameter over a thirty mm or forty mm length. Likewise, as with the uniform diameter stent, previous methods employed to expand a stent into a tapered stent involved forcing the stent onto a tapered mandrel and heating. Such methods suffer similar drawbacks to the methods used to uniformly expand stents. 
         [0004]    During the expansion process, the mechanical stress in the Nitinol causes a phase transformation from austenite to martensite to accomplish a change in diameter. Stents may be chilled to lower temperatures to transform them to martensite as a way to lower the forces required by an operator to perform the expansion process. Once the stent has been shaped to the increased diameter, a heat treatment process at approximately 525 degrees Centigrade (° C.) is used to transform the atomic structure of the stent back to austenite and relieve built up internal stresses. 
         [0005]    Current expansion tooling consists of a cylindrical mandrel with a tapered end. In order to perform shape setting, an operator may use a push-pull technique to load the stent over the tapered mandrel. The superelastic property of Nitinol allows it to recover from up to eight to ten percent strain without deformation. The theoretical plane strain of a stent strut is up to six percent for practical expansions steps, when considering ideal radial expansion only. Additional strain provided by this technique may result in an amount of strain which exceeds the capability of the material to recover without deformation. Such a result is also associated with stents formed from materials which are not inherently superelastic. Inspection is required to determine whether further processing is needed to overcome the effects of this deformation. The repetitive nature of the push-pull technique can also lead to carpel tunnel syndrome in the operator. 
         [0006]    Previous methods employed successive one to two millimeter expansions of stents by employing mandrels of successively larger diameters. Though so intended, these methods did not eliminate the presence of cracks and notch defects. Notch defects occur after the post expansion treatment of a cracked stent. 
         [0007]    An improved method is needed, therefore, which accomplishes diameter expansion of an expandable or self-expanding stent by applying forces to the stent in an outward radial direction only. Such a technique would limit the strain of individual struts to a minimal level while eliminating the presence of longitudinal forces on the stent during the process of loading the stent onto shape setting tooling. The elimination of longitudinal forces is especially important for stents of designs that do not have sufficient longitudinal rigidity, as such designs are especially susceptible to excessive elongation or contraction. An improved method is desired that will minimize the potential for injury to the operator, that is also capable of automation and reduces or eliminates the influence of human error. 
         [0008]    The present invention satisfies these and other needs. 
       SUMMARY OF THE INVENTION 
       [0009]    Briefly and in general terms, the present invention is directed towards a stent expanding device for expanding the dimensions of stents. 
         [0010]    In one embodiment, the stent expanding device may uniformly expand the diameter of a stent. The device includes an expansion mandrel having a side, two open ends and a plurality of longitudinal slots along the mandrel&#39;s side. The device also includes an expansion pin having a cylindrical body and a tapered end. The expansion pin has an upper cylindrical body having a side face, a top face, and may include a closed channel in the side face and an open channel in the top face. 
         [0011]    In one aspect, the stent expanding device may include an expanding mandrel that has a cavity and a cut along the length of the side. The device also includes an expansion pin having a tapered tip. The mandrel may include overlapping members configured to fit into receiving grooves in the mandrel. In a method of use, a stent is loaded onto a mandrel that has a cavity and a cut along the length of the side. An expansion pin is then inserted into the cavity of the mandrel. 
         [0012]    An alternative embodiment of the stent expanding device has an expansion mandrel having a cavity, a side, two open ends, and a plurality of longitudinal slots along the side. The slots are spaced at regular intervals and have a terminus that is continuous with the ends of the mandrel. The slots commence at a keyhole in the side of the mandrel, and each consecutive slot terminates at an end of the mandrel opposite to the end of the preceding slot. The device has an expansion pin having a cylindrical body and a tapered end, an expansion crown that has teeth and a bore. The teeth are configured to slide into the termini of the slots and the bore is configured to receive the cylindrical body of the expansion pin. A rounding rod is provided and is configured to be received into the cavity of the mandrel. In a method of use, an expansion pin is inserted into an expansion crown to form a loaded expansion pin. A stent is slid onto a mandrel to form a loaded mandrel. The loaded expansion pin is then partially inserted into each end of the mandrel. Expansion crowns are slid down the expansion pins until fingers of the crowns are seated in slots of the mandrel. The loaded expansion pin is completely inserted into each end of the mandrel to form an expanded stent. 
         [0013]    Another embodiment of the stent expanding device expands the stent into a tapered stent. The device includes a tapered mandrel that has a closed end, an open end, and slots along the side of the tapered mandrel. The slots extend from the closed end of the mandrel and terminate at and are continuous with the open end of the mandrel. The device also includes a tapered expansion pin that has a tapered cylindrical body. The tapered stent expanding device may further include teeth on the tapered expansion pin. The teeth are configured to be received into the termini of the slots. The tapered stent expanding device may further include a contraction ring that has a circular passageway. The passageway is configured to receive the tapered mandrel. In another method of use, a contraction ring is slid over a mandrel that has a closed end and an open end. A stent is loaded onto the mandrel from the closed end. The contraction ring is slid away from the stent. A tapered pin is inserted into the open end of the mandrel. 
         [0014]    In another aspect, the stent expanding device includes a threaded mandrel that has a tapered tip. The device further includes a rotating device for rotating the threaded mandrel. In a method of use, a threaded mandrel that has a tapered tip is rotated, and a stent is fed onto the mandrel while the mandrel rotates. 
         [0015]    The above described device has broad applicability to stents made of any shape settable material. Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective view, depicting a stent expanding device of the present matter; 
           [0017]      FIG. 2  is a perspective view, depicting another embodiment of an expanding mandrel of the present invention, in an expanded state; 
           [0018]      FIG. 3  is a perspective view, depicting the expanding mandrel of  FIG. 2 , in an unexpanded state; 
           [0019]      FIG. 4  is a perspective view, depicting another embodiment of a stent expanding device in an expansion kit; 
           [0020]      FIG. 5  is a perspective view, depicting an expansion pin; 
           [0021]      FIG. 6  is a perspective view, depicting a rounding rod; 
           [0022]      FIG. 7  is a perspective view, depicting an expansion crown; 
           [0023]      FIG. 8  is a perspective view, depicting the expansion crown of  FIG. 7  loaded on the expansion pin of  FIG. 5 ; 
           [0024]      FIG. 9  is a perspective view, depicting the expanding mandrel of  FIG. 4 ; 
           [0025]      FIG. 10  is a perspective view, depicting the expanding mandrel of  FIG. 9  with the rounding rod of  FIG. 6  inserted therein; 
           [0026]      FIG. 11  is a perspective view, depicting the assembly of  FIG. 10  having a stent loaded thereon; 
           [0027]      FIG. 12  is an enlarged partial view, depicting the mandrel having a stent loaded thereon; 
           [0028]      FIG. 13  is a perspective view, depicting the mandrel of  FIG. 9  having two stents loaded thereon; 
           [0029]      FIG. 14  is a perspective view, depicting the loaded expanding mandrel of  FIG. 13  in operation with a pair of loaded expansion pins; 
           [0030]      FIG. 15  is an enlarged partial view, depicting the loaded expanding mandrel of  FIG. 14  with a loaded expansion pin further advanced into the mandrel; 
           [0031]      FIG. 16  is a perspective view, depicting a stent expanding device with the pins completely inserted and a pair of expanded stents loaded thereon; 
           [0032]      FIG. 17  is a perspective view, depicting a tapered stent expanding device; 
           [0033]      FIG. 18  is a perspective view, depicting a contraction ring in operation with the tapered stent expanding device of  FIG. 17  without the tapered expansion pin; 
           [0034]      FIG. 19  is a perspective view, depicting the tapered expanding mandrel of  FIG. 18  with a stent loaded thereon; 
           [0035]      FIG. 20  is a perspective view, depicting the tapered expansion pin of  FIG. 17  in operation with the tapered expanding mandrel of  FIG. 17 ; 
           [0036]      FIG. 21  is an enlarged partial view, depicting a tapered expansion pin seated completely in the tapered expanding mandrel; 
           [0037]      FIG. 22  is a plan view, depicting the tapered stent expanding device in combination with handling structures; 
           [0038]      FIG. 23  is a cross-sectional view, depicting a terminal end portion of a tapered threaded mandrel; 
           [0039]      FIG. 24  is a plan view, depicting the tapered threaded mandrel of  FIG. 24  in operation with a rotating device; and 
           [0040]      FIG. 25  is a cross-sectional view, depicting the tapered threaded mandrel of  FIG. 24  with a stent loaded thereon. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    Turning now to the figures, which are provided for example and not by way of limitation, there is shown the stent expanding device of the present invention. Incorporated into the stent expanding device are components designed to integrate with each other to expand a stent to an expanded diameter. The device is appropriate for both open cell and closed cell stents. 
         [0042]    Referring to the drawings, which are provided for purposes of illustration and by way of example, the present invention provides for a stent expanding device  10  for stents and a method of using same. In one aspect, as shown in  FIG. 1 , the device  10  includes an expanding mandrel  20 , and expansion pins  21 . The pins  21  are generally in the shape of cylinder with a tapered end  23  for ease of insertion into the expanding mandrel  20 . The expanding mandrel  20  is shaped in the form of a hollow right cylinder with a cut  22  along the length of a side  24  and includes a hollow cavity  33 . In another aspect, as shown in  FIGS. 2 and 3 , the mandrel  20  has overlapping members  26  that fit into corresponding receiving grooves  28 . In operation, a stent to be expanded is loaded entirely onto the mandrel  20  and the expansion pins  21  are inserted very close in time to one another, into the cavity  33  of the mandrel  20 . The stent is expanded by the insertion of the pins  21 . After undergoing a shape setting procedure and subsequent removal of the pins  21 , the stent may be removed from the mandrel  20 . The mandrel  20  can be biased to remain in an unexpanded state to facilitate removal of the expanded stent. 
         [0043]    In another aspect, as shown in  FIG. 4 , a stent expanding device  27  includes a rounding rod  15 , an expanding mandrel  29 , expansion pins  25  and expansion crowns  30 . The device may be provided in kit form, neatly stored in a base  32 . The device  27  can be made of Inconel® or another suitable material that does not deform or shape set at a heat treatment temperature of 525° C. 
         [0044]    With reference to  FIGS. 5 and 6 , the rounding rod  15  has a cylindrical body  35  with two conical shaped tips  40 . As shown in  FIG. 5 , the expansion pin  25  has a lower cylindrical body  45  connected to an upper cylindrical body  50 . The upper cylindrical body  50  has a closed channel  55  in a side face  60  and an open channel  65  in a top face  70  of the upper cylindrical body  50 . The lower cylindrical body  45  is connected to and coaxial with a bottom face  75  of the upper cylindrical body  50  and terminates at a tapered conical end  80 . The closed channel  55  and open channel  65  can be used in the handling of the stent expanding device  27  as described in further detail below. The expansion pin  25  may have an internal bore  68  for receiving the rounding rod  15 . 
         [0045]    As shown in  FIG. 7 , the expansion crown  30  is generally shaped as a right cylinder with a bore  85  through a center of the structure. The crown  30  has a top face  90  and a bottom face  95 . The bore  85  is sized and shaped to receive the lower cylindrical body  45  of the expansion pin  25 , as shown in  FIG. 8 . Along the bottom face are fingers  100 , symmetrically located every thirty degrees although other spacing including variable spacing is contemplated. The fingers  100  have tapered tips  105 . In one aspect, the top face  90  of the crown  30  can be integral with the bottom face  75  of the pin  25 . 
         [0046]    The expanding mandrel  29 , as shown in  FIG. 9 , is generally in the shape of a right cylinder. The mandrel  29  has slots  110  that run parallel to a long axis  115  of the mandrel  29  and located symmetrically around a side  120  of the mandrel  29  at thirty degree intervals. It is to be recognized, however, that various numbers of slots can be incorporated into the mandrel  29  and accordingly, such slots can be spaced optimally about the mandrel  29 . In one particular embodiment, the slots  110  commence at and are also open at the ends  125  of the mandrel  29  and run along a substantial length of the mandrel  29  and terminate at keyholes  130 . The slots  110  alternate in orientation such that each slot  110  is located between two other slots  110  that commence at an opposite end  125  of the mandrel  29 . The mandrel  29  has a hollow interior cavity  135  with a diameter approximately equal in size to a diameter  18  of the rounding rod  15 . The mandrel  29  has a smooth transition portion  140  between the end  125  and the cavity  135  and in certain applications is curved inward for facilitating reception of the lower cylindrical body  45  of the expansion pin  25  into the cavity  135 , as shown in  FIG. 10 . 
         [0047]    Referring now to  FIGS. 11-16 , a method of using the stent expanding device  27  is described.  FIG. 11  depicts the rounding rod  15  inserted into the cavity  135  of an expanding mandrel  29  that is, for example, 2-6 millimeters in diameter to form the mandrel  29  into a smooth circular tube. As shown in  FIGS. 11 and 12 , a stent  12  is then slid onto mandrel  29  to form a loaded mandrel. If the stent  12  is 40 millimeters or less in length, for example, two stents  12  may be placed on the mandrel  29 , as shown in  FIG. 13 . The stents  12  are placed completely between the keyholes  130 , which are located near both ends  125  of the mandrel  29 . The spines  145  of the stents  12  can be aligned with the slots  110 . Next, the rounding rod is removed from the mandrel  29 . The loaded mandrel is then immersed in alcohol to cool the stent  12  to approximately −10° C. The cooling causes a Nitinol stent to transition to the martensite phase in order to reduce the forces exerted by the operator in the loading of the shape setting tool. Accordingly, it is contemplated that not all stents require the same cooling step. 
         [0048]    Thereafter, as shown in  FIG. 14 , the expansion pins  25  are inserted into the expansion crowns  30  to form loaded expansion pins (see  FIG. 8 ). After cooling of the stents  12  is completed, the loaded mandrel  29  is removed from the alcohol and a loaded expansion pin  25  is inserted straight into each end  125  of the mandrel  29 , to a midpoint  150  of the expansion pin  25 , as shown in  FIGS. 14 and 15 . The rounding rod  15  may be received into the cavity  68 , when the pins  25  are inserted into the mandrel  29  or the rounding rod  15  is removed prior to placing the expansion pins  25  into the loaded mandrel  29 . As shown in  FIG. 15 , the expansion crowns  30  are slid down the expansion pins  25  until the fingers  100  of the crowns  30  are seated in the slots  110  of the mandrel  29 . The pins  25  are then pressed completely into the mandrel  29 , as shown in  FIG. 16 . With the aid of a microscope, if necessary, the spines  145  of the stent  12  are aligned with the slots  110 . The stent  12  is then treated in a salt solution, and thereafter, the expanded stent  12  and the stent expanding device  27  are heat treated at a temperature of 525° C. The foregoing procedure may be repeated with successively larger mandrels  29  until the stent  12  is expanded to the desired size. The above described process may reversed to removed the stent  12  from the device  27 . Final stent diameters may range from five mm to ten mm for uniform diameter stents. 
         [0049]    In another aspect, as shown in  FIGS. 17-22 , the stent expanding device  147  includes a tapered expanding mandrel  155 . The tapered mandrel  155  has a closed end  158  and an open end  160 . Referring to  FIG. 17 , the tapered mandrel  155  has slots  111  that run along a long axis  112  of the tapered mandrel  155  and located symmetrically around a side  120  of the tapered mandrel  155  at regular intervals (for example, between 15 and 40 degree intervals). The slots  111  commence at, and are also open at, the open end  160  of the tapered mandrel  155  and run along a substantial length of the tapered mandrel  155  and terminate at keyholes  130 . Indicator marks  162  are provided on the side  120  to aid in the proper placement of the stent  12  on the mandrel  155 . 
         [0050]    As shown in  FIGS. 17 and 20 , a tapered expansion pin  165  is provided. The tapered expansion pin has a lower tapered cylindrical body  175  connected to an upper cylindrical body  180 . The upper cylindrical body  180  has a channel  182  in a side face  184  and an open channel  183  in a top face  187  of the upper cylindrical body  180 . The lower tapered cylindrical body  175  is connected to and coaxial with a bottom face  189  of the upper cylindrical body  180 . The tapered expansion pin  165  includes fingers  191  along the bottom face  189 , symmetrically located every thirty degrees. Again, the spacing and number of fingers can be varied for a particular purpose. The fingers  191  have tapered tips  193 . The device  147  also includes a contraction ring  185 , as shown in  FIG. 18 , that is generally doughnut shaped having a circular passageway  190 . 
         [0051]    In a first step, the contraction ring  185  is slid over the mandrel  155  commencing at the closed end  158  and until the open end  160 . As shown in  FIG. 19 , a stent  12  that is to become tapered is loaded onto the mandrel  155  at the closed end  158  and is placed between the indicator marks  162 . The indicator marks  162  identify the optimal placement of the stent  12  for expansion to a desired shape. After placement of the stent  12  the contraction ring  185  is removed. The tapered pin  165  is inserted into the open end  160  of the mandrel  155  and advanced until the fingers  100  are completely seated in the slots  111 , as shown in  FIGS. 20 and 21 . Thereafter, the stent  12  is in an expanded, tapered configuration. The stent  12  along with the stent expanding device  147  may be heat treated (and cooled) in a manner similar to that described in previous embodiments, and thereafter, the pin  165  may be removed from the mandrel  155  so the expanded stent  12  may be retrieved from the device  147 . 
         [0052]    As shown in  FIG. 22 , structures can be employed to facilitate handling of the stent expanding device  147 . For example, arms  157  may be slid through the closed channels  182  of the pin  165  and the mandrel  155  to aid in the manipulation of the device  27  and to remove the expansion pin  165  from the expanding mandrel  155 . In one instance, the stent expanding device  147  may be automatically moved to and from a chilled solution of isopropyl alcohol. Such an arrangement can be employed with other embodiments previously described, such as the device shown in  FIGS. 5 and 6 . 
         [0053]    In still a further aspect, as shown in  FIGS. 23-25 , the stent expanding device  188  includes a tapered threaded mandrel  195 . The mandrel  195 , as shown in  FIG. 23 , is generally cylindrically shaped with a conical shaped end  198 . The mandrel  195  has a shape set portion  200  and an expansion portion  205 . The mandrel  195  has threads  210  that commence at a thread commencing point  215  on the expansion portion  205  and continue over the cylindrical body portion  200 . The device  188  further includes a motorized rotating member  220 , as shown in  FIG. 24 . The threaded mandrel  195  is loaded into the motorized rotating member  220  and the stent expansion process may be begun. As the mandrel is rotated  220 , the stent  12  is guided onto the mandrel  195  over the threads  210  to expand the diameter of the stent  12 , as shown in  FIG. 25 . The stent  12  along with the mandrel  195  may be heat treated in a manner similar to that described in previous embodiments, and thereafter, the expanded stent  12  may be retrieved from the  195 . 
         [0054]    In another aspect, a procedure for verifying the outer diameter of the mandrel in its expanded state is provided. First the rounding rod is inserted into the mandrel. Next, two O-rings, configured to fit on the unexpanded mandrel, are slid onto the mandrel and position five to ten mm apart near the center of the mandrel. The rounding rod is then removed and the expansion pins are inserted halfway into the mandrel. The expansion crowns are then slid down into the slots of the mandrel. The pins are thereafter pushed completely into the mandrel until they flush against the crowns. Then, a laser micrometer is used to take three measurements of the outer diameter of the expanded mandrel between the O-rings. Each measurement is taken at a one third rotations apart. 
         [0055]    The invention described herein has the benefit of improving the efficiency and effectiveness of the stent expansion processes. The invention also lends itself to increased automation or semi-automation thus reducing or eliminating the impact of operator technique on quality. Furthermore, the invention has the advantage of being capable of expanding long stents, up to at least 150 millimeters, and accommodating the expansion of multiple stents simultaneously. 
         [0056]    While the specification describes particular embodiments of the present invention, those of ordinary skill can devise variations of the present invention without departing from the inventive concept. Accordingly, it is not intended that the invention be limited, except as by the appended claims.