Patent Publication Number: US-8533925-B2

Title: Method for contracting or crimping stents

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/537,044, filed Aug. 6, 2009, issued as U.S. Pat. No. 7,992,273 B2, which is a continuation of Ser. No. 11/159,490, filed Jun. 23, 2005, issued as U.S. Pat. No. 7,587,801, which is a continuation of U.S. patent application Ser. No. 10/444,807, filed on May 23, 2003, issued as U.S. Pat. No. 6,915,560, which is a divisional of U.S. patent application Ser. No. 09/966,686, filed on Oct. 1, 2001, issued as U.S. Pat. No. 6,823,576, which is a continuation of U.S. patent application Ser. No. 09/401,218, filed on Sep. 22, 1999, issued as U.S. Pat. No. 6,360,577, which are all herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus and a method for reducing in size a medical device such as a stent, stent-graft, graft, or vena cava filter. The apparatus may be used in particular for fastening a medical device onto a catheter. 
     Medical devices such as stents, stent-grafts, grafts, or vena cava filters and catheters for their delivery are utilized in a number of medical procedures and situations, and as such their structure and function are well known. 
     A stent, for example, is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition. 
     Stents are typically inflation expandable or self-expanding. Self expanding stents which are constrained by a sheath or other restraining means, must be provided in a reduced diameter. 
     An example of a stent described in PCT Application No. 960 3092 A1, published 8 Feb. 1996. 
     In advancing a stent through a body vessel to the deployment site, the stent must be able to securely maintain its axial position on the delivery catheter, without translocating proximally or distally, and especially without becoming separated from the catheter. Stents that are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location. The stent must be crimped in such a way as to minimize or prevent altogether distortion of the stent and to thereby prevent abrasion and/or reduce trauma of the vessel walls. 
     In the past, this crimping or size reduction has been done by hand often resulting in the application of undesired uneven forces to the stent. Such a stent must either be discarded or re-crimped. Stents which have been crimped or otherwise reduced in size multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. A poorly crimped stent can also damage the underlying balloon. 
     Recently, stent crimping devices have been disclosed in U.S. Pat. No. 5,546,646 to Williams et al, U.S. Pat. No. 5,183,085 to Timmermans et al., U.S. Pat. No. 5,626,604 to Cottone, Jr., U.S. Pat. No. 5,725,519, U.S. Pat. No. 5,810,873 to Morales, WO 97/20593 and WO 98/19633. 
     A cam actuated stent crimper, shown in  FIG. 1 , employs a plurality of arc-shaped or curved slots with semi-circular ends, disposed such that each slot or cam engages a cam follower bearing  22 . The arc-shaped or curved surfaces of the slots are inclined to be non-concentric relative to the axis of rotation  26 , and therefore rotation of the cam plate  28  transmits equal radial displacements to the cam follower bearings  22 , to simultaneously actuate a like number of linear bearings  24 , which have their corresponding linear tracks or rails mounted on a fixed plate. As shown in  FIG. 1  the cam plate rotary drive  29  comprises a pneumatic cylinder mounted on a pivot or trunnion, arranged with the cylinder rod connected rotatably to a short arm fixed rigidly to the cam plate. Accordingly, linear motion produced by the pneumatic cylinder translates into controllable arcs of motion of the circular cam plate, which has a projecting V-shaped profile on its outer edge in rolling engagement with three equally spaced rollers with mating inverse V-shaped profiles to provide precise rotatable support to the cam plate. Depending on the direction of rotation, the linear slides which each carry a radially disposed crimping blade, are either moved inwards to apply a crimping force to the stent, or outwards to release the stent. Also when crimping, depending on the degree of rotation of the cam plate, a specific radial crimping displacement may be obtained to match the diametral reduction required for any particular stent. 
     All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety. 
     BRIEF SUMMARY OF THE INVENTION 
     It would be desirable to produce a device capable of crimping a stent uniformly while minimizing the distortion of and scoring and marking of the stent due to the crimping. The present invention is directed to that end. 
     The present invention is particularly concerned with the crimping and otherwise reducing in size of inflation expandable stents, self-expanding stents and other expandable medical devices. For the purpose of this disclosure, it is understood that the term ‘stent’ includes stents, stent-grafts, grafts and vena cava filters. It is also understood that the term ‘crimping’ refers to a reduction in size or profile of a stent. 
     In the description that follows it is understood that the invention contemplates crimping a medical device either directly to a catheter tube or to a catheter balloon which is disposed about a catheter tube. When reference is made to crimping a medical device to a catheter, a balloon may be situated between the medical device and the catheter tube or the medical device may be crimped to a region of a catheter tube directly. The invention also contemplates crimping a stent in the absence of a catheter to reduce the stent in size. 
     The present invention is directed, in one embodiment, to an apparatus for reducing a medical device in size. Desirably, the medical device is a stent, a stent-graft, a graft or a vena cava filter, whether self-expandable, balloon expandable or otherwise expandable, although the inventive apparatus may also be employed with any other suitable, generally tubular medical device which must be reduced in size. 
     The inventive apparatus comprises at least three coupled movable blades disposed about a reference circle to form an aperture whose size may be varied. Each blade is in communication with an actuation device which is capable of moving the blade to alter the size of the aperture. Each blade includes a single radial point on the surface of the blade which a) lies on the circumference of the reference circle prior to movement of the blade, and b) may be moved only along a radius of the reference circle on movement of the blade. 
     The apparatus further includes an actuation device which comprises a cam and a plurality of linear slide devices. Each linear slide device is in communication with a blade. Each of the linear slide devices is also in mechanical communication with the cam. Rotation of the cam results in linear translation of the slide device and blade, such that the slide device moves along an axis parallel to the radius on which the radial point of the blade lies or along the radius itself. 
     The invention is also directed to an apparatus similar to that described above, with blades disposed about a reference tube to form a tubular aperture whose size may be varied. Each blade is in communication with an actuation device which is capable of moving the blade to alter the size of the tubular aperture. Each blade includes a single line which a) lies on the surface of the reference tube prior to movement of the blade, and b) may be moved only along a radial plane of the reference tube on movement of the blade. 
     The inventive apparatus finds particular utility in crimping a medical device such as those mentioned above to a catheter or to a balloon disposed about a catheter. 
     The inventive apparatus also finds utility in reducing the diameter of a medical device such as those mentioned above prior to crimping. 
     The invention is also directed to a method of manipulating a medical device which comprises the steps of providing the medical device and providing at least three blades capable of applying a radial inward force. The blades are disposed about a reference circle to form a shrinkable aperture. A medical device such as a stent is placed into the shrinkable aperture and the blades simultaneously moved inward to apply a radial inward force to the medical device. The blades are constructed and arranged such that each blade has a single point which a) lies on the circumference of the reference circle prior to movement of the blade, and b) is moved along a radius of the reference circle on movement of the blade. 
     The inventive apparatus may also be used as a variable size balloon mold. To that end, the invention is further directed to a method of molding a medical balloon. In the practice of the method, a balloon preform prepared through any suitable technique known in the art is provided. The preform is placed in an apparatus which has a shrinkable tubular aperture formed by at least three movable blades disposed about a reference tube. The blades are constructed and arranged such that each blade has a single line which a) lies on the surface of the reference tube prior to movement of the blade, and b) is moved along a radial plane of the reference tube on movement of the blade. The aperture may be set to a predetermined size prior to placement of the preform therein or after placement of the preform therein. An inflation fluid is supplied to the balloon preform to expand the balloon preform until it contacts the blades. The preform may optionally be heated prior to, during or after the blowing step. The thus formed balloon is then pressure relieved and removed from the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  shows a perspective view of a stent crimper; 
         FIG. 2   a  is a schematic front view of an embodiment of the inventive apparatus; 
         FIG. 2   b  is a schematic front view of the embodiment of  FIG. 2   a  after the stent has been reduced in size; 
         FIGS. 3   a  and  3   b  are schematics of blades; 
         FIG. 3   c  is a partial schematic front view of an embodiment of the inventive apparatus employing the curved blades of  FIG. 3   b;    
         FIG. 4   a  is a partial front view of an embodiment of the inventive apparatus; 
         FIG. 4   b  is a partial front view of an embodiment of the inventive apparatus; 
         FIG. 4   c  shows a side view of the embodiment of  FIG. 4   b  taken along lines  4   c - 4   c;    
         FIG. 5   a  shows a partial front view of another embodiment of the inventive apparatus; 
         FIG. 5   b  shows a link connected to a blade; 
         FIG. 6  is a schematic, perspective view of an embodiment of the inventive apparatus; 
         FIG. 7  shows a partial view of the embodiment of  FIG. 6 ; 
         FIGS. 8   a  and  8   b  are partial side elevational views of an embodiment of the inventive apparatus taken along a radial plane during the size reduction process; 
         FIG. 8   c  is a partial side elevational view of an embodiment of the inventive apparatus taken along a radial plane following crimping of a stent to a catheter; 
         FIG. 9  is a diagrammatic side elevational view of an embodiment of the inventive apparatus; 
         FIG. 10  is a partial side elevational view of an embodiment of the inventive apparatus taken along a radial plane of an embodiment of the invention consisting of three individual apparatuses arranged sequentially; 
         FIG. 11  is a schematic showing a stent being reduced in size and loaded into a sheath; 
         FIG. 12  is a partial side elevational view of an embodiment of the inventive apparatus taken along a radial plane showing a balloon that has been molded with the inventive device; and 
         FIG. 13  is a partial side elevational view taken along a radial plane  5  showing a stepped balloon that has been molded with the inventive device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. 
     As shown generally at  100  in  FIGS. 2   a  and  2   b , the inventive apparatus comprises eight coupled blades  106  disposed about a reference circle  114  to form an aperture  118  whose size may be varied. The apparatus may comprise as few as three blades and as many as sixteen or more blades. Desirably, the apparatus will have four or more blades and more desirably, eight or more blades. The maximum number of blades is limited only by how many blades can physically be coupled together under the relevant size constraints. As the number of blades is increased, the profile of the aperture and hence of the medical device following reduction in size, becomes smoother.  FIG. 2   b  shows the apparatus of  FIG. 2   a  after the stent has been reduced in size. 
     Blades  106  as shown in  FIG. 3   a  have an inner end  108  which is desirably beveled  111  so as to mesh with adjacent blades and an outer end  110  which is displaced from aperture  118 . Aperture  118  is polygonal. Blades  106  may also be shaped with a curved end  112 , as shown in  FIGS. 3   b  and  3   c  so as to form a substantially circular shaped aperture, when the aperture is fully closed. 
     Each blade  106  includes a single radial point  122  which lies on a radial line  126  of reference circle  114  prior to movement of blade  106  and which may be moved only along the radius  126  of reference circle  114  on movement of blade  106 . Desirably, the single radial point  122  will be disposed at the tip of the blade adjacent to beveled end  111 . 
     In the embodiment shown in  FIG. 4   a , radial point  122  lies at the tip of blade  106 . Each blade  106  has a connecting link  130  extending from second end  110 . Connecting link  130  ends in mounting means  134 , typically a mounting flange adapted for attachment to a linear bearing block, for interfacing with an actuation device, shown generally at  138 . Actuation device  138  is capable of simultaneously moving blades  106  to alter the size of aperture  118 . 
     Actuation device  138  includes actuation plate  142  which is coaxial with reference circle  114 . Actuation plate  142  has eight equi-spaced radial slots  146 . More generally, for every blade there will be a corresponding radial slot on actuation plate  142 . Each radial slot  146  overlaps a mounting means  134  for a linear bearing block at the end of a connecting link  130 . Each blade  106  is engaged to actuation plate  142  via a cam follower bearing  150  disposed in radial slot  146  and attached to mounting means in slotted end  134 . 
     Each bearing  150  extends from a linear slide  154 . Linear slide  154  is mounted on a non-rotating plate  156  (shown in  FIG. 8 ). Linear slide  154  is constructed and arranged to slide along a line  158  which is parallel to the radius  126  on which radial point  122  of blade  106  lies. 
     For the purposes of this disclosure, the term ‘cam follower bearing’ includes cam follower bearings, low friction rollers, roller bearings, needle roller bearings and a slipper block pivot mounted on a bearing and stub shaft.  FIG. 4   b  is a partial front view of an embodiment in which a slipper block is used. A side view of the embodiment of  FIG. 4   b  taken along lines  4   c - 4   c  is shown in  FIG. 4   c . Slipper block  150  resides in slot  146  of actuation plate  142 . Slipper block  150  is mounted on stub shaft  151  which extends from connecting link  130 . Desirably, bearings  153  will be present between shaft  151  and slipper block  150 . Connecting link  130 , in turn, is fastened to linear bearing block  212  via fasteners  214 . Bearing block  212  is linearly mounted on linear slide which is mounted on fixed plate  156 . Linear motion is facilitated by the presence of bearings  216 . 
     Cam follower bearing  150  may be replaced by any other suitable connecting member which can connect the slide and the link. 
     In use, as actuation plate  142  is rotated in a clockwise direction, the clockwise motion of the actuation plate is translated into linear motion of each of linear slide  154  and blade  106  via bearing  150 . Each blade  106  moves outward in a direction parallel to the radius  126  on which the radial point  122  of the blade  106  lies, resulting in the opening of aperture  118 . As actuation plate  142  is rotated in a counterclockwise direction, each blade  106  moves inward in a direction parallel to the radius  126  on which the radial point  122  of the blade  106  lies, resulting in the closing of aperture  118 . As aperture  118  closes, a radially inward force is applied to a medical device disposed in the aperture. The actuation plate is rotated until the desired size reduction of the aperture and medical device has been achieved. Following the reduction, the actuation plate is rotated in the opposite direction to allow for removal of the medical device from the aperture. 
     The apparatus may be used to reduce the diameter of a suitable medical device such as those disclosed above or may be used to crimp a medical device to a catheter. 
     Another embodiment of the invention is shown in  FIG. 5   a . Each blade  106 , as shown in  FIG. 5   a , has a connecting link  130  extending therefrom. Connecting link  130  is rigidly attached to blade  106 . Connecting link  130  ends in an angled end  134  for interfacing with an actuation device, shown generally at  138 . Actuation device  138  is capable of simultaneously moving blades  106  to alter the size of aperture  118 . 
     Actuation device  138  includes a rotatable actuation plate  142  which is co-axial with reference circle  114 . Rotatable actuation plate includes cam slots  146  which are not concentric with the axis of rotation, arcing inward. Each connecting link  130  is engaged to actuation plate  146  via a cam follower bearing  150  disposed in slot  146  and attached to both angled end  134  of connecting link  130  and to a linear slide  154 . Linear slide  154  is mounted on a non-rotating plate similar to that shown in  FIG. 8 . Linear slide  154  is constructed and arranged to slide along a radial line  158  on which radial point  122  of blade  106  lies. 
     Connecting link  130  may be bonded adhesively, welded, joined with a fastener or otherwise joined to blade  106 . As shown in  FIG. 5   a , a single screw  131  is used to connect link  130  to blade  106 .  FIG. 5   b  shows a connecting link  130  including a right angle portion which is fastened to a blade  106  using two screws  131 . Connecting link  130  and blade  106  may optionally be formed of a single piece of material. Regardless of how the connecting member is joined to the blade, no movement of the blade relative to the connecting link is permitted. 
     In use, as actuation plate  142  is rotated in a clockwise direction, the clockwise motion of the actuation plate is translated into a linear outward motion of each of linear slides  154  and blades  106  via bearings  150  resulting in the opening of aperture  118 . The outward motion results from the radially outward arcing of cam slot  146 . As actuation plate  142  is rotated in a counterclockwise direction, each blade  106 , because of the radially inward arc of cam slots  146 , moves inward in a direction parallel to the radius  126  on which the radial point  122  of the blade  106  lies, resulting in the closing of aperture  118 . As discussed above, as the aperture is decreased in size, a radial inward force is brought to bear against a medical device disposed in the aperture, thereby reducing the size of the medical device. 
     The embodiment of  FIG. 5   a  differs from the embodiment of  FIG. 4   a  in that in the embodiment of  FIG. 5   a , the slide moves along the radial line on which the radial point of the attached blade lies whereas in  FIG. 4   a  the slide moves parallel to the radial line. In both of the embodiments, each of the blades is constrained with two degrees of freedom to satisfy the condition that the movement of the tip be radial in accordance with the invention. 
     In the embodiments of  FIGS. 4   a  and  5   a , the slots in the actuation plate are constructed and arranged to allow for a sufficient reduction in size of the aperture so that a medical device can be reduced in size to a desired diameter. Those of ordinary skill in the art will recognize other suitable actuation devices that may be used in the practice of this invention. 
     Desirably, in the above embodiments, the blades will be as long as or longer than the medical device disposed within so that the medical device is uniformly reduced in size along its entire length. 
     This is illustrated in the embodiment of  FIGS. 6 and 7  and further in  FIGS. 3   a  and  3   b  in which blades  106  are disposed about a reference tube  160  to form a tubular aperture  162  whose size may be varied. Reference circle  114  is seen to lie along reference tube  160 . Each blade  106  is in communication with an actuation device such as that shown in  FIG. 4  or  5 . The actuation device is capable of moving blades  106  to alter the size of tubular aperture  162 . Each blade  106  includes a single line  166  which a) lies on a radial plane  170  of the reference tube  160  prior to movement of blade  106 , and b) may be moved only along a radial plane  170  of reference tube  160  on movement of blade  106 . Desirably, reference tube  160  is cylindrical and exceeds the length of the medical device to be reduced in size. 
     Another embodiment of the invention is illustrated in  FIGS. 8   a  and  8   b . In the embodiment of  FIGS. 8   a  and  8   b , two non-rotating plates  156  are present, one at each end of the apparatus. Each blade  106  is connected at first end  174  to a linear slide  154   a  via a connecting link  130   a  and at second end  178  to a linear slide  154   b  via a connecting link  130   b . Linear slide  154   a  is mounted on non-rotating plate  156   a  and linear slide  154   b  is mounted on non-rotating plate  156   b . The presence of the second non-rotating plate  156   b , linear slide  154   b  and connecting link  130   b  is optional but contributes to providing a rigid frame upon which the connecting links and associated blades may slide without misalignment relative to the reference circle. 
       FIGS. 8   a  and  8   b  illustrate the use of the inventive apparatus in various stages of the size reduction process. In  FIG. 8   a , stent  180  has been placed in tubular aperture  162  which is characterized by a diameter d 1 . In  FIG. 8   b , the device has been actuated by rotating actuation plate  142  so as to move blades  106  inward. Aperture  162 , as shown in  FIG. 8   b  is characterized by a diameter d 2  which is reduced relative to diameter d 1 . Stent  180  is seen to be of reduced diameter relative to its previous diameter as shown in  FIG. 8   a.    
       FIG. 8   c  differs from  FIG. 8   b , only in that stent  180  has been crimped onto catheter  184  in  FIG. 8   c.    
     Blades  106  may be made of any suitable, hard material including hardened steel. Desirably, the blades will be made of a material such as zirconia ceramic. Blades made of zirconia ceramic may be used without lubrication. Furthermore, because of their low thermal conductivity, they may be used to create a highly insulated chamber suitable for cryogenic processing of martensite in nitinol stents. 
     Such an embodiment is shown in  FIG. 9 . Stent  180  is disposed between blades  106  which can move inward in the direction of the arrows. Blades  106  are cooled by a first source of cooling fluid  184  located at first end  174  of blades  106 . Although not shown, a second source of cooling fluid may be provided at second end  178  of blades  106  as well. The cooling fluid may be a liquid cryogenic. Exemplary cryogenics include liquid nitrogen, argon or carbon dioxide although other cryogens may also be used. The cooling fluid may also be a chilled gas such as air. The cooling fluid may also be a cooled inert gas such as nitrogen, argon or other inert gasses. 
     The aperture formed by the blades is a highly insulated chamber which is suitable for cryogenic processing of martensite in nitinol stents. The chamber is maintained at −80° C. and a nitinol stent inserted therein. Upon equilibration of the temperature of the stent, the blades are moved inward to reduce the diameter of the stent. The stent is thus reduced in diameter while being maintained in the martensitic state. 
     The embodiment of  FIG. 9  further has a loading plunger  188  for loading a stent or other suitable medical device into the aperture. A sheath housing  192  which houses sheath  196  is provided at second end  178  of blades  106 . Plunger  188  may be further used to transfer the stent after it has been reduced in diameter or size to sheath  196 . Desirably, sheath  196  will have a slightly larger diameter than stent  180  following reduction in size of the stent. More desirably, the fit of the stent within the sheath will be within about 1/32″ and even more desirably, within about 1/64″. 
     Where lengthy stents or other medical devices are to be reduced in size, the invention contemplates using one of the above described apparatuses with long blades to accommodate the stent. As an alternative, the invention also contemplates disposing two or more of such apparatuses sequentially to form one long aperture. The two or more apertures may then be reduced in size simultaneously or consecutively. 
     The arrangement of  FIG. 10  shows an embodiment with three devices  100   a - c  arranged sequentially. A stepped reduction in size may be achieved by placing a stent  180  or similar medical device in the apparatus and independently reducing each aperture  118   a - c  to a desired size. To that end, the invention may provide particular utility in manipulating bifurcated stents or other stents whose diameter varies along its length. The embodiment of  FIG. 10  shows the end portions of the stent being reduced in size prior to the middle portion of the stent. The device may also be operated so as to reduce the middle portion in size prior to the end portions or in any other sequence. 
     The invention contemplates yet another approach to reducing the diameter of lengthy stents or similar medical devices, namely walking the stent through the apparatus. This may be accomplished by either moving the stent relative to the apparatus or moving the apparatus relative to the stent as shown schematically in  FIG. 11 . To that end, stent  180  is inserted in device  100 . Aperture  118   a  is reduced in size with blades  106   a  in turn reducing portion  180   a  of stent  180  in size. Aperture  118   a  is then opened and aperture  118   b  reduced in size thereby reducing portion  180   b  of stent  180 . Simultaneously, or shortly thereafter, sheath  196  is pushed by plunger  188  over the portion of the stent that has been reduced in size. Aperture  118   b  is opened and the stent advanced in the apparatus. The process is repeated until the entire length, or the desired portion of the stent or medical device is reduced in size. 
     The reduction in size of the stent or other medical device may occur as part of a precrimping step or it may occur as part of crimping a stent onto a catheter and desirably, onto a balloon disposed about a catheter. In a general sense, it may be used for manipulating a medical device and specifically, for applying a radial inward force to a medical device. 
     In another embodiment, the invention is directed to a method of manipulating a medical device. As part of the method, a medical device such as those disclosed above is provided. The device has at least three blades capable of applying a radial inward force. The blades are disposed about a reference circle to form a shrinkable aperture. The blades are constructed and arranged such that each blade has only a single point which a) lies on the circumference of the reference circle prior to movement of the blade, and b) is moved along a radius of the reference circle on movement of the blade. The medical device is placed into the shrinkable aperture and the blades simultaneously moved inward to apply a radial inward force to the medical device and thereby reduce the medical device in size, and desirably, in diameter. Following reduction in size of the medical device, the blades are simultaneously moved outward and the medical device removed from the aperture. 
     The inventive apparatus may also be incorporated into a blow molding tool to provide a variable size balloon mold as shown generally at  100  in  FIG. 12 . The various parts of the apparatus of  FIG. 12  have been discussed in conjunction with  FIGS. 8   a - c  and, with exception of balloon  181  and mold cavity ends  193 , the reference numerals used in  FIG. 12  correspond to those used for  FIGS. 8   a - c . Mold cavity ends  193  maybe provided in a variety of sizes and lengths to contain the balloon at each end. Desirably, the end molds will be adjustably mounted to a portion of the apparatus such as fixed plates  156  to provide for an adjustable length balloon mold. 
     The invention is also directed to a method for molding a medical balloon using the inventive apparatus described above. A balloon preform prepared through any standard method is provided. The inventive mold, shown generally at  100  is also provided. Balloon  181  is inserted into aperture  162 . Aperture  162  is optionally reduced to a predetermined size and the preform expanded using standard techniques. An inflation fluid, for example, may be supplied to the preform and the preform expanded and heated. The balloon in its expanded state is shown in  FIG. 12 . 
     More generally, the invention may be practiced by providing at least three movable blades disposed about a reference tube to form a shrinkable tubular aperture. The blades are constructed and arranged such that each blade has a single line which a) lies on the surface of the reference tube prior to movement of the blade, and b) is moved along a radial plane of the reference tube on movement of the blade. A balloon preform is placed into the shrinkable aperture. The aperture may be set at a predetermined size prior to or following insertion of the balloon therein. An inflation fluid is provided and the balloon preform inflated so that the preform expands to the size of the aperture. The preform may be heated during this inflation/blowing step. The inflation fluid is then removed from the thus formed balloon and the balloon removed from the apparatus. 
     The balloon may also be molded in accordance with the method described in U.S. Pat. No. 5,163,989, or in accordance with other methods as are known to those of ordinary skill in the art, substituting the instant apparatus for the standard balloon mold. Other patents which discuss balloon molding include U.S. Pat. No. 5,807,520. Other references illustrating the materials and methods of making catheter balloons include: U.S. Pat. No. 4,413,989 and U.S. Pat. No. 4,456,000 to Schjeldahl et al, U.S. Pat. No. 4,490,421, U.S. Re 32,983 and Re 33,561 to Levy, and U.S. Pat. No. 4,906,244, U.S. Pat. No. 5,108,415 and U.S. Pat. No. 5,156,612 to Pinchuck et al. 
     The use of the inventive apparatus as a mold allows for the blowing of a balloon to a predetermined size using a single adjustable size balloon mold thereby eliminating the need to have multiple molds of different sizes. 
     The invention further contemplates molding a balloon to a desired shape using a plurality of the inventive devices arranged sequentially. As an example of this, shown in  FIG. 13 , a stepped balloon  181  maybe prepared by arranging several devices  100   a ,  100   b  and  100   c  sequentially. A balloon preform is inserted in the aperture formed by the device. The aperture of each device may be preset at a desired size or may be reduced in size to a predetermined size after the balloon preform is inserted therein. The balloon may then be blow molded in accordance with any suitable blow molding technique known in the art. 
     The invention is also understood to be directed to embodiments employing various combinations of the features disclosed herein. 
     The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.