Abstract:
The present disclosure relates to embolic coils that eliminate kick-back into a parent vessel by providing a proximal end that retracts following deployment within the vasculature. Also disclosed are methods of making such coils, delivery systems that comprise such coils, and methods of delivering such coils to a patient.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    This application claims priority to and the benefit of, U.S. patent application Ser. No. 62/112,384, filed on Feb. 5, 2015, which is incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to the field of embolic coils. More particularly, the present disclosure relates to embolic coils that address kick-back into the parent vessel by providing a proximal end that retracts following deployment within the vasculature. 
       BACKGROUND 
       [0003]    Embolic coils are used for a variety of medical applications, including treatment of intra-vascular aneurysms. A common embolic coil takes the form of a soft, helically wound coil formed by winding a platinum (or platinum alloy) wire strand about a primary mandrel. The relative stiffness of the coil depends, among other things, on its composition, the diameter of the wire strand, the diameter of the primary mandrel, and the pitch of the primary windings. The coil is then wrapped around a larger, secondary mandrel, and heated to impart a secondary shape. For example, U.S. Pat. No. 4,994,069, issued to Ritchart et al., describes an embolic coil that assumes a linear, helical primary shape when stretched for placement through the lumen of a delivery catheter, and a folded, convoluted secondary shape when released from the delivery catheter and deposited in the vasculature. 
         [0004]    Embolic coils are typically delivered to a selected site (e.g., aneurysm) within the vasculature using a delivery catheter in a minimally invasive procedure. To achieve an adequate density for embolus formation, it is common for multiple embolic coils to be implanted within the site. One issue with some existing embolic coils is the tendency of the proximal end of the coil to protrude out of the aneurysm into the parent vessel after being released from the delivery catheter. This phenomenon, referred to as kick-out or kick-back, has the potential to cause disruption of blood flow in the parent vessel that can lead to thrombosis. 
         [0005]    The present disclosure is directed to embolic coils that address kick-back by providing a proximal end (also referred to herein as a “tail”) that retracts following deployment within the vasculature. 
       SUMMARY 
       [0006]    The present disclosure, in its various aspects, addresses an ongoing need in the field of embolization for accurate placement of embolic coils within a body lumen of a patient without a significant portion of the embolic coil extending into to the parent vasculature. 
         [0007]    In accordance with some aspects, the present disclosure provides an embolic coil comprising an elongate helical primary shape having a diameter, a first end (also referred to herein as a proximal end) and a second end (also referred to herein as a distal end), wherein the primary shape is formed into a secondary shape in which a free energy state of the secondary shape (also referred to herein as the “free energy secondary shape”) is a three-dimensional shape (e.g., a cone, dual cone, cylinder, sphere, cube, etc.) that defines a volume and comprises a bend in the first end of the primary shape. In this regard, as seen from the description following and various drawings herein, the secondary shape need not fully enclose the volume. As used herein, an “end” of the coil is that portion of the coil that is adjacent a tip of the coil. In certain embodiments, the first end of the coil (which comprises the bend) may correspond to a portion of the coil ranging up to 20% of the total length of the coil, a portion of the coil ranging up to 15% of the total length of the coil, a portion of the coil ranging up to 10% of the total length of the coil, a portion of the coil ranging up to 5% of the total length of the coil, or a portion of the coil ranging up to 2.5% of the total length of the coil. 
         [0008]    In various embodiments, which may be used in combination with any of the above aspects, a bending radius of the first end is less than five times the diameter of the elongate helical primary shape when the coil is in the free energy state. 
         [0009]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the greatest width of the volume is greater than a bending radius of the first end, for example, ranging from 2 to 5 to 10 to 25 to 50 times the bending radius of the first end (by which is meant ranging between any two of the preceding numerical values, specifically, ranging from 2 to 50 times the bending radius of the first end, ranging from 2 to 25 times the bending radius of the first end, ranging 2 to 10 times the bending radius of the first end, ranging from 2 to 5 times the bending radius of the first end, ranging from 5 to 50 times the bending radius of the first end, ranging from 5 to 25 times the bending radius of the first end, ranging from 5 to 10 times the bending radius of the first end, ranging from 10 to 50 times the bending radius of the first end, ranging from 10 to 25 times the bending radius of the first end, or ranging from 25 to 50 times the bending radius of the first end). 
         [0010]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the first end bends at an angle greater than 360 degrees when the coil is in the free energy state. 
         [0011]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the first end comprises a two-dimensional spiral or a three-dimensional spiral when the coil is in the free energy state. 
         [0012]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the first end of the primary shape bends at least partially back into the volume when the coil is in the free energy state. In preferred embodiments, at least a tip of the first end of the primary shape is positioned in the volume when the coil is in the free energy state. In some of these embodiments, a two-dimensional spiral or a three-dimensional spiral of the first end may be disposed entirely within the volume when the coil is in the free energy state. 
         [0013]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the secondary shape defines a lumen therethrough, and the first end of the primary shape is at least partially disposed within the lumen when the coil is in the free energy state. For example, the secondary shape may be substantially in the form of a cylinder which forms the lumen, or the secondary shape may be substantially in the form of a single or dual cone which forms the lumen, among other possibilities. In some of these embodiments, a two-dimensional spiral or a three-dimensional spiral of the first end may be disposed entirely within the lumen when the coil is in the free energy state. 
         [0014]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the bend is such that a tip of the first end points in a direction of the volume. 
         [0015]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the first end bends at an angle greater than 60 degrees and less than 225 degrees, e.g., between 90 degrees and 180 degrees in some embodiments, when the coil is in the free energy state. 
         [0016]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the secondary shape has a secondary axis, and an axis of the primary shape at the tip of the first end is within 45 degrees (beneficially within 30 degrees, more beneficially within 15 degrees) of parallel to the secondary axis. 
         [0017]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the volume may be a single conic volume, a dual conic volume, or a cylindrical volume, a spherical volume, or a cubic volume, among other possible volume shapes. 
         [0018]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the first end of the elongate helical primary shape is provided with an attachment feature. For example, the first end may be provided with an electrolytically dissolvable region or may be provided with a mechanical attachment feature that is configured to temporarily interlock with another component such as a delivery wire. 
         [0019]    In various embodiments, which may be used in combination with any of the above aspects and embodiments, the embolic coil may be loaded into a delivery sheath. 
         [0020]    Other aspects of the present disclosure pertain to delivery systems comprising (a) an embolic coil in accordance with any of the above aspects and embodiments and (b) a delivery wire that is temporarily attached to the embolic coil via an attachment feature. For example, the delivery wire may be detachably connected to the embolic coil via an attachment feature such as an electrolytically dissolvable attachment feature or a mechanical attachment feature, first instance, via a first attachment member on the embolic coil that temporarily interlocks with a second attachment member on the delivery wire (e.g., first and second interlocking attachment members such as first and second threaded members, first and second interlocking arms, etc.). 
         [0021]    Other aspects of the present disclosure pertain to methods of embolic coil delivery that comprise (a) advancing an embolic coil of a delivery system in accordance with any of the above aspects and embodiments to a target occlusion area in a patient, and (b) releasing the embolic coil. 
         [0022]    Still other aspects of the present disclosure pertain to methods of making an embolic coil (e.g., an embolic coil in accordance with any of the above aspects and embodiments). The methods comprise wrapping an elongate helical primary shape having a diameter, a first end and a second end around a first mandrel and disposing the first end in an interior of the first mandrel, thereby forming a secondary shape, and heating the elongate helical primary shape for a time and temperature sufficient to memorize the secondary shape. 
         [0023]    In various embodiments, which may be used in combination with any of the above aspects, the first end may be inserted into a channel formed extending into the interior of the first mandrel (e.g., a straight or curved channel) or the first end may be wrapped around a smaller second mandrel that is disposed within the interior of the first mandrel (e.g., a cylindrical second mandrel or a conic second mandrel). 
         [0024]    Other aspects of the present disclosure pertain to embolic coils formed by these methods. 
         [0025]    These and other aspects, features, and advantages of the present disclosure will become immediately apparent to those of ordinary skill in the art upon review of the detailed description and claims to follow. 
     
    
     
       DRAWINGS 
         [0026]    Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. 
           [0027]      FIG. 1  depicts a primary shape of an embolic coil, in accordance with one embodiment of the present disclosure. 
           [0028]      FIG. 2  depicts a side view of an embodiment of a process for forming an embolic coil, in accordance with the present disclosure. 
           [0029]      FIG. 3A  provides a perspective view of an embodiment of an embolic coil with a kick-in tail, in accordance with the present disclosure. 
           [0030]      FIG. 3B  provides a partially transparent perspective view of an embodiment of an embolic coil with a kick-in tail, in accordance with the present disclosure. 
           [0031]      FIG. 3C  provides a cutaway perspective view of an embodiment of an embolic coil with a kick-in tail, in accordance with the present disclosure. 
           [0032]      FIGS. 4A-D  provide perspective views of embodiments of embolic coils with kick-in tails, in accordance with the present disclosure. 
           [0033]      FIG. 5A  is a schematic view of a proximal end of an embolic coil without a kick-in tail. 
           [0034]      FIG. 5B  is a schematic view of a proximal end of an embodiment of an embolic coil with a kick-in tail, in accordance with the present disclosure. 
           [0035]      FIG. 6A  depicts a side view of a mandrel, in accordance with one embodiment of the present disclosure. 
           [0036]      FIGS. 6B-C  depict an embodiment of a process for forming an embolic coil with a kick-in tail using the mandrel of  FIG. 6A . 
           [0037]      FIG. 7A  provides a cutaway perspective view of an embodiment of an embolic coil with a kick-in tail, in accordance with the present disclosure. 
           [0038]      FIG. 7B  provides a cutaway perspective view of another embodiment of an embolic coil with a kick-in tail, in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    The present disclosure may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. 
         [0040]    The terms “proximal” and “distal” generally refer to the relative position, orientation, or direction of an element or action, from the perspective of a clinician using the medical device, relative to one another. Thus, “proximal” may generally be considered closer to the clinician or an exterior of a patient, and “distal” may generally be considered to be farther away from the clinician, along the length or beyond the end of the medical device. 
         [0041]    The present disclosure is related to medical devices used to block the flow of blood through a blood vessel such as, for example, embolic coils. 
         [0042]    Embolic coils can generally be used in a number of different applications, such as neurological applications and/or peripheral applications. In some embodiments, embolic coils can be used to occlude a vessel and/or to treat an aneurysm (e.g., an intercranial aneurysm), an arteriovenous malformation (AVM), or a traumatic fistula, among other uses. In some embodiments, embolic coils can be used to embolize a tumor (e.g., a liver tumor). In certain embodiments, embolic coils can be used in transarterial chemoembolization (TACE). 
         [0043]    Frequently, an embolic coil is a “coil of a coil.” In other words, as used herein, the “primary shape” refers to the configuration obtained when a wire is wound into a coil (i.e., the primary winding). The “secondary shape” refers to the configuration obtained when the primary shape is further shaped, e.g., by winding about a mandrel (i.e., the secondary winding). The “free energy state” refers to the theoretical three-dimensional configuration assumed by the embolic coil as it would exist with no outside forces exerted upon it in the secondary shape (also referred to herein as the “free energy secondary shape”). The “deployed shape” refers to the configuration after the embolic coil has been deployed from the delivery catheter. The deployed shape of a particular embolic coil may differ, depending on whether it is deployed into an open space, or whether it is deployed into a body cavity which may influence the three-dimensional structures. The deployed shape may comprise, for example, overlapping and intertwining loops or ovals of the secondary winding. 
         [0044]      FIG. 1  illustrates a primary shape of an embolic coil  10  with a distal end  18  and proximal end  16  that is formed of consecutive windings of wire  12  and having a primary axis A. It should be noted that the cross-sectional dimension of the wire can be varied depending on the requirements of a particular coil design. For example, the diameter of the wire  12  can be selected, for instance, based on the desired properties (e.g., size, strength) and/or applications of embolic coil  10 . In some embodiments, wire  12  can have a diameter of from 0.001 inch (0.025 mm) to 0.005 inch (0.13 mm), among other values. 
         [0045]    In some embodiments, the overall diameter D of the primary shape coil may range, for example, from 0.01 inch (0.25 mm) to 0.05 inch (1.3 mm), for instance, ranging from 0.0125 inch (0.32 mm) to 0.025 inch (0.64 mm) or ranging from 0.025 inch (0.64 mm) to 0.045 inch (1.14 mm), among various other possible values. 
         [0046]    In some embodiments, the wire  12  has a diameter that is sufficient to provide an embolic coil  10  with a hoop strength capable of holding the embolic coil  10  in place within the chosen body site, lumen or cavity, without substantially distending the wall of the site and without moving from the site as a result of the repetitive fluid pulsing of the vascular system. 
         [0047]    In certain embodiments described herein, the overall axial length L of the primary embolic coil  10  may be in the range of 0.5 to 100 cm, and more typically, in the range of 2 to 60 cm. Depending on the use, the embolic coil  10  may have, for example, 10-75 or more turns per centimeter. In other embodiments, the embolic coil  10  can have other lengths and/or numbers of turns per centimeter. 
         [0048]    Wire  12  can be formed of, for example, one or more metals or metal alloys, including platinum group metals, particularly platinum, rhodium, palladium, and rhenium, as well as tungsten, gold, silver, tantalum, and alloys of these metals including platinum alloys (e.g., a platinum-tungsten alloy), as well as stainless steel, nickel-titanium alloys (nitinol), and Elgiloy® (from Elgiloy Specialty Metals). In certain embodiments, wire  12  may be formed of one or more polymers. Examples of polymers include polyolefins, polyurethanes, block copolymers, polyethers, and polyimides. Other examples of polymers are disclosed, for example, in Buiser et al., U.S. Patent Pub. No. 2007/0141099, which is incorporated herein by reference. 
         [0049]    Coils formed from various metals and alloys including platinum and its alloys, among many others, are known to exhibit elasticity in that they can be deformed under stress and recover to or toward an original or “memorized” shape once the stress is removed (i.e., where the coil is in a free energy state). 
         [0050]    Those skilled in the art will also understand that alloys such as Nitinol exhibit what are known as superelasticity effects. That is, when a stress is applied to the alloy element in the austenitic phase, the element deforms. This deformation may generate large areas of strain-induced martensite material even if there is no temperature change. These areas occur primarily at points where the strain is highest and may result in deformations that would be unrecoverable in normal materials. However, at that temperature martensite is not the stable phase of the alloy, and as soon as the stress has been removed the alloy returns to an austenitic state and reverts to its original shape. 
         [0051]      FIG. 2  illustrates one example of a process for forming a coil (e.g., embolic coil  10 ) in its primary shape. As shown in  FIG. 2 , a coil-forming apparatus  200  may include a mandrel  210  held by two rotatable chucks  220  and  230 . A spool  240  of wire  12  is disposed above mandrel  210 , and is attached to a linear drive  260 . To form a coil in its primary shape, chucks  220  and  230  are activated so that they rotate in the direction of arrows A 2  and A 3 , thereby rotating mandrel  210 . Linear drive  260  is also activated, and moves spool  240  in the direction of arrow Al. The rotation of mandrel  210  pulls wire  12  from spool  240  at a predetermined pull-off angle, and causes wire  12  to wrap around mandrel  210 , forming a coil  10 . 
         [0052]    As  FIG. 2  shows, the pull-off angle (a) is the angle between axis PA 1 , which is perpendicular to longitudinal axis LA 1  of mandrel  210 , and the portion  250  of wire  12  between spool  240  and coil  10 . In some embodiments, angle (a) may be from about one degree to about six degrees, among other values. In certain embodiments, a controller (e.g., a programmable logic controller) can be used to maintain the pull-off angle in coil-forming apparatus  200 . Because mandrel  210  is rotating as it is pulling wire  12  from spool  240 , and because linear drive  260  is moving spool  240  in the direction of arrow A 1 , wire  12  forms coil  10  in a primary shape around mandrel  210 . Coil  10  can be formed, for example, at room temperature (25° C.). The tension of mandrel  210  as it is held between chucks  220  and  230  may be sufficiently high to avoid vibration of mandrel  210  during the winding process, and sufficiently low to avoid stretching of mandrel  210  during the winding process. 
         [0053]    After coil  10  has been formed, chucks  220  and  230 , and linear drive  260 , are deactivated, and portion  250  of wire  12  is cut. Mandrel  210  may then be released from chuck  220 , and coil  10  is pulled off of mandrel  210 . In embodiments, coil  10  may have a length of from about five centimeters to about  225  centimeters after being removed from mandrel  210 , among other values. After coil  10  has been removed from mandrel  210 , coil  10  may be cut into smaller coils, if desired. While coil  10  might lose some of its primary shape as it is pulled off of mandrel  210 , coil  10  can generally return to its primary shape shortly thereafter, because of memory imparted to coil  10  during formation. In some embodiments, after coil  10  has been removed from mandrel  210 , one or both of the ends of coil  10  can be heated and melted to form rounder, more biocompatible (e.g., atraumatic) ends. 
         [0054]    Once coil  10  has been formed in its primary shape, coil  10  can be further shaped into a secondary shape, for example, as discussed below in conjunction with  FIGS. 6A-6C . 
         [0055]    In general, the embolic coils  10  described herein only exhibit a primary shape when fully extended within the lumen of a delivery catheter. As embolic coil  10  exits the delivery catheter it assumes its secondary shape, which allows embolic coil  10  to fill aneurysmal sac or other structure. Typically, the primary shape of embolic coil  10  is selected for deliverability, and the secondary shape of embolic coil  10  is selected for application (e.g., embolization of an aneurysm). 
         [0056]    One exemplary secondary shape in accordance with an embodiment of the present disclosure is illustrated in  FIGS. 3A-C , which show various views of an embolic coil  10  with free energy secondary shapes in which a main portion  10   m  defines a volume, specifically a cylindrical volume, and in which a proximal end  10   p  is disposed within the volume. Additional secondary shapes in accordance with embodiments of the present disclosure are illustrated in  FIG. 7A and 7B , which show additional cutaway views of embolic coils  10  with free energy secondary shapes in which a main portion  10   m  defines a volume, specifically a cylindrical volume, and in which a proximal end  10   p  is disposed within the volume. 
         [0057]      FIGS. 4A-4D , illustrate that other embolic coils may be formed which can have any number of different secondary shapes. In these figures, embolic coils  10  have been formed with free energy secondary shapes in which a main portion  10   m  defines a volume, specifically a cylindrical volume ( FIG. 4B ), a conic volume ( FIGS. 4A and 4D ) and a dual conic volume ( FIG. 4C ). In each case, the free energy secondary configuration is one in which the proximal end  10   p  of the coil  10  bends back in the direction or into the volume formed by the coil. In a typical coil, the maximum width of the secondary structure may range from 2 to 50 times the diameter of the primary coil, for example, ranging from 2 to 5 to 10 to 25 to 50 times (i.e., ranging between any two of the preceding numerical values) (e.g., ranging from 2 to 25 times, ranging from 5 to 50 times, ranging from 5 to 25 times, etc.) the diameter of the primary coil. 
         [0058]    In embodiments where the secondary shape defines a volume and a proximal end of the primary shape bends back in the direction of or into the volume, the greatest width of the volume may be at least one times the bending radius of the proximal end. For example, the greatest width of the volume may range from 1 to 2.5 to 5 to 10 to 25 to 50 to 100 times (i.e., ranging between any two of the preceding numerical values) (e.g., ranging from 1 to 100 times, ranging from 2.5 to 50 times, ranging from 5 to 25 times, etc.) the bending radius of the proximal end, among other values. 
         [0059]    More particularly,  FIGS. 3A-3C, 4B, 7A and 7B  show embolic coils  10  with a kick-in tail  10   p  and a generally cylindrical secondary shape, also referred to as a helical shape, which can be used, for example, to provide a supportive framework along a vessel wall. Alternatively, an embolic coil with a cylindrical secondary shape can be used to retain other embolic coils that are subsequently delivered to the target site, among other uses.  FIGS. 4A and 4D  show embolic coils  10  with a kick-in tail  10   p  and a conic secondary shape, also known in the art as a single apex vortex secondary shape, which can be used, for example, to close the center of a target site that is to be occluded, and/or to occlude a target site, among other uses. For example, an embolic coil with a single apex vortex secondary shape may be used to occlude a vessel having low flow, intermediate flow, or high flow. In certain embodiments, an embolic coil with a single apex vortex secondary shape can be used as a packing coil, such that the coil can be packed into a vessel that is slightly smaller than the diameter of the coil. In some embodiments, an embolic coil with a single apex vortex secondary shape can be used to embolize a tumor and/or treat gastrointestinal bleeding, among other uses.  FIG. 4C  shows an embolic coil  10  with a kick-in tail  10   p  and a dual conic secondary shape, also known in the art as a dual apex vortex secondary shape or a “diamond” secondary shape, which, like the single apex vortex secondary shape, can be used, for example, to close the center of a target site that is to be occluded, and/or to occlude a target site in conjunction with an embolic coil such as helical embolic coil  10  ( FIGS. 3A-3C, 4A ), among other uses. 
         [0060]      FIGS. 5A-B  schematically illustrate proximal ends  10   p  of embolic coils  10  without ( FIG. 5A ) and with ( FIG. 5B ) a kick-in tail. As depicted in  FIG. 5B , a bend introduced sufficiently close to the proximal end of coil  10  can provide a kick-in tail that points toward, but does not enter, the volume defined by the secondary coil shape. In some embodiments, a bend with a relatively tight radius may be formed, for example, ranging from 0.1 to 25 times the diameter of the coil  10 , for example, ranging from 0.1 to 0.25 to 0.5 to 1 to 2.5 to 5 to 10 to 25 times (i.e., ranging between any two of the preceding numerical values) (e.g., ranging from 0.25 to 10 times, ranging from 0.5 to 5 times, ranging from 0.5 to 2.5 times, etc.) the diameter of the coil  10 . 
         [0061]    As seen from  FIGS. 3A-3C, 4D, 7A and 7B , in some embodiments, a bend of more than 180 degrees, for example, ranging from 180 degrees to 270 degrees to 360 degrees to (at which point a loop is formed) to 540 degrees to 720 degrees to 1080 degrees or more (i.e., ranging between any two of the preceding numerical values) (e.g., ranging from 180 degrees to 1080 degrees, ranging from 180 degrees to 720 degrees, ranging from 360 degrees to 1080 degrees, etc.) may be formed (in this regard,  FIGS. 3A-3C  show a bend of approximately four turns or 1440 degrees, whereas  FIGS. 7A and 7B  show a bend of approximately three turns or 1080 degrees).  FIG. 4D  shows an embolic coil  10  with a single apex vortex secondary shape having a kick-in tail that forms a tight two-dimensional spiral. In an analogous embodiment, the kick-in tails provided in  FIGS. 3A-3C, 7A and 7B  form a tight three-dimensional spiral (e.g., a helix in  FIGS. 3A-3C and 7A  and a conic spiral in  FIG. 7B ). In this regard, the embolic coils of  FIGS. 3A-3C and 7A  have a free energy secondary shape in which a main portion  10   m  defines a volume, specifically a cylindrical volume defined by a first helix and in which a proximal end  10   p  is disposed within the volume that comprises a second helix, whereas the embolic coil of  FIG. 7B  has a free energy secondary shape in which a main portion  10   m  defines a volume, specifically a cylindrical volume defined by a helix and in which a proximal end  10   p  is disposed within the volume that comprises a conic spiral. An advantage of such spiral designs is that a kick-in tail may be formed which rolls itself up after being released from a delivery sheath or catheter. As discussed below, such a coil may be made, for example, by disposing a smaller diameter mandrel within a larger diameter mandrel such that the smaller mandrel forms the tail and the larger mandrel forms the secondary shape of the remainder of the coil. 
         [0062]    The location of the bend along the length of the proximal end of coil  10  can determine the configuration of the kick-in tail relative to the secondary shape of coil  10 . For example, a bend introduced near the proximal end of coil  10  (e.g., 0.5 to 5.0 cm from the proximal end of coil  10 ) may allow the kick-in tail to fold within the lumen defined by the secondary coil shape (see, e.g.,  FIGS. 4A-C ). However, a bend introduced at a greater length from the proximal end of coil  10  (e.g., 5.0 to 10.0 cm) may result in a kick-in tail disposed outside and adjacent to the secondary coil shape (see, e.g.,  FIG. 4C ). This occurs due to the steric hindrance of the secondary coil shape, which begins to form prior to the proximal portion of coil  10  exiting the delivery catheter, physically blocking the kick-in tail from entering the lumen defined by the final coil shape. 
         [0063]    Various methods for forming secondary shapes for the embolic coils described herein will now be described. Once coil  10  has been formed in its primary shape (see  FIGS. 1-2 ), coil  10  can be further shaped into a secondary shape using a suitable mandrel or mandrels. 
         [0064]      FIG. 6A  shows a mandrel  610  which may be used to form a secondary shape of coil  10 . While mandrel  610  is shaped to form a “diamond-shaped” coil, other types of mandrels can be used to form other secondary shapes. Mandrel  610  comprises a “diamond-shaped” block  620  with grooves  630  cut into its surface, and an aperture  640  (e.g., a channel) extending at least partially therethrough. As shown in  FIGS. 6B and 6C , coil  10  in its primary shape may be wrapped around mandrel  610 , such that coil  10  fills grooves  630 , creating the secondary shape. The ends of coil  10  are fixed to mandrel  610 . In accordance with an embodiment of the present disclosure, one end of the primary coil  10 , specifically the proximal end of the deliverable coil is inserted into the aperture  640  as shown in  FIG. 6C . The coil  10  is heat-treated at a temperature and for a time sufficient to set or program the coil in a three-dimensional secondary shape, thereby imparting memory to the coil  10 . After being heat-treated, coil  10  is unwrapped from mandrel  610 . The removal of coil  10  from mandrel  610  allows coil  10  to reassume its secondary shape. In some embodiments, after coil  10  has been removed from mandrel  610 , one or both of the ends of coil  10  can be heated and melted to form rounder, more biocompatible (e.g., atraumatic) ends. 
         [0065]    In one embodiment, the configuration of the kick-in tail relative to the secondary shape of coil  10  is determined by the (a) extent (i.e., degree) to which the proximal end of the coil  10  is bent during the wrapping of coil  10  around mandrel  610  and, (b) the location at which the bend is introduced along the proximal end of coil  10 . For example, with regard to extent, a bend of at least 90 degrees, in some embodiments, at least 180 degrees, at least 270 degrees, at least 360 degrees (at which point a loop is formed), for instance ranging anywhere from 90 to 720 degrees or more can be introduced into the proximal end of the coil  10 . In the embodiment shown, the bend angle is determined by the amount of slack that is provided before the proximal end of the coil  10  is inserted into the aperture  640  of mandrel  610 . As used herein, “slack” refers to the portion of coil  10  that is not wound around mandrel  610 . For example, a sharp angle can be obtained by inserting coil  10  directly into aperture  640  as the coil  10  comes off mandrel  610 . Similarly, a more gradual angle can be achieved by leaving a slack portion at a point where the proximal end of coil  10  into aperture  640 . 
         [0066]    In the embodiment shown in  FIGS. 6A-6C , the aperture  640  corresponds to a linear channel that is disposed at a 90 degree angle relative to the surface. In other embodiments the aperture is disposed at a lesser angle. In some embodiments, the aperture  640  may be made non-linear in order to form a distal tip having a desired shape. For example, a non-linear aperture  640  may be formed which meets the mandrel surface at an angle that is substantially less the 90 degrees and which gradually curves away from the surface. 
         [0067]    In another embodiment, the proximal end of coil  10  that is not wound around mandrel  610  can be formed into a tight curl (i.e., rolled up) prior to being disposed within an aperture or hollow volume of the mandrel. When in the secondary shape, this embodiment would provide a coil  10  with a kick-in tail having a two-dimensional spiral shape (e.g., a watch-spring shape) or a three-dimensional shape (e.g., a helical or corkscrew shape), depending on how the proximal end is curled. 
         [0068]    In this regard, more complex coil designs such as that shown in  FIGS. 3A-3C  may be formed by disposing a smaller mandrel within a larger hollow mandrel. For instance, a primary coil may be wrapped around a larger cylindrical mandrel as well as a smaller cylindrical mandrel which is disposed within a hollow volume of the larger cylindrical mandrel, in order to form the coil of  FIGS. 3A-3C . 
         [0069]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. Certain embodiments of the present disclosure have described above. It is, however, expressly noted that the present disclosure is not limited to those embodiments, but rather the intention is that additions and modifications to what was expressly described herein are also included within the scope of the disclosure. Moreover, it is to be understood that the features of the various embodiments described herein were not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express herein, without departing from the spirit and scope of the disclosure. In fact, variations, modifications, and other implementations of what was described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the disclosure. As such, the disclosure is not to be defined only by the preceding illustrative description. 
         [0070]    All of the devices and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the devices and methods of this disclosure have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations can be applied to the devices and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the disclosure. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the disclosure as defined by the appended claims.