Abstract:
The present invention is directed towards the holding of medical devices during manufacture to enable the application of therapeutic and/or protective coatings. More specifically, the present invention provides medical device holders that securely retain stents and other medical devices during the application of a coating while minimizing compressive and tensile forces applied to the stents. The invention avoids disruptions to coating quality due to holder blockage during coating deposition. The invention discloses an improved device containing a mandrel and frame that may improve coating uniformity by eliminating shadowing from the frame of the medical device holder when applying coatings to stents and other medical devices.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally regards the holding of medical devices during manufacture to enable the application of therapeutic and/or protective coatings. More specifically, the present invention provides a method that securely retains a medical device during the application of a coating while minimizing compressive and tensile forces applied to the medical devices and disruptions to the coating due to holder blockage of coating deposition. The invention discloses an improved method that may improve coating uniformity by reducing shadowing from the frame of the medical device holder when applying coatings to medical devices. 
         [0003]    2. Background 
         [0004]    A wide variety of medical devices have been developed as medical implants and are used for innumerable medical purposes, including the reinforcement of recently re-enlarged lumens, the replacement of ruptured vessels, and the treatment of disease such as vascular disease by local pharmacotherapy, i.e., delivering therapeutic drug doses to target tissues while minimizing systemic side effects. Such localized delivery of therapeutic agents has been proposed or achieved using medical implants which both support a lumen within a patient&#39;s body and place appropriate coatings containing therapeutic agents at the implant location. 
         [0005]    The term “medical device” as used in this application includes stents, catheters, synthetic veins and arteries, artificial valves or other similar devices with a hollow or open center portion amenable to coating on the holder. For clarity, understandability and by way of example, the term “stent” in this application is used interchangeably with the term “medical device”. The delivery of expandable stents is a specific example of a medical procedure that involves the deployment of coated implants. Expandable stents are tube-like medical devices, typically made from stainless steel, tantalum, platinum or nitinol alloys, designed to be placed within the inner walls of a lumen within the body of a patient. These stents are typically maneuvered to a desired location within a lumen of the patient&#39;s body and then expanded to provide internal support for the lumen. The stents may be self-expanding or, alternatively, may require external forces to expand them, such as by inflating a balloon attached to the distal end of the stent delivery catheter. 
         [0006]    Because of the direct contact of the stent with the inner walls of the lumen, stents have been coated with various compounds and therapeutic agents to enhance their effectiveness. These coatings may, among other things, be designed to facilitate the acceptance of the stent into its applied surroundings. Such coatings may also be designed to facilitate the delivery of one of the foregoing therapeutic agents to the target site for treating, preventing, or otherwise affecting the course of a disease or tissue or organ dysfunction. 
         [0007]    The mechanical process of applying a coating onto a stent may be accomplished in a variety of ways, including, for example, the spraying of the coating substance onto the stent. While applying the coating to the stent, there is a need to contact the stent with the spray to ensure an even, intact, robust coating of the desired thickness on the stent. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is directed to a method for overcoming the foregoing disadvantages. Specifically, there is provided a stent holder comprising a frame and a mandrel. The frame is fixed, with the mandrel free to rotate within the frame. The mandrel is provided with a stent support preferably consisting of a wire loop passing through the center of a stent. The stent support is held at both ends by support retainers such as a hook, clasp and/or clamp. The support retainers spread the wire loop apart such that the loop contacts the inside edge of its respective end of the stent at each end. The stent holders simultaneously maintain sufficient tension on the wire loop to generate a relatively light force on the stent to positively locate it between the holders. Due to the light force and the location of the cross wire within the stent, the stent holder does not apply damaging forces to the stent, and minimizes the creation of spray shadows. Moreover, due to the interchangeability of various wire loops, the stent holders can easily and inexpensively accommodate a range of stent lengths and diameters. 
         [0009]    The mandrel, supported by bearing surfaces on the frame, rotates within the frame exposing the stent to the spray pattern. A uniform coating may be deposited on the stent since the spray has an unobstructed path to the rotating stent. The mandrel rotation is provided by a directly coupled motor or other drive source. 
         [0010]    Where the stent has been coated, care must be taken during its manufacture and delivery within the patient to ensure the coating is evenly applied and firmly adherent to the stent, and further that the coating is not damaged or completely removed from the implant during the deployment process. When the amount of coating is depleted the implant&#39;s effectiveness may be compromised and additional risks may be inured into the procedure. For example, when the coating of the implant includes a therapeutic agent, if some of the coating were removed during deployment, the therapeutic may no longer be able to be administered to the target site in a uniform and homogenous manner. Thus, some areas of the target site may receive high quantities of therapeutic while others may receive low quantities of therapeutic. In certain circumstances, the removal and reinsertion of the stent through a second medical procedure may be required where the coatings have been damaged or are defective. 
         [0011]    Stent holders as described in the prior art typically have a solid mandrel wherein the stent is supported by at least one end. In one embodiment, Narayanan, U.S. Pat. No. 6,723,373, a stent is slid entirely over a solid mandrel. This results in extensive contact between the interior of the stent and the mandrel, resulting in poor coating of the stent interior. In another embodiment, a mandrel supporting a stent by one end, the stent must be sprayed, flipped end for end, and then resprayed. This results in an inefficient spray process, and may result in coating non-uniformity do to spray overlap near the center of stent. In another embodiment, Epstein patent application Ser. No. 10/198,094 describes a stent holder using a wire mounted on a frame. The wire feature minimizes direct contact between the holder and the interior of the stent, however, rotating the stent according to the disclosed invention, requires rotating the frame holding the stent. Shadowing, the incomplete coating spray application onto the stent due to structural elements of the stent holder blocking the spray, occurs as the frame rotates since it cuts across the coating spray path creating a shadow on the stent as a result of the interference of the holder on the spray pattern of the coating. 
         [0012]    Shadowing resulting in non-uniform coating application is one problem with prior art devices. In addition, if the stent is held too loosely, it may either shift during the coating process or it may become prematurely separated from the holder, resulting in an inconsistent or damaged coating. Difficulties with properly aligning the stent on this device, high centripetal forces generated during spinning, and low retention forces on the stent can result in premature separation of the stent from the holder. Further, prior art devices are not easily interchangeable across a range of stent sizes, and often must be custom built for each specific stent size. Further disadvantages of the prior art stent holders are the relatively high expense given their complexity and the need to use high strength materials 
         [0013]    The present invention discloses a method of use for a relatively inexpensive, robust flexible stent holder which eliminates shadowing from the holder and can positively hold, locate and retain a stent during stent coating processes such as spray coating, while not mechanically shadowing the stent or otherwise interfering with the application of the coating. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an illustration of the stent holding apparatus as used for stent coating. 
           [0015]      FIG. 2  is an elevational view of the mandrel portion of the stent holding apparatus. 
           [0016]      FIG. 3  is a detail elevational view of the mandrel end. 
           [0017]      FIG. 4  is a detail plan view of an alternative embodiment of the mandrel end. 
           [0018]      FIG. 5  is a detail plan view of an alternative embodiment of the mandrel end. 
           [0019]      FIG. 6  is a detail plan view of an alternative embodiment of the mandrel end. 
           [0020]      FIG. 7  is a detail plan view of an alternative embodiment of a stent support. 
           [0021]      FIG. 8  is a detail plan view of an alternative embodiment of a stent support. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The present invention is directed to a method for overcoming the foregoing disadvantages. The term “medical device” as used in this application includes stents, catheters, synthetic veins and arteries, artificial valves or other similar devices with a hollow or open center portion amenable to coating on the holder. For clarity, understandability and by way of example, the term “stent” in this application is used interchangeably with the term “medical device”. The stent holder  10  may be used for a heating, coating or other processes useful with stent manufacturing. For illustrative purposes, a coating apparatus is shown in  FIG. 1 . It is understood that the stent holder  10  may also be used for other stent manufacturing processes. As shown in  FIG. 1  a coating feed  90  is supplied to a spray gun  80  from where it is discharged as a coating spray  91  on to a stent  20 . The spray gun  80  is preferably an ultrasonic spray gun, but alternative embodiments such as a pressure spray may also be suitable. The spray gun  80  is positionable along the length of the stent  20  using a linear motor  60  which directs the coating spray  91  to different portions of the stent  20  in a precisely controlled and reproducible manner. A wide variety of options are known in the prior art as to the active coating ingredients, carrier fluids and spray patterns. 
         [0023]    A stent holder  10  in  FIG. 1  comprises a frame  30  and a mandrel  50  supporting the stent  20 . As shown in  FIG. 2 , the mandrel  50  consists of at least a stent support  53 , drive portion  54 , first shaft  51 , a first support retainer  55 , and a support tensioner  57 . The frame  30  remains in a fixed position, with the mandrel  50  supported by preferably two, but at least one bearing free to rotate within the frame. 
         [0024]    As is shown in  FIGS. 2 and 3 , in accordance with the present invention the frame has a first end  31  and a second end  32  with the mandrel  50  being largely positioned on the inside of the frame  30  between the first and second ends. The mandrel is supported by at least a first bearing  33  and preferably a second bearing  34  located at the first and second ends respectively. The mandrel  50  is provided with a stent support  53  consisting of a wire loop passing through the center of a stent  20 . The stent  20  is gently but firmly supported on the stent support  53 . Other embodiments of the stent support  53  might include a coil spring or ribbon. 
         [0025]    In a preferred embodiment, the mandrel  50  is driven at its drive portion  54  by a rotary motor  70 . The mandrel drive portion  54  may also be rotated by other means such as gears or a belt and pulley drive. The rotary motor  70 , preferable directly coupled to the mandrel at the drive portion  54 , may be automatically controlled to change speed and/or direction as well as to stop and/or start suddenly. This allows flexibility with respect to coating distribution over the exterior as well as interior of the stent  20 , as sudden rotational changes may be used to intentionally shift the location of the stent  20  on the mandrel  50  which may improve coating distribution at the contact points between the stent  20  and the stent support  53  of the mandrel  50 . A second rotary motor synchronized with rotary motor  70  may be used to provide a balanced rotational force to both ends of mandrel  50 , thereby eliminating differential torque forces across the mandrel and/or stent as needed for optimum stent coating application. 
         [0026]    The mandrel consists of a first shaft  51  and a second shaft  52  rotatably connected to the frame  30  through the bearings. As shown in  FIG. 2 , on the interior portion of the frame  30 , a first support retainer  55  is attached to the distal end of the first shaft  51  and a second support retainer  56  is attached to the distal end of second shaft  52  within the interior portion of the frame  30 . The stent support  53 , which is a semi-rigid element, preferably a wire loop, attaches to each support retainer thereby spanning the opening between the first and second shaft. To achieve balanced centrifugal forces, the first and second shafts and the stent support generally share a common the longitudinal axis with the mandrel  50 . During mandrel  50  rotation, the centrifugal forces produced in combination with the symmetrical geometry of the semi-rigid stent support  53  of the mandrel  50  allow for an inherent automatic centering of the stent  20  for coating, even if the stent  20  is initially placed off-center along the stent support  53 . 
         [0027]    The stent support  53  may be a wire loop made from a variety of materials. The wire may be electrically conducting or non-conducting depending on electrostatic properties of the stent  20  and the stent coating desired. For example, it may be desirable to manufacture the stent support  53  of the same material as used for the stent  20 . In addition, if it is desirable to maintain a positive electrostatic charge on the stent  20  while applying a stent coating, a non-conducting polymer wire or coated metallic wire may be preferable to use. With other embodiments, it may be preferable to use, copper, nitinol or stainless steel wire. The stent support  53  is preferably a semi-rigid element for optimum utility. The preferred diameter of the stent support  53  wire loop is highly dependent on the characteristics of the stent to be coated. 
         [0028]    For an embodiment wherein the first bearing  33  is driven and the second bearing  34  is not, especially during starting and stopping, rotational forces will be transmitted between the first and second bearings through the stent support  53  and the stent  20  itself. The stent support  53  must be of sufficient rigidity to withstand this torque without collapse of the stent support  53  or excessive deformation to the stent support  53  or stent  20 . This factor tends to favor utilizing a stent support  53  with a larger wire diameter. 
         [0029]    A countervailing consideration, tending to favor stent support  53  using smaller wire diameter is to minimize internal shadowing from the stent support  53  when coating stent interiors. The optimum stent support  53  will provide a balance between overcoming friction during start/stop operations and minimizing internal shadowing. Furthermore, if it is desirable to reuse a given stent support  53  multiple times, a shape memory alloy such as nitinol may provide advantages for use as a stent support  53  due to its ability to resist permanent deformation. As an alternative embodiment, the differential torque across the stent support  53  can also be minimized by providing a second drive portion and/or second rotary motor which allows greater flexibility when selecting wire diameter and material to be used for a stent support  53 . 
         [0030]    The preferred diameter of the stent support  53  wire loop is also dependent on the physical characteristics of the stent to be coated. A maximum diameter of the stent support  53  wire loop is generally less than the radius of the stent  20 . This is preferred to prevent deformation of the stent  20  as it is installed and/or removed from the stent support  53 . It is also desirable that the stent support  53  be easily threadable through the stent  20  without breaking through the relatively delicate and permeable wall of the stent  20 . A minimum wire diameter selected as useable under the present invention would be large enough so that the support tensioner  57  wire loop stays in the interior of the stent  20  as it is threaded through the interior of the stent  20 . Therefore, the wire used for stent support  53  should be compliant enough to hold the stent  20  without deforming it when stent support  53  is biased and expanded open by the support tensioner  57 , which is preferably a spring, with the stent support  53  also being resilient enough to transfer torque of rotation. The preferred embodiment for the support tensioner  57  under the present invention is an enamel coated copper wire with a thickness between  32  to  36  gauge. 
         [0031]    The stent support  53  is held at both ends by a first support retainer  55  and/or a second support retainer  56 . The support retainer may be a device for attachment to a wire loop such as a hook, clasp or clamp.  FIGS. 4 ,  5  and  6  show alternative embodiments of the support retainer. The support retainer must generally spread the stent support  53  to a width at least as wide as the inside diameter of the stent  20 . The support retainers spread the wire loop apart sufficiently such that the loop engages the inside edge of the respective ends of the stent  20  at contact point(s)  458  as shown in  FIGS. 4 ,  5  and  6 . The first alternative support retainer  455  shown in  FIG. 4  is an open tube shaped support retainer. In  FIG. 5  a second alternative support retainer  555  shows a triangular shaped support retainer with a pointed leading attachment point  459 . In  FIG. 6  third alternative support retainer  655  shows a triangular shaped support retainer with a rounded leading attachment point  459 . At least one support tensioner  57 , such as a spring, simultaneously maintains sufficient tension on the stent support  53  to generate a relatively light force on the stent  20  to positively locate it between the support retainers  55  and  56 . Due to the relatively light force from the stent support  53  within the stent  20 , the stent support  53  does not apply damaging forces to the stent  20  which would stretch the stent  20  from the interior of the stent  20  at the contact point(s)  458 . Moreover, due to the stent supports&#39;flexibility, the stent support  53  and stent holders  10  can accommodate a range of stent lengths and diameters before a larger or smaller stent support  53  is needed. Furthermore, a variety of stent supports  53  can be used by the same stent holder  10  for greater versatility with a given stent holder  10 . 
         [0032]    Under the preferred embodiment, the stent support  53  is reusable. In its wire loop embodiment, as the stent support  53  is installed through the stent  20 , the lead edge is necessarily compressed or crimped to pass through the stent with the amount of crimping dependant on the inside diameter of the stent  20  and the diameter of the wire used for the stent support  53 . A crimped portion of the stent support  53  could interfere with proper centering of stent  20  and other coating aspects of a rotating stent support  53  by creating an asymmetrical longitudinal axis with respect to the stent support  53 . If a spring or resilient material is used for the support tensioner  57  the crimped portion will relax as the stent support  53  emerges from the stent  20  and is installed on the support retainer  55 . As an alternative embodiment shown in  FIG. 6 , a crimped portion can be designed into the stent support as shown in  FIG. 7  and aligned with a corresponding support retainer  655  so that the crimped stent support  653  remains symmetrical along its longitudinal axis. 
         [0033]    Although the preferred embodiment stent support is a wire loop, other non-loop embodiments such as a ribbon, spring, twisted or curved wire are possible. In  FIG. 8  an alternative stent support  853  in the form of an expanded flat spring is shown. 
         [0034]    Because the light holding force on the stent  20  can be easily released by biasing the support tensioner  57 , installing and/or removing a stent  20  from the mandrel  50  for coating is fast and convenient without special tools or equipment required for disassembly. 
         [0035]    The mandrel  50 , supported by bearing surfaces  33  on the frame  30 , rotates within the frame  30  exposing the stent  20  to the coating spray  91 . Attached to the mandrel  50  is at least one drive portion  54  located preferably on the exterior portion of the frame on the first and/or second shaft. The coating feed  90  is typically pumped to the spray gun  80  often with a syringe pump. A spray gun  80 , preferably using ultrasonic energy generates a coating spray  91  from a coating feed  90  solution. The coating spray  91 , preferably a mist or aerosol can also be generated with a pressurized nozzle. The coating feed  90  consists of the coating material for the stent  20  usually dissolved or suspended within a carrier solvent. The ultrasonic spray gun  80  is driven by a linear motor  70  so that the relatively narrow band of coating spray  91  may deposit a uniform coating over the entire length of the stent  20 . Except for the rotating mandrel  50  carrying the stent  20 , the stent holder  10  is fixed relative to the spray gun. Therefore, the spray gun can be positioned so that the coating spray  91  has an unobstructed path to the rotating stent. Other than the rotating stent  20  that is being coated, there are no elements of the present invention that interfere with the coating spray path. The mandrel rotation is provided by a directly coupled motor or other drive source positioned beyond the coating spray path. 
         [0036]    It should be appreciated that elements described with singular articles such as “a”, “an”, and/or “the” and/or otherwise described singularly may be used in plurality. It should also be appreciated that elements described in plurality may be used singularly. 
         [0037]    Although specific embodiments of apparatuses and methods have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, combination, and/or sequence of that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. It is to be understood that the above description is intended to be illustrative and not restrictive. Combinations of the above embodiments and other embodiments as well as combinations and sequences of the above methods and other methods of use will be apparent to individuals possessing skill in the art upon review of the present disclosure. 
         [0038]    The scope of the claimed apparatus and methods should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.