Abstract:
This invention relates to a multi-purpose holding device to handle, support and rotate one or more hollow cylindrical objects. The holding device consists of a rigid frame and support members for precise alignment and rotation of one or more objects within the frame structure. A method is also provided to reproducibly support, rotate and inspect the hollow cylindrical objects.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application relates to and claims priority from commonly owned U.S. Provisional Patent Application Ser. No. 60/776,522, filed on Feb. 24, 2006. 
     
    
     FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable 
       SEQUENCE LISTING OR PROGRAM 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of Invention 
         [0005]    This invention relates to a holding device and a method of coating hollow cylindrical objects using the device. More specifically, the present invention provides a holding device and a method of reproducibly and securely supporting and rotating one or more hollow cylindrical objects, such as stents, during a coating process, while minimizing runout of the hollow cylindrical object during rotation and surface contact between the hollow cylindrical object and the holding device. 
         [0006]    2. Background of the Invention 
         [0007]    Coatings are often applied to medical appliances, such as pacemakers, vascular grafts, stents, and heart valves, to have desired effects and increase their effectiveness. These coatings may deliver a therapeutic agent or drug to the lumen that reduces smooth muscle tissue proliferation or restenosis. Furthermore, medical devices may be coated to provide beneficial surface properties achieving enhanced biocompatibility and to improve surface properties such as lubriciousness. Balloon delivery systems, stent grafts and expandable stents are specific examples of medical appliances or implants that may be coated and inserted within the body. Stents such as described in U.S. Pat. No. 4,733,665, are tiny, expandable mesh tubes supporting the inner walls of a lumen used to restore adequate blood flow to the heart and other organs. 
         [0008]    Conventionally, coatings are applied to the stent in a number of ways including, though not limited to, dip coating, spin coating, or spray coating processes. Spray coating processes generally require an apparatus to securely hold and rotate the flexible, tiny stent structure during the coating operation to allow a repeatable and homogeneous coating application of the whole surface. 
         [0009]    However, holding devices known from the prior art have several drawbacks which may result in low volume production of medical devices, damage to the fragile stent structure, inhomogeneous coatings, uncoated areas, coating accumulations, and the like. Coating accumulations, such as shown in  FIG. 13 , can lead to severe damages of the coating due to a possible loss of the coating during loading, transportation, and/or deployment of the stent. Coating defects, such as uncoated areas and coating thickness variations on the stent surface may compromise the implant&#39;s effectiveness due to potential complications arising from an inhomogeneous distribution of the therapeutic agent at the target site. 
         [0010]    Stent holding devices, as described in U.S. Pat. No. 6,605,154, comprising a mandrel passing all the way through the inner hollow body of the stent to support the stent via support members, which partially penetrate into the opposing sides of the hollow body of the stent by incrementally moving at least one support member closer to the other, can have several disadvantages. 
         [0011]    When using such stent holding devices there may be a risk of coating defects at the ends of the stent due to the design of the support elements. The clamping force can vary from stent to stent, which may lead to sagging or buckling of the stent. Mandrels having a small diameter and a comparatively long length of approximately 40-80 mm may easily bend resulting in a runout of the stent. Moreover, stent holding devices comprising members projecting out of a body to contact the stent, such as described in U.S. Pat. No. 6,572,644, may not center and secure the stent sufficiently. 
         [0012]    Runout, sagging and buckling of the stent may cause an inhomogeneous coating thickness, coating defects on the stent surface and coating weight deviations. Coating consistency may vary from stent to stent depending on runout and positioning accuracy of the support members. 
         [0013]    In addition, coating defects, such as uncoated areas on the stent surface, may arise when stent holding devices are used having a structure which interferes with the spray plume, such as described in WO Pat. No. 2004/008995. 
         [0014]    Damage of the coating may also occur after competition of the coating process during handling and inspection. Inspection of medical devices generally requires dismounting the stent from the holding device being used during the coating process in order to mount the stent on an inspection fixture which typically contacts the outer surface of the stent. 
         [0015]    Finally, stent holding devices known by the prior art are not designed to allow supporting and coating of multiple stents simultaneously or to be used for subsequent inspection of the coated stents. 
       SUMMARY 
       [0016]    There is therefore a need for a device and a coating method which will improve the efficiency, stability and reproducibility of the stent coating process by securing the stent during the coating operation without disturbing the coating process, damaging the medical device and/or coating and by permitting higher volume, low cost production of high quality coated medical devices. 
         [0017]    Accordingly, a multi-purpose holding device for handling, securing and rotating one or more medical devices and a method to apply motion and coating to one or more medical devices, such as stents, is provided. The holding device includes a rigid frame structure and interchangeable support members to allow precise alignment of the medical device within the frame structure and minimized runout. To avoid coating defects, the holding device does not extend completely through the medical device, provides minimized surface contact with respect to the medical device and does not block the spray plume from uniformly coating the entire stent. 
         [0018]    In one embodiment of the present invention, the holding device comprises a frame, which surrounds one or more stents and at least two support members. The support members are bearing mounted to the frame and are in contact with at least a portion of the stent. In a first position, the support members are engaged with the stent at two opposing sides and the stent is securely held and can be rotated in relation to the frame. At least one support member has a second position of being disengaged from the stent. In one or more embodiments, the support members are in contact with the inner surface of the stent in the first position. The support members have a body without structures projecting out of the body. At least a portion of the support members may comprise a polygonal cross-section and the support members may be interchangeable. The holding device of the present invention may further comprise one or more shafts which are bearing mounted to the frame in order to transmit rotary motion to one or more support members. It may also comprise sleeves which are bearing mounted to the frame to connect the support members to the frame, wherein in a first position the support members may be coupled to the sleeve to transmit rotary motion, and in a second position the support members may be uncoupled from the sleeve. The holding device may furthermore comprise members, such as belts, to transmit rotary motion between the shaft and the support member. In addition, one or more guide sections may be included. 
         [0019]    In a next embodiment, the holding device includes a frame which surrounds one or more stents and at least two support members which are bearing mounted at a predetermined position to the frame. The support members include a first member having a flexible and sheet-like structure, a second member having a cylindrical shape and a third member. The second member is connected to the first member and comprises an aperture for receiving the third member. In a first position, the third member is located within the inner hollow section of the stent to expand the first member such that the resulting surface of the first member contacts the stent around its entire perimeter. The stent is securely held at two opposing sides and can by rotated in relation to the frame. In a second position, the third member is located outside the hollow section of the stent and the first member is retracted and not in contact with the stent. 
         [0000]    In one or more embodiments, the holding device may comprise one or more shafts which are bearing mounted to the frame to transmit rotary motion to one or more support members. In addition, it may include members, such as belts, to transmit rotary motion between the shaft and the support members. Furthermore, one or more guide sections may be included. 
         [0020]    In a further embodiment, the holding device comprises a frame, which surrounds one or more stents, and at least two support members being bearing mounted to the frame. The support members include a coil spring and a shaft to which the coil spring is connected. The coil spring has a first position of being engaged with the inner surface of the stent in which the stent is securely held at two opposing sides and can be rotated in relation to the frame. In a second position, the coil spring is disengaged from the stent and the coil spring can pass through the inner diameter of the stent to allow dismounting of the stent. 
         [0000]    In one or more embodiments, the holding device may comprise one or more shafts which are bearing mounted to the frame to transmit rotary motion to one or more support members. Moreover, it may comprise sleeves being bearing mounted to the frame, wherein each support member is in contact with one sleeve and wherein in a first position, the support member is coupled to the sleeve to transmit rotary motion, and in a second position, the support member is uncoupled. Also, the holding device may include members, such as belts, to transmit rotary motion between the shaft and the support member. Furthermore, one or more guide sections may be provided. 
         [0021]    In still another embodiment, an apparatus for applying linear and rotary motion to one or more stents is provided. The apparatus comprises a stent holding device including a frame which surrounds the stents, at least one shaft being rotably mounted to the frame and at least two support members being bearing mounted to the frame with two support members securing one stent at two opposing ends and one or more guide members. The holding device is in contact with one or more guide members and can be moved along the guide members to apply linear motion to the stents, and the stent can be rotated in relation to the holding device by applying rotary motion to at least one of the bearing mounted members. 
         [0000]    In one or more embodiments, the apparatus may further comprise at least one inspection device, wherein the holding device can be moved along the guide members to allow positioning of the stents in relation to one or more inspection devices. In addition, at least one motion unit, such as a linear and rotary actuator, may be provided to transmit rotary and linear motion to the holding device in order to rotate and translate the stents. 
         [0022]    In still another embodiment, a holding device for handling, securing and rotating one or more stents is provided, comprising a frame and at least one support member being bearing mounted to the frame and contacting at least a portion of the inner surface of the stent, wherein one support member is engaged with the stent at one end and the stent is securely held and can be rotated in relation to the frame. 
         [0023]    In another embodiment, a method for securing and applying rotary motion to one or more stents is provided comprising the steps of locating two opposing support members in a first position, the support members being bearing mounted to the frame of a holding device surrounding the stent, and positioning a stent between the support members, locating the two support members at a second predetermined position in which the distance between the support members is smaller than the stent length to provide a repeatable securing of the stent, and transmitting rotary motion to at least one member which is bearing mounted to the holding device to rotate one or more stents in relation to the holding device. 
         [0000]    In one or more embodiments, the method may comprise the step of applying a coating to one or more stents. It may also include the step of positioning the holding device so that one or more guide sections are in contact with one or more guide members. In addition, it may comprise the step of moving the holding device along the guide members to adjust the stent in relation to one or more inspection apparatus. 
     
    
     
       DRAWINGS 
         [0024]    The accompanying drawings, which are incorporated in and constitute a part of this specification, serve to explain the principles of the invention. The drawings are in simplified form and not to precise scale. 
           [0025]      FIG. 1A  is a front view showing a holding device to support and to rotate one or more stents; 
           [0026]      FIG. 1B  is a front view showing the holding device with mounted stent; 
           [0027]      FIG. 2A  is a longitudinal cross-section view of a holding device to support and rotate one stent equipped with gears; 
           [0028]      FIG. 2B  is an isometric view of the holding device of  FIG. 2A ; 
           [0029]      FIG. 3A  is a longitudinal cross-section view showing a holding device comprising sleeves and gears to support and to rotate one stent; 
           [0030]      FIG. 3B  is an isometric view of the holding device of  FIG. 3A ; 
           [0031]      FIG. 4  is a front view showing a holding device to support and to rotate one or more stents including a shaft and a guide section; 
           [0032]      FIG. 5  is a top view showing a holding device to support and to rotate six stents; 
           [0033]      FIG. 6  is a front view showing an apparatus comprising a holding device to support and to rotate one or more stents; 
           [0034]      FIG. 7  is an isometric view showing an apparatus comprising a holding device to support and to rotate two stents during a spray coating process; 
           [0035]      FIG. 8  is an isometric view showing a holding device to support and to rotate two stents during the step of optical inspection; 
           [0036]      FIG. 9A  is an isometric view showing a cylindrical support member to contact a stent; 
           [0037]      FIG. 9B  is an isometric detail view of  FIG. 9A ; 
           [0038]      FIG. 10A  is a longitudinal cross-section view of a support member assembly comprising a flexible sheet-like member (retracted state); 
           [0039]      FIG. 10B  is a longitudinal cross-section view of a support member assembly comprising a flexible sheet-like member (expanded state); 
           [0040]      FIG. 11A  is an isometric view showing a support member assembly with a coil spring (retracted state); 
           [0041]      FIG. 11B  is an isometric view showing a support member assembly with a coil spring (expanded state); 
           [0042]      FIG. 12  is an image of a portion of a coated stent coated with the apparatus of the invention; and 
           [0043]      FIG. 13  is an image of a portion of a coated stent comprising a coating defect. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    The following figures illustrate embodiments of a holding device and a method to secure and rotate hollow cylindrical objects, such as stents.  FIG. 1  depicts a schematic of an exemplary holding device to support one stent, including frame  17  and one set of support members  6  being bearing mounted to the frame. The rigid structure of the frame allows for secure support of the stent. The frame structure is designed to precisely coaxially align the support members, which secure the stent at both ends. To ensure optimum alignment and to compensate the error of concentricity of the two support members securing the stent, the points of support are preferably machined in one setup by a reaming operation. The holding device of the present invention can include support members of different types, which may be interchangeable to allow securely holding stents of various sizes, designs and rigidity. The support members are designed to securely hold the stent, preferably along its entire perimeter, and to center the stent such that the longitudinal axis of the stent is coaxial with the rotation axis. The diameter of the support members should be sufficiently sized to provide a stable connection during transmission of rotary motion to the stent and to prevent slipping of the stent. In order to prevent deposition of coating material on the stent holding device, the contact area between the support member and the stent is minimized, namely limited to the edges and/or to a small section within the inner surface near the ends of the stent. The support members can have a polygonal cross-section and are preferably triangular or square-shaped. Alternatively, the support members may have a cylindrical or elliptical-shaped cross-section. To facilitate stent mounting, the tips of the support members are preferably rounded. Alternatively, the tips can have a hemispherical shape. The holding device can connect to a motor to transmit rotational and/or translational motion to the stent. 
         [0045]    Referring to  FIG. 1B , stent  1  is positioned between support members  6 , which are engaged with the stent at two opposing sides such that the stent is securely held and can be rotated in relation to the frame (first position). 
         [0046]    As shown in  FIG. 1A , the support members are disengaged from the stent by moving at least one support member in axial direction away from the stent (second position). 
         [0047]      FIG. 2A  and  FIG. 2B  depicts an exemplary mechanism for repeatably mounting and dismounting a stent and for transmitting rotary motion to the stent. A shaft equipped with gears is rotably mounted to the frame to transmit rotary motion between two support members. Both support members are preferably driven from either side to ensure that they rotate at the same speed, thereby preventing stress due to torsion. Support members  6  are engaged with stent  1  at two opposing sides, such that the stent is securely held and can be rotated in relation to the frame. 
         [0048]    The position of the support members is determined by lock members  22 , such as a pin or a securing ring, and by gears  7 . In this embodiment, a pin is removably coupled to the support members to avoid axial displacement and to ensure a repeatable positioning of the support members in relation to the stent. To rotate the stent about its longitudinal axis within the frame structure, rotary motion may be transmitted from shaft  19  or from one of the support members  6  to the other support member via gears, which are provided at the support members and both ends of shaft. 
         [0049]    The embodiment shown in  FIG. 3A  and  FIG. 3B  depicts a securing mechanism to precisely adjust the position of the support member using adjustable stop members and a mechanism to transmit rotary motion via sleeves and gears. The support members are mounted to sleeves  29  and gears  7 . A magnetic coupling is provided to connect the support members to the sleeves during engagement with the stent and to transmit rotary motion from the sleeves to the support members. The use of sleeves in combination with a magnetic coupling is preferred because the positioning and securing of the support members is facilitated. Stop members  34  are used to define the securing position of the support member in relation to the stent, such that the stent can be contacted at a defined predetermined position. In a first position, the support members are engaged with stent. The stop members  10 , 34  are coupled to the sleeves to secure the stent and to transmit rotary motion. Rotary motion is transmitted between shaft  19  and stent  1  via gears  7 , sleeves  29 , magnetic coupling and support members  6 . In a second position, the support members are uncoupled from the sleeve to release the stent. 
         [0050]    Referring to  FIG. 4 , there is shown an alternative embodiment to transmit rotary motion to the stent using belts. In addition, guide section  21  is provided to guide the device during translation movement and to prevent revolving of the holding device during rotation of support members  6 . Two support members  6  are connected with belts  20  to shaft  19  and rotary motion can be transmitted from one support member or from the shaft  19  via belts to the other support member. 
         [0051]    It is desirable to coat several stents simultaneously to allow higher volume production of medical devices.  FIG. 5  illustrates an exemplary holding device for the support of six stents. Six sets of support members  6  and shaft  19  are rotably mounted to frame  17 . Belts  20  are used to connect the support members to the shaft. Rotary motion may be induced at shaft  19  or at one of the support members  6  and transmitted via belts to the other support member to rotate the six stents simultaneously within the frame structure. 
         [0052]    With reference to  FIG. 6 , a schematic representation of a stent holding apparatus is shown comprising a holding device, such as described in  FIG. 4 , which is removably connected via coupling  23  to drive shaft  26  of motion unit  25  and mounted at guide section to a guide member. Guide member  24  is connected to motion unit  25  or to a base (not shown). The longitudinal axis of guide member  24  is preferably parallel to the longitudinal axis of drive shaft  26  in order to align the holding device in relation to the motion unit  25  and to secure the holding device against revolving. One support member  6  is connected via drive shaft  26  to motion unit  25 . The motion unit induces rotational and translational movement, which is transmitted via drive shaft and coupling  23  to one support member and via belts and shaft to the other support member to rotate the stent within frame structure  17  and to move the stent in a linear direction. By using a compact motion unit capable of transmitting linear and rotary motion, the size of the overall spray coating setup can be reduced. For enhanced production output two or more apparatus may be integrated in a standard sized isolator. 
         [0053]    Alternatively, rotary motion can be transmitted from the motion unit to the support member and linear motion is transferred to the frame. 
         [0054]    In a further alternative embodiment, each support member may be connected to a dedicated motion unit to transmit linear and/or rotary motion to the stent. 
         [0055]    Referring to  FIG. 7 , an exemplary spray coating setup is illustrated to coat two stents simultaneously. Stents  1  are supported by the holding device of the present invention and two atomizers  27  to apply a coating composition to both stents are provided. 
         [0056]    Motion unit  25 , comprising guide member  24  on which the holding device  30  is removably mounted, is aligned via guide sections  21  in relation to guide member  24  and coupled to drive shaft  26 . To easily connect or disconnect shaft  19  to drive shaft  26 , the drive shaft may be equipped with an automated clamping mechanism. Linear and rotary motion is applied via drive shaft  26  to holding device  30 . The motion is induced via shaft  19 , belts  20 , sleeves  29 , which are magnetically coupled to stop member  34  and via support members  6  to the stents. The support members  6  are engaged with the stent at two opposing sides and the stent is securely held and can be rotated in relation to the frame. Adjustable stop members  34  are coupled to the sleeves  29  to secure the stent. 
         [0057]    During the application of the coating, holding device  30  is moved in a linear direction relative to the two atomizers  27 , which generate spray plume  28 , and the stents are rotated. The two atomizers  27  are preferably aligned in relation to the stents, such that the center axis of the spray plume  28  is perpendicular to the rotation axis of stents  1  and both axes are located on the same plane. 
         [0058]    After application of the coating, the holding device can be removed from drive shaft  26  and guide member  24 . 
         [0059]    For increased production output, the apparatus of  FIG. 7  can be equipped with a larger frame to accommodate twelve support members to support up to six stents, as shown in  FIG. 5 . The compact design allows the integration of two apparatus in a standard sized isolator to coat twelve or more stents simultaneously. 
         [0060]    Another feature of the present invention is that the holding device can be furthermore used during subsequent inspection of the coated stents. An exemplary inspection setup is shown in  FIG. 8 . The stent holding device  30  can be removably connected to guide members  24 , which may be coupled to linear stage  33 . Stent  1  can be moved in the x-axis direction along guide members  24  and in the y-axis direction along linear stage  33  to position the stent in relation to a measurement or inspection apparatus. By turning shaft  19  of the holding device along its c-axis, stent  1  may be rotated to inspect the coating using microscope  32 . 
         [0061]    By using the holding device of the present invention it is not required to dismount and remount the stents for inspection purposes or to use inspection fixtures, which may damage the outer surface of the stent. Hence, coating damages during handling and inspection can be prevented or minimized resulting savings in time and cost. 
         [0062]      FIGS. 9 to 11  illustrate alternative support members used to secure stents.  FIG. 9A  and  FIG. 9B  is an isometric view showing a cylindrical support member. In order to reduce the contact area between support member  6  and stent  1  while securely holding stent  1 , the support members may comprise one or more passages  9 . Passages  9  may be equally distributed on the circumferential surface of the support members and extend to inner hollow section. Passages  9  which are preferably manufactured using a micro mill or micro ECM may have the shape of slots being equally distributed over the entire perimeter of the shaft. Crosspieces  8 , which comprise the outer surface of support members  6 , should be designed to provide a stable connection while minimizing the contact area between support element and stent. 
         [0063]    Alternatively, the support members may be made from a folded sheet or may be constructed from a hollow profile, which can be polygon-shaped. They may also comprise passages having the shape of holes or slots. The support members can be made from a suitable metallic material such as stainless steel, titanium, cobalt chromium alloys or a suitable polymeric material such as Polyetheretherketone (PEEK). 
         [0064]      FIG. 10  illustrates alternative support members to secure a stent. Each support member assembly comprises a first sheet-like and flexible member  2 , a second cylindrical shaped member  3  and a third member or rod  4 . Flexible member  2  can be attached to second member  3  using a clamp connection. In order to prevent coating defects and deformation of the stent, first member  2  is preferably composed of a flexible material having a sheet-like structure. A polymeric material such as latex, which can be elastically deformed during operation, may be used. The polymeric material typically has a thickness of approximately 0.08 mm to 0.25 mm. Second  3  and third member  4  may be composed of any suitable metallic material, such as stainless steel or polymeric material including Polyetheretherketone (PEEK). A tube may be used to construct second member  3  having preferably an outside diameter larger than the stent diameter and comprising an aperture for receiving third member or rod  4 . This embodiment is based on a mechanism capable of expanding flexible member  2  from an expanded configuration (first position) to a retracted configuration (second position). During the first and second state the distance between second members  3  remains unchanged. The position of rod in relation to second member  3  changes in order to expand or retract first member  2 . 
         [0000]    In a first position shown in  FIG. 10B , the third member is located within the inner hollow section of the stent to expand the first member such that the resulting surface of the first member contacts the stent around its entire perimeter and the stent is securely held at two opposing sides and can be rotated in relation to the frame. Referring to  FIG. 10A , the third member is located outside the hollow section of the stent and the first member is retracted and a sufficient clearance is provided between third member  4  and stent  1  such that the stent can be carefully loaded or unloaded. Rod  4  preferably comprises a portion or an additional member having a diameter larger than the section surrounded by second member  3  to limit the travel of rod  4  in relation to second member  3 , to determine the force to be exerted to stretch the first member  2  and to define the retraction point. The preset force exerted to stretch second member  3  should be sufficiently strong to provide a stable contact surface. 
         [0065]    A highly repeatable clamping mechanism is therefore provided which ensures that all supported stents are secured with an equal clamping force. High clamping forces, which can lead to a compressive and tensile load that may cause damage and deformation of the stent, can be therefore prevented. 
         [0066]      FIG. 11  is a variation of a support member assembly designed to prevent coating material deposition at the ends of the stent that may lead to coating defects. The support member assembly includes coil springs to secure the stent at its inner surface. An additional member, such as a sleeve, may be used to align the coil spring to the support member. Support member  6  comprises connection  13  for receiving one end of coil spring  16 . The opposing end of the coil spring is attached to sleeve  15 . Sleeve  15  can be moved along the longitudinal axis of support member  6  to tension or relax coil spring  16 , thereby securing and releasing stent  1 . The coil spring has a first position of being engaged with the inner surface of the stent, in which the stent is securely held at two opposing sides and can be rotated in relation to the frame. In a second position, the coil spring is disengaged from the stent and can pass through the inner diameter of the stent to allow dismounting of the stent. Referring to  FIG. 11A , sleeve  15  is moved away from the tip of support member  6  and the coil spring  16  is tensioned. The radius of the coils is decreased such that coil spring  16  can be inserted into stent  1  without contacting its inner surface. Sleeve  15  is released to untension coil spring  16  so that coil spring is in contact with the inner surface of stent  1 , as shown in  FIG. 11B . The coil spring has preferably a radius, which decreases towards both ends and should be sufficiently sized to provide a stable connection without causing slipping of the stent during transmission of rotary motion to the stent. The supported stents are secured using a highly repeatable clamping mechanism. 
         [0067]    The following method of precisely aligning and transmitting rotary and/or linear motion to one or more stents using the apparatus of the present invention is being provided by way of illustration and is not intended to limit the embodiments of the present invention. 
         [0068]    Referring back to  FIG. 7 , stents  1  are mounted, such that a portion of each support member is in contact with the stents. The axial position of support members  6  is secured by connecting stop members  34  to sleeves  29 . To check proper mounting of the stents, shaft  19  may be manually rotated. In another step, holding device  30  with loaded stents  1  is placed on guide member  24 . The holding device is slid along guide member  24  and is moved towards and connected to drive shaft  26  of motion unit  25 . Rotary motion is transmitted from drive shaft  26  via shaft  19 , belts  20 , sleeves  29 , and stop members  34  to support members  6 , in order to rotate stents  1  about their longitudinal axis. To move the holding assembly along guide member  24  in relation to atomizers  27 , linear motion may be induced by motion unit  25 . A coating can be applied by spraying a coating composition using atomizers  27 . The coating solution is disintegrated into a fine spray and applied to the stents. After application of the coating, shaft  19  is disconnected from drive shaft  26  of motion unit  25  and the holding device is removed from guide member  24 . The stents may remain mounted on the holding device to allow drying of the coating and subsequent inspection. One skilled in the art can appreciate that drying may be accomplished in a variety of ways based on the coating formulation used. 
         [0069]    To inspect the stent, stent holding device  30  may be placed with mounted stent  1  on inspection table  31 , as shown in  FIG. 8 , and may be moved along the x-axis and/or the y-axis to align the stent in relation to a measurement apparatus such as a microscope  32 . The stent may be rotated about its longitudinal axis by turning the shaft of the stent holding device along its c-axis in order to inspect the coating. 
       STENT COATING EXAMPLE USING THE APPARATUS OF THE PRESENT INVENTION 
       [0070]    The following example is being provided by way of illustration and is not intended to limit the embodiments of the present invention. 
         [0071]    Stents (manufactured by STI, Israel) having a diameter of 2 mm and a length of 20 mm may be coated. The coating composition may include a solvent capable of dissolving the polymer at the concentration desired in the composition, a non-bioabsorbable or bioabsorbable polymer that can be dissolved in the composition, and a therapeutic substance. The composition can also include active agents, radiopaque elements, or radioactive isotopes. 
         [0072]    The stents may be mounted on the holding device of the present invention as illustrated in  FIG. 7 . Two air-assisted external mixing atomizers can be used to disintegrate the coating composition into fine droplets and apply the coating to the stents. Alternatively, ultrasonic nozzles, or dispensers can also be employed for the application of the composition. 
         [0073]    The holding device may move in a linear direction along the guide member in relation to the atomizers and may rotate both stents simultaneously at the same angular velocity. The two spray nozzles can disintegrate the coating solution into fine droplets at a liquid flow rate of about 0.1 to 80 ml/h and an atomizing pressure ranging from about 0.3 bar to about 1.5 bar. In order to achieve a fine atomization, the nozzles are preferably operated at an atomizing gas flow rate of 5 l/min at 0.8 bar atomizing pressure. For best results, the atomizer may be aligned in relation to the stent, such that the spray axis of the atomizer is perpendicular to the rotation axis of the stent and both axes are in the same plane. The spray nozzles are preferably positioned at a distance of approximately 12 to 35 mm from the nozzle tip to the outer surface of the stent. A syringe pump, which is operated at a constant flow rate, can be used to feed the coating substance to the atomizer. The flow rate of the coating solution may range from about 1 ml/h to 50 ml/h and is preferably 5 ml/h 
         [0074]    During the application of the coating solution, rotary motion is transmitted from the drive shaft of the motion unit to the stents to rotate the stents about their central longitudinal axes. The rotation speed can be from about 5 rpm to about 250 rpm. By way of example, the stent may rotate at 130 rpm. The stents are translated along their central longitudinal axes along the atomizers. The translation speed of the stents can be from about 0.2 mm/s to 8 mm/s. When applying the coating solution, the translation speed is preferably 0.5 mm/s. The stents can be moved along the atomizer one time to apply the coating in one pass or several times to apply the coating in several passes. Alternatively, the atomizer may be moved one time or several times along the stent length. 
         [0075]    Coating trials of several stents were performed using the holding device of the present invention.  FIG. 12  shows a portion of a stent coated using the device. The number of coating defects especially at the ends of the stents could be reduced by using the holding device of the present invention. 
         [0076]    While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention. Details in the Specification and Drawings are provided to understand the inventive principles and embodiments described herein, to the extent that would be needed by one skilled in the art to implement those principles and embodiments in particular applications that are covered by the scope of the claims.