Patent Publication Number: US-6709712-B2

Title: Coating method

Description:
This application is a divisional of application Ser. No. 09/657,885, filed Sep. 8, 2000, U.S. Pat. No. 6,562,136, which application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a coating apparatus and method for applying a uniform coating on a substrate. More specifically, the invention relates to an apparatus and method for providing a uniform coating on a substrate having a surface geometry, such as a medical device. 
     BACKGROUND OF THE INVENTION 
     Medical devices are becoming increasingly complex in terms of function and geometry. Traditional coating methods, such as dip coating, are often undesirable for coating these complex geometries since coating solution may get entrapped in the device structure. This entrapped solution may cause webbing or bridging of the coating solution and may hinder the device function. 
     Spray coating techniques have also been used to apply coatings to medical devices. However, current methods of spray coating have introduced operator error, and have resulted in reduced coating consistency and reduced coating efficiency. 
     SUMMARY OF THE INVENTION 
     The invention provides a device and method for applying a coating onto a substrate having surface geometry. The invention is particularly useful for such substrates as medical devices, since such devices are often relatively small in size and can include complex surface configurations. Preferably, the invention is used to coat such medical devices as stents or other devices involving coils, coiled portions or cylinders having cut stent patterns. 
     A preferred device of the invention includes a rotation member rotatable about a central axis; a plurality of substrate mounts positioned on the rotation member, the substrate mounts being rotatable about second axes; and a drive arrangement for rotating the rotation member about the central axis and rotating the substrate mounts about the second axes. In one embodiment, the rotation member is a wheel. In one embodiment, the second axes extend radially from the central axes, and the drive arrangement rotates the substrate mounts about radial axes. In another aspect, the device of the invention includes a plurality of substrate mounts that are rotatable about second axes that are parallel to the central axis. 
     A preferred method of the invention includes the following steps. A substrate holder is provided that includes a rotation member rotatable about a central axis, a plurality of substrate mounts positioned on the rotation member, and a drive arrangement for rotating the rotation member about a central axis and rotating the substrate mounts about radial axes. At least one coating station is provided adjacent to the rotation member, so that substrate mounts can be passed in proximity to the coating station or stations. The coating station includes a nozzle for delivery of a coating solution to the substrate surface, and a solution delivery channel for delivery of the coating solution from a source to the nozzle. The substrates to be coated are mounted onto the substrate mounts, and the rotation member is rotated about its central axis to position one or more substrates at the coating station. The substrate mounts are rotated about the radial axes to rotate the substrates at a uniform rate during the coating process. During the coating process, the nozzle of the coating station is moved in a direction parallel to the substrate at a predetermined rate and is positioned a predetermined distance from the substrate to form a uniform coating on the substrate. 
     The invention provides a combination of advantages, including the ability to adjust or accommodate for surface geometries of a substrate to be coated, as well as the ability to provide substantially uniform coatings on such substrates. The invention eliminates human factors in the coating system, and allows for increased throughput of coated substrates. Further, the invention provides a reduction of coating solution waste during application of one or more coating solutions. According to the invention, substrates mounted on the rotation member can be expeditiously moved through a coating zone in sequence by the rotation of the rotation member, thereby reducing overall processing time. Additionally, the rotation of the substrate about second axes (e.g., radial axes or axes that are parallel to the central axis) during the coating process assists in achieving a uniform coating on the substrate. 
     The invention provides a device that is easy to use. The substrate mounts can be removable, so that an operator can easily insert and remove the substrates without disassembling the apparatus. The invention also eliminates variability in such parameters as coating thickness that can result from variations in substrate positioning on the holding apparatus. The invention allows positioning of the substrate in a manner that is substantially parallel to the coating station for coating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a preferred embodiment of the invention, including a substrate holder and coating stations. 
     FIG. 2 shows a top cross-sectional view of the wheel of the embodiment of FIG.  1 . 
     FIG. 3 shows a side view of a preferred embodiment of the right angle drive of the invention. 
     FIG. 4 shows a side view of a preferred embodiment of the substrate holder of the invention. 
     FIG. 5 shows a cross-sectional side view of the embodiment shown in FIG. 1, showing the wheel, and the right angle drive coupled to the substrate mount. 
     FIG. 6 shows a cross-sectional view of a preferred embodiment of the drive arrangement and wheel of the invention. 
     FIG. 7 shows a cross-sectional view of a preferred nozzle of the invention. 
     FIG. 8 shows a perspective view of an alternative embodiment of the rotation member of the invention. 
     FIG. 9 shows a side view of an alternative embodiment of the substrate gripper of the invention. 
     FIG. 10 shows a perspective view of an alternative embodiment of the device of the invention. 
    
    
     DETAILED DESCRIPTION 
     One aspect of the present invention relates to a device for holding a substrate that includes a rotation member rotatable about a first, central axis, a plurality of substrate mounts positioned on the rotation member, the substrate mounts being rotatable about second axes, and a drive arrangement for rotating the rotation member about a central axis and rotating the substrate mounts about second axes. Preferably, the drive arrangement comprises a first drive arrangement and a second drive arrangement. In a preferred embodiment, the first drive arrangement drives rotation of the rotation member, while the second drive arrangement drives rotation of the substrate mounts. The invention provides a substrate holder that allows for the application of a substantially uniform coating on a substrate, such as a medical device. In use, the substrate projects from the rotation member and is rotated about a second axis during the coating application. Preferably, the substrate to be coated is rotated by the rotation member about a central axis to position the substrate within a coating zone. Once within the coating zone, the substrate is preferably rotated about a second axis to allow for the application of a uniform coating. 
     Elements in common among the embodiments shown in the figures are numbered identically, with the addition of a letter to distinguish the second embodiment (e.g.,  4  and  4   a  to distinguish embodiments of element identified by numeral  4  in the figures), and such elements need not be separately discussed. 
     The invention will be described generally with reference to FIGS. 1 and 2. FIG. 1 depicts one embodiment of a device for holding a substrate that is indicated generally as  1 . In the embodiment shown in FIG. 1, the invention includes a rotation member  4  and a coating station  2  that is movable in direction of arrows  3  and  3 ′, which is toward and away from the rotation member  4 , respectively. Rotation member  4  is rotatable in direction of arrow  5  and includes substrate mounts  9  that project radially from the rotation member  4 , the substrate mounts  9  being rotatable in direction of arrow  7 . Substrates  48  are coupled with the substrate mounts  9  for application of a coating. Referring to FIG. 2, the rotation member  4  can be provided as a wheel that is rotatable about a central axis  29  (i.e., in direction of arrow  5 ). Substrate mount  9  includes a shaft  26  and is rotatable about radial axes  27  (which is in direction of arrow  7  shown in FIG.  1 ). 
     The invention will now be described in more detail. 
     Rotation Member 
     FIG. 2 shows one embodiment of the rotation member in the form of a wheel  4  according to the invention. In a preferred embodiment, the wheel  4  is rotatably driven by a motor  62  (shown in FIG. 6) about its central axis  29 , in direction of arrow  5 . Rotation of the motor  62  is preferably controlled by a driver unit  81  (FIG.  6 ). The wheel can be provided in any suitable dimensions, to accommodate the desired number of substrates to be coated and to fit into a total area for the coating operations, such as a fume hood. 
     FIG. 8 shows another embodiment of the wheel, indicated as  4   a . In this embodiment, portions of the rim of the wheel are flattened to produce portions  72  that include substrate mounts  9 . While the figure depicts two such substrate mounts  9  in each portion  72 , it is understood that any suitable number of substrate mounts  9  can be provided within each portion  72  of the wheel  4   a . The dimensions of each portion  72  can be adjusted to contain the number of desired substrate mounts  9  and will be determined by such factors as the diameter of the nozzle used in connection with the coating station, the width or diameter of the substrate to be coated using the device, the size of the coating zone, and the like. Further, any number of portions  72  can be provided on wheel  4   a , depending upon the desired use. 
     The embodiment shown in FIG. 8 has been found to be particularly useful when coating relatively long substrates. The use of flattened portions  72  allows substrates to be mounted on wheel  4   a  in a manner that is parallel to the nozzle  52  of coating station  2 . In this embodiment, substrates extend from the wheel  4   a  in parallel fashion, and the substrates are lined up more closely in line with nozzle  52  of the coating station. This embodiment provides a combination of advantages, such as a more uniform coating along the length of the (relatively long) substrate, as well as reduced waste of coating solution during the application process. This embodiment can be contrasted with the wheel  4  shown in FIGS. 1 and 2, where substrate mounts  9  extend from the rounded periphery of the wheel  4  and therefore are not aligned in a parallel manner with respect to each other. 
     It is understood that the rotation member can be provided in any suitable configuration, such as circular (e.g., a wheel as depicted in FIGS.  1  and  2 ), square, rectangular, or other, to achieve the purposes herein described. In one such alternative embodiment, for example, the rotation member is provided in the form of a square member including an equal number of substrate mounts on each peripheral side of the square. Any number of substrate mounts can be provided on each such face or side of the rotatable member, and the number of substrate mounts can be determined, for example, by the number of nozzles contained within each coating station, the distance between coating stations, overall dimensions of the device, dimensions of each substrate to be coated, and the like. 
     Substrate Mounts 
     Referring to FIG. 1, the substrate mounts  9  of the device  1  are positioned around the outer periphery of the rotation member  4 . Preferably, the substrate mounts  9  mount the substrate  48  onto the wheel in such a manner that the substrate is a predetermined distance from the coating station and is positioned substantially horizontally for application of a coating material from the coating station. 
     As shown in FIGS. 1,  2  and  5 , the substrate mounts  9  project radially from the wheel  4  and are rotatable about radial axes  27 . In a preferred embodiment, substrate mounts  9  include a shaft  26 , a gripper carrier  40  and a substrate gripper  44 . Shaft  26  projects from the periphery of the wheel  4  and engages the gripper carrier  40 . Gripper carrier  40  is thus configured to be seated onto the shaft  26  and is frictionally held in place. In one embodiment shown in FIG. 5, gripper carrier  40  includes a chamber  39  for receiving the shaft  26 . Other configurations of the shaft  26  and gripper carrier  40  can be substituted for that shown in the figure to achieve the same purpose. Additional securement of the gripper carrier  40  on the shaft  26  can be provided in the form of screws, magnets, pins, clamps, and the like. Preferably, the gripper carrier  40  is removable from the wheel  4 , to allow the user to remove the gripper carrier  40  for insertion or removal of the substrate gripper  44  (discussed in more detail below) and substrate  48 . The gripper carrier  40  can then be re-mounted on the wheel  4  for the coating operation. 
     A variety of configurations can be used for the gripper carrier  40  of the invention, while still utilizing one wheel  4 . For example, the gripper carrier  40  can be configured to receive a medical device such as a stent, or it can be configured to receive a larger device with different dimensions. At the same time, the gripper carrier  40  can preferably be configured so that it has a standard (e.g., universally sized) chamber  39  for mounting onto the wheel, as described in more detail below, to allow the user to choose a particular gripper carrier  40  for a particular application without having to use a different wheel  4 . The invention thus preferably provides a rotation member that is adaptable to be used to coat any suitable substrate, by simply changing the gripper carriers used in connection with the rotation member. 
     In yet another embodiment, gripper carrier  40  does not comprise a separable element of the device. Gripper carrier  40  can be provided as a part of the rotation member (e.g., wheel) or as part of the substrate gripper  44 . One of skill in the art, given the teachings herein, could readily modify the device to provide the gripper carrier  40  as a part of either the rotation member or the substrate gripper  44 . 
     Referring to FIGS. 4 and 5, gripper carrier  40  includes a chamber  42  (shown in hidden lines in FIG. 4) for receiving the substrate gripper  44 . Chamber  42  is sized and configured to receive substrate gripper  44  and frictionally engage the substrate gripper  44  in place during operation. In one preferred embodiment shown in FIG. 4, the gripper carrier  40  is provided in two parts  41  and  43  that can be assembled to receive the substrate gripper  44 . This two-part configuration of the gripper carrier  40  allows the operator to remove part  41  of the gripper carrier  40  to insert or remove substrate gripper  44  by opening the chamber  42  and laying the substrate gripper  44  within the chamber, then replacing the part  41  in position to thereby confine the substrate gripper  44 . Parts  41  and  43  can be held together using any suitable connector mechanism, including screws, pins, clamps, or the like. Alternatively, the parts  41  and  43  are magnetized, so that the parts are held together by magnetic force. In an alternative embodiment, gripper carrier  40  is configured as a one-piece assembly, and the substrate gripper  44  is simply inserted into the chamber  42  through the end opening of the chamber, until it is frictionally held in place. 
     Preferably, substrate gripper  44  is provided in the form of tweezers or other suitable grasping and holding device. Optionally, the substrate gripper  44  is used in connection with a collar  46  that slidably fits around the outer surface of the substrate gripper  44  once a substrate  48  has been provided within the substrate gripper  44 . As shown in FIG. 4, in use, a substrate  48  is grasped with the substrate gripper  44 . Collar  46  is then slipped around the outer surface of substrate gripper  44 . Collar  46  thus provides a splashguard to keep the coating solution from coating and building up on the substrate gripper  44 . Collar  46  also preferably provides additional stabilization of the gripper/substrate engagement. Once the collar  46  has been seated on the substrate gripper  44 , the substrate gripper  44  is inserted into the gripper carrier  40  until the substrate gripper  44  is seated within the chamber  42 . 
     The substrate gripper  44  is preferably held within chamber  42  of the gripper carrier  40  by frictional force, and the connection can be reinforced using any suitable connecting device, such as screws, magnets, pins, clamps, or similar coupling mechanism. 
     Referring to FIG. 9, an alternative embodiment of the substrate gripper  44  of the invention is shown. As shown in the figure, substrate gripper  44   a  comprises a unitary holder that includes a collar portion  74 . Preferably, the collar portion comprises a flared portion of the substrate gripper  44   a , to allow easy insertion of a pin  76 . In the embodiment shown in the figure, the entire substrate gripper  44   a  comprises one piece. The substrate gripper  44   a  can be fabricated by taking a rod, such as a metal rod (e.g., stainless steel), and forming a chamber in one end, for example, by drilling. A collar portion  74  can be cut out of the rod, for example, using an auger. Once a chamber has been drilled into the end of the rod, a pin  76  is inserted into the formed chamber. The pin  76  can comprise any suitable material and is preferably Teflon™. Pin  76  is held within substrate gripper  44   a  in a sufficiently stable manner and can be secured using any mechanism, including adhesive, pins, screws, and the like. Pin  76  is inserted into the substrate gripper  44   a  through the collar portion  74  and is seated within the chamber or hole contained within the substrate gripper  44   a.    
     Once the substrate gripper  44   a  is assembled, a substrate to be coated, such as a stent, is seated onto pin  76 . This embodiment of the substrate gripper  44   a  can be used with the gripper carrier  40  described above. 
     In one preferred embodiment, the substrate mounts  9  are rotatable about radial axes  27  (shown in FIG. 2) that are perpendicular to the central axis  29  of the wheel, as discussed in more detail below. 
     In an alternative embodiment, the substrate mounts  9  rotate about second axes that are parallel to the central axis. As shown in FIG. 10, substrate mounts can be rotatable about second axes  78 . In the embodiment shown, the substrate mounts  9  are positioned on the upper face of the wheel  4  and are provided in a vertical position. It is understood that the substrate mounts  9  could alternatively be positioned on the downward face of the wheel, in which case the substrate mounts would still be rotatable about second axes  78 . Preferably, when using this embodiment of the rotation member, the solvent used for the coating solution flashes off quickly, so that uneven application of the coating onto the substrates can be minimized or avoided. One such solvent is tetrahydrofuran, for example. 
     While the substrate mounts  9  have been described as being positioned at the periphery of the rotation member, it is understood that the substrate mounts can be positioned at any suitable location on the rotation member, to allow deposition of a coating solution using the invention described herein. 
     Drive Arrangement 
     According to the invention, the device further includes a drive arrangement for rotating the rotation member about a central axis and for rotating the substrate mounts about second axes. In one embodiment, the device includes a first drive arrangement for rotating the wheel  4  about the central axis  29  and for rotating the substrate mounts  9  about the radial axes  27  (see FIG.  2 ). As shown in FIG. 6, one embodiment of the drive arrangement includes a first (e.g., rotation member) drive arrangement and a second (e.g., substrate mount) drive arrangement. The configuration shown allows independent rotation of the wheel  4  about the central axis  29  and of the substrate mounts  9  about the radial axes  27 . In a preferred embodiment, the rotation member drive arrangement includes motor  62  (e.g., an electric motor such as a megatorque motor sold by NSK Ltd, Precision Machinery and Parts Tech Center, Gunma-Ken, Japan). The wheel  4  is preferably mounted on or otherwise fastened to a rotor  60  of the motor  62 . Rotation of the rotor  60  by motor  62  thus causes rotation of the wheel  4 . 
     As shown in FIGS. 2,  3  and  6 , a preferred embodiment of the substrate mount drive arrangement includes a vertical drive shaft  6 , a plurality of right angle drive mechanisms  12 , and a continuous drive belt  8  that engages the vertical drive shaft  6  and the right angle drive mechanism  12 . Referring to FIG. 6, the vertical drive shaft  6  preferably passes through a central channel  64  defined by the motor  62 , and into the wheel  4 , where the vertical drive shaft includes center pulley  90 . Preferably, vertical drive shaft  6  is coupled via coupler  66  to a motor  70  to provide rotation of the vertical drive shaft  6 . Bearings  68  can be provided to stabilize the vertical drive shaft  6  within the wheel  4 . At its top, vertical drive shaft  6  includes center pulley  90 . 
     The vertical drive shaft  6  of the drive arrangement is coupled at one end to the motor  70  and engages the drive belt  8  at its other end (e.g., at pulley  90 ). The vertical drive shaft  6  thus translates movement from the motor  70  to the drive belt  8  for rotation of the substrate mounts  9  about the radial axes  27 . Any suitable motor can be used with the invention, and the type of motor is not considered critical to the invention. Preferably, the motor is a DC motor, such as an FBL Series II Brushless DC Motor, with 5:1 bear box (available from Oriental Motor, Torrance, Calif.). Another exemplary motor is a stepper servo AC motor. 
     Referring to FIGS. 2 and 3, right angle drive mechanisms  12  are positioned around the periphery of the wheel. Referring now to FIG. 3, each right angle drive mechanism  12  preferably includes pulley  14  located on top of a right angle drive  12  in the interior of the wheel  4 . In a preferred embodiment, each right angle drive  12  further includes a vertical shaft  16  that is connected to the pulley  14 , a gear mechanism  20  coupled to the vertical shaft  16 , and a horizontal shaft  25  coupled to the gear mechanism. Each right angle drive preferably further includes bearings  18  and  28  for stability of the drive mechanism. Other stabilizing mechanisms can be provided as desired. Preferably, the gear mechanism  20  comprises a pair of gears  22  and  24 , shown as bevel gears in FIG.  3 . Other gear mechanisms can be substituted for the bevel gears shown to achieve the desired coupling of the vertical shaft  16  and horizontal shaft  25  and translation of rotational movement as described herein. 
     Referring now to FIG. 2, drive belt  8  is stretched around the center shaft pulley  90  of drive shaft  6  and loops around each pulley  14  of the right angle drives  12  of the wheel  4 . Drive belt  8  is driven by vertical drive shaft  6 , which is driven by a drive motor  70 . The drive belt  8  also engages pulleys  14  of right angle drives  12  for translation of the rotational movement of the vertical drive shaft  6  about the axis  29  to the rotational movement of substrate mounts  9  about their corresponding radial axes  27 . Preferably, in use, drive belt  8  selectively engages and disengages the center shaft pulley  90  and pulleys  14  during rotation of the respective component. For example, during rotation of the rotation member about the central axis  29 , drive belt  8  can selectively disengage pulleys  14 , to allow rotation of the rotation member without rotation of the substrate mounts. Alternatively, during the coating process, drive belt  8  can selectively disengage vertical shaft  6  to allow rotation of the substrate mounts about second axes, without attendant rotation of the rotation member about the central axis  29 . 
     In one preferred embodiment, drive belt  8  is provided as a two-sided timing belt. However, one of skill in the art would readily appreciate that other suitable drive belts can be used in the invention to achieve the desired result. For example, any mechanism for transferring torque is contemplated, such as mechanisms employing belts, teeth, pulleys, or frictional devices. Examples of suitable drive mechanisms include belts, O-rings, gears, chains, sprockets, and the like. 
     The substrate mount drive arrangement preferably further includes a belt tensioner  10  to maintain adequate tension in the drive belt  8 . As shown in FIG. 2, the belt tensioner  10  is preferably provided in a half moon configuration and is slidably mounted on the wheel  4  through slots  11  for movement relative to the wheel  4  to tighten or loosen the belt  8 . One of skill in the art would appreciate that belt tensioner  10  could be provided in a variety of configurations to achieve the desired result. 
     Referring to FIGS. 2 and 5, rotation of the substrate mounts  9  about radial axes  27  is achieved by the substrate mount drive arrangement. Preferably, the radial axes  27  are arranged perpendicular to the central axis  29 . As discussed above, vertical drive shaft  6  drives movement of drive belt  8 , which in turn drives movement of pulleys  14 . Pulleys  14  are attached to the vertical shafts  16  of the right angle drive  12 . Thus, rotation of the pulleys  14  by the belt  8  causes rotation of the vertical shafts  16 , which in turn cause rotation of the horizontal shafts  25 . The horizontal shaft  25  of right angle drive  12  is coupled to the substrate mounts  9  of the device. Therefore, rotation of the shafts  25  about the radial axes  27  causes the substrate mounts  9  to rotate about the radial axes  27 . Preferably, the drive belt  8  is disengaged from contact with the pulleys  14  when the rotation member is rotated, and rotation of the substrate mounts  9  is not desired. 
     One embodiment of the coupling mechanism for coupling the horizontal shaft  25  of the right angle drive  12  to the substrate mount  9  is shown in FIGS. 2 and 5. As shown, the wheel  4  includes a peripheral rim area  30  that is located outwardly from the right angle drive  12  and within the interior of the wheel  4 . Peripheral rim area includes pocket  32 . Horizontal shaft  25  projects from right angle drive  12  and is coupled via coupler  34  to shaft  26  of the substrate mount  9 . Shaft  26  projects through the pocket  32  of the peripheral rim area  30 , where it is preferably provided with bearings  36  for stabilization. 
     Referring to FIG. 5, the right angle drive  12  with projecting vertical shaft  16  and horizontal shaft  25  is shown. Horizontal shaft  25  is coupled through coupler  34  to the shaft  26  of substrate mount  9  within the interior of the wheel  4 . As shaft  26  of the substrate mount  9  passes through the pocket  32  of peripheral rim area  30 , it is preferably stabilized by bearings  36 . The bearings  36  are optionally provided to stabilize the shaft  26  of substrate mount  9  as it passes through the periphery of the wheel and projects outwardly therefrom. In operation, movement of pulley  14  causes rotation of vertical shaft  16  of the right angle drive, which in turn causes movement of gear mechanism  20  (FIG. 3) which translates movement of vertical shaft  16  to movement of horizontal shaft  25 . Rotation of horizontal shaft  25  in turn causes rotation of substrate mounts  9  about their radial axes. 
     In an alternative embodiment, when the rotatable member is rotated about the central axis, and the substrate mounts are rotated about second axes that are parallel to the central axis (e.g., as shown in FIG.  10 ), substrate mount  9  is coupled to pulley  14  to provide rotational movement about vertical axes  78 . In this embodiment, the right angle drive  12  is not required. 
     Substrate mounts  9  are rotated at a suitable speed to achieve the desired coating uniformity, and the speed will depend upon such factors as the viscosity of the coating solution and the surface geometry of the substrate. Typically, the substrate mounts  9  are rotated about their radial axes at a rate of approximately 50 rpm (revolutions per minute) to approximately 500 rpm, preferably about 100 rpm. 
     As shown in FIG. 6, motor  70  is preferably mounted to a platform  65 , and rotation member motor  62  is mounted to platform  65  as well. In one embodiment, shown in the figure, the motor  70  is mounted on an opposite face of platform  65  from rotation member motor  62 . Motor  70  thus drives rotation of drive shaft  6 , which in turn causes rotation of center pulley  90  to cause radial rotation of substrate mounts  9 . 
     Coating Station 
     Preferably, the invention further includes at least one coating station for application of a coating on the substrate. As shown in FIG. 1, the coating station  2  is provided in spaced relation to the projecting substrate mounts  9  around the wheel  4 . Preferably, the coating station is adjacent to the rotation member. As used herein, “adjacent” means in sufficient proximity to allow the coating station to apply coating solution to substrates mounted onto the rotation member. Thus, this distance will be adjusted depending upon such factors as the dimensions of the coating station and rotation member, as well as dimensions of the substrates to be coated. Referring to FIG. 7, the coating station  2  includes a nozzle  52  and a solution delivery channel  54  (e.g., a conduit, tube, passage, or the like) for delivery of a coating solution from a solution source (not shown) to the nozzle  52 . Optionally, the coating station further includes a gas delivery channel  56  for delivery of gas from a gas source (not shown) to the nozzle  52 . The solution delivery channel  54  and gas delivery channel  56  can be provided as separate channels that are joined within the nozzle  52 , so that the gas and solution are delivered from the nozzle through a single opening. 
     Preferably, the gas is inert, such as nitrogen. The gas preferably atomizes the coating solution. The gas is provided at sufficient pressure to provide good atomization to shear the solution on the surface of the substrate. Preferably, the gas delivery channel supplies the gas to the same nozzle that is used for delivery of the coating solution, although a separate gas delivery nozzle could also be used with the invention. 
     An example of a suitable nozzle is commercially available from Ivek Corporation (North Springfield, Vt.) under catalog number 191.2. 
     Preferably, the coating station comprises a movable arm to allow movement of the coating station into proximity to the substrate during application of the coating, and out of proximity when coating solution is not provided to the nozzle. In a preferred embodiment, the arm of the coating station is movable in both the X and Y axes, providing vertical and horizontal movement of the nozzle. 
     In the preferred embodiment shown in FIG. 1, the coating station  2  is movable in a direction of arrows  3  and  3 ′, which is toward and away from the rotation member  4 , respectively. Movement of the entire coating station provides the ability to remove the nozzle from the coating zone when coating is not being applied to the substrate, for cleaning or other operations. Once the coating operation is in use, the coating station is moved into the coating zone and the solution is supplied. 
     In the embodiment shown in FIG. 1, two coating stations  2  are provided around the periphery of wheel  4 . As shown in this embodiment, the two coating stations are opposite each other, one on each side of the wheel  4 . Spacing of the coating stations can be varied by the user as desired, in light of space considerations and coating methods. When two or more coating stations are used, they are preferably spaced a sufficient distance apart to allow spray deposition without cross-contamination of coating solution from station to station. In one preferred embodiment shown in FIG. 1, the invention is configured on a benchtop so that it is easily used within a standard fume hood of a laboratory. 
     The embodiment shown in the figures includes two sets of nozzles in each coating station. However, it is contemplated that any number of nozzles can be provided in connection with each coating station, and the number of nozzles will be determined by the configuration of the rotation member, and the positioning of the substrates on the rotation member. 
     According to the invention, the vertical position of the coating station is controlled so that the space between the substrate and the nozzle is maintained at a constant, predetermined distance. The coating deposition area is limited to minimize waste. 
     As used herein, “coating zone” will refer to an area surrounding the substrate  48  to be coated that is defined by the area of solution sprayed over and around the substrate. The coating zone is limited by such factors as the relative positions of the nozzle and substrate, movement of the nozzle, diameter of the nozzle, amount of atomization of the solution, the distance between the nozzle and substrate, and the speed of solution delivery from the nozzle. For example, in a first axis, the coating zone is defined by such factors as the relative vertical positions of the nozzle and substrate. In a second axis, the coating zone is defined by such factors as the diameter of the nozzle  52 , the speed of the solution delivery from the nozzle, and the length of the substrate  48  to be coated (and thus the distance the movable arm of the coating station travels during application). Optimizing the coating factors will allow one to achieve the desired coating with minimal reagent waste. 
     Preferably, the invention is used in connection with spray deposition, although other deposition may be used in connection with the invention. Alternatively, the substrates could be passed under or through a coating solution stream, or coating can be provided to the substrate or a section of the substrate through a needle or the like. 
     Method 
     Generally, the coating operation of the invention is performed by rotating or indexing the rotation member to position the substrates in proximity to a coating station, rotating the substrate mounts about the second (e.g., radial) axes, thereby rotating the substrates, and supplying coating solution through the nozzle at a sufficient rate and direction to apply a substantially uniform coating while the substrates are rotating about the second axes. 
     The method according to the invention includes steps of: (a) providing a device that includes (i) a rotation member rotatable about a central axis, (ii) a plurality of substrate mounts positioned on the rotation member that are rotatable about second axes, and (iii) a drive arrangement for rotating the rotation member about a central axis and rotating the substrate mounts about second axes; (b) mounting a substrate onto the substrate mounts; (c) providing at least one substrate coating station adjacent to the rotation member; (d) rotating the rotation member about the central axis to position one or more of the substrate mounts at the substrate coating station; (e) supplying the coating through the nozzle; (f) moving the nozzle of the coating station in a direction parallel to the substrate to form a uniform coating on the substrate; and (g) rotating the substrate mounts about second axes during the supplying and moving steps. 
     Preferably, a gas is provided through gas delivery channel to the nozzle  52  (FIG. 1) simultaneously with the flow of coating solution. In a preferred embodiment, the gas is an inert gas, such as nitrogen. The gas is provided at suitable pressure, for example from 1 to 50 psi (pounds per square inch), to sufficiently atomize the solution on the surface of the substrate. The rate of delivery of the solution is adjusted to provide a suitable thickness of coating on the surface of the substrate, for example, 600 μg per cm 2 . 
     Preferably, when gas is provided with the solution, the gas supply is continued before and after supply of the solution through the nozzle. This allows cleaning of the nozzle prior to solution application and some drying of the coating after the solution is applied to the substrate, although this step is not required. Additionally, supply of the solution can be started before the nozzle reaches the coating zone, to purge an amount of the solution prior to applying the solution to the substrate, when desired. 
     In a preferred embodiment, the distance between the nozzle and the substrate is maintained at a constant, predetermined distance, for example, approximately 2 cm to approximately 10 cm, preferably about 4 cm to about 6 cm. When solution is supplied through the nozzle, the nozzle forms a spray deposition pattern of a diameter approximately 0.5 to approximately 2 cm, preferably about 1 cm. The diameter of the spray deposition pattern will vary depending upon the nozzle used. 
     The delivery rate of the solution through the nozzle is preferably about 5 μμl per second to about 30 μl per second, more preferably about 10 μl to about 20 μl per second when the viscosity of the solution is about 1 centipoise (cp). As used herein, the “delivery rate” refers to the rate at which the coating solution is supplied through the nozzle. The delivery rate of the coating solution can be adjusted depending upon such factors as the viscosity of the coating solution, and the solvent system used with the coating solution. For example, when a solvent such as tetrahydrofuran (THF) is used, which flashes off substrates quickly, the delivery rate can be increased, whereas when a solvent such as water is used, a slower delivery rate is used. 
     In use, the nozzle  52  is positioned at position  50 , shown in FIG. 1, wherein the coating station is moved in a direction of arrow  3 ′ to a position away from a coating zone. Preferably, nozzle  52  is brought in contact with a cleaning solution or other solution to remove any residual coating solution from the nozzle and to prevent dehydration of the nozzle, while substrate to be coated is mounted onto the rotation member  4 . Subsequently, coating solution is supplied from a solution source (not shown) and through solution delivery channel  54  (FIG. 7) to nozzle  52  as the nozzle is moved in the direction of arrow  3  toward the coating zone. Preferably, a gas is supplied from a gas source (not shown) through gas delivery channel  56  (FIG. 7) to nozzle  52  to atomize the coating solution to shear the solution on the substrate surface. Supply of the coating solution, and gas if desired, is preferably started before the nozzle reaches the coating zone, so that the nozzle is purged to rid the nozzle of any unwanted debris or dried coating solution. 
     Once the nozzle  52  reaches the coating zone, the coating solution is applied to the substrate in a sweeping, back and forth manner. The nozzle continues to travel along the axis parallel to the substrate and along the direction of arrows  3  and  3 ′, along the length of the substrate to be coated. The nozzle completes one coating “shot” by completing one back and forth coating motion along the length of the substrate. Multiple shots can be applied to the substrate as desired, and the number of shots applied to the substrate is adjusted to achieve the desired coating weight. 
     The volume of coating solution applied for each shot can be adjusted depending upon such factors as the solvent system used and the viscosity of the coating solution. Typically, for a coating solution using THF as a solvent, the coating solution is applied in approximately 50 μl to approximately 70 μl shots, preferably approximately 50 μl to approximately 65 μl shots. For this shot volume, typically three shots will be applied to the substrate in one coating application. 
     The coating station can be adjusted so that there is a delay between shots of the coating solution onto the substrate. The length of delay between shots depends upon such factors as the shot volume and the length of time required to dry the coating solution before applying additional coating solution. Typically, a delay of approximately 2 seconds to approximately 10 seconds, preferably about 4 seconds to about 6 seconds is preferred for a shot volume of approximately 65 μl, when the coating solution comprises a THF solvent system. 
     The above parameters are exemplary only and can be adjusted to achieve the desired coating thickness and characteristics desired, while minimizing waste of the coating solution. 
     After the coating solution is applied, the nozzle  52  is moved to position  50 . Once the nozzle has cleared the coating zone, the solution delivery and gas delivery, when desired, are shut off to avoid waste of the materials. Alternatively, the gas delivery is kept on while the nozzle is returning to position  50 , to improve drying of the coating, when desired. The point at which the solution and gas delivery are turned on and off are not considered critical to the invention. 
     Once the nozzle is moved back to position  50 , the rotation member  4  is advanced to position the next substrate or substrates to be coated by the coating station. When multiple coating stations are provided in association with the rotation member  4 , stepwise rotation of the rotation member positions the substrates within multiple coating zones for coating with multiple coating solutions. The rotation member is rotated stepwise until all stents are properly coated. The coating application is repeated until all of the loaded substrates have been coated; i.e., one full revolution of the rotation member  4  about its central axis  29 . 
     A program control can be provided to allow required adjustments and monitoring of conditions of coating to achieve desired coating thickness. 
     When coating stents, only the portion of the stent projecting radially from the substrate gripper  44  will be coated, for example, using the embodiment shown in FIG.  4 . When it is desired to coat the entire surface of the stent, the stents are removed from the rotation member by an operator, inverted, and reinserted into the rotation member so that the other half of the stent (the uncoated portion of the stent) is projected radially from the rotation member and is thereby coated. The coating operation is repeated for the second half of the stent. 
     The duration of a coating cycle will depend upon the number of substrates loaded onto the rotation member, as well as the number coating stations and the type of coating applied. Typically, substrate mounts are positioned approximately 10 cm to approximately 20 cm apart. The distance separating the substrate mounts can be adjusted depending upon the geometry of the substrates to be coated, the speed of the coating, the coating solution, and the like. Additionally, the use of any drying or curing stations will affect the duration of a coating cycle. Typically, the duration of a coating cycle will be in the range of 3 minutes to 2 hours. 
     When the substrate mounts  9  project vertically from wheel  4  as shown in FIG. 10, the coating station movement is adjusted to move vertically in a direction parallel to the substrate. The coating solution is applied in a sweeping, up and down manner. The nozzle continues to travel along the axis parallel to the substrate along the length of the substrate to be coated. 
     In a preferred embodiment, the invention includes a stepping advance of the rotation member. Thus, for example, when the rotation member carries 20 substrates, and two substrates are coated by one coating station, the rotation member will make 10 steps per revolution. At least one full revolution is performed for a coating operation. 
     As a result of the arrangement and rotation of components, the invention provides a combination of such advantages as efficiency, reduction of human factors in the coating operation, and uniform coating of substrate. The invention provides an improved device and method for coating medical devices, particularly medical devices having surface geometries that are otherwise difficult to uniformly coat. Moreover, a large number of substrates can be coated, and a plurality of coating layers can be applied to each substrate, in a relatively short period of time. 
     The invention can accommodate a variety of substrates of different configurations. The gripper carrier can be modified to carry different substrates. The gripper carrier can then be mounted onto the rotation member via standard sized substrate mounts. 
     Radial or axial displacement of the substrates is reduced by the configuration of the gripper carrier mounted onto the substrate mounts. Also, bearings included in the rotation member stabilize the substrate mounts, further reducing any movement of the mounted substrates. 
     Optionally, illumination stations including a light-exposure device can be provided if a photoreactive coating is applied such as those described in U.S. Pat. No. 5,637,460 (“Restrained Multifunctional Reagent for Surface Modification,” Swan et al.) and U.S. Pat. No. 5,714,360 (“Photoactivatable Water Soluble Cross-Linking Agents Containing an Onium Group,” Swan et al.) (commonly assigned to the present Assignee, the disclosures of which are incorporated by reference) or one or more heating stations can be provided if thermal curing of the coating is required. 
     EXAMPLE 1 
     Coating Cardiovascular Stents 
     A preferred method of the invention is performed by way of the example as follows. Cardiovascular stents of length approximately 15-20 mm were inserted into substrate grippers and a collar was slid over the juncture between the substrate gripper and stent. The substrate gripper, stent and collar were then inserted into a chamber formed in the gripper carrier. The substrate gripper was inserted into the gripper carrier and pushed until the substrate gripper seated into the chamber of the gripper carrier and was frictionally held in place. The gripper carrier was then mounted onto shaft of the substrate mount of the device. The desired number of stents were mounted onto wheel  4  as shown in FIG.  1 . 
     Once the desired number of stents were mounted onto the wheel, the wheel was rotated about its central axis to bring two stents into a first coating zone. In this example, the first coating zone is defined as being positioned within proximity to coating station  2  shown in FIG.  1 . Once the stents were positioned as shown in FIG. 1, a coating cycle was started. 
     A 5 mg/ml coating solution comprising 30% by weight drug, 35% by weight poly(ethylene-co-vinyl acetate) (PEVA) and 35% by weight poly(butylmethacrylate) (PBMA) in THF as described in PCT Publication Number WO 99/55396 (International Application Number PCT/US99/08310, Chudzik et al., commonly assigned to the assignee of the present invention and incorporated herein by reference) was provided through the solution supply channel of the coating station from a solution source to the nozzle. During the coating operation, the nozzle was moved in a direction parallel to the stent, shown as arrows  3  and  3 ′ in FIG.  1 . The speed of movement of the nozzle is typically about 6 mm per second. The coating solution pump was adjusted to provide a solution delivery rate of 20 μl per second to the stent surface. According to the invention, the nozzle was moved along the axis parallel to the stent a sufficient number of times to apply suitable coating thickness. Ten (10) shots (e.g., passes of the nozzle), with each shot being one trip back and forth along the length of the stent, were applied, each shot equaling 51 μl-67 μl of coating solution. A delay of four (4) seconds was provided between each coating shot. 
     The distance from the nozzle to the stent was adjusted to minimize waste of the coating solution and provide a coating to the surface of the stent. The distance from nozzle to stent was 4.5 cm. Nitrogen, N 2 , was provided at a rate of 4 psi. 
     Simultaneously with the application of the coating, the substrate mounts were rotated at a constant rate about radial axes at a speed of 100 rpm to allow uniform application of the coating. 
     Once sufficient coating solution was applied, the solution supply channel was shut off and the nozzle was moved out of the coating zone. Nitrogen supply was continued after the solution supply was cut off, to allow cleaning of the nozzle and some extent of drying of the coating. 
     The above application of a coating of approximately 4 μm-6 μm thickness to the stent is referred to as a coating application. Once a coating application was performed, the wheel was rotated sequentially to position the next two stents in the coating zone for coating application. Rotation of the wheel positions stents sequentially through coating stations for application of multiple coatings. The wheel was rotated stepwise until all stents were properly coated. 
     Once the wheel completed a coating application, the stents were removed from the substrate mounts, inverted, and re-mounted onto the wheel so that the other half of the stents (uncoated) projected radially from the wheel. The coating application was repeated to coat the second half of the stents. Stents were removed and weighed to determine coating thickness. Results are shown in Table I below. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Stent A 
                 Stent B 
                 Stent C 
                 Stent D 
                 Average 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 First half 
                 271 μg 
                 301 μg 
                 289 μg 
                 291 μg 
                 288 ± 12.5 μg 
               
               
                 Second half 
                 282 μg 
                 309 μg 
                 286 μg 
                 303 μg 
                 295 ± 13.0 μg 
               
               
                   
               
            
           
         
       
     
     The results show a substantially uniform coating thickness when the invention is used to apply a coating on stents. 
     The invention has been described with reference to various specific and preferred embodiments and techniques. However, it will be apparent to one of ordinary skill in the art that many variations and modifications may be made while remaining within the spirit and scope of the invention. While the invention has been described in relation to coating stents, one of skill in the art would readily appreciate the applicability of the invention to a variety of substrates. 
     All publications and patent applications in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually incorporated by reference.