Abstract:
An ultrasound apparatus and technique produces precise and uniform coatings on various substrates such as stents or other medical devices. The apparatus and technique increases adhesiveness of the surface of the stent or other medical device. In addition, the coating, drying, sterilization processes take place concurrently. The apparatus generate and deliver targeted, gentle, and highly controllable dispensation of continuous liquid spray. The ultrasound coating apparatus and techniques provide an instant on-off coating process with no atmospheric therapeutic agent contamination, no “webbing,” no “stringing” or other surface coating anomalies. Furthermore, the technology reduces wastage of expensive pharmaceuticals or other expensive coating materials.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of and claims benefit of U.S. application Ser. No. 11/197,915 filed Aug. 4, 2005, the teachings of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to coating technologies, and more particularly, to methods of use of an apparatus using ultrasound energy for coating the surfaces of various types of medical devices such as stents, catheters, implants, etc.  
         [0003]     Human and animal blood vessels and other cavities and lumens are commonly treated by mechanically enhancing blood flow through expanding the damaged wall area with stents, which are implantable mesh tub devices. Stents generally can be divided into two categories: metallic bar stents and therapeutic agent eluting stents. The therapeutic agent eluting stents are coated with a polymer and therapeutic agent to reduce adverse physiological reactions, such as restenosis, etc. Due to specific construction and design of stents and insufficient existing coating technologies and methodologies, it has been extremely difficult to coat the inner and outer surface of stents uniformly and/or evenly. Moreover, issues also exist with respect to coating repeatability without webbing or stringing and controlling the dosage of therapeutic agent-polymer coating.  
         [0004]     In some instances, a release profile of a therapeutic agent can be optimized by varying coating thickness along the surface of the medical device. For example, the coating thickness may be varied along the longitudinal axis of a stent by increasing the thickness of the coating at the end section of the stent as compared to the middle portion in order to reduce risk of restenosis caused by the stent&#39;s end sections. Coatings have been applied to the surface of stents and other medical devices on both the interior and exterior of the device both by different techniques such as mechanical coating, gas spray coating, dipping, polarized coating, electrical charge (electrostatic) coating, ultrasound coating, etc. Coatings have been applied by combinations of dipping and spraying. Ultrasound energy or ultrasound spraying have also been used for applying coatings, as has dipping the stent in an ultrasonic bath.  
         [0005]     All of the coating technologies and methods existing to date have critical shortcomings. Such shortcomings include non-uniformity of coating thickness, webbing, stringing, bare spots on the surface, therapeutic agent wasting, over spray, difficulties with control of therapeutic agent flow volume, and adhesivity problems. Current coating technologies also require a long drying time and subsequent sterilization. Therefore, there is a need for a method and device for defect-free, controllable coating technologies and methods for stents and other medical devices.  
         [0006]      FIGS. 1, 2 , and  3  show a prior art ultrasonic sprayer in use with the cone spray pattern according to U.S. Pat. No. 6,569,099. According to the prior art, a liquid drop or flow from tube being delivered directly to the radial surface or radiation surface of the ultrasonic tip, which creates the spray and delivers it to the wound.  
         [0007]      FIGS. 4 and 5  show drawbacks of prior art, in this case, portion of liquid is being dripped from the radial surface or radiation surface and being wasted without getting sprayed. Additionally, dripping of the liquid creates turbulence and non-uniformity of spray, which causes a non-uniform coating layer. Dripping results in excessive waste of expensive therapeutic agents and changing the uniformity of the spray particles which prevent even coating of the stent. Furthermore, the spray pattern of the prior art is conical and the cross section of the spray pattern is rounded, which does not match the stent configuration profile. This is an important distinction because such a pattern oversprays the stent surface which results in more therapeutic agent waste and the inability to control the thickness of the coating layer. The prior art methods and devices can be successfully used in wound treatment because of the cheap price of saline and other antibiotics and relatively big size of treatment area. The prior art device cannot be used effectively in stent coating because of very expensive therapeutic agents for stent coating and the high demand for quality such as uniformity and control of coating layer.  
         [0008]     Therapeutic agents, polymers, their combination or mixtures do not easily wet the stent surfaces, and it is difficult to achieve easy contact between the coating and the stent surface. Furthermore, therapeutic agent and polymer mixtures reduce the wettability of stents made from different materials such as: 316-L, 316-LS stainless steel, MP-35 alloy, nitinol, tantalum, ceramic, aluminum, titanium 6AL-4V, nickel, niobium, gold, polymeric materials, and their combination. Wettability or adhesivity can be increased by different methods, such as: primer coating, etching by chemicals, exposing the stent surface to electrical corona (ionization of air around electrical conductors), plasma, etc., but surface energy from such methods dissipates quickly, limiting the available time when stent should be coated. Primer coating such as urethane, silicons, epoxies, acrilates, polyesters need to be very thin and compatible with the therapeutic agent, polymer or the mixtures that are applied on top of it.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is directed toward methods for defect-free, controllable coating technologies and methods applicable to stents and to other medical devices. The present invention, an ultrasonic method and device for stent coating, will provide a controllable coating thickness without webbing and stringing. The thickness of the coating may be changed along the axis of the stent or other medical device. The term stent will be used throughout this application, not to limit the invention, but as an example of a typical medical device suitable for use with this invention.  
         [0010]     According to the most general aspect of the invention, a controlled amount of liquid is delivered to the distal end of an oscillating member, an ultrasonic tip with a rectangular shape to create a rectangular pattern of fine spray. Liquid may be delivered via precise syringe pumps or by capillary and/or gravitational action. In this case, the amount of delivered liquid must be approximately the same volume or weight as the coating layer and must be determined experimentally.  
         [0011]     The distal end of the liquid delivery tube/vessel are preferably rectangular or flat to match the geometrical shape of ultrasonic tips distal end to create an even and uniformed flat or elongated spray pattern.  
         [0012]     Ultrasonic sprayers typically operate by passing liquid through the central orifice of the tip of an ultrasound instrument. A gas stream delivers aerosol particles to the surface being coated. Currently, no ultrasound stent coating application without the use of gas/air stream delivery with the precise control of delivered liquid volume has been indicated because of the following problems.  
         [0013]     First, a rounded spray pattern/cone cannot deliver the therapeutic agent directly to the stent surface without waste of the expensive therapeutic agent.  
         [0014]     Second, a device which can produce a minimum diameter of liquid particles in the 40 to 60 micron range cannot coat the stent with the preferred 5-30 micron coating thickness.  
         [0015]     Furthermore, the drip of the liquid from the radiation surface results in the waste of the expensive therapeutic agent and changes the uniformity of the coating layer. The proposed technique for coating medical devices and stents, includes creation of a spray pattern, which matches the geometrical shape of stents or surface to be coated. The technique also consists of using a number of acoustic effects of low frequency ultrasonic waves. These acoustic effects have never been used in coating technology. In addition, the technique includes spinning the stent and moving the ultrasound coating head during the coating process to create special ultrasonic—acoustic effects, which will be described in detail below. All coating operations are controlled by special software programs to achieve high quality results.  
         [0016]     The proposed method can coat rigid, flexible, and self expanded stents made of different materials, such as metals, memory shape alloys, plastics, biological tissues and other biocompatible materials. The volume of coating liquid starts from 1 micro liter and increases with very precise control of spray delivery process with 100% delivery. The technique may also include directing additional gas flow into the coating area. Gas flow may be hot or cold and directed through the particle spray or separate from the particle spray.  
         [0017]     The apparatus consists of ultrasonic tips specifically fabricated to avoid the waste of spray liquid and allow control of the spraying process. The rate of ultrasound frequency may be in the range between 20 KHz and 200 KHz or more. The preferable ultrasound frequency is in the range of 20-60 KHz, with a recommended frequency of 60 KHz. Under robotic control, each tabletop device can coat, dry, and sterilize 60 to 100 stents per hour or more depending upon the requested thickness of the coating layer.  
         [0018]     Thereby, the proposed apparatus and method for ultrasound stent coating results in uniform, even, controllable and precise therapeutic agent or polymer delivery with no webbing, stringing. Furthermore, coating, drying and sterilization of the coating layer may occur simultaneously with the increased adhesivity properties of the stent surface.  
         [0019]     One aspect of the invention may provide improved methods and devices for the coating of medical implants such as stents.  
         [0020]     Another aspect of this invention may provide methods and devices for drug and polymer coating of stents using ultrasound.  
         [0021]     Another aspect of this invention may provide methods and devices for coating stents, that provides for controllable thickness of the coating layer.  
         [0022]     Another aspect of the invention may provide methods and devices for the coating of stents that provides changeable thickness of coating layer along the longitudinal axis of the structure.  
         [0023]     Another aspect of the invention may provide methods and devices for coating of stents that avoid the coating defects like webbing, stringing, and the like.  
         [0024]     Another aspect of the invention may provide methods and devices for coating of stents, which increases the adhesivity property of stents along the longitudinal axis of the structure without supplemental chemicals.  
         [0025]     Another aspect of the invention may provide methods and devices for the coating of stents, that provide for drying of the coating layer along the longitudinal axis of the structure simultaneously with the coating process.  
         [0026]     Another aspect of the invention may provide methods and devices for coating of stents, that provides sterilization of the coating layer along the longitudinal axis of the structure simultaneously with the coating process.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The present invention will be shown and described with reference to the drawings of preferred embodiments and will be clearly understood in details.  
         [0028]      FIG. 1  is a cross sectional view of an ultrasonic sprayer in use with the cone spray pattern in currently available devices.  
         [0029]      FIG. 2  illustrates the delivery of liquid directly to radiation surface of ultrasonic tip according in currently available devices.  
         [0030]      FIG. 3  illustrates the delivery of liquid directly to radial surface of ultrasonic tip according in currently available devices.  
         [0031]      FIG. 4  is a cross sectional view of ultrasonic sprayer in currently available devices that shows the dripping of liquid from radial or radiation surface of the ultrasonic tip.  
         [0032]      FIG. 5  is a three-dimensional view of the ultrasonic sprayer with the cone spray pattern in currently available devices with the dripping of liquid from radial or radiation surface of ultrasonic tip.  
         [0033]      FIG. 6  is a cross sectional view of an ultrasonic sprayer tip with landing space for liquid drops or flow in use with the flat spray pattern according to concept of present invention.  
         [0034]      FIG. 7  is a three dimensional view of an ultrasonic sprayer tip with landing space for liquid drops or flow in use with the flat spray pattern according to concept of present invention.  
         [0035]      FIG. 8  is a cross sectional view of an alternative embodiment of the ultrasonic sprayer tip with landing space for liquid drops or flow according to concept of the present apparatus.  
         [0036]      FIG. 9  is a three dimensional view of an alternative embodiment ultrasonic sprayer tip with landing space for liquid drops or flow according to concept of the present apparatus.  
         [0037]      FIG. 10  is a three dimensional view of an ultrasonic sprayer tip with landing space for liquid drops or flow in use and rectangular form of radiation surface to create rectangular or flat spray without dripping according to concept of the present apparatus.  
         [0038]      FIG. 11  is a three dimensional view of an rectangular ultrasonic sprayer tip with landing space for liquid drops in one point via liquid delivery tub/vessel in use and rectangular form of radiation surface to create rectangular or flat spray without dripping according to concept of the present apparatus.  
         [0039]      FIG. 12  is a three dimensional view of a rectangular ultrasonic sprayer tip with landing space for liquid drops via multiple tub/vessels in width of cross section in use and rectangular form of radiation surface to create a rectangular or flat spray without dripping according to the concept of the present apparatus, and also shows the spinning stent on a spindle or mandrel.  
         [0040]      FIG. 13  is a three dimensional view of an rectangular ultrasonic sprayer tip with landing space for liquid flow in width of cross section in use and rectangular form of radiation surface to a create rectangular or flat spray without dripping according to the concept of the present apparatus wherein the liquid delivery tube/vessel&#39;s cross-section is as rectangular as the ultrasonic tip&#39;s distal end or radiation surface.  
         [0041]      FIG. 14  is an illustration of acoustic effects of part of ultrasound stent coating process with no spray.  
         [0042]      FIG. 15  is an illustration of acoustic effects of ultrasound stent coating process with spray.  
         [0043]      FIG. 16  is a three dimensional illustration of ultrasonic tip with the specific construction of distal end for stent coating.  
         [0044]      FIG. 17  is a cross sectional view of an ultrasonic sprayer with the axial orifice in use with the rectangular/flat spray pattern according to present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]     The present invention is a method and device, which uses ultrasonic energy to coat medical devices such as stents. An apparatus in accordance with the present invention may produce a highly controllable precise, fine, targeted spray. This highly controllable precise, fine, targeted spray can allow an apparatus in accordance with the present invention to coat stents without or with reduced amounts of webbing, stringing and wasting of expensive therapeutic agent than many current techniques. The following description of the present invention refers to the subject matter illustrated in the accompanying drawings. The drawings illustrate various aspects of the present inventions in the form of exemplary embodiments in which the present inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present invention. Upon review of the present disclosure, it will be apparent to one skilled in the art that the various embodiments may be practiced without inclusion of some of the specific aspects. The listing of method steps in the claims and disclosure is not intended to limit the steps to a particular order. References to “an”, “one”, or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references contemplate more that one embodiment. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope is defined only by the appended claims, along with the full scope of legal equivalents to which such claims are entitled.  
         [0046]     The present invention provides a novel ultrasonic tip  1  and methods for dispersing a volume of fluid to coat a stent. Embodiments of ultrasonic tips  1  in accordance with the present invention are illustrated in FIGS.  6  to  17 . In accordance with the present invention, ultrasonic tip  1  includes a landing space  17  on a distal end of the ultrasonic tip  1 . The landing space provides a surface on which liquid drops  2  or liquid flow  2  may be introduced onto the ultrasonic tip  1 . The ultrasonic tip  1  is typically constructed from a metal. In one aspect, the metal used can be titanium. Those skilled in the art will recognize additional materials from which the ultrasonic tips in accordance with the present invention may be manufactured. The ultrasonic tip  1  is typically connected to an apparatus (not shown) to ultrasonically vibrate the ultrasonic tip  1  as will be recognized by those skilled in the art upon review of the present disclosure.  
         [0047]     Various configurations for landing space  17  are illustrated in FIGS.  6  to  17 . In one aspect, the landing space  17  can provide a substantially planar surface for introducing a liquid or therapeutic agent which avoids dripping and wasting liquid/therapeutic agent  7 . In another aspect, the landing space  17  may have a curved surface. As the tip vibrates, the liquid therapeutic agent  7  is draw from the landing space  17  where it was introduced to the radiation surface  6  of ultrasonic tip  1  from which the liquid/therapeutic agent  7  is dispersed.  
         [0048]     In one aspect, the line formed by the intersection of the surface defining the landing space  17  and the surface defining the radiation surface  6  will be perpendicular to the longitudinal axis  27  of the ultrasonic tip  1  when viewed from above with reference to the orientations of the embodiments presented in  FIGS. 6, 8  and  17  for example.  
         [0049]     In one aspect, landing space  17  may create a substantially flat plane in the spray pattern as is illustrated in FIGS.  6  to  17 . Landing space  17  can be tilted from the horizontal axis under angle α, so that α is in the range 0&lt;α&lt;90°. The recommended range for the angle α is 30°&lt;α&lt;60°, and the preferred angle is α=45°. A syringe pump  8  may be provided for delivery of liquid  2  to the landing space  17  of ultrasonic tip  1 . A syringe pump  8  can provide with precise control of the flow of liquid/therapeutic agent  7  onto an ultrasonic tip  1 .  
         [0050]      FIGS. 8 and 9  illustrate the creation of an elongated or substantially oval shaped spray pattern  10  by providing a second planar surface  12  geometrically opposite to landing space  17 . Second planar surface being formed at an angle β measured from the longitudinal axis  27  which is substantially perpendicular to the radiation surface  6 . This can disperse liquid/therapeutic agent  7  in a spray pattern  10  which is substantially flat on an upper side and substantially flat on a lower side. Preferably α=β.  FIG. 10  shows an embodiment that creates a rectangular spray pattern  10 .  
         [0051]      FIG. 11  illustrates a three dimensional view of an embodiment of a rectangular ultrasonic sprayer tip  1  with landing space  17  for liquid drops in one point via delivery tub/vessel  9 , illustrated in  FIGS. 12 and 13 , in use and rectangular form of radiation surface  6  to create rectangular or flat spray  3  without dripping of liquid  7  according to the concept of present invention.  
         [0052]      FIG. 12  is an illustration of a three dimensional view of an embodiment with a rectangular ultrasonic sprayer tip  1  with landing space  17  for liquid drops  2  via multiple tub/vessels  9  ( a, b, c ) in width of cross section in use and rectangular form of radiation surface  6  to create rectangular or flat spray  3  without dripping portion of liquid  7 .  FIG. 12  also shows the stent  19  spinning on a spindle or mandrel  20 . The advantage or benefit of this exemplary embodiment is that by controlling the liquid flow from separate tubes, the stent surface can be coated with different or changeable thickness of the coating layer along the longitudinal axis of the structure. Further, such systems allow the use of different therapeutic agents for coating the stents along their longitudinal axis.  
         [0053]      FIG. 13  is a three dimensional view of an rectangular ultrasonic sprayer tip  1  with a landing space  17  for liquid flow  2  in width of cross section in use and rectangular form of radiation surface  6  to uniformily create a rectangular or flat spray  3  without dripping  7  according to this embodiment. Please note that liquid delivery tube/vessel&#39;s  9  cross-section  21  is rectangular as ultrasonic tip  1 .  
         [0054]      FIG. 14  is an illustration of the use of acoustic effects as part of ultrasound stent coating technique with no spray. Specifically,  FIG. 14  shows a technique for improvement of the stent surface&#39;s adhesivity. Currently, one of the critical problems is getting the coating to adhere to the bare metal surface of a sent or other medical device. This embodiment provides a new approach to improve surface adhesion of bare metal stent to increase coating adherence. In this embodiment, the surface adhesivity is improved by placing the stent  19  on the front of the ultrasonic tip&#39;s  1  radiation surface  6 . The ultrasonic tip  1  must be able to move toward the stent and back (x-x) and in direction of the axis of stent  19  (y-y). The reason for placing the stent in front of the radiation surface is to improve coating surface adhesion based on ionization effect of ultrasound waves in “near field” (Fresnel zone).  
         [0055]     Clarification and description of ultrasound air ionization effect: Stable air (mainly nitrogen and oxygen) molecules are not polarized, and an ultrasound field does not affect them. Air also contains many free electrons (negative ions), which move back and forth in the ultrasound field. Overstressing of air (preferably between radiation surface and barrier) at greater than about 1 w/cm2 [watts per square centimeter] can cause the free electrons in the air to attain sufficient energy to knock the free electrons from stable molecules in the air. These newly freed electrons knock off even more electrons, producing more negative and positive ions. When the oxygen molecules in the air lose electrons they become polarized positive ions. These positive ions form ozone: 
 
0 2 →0+0 
 
0+0 2 →0 3  
 
         [0056]     The fast-moving negative ions, as well as the slower heavy positive ions, bombard stent surface, eventually destroying the insulation layers such as oxides or producing conductive “tracking” in the surface of the insulation. This produces clean surface free of oxides.  
         [0057]     According to the theory of classical physics, free electrons are electrons not held in molecular orbit. Negative ions are free electrons. Positive ions are molecules that have lost electrons and are polarized. It is important to notice that significant ultrasonic air ionization process occurs more durable and active in-between radiation surface of the tip and barrier on front of it, such as a stent in coating process. In this condition ionization of air occurs on near field-far field interface between tip radiation surface and barrier during sonication period.  
         [0058]     The length, L, of the near field (Fresnel zone) is equal to L=r 2 /λ=d 2 /4λ, where r is the radius and d is the diameter of the radiation surface or distal end diameter of ultrasonic tip, and λ is the ultrasound wavelength in the medium of propagation. Maximum ultrasound intensity occurs at the interface between the near field (Fresnel zone) and the far field (Fraunhofer zone). Beam divergence in the far field results in a continuous loss of ultrasound intensity with distance from the transducer. As the transducer frequency is increased, the wavelength λ decreases, so that the length of the near field increases. Ionization time can range from a fraction of a second up to minutes depending on ultrasound energy parameters and design of the ultrasound transducer/tip.  
         [0059]     It is relevant to note that in present invention air ionization also occurs during ultrasound coating process in between spray particles in air, which also increases surface adhesion. After adhesivity improvement or surface cleaning cycle is done, without interruption of process, the coating cycle must begin.  
         [0060]      FIG. 15  illustrates the ultrasound stent coating process with spray. Stent  19  can be coated in near or far field of ultrasound field during coating process. Preferably stent must be coated at little away from near field (or in far field close to near field). Most preferably stent coating process must begin in far field, continue and finish in near field or on peak of wave amplitude. Movement of the stent back and forth in a spinning mode during coating process allows spray particles land to coating surface uniformly, in gentle manner and streamline over the surface under ultrasound pressure without stringing. At the same time ultrasound pressure wave forces, particularly ultrasound wind prevents/avoids the webbing, simply blowing up from narrow, small spaces and pushing spray particles through gaps and coating inside surface of stent walls. Further, after coating cycle and during drying cycle, as shown in  FIG. 18 , pressure forces including ultrasound wind dry the coating layer. Partially, wind and vaporization effect which occurs during coating acts as a drier. The thickness of the coating layer is controlled by ultrasound parameters, such as frequency/wave length, amplitude, mode of the waves (CW-continued, PW-pulse), signal form and non-ultrasound parameters like the spinning speed of stent, the distance from radiation surface, time and liquid characteristics.  
         [0061]     Simultaneously, all three-adhesivety improvement, coating and drying cycles allows sterilization of coated stent. Sterilization occurs as a fourth cycle of the coating process due to well-known ozone bacteria and virus destruction properties.  
         [0062]     It is important to note that the above described process can coat a portion or half a stent because the mandrel&#39;s contact area with stent on the inside cannot be coated. After reloading the stent to mandrel, the other side of the stent can be coated by repeating the process. Furthermore, the new design and construction of the holder/mandrel, the stent can be coated in one step/cycle. It is also possible to use more than one spray head with the combination of different polymer+therapeutic agent.  
         [0063]      FIG. 16  is a three dimensional illustration of ultrasonic tip  1  with the specific construction of distal end for stent coating. In  FIG. 16 , the ultrasonic tip&#39;s distal end  6  is rectangular in order to avoid over-use or loss of expensive coating liquid such as therapeutic agent or polymer. Rectangular shape of tip&#39;s distal end matches the stent&#39;s rectangular profile in front view.  
         [0064]      FIG. 17  is a cross sectional view of an ultrasonic sprayer  30  with the axial orifice  26  in use with the rectangular/flat spray  3  pattern  10  according to present invention.  
         [0065]      FIG. 18  describes flow chart of an exemplary method for ultrasound stent coating process in detail and cycles in accordance with the present invention: At step  31  stent is provided, meaning that stent has to be put on the mandrel.  
         [0066]     Ultrasound ionization effect in the air occurs in “near field” (Fresnel zone) and disappears in a very short time (in fraction of seconds) when radiation of ultrasound waves is off. Ozone is very unstable and decomposes with the ejection of atomic oxygen: 
 
0 3 -&gt;0 2 +0 
 
         [0067]     Because of this, all four cycles—adhesivity improvement, coating, drying and sterilization-occur without interruption of the coating cycle process.  
         [0068]     Stent  19  in  FIG. 18  must be placed in near field or preferably at the near field-far field interface during the adhesivity improvement cycle  32 . Next cycle  33  turns on the ultrasound or activates the ultrasound transducer tip.  
         [0069]     On the cycle  34  mandrel with the stent begins spinning. On the next cycle  35  the spray coating is applied to the stent. Cycle  36  includes stopping the coating and continuing spinning with the sonication process. On cycle  37 , the stent is being pulled to the distance of wave length and being spun and sonicated for surface sterilization and drying purposes.  
         [0070]     To achieve high quality and productivity method and device of present invention considers use of special hi-tech robotic system with specific Software-&gt;Hardware-&gt;Controller-&gt;Coating system with spinning mandrel (with changeable speed) and X-Y-Z direction movement.  
         [0071]     It is important to note that all figures illustrate specific applications and embodiments of the coating process with the adhesivity improvement, coating, drying and sterilization, and are not intended to limit the scope of the present disclosure or claims to that which is presented therein. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiment shown. For example, many combinations of therapeutic agent, polymer, their temperature, cycle, sequence and times, additional gas stream (with different temperature) can be used to achieve increasing quality of coating. In various embodiments, the device can be used to coat stents with highly controllable uniformed coating layer. The modification of the device can coat the stent with changeable thickness of coating layer along the longitudinal axis of the structure.  
         [0072]     Therefore, 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 will be apparent to those having skill in the art upon review of the present disclosure. The scope of the present invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.