WO2008002601A1 - Process for coating a substrate - Google Patents
Process for coating a substrate Download PDFInfo
- Publication number
- WO2008002601A1 WO2008002601A1 PCT/US2007/014896 US2007014896W WO2008002601A1 WO 2008002601 A1 WO2008002601 A1 WO 2008002601A1 US 2007014896 W US2007014896 W US 2007014896W WO 2008002601 A1 WO2008002601 A1 WO 2008002601A1
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- WO
- WIPO (PCT)
- Prior art keywords
- coating
- droplets
- medical device
- substrate
- stent
- Prior art date
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
- A61L31/08—Materials for coatings
- A61L31/10—Macromolecular materials
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
- A61L31/14—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
- A61L31/16—Biologically active materials, e.g. therapeutic substances
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L2300/00—Biologically active materials used in bandages, wound dressings, absorbent pads or medical devices
- A61L2300/60—Biologically active materials used in bandages, wound dressings, absorbent pads or medical devices characterised by a special physical form
- A61L2300/606—Coatings
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L2420/00—Materials or methods for coatings medical devices
- A61L2420/02—Methods for coating medical devices
Definitions
- the present invention relates to an apparatus and method for applying a coating to at least a portion of a substrate having desired surface properties.
- the invention relates to a method for producing polymer coatings with various morphologies on medical implants like stents.
- Coatings are often applied to medical implants such as pacemakers, vascular grafts, catheters, stents, heart valves, tissues or sensors to have desired effects and increase their effectiveness. These coatings may deliver a therapeutic agent to the lumen that reduces smooth muscle tissue proliferation or restenosis and may comprise a polymer carrier. Furthermore, implants may be coated to improve surface properties such as lubriciousness, to achieve enhanced biocompatibility and to control the timing and rate of release of the therapeutic agent being delivered. Balloon delivery systems, stent grafts and expandable stents are specific examples of 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.
- Such coatings have been often applied to the surface of an implant by spray coating.
- An atomizing device including an orifice and an internal fluid passage leading to said orifice is typically placed perpendicular to the longitudinal axis of the substrate to be coated.
- the comparatively high coating compaction of the produced coating may however result in an inhomogeneous coating thickness and cracks.
- porous coatings which can be used in medical implants as reservoirs for the retention of therapeutic agents and may be desirable to enhance tissue ingrowth and tissue healing.
- conventional coating methods may not allow changing the morphology of the coating layer instantaneously which can be desirable to accommodate the need for different elution profiles as may be required by the medical application.
- the main object of the invention is to provide a cost-effective and flexible method to form a polymer coating on a substrate having desired surface properties in terms of surface texture, roughness and surface area.
- a further object is to provide a homogeneous coating thickness on the entire surface and particularly on hard to reach areas of the medical implant, in order to improve the quality and integrity of the coating. Another object is to allow immediate adjustment of coating properties so that a variable coating thickness and morphology along the surface of the substrate can be produced.
- the method of the invention provides a process for the formation of coatings having an improved quality and a desired surface morphology.
- the coatings may include a polymer carrier and a therapeutic substance.
- Coatings formed by the process of the invention can be designed to exhibit different properties according to the particular requirements. For example, the porosity, the roughness and the total surface area of the coating can be varied during the spray run.
- the mass diffusion rates through the surface may be controlled by either increasing or decreasing the surface area of the coating and the porosity in the process of the present invention.
- the surface area and porosity may be varied to provide selective coating properties of the coating layer along the surface of the substrate.
- the process of the present invention comprises the steps of generating droplets from a coating composition, transporting the droplets to the substrate so that the majority of the droplets have a tangential velocity component in relation to the surface of the substrate, and depositing the droplets on the substrate with an impact angle other than 90 degrees to form a coating layer.
- the droplets may be deposited at an impact angle between 30 and 85 degrees so that a textured coating is obtained.
- the droplet generation and/or transportation process may be controlled to provide selective surface properties by changing the impact angle of the generated droplets, wherein the impact angle is defined as the angle between the direction vector of the droplet and the surface of the substrate.
- a method to apply a coating to a medical implant using an atomizer to disintegrate a coating solution comprising a therapeutic agent into droplets is provided.
- the atomizer is tilted in relation to the surface of the medical implant. The method comprises the steps of
- the method may further comprise the step of changing the tilt angle between the spray axis and the surface of the medical implant during the coating process in order to vary the morphology of the coating layer.
- the medical implant may be a stent.
- a method to apply a coating to a medical device using means to disintegrate a coating composition into droplets and means to generate a vortical gas flow field having a swirl intensity between 0.01 and 2.5 to transport the droplets to the medical implant, is provided.
- the method comprises the steps of disintegrating the coating composition into droplets, transporting the droplets in said gas flow field to
- the medical device so that the majority of the droplets have a tangential velocity component in relation to the surface of the medical device and depositing the droplets on the medical device.
- the method may further comprise the step of changing the swirl intensity during the coating run in order to vary the morphology of the coating along the surface of the substrate.
- the coating composition may be disintegrated by the vortical gas flow field. The means to generate the vortical gas flow
- the 95 field can comprise a conduit with at least a first and a second gas inlet, wherein swirl motion is induced in the gas flow through at least one gas inlet.
- the swirl intensity may be changed by adjusting the ratio between the axial gas flux of swirl momentum and the axial gas flux of axial momentum.
- the medical device may be a stent and the coating composition may comprise a therapeutic agent and/or may include pores.
- a method to apply a coating to a medical device using means having at least one exit aperture to generate droplets from a coating composition and suction means to generate a gas flow field including at least one entrance aperture is provided.
- the medical device is positioned between said exit aperture and said entrance aperture.
- the method comprises the steps of disintegrating the coating composition into droplets, generating a gas flow field to direct the droplets to the substrate so that the majority 105 of the droplets comprise a tangential velocity component in relation to the surface of the medical device and depositing the droplets on the medical device with an impact angle other than 90 degrees.
- the droplets are formed through vibration or electrostatic energy and the medical device may be a stent.
- the entrance aperture may be tilted in relation to the spray axis.
- the tilt angle of the entrance aperture can be changed during the application of the coating to vary the 110 morphology of the coating.
- the entrance aperture of the suction means may be positioned at an offset distance from the spray axis of the droplet generating means and the position of the entrance aperture can be changed during the application of the coating to vary the morphology of the coating.
- FIG. 1 A is a schematic representation of an droplet impact onto a substrate with a normal impact angle (90 degrees);
- FIG. 1B is a schematic representation of a droplet impact onto a substrate at an angle smaller than
- FIG. 2 is a flow chart of the coating method of the present invention
- FIG. 3 is a spray coating setup of a substrate (atomizer tilted with respect to substrate)
- FIG. 4 is a is a spray coating setup of a substrate (suction device positioned at an offset distance with 125 respect to atomizer);
- FIG. 5 is a Computational Fluid Dynamics (CFD) simulation of a stent coating process visualizing the droplet trajectories (suction device positioned at an offset distance/angle with respect to atomizer);
- CFD Computational Fluid Dynamics
- FIG. 6 is a spray coating setup of a substrate comprising a vortical flow (atomizer positioned perpendicular to substrate);
- FIG. 7A is a cross sectional view of a twin-fluid atomizer having radial and tangential gas inlets
- FIG. 7B is a perspective view of the gas conduit of the atomizer of FIG. 7 A;
- FIG. 8 is a diagrammatic representation of an exemplary coating setup;
- FIG. 9 is a portion of a screen dump of the software used to control the swirl intensity;
- FIG. 10 is a spatial droplet distribution of a spray pattern at a swirl intensity of 0.3;
- FIG. 11 A is a SEM image of a portion of a stent at a swirl number of 0;
- FIG. 11 B is a SEM image of a portion of a stent at a swirl number of 0.3
- FIG. 11C is a SEM image of a portion of a stent at a swirl number of 0.6
- FIG. 12A is a SEM image (magnification 15Ox) showing the surface morphology of a portion of a stent
- FIG. 12B is a SEM image (magnification 1000x) showing the surface morphology of a portion of a stent.
- FIG. 12C is a SEM image (magnification 1000Ox) showing the surface morphology of a portion of a stent.
- the method to apply a coating layer to a substrate comprises the steps of generating droplets from a coating composition, transporting the droplets to the substrate so that the majority of the droplets have a tangential velocity
- the droplet generation and transportation step can be controlled as described in detail in FIG. 8 to fine tune the surface properties of the substrate to be coated.
- the substrate is preferably an implant and may include pacemakers, vascular grafts, catheters, stents, heart valves, tissues, sensors and the like.
- the coating composition may comprise one or more a solvents, one or more polymers, and/or one or more therapeutic substances.
- the therapeutic substance may include, but is not limited to, proteins, hormones, vitamins, antioxidants, DNA, antimetabolite agents, anti-inflammatory agents, anti-restenosis agents, anti-thrombogenic agents, antibiotics, anti-platelet agents, anti-clotting agents, chelating agents, or antibodies.
- suitable polymers include, but are not limited to, synthetic polymers including
- polyethylen PE
- poly(ethylene terephthalate) PET
- polycarbonates PC
- polyvinyl halides such as polyvinyl chloride) (PVC), polyamides (PA), poly(tetrafluoroethyle ⁇ e) (PTFE), poly(methyl methacrylat ⁇ ) (PMMA), polysiloxanes, ethylene-vinyl acetate (EVAc), polyurethane, and poly(vinylidene fluoride) (PVDF); biodegradable polymers such as poly(glycolide) (PGA), poly(lactide) (PLA), poly(lactic-co-glycolic acid) (PLGA), and poly(anhydrides); or
- the coating composition can also comprise active agents, radiopaque elements or radioactive isotopes.
- the solvent is selected based on its biocompatibility as well as the solubility of the polymer.
- Aqueous solvents can be used to dissolve water-soluble polymers, such as Poly(ethylene glycol) (PEG) and organic solvents may be used to dissolve hydrophobic and some hydrophilic polymers. Examples of suitable solvents include methylene
- solvent is used to refer to any fluid dispersion medium whether a solvent of a solution or the fluid base of a suspension, as the invention is applicable in both cases.
- FIG. 1 B is a schematic of a droplet impact on a substrate according to the method of the present invention.
- the impact velocity V of the droplet 52 comprises a normal velocity component VN and a tangential velocity component VT resulting in an impact angle ⁇ other than 90 Degrees between droplet and substrate surface.
- the tangential velocity component VT promotes droplet spreading over the substrate 54 rather than impacting on it.
- An asymmetric splat morphology is expected to occur because VT contributes to the spreading of unsolidified materials toward point a. If the spray angle is decreased, especially for ⁇ less than 45 degrees, and the tangential velocity component W is increased, porosity and roughness of the coating increase.
- atomizer 1 is tilted in relation to the substrate so that the spray angle ⁇ between the spray axis 51 and the surface of the substrate is less than 90 degrees.
- a twin-fluid atomizer is preferably used to disintegrate the liquid to be atomized.
- liquid is supplied to the liquid inlet, travels through the liquid path and exits the atomizer orifice. Gas, which is fed in the gas inlet, breaks up the liquid into fine droplets when it exits the gas orifice and directs the droplets to the substrate.
- droplets having a tangential velocity component in relation to the surface of the substrate are deposited on the substrate 54 at an impact angle ⁇ of less than 80 degrees.
- twin-fluid atomizer such as depicted in FIG. 7, is preferably used in this embodiment, it is to be understood that the principles of the present invention may be applied to other nozzle types and geometries as well, including atomizers that employ electrostatic or ultrasonic energy, for example. Dispensing and atomization systems incorporating multiple nozzles and/or atomizer assemblies of a single configuration or differing configurations may incorporate the principles of the present invention.
- the impact angle ⁇ of the droplets may be varied during the coating process by increasing or decreasing the angle ⁇ between spray axis 51 of the atomizer and substrate 54.
- the following exemplary embodiment is suitable if a coating having a comparatively low compaction and an increased porosity is desired.
- the droplet impulse and compaction of the coating layer is minimized by generating a low droplet velocity of preferably less than 5 m/s and a comparatively small droplet size.
- an ultrasonic atomizer 1 an entrance aperture of a suction device 55 and a substrate 54 located therebetween are depicted.
- the atomizer 1 is positioned above the substrate and located perpendicular relation to the surface of the substrate. Alternatively, the atomizer may be tilted.
- the entrance aperture of the suction device 55 which is preferably provided underneath the substrate, has an offset distance d from the spray axis 51.
- the suction device may comprise an ejector or fan, which is connected to the entrance aperture of the suction device 55 and having a suction capacity ranging from 5 to 25 l/min.
- a coating composition is supplied to the ultrasonic atomizer and is broken-up into fine droplets at an operation frequency of approximately 130 kHz. Droplets having a size of less than 20 ⁇ m and comparatively low droplet velocities of less than 5 m/s are produced in the proximity of the liquid orifice. The generated droplets are transported from the atomizer orifice to the substrate 54 by gravity and/or by the gas stream produced by the suction device.
- tangential velocity components are generated in relation to the substrate 54 and the majority of the transported droplets 52 are deposited under an impingement angle other than 90 degrees.
- the impingement angle may be changed during the coating process by altering the position or the tilt angle of the entrance aperture of the suction device.
- the coating properties in terms of roughness and porosity can be therefore varied along the surface of the substrate.
- FIG.5 is a Computational Fluid Dynamics (CFD) simulation of a droplet transport and deposition process on a stent.
- the volume model consists of an atomizer orifice 1, an entrance aperture 55 of a suction device and a stent 54 placed therebetween.
- the stent is supported by a holding device and located approximately 15 mm downstream from the atomizer orifice.
- the entrance aperture 55 of the suction device is placed at a distance of approximately 8 mm from the stent.
- the atomizer may also be tilted towards the
- the trajectories 56 were simulated for droplets having a diameter of approximately 18 ⁇ m.
- the droplets are transported from the atomizer orifice to the stent by gravity and by the gas flow field generated by the suction device.
- a suction with a flow rate of 10 l/min was generated.
- the suction was generated. Depending on the size of the substrate and the position of the entrance aperture, the suction
- 235 capacity may vary between 5 and 25 l/min.
- a second low velocity gas flow field may be produced at the atomizer orifice to improve process stability and to prevent deflection of the droplets, which may be caused by the air flows within the coating chamber.
- Atomizer 1 is preferably located perpendicular to the surface of the substrate 54. Droplets are generated from a coating
- composition and a gas flow field comprising a vortex is produced to direct the generated droplets to the substrate 54.
- Various atomizers including, but not limited to, devices employing pneumatic, electrostatic or ultrasonic energy may be used to disintegrate the fluid to be atomized. Such devices may also comprise means to generate a gas flow field with a vortex.
- an exemplary coating setup comprising atomizer, liquid and gas supply,
- twin-fluid atomizer of FIG. 7 is used to atomize a liquid composition and to generate a gas flow field with a vortex through pressurized gas, provided, for example, by a compressor or by a pressurized container.
- Atomizer 1 comprises a liquid path extending from liquid inlet 9 to liquid orifice 15. The pressurized gas is fed through gas inlets 21 and 22 into gas conduit 6 having a radius ro and expelled
- FIG.7B A perspective view of gas conduit 6 depicting the position of the two inlets 21 for axial gas flow and the two tangential gas inlets 22 used to induce swirl motion into the axial gas flow is shown in FIG.7B.
- the spray axis of the atomizer is located perpendicular to the surface of the substrate and positioned on the same plane.
- the distance between the atomizer tip and the substrate may
- the liquid inlet of the atomizer is connected to a liquid supply source.
- a syringe pump may be used to feed the coating composition into the atomizer.
- the compressed gas is fed into valves, which regulate the axial and tangential gas flow. Gas mass flows (m axial, m tang) are measured, respectively, by means of a thermal mass flow meter.
- FIG. 9 is a portion of the Graphical User Interface of the control software displaying the current values for total flow, axial flow, tangential flow and swirl intensity.
- the swirl intensity of the gas can be varied instantaneously by regulating the axial and tangential gas ratio during the coating process.
- the impingement angle and the droplet trajectory can be thereby controlled to produce desired coating properties in terms of
- S- swirl intensity or swirl number defined as a number representing axial flux of swirl momentum G ⁇ divided by axial flux of axial momentum G x , multiplied by the nozzle radius R
- the swirl intensity S is expressed by the following equation and obtained by integration of axial U and tangential W gas velocity profiles where r is the radial distance and p is the density.
- the swirl number can be related to the measured total gas mass flow rate m ⁇ and the tangential mass flow rate m t ⁇ ng .
- the value ro is the axial radius of the gas conduit in which the tangential 280 gas flow is introduced, R is the nozzle exit radius and A, is the total area of the two tangential inlets.
- the swirl intensity S can be changed.
- the desired swirl 285 number and the total gas flow are entered by the operator.
- Axial gas mass flow is supplied through two symmetric inlets 21 and swirl motion is imparted to the annular flow by means of two tangential inlets 22.
- the gas flux comprising swirl motion is expelled through annular gap 16.
- a gas flow with an angular momentum is generated, resulting in a flow field with axial and tangential velocity components and increased shear forces at the atomizer orifice.
- the liquid flows through the liquid tube to the atomizing end, exits the liquid orifice 15 290 and is broken up by the atomizing air into very fine droplets having a tight droplet size distribution.
- By generating an angular momentum an improved atom izat ion of the liquid and a stabilized spray with minimized pulsation is obtained.
- a homogeneous spatial droplet size distribution is produced as shown in FIG. 10.
- 300 devices such as single fluid nozzles, ultrasonic nozzles, electrostatic nozzles or twin-fluid nozzles, may be used to atomize the coating composition. They may also include means to support the droplet transportation and deposition process. All such variations are intended to be within the scope and spirit of the invention.
- the following examples are presented to illustrate the advantages of the present invention. These examples are not intended in any way otherwise to limit the scope of the disclosure.
- Stents manufactured by STI, Israel having a diameter of 2 mm and a length of 20 mm were coated using two different polymer compositions.
- the swirl intensity has been varied between 0 and 0.6 and in example 2 the swirl intensity was set to 0.3.
- the stents were mounted on a holding device as described in US Pat. App. No. 60/776,522 incorporated herein as a reference.
- the atomizer of FIG.7 was used to disintegrate the coating composition
- the atomizer may be aligned in relation to the stent so 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 atomizer orifice is preferably positioned at a distance of approximately 12 to 35 mm from the outer surface of the stent.
- the liquid inlet of the atomizer is connected to a liquid supply source.
- a syringe pump (Hamilton Inc., Reno, NV, USA) is preferably used to feed the coating substance to the atomizer.
- the compressed gas is fed
- valves which regulate the axial and tangential gas flow.
- Gas mass flows (m axial, m tang) are measured, respectively, by means of a thermal mass flow meter (TSI, Shoreview, MN, USA).
- the tangential component of velocity vt induced during the droplet generation and/or transportation process is responsible for the deposition of the droplets at an impact angle other than 90 degrees resulting in a coating having a desired roughness and porosity. It can be varied during the coating process by changing
- a PC based controller is used to adjust the swirl intensity by regulating the axial gas mass flow rate m axial and the tangential gas mass flow rate m tang.
- the flow rate of the coating solution may range from about 0.5 ml/h to 50 ml/h.
- the atomizer can disintegrate the coating solution into fine droplets at an atomizing pressure ranging from about 0.3 bar to 330 about 1.5 bar. In order to achieve a fine atomization, the atomizer is preferably operated at a total gas flow rate of 6.2 l/min at 0.8 bar atomizing pressure.
- the spraying process may be monitored using an optical patternator in order to ensure that the spatial droplet distribution of the generated spray plume is in the desired limits as 335 described in US. Pat. App. No. 60/674,005 incorporated by reference herein.
- rotary motion is transmitted to the stent to rotate the stent about its central longitudinal axis.
- the rotation speed can be from about 5 rpm to about 250 rpm.
- the stent may rotate at 130 rpm.
- the stent is translated along its central longitudinal axis along the atomizer.
- the translation speed of the stent can be from about 0.2 mm/s to 8 mm/s.
- the translation speed is preferably 0.5 mm/s.
- the stent 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.
- the stents may remain mounted on the holding device to allow drying of the coating and subsequent inspection.
- drying may be accomplished in a variety of ways based 345 on the coating formulation used.
- stents were coated according to the process of the present invention.
- Solvay Advanced Polymers Houston, TX, USA
- FIG. 11 A shows a portion of a coated stent having a smooth compacted coating with an inhomogeneous thickness around the struts due to an increased coating accumulation on the outer circumferential surface of the stent.
- FIG. 11 B depicts a portion of the coating having a homogeneous coating thickness covering the struts of the stent with a relatively smooth coating layer. Accumulation of excess material on the outer circumferential surface of the stent was not observed and the coating looked uniform. Compared to stent #1 the coating seems more homogeneous especially on the outer circumferential surface and at the side faces of the struts
- FIG. 11C illustrates a portion of a stent having a homogeneous thickness at the outer surface and at the side faces of the struts. Accumulation of excess material on the outer circumferential surface of the stent was not observed and the coating looked uniform. Compared to stent #1 and #2 an increased surface roughness and
- the difference between these stents is the thickness of the coating, with the coating on stent #1 being the thickest and with an inhomogeneous coating accumulation on the outer circumferential surface of the stent.
- the coating seems to be more homogeneous in terms of thickness with increased swirl numbers.
- the morphology in terms of roughness changes and a substantially increased surface area is noted
- FIGS. 12A-C are scanning electron microscope (SEM) images of the coating morphology produced on a stent according to the process of the present invention.
- a stent having a homogeneous coating with a comparatively large surface area and roughness is shown. Accumulation of excess material on the surface of the stent was not observed and 390 the coating looked uniform.
- FIG. 12B a small portion of the stent having an increased surface roughness and surface area is depicted at a magnification of 100Ox.
- the image reveals the presence of pores.
- FIG. 12C shows the portion of the stent at a magnification of 1000Ox to better visualize the 395 mo ⁇ hology of the coating and to show the pores in more detail.
- the different types of coatings exhibit a variety of properties with respect to the surface area, porosity and thickness of the coating. It has been found that the surface properties can be varied during the process by controlling the impact angle of the droplets with respect to the substrate to be coated. A more homogeneous coating having increased surface area, roughness and porosity can be obtained by increasing 400 the tangential velocity component of the droplets. In contrast, when spraying higher viscosity polymer compositions without inducing a tangential velocity component the coating tends to accumulate at the outer circumferential surface of the stent which may result in coating defects such as webbing and peeling.
Abstract
Description
Claims
Priority Applications (1)
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DE112007001479T DE112007001479T5 (en) | 2006-06-27 | 2007-06-26 | Process for coating a substrate |
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US11/476,493 | 2006-06-27 | ||
US11/476,493 US7892593B2 (en) | 2006-06-27 | 2006-06-27 | Process for coating a substrate |
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WO2013148213A1 (en) * | 2012-03-26 | 2013-10-03 | The Regents Of The University Of California | Aerosol coating process based on volatile, non-flammable solvents |
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Also Published As
Publication number | Publication date |
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US7892593B2 (en) | 2011-02-22 |
DE112007001479T5 (en) | 2010-02-11 |
US20080286440A1 (en) | 2008-11-20 |
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