Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/14—Metallic material, boron or silicon
  • C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
  • C23C14/165—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon by cathodic sputtering
• • 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
  • A61L31/082—Inorganic materials
  • A61L31/088—Other specific inorganic materials not covered by A61L31/084 or A61L31/086
• • 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
  • A61L31/146—Porous materials, e.g. foams or sponges
• • 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
  • A61L31/18—Materials at least partially X-ray or laser opaque
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/34—Sputtering
  • C23C14/3435—Applying energy to the substrate during sputtering
  • C23C14/345—Applying energy to the substrate during sputtering using substrate bias

Definitions

• Radiopaque Coating for Biomedical Devices Invented by David A. Glocker Mark M. Romach Cross Reference To Related Application
• a stent is introduced into the patient's system through the brachial or femoral arteries and moved into position using a catheter and guide wire. This minimally invasive procedure replaces surgery and is now used widely because of the significant advantages it offers for patient care and cost.
• stents and guide wires are made of an alloy of nickel and titanium, known as nitinol, which has the unusual properties of superelasticity and shape memory. Both of these properties result from the fact that nitinol exists in a martensitic phase below a first transition temperature, known as M f , and an austenitic phase above a second transition temperature, known as Af. Both Mf and Af can be manipulated through the ratio of nickel to titanium in the alloy as well as thermal processing of the material.
• nitinol In the martensitic phase nitinol is very ductile and easily deformed, while in the austenitic phase it has a high elastic modulus. Applied stresses produce some martensitic material at temperatures above Af and when the stresses are removed the material returns to its original shape. This results in a very springy behavior for nitinol, referred to as superelasticity or pseudoelasticity. Furthermore, if the temperature is lowered below M f and the nitinol is deformed, when the temperature is raised above A f it will recover its original shape. This is described as shape memory.
• Stents having superelasticity and shape memory can be compressed to small diameters, moved into position, and deployed so that they recover their full size.
• an alloy composition having an A f below normal body temperature the stent will remain expanded with significant force once in place.
• the nitinol must typically withstand strain deformations of as much as 8%.
• Stents and similar intraluminal devices can also be made of materials like stainless steel and other metal alloys. Although they do not exhibit shape memory or superelasticity, stents made from these materials also must undergo significant strain deformations in use.
• Figure 1 illustrates one of many stent designs that are used to facilitate this compression and expansion.
• This design uses ring shaped "struts" 12, each one having corrugations that allow it to be collapsed to a small diameter.
• Bridges 14, a.k.a. nodes, that also must flex in use connect the struts.
• Many other types of expandable geometries, such as helical spirals, braided and woven designs and coils, are known in the field and are used for various purposes.
• Radio transparent There are many advantages that would result from being able to see a stent in an X-ray. For example, radiopacity, as it is called, would result in the ability to precisely position the stent initially and in being able to identify changes in shape once it is in place that may reflect important medical conditions.
• Physical vapor deposition techniques such as sputtering, thermal evaporation and cathodic arc deposition, can produce dense and conformal coatings of radiopaque materials like gold, platinum, tantalum, tungsten and others. Physical vapor deposition is widely used and reliable. However, coatings produced by these methods do not typically adhere well to substrates that undergo strains of up to 8% as required in this application. This problem is recognized in US 6,174,329, which describes the need for protective coatings over radiopaque coatings to prevent the radiopaque coatings from flaking off when the stent is being used.
• Radiopaque coatings deposited by physical vapor deposition is the temperature sensitivity of nitinol and other stent materials.
• shape memory biomedical devices are made with values of A f close to but somewhat below normal body temperature. If nitinol is raised to too high a temperature for too long its A f value will rise and sustained temperatures above 300- 400 C will adversely affect typical A f values used in stents. Likewise, if stainless steel is raised to too high a temperature, it can lose its temper. Other stent materials would also be adversely affected. Therefore, the time-temperature history of a stent during the coating operation is critical. In the prior art it is customary to directly
• 105 control the temperature of a substrate in such a situation, particularly one with a very low thermal mass such as a stent. This is usually accomplished by placing the substrate in thermal contact with a large mass, or heat sink, whose temperature is controlled. This process is known as controlling the temperature directly or direct control. Because of its shape and structure, controlling the temperature of a stent
• the present invention is directed towards a medical device having a radiopaque outer coating that is able to withstand the strains produced in the use of the device without delamination.
• a medical device in accordance with the present invention can include a body at least 125 partially comprising a nickel and titanium alloy and a Ta coating on at least a portion of the body; wherein the Ta coating is sufficiently thick so that the device is radiopaque and the Ta coating is able to withstand the strains produced in the use of the device without delamination.
• the Ta coating can consist primarily of the bcc crystalline phase.
• the coating thickness is preferably between approximately 3 and 130 10 microns.
• the device can be a stent or a guidewire, for example.
• the coating preferably is porous.
• a process for depositing a Ta layer on a medical device consisting of the steps of: maintaining a background pressure of inert gas in a sputter coating system containing 135 a Ta sputter target; applying a voltage to the Ta target to cause sputtering; and sputtering for a period of time to produce the desired coating thickness; wherein the Ta layer preferably has an emissivity in the visible spectrum of at least 80%.
• the device preferably is not directly heated or cooled and the equilibrium temperature of the device during deposition is controlled indirectly by the process. The equilibrium
• a voltage, ac or dc can be applied steadily or in pulses to the medical device during the process.
• An initial high voltage preferably between 300 and 500 volts, can be applied to preclean the device for a first period of time, preferably between 1 minute and 20 minutes.
• a second, lower voltage preferably between 50 and 200 volts, can be applied for a period of
• the inert gas is from the group comprising Ar, Kr and Xe.
• the voltage on the target(s) produces a deposition rate of 1 to 4 microns per hour.
• the target preferably is a cylinder or a plate.
• a medical device comprises a body having an outer layer and a radiopaque coating on at least a portion of the outer layer; wherein the coating is applied using a physical vapor deposition technique.
• Figure 4 illustrates a cross section of a conformal coating of Ta on a strut 12 of a stent
• Figure 5 is a graph showing the reflectance of a Ta coating made according to the present invention with respect to wavelength
• Figure 6 is a graph showing the x-ray diffraction pattern of a Ta coating made according to the present invention
• Figure 7 is a side cross-sectional view of the target surrounding stents in position C of Figure 3 with a plate above the stents
• Figure 8 is a top view of a Ta target surrounding stents
• Figure 9 is a side cross-sectional view of the target surrounding stents of Fig. 8
• Figure 10 is a side elevation view of stents positioned beside a planar target at a high angle of incidence
• Figure 11 shows s scanning electron micrograph of the surface of a Ta coating 175 applied to a polished stainless steel surface.
• Tantalum has a high atomic number and is also biomedically inert and corrosion
• Ta has a melting point of almost 3000 C, any coating process must take place at a low homologous temperature (the ratio of the deposition temperature to the melting temperature of the coating material in degrees Kelvin) to
• the equilibrium temperature will be determined by factors such as the heat of condensation of the coating material, the energy of the atoms impinging on the substrate, the coating rate, the radiative cooling to the 200 surrounding chamber and the thermal mass of the substrate. It is surprising that this energy balance permits high-rate coating of a temperature sensitive low mass object such as a stent without raising the temperature beyond acceptable limits. Eliminating the need to directly control the temperature of the stents significantly simplifies the coating operation and is a particularly important consideration for a manufacturing 205 process.
• This patent relates to coatings that render biomedical devices including intraluminal biomedical devices radiopaque and that withstand the extremely high strains inherent in the use of such devices without unacceptable delamination. Specifically, it relates 210 to coatings of Ta having these properties and methods for applying them that do not adversely affect the thermomechanical properties of stents.
• FIGS. 2 and 3 illustrate the setup.
• Other devices well known to those in the art,
• Position B- The stents 22 were supported from a rotating axis that was approximately 7 cm from the chamber centerline. The vertical position of the stents was in the center of the upper cathode.
• each stent 22 was on a 10 cm diameter fixture or plate 24 that rotated about a vertical axis, which was approximately 7 cm from the cathode centerline. The vertical position of the stents was in the center of the chamber, midway between the upper and lower cathodes. Finally, each stent was periodically rotated about its own 240 vertical axis with a "kicker.”
• the stents Prior to coating, the stents were cleaned with a warm aqueous cleaner in an ultrasonic bath. Crest 270 Cleaner (Crest Ultrasonics, Inc.) diluted to 0.5 pounds per gallon of water was used at a temperature of 55 C. This ultrasonic detergent cleaning was done
• the stents were then rinsed for 2 minutes in ultrasonically agitated tap water and 2 minutes in ultrasonically agitated de-ionized water. The stents were then blown dry with nitrogen and further dried with hot air. The manner in which the stents were cleaned was found to be very important. When the stents were cleaned ultrasonically in acetone and isopropyl alcohol, a residue could be seen on the stents
• This residue may be a consequence of material left after the electropolishing process, which is often done using aqueous solutions.
• the Ta sputtering targets were preconditioned at the power and pressure to be used in that particular coating run for 10 minutes. During this step a shutter isolated the stents
• the coating time was adjusted so that a coating thickness of approximately 10 microns resulted. At a power of 4 kW the time was 2 hours and 15 minutes and at a power of 2 kW the time was 4 hours and 30 minutes. These are very acceptable coating rates for a manufacturing
• the stents were not heated or cooled directly in any way during deposition. Their time-temperature history was determined entirely by the coating process.
• Figure 4 illustrates the cross section of a conformal coating of Ta 40 on a strut 12, shown approximately to scale for a 10-micron thick coating. Stents coated in this
• Level 5 Approximately 10% or more of the coated area flaked.
• Level 4 Between approximately 5% and 10% of the coated area flaked.
• Level 3 Between approximately 1% and 5% of the coated area flaked.
• Level 2 Between approximately 0.1% and 1% of the coated area flaked.
• Level 1 An occasional flake was observed, but less than approximately 0.1% of the coated area flaked. Level 0: No flakes were observed.
• Run Number 5 An obvious and important exception to the need for high bias to produce good 300 adhesion is Run Number 5, which has both excellent adhesion and the lowest value for A f among the coatings. Moreover, the coating appearance of Run Number 5 was black, which could be appealing visually. This is indicative of a very high emissivity in the visible spectrum, characteristic of a so-called black body. As charted in Figure 5, the reflectance was measured to be about 0.5% at a wavelength of 400nm and rises 305 to about 1.10% at 700nm. This is an emissivity of approximately 99% or greater across the visible spectrum.
• the coating is very porous.
• Low homologous temperatures the ratio of the substrate temperature during coating to the melting point of the coating material, in degrees Kelvin
• the observed black appearance may be the result of an extremely porous coating. It is also known in the art that such morphology is also associated with very low coating
• sputtered Ta typically exists in one of two crystalline phases, either tetragonal (known as the beta phase) or body centered cubic (known as the alpha phase).
• the alpha phase of Ta is much more ductile than the beta phase and can withstand greater strains. Therefore, the alpha phase of Ta is more desirable in this application.
• Figure 6 is an X-ray diffraction pattern of a coating 330 made under the conditions of Run No. 5 described above, showing that the coating is alpha tantalum. It is known in the art that sputtering Ta in Kr or Xe with substrate bias can result in the alpha phase being deposited.
• alpha Ta coatings of 10 microns 335 thickness can withstand the very high strains inherent in the use of stents without delamination and coating failure.
• alpha Ta can be deposited in such an open, porous structure.
• An open, porous structure may have other advantages as well.
• the 340 microvoids in the coating would permit the incorporation of drugs or other materials that diffuse out over time.
• drug-eluting coatings on stents are presently made using polymeric materials.
• a porous inorganic coating would allow drug- eluting stents to be made without polymeric overcoats.
• the stents at position C all had adhesion equal to or better than the stents at positions A and B, regardless of conditions.
• Table 2 illustrates the surprising results. (NA indicates coating runs for which no data was taken at those positions.)
• the stents at position C always had very little or no flaking, even under coating conditions where stents in positions A or B had significant flaking. As can be seen
• Stents in position C receive a generally more oblique and lower energy coating flux than stents in positions A or B.
• an oblique coating flux we mean that the majority of the depositing atoms arrive in directions that are not generally perpendicular to the surface being coated. Some of the atoms arriving at the surfaces of the stents in position C from the upper and lower targets will have done so without losing significant energy or directionality because of collisions with the background sputter gas. Those atoms, most of which will come from portions of the targets close to the stents as seen in Figures 2 and 3, will create an oblique coating flux. Other atoms will undergo several collisions with the background gas and lose energy and directionality before arriving at the substrate surfaces.
• the plate above the stents restores the symmetry of the situation and the coatings on the stents become uniformly black overall.
• An alternative, although less desirable, approach to oblique incidence coatings or large target to substrate distances in order to reduce the energy of the arriving atoms 450 through collisions is to raise the pressure of the sputtering gas.
• Sputtering takes place under conditions of continuous gas flow. That is, the sputtering gas is brought into the chamber at a constant rate and is removed from the chamber at the same rate, resulting in a fixed pressure and continuous purging of the 455 gas in the chamber. This flow is needed to remove unwanted gases, such as water vapor, that evolve from the system during coating. These unwanted gases can become incorporated in the growing coating and affect its properties.
• the high vacuum pumps used in sputtering such as diffusion pumps, turbomolecular 460 pumps and cryogenic pumps, are limited with respect to the pressure that they can tolerate at their openings. Therefore, it is well known that in order to achieve high sputtering pressures it is necessary to "throttle” such pumps, or place a restriction in the pump opening that permits the chamber pressure to be significantly higher than the pressure at the pump. Such “throttling” necessarily reduces the flow of gas 465 through the chamber, or gas throughput. Surprisingly, we have found that the adherence of the coatings is improved at high gas throughputs.
• a cylindrical magnetron cathode with an inside diameter of 19 cm and length of 10 cm was used to coat a stent with Ta at a sputtering pressure of 30
• planar targets While the geometry of a cylindrical magnetron makes this possible in an efficient way, as we have shown, the same results can be accomplished using planar targets as well. In the case of planar targets, the requirement is to place the substrates far enough from the target surface(s) that a large target-to-substrate distance is achieved. Alternatively, the substrates could be placed to the side of a planar target so that the
• Figure 10 illustrates how the inventive method could be used with geometries other than cylindrical magnetrons.

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• 2005
  • 2005-03-23 WO PCT/US2005/009651 patent/WO2005094486A2/en not_active Application Discontinuation
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