Medical devices with selective titanium oxide coatings

Abstract

Medical devices, such as endoprostheses, and methods of making the devices are described. In some embodiments, a medical device includes a body of interconnected bands and connectors forming an elongated tubular structure having an inner luminal wall surface and an outer abluminal wall surface and defining a central lumen or passageway. The inner luminal wall surface and side wall surface of the bands and connectors forming transverse passageways through the elongated tubular structure can bear a coating of hydrophilic material and the outer abluminal wall surface of the tubular structure can bear a coating of hydrophobic material.

Description

TECHNICAL FIELD

This invention relates to medical devices, such as endoprostheses (e.g., stents).

BACKGROUND

The body defines various passageways such as arteries, other blood vessels, and other body lumens. These passageways sometimes become occluded or weakened. For example, the passageways can be occluded by a tumor, restricted by a plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced, or even replaced, with a medical endoprosthesis. An endoprosthesis is typically a tubular member that is placed in a lumen in the body. Examples of endoprostheses include stents, covered stents, and stent-grafts.

Endoprostheses can be delivered inside the body by a catheter that supports the endoprosthesis in a compacted or reduced-size form as the endoprosthesis is transported to a desired site. Upon reaching the site, the endoprosthesis is expanded, for example, or allowed to expand, so that it can contact the walls of the lumen.

Endoprostheses can be coated with biocompatible materials and/or biomolecules, including active pharmaceutical agents.

SUMMARY

The disclosure relates to medical devices, such as endoprostheses. The invention is based, inter alia, on the discovery that coating endoprostheses, e.g., stents, with hydrophilic and/or hydrophobic material(s) allows for generation of complex biomolecule coating patterns on the endoprostheses.

In one aspect, the disclosure features a medical device having a body of interconnected bands and connectors forming an elongated tubular structure having an inner luminal wall surface and an outer abluminal wall surface and defining a central lumen or passageway, wherein the inner luminal wall surface and side wall surface of the bands and connectors forming transverse passageways through the elongated tubular structure bear a coating of hydrophilic material and the outer abluminal wall surface of the tubular structure bears a coating of hydrophobic material.

Embodiments may include one or more of the following features.

At least one or more selected regions of the luminal and side wall surfaces of the medical device can bear a coating of hydrophilic material, e.g., superhydrophilic material, or the entire luminal and side wall surfaces of the medical device can bear a coating of hydrophilic material, e.g., superhydrophilic material. At least one or more selected regions of the abluminal surface of the medical device can bear a coating of hydrophobic material or the entire abluminal wall surface of the medical device can bear a coating of hydrophobic material.

The coating of the luminal, side and abluminal wall surfaces can include titanium (+y) oxide (−x) (Ti_xO_y) e.g., titanium dioxide. Titanium (+y) oxide (−x) can have a crystalline structure, e.g., be in an anatase or rutile phase. Titanium (+y) oxide (−x) can be in an amorphous phase. Titanium (+y) oxide (−x) can be in an anatase phase combined with at least one of the following phases: rutile, brookite, monoclinic, amorphous, titanium (+y) oxide (−x) (II), and titanium (+y) oxide (−x) (H). Titanium (+y) oxide (−x) can be nano-porous, e.g., meso-porous or micro-porous. Titanium (+y) oxide (−x) can be generally smooth, i.e., not nano-porous. In addition to the titanium (+y) oxide (−x), the coating can include phosphorus, e.g., up to 5% of phosphorus by weight. In addition to the titanium (+y) oxide (−x) and/or phosphorus, the coating can include iridium oxide or ruthenium oxide or both. Titanium (+y) oxide (−x) can be doped with at least one of the following elements: iron, carbon, nitrogen, bismuth and vanadium, e.g., it can be doped with both bismuth and vanadium. A layer of organic compound, e.g., alkyl silane, aryl silane and/or fluoroalkyl silane, can be deposited over the titanium dioxide coating. Specific examples of organic compounds that can be deposited over the coating include octadecylsilane and octadecylphosphonic acid.

The coating upon the abluminal wall surface can also include biomolecules, e.g., paclitaxel, and a polymer, e.g., poly(styrene-b-isobutylene-b-styrene). The coating upon the abluminal wall surface can also include an organic solvent or a hydrophobic lipid capsule. The coating upon the abluminal wall surface, e.g., titanium (+y) oxide (−x) coating with biomolecules, e.g., titanium dioxide coating with biomolecules, can include a second layer of titanium (+y) oxide (−x), e.g., titanium dioxide.

The coating upon the luminal and side wall surfaces can also include biomolecules, e.g., heparin.

The coating upon the abluminal, luminal and side wall surfaces can include biomolecules. Biomolecules of the abluminal wall surface coating can be of a type different from biomolecules of the luminal and side wall surfaces coating.

In another aspect, the disclosure features a medical device having a body of interconnected bands and connectors forming an elongated tubular structure having an inner luminal wall surface and an outer abluminal wall surface and defining a central lumen or passageway, wherein the inner luminal wall surface and side wall surface of the bands and connectors forming transverse passageways through the elongated tubular structure bear a coating of hydrophobic material and the outer abluminal wall surface of the tubular structure bears a coating of hydrophilic material.

Embodiments may include one or more of the following features.

At least one or more selected regions of the luminal and side wall surfaces of the medical device can bear a coating of hydrophobic material or the entire luminal and side wall surfaces of the medical device can bear a coating of hydrophobic material. At least one or more selected regions of the abluminal surface of the medical device can bear a coating of hydrophilic material, e.g., superhydrophilic material, or the entire abluminal wall surface of the medical device can bear a coating of hydrophilic material, e.g., superhydrophilic material.

The coating of the luminal, side and abluminal wall surfaces can include titanium (+y) oxide (−x), e.g., titanium dioxide. Titanium (+y) oxide (−x) can have a crystalline structure, e.g., be in an anatase or rutile phase. Titanium (+y) oxide (−x) can be in an amorphous phase. Titanium (+y) oxide (−x) can be in an anatase phase combined with at least one of the following phases: rutile, brookite, monoclinic, amorphous, titanium (+y) oxide (−x) (II), and titanium (+y) oxide (−x) (H). Titanium (+y) oxide (−x) can be nano-porous, e.g., meso-porous or micro-porous. Titanium (+y) oxide (−x) can be generally smooth, i.e., not nano-porous. In addition to the titanium (+y) oxide (−x), the coating can include phosphorus, e.g., up to 5% of phosphorus by weight. In addition to the titanium (+y) oxide (−x) and/or phosphorus, the coating can include iridium oxide or ruthenium oxide or both. Titanium (+y) oxide (−x) can be doped with at least one of the following elements: iron, carbon, nitrogen, bismuth and vanadium, e.g., it can be doped with both bismuth and vanadium. A layer of organic compound, e.g., alkyl silane, aryl silane and/or fluoroalkyl silane, can be deposited over the titanium (+y) oxide (−x) coating. Specific examples of organic compounds that can be deposited over the coating include octadecylsilane and octadecylphosphonic acid.

The coating upon the abluminal wall surface can also include biomolecules. The coating upon the abluminal wall surface, e.g., titanium (+y) oxide (−x) coating with biomolecules, e.g., titanium dioxide coating with biomolecules, can include a second layer of titanium (+y) oxide (−x), e.g., titanium dioxide.

The coating upon the luminal and side wall surfaces can also include biomolecules. The coating, e.g., including biomolecules, can also include a polymer, e.g., poly(styrene-b-isobutylene-b-styrene). The coating upon the luminal and side wall surfaces can also include an organic solvent or a hydrophobic lipid capsule. The coating upon the luminal and side wall surfaces, e.g., titanium (+y) oxide (−x) coating with biomolecules, e.g., titanium dioxide coating with biomolecules, can include a second layer of titanium (+y) oxide (−x), e.g., titanium dioxide.

The coating upon the abluminal, luminal and side wall surfaces can include biomolecules. Biomolecules of the abluminal wall surface coating can be of a different type than the biomolecules on the luminal and side wall surfaces coating.

In another aspect, the disclosure features a method of producing a medical device, the method having the following steps:

(i) coating wall surfaces of a medical device having a body of interconnected bands and connectors forming an elongated tubular structure having an inner luminal wall surface and an outer abluminal wall surface and defining a central lumen or passageway, wherein the inner luminal wall surface and side wall surface of the bands and connectors form transverse passageways through the elongated tubular structure with hydrophilic titanium (+y) oxide (−x), e.g., titanium dioxide;

(ii) exposing the medical device to conditions sufficient to cause the titanium (+y) oxide (−x) coating to become hydrophobic;

(iii) exposing selected surfaces of the medical device to conditions sufficient to cause the titanium (+y) oxide (−x) coating to become superhydrophilic; and

(iv) coating the medical device in a first solution compatible with desired biomolecules.

Embodiments may include one or more of the following features.

The first solution can be non-polar or polar. The first solution can include a desired biomolecule, e.g., paclitaxel or heparin. The first solution can also include a polymer, e.g., poly(styrene-b-isobutylene-b-styrene). The first solution can include a hydrophobic lipid capsule.

The first solution can include at least one polar solvent configured to adhere to the hydrophilic surfaces of the medical device and at least one non-polar solvent configured to adhere to the hydrophobic surfaces of the medical device. The solution can include at least one biomolecule compatible with at least one solvent, e.g., a first biomolecule compatible with the polar solvent and a second biomolecule compatible with the non-polar solvent. The first biomolecule can be heparin and the second biomolecule can be paclitaxel. The first solution can further comprise a polymer, e.g., poly(styrene-b-isobutylene-b-styrene). The first solution can include hydrophobic lipid capsules containing biomolecules, as well as hydrophilic groups.

The method can have a further step of coating the medical device in a second solution compatible with desired biomolecules. The second solution can be non-polar or polar. The second solution can include biomolecules, e.g., paclitaxel or heparin. The second solution can include a polymer. The second solution can include a hydrophobic lipid capsule.

The method can include a further step of coating the medical device of step (i) with a layer of organic compound, e.g., alkyl silane, aryl silane and/or fluoroalkyl silane, specifically, octadecylsilane or octadecylphosphonic acid.

The conditions of step (ii) can include placing the medical device in the dark and/or wet-rubbing. The conditions of step (iii) can include illuminating surfaces of the medical device that bear the coating with ultraviolet light. At least a region of the luminal and side wall surfaces that bear the coating can be illuminated. At least a region of the abluminal wall surface that bears the coating can be illuminated. Step (iii) can also include exposing at least a region of the surfaces that have become superhydrophilic to conditions sufficient for the surface region to become hydrophobic, e.g., by wet-rubbing or by placing the medical device in the dark.

The coating process of step (iv) can be dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning and/or roll-coating.

The titanium (+y) oxide (−x) coating can be titanium dioxide coating. The coating can have a crystalline structure, e.g., be in a rutile or anatase phase. Titanium (+y) oxide (−x) can be in an amorphous phase. Titanium (+y) oxide (−x) can be in an anatase phase combined with at least one of the following phases: rutile, brookite, monoclinic, amorphous, titanium (+y) oxide (−x) (II), and titanium (+y) oxide (−x) (H). Titanium (+y) oxide (−x) can be nano-porous, e.g., meso- or micro-porous. Titanium (+y) oxide (−x) can be generally smooth, i.e., not nano-porous. In addition to the titanium dioxide, the coating can include phosphorus, e.g., up to 5% of phosphorus by weight. In addition to the titanium (+y) oxide (−x) and/or phosphorus, the coating can include iridium oxide or ruthenium oxide or both. Titanium (+y) oxide (−x) can be doped with at least one of the following elements: iron, carbon, nitrogen, bismuth and vanadium, e.g., it can be doped with both bismuth and vanadium. A layer of organic compound, e.g., alkyl silane, aryl silane and/or fluoroalkyl silane, can be deposited over the titanium (+y) oxide (−x) coating. Specific examples of organic compounds that can be deposited over the coating include octadecylsilane and octadecylphosphonic acid.

The instant disclosure provides stents with various patterns of hydrophobic and hydrophilic coating. These coating patterns allow placement of various biomolecules on various regions of a stent resulting in complex biomolecule patterns on stents. The disclosure also provides methods of generating stents with such complex coating and/or biomolecule patterns.

The term “biomolecule” as used herein refers to chemical compounds, therapeutic agents, drugs, pharmaceutical compositions and similar substances that exert biological effects.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. Other features and advantages of the disclosure will be apparent from the following detailed description, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a perspective view of a stent.

FIG. 1B is a cross-section of a wall of the stent taken along the lines A1-A1.

FIG. 2 is a flow chart of an embodiment of a method of selectively coating the stent.

FIG. 3A is a cross-section of a wall of the stent of FIG. 1A, taken along the lines A1-A1.

FIG. 3B is a cross-section of a wall of the stent of FIG. 1A, taken along the lines A1-A1.

FIG. 4 is a flow chart of another embodiment of a method of selectively coating the stent.

DETAILED DESCRIPTION

Referring to FIG. 1A, stent 10 having a body of interconnected bands 12 and connectors 11 forming an elongated tubular structure is shown. Referring to FIG. 1B, the cross-section of the body of stent 10 shows that the stent has an inner luminal surface 13, side wall surface 14 and an outer abluminal surface 15. The surfaces 13, 14 and 15 bear a coating 16 of titanium (+y) oxide (−x) (Ti_xO_y) e.g., titanium dioxide (TiO₂). Coating 16 of luminal surface 13 and side wall surface 14 further includes biomolecules 17. Coating 16 of abluminal surface 15 further includes biomolecules 18.

Stent 10 can be produced in a variety of ways. For example, referring to FIG. 2, a method 20 of producing stent 10 with selectively coated surfaces is described. Stent 10 is generated (step 21). Surfaces 13, 14 and 15 of stent 10 are coated with Ti_xO_y (step 22), e.g., hydrophilic Ti_xO_y, e.g., superhydrophilic Ti_xO_y, e.g., superhydrophilic TiO₂, resulting in coating 16. Stent 10 is then be exposed to conditions sufficient to cause the Ti_xO_y coating 16 to become hydrophobic (step 23), e.g., by placing stent 10 in a dark environment for a couple of days or by a process called “wet-rubbing” (see, e.g., Kamei et al., Surf. Science 463:L609-12, 2000), in which a superhydrophilic surface is turned to a hydrophobic surface by removal of the surface hydroxyl groups.

Selected surfaces of stent 10 are then exposed to conditions sufficient to cause coating 16 of the selected surfaces to become hydrophilic, e.g., superhydrophilic (step 24), e.g., by exposure to ultraviolet light. For example, referring to FIG. 3A, a source of ultraviolet light 30 can be placed generally on the luminal side of stent 10, e.g., inside stent 10. Light source 30 illuminates luminal surface 13 and side wall surface 14 bearing Ti_xO_y coating 16. Such illumination will cause coating 16 to become superhydrophilic. While light source 30 illuminates surfaces 13 and 14, abluminal surface 15 bearing coating 16 is blocked from exposure, e.g., with a mandrel. Thus, after sufficient illumination, the resulting stent 10 bears coating 16 that is superhydrophilic on luminal surface 13 and side walls surface 14, and hydrophobic on abluminal surface 15.

In another embodiment, illustrated in FIG. 3B, a source of ultraviolet light 30 can be placed generally on the abluminal side of stent 10. Light source 30 illuminates the abluminal surface 15 that bears coating 16 of Ti_xO_y. While light source 30 illuminates surface 15, surfaces 13 and 14 are blocked. Thus, after sufficient illumination, the resulting stent 10 bears coating 16 that is hydrophilic on abluminal surface 15 and hydrophobic on luminal surface 13 and side surface 14.

Both the light exposure, e.g., ultraviolet light exposure, and wet-rubbing can be carried out on a selective micro-scale, vastly expanding the range of hydrophilic and hydrophobic regions of stent 10 that can be realized. Other patterns, in addition to the ones described above can be realized. For example, coating 16 of both luminal surface 13 and abluminal surface 15 can be turned hydrophilic with selective light exposure. In another example, only portions of coating 16 of any of the surfaces 13, 14 and/or 15 may be turned hydrophilic. The possible patterns are numerous.

Further referring to FIG. 2, stent 10 bearing coating 16 that is selectively hydrophilic and hydrophobic is then coated, e.g., by dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning, or roll-coating, in desired substances compatible with desired biomolecules 17 and 18 (step 25). For example, stent 10 can be coated, e.g., dipped in a non-polar solution containing a biomolecule, e.g., paclitaxel in Xylene (e.g., up to 1% by weight of paclitaxel) and optionally a polymer, e.g., poly(styrene-b-isobutylene-b-styrene) (SIBS). Non-polar solution and biomolecule adhere to non-illuminated surfaces bearing hydrophobic coating 16. The stent can be dried and the process repeated, building layers upon the hydrophobic surfaces. In another embodiment, stent 10 can be further coated, e.g., dipped in a polar solution containing another biomolecule, e.g., heparin. The polar solution will adhere to illuminated surfaces bearing hydrophilic coating 16. In yet another embodiment, stent 10 can be coated, e.g., by dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning, or roll coating, in a solution that includes a combination of both polar and non-polar solvents with respectively dissolved biomolecules and, optionally, polymers. In this embodiment, the polar solvent will adhere to the hydrophilic regions of stent 10, while the non-polar solvent will adhere to the hydrophobic regions of stent 10. The resulting stent 10 will have surfaces selectively coated with multiple biomolecules.

Thus, in one embodiment, stent 10 bears coating 16 of hydrophilic Ti_xO_y. Stent 10 is left in the dark for a time sufficient for coating 16 to become hydrophobic. Next, luminal surface 13 and side wall surface 14 are illuminated with UV light source 30, turning them superhydrophilic. Such luminal surface 13 and side wall surface 14 bearing hydrophilic coating 16 are coated with polar solutions and biomolecules, e.g., heparin. The abluminal wall surface 15 bearing hydrophobic coating 16, on the other hand, is coated with non-polar solutions and biomolecules, e.g., paclitaxel, e.g., paclitaxel and binder polymer, e.g., SIBS. In one embodiment, stent 10 can be coated with a solution that includes a combination of both polar and non-polar solvents with respectively dissolved biomolecules and, optionally, polymers.

In another embodiment, stent 10 bears coating 16 of hydrophilic Ti_xO_y. Stent 10 is left in the dark for a time sufficient for it to become hydrophobic. Next, abluminal wall surface 15 bearing coating 16 is illuminated with UV light source 30, turning it superhydrophilic. Luminal surface 13 and side wall surface 14 bearing coating 16 are coated with non-polar solutions and biomolecules. The abluminal surface 15 is coated with polar solutions and biomolecules. In one embodiment, stent 10 can be coated with a solution that includes a combination of both polar and non-polar solvents with respectively dissolved drugs and, optionally, polymers.

As discussed supra, in another embodiment, rather than illuminating the entire luminal surface 13 and side wall surface 14 bearing coating 16 or the entire abluminal surface 15 (in step 24 of FIG. 2), selected regions of any of surfaces 13, 14 and 15 may be illuminated, and selected regions may be coated in desired polar and non-polar solutions. Any number and variation of coating patterns is possible.

Referring to FIG. 4, another method of generating a selectively coated stent 10 is illustrated. Stent 10 is generated (step 41). Surfaces 13, 14 and 15 of stent 10 are coated with Ti_xO_y (step 42), e.g., hydrophilic Ti_xO_y, e.g., superhydrophilic Ti_xO_y, e.g., superhydrophilic TiO₂, resulting in coating 16. Stent 10 is then exposed to conditions sufficient to cause the Ti_xO_y coating 16 to become hydrophobic (step 43), e.g., by placing stent 10 in a dark environment for a few days. Surfaces 13, 14 and/or 15 or selected portions of surfaces 13, 14 and 15 of stent 10 bearing coating 16 are then exposed to conditions sufficient to cause the coating 16 to become hydrophilic, e.g., superhydrophilic, e.g., by UV illumination (e.g., XE lamp, 20 minutes exposure time) (step 44). Selected surfaces exposed to UV illumination can include the entire surfaces 13, 14 and 15 bearing coating 16. Selected surfaces that have been exposed to UV illumination are subsequently exposed to conditions sufficient to cause coating 16 to become hydrophobic (step 45). The conditions can include wet-rubbing selected surfaces, e.g., luminal and abluminal surfaces, or any other combination of surfaces, with either a glass, a steel or a paper surface (see, e.g., Kamei et al.). Again, both the wet-rubbing and the UV exposure can be done on a selective micro-scale, vastly expanding the range of patterns of hydrophobic and hydrophilic regions that can be realized.

Further referring to FIG. 4, stent 10 is coated, e.g., by dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning or roll-coating, in desired substance(s) (step 46). One interesting application of wet-rubbing is that it allows just the surface to be turned from a hydrophilic porous Ti_xO_y coating into a hydrophobic surface, while leaving the buried (underlying) porous structure hydrophilic. This can enable coating stent 10 with various combinations of polar and non-polar solvents with different dissolved drugs and/or polymers to create contrasting coating composition from top to bottom inside of the porous Ti_xO_y coating. In one embodiment, stent 10 can be coated, e.g., by dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning or roll-coating, in a non-polar solution containing biomolecules, e.g., paclitaxel, e.g., paclitaxel and binder polymer, e.g., SIBS, and in a polar solution containing biomolecules, e.g., heparin, e.g., heparin and polymer. In another embodiment, stent 10 can be coated, e.g., by dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning or roll-coating, in a solution that includes a combination of both polar and non-polar solvents with respectively dissolved biomolecules, e.g., drugs, and, optionally, polymers.

In another embodiment, once stent 10 has been coated with desired biomolecules and/or polymers, a second porous coating of Ti_xO_y can be applied. In this embodiment, Ti_xO_y can be applied without the use of high-temperature step. Ti_xO_y can be applied, e.g., via microwave-assisted deposition. In this embodiment, biomolecules on the stent, e.g., paclitaxel, can diffuse through the pores of the second Ti_xO_y layer.

In another embodiment, hydrophilic biomolecules can be packaged into hydrophobic lipid capsules (e.g., liposomes) and applied to hydrophobic coating 16.

Further referring to FIG. 4, step 42 of method 40 can include coating selected regions stent 10 with Ti_xO_y that is nano-porous, e.g., meso-porous or micro-porous, and other selected regions with Ti_xO_y that is generally smooth, i.e., not nano-porous. In one embodiment, the regions coated with nano-porous coating can be luminal and side wall surfaces 13 and 14, while the regions with smooth coating can be abluminal wall surfaces 15. In another embodiment, the regions with nano-porous coating can be abluminal wall surfaces 15, while the regions with smooth coating can be luminal and side wall surfaces 13 and 14. Entire stent 10 coated with nano-porous and smooth Ti_xO_y can then be exposed to conditions sufficient for coating 16 to become superhydrophilic, e.g., by UV irradiation (step 44). Entire stent 10 can then be exposed to conditions sufficient to cause selected regions of coating 16 to become hydrophobic, e.g., by placing stent 10 in dark conditions for a certain timeframe, e.g., a number of days or weeks (step 45). In step 45, the regions coated with nano-porous Ti_xO_y will remain superhydrophilic (see, e.g., Gu, App. Phys. Lett. 85(21):5067-69, 2004), while the regions coated with smooth Ti_xO_y will become hydrophobic. The resulting stent 10 can be coated e.g., by dipcoating, gas-assisted spraying, electrostatic spraying, electrospinning or roll-coating, in desired substance(s) (step 46). Stent 10 can be coated with polar solutions, non-polar solutions or solutions containing a combination of polar and non-polar solvents, containing compatible biomolecules and/or polymers, as discussed above.

In use, stent 10 can be used, e.g., delivered, using a catheter delivery system. Catheter systems are described, e.g., in Wang U.S. Pat. No. 5,195,969, Hamlin U.S. Pat. No. 5,270,086, and Raeder-Devens U.S. Pat. No. 6,726,712. Stents and stent delivery are also exemplified by the Radius® or Symbiot® systems, available from Boston Scientific Scimed, Maple Grove, Minn. Stent 10 bearing more than one type of a biomolecule, e.g., biomolecules 17 and 18, can deliver the biomolecules to, e.g., a blood vessel. Biomolecules 17 and 18 can target various cells of the blood vessels, e.g., endothelial cells or smooth muscle cells.

As discussed, coating 16 of stent 10 can include Ti_xO_y, preferably, titanium dioxide. Titanium dioxide, also known as titanium (IV) oxide or titania is the naturally occurring oxide of titanium, chemical formula TiO₂. TiO₂ occurs in a number of forms: rutile, anatase, brookite, titanium dioxide (B) (monoclinic), titanium dioxide (II), and titanium dioxide (H). Carp et al., Prog. Solid State Chem. 32:33-177, 2004. TiO₂ coatings are known to be blood-compatible. Maitz et al., Boston Scientific Corporation internal report, 2001; Tsyganov et al., Surf. Coat. Tech. 200:1041-44, 2005. Blood-compatible substances show only minor induction of blood clot formation. TiO₂ in both rutile and anatase phases shows low platelet adhesion. Implantation of phosphorus in the top surface of the rutile phase (e.g., at an ion density of about 2% to about 5%) decreases platelet adhesion to TiO₂. Maitz et al.

Morphology, crystal structure and doping of Ti_xO_y coating 16 are some elements that need to be taken into account when making and using stent 10. Ti_xO_y coating 16 of stent 10 can be a crystal (anatase or rutile structure). Crystal structure is photoactive. Crystal structure also has porosity or roughness that facilitates adhesion and storage of biomolecules 17 and 18, that can be placed on coating 16 alone or in combination with polymers and/or other biomolecules. Coating 16 can also be amorphous (Karuppuchamy et al., Vacuum 80:494-98, 2006) or be a combination of one or more of the following phases: anatase, rutile, brookite, amorphous, monoclinic, titanium (+y) oxide (−x) (II) and/or titanium (+y) oxide (−x) (H).

Instead of using pure Ti_xO_y for coating, phosphorus can be embedded at a low percentage (e.g., about 0.5 to about 5%) into the Ti_xO_y layer (e.g., using plasma immersion process) to increase blood compatibility of the coating. Maitz et al.

In other embodiments, coating 16 can be a combination of Ti_xO_y and iridium oxide (IrOx); or a combination of Ti_xO_y and ruthenium oxide (RuOx); or a combination of Ti_xO_y, IrOx and RuOx. RuOx and IrOx can decrease any potential inflammation ongoing in the cells surrounding stent 10 in the body, because these compounds can catalyze breakdown of by-products of stressed cells.

In one embodiment, Ti_xO_y coating 16 can be doped, e.g., with iron (Fe), carbon (C), nitrogen (N), bismuth (Bi), vanadium (V) or their combination. Fe-doping enhances Ti_xO_y conversion rate of photoinduced hydrophilicity and reduces the rate of conversion from hydrophilic to hydrophobic state. Yu et al., Mat. Chem. Phys. 95:193-96, 2006. Bi- and/or V-doping can decrease the water contact angle, while Bi-V-doping can enhance maintenance of a low water contact angle under dark conditions. Hong et al., Mat. Lett. 60:1296-1305, 2006. C-doping has also been reported to influence hydrophilic properties of TiO₂. Irie et al, Thin Solid Films 510:21-5, 2006.

A number of techniques can be used to deposit Ti_xO_y coating 16 on stent 10, including sol-gel routes and cathodic electrodeposition. Karuppuchamy et al., Solid State Ionics 151:19-27, 2002; Karuppuchamy et al., Mat. Chem. Phys. 93:251-54, 2005; Hattori et al., Langmuir 15:5422-25, 1999. Many deposition techniques utilize a high-temperature processing step (e.g., heating to about 400° C.) to turn deposited film into crystal structure. If such a high-temperature step is undesirable (e.g., if the stent already has a coating of thermo-sensitive elements, such as certain polymers, microelectromechanical systems (MEMs), or biomolecules), microwave-assisted deposition of Ti_xO_y can be used. Vigil et al., Langmuir 17:891-96, 2001, Gressel-Michel et al., J. Coll. Interf. Science 285:674-79, 2005. In one method of microwave-assisted deposition, anatase particles are synthesized directly in suspension using a microwave reactor and the particles (of about 70 nm in diameter) are deposited by a dipcoat process at room temperature. Gressel-Michel et al. Chemical bath deposition is another method that avoids a high-temperature step in Ti_xO_y deposition. Pathan et al., App. Surf. Science 246:72-76, 2005.

As mentioned above, hydrophilic Ti_xO_y coating 16 will turn hydrophobic when left in the dark. Yu et al.; Karuppuchamy et al., 2005. Ti_xO_y coatings, however, are known to switch from hydrophobic to superhydrophilic when exposed to ultraviolet (UV) light illumination. This effect exists not only in the anatase and rutile phases (Yu et al.), but also in the amorphous phase (Karuppuchamy et al, Vacuum 80:494-98, 2006). Ti_xO_y is also a photocatalyst under UV light, but the photocatalytic effect only exists in the anatase phase. A superhydrophilic surface can contact water with an angle of less than 5°. The superhydrophilic effect of Ti_xO_y is larger for nano-porous structure, e.g., meso-porous structure (that with pore diameters between 20 and 500 angstroms) due to the enlarged surface area (Yu et al., J. Photochem. Photobiol. A, 148:331-39, 2002) and micro-porous structure. Thus, exposure of hydrophobic Ti_xO_y coating 16 to UV light source 30 (e.g., 365 nm, 5 mWcm⁻²) will switch the material back to superhydrophilic.

The source of UV light 30 for illuminating stent 10 bearing Ti_xO_y coating 16 can be, e.g., fibers coupled to high-power diode lasers. The fibers can be fitted with diffusers that allow sideways radiation. When fibers or plastic rods or sheets are notched, light is reflected out from the opposite side of the material. Light uniformity is achieved by increasing the notch depth and frequency, as the distance from the light source increases. Rotating this fiber inside stent 10 can provide uniform illumination in all directions. Instead of rotating the fiber, a threaded notch can be generated that will illuminate all directions without the need for rotation. Fibers can be obtained from, e.g., polyMicro (www.polymicro.com). Silica fibers offer good UV transmission. The fibers can be, e.g., about 600 μm to about 2 mm in diameter.

As discussed, placing stent 10 coated with hydrophilic, e.g., superhydrophilic, Ti_xO_y, e.g., superhydrophilic TiO₂, in the dark will turn Ti_xO_y coating 16 hydrophobic. In some embodiments, however, it may be desirable to store (e.g., in the dark, e.g., in packaging) stents coated with hydrophilic, e.g., superhydrophilic Ti_xO_y, without its turning hydrophobic. Reversal from superhydrophilic to hydrophobic surface can be prevented by using a nano-porous (inverse-opal) structure of Ti_xO_y Gu, App. Phys. Lett. 85(21):5067-69, 2004.

In one embodiment, a layer of organic compound, e.g., alkyl silane, aryl silane and/or fluoroalkyl silane, can be deposited over the hydrophobic Ti_xO_y. For example, a layer of octadecylsilane or octadecylphosphonic acid over the hydrophobic Ti_xO_y coating 16 can enhance the superhydrophobic state and stability of coating 16. Balaur et al., Electrochem. Communic. 7:1066-70, 2005. Coating 16 in this embodiment can be turned hydrophilic, e.g., superhydrophilic, by UV light illumination, as desired.

Stent 10 can include (e.g., be manufactured from) metallic materials, such as stainless steel (e.g., 316L, BioDur® 108 (UNS S29108), and 304L stainless steel, and an alloy including stainless steel and 5-60% by weight of one or more radiopaque elements (e.g., Pt, Ir, Au, W) (PERSS®) as described in US-2003-0018380-A1, US-2002-0144757-A1, and US-2003-0077200-A1), Nitinol (a nickel-titanium alloy), cobalt alloys such as Elgiloy, L605 alloys, MP35N, titanium, titanium alloys (e.g., Ti-6Al-4V, Ti-50Ta, Ti-10Ir), platinum, platinum alloys, niobium, niobium alloys (e.g., Nb-1Zr) Co-28Cr-6Mo, tantalum, and tantalum alloys. Other examples of materials are described in commonly assigned U.S. application Ser. No. 10/672,891, filed Sep. 26, 2003; and U.S. application Ser. No. 11/035,316, filed Jan. 3, 2005. Other materials include elastic biocompatible metal such as a superelastic or pseudo-elastic metal alloy, as described, for example, in Schetsky, L. McDonald, “Shape Memory Alloys”, Encyclopedia of Chemical Technology (3rd ed.), John Wiley & Sons, 1982, vol. 20. pp. 726-736; and commonly assigned U.S. application Ser. No. 10/346,487, filed Jan. 17, 2003.

In some embodiments, materials for manufacturing stent 10 include one or more materials that enhance visibility by MRI. Examples of MRI materials include non-ferrous metals (e.g., copper, silver, platinum, or gold) and non-ferrous metal-alloys containing superparamagnetic elements (e.g., dysprosium or gadolinium) such as terbium-dysprosium, dysprosium, and gadolinium. Alternatively or additionally, stent 10 can include one or more materials having low magnetic susceptibility to reduce magnetic susceptibility artifacts, which during imaging can interfere with imaging of tissue, e.g., adjacent to and/or surrounding the stent. Low magnetic susceptibility materials include those described above, such as tantalum, platinum, titanium, niobium, copper, and alloys containing these elements.

Stent 10 can be of a desired shape and size (e.g., coronary stents, aortic stents, peripheral vascular stents, gastrointestinal stents, urology stents, and neurology stents). Depending on the application, stent 10 can have a diameter of between, e.g., about 1 mm to about 46 mm. In certain embodiments, a coronary stent can have an expanded diameter of from about 2 mm to about 6 mm. In some embodiments, a peripheral stent can have an expanded diameter of from about 5 mm to about 24 mm. In certain embodiments, a gastrointestinal and/or urology stent can have an expanded diameter of from about 6 mm to about 30 mm. In some embodiments, a neurology stent can have an expanded diameter of from about 1 mm to about 12 mm. An abdominal aortic aneurysm (AAA) stent and a thoracic aortic aneurysm (TAA) stent can have a diameter from about 20 mm to about 46 mm. Stent 10 can be balloon-expandable, self-expandable, or a combination of both (e.g., U.S. Pat. No. 5,366,504).

Stent 10 can include a releasable biomolecule, e.g., a therapeutic agent, drug, or a pharmaceutically active compound, such as described in U.S. Pat. No. 5,674,242, U.S. application Ser. No. 09/895,415, filed Jul. 2, 2001, and U.S. application Ser. No. 10/232,265, filed Aug. 30, 2002. The therapeutic agents, drugs, or pharmaceutically active compounds can include, for example, anti-proliferative agents, anti-thrombogenic agents, antioxidants, anti-inflammatory agents, immunosuppressive compounds, anesthetic agents, anti-coagulants, and antibiotics. Specific examples of such biomolecules include paclitaxel, sirolimus, everolimus, zotarolimus, picrolimus and dexamethasone.

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A medical device comprising: an elongated tubular structure having an inner luminal wall surface, an outer abluminal wall surface, and side wall surfaces extending therebetween,a first coating on at least one or more regions of the luminal wall surface and/or the side wall surfaces comprising a material comprising titanium (+y) oxide (−x),a second coating on at least one or more regions of the abluminal wall surface comprising the material comprising the titanium (+y) oxide (−x), the material in one of the first coating and the second coating being hydrophobic and the one of the first coating and the second coating being hydrophobic, and the material in another of the first coating and the second coating being hydrophilic and the other one of the first coating and the second coating being hydrophilic, anda layer of organic compound over the first and second coatings.

2. The medical device of claim 1, wherein the first coating is hydrophilic and the second coating is hydrophobic.

3. The medical device of claim 2, wherein the first coating is superhydrophilic.

4. The medical device of claim 2, wherein the second coating further comprises a biomolecule and a polymer.

5. The medical device of claim 1, wherein the first coating is hydrophobic and the second coating is hydrophilic.

6. The medical device of claim 5, wherein the second coating is superhydrophilic.

7. The medical device of claim 1, wherein the first coating covers the luminal wall surface.

8. The medical device of claim 5 or claim 7, wherein the first coating further covers the side wall surfaces.

9. The medical device of claim 1, wherein the second coating covers the abluminal wall surface.

10. The medical device of claim 1, wherein the second coating further comprises a biomolecule.

11. The medical device of claim 1, wherein the first coating further comprises a biomolecule.

12. The medical device of claim 11, wherein the first coating further comprises a polymer.

13. The medical device of claim 1, wherein the first coating and the second coating comprise phosphorus.

14. The medical device of claim 1, wherein one of the first coating and the second coating is porous.

15. The medical device of claim 14, wherein another of the first coating and the second coating is smooth.

16. The medical device of claim 14 further comprising biomolecules in pores of the one of the first coating and the second coating.

17. The medical device of claim 1, wherein the material comprises a crystal.

18. The medical device of claim 1, wherein the material is photoactive.

19. The medical device of claim 1, wherein the material in a first selectable state is hydrophilic and the material in a second selectable state is hydrophobic.

20. The medical device of claim 19, wherein the material is selected between the first state and the second state by exposure to UV light.

21. The medical device of claim 19, wherein the material is selected between the first state and the second state by wet-rubbing.