Patent Description:
Implantable medical devices are fabricated of materials that are sub-optimal in terms of the biological response they elicit in vivo. Many conventional materials used to fabricate <NUM> implantable devices, such as titanium, polytetrafluoroethylene, silicone, carbon fiber and polyester, are used because of their strength and physiologically inert characteristics. However, tissue integration onto these materials is typically slow and inadequate. Certain materials, such as silicone and polyester, elicit a significant inflammatory, foreign body response that drives fibrous encapsulation of the synthetic material. The fibrous encapsulation may have significant adverse effects on the implant. Moreover, conventional biomaterials have proved inadequate in eliciting a sufficient healing response necessary for complete device integration into the body. For example, in devices that contact blood, such as stents and vascular grafts, attempts to modify such devices to promote endothelial cell adhesion may have a concomitant effect of making the devices more thrombogenic.

<CIT> discloses an implantable, biocompatible material, of which at least one surface has a patterned array of features having at least one of chemical, physiochemical and electrochemical activity different than regions without the features. <CIT> relates to an implantable medical device comprising a self-supporting structural member fabricated of a plurality of laminated layers of at least one biocompatible material. <CIT> discloses a method of producing a biocompatible prosthesis based on a substrate made essentially of metal or ceramic. <CIT> discloses a coated implantable medical device that includes a structure adapted for introduction into a vascular system, esophagus, trachea, colon, biliary tract, or urinary tract; a layer of an immunosuppressive agent posited on one surface of the structure; and a porous layer posited over the layer of an immunosuppressive agent. <CIT> relates to an activated metallic, semiconductor, polymer, composite and/or ceramic substrate that is bound through a mixed or graded interface to a hydrophilic plasma polymer surface. The polymer surface is activated to enable direct covalent binding to a functional biological molecule, and comprises a sub-surface that includes a plurality of cross-linked regions. <CIT> discloses an implantable medical device having enhanced endothelial migration features. <NPL>) provide an overview on ways of providing prosthetic implants that are scrupulously free of contaminating overlayers at the instant of their biological placement. <CIT> relates to a method and device for preparing implant surfaces of metallic or ceramic material, using gas-discharge plasma with the aim of obtaining a well-defined and reproducible implant surface.

There still remains a need for a medical device that stimulates endothelial proliferation and movement when implanted in order to form an endothelial layer over the medical device. Furthermore, there is a remaining need for a method of fabricating such a medical device.

The present invention is defined by the implantable, biocompatible material according to appended claim <NUM>. The present invention is furthermore defined by the method for making the implantable, biocompatible material according to appended claim <NUM>.

In one embodiment, an implantable biocompatible material includes one or more vacuum deposited layers of biocompatible materials deposited upon a biocompatible base material. At least a top most vacuum deposited layer includes a homogeneous molecular pattern of distribution along the surface thereof and comprises a patterned array of geometric physiologically functional features.

In another embodiment, an implantable biocompatible material includes a plurality of layers of biocompatible materials formed upon one another into a self-supporting multilayer structure. The plurality of layers includes a vacuum deposited surface layer having a homogeneous molecular pattern of distribution along the surface thereof and comprises a patterned array of geometric physiologically functional features.

In a further embodiment, a method for making an implantable biocompatible material is presented. The method includes the steps of providing an implantable biocompatible material having at least one surface intended to contact tissue of body fluids in vivo and providing a mask having a defined pattern of openings corresponding in size and spacing to a predetermined distribution of binding domains to be imparted to the at least one surface.

The method further includes the steps of treating the at least one surface of the biocompatible material through the mask by at least one of three techniques. The first technique includes vacuum depositing a layer of material onto the at least one surface, wherein the vacuum deposited layer is different from the at least one surface immediately therebeneath in a material property selected from the group of material properties consisting of: grain size, grain phase, grain material composition, surface topography, and transition temperature, and removing the mask to yield a plurality of binding domains defined on the at least one surface of the implantable, biocompatible material. The second technique includes vacuum depositing a layer of sacrificial material onto the at least one surface, removing the mask from the at least one surface, vacuum depositing a second layer of material onto the at least one surface, wherein the second vacuum deposited layer is different from the at least one surface immediately therebeneath in a material property selected from the group of material properties consisting of: grain size, grain phase, grain material composition, surface topography, and transition temperature, and removing the sacrificial material to yield a plurality of binding domains defined on the at least one surface of the implantable, biocompatible material. The third technique includes photo irradiating the at least one surface to photochemically alter the at least one surface, and removing the mask to yield a plurality of binding domains defined on the at least one surface of the implantable, biocompatible material.

In accordance with one embodiment, the capacity for complete endothelialization of conventional implantable materials, including metals and polymers, may be enhanced by imparting a pattern of chemically and/or physiochemically active geometric physiologically functional features onto a blood contacting surface of the implantable material. The inventive implantable devices may be fabricated of polymers, pre-existing conventional wrought metallic materials, such as stainless steel or nitinol hypotubes, or may be fabricated by thin film vacuum deposition techniques. The inventive implantable devices may be intravascular stent, stent-grafts, grafts, heart valves, venous valves, filters, occlusion devices, catheters, osteal implants, implantable contraceptives, implantable antitumor pellets or rods, shunts and patches, or other implantable medical devices having any construction or made of any material as will be hereinafter described. A medical device is an instrument, apparatus, implant, in vitro reagent, or other similar or related article, which is intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease, or intended to affect the structure or any function of the body and which does not achieve any of it's primary intended purposes through chemical action within or on the body. Similarly, the improvement of the embodiments for the methods for manufacturing intravascular stents is also believed to be applicable to the manufacturing of any type of intravascular medical device, stent-grafts, grafts, heart valves, venous valves, filters, occlusion devices, catheters, osteal implants, implantable contraceptives, implantable antitumor pellets or rods, shunts and patches, pacemakers, medical wires or medical tubes for any type of medical device, or other implantable medical devices, as will also be hereinafter described. A pacemaker (or artificial pacemaker, so as not to be confused with the heart's natural pacemaker) is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart. The electrodes may be covered by tubing or other material that includes a surface that may require endothelialization and grooves thereon.

The inventive implantable metal devices may be fabricated of polymers, pre-existing conventional wrought metallic materials, such as stainless steel or nitinol hypotubes, or may be fabricated by thin film vacuum deposition techniques. In accordance with one embodiment, it is preferable to fabricate the inventive implantable materials and resulting devices by vacuum deposition of either or both of the base implant material and the chemically and/or physiochemically active geometric physiologically functional features. Vacuum deposition permits greater control over many material characteristics and properties of the resulting material and formed device. For example, vacuum deposition permits control over grain size, grain phase, grain material composition, bulk material composition, surface topography, mechanical properties, such as transition temperatures in the case of a shape memory alloy. Moreover, vacuum deposition processes will permit creation of devices with greater material purity without the introduction of large quantities of contaminants that adversely affect the material and, therefore, the mechanical and/or biological properties of the implanted device. Vacuum deposition techniques also lend themselves to fabrication of more complex devices than those that are manufactured by conventional cold-working techniques. For example, multi-layer structures, complex geometrical configurations, extremely fine control over material tolerances, such as thickness or surface uniformity, are all advantages of vacuum deposition processing. The embodiments disclosed herein to may replace polymer grafts with metal grafts that can potentially become covered with EC and can heal completely. Furthermore, heterogeneities of materials in contact with blood flow are preferably controlled by using vacuum deposited materials.

In vacuum deposition technologies, materials are formed directly in the desired geometry, e.g., planar, tubular, etc. The common principle of vacuum deposition processes is to take a material in a minimally processed form, such as pellets or thick foils, known as the source material and atomize them. Atomization may be carried out using heat, as is the case in physical vapor deposition, or using the effect of collisional processes, as in the case of sputter deposition, for example. In some forms of deposition a process such as laser ablation, which creates microparticles that typically consist of one or more atoms, may replace atomization; the number of atoms per particle may be in the thousands or more. The atoms or particles of the source material are then deposited on a substrate or mandrel to directly form the desired object. In other deposition methodologies, chemical reactions between ambient gas introduced into the vacuum chamber, i.e., the gas source, and the deposited atoms and/or particles are part of the deposition process. The deposited material includes compound species that are formed due to the reaction of the solid source and the gas source, such as in the case of chemical vapor deposition. In most cases, the deposited material is then either partially or completely removed from the substrate, to form the desired product.

A first advantage of vacuum deposition processing is that vacuum deposition of the metallic and/or pseudometallic films permits tight process control and films may be deposited that have a regular, homogeneous atomic and molecular pattern of distribution along their fluid-contacting surfaces. This avoids the marked variations in surface composition, creating predictable oxidation and organic adsorption patterns and has predictable interactions with water, electrolytes, proteins and cells. In particular, EC migration is supported by a homogeneous distribution of binding domains that serve as natural or implanted cell attachment sites in order to promote unimpeded migration and attachment.

Secondly, in addition to materials and devices that are made of a single metal or metal alloy layer, the inventive grafts may be comprised of a layer of biocompatible material or of a plurality of layers of biocompatible materials formed upon one another into a self-supporting multilayer structure because multilayer structures increase the mechanical strength of sheet materials, or to provide special qualities by including layers that have special properties such as superelasticity, shape memory, radio-opacity, corrosion resistance etc. Vacuum deposition technologies may deposit layered materials and thus films possessing exceptional qualities may be produced. Layered materials, such as superstructures or multilayers, are commonly deposited to take advantage of some chemical, electronic, or optical property of the material as a coating; a common example is an antireflective coating on an optical lens. Multilayers are also used in the field of thin film fabrication to increase the mechanical properties of the thin film, specifically hardness and toughness.

Thirdly, the design possibilities for possible configurations and applications of the inventive graft are greatly realized by employing vacuum deposition technologies. Specifically, vacuum deposition is an additive technique that lends itself toward fabrication of substantially uniformly thin materials with potentially complex three dimensional geometries and structures that cannot be cost-effectively achieved, or in some cases achieved at all, by employing conventional wrought fabrication techniques. Conventional wrought metal fabrication techniques may entail smelting, hot working, cold working, heat treatment, high temperature annealing, precipitation annealing, grinding, ablation, wet etching, dry etching, cutting and welding. All of these processing steps have disadvantages including contamination, material property degradation, ultimate achievable configurations, dimensions and tolerances, biocompatibility and cost. For example conventional wrought processes are not suitable for fabricating tubes having diameters greater than about <NUM>, nor are such processes suitable for fabricating materials having wall thicknesses down to about <NUM> with sub-µm tolerances.

The embodiments disclosed herein takes advantage of the discovered relationship between chemically or physiochemically-active geometric physiologically functional features defined and distributed on a blood contact surface and enhanced endothelial cell binding, proliferation and migration over the blood contact surface of the implantable material. The embodiments disclosed herein involve focal adhesion point formation during cellular movement and the anchorage dependence, that spreading cells proliferate faster than non-spreading cells. The addition of a patterned array of geometric physiologically functional features, which have a hydrophobic, hydrophilic or surface energy difference relative to the surface onto which the geometric physiologically functional features are added, enhances the binding, proliferation and migration of endothelial cells to and between the geometric physiologically functional features and across the surface.

The geometric physiologically functional features disclosed herein may be formed on, in, or through one or more layers of vacuum deposited biocompatible material. In a first embodiment, the one or more layers of vacuum deposited biocompatible material are deposited on a layer of bulk material. In a second embodiment, a plurality of layers of vacuum deposited biocompatible material is deposited on one another to form a self-supporting multilayer structure. Each of the first and second embodiments includes several aspects. In a first aspect, the geometric physiologically functional features may have a non-zero thickness corresponding to a thickness of one or more layers of the vacuum deposited material. Alternatively, in other aspects, the geometric physiologically functional features may have a zero thickness or a thickness greater than one or more layers of the vacuum deposited material.

Below about <NUM> in thickness, the interactions between endothelial cells and the geometric physiologically functional features are primarily chemical and electrochemical. Geometric physiologically functional features having thicknesses greater than <NUM> and up to about <NUM> may also be employed in the embodiments disclosed herein, it being understood that as the thickness of the geometric physiologically functional feature increases there is a decreasing chemical and/or electrochemical interaction between the geometric physiologically functional feature and the endothelial cells and an increasing physical interaction (topographic guidance effect).

Additionally, UV irradiation may be employed to oxidize titanium or titanium-alloy surfaces, photochemical alteration of the surface titanium oxides alter the hydrophobicity of the exposed titanium oxides and act as affinity binding and migration sites for endothelial cell attachment and proliferation across a titanium or titanium-alloy surface. Where UV irradiation is employed, the thickness of the photochemically altered regions of titanium oxide are, for all practical purposes, <NUM>. Thus, within the context of the present application, the term "geometric physiologically functional features" is intended to include both physical members and photochemically-altered regions having thicknesses having thicknesses down to <NUM>.

In <FIG>, a portion of an implantable material <NUM> showing the surface material <NUM> with described elevated geometric physiologically functional features <NUM> is illustrated. The geometric physiologically functional features are elevated from the surface of the implantable material to a height ranging from about <NUM> to about <NUM>. Preferably, the height of the geometric physiologically functional feature <NUM> ranges from about <NUM> to about <NUM>. The shape of geometric physiologically functional features can be either circular, square, rectangle, triangle, parallel lines, straight or curvilinear lines or any combination thereof. Each of the geometric physiologically functional features is preferably from about <NUM> to about <NUM>, and preferably from about <NUM> to <NUM> in feature width <NUM>, or feature diameter if the geometric physiologically functional feature is circular. A gap distance <NUM> between each of the geometric physiologically functional features may be less than, about equal to or greater than the feature width <NUM>, i.e., between about <NUM> to about <NUM> edge-to-edge.

<FIG> is a cross-sectional view along line <NUM>-<NUM> in <FIG>. One of the elevated geometric physiologically functional features <NUM> is shown on the surface <NUM> of the implantable material.

In <FIG>, a layer of a titanium or titanium-alloy material <NUM> is heating to oxidize and form titanium dioxide on the surface of the material <NUM>. In one embodiment, the layer of titanium or titanium-alloy material <NUM> is deposited over one or more layers of vacuum deposited material in a self-supporting multilayer structure. In another embodiment, the layer of titanium or titanium-alloy material <NUM> is deposited over a bulk material that may have one or more layers of vacuum deposited material deposited thereon.

The geometric physiologically functional features <NUM> are formed by exposing the layer of material <NUM> to UV through a pattern mask. UV irradiation alters the titanium oxides in the areas of geometric physiologically functional features <NUM>, thereby chemically altering the geometric physiologically functional features <NUM> relative to the surrounding the surrounding surface area <NUM> of material layer of material <NUM>. The shape of geometric physiologically functional features can be circular, square, rectangle, triangle, parallel lines, intersecting lines or any combination. Each of the geometric physiologically functional features is from about <NUM> nanometer to about <NUM>, and preferably from about <NUM> nanometer to about <NUM> in feature width <NUM>, or feature diameter if the geometric physiologically functional feature is circular. The gap distance <NUM> between each component of the geometric physiologically functional features may be less than, about equal to or greater than the feature width <NUM>.

<FIG> is a cross-sectional view of <FIG> along line <NUM>-<NUM>. The described geometric physiologically functional features <NUM> are indicated by the dotted lines, which indicate that the geometric physiologically functional features <NUM> are at the same level of the surrounding surface <NUM>.

<FIG> shows geometric physiologically functional features that are evenly distributed across the at least one surface of the implantable material that contacts body fluid, preferably blood. As disclosed in <FIG>, the geometric physiologically functional features are elevated from the rest of the surface to a height ranging from about <NUM> nanometer to about <NUM> micrometers. Preferably, the height of the geometric physiologically functional feature ranges from about <NUM> nanometer to about <NUM> micrometers. The shape of the geometric physiologically functional features is not confined within the shape that is shown. The shape of the chemically defined domain can also be any of circle, square, rectangle, and triangle, parallel lines, intersecting lines or any combination of the above.

<FIG> shows the cell <NUM> spreading on the surface of hydrophilic treated Si. <FIG> shows the cell <NUM> spreading on the surface of hydrophilic treated Si with circular dots that are <NUM> microns in diameter. Cells in <FIG> appear to have much more focal adhesion points <NUM> than those in <FIG>. Because these geometric physiologically functional features provide for cell attachment, acting as affinity domains, the size of each of these affinity domains relative to the size of an endothelial cell determines the availability of affinity domains to the subsequent round of cell movement. According to one embodiment, the preferred size of each of the individual component of the geometric physiologically functional features is about <NUM> to about <NUM>, and preferably from about <NUM> to <NUM> in feature width, or diameter if the geometric physiologically functional feature is circular. Focal adhesion point formation is the critical step in cell movement and cell proliferation; therefore, geometric physiologically functional features such as carbon dots on the hydrophilic Si surface promote cell movement. Spreading of cells promotes cell proliferation, protein synthesis, and other cell metabolic functions. Promoting cell movement and cell proliferation ultimately accelerates covering of the implanted implantable material with endothelial cells on exposed surfaces having the geometric physiologically functional features. Although the geometric physiologically functional features shown in <FIG> are circular, the shape of the geometric physiologically functional features are not limited to this particular embodiment.

<FIG> is a magnification of a portion of the image of <FIG>. Multiple focal adhesion points <NUM> are again shown. Wide spreading of the cell is primarily due to the formation of multiple focal adhesion points on the circular geometric physiologically functional features. Extensive spreading of the cells is beneficial towards endothelialization because it promotes cell movement and cell proliferation.

<FIG> shows the stained focal adhesion points <NUM> of human aotic endothelial cells (HAEC) on the surface of an implantable material with geometric physiologically functional features <NUM> that are in the form of carbon dots. The focal adhesion points are located at or very close to the geometric physiologically functional features <NUM>. These focal adhesion points serve as tension points for the cell to contract from the opposite end of the cell and hence promote cell movement.

<FIG> shows the wide spreading of cells <NUM> and focal multiple focal adhesion points <NUM> on the surface of an implantable material with geometric physiologically functional features that are in the form of NiTi dots of <NUM> micrometers in diameter. The NiTi dots are invisible due to the weak contrast between the NiTi dots and surrounding Si surface.

<FIG>shows a magnified slide of a human aortic epithelial cell <NUM>, as shown in <FIG>. Multiple focal adhesion points <NUM> are shown to encapsulate the NiTi dots patterned on the hydrophilic Si surface. Referring to <FIG>, a portion of an implantable material <NUM> with surface <NUM> and <NUM> is shown. Referring to <FIG>, according to one embodiment, a machined mask <NUM> having laser-cut holes <NUM> of defined size ranging from about <NUM> to about <NUM>, and preferably from about <NUM> to <NUM>, patterned throughout coats at least one surface <NUM> of the implantable material <NUM> and is tightly adhered to the covered surface <NUM>. Referring to <FIG>, a thin film of material <NUM> was deposited into the space as defined by the holes <NUM>, as seen in <FIG>, in the mask <NUM> by thin film deposition procedures. Referring to <FIG>, after deposition, the mask is removed to reveal the geometric physiologically functional features <NUM> patterned across the at least one surface <NUM> of the implantable material <NUM>.

As described above, the shape of the holes in the mask could be in any of the shapes described for the geometric physiologically functional features including: circle, square, rectangle, triangle, parallel lines and intersecting lines, or any combination thereof. In the thin film deposition embodiment of the manufacturing the geometric physiologically functional features, the geometric physiologically functional features are elevated from the surface of the implantable material. The thickness of the geometric physiologically functional features is based upon the thickness of the holes in the mask, the thickness ranging from about <NUM> to about <NUM> micrometers. Preferably, the thickness of the holes in the mask range from about <NUM> to about <NUM> micrometers.

The variations of geometric physiologically functional features may be added to a surface of an implantable biocompatible material by vacuum depositing a layer or layers of biocompatible material on the surface. In one embodiment, the geometry of the layer or layers of deposited material defines the geometric physiologically functional features. For example, an implantable material <NUM> has a surface <NUM>, as illustrated in <FIG>. In one embodiment, the implantable biocompatible material may comprise one or more layers <NUM> of vacuum deposited material formed into a self-supporting structure, as illustrated by <FIG> showing a first layer 102a, a second layer 102b, a third layer 102c, a fourth layer 102d, and a fifth layer 102e. In another embodiment, the implantable biocompatible material includes a bulk material, either a bulk material alone or a bulk material covered by the one or more layers 102a-102e of vacuum deposited biocompatible material. Five layers 102a-102e of vacuum deposited material are illustrated; however, any number of layers may be included as desired or appropriate.

The one or more layers <NUM>, may have thicknesses that are the same or different as desired or appropriate. Each layer may have a thickness in a range from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, or from about <NUM> nanometer to about <NUM> micrometers. Alternating layers <NUM> of varying thicknesses may be applied as to accommodate the geometric physiologically functional features.

In this embodiment, the geometric physiologically functional features may be added to the surface <NUM> by adding one or more layers <NUM> of vacuum deposited material. For example, referring to <FIG>, in one process, a mask <NUM> having holes <NUM> of defined size disposed therethrough and patterned throughout coats and is tightly adhered to at least a first portion of the surface <NUM>. The holes <NUM> may be cut through the mask <NUM>, for example, by using a laser, wet or dry chemical etching, or other like methods for forming holes through a material, or the mask <NUM> may be fabricated including the holes <NUM>. The thickness of the holes <NUM> may range about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, or from about <NUM> nanometer to about <NUM> micrometers.

The shape of the holes <NUM> as seen in <FIG> or as looking in the direction of arrow <NUM> may be any of the shapes described for the geometric physiologically functional features including: circle, square, rectangle, triangle, polygonal, hexagonal, octagonal, elliptical, parallel lines and intersecting lines, or any combination thereof. The holes <NUM> may have a width <NUM>, or diameter <NUM> if the holes are circular, in a range between about <NUM> nanometer and about <NUM> micrometers, between about <NUM> nanometer and about <NUM> micrometers, between about <NUM> nanometer and about <NUM> nanometers, or between about <NUM> nanometer and about <NUM> nanometers. Adjacent holes <NUM> may be spaced apart by a distance D in a range from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, or from about <NUM> nanometer to about <NUM> micrometers. The distance D may be less than, about equal to or greater than the width <NUM>. In another embodiment (not shown), the width <NUM> of each of the holes <NUM> and/or the distance D between adjacent holes <NUM> may vary in size to form a patterned array of the holes <NUM>.

Referring to <FIG>, a layer <NUM> of material was deposited into a space as defined by the holes <NUM> in the mask <NUM> by vacuum deposition. The layer <NUM> has a thickness essentially the same as that of the mask <NUM>. In some embodiments, the thickness of the mask may be variable across the mask <NUM>. After removal of the mask <NUM>, geometric physiologically functional features <NUM> are revealed patterned across the surface <NUM> of the implantable material <NUM>. Each of the geometric physiologically functional features <NUM> includes a top surface <NUM>. Each of the geometric physiologically functional features <NUM> has dimensions as described hereinabove for the holes <NUM> in the mask <NUM>.

In another embodiment where geometry of the layer or layers of deposited material defines the geometric physiologically functional features, a patterned array of recesses may be formed each having a hydrophobic, hydrophilic or surface energy difference relative to the surface into which the recesses are added, meaning a top most surface of the deposited layers, the difference enhancing the binding, proliferation and migration of endothelial cells to and between the recesses and across the surfaces, recessed and top most. The hydrophobic, hydrophilic or surface energy differences relative to the surface may be formed, by way of example, any of the methods disclosed in commonly assigned <CIT>.

In this embodiment, the recesses may be formed by a relative lack of deposition of a layer or layers onto a surface, or by machining recesses through a layer or layers of material vacuum deposited on a surface. For example, to produce a pattern of recesses similar to the pattern of geometric physiologically functional features <NUM> illustrated in <FIG>, in one example, a process begins by executing the steps described hereinabove with regard to <FIG>, to produce the pattern of geometric physiologically functional features <NUM> illustrated in <FIG>, except in this embodiment, the layer <NUM> of material is a sacrificial layer of material that is removed in a subsequent step.

Referring to <FIG>, a layer <NUM> of material is deposited into spaces between the geometric physiologically functional features <NUM> by vacuum deposition. The layer <NUM> has a thickness essentially the same as that of the geometric physiologically functional features <NUM>. In this embodiment, after vacuum deposition of the layer <NUM>, the geometric physiologically functional features <NUM> of the sacrificial layer <NUM> are removed, for example, by chemical etching, photo etching, laser ablation, or other method reveal geometric physiologically functional features <NUM> patterned across the surface <NUM> of the implantable material <NUM>. Each of the geometric physiologically functional features <NUM> is a recess that has a thickness or depth between a surface <NUM> of the layer <NUM> and the surface <NUM>.

The shape of the recesses <NUM> as seen looking in the direction of arrow <NUM> in <FIG> may be any of the shapes described for the geometric physiologically functional features including: circle, square, rectangle, triangle, polygonal, hexagonal, octagonal, elliptical, parallel lines and intersecting lines, or any combination thereof. The recesses <NUM> may have the width <NUM>, or diameter if the recesses <NUM> are circular, in a range between about <NUM> nanometer and about <NUM> micrometers, alternatively between about <NUM> nanometer and about <NUM> micrometers, alternatively between about <NUM> nanometer and about <NUM> nanometers, or alternatively between about <NUM> nanometer and about <NUM> nanometers. Adjacent recesses <NUM> may be spaced apart by the distance D in a range from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, from about <NUM> nanometer to about <NUM> micrometers, or from about <NUM> nanometer to about <NUM> micrometers. The distance D may be less than, about equal to or greater than the width <NUM>. In another embodiment (not shown), the width <NUM> of each of the recesses <NUM> and/or the distance D between adjacent recesses <NUM> may vary in size to form a patterned array of the recesses <NUM>.

In another embodiment, the recesses <NUM> having width and spacing as described hereinabove with regard to <FIG> may be formed by machining the recesses <NUM> through a layer or layers <NUM> of vacuum deposited material. For example, an implantable material <NUM> having a surface <NUM>, may comprise a bulk material <NUM>, the one or more layers <NUM> of vacuum deposited material, or the bulk material <NUM> and the one or more layers <NUM> of vacuum deposited material, as illustrated in <FIG>.

Alternatively, as shown in <FIG>, the geometric physiologically functional features <NUM> themselves include a plurality of deposited layers, wherein the geometric physiologically functional features <NUM> include the first layer 102a, the second layer 102b, and the third layer 102c. The geometric physiologically functional features <NUM> are deposited through a mask as previously indicated, on top of structural material of the stent or other medical device include deposited layer 102d and 102e. Alternatively, the geometric physiologically functional features <NUM> include the first layer 102a and the second layer 102b, deposited through the mask whereby the structural material of the stent or other medical device includes the layers 102c-102d. Alternatively, the geometric physiologically functional features <NUM> include the first layer 102a, the second layer 102b, the third layer 102c, and the fourth layer 102d, whereby the structural material of the stent or other medical device includes the fifth layer 102e. When additional layers 102a-102d are included in the geometric physiologically functional feature <NUM>, the thickness of the layers as deposited can be modified to be a narrower or decreased thickness as to allow for the geometric physiologically functional feature <NUM> to be adjusted to a particular thickness. The layers of different vacuum deposited materials can be deposited to create the elevated surfaces having inherently different material properties. Alternatively, layers of the same vacuum deposited material can be deposited having differences in grain size, grain phase, and/or surface topography or variations of hydrophobic, hydrophilic or surface energy difference relative to the surface of the stent or structural material. The grain size, grain phase, and/or surface topography or variations of hydrophobic, hydrophilic or surface energy difference relative to the surface of the stent or structural material may be formed or included on the surface as shown in <CIT>.

Alternatively, as shown in <FIG>, the recesses <NUM> may include a plurality of layers <NUM> to provide for differences in grain size, grain phase, and/or surface topography or variations of hydrophobic, hydrophilic or surface energy difference relative to the surface of the stent or structural material. The recesses <NUM> may be formed by the surface <NUM> being deposited through a mask as to form the layer <NUM> that gives rise to the plurality of recesses <NUM> with a wall <NUM>. As such, the recesses <NUM> include an inner wall <NUM> including the first layer 102a, the second layer 102b, and the third layer 102c, whereby the surface <NUM> is on layer 102d, which is exposed on the bottom of the recess <NUM> and surface <NUM> is on top of layer 102a. Alternatively, the recesses <NUM> may include a wall of the first layer 102a and the second layer 102b, whereby the surfaces <NUM> are deposited through a mask, and the structural material of the stent or other medical device includes the layers 102d-102e. Alternatively, the recesses <NUM> include a wall of the first layer 102a, the second layer 102b, the third layer 102c, and the fourth layer 102d, and surfaces <NUM> are deposited through a mask whereby surface 102e that acts as the surface <NUM> of the structural material of the medical device. When additional layers 102a-102d are included as the wall in the geometric physiologically functional feature <NUM>, the thickness of the layers as deposited can be modified to be a narrower or decreased thickness as to allow for the geometric physiologically functional feature <NUM> to be adjusted to a particular thickness. The layers of different vacuum deposited materials can be deposited to create recesses having inherently different material properties. Alternatively, layers of the same vacuum deposited material can be deposited having differences in grain size, grain phase, and/or surface topography or variations of hydrophobic, hydrophilic or surface energy difference relative to the surface of the stent or structural material.

Referring to <FIG>, recesses <NUM> may be machined into the surface <NUM> of the implantable material <NUM> to have a depth greater than a thickness of a first layer of material 128a or recesses <NUM> may be machined into the surface <NUM> of the implantable material <NUM> to have a depth greater than a thickness of the first and second layers 128a, 128b of material. Two layers are illustrated for convenience of explanation and illustration; however, any number of layers <NUM> of material may be used as desired or appropriate. In this embodiment, each of the recesses <NUM> has a thickness or depth between the surface <NUM> of the layer 128a and a surface <NUM> that is within a second layer 128b. Similarly, each of the recesses <NUM> has a thickness or depth between the surface <NUM> of the layer 128a and a surface <NUM> that is within the bulk material <NUM>.

An implantable material including geometric physiologically functional features comprising a layer or layers of vacuum deposited material, as illustrated by the geometric physiologically functional features <NUM> in <FIG>, recesses disposed through one or more layers of vacuum deposited material, as illustrated by the recesses <NUM> in <FIG> or the recesses <NUM> or <NUM> in <FIG>, has an inherently different structure than a block of material having recesses cut into it. The reason for this inherent difference lies in the differences in the materials making up surfaces exposed by the recesses. For example, in the case of a block of material and assuming that the block material is uniform in regard to material properties, an undisturbed surface of the block and a surface within a recess or groove cut into the block have the same material properties.

In contrast, layers of different vacuum deposited materials can be deposited to create recessed and/or elevated surfaces having inherently different material properties. In fact, layers of the same vacuum deposited material can be deposited having differences in grain size, grain phase, and/or surface topography. The alternative grain size, grain phase, and/or surface topography may be included or formed, by way of example, any of the methods disclosed in commonly assigned <CIT>. For example, surfaces of the recesses <NUM>, <NUM> can be deposited to have a roughened surface topography and a large grain size and surfaces of the material deposited defining the recesses <NUM>, <NUM>, for example the layer <NUM> illustrated in <FIG>, can have a relatively smoother surface topography and/or a smaller grain size. Alternative grain sizes and surfaces may be formed and included as shown in <CIT>.

It is contemplated that a factor in increasing endothelialization of a surface of an implanted medical device may be the cleanliness of the surface. In this context, cleanliness refers to the presence or lack of contaminant molecules bonding to otherwise unsaturated chemical bonds at the surface. A perfectly clean surface, for example as may exist in a vacuum, comprises unsaturated bonds at the surface that have not bound to any contaminant molecules. The unsaturated bonds provide the surface with a higher surface energy as compared to a contaminated surface having fewer unsaturated bonds, which have a lower surface energy. Measurements of surface energy may be accomplished by contact angle measurements, as disclosed in <CIT>.

Unfortunately, unsaturated chemical bonds at the surface will bond to contaminant molecules when exposed thereto. For example, there are many air-borne chemistries such as phthalates, hydrocarbons, and even water that may bond to unsaturated bonds or otherwise attach to reactive spots such as, for example, residual negative charges on the surface of a metal oxide. Such contaminant molecules, for example, normally occurring hydrocarbons, SO<NUM>, NO, etc., occupy otherwise unsaturated bonds thereby reducing the number of unsaturated bonds and lowering the surface energy of the surface. Such reduction in the number of unsaturated bonds decreases the availability of such unsaturated bonds for interaction with blood proteins.

The air atmosphere around the surface include normally occurring impurities which will be attracted to the unsaturated chemical bonds at levels in the air around 1x10<NUM> to 1x10<NUM> so it will take a few seconds before the surface is contaminated by their Brownian motion, after <NUM>, most of the unsaturated bond are saturated with contaminants. One molecular monolayer (i.e. a single layer of molecules) will be adsorbed on the surface. On longer time scales, additional molecules may bond to the surface and build multi-layers of contaminant molecules. The surface of a few molecular monolayers of contaminants may have thickness of about <NUM>-<NUM>, which may be detected by sensitive surface analysis as indicated above.

Thus, as relates to endothelialization, a cleaner surface having more unsaturated bonds provides increased potential for interaction with blood proteins. It is contemplated that a contaminated surface of a vacuum deposited or bulk material can be activated, or made more likely to interact with blood proteins, by removing the contaminant molecules that occupy the otherwise unsaturated bonds at the surface. In addition to plasma etching according to the method of the invention, there may be several techniques for accomplishing such activation, including by way of example and not limitation, chemical etching, wet chemical etching, oxidation, electrochemical treatment, thermal treatment, UV-ozone cleaning, coating by evaporation or sputtering, etc. For example, another technique for activating a vacuum deposited surface may be by using plasma electron bombardment under vacuum, a technique also known as plasma etching. The contaminant layer may be detected by surface-sensitive spectroscopies, such as Auger electron spectroscopy (AES), x-ray photoemission spectroscopy (XPS or ESC), infrared reflection absorption spectroscopy (IRAS, FT-IR, etc.) secondary ion mass spectroscopy (SIMS), and those disclosed in <CIT>.

Plasma etching the sample to be treated is positioned within a controlled electrical gas discharge (a plasma), as schematically shown in <FIG>. The plasma may be formed by applying a high voltage (AC or DC) over a gas under considerably lower pressure than one atmosphere (typically <NUM>-lmm Hg, or a vacuum). Because of the low pressure and because gas <NUM> purity is vital for the process, the discharge and the sample must be housed in a hermetically closed system that can be evacuated by vacuum pumps, and whose gas composition can be controlled. The plasma also has sufficient energy and momentum to remove atoms and molecules that are adsorbed on unsaturated bonds, or are constituents of the native surface. As such, the contamination layer bond to unsaturated bonds may be removed, to recreate the <NUM> unsaturated bonds on the surface and thus increasing the surface energy. Depending on the parameters of the discharge (gas pressure and composition, applied voltage, current density, position of the sample, etc.) the surface treatment can be mild (mainly removal of the contamination layer) or more aggressive. The complete surface oxide layer on a metal may be removed so that the bare metal is exposed. The latter occurs only provided that no oxidizing or other reactive gases are present, i.e., the used gas must be a noble gas such as Ar, Kr, or Xe. By controlling the gas atmosphere, the composition of the newly formed surface is controlled; if oxygen is added, oxide will be formed; if nitrogen or hydrocarbons are added, surface nitride or surface carbide, respectively, will form, etc. The gas purity must be high, as impurities within the gas will react to the high energy cleaned surfaces.

Because of the omnipresence of contaminant molecules in the environment, a surface once activated may not remain activated until implantation into a patient. Thus, an important consideration of the activation process is how to preserve the activated surface long enough to provide the benefit of activation upon implantation. In this context, according to the method of the invention, the activated surface can be preserved by introducing a contaminant gas or liquid into the plasma etching process in a controlled manner, which may be easily removed before use of the medical device. The contaminant layer may be a known biodegradable material or may be a contaminant layer or coating of inorganic or organic nature or a mixture of both. The contaminant layer may be a layer readily removed by a saline or water solution, which are typically used in flushing procedures or washing procedures.

Alternatively and also according to the invention, the activated surface may also be coated with a protective coating of a biodegradable material that dissolves upon exposure to the in vivo environment when implanted. The biodegradable material may alternatively be dissolved via introduction of an externally delivered fluid solvent during implantation. In further examples not falling within the claims, the protective coating may be a fluid in which the activated device is immersed until implantation. For example, it is contemplated that storing the activated surface in water facilitates preservation of the activation as compared to exposure of the activated surface to air. The biodegradable material may be any material, natural or synthetic, that may be broken down by living organisms, including, but not limited to a biodegradable organic substance, biodegradable polymer substances (Poly(lactic acid) PLA, poly(L-lactic acid) (PLLA), poly(lactic-co-glycolic acid) PLGA, poly(glycolicacid) (PGA), Polyethylene glycol, PEG, polytetrafluoroethylene (PTFE), and the like), peptides or proteins, carbohydrates, nucleic acids, fatty acids, carbon-containing compounds, nanoparticles, microparticles, biocomposites, sol-gel coatings, hydrogels water-soluble bioactive agent and poly(alkyl cyanoacrylate) polymer coating; nanoparticle coating formed by electrospraying; a poly(diol citrates)-based coatings; natural biodegradable hydrophobic polysaccharides coatings, hydrophilic polymers, and the like. Alternatively, other materials may be used, such as gold, other metals, heparin, silicon carbide, titanium-nitride-oxide, phoshphorylcholine, and other medical device coatings.

The method disclosed herein comprehends the creation of a patterned array of geometric physiologically functional features elevated relative to a surface of an implantable biocompatible material, recessed relative to the surface, or disposed on the surface. For example, in accordance with an alternative embodiment, the implantable biocompatible material is formed of a bulk material of titanium, nickel-titanium alloy or other titanium-rich alloy metals or a top most layer of titanium, nickel-titanium alloy or other titanium-rich alloy metals deposited over the bulk material. The titanium, nickel-titanium alloy or other titanium-rich alloy metal is oxidized to convert surface titanium to titanium dioxide, then covered with a pattern-mask and exposed to high intensity UV irradiation. It is well-known that titanium dioxide (TiO<NUM>) absorbs UV radiation and has been used in a variety of applications as a UV inhibitor to prevent UV transmission across a TiO<NUM> barrier layer. It has been discovered that upon exposure to UV irradiation, an originally hydrophobic and oleophilic titanium oxide layer becomes amphiphilic.

The effect of UV irradiation on a titanium oxide surface is believed to occur because of unsymmetrical cleavage of the Ti-O bond to leave Ti <NUM>+ ions on the surface in some regions. Presently, these amphiphilic surfaces are being used in a range of technological applications, such as self-cleaning paints and anti-misting glasses. It has been recognized that these amphiphilic titanium oxide layers have use in medical applications. <NPL> (which may be found on the internet at: www. uk/isis2001/reports/<NUM>.

The amphiphilic state of the UV irradiated titanium oxide may be advantageously employed as an alternative to depositing patterned elevated or recessed geometric physiologically functional features onto the implantable biocompatible material. An implantable biocompatible material fabricated having a bulk substrate or a top most vacuum deposited layer of titanium or a titanium alloy is masked with a pattern mask having a plurality of openings passing there through. As with the above-described embodiment, the plurality of openings preferably have a size and special array selected to define affinity binding domains and cellular migration cites for promoting endothelial cell binding and proliferation across the substrate surface.

The open surface area of each of the plurality of openings in the pattern mask is preferably in the range of between about <NUM> to about <NUM>, and with adjacent pairs of openings being in a spaced apart relationship such that a distance of about <NUM> to about <NUM> exists between the openings, the inter-opening being greater than, about equal to, or less than the size of the opening. By interposing the pattern mask between a UV source and the surface of the implantable biocompatible material, a pattern of UV irradiated regions is imparted to the surface implantable biocompatible material, thereby altering the titanium dioxides present at the irradiated regions and forming affinity domains at the surface implantable biocompatible material.

Referring to <FIG>, a portion of an implantable material <NUM> made of titanium or a titanium-alloy is shown having at least one surface <NUM> and <NUM> that is oxidized by heating or an equivalent known by the person skilled in the art. Referring to <FIG>, according to one embodiment, a machined mask <NUM> that had laser-cut holes <NUM> of defined size from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, and preferably from about <NUM> to about <NUM>, patterned throughout to coat the at least one surface <NUM> of the implantable material <NUM> and is tightly adhered to the covered surface <NUM>.

Referring to <FIG>, the implantable material <NUM> covered with the mask <NUM> is then illuminated by the ultraviolet rays. Because TiO<NUM> is sensitive to ultraviolet, the chemical composition in holes <NUM> is different from the area that is covered by the mask. In contrast to the geometric physiologically functional features illustrated in <FIG>, <FIG>, <FIG>, and <FIG>, the geometric physiologically functional features <NUM> in <FIG> are not elevated and therefore have zero thickness relative to the surrounding surface of the implantable material.

Referring to <FIG>, after ultraviolet irradiation, the mask is removed to reveal the surface <NUM> that surrounds the geometric physiologically functional features <NUM> formed by ultraviolet irradiation. As described above, because the shape of the holes <NUM> in the mask <NUM> could be in any of the shapes described for the geometric physiologically functional features including: circle, square, rectangle, triangle, parallel lines and intersecting lines, and combinations thereof, the geometric physiologically functional features <NUM> accordingly adopts such shapes also.

Nickel-titanium sheets were heated to oxidize titanium present at the surface of the sheet. Pattern masks fabricated from machined metal were laser drilled a pattern of holes having diameters ranging from <NUM> to <NUM>, with a single diameter of holes on each pattern mask. A single pattern mask was placed over a single nickel-titanium sheet and the assembly was exposed to high intensity ultra-violet irradiation. After UV irradiation, the irradiated nickel-titanium sheet was placed on a fully endothelialized test surface and maintained at <NUM>° C. under simulated in vivo flow conditions and under static flow conditions. Qualitative observations were periodically made and it was found that endothelial cells bound to the pattern of UV irradiated affinity domains and migrated across the nickel-titanium sheet by proliferating across the pattern of affinity domains, eventually fully seeding endothelium on the nickel-titanium sheet.

Selected metal pieces (Flat, 1x1 cm square pieces (<NUM>/<NUM> in. thick) of electropolished <NUM> stainless steel, electropolished and heat-treated, electropolished Nitinol, gold and titanium) were subjected to radiofrequency plasma glow discharge using an EMS-<NUM> glow discharge unit (Electron Microscopy Services, Fort Washington, PA). For this procedure, the flat metal piece is placed on a flat metal platform within the glow discharge vacuum chamber. The plasma treatments were conducted at a base vacuum pressure of <NUM>-<NUM> mbar in the presence of a purified argon gas atmosphere. The sample was always at negative potential as the cathode using an applied current of <NUM> mamps for the treatment time of <NUM>. Under these conditions the surface of the sample is bombarded with argon ions resulting in the removal of surface oils and other surface contaminating molecules. Electrostatic force analyses were performed on these samples within <NUM> hr after removal from glow discharge treatment.

For calculation of metal surface energy values, contact angle measurements were performed using a VCA-2500XE video contact angle system (AST systems, Billerica, MA) on the flat metal pieces after cleaning as described above. The surface energy of all materials studied was determined by the advancing contact angle measurement of three standard liquids; water, formamide and xylene; on each metal surface and calculated by the harmonic mean method. Ten videocaptures per second of the advancing fluid droplet/solid interface were obtained for water and formamide and <NUM> captures per second for xylene. All experiments were repeated <NUM> times.

Claim 1:
An implantable, biocompatible material, comprising one or more vacuum deposited layers of biocompatible materials deposited upon a biocompatible base material, wherein at least a top most vacuum deposited layer includes a homogeneous molecular pattern of distribution along the surface thereof and comprises a patterned array of geometric physiologically functional features, the geometric physiologically functional features being physical members and photochemically-altered regions having thicknesses down to <NUM>, wherein the top most vacuum deposited layer has been activated by removing contaminant molecules that occupy otherwise unsaturated bonds of this surface by plasma etching and where the activation is preserved by introducing a gas or liquid into the plasma etching process in a controlled manner to form a further layer on the surface and where this further layer is able to be removed by saline or water solution or alternatively the activated surface may be coated with a protective coating of a biodegradable material that dissolves upon exposure to the in vivo environment when implanted or dissolves via introduction of an externally delivered fluid solvent during implantation.