Patent Description:
A wide range of medical treatments exist that utilize medical devices including stents or endoluminal prostheses. As used herein, the term "stent" is intended to cover medical devices that are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring and artificially made lumens, such as, but not limited to: arteries, whether located within the coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes.

Accordingly, different stents have been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted lumen wall. For example, stent prostheses are known for implantation within body lumens to provide artificial radial support to the wall tissue, which forms the various lumens within the body.

Stents have been made by a variety of methods, including forming a wire into a waveform and helically wrapping the waveform around a mandrel, removing material from a tubular cylinder such as by a laser to leave a stent (sometimes referred to as a tubular slotted stent or laser cut stent), and forming individual cylindrical components and attaching adjacent cylindrical components to each other to form a tube. Such methods can be laborious, expensive, and time-consuming. It would be desirable to use additive manufacturing techniques to make stents and other medical devices. However, additive manufacturing techniques may be limited in making certain shapes for medical devices, and particularly for certain shapes of stents. For example, and not by way of limitation, certain medical devices that are generally tubular, such as stents, may be formed by additive manufacturing by building the medical device vertically. In other words, the longitudinal axis of the medical device is perpendicular to the surface or substrate upon which the medical device is built. In additive manufacturing, layers, also referred to as clads of material for the medical device, are built upon previous layers of the material. In certain medical devices, such as certain stents, it is desirable for a significant portion of a perimeter of a first portion of the device to not be connected to a second portion of the device. For example, and not by way of limitation, in a stent with a plurality of bands formed from struts and crowns, it is often desirable for only some of the crowns of a band to be connected to crowns of an adjacent band. However, when building such a stent vertically by additive manufacturing as described above, it is desirable for connectors to be built between most or all of the crowns of adjacent bands in order to provide a support for the following layer of material.

In a solution described in <CIT> assigned to Medtronic Vascular, Inc. connectors are formed between crowns of a stent by additive manufacturing. However, some of the connectors are then removed by laser removal, chemical etching, or other methods. Removal of connectors after being formed requires additional steps and care must be taken to avoid adversely affecting the remaining stent components during removal of the unwanted connectors.

Further, medical devices such as stents are made from a variety of alloy materials such as, but not limited to cobalt-chromium or stainless steel. These alloys provide the desired characteristics, such as flexibility and rigidity, to the stent. However, these alloys are not dense enough to be visible during the interventional process by current imaging methods such as fluoroscopy. To increase the radiopacity of the stents, and in an additional processing step, a radiopaque material is often welded to the stent after the stent is manufactured.

Accordingly, it would be desirable to build a medical device such as a stent by an additive manufacturing process with connectors between portions of the medical device that can be more easily, efficiently, and effectively removed without adversely affecting the remaining medical device. It would also be desirable to impart portions of a medical device with increased radiopacity in the same process.

The invention relates to a method of making a stent as defined in claim <NUM> and to a precursor stent as defined in claim <NUM>. Further embodiments of the invention are defined in the dependent claims. Embodiments hereof relate to a method of making a medical device using micro-cladding. The method includes forming a precursor medical device comprising a plurality of bands made of a first material disposed adjacent to each other, wherein each band is attached to an adjacent band by a plurality of first connectors configured to remain and a plurality of second connectors configured to be removed. The plurality of second connectors are made by functionally grading the first material with a second material to create embrittlement in the plurality of second connectors. The method further includes processing the precursor medical device to remove the plurality of second connectors without adversely affecting the bands and the plurality of first connectors.

Embodiments hereof also to a method of forming a medical device with radiopaque portions. The precursor medical device comprises forming a precursor medical device using micro-cladding, wherein the precursor medical comprises a plurality of bands made of a first material disposed adjacent to each other, wherein each band is attached to an adjacent band by a plurality of first connectors configured to remain and a plurality of second connectors configured to be removed. At least a portion of at least one of the plurality of bands and/or at least one of the plurality of first connectors is made radiopaque by functionally grading the first material with a second, radiopaque material. The method further includes processing the precursor medical device to remove the plurality of second connectors without adversely affecting the bands and the plurality of first connectors.

Embodiments hereof also relate to a precursor medical including a plurality of portion or bands made of a first material disposed adjacent to each other, a plurality of first connectors connecting each band to an adjacent band, and a plurality of second connectors connecting each band to an adjacent band. The plurality of first connectors are configured to remain and the plurality of second connectors are made by functionally grading the first material with a second material to create embrittlement such that the second plurality of connectors are configured to be removed.

Embodiments hereof also relate to a medical device including a plurality of portions or bands made of a first material disposed adjacent to each other and at least one connector connecting each band to an adjacent band. The at least one connector is made by functionally grading the first material with a second, radiopaque material.

Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements.

<FIG> is a flow chart showing an embodiment of a method <NUM> of forming a medical device according to an embodiment hereof. The method as described with respect to <FIG> is a method for making a medical device using laser micro-cladding, generally known as micro-cladding. Micro-cladding is a "laser metal deposition (LMD)" additive manufacturing process. The term "micro-cladding", also known generally as "additive manufacturing", "three-dimensional printing" or "rapid prototyping" refers to a process of making a three-dimensional solid object of virtually any shape from a digital model. Micro-cladding is achieved using an additive process, where successive layers of material are laid down in different shapes. The terms, as used herein, may refer to methods including, but not limited to laser metal deposition (LMD), laser cladding, and laser micro-cladding. Further, any type of additive manufacturing machine that can layer or clad the materials described herein may be used.

In general, micro-cladding makes parts by adding material instead of removing it. Laser additive manufacturing (LAM) is the process of using a laser to join materials to make structures. LAM is normally accomplished sequentially, layer by layer, using the information contained in 3D CAD files. LAM is generally divided into two categories: selective laser melting (SLM) or laser metal deposition (LMD). Laser Metal Deposition (LMD), also known as laser cladding, is the projection of metal powder melted in-flight using a high power energy beam such as a laser, and deposited on a substrate. The metal powder, requisite shielding gas, and energy beam may be simultaneously delivered, creating a melt pool on the substrate (work surface). Laser metal deposition (LMD) results in a full metallurgical bond between a layered, or clad material and the existing substrate. Laser micro-cladding is a sub-category of laser cladding and refers to the process as described above to fabricate miniaturized structures and components, such as certain types of medical devices.

Accordingly, <FIG> shows a simplified exemplary embodiment of a micro-cladding system <NUM> suitable for the purposes described herein. The micro-cladding system <NUM> of <FIG> includes a first powder delivery system <NUM>, a second powder delivery system <NUM>, a substrate <NUM>, and an energy source or laser <NUM>. The first powder delivery system <NUM> includes a first hopper <NUM>, a first feed tube <NUM>, and a first nozzle <NUM>. The second powder delivery system <NUM> includes a second hopper <NUM>, a second feed tube <NUM>, and a second nozzle <NUM>. In general, a first powder material <NUM> is dispensed from the first hopper <NUM> through the first feed tube <NUM> and the first nozzle <NUM>. Similarly, a second powder material <NUM> is dispensed from the second hopper <NUM> through the second feed tube <NUM> and the second nozzle <NUM>. The energy source <NUM>, or laser, is targeted by a mirror <NUM> to creating a melt pool on the substrate <NUM> and selectively bond the first powder material <NUM> and/or the second powder material <NUM> at a fusion zone or laser focal zone <NUM> in a desired pattern. The substrate <NUM> is movable in three planes. The substrate <NUM> is retracted in a first direction Y1 and then moved in directions X1, X2, Z1, and Z2 such that successive layers of distributed first powder material <NUM> and/or second powder material <NUM> are deposited thereon and bonded until a desired object, in this example a precursor stent <NUM>, is formed. The first powder material <NUM> may be materials conventionally used as materials for stent. For example, and not by way of limitation, the first powder material <NUM> may be stainless steel (e.g. SS316L), cobalt-chromium alloys, nickel titanium alloys (e.g. NITINOL), magnesium and magnesium alloys, or combinations thereof. The term "cobalt-chromium" alloys as used herein includes alloys with cobalt and chromium. Generally, materials such as, but not limited to, cobalt-nickel-chromium alloys (e.g. MP35N, MP20N, and MP35NLT) and chromium-nickel-tungsten-cobalt alloys ("L605") are the types of materials included in the term "cobalt-chromium alloys" as used herein. The second powder material <NUM> may be materials to modify characteristics of portions of a precursor stent, as described in more detail below. Specific embodiments of material that can be used as the second powder material <NUM> are described in more detail below.

The layered, or cladded bonding of the first and/or second powder materials <NUM>, <NUM> requires an underlying support for the material to be bonded. Typically, after the first layer of material is deposited on the substrate <NUM>, support is provided by the preceding bonded material. However, with certain medical devices, such as stents, it is desirable for a significant portion of a perimeter of a first band (portion) of the stent to not be connected to a second band (portion) of the stent. However, in many embodiments, these connecting potions cannot be excluded during additive manufacturing because the following layers need support upon which to build. Thus, when building such a stent vertically, it is desirable for connectors to be built between most or all of the crowns of adjacent bands in order to provide a support for the following layer of material. The micro-cladding system <NUM> of <FIG> is provided for exemplary purposes only and not meant to limit the invention. Other micro-cladding systems are possible including, but not limited to micro-cladding systems with more or fewer powder delivery systems and systems wherein the energy source is directed through the nozzles of the system.

The method of <FIG> using the micro-cladding system <NUM> such as described with respect to <FIG> will now be described in greater detail. In this description, the method of <FIG> will be described with respect to forming a stent. However, it is understood that other similar medical devices may be formed using the method of <FIG>. In an embodiment, in step <NUM> of <FIG>, the micro-cladding system <NUM> receives a dataset corresponding to a medical device such as a precursor stent <NUM>, as shown in <FIG>. In particular, the dataset is information regarding the characteristics of the precursor stent <NUM> from which the micro-cladding system <NUM> can form the precursor stent <NUM>. For example, the sizes and locations of parts of the precursor stent <NUM> may be part of the dataset such that the micro-cladding system <NUM> can form the precursor stent <NUM>. For example, and not by way of limitation, the dataset may be a 3D printable file such as an STL file. STL (STereoLithography) is a file format native to the stereolithography CAD software created by 3D Systems. STL is also known as Standard Triangle Language and Standard Tessellation Language. This file format is supported by many software packages for use with additive manufacturing.

In step <NUM> of the method of <FIG>, the micro-cladding system <NUM> forms the precursor stent <NUM>, as shown in <FIG>. In step <NUM>, the micro-cladding system <NUM> lays down successive layers or clads of a powder or powders of the desired materials to build the precursor stent <NUM> from a series of cross sections. <FIG> shows an embodiment of the precursor stent <NUM>. According to an embodiment hereof, the precursor stent <NUM> is built by micro-cladding such that the precursor stent <NUM> is built vertically on the substrate <NUM>. The substrate <NUM> may be any material suitable to be used in the environment of and with the materials used for the micro-cladding manufacturing process. In the embodiment shown, the precursor stent <NUM> includes a plurality of ring-shaped elements or bands <NUM> formed of a first material. The bands <NUM> may also be referred to as cylindrical elements or portions. In the embodiment of <FIG>, the precursor stent <NUM> includes eight bands <NUM>a-<NUM>h, however, more or fewer bands <NUM> may be utilized. Each band <NUM> is disposed adjacent to another band <NUM> along a longitudinal axis LA to form a tube or cylinder. Each band <NUM> is a waveform formed from a plurality of struts <NUM> connected together by bends or crowns <NUM>. Further, the crowns <NUM> of the adjacent bands <NUM> are connected to each other by at least one first connector <NUM> and a plurality of second connectors <NUM>. Further, in an embodiment, the first band <NUM> may be separated from the substrate <NUM> by stilts or connectors <NUM>, as shown in <FIG>, which may also be built by the micro-cladding manufacturing process.

Further, in some embodiments, it may be desirable for portions of the precursor stent to be radiopaque. Therefore, in some embodiments, step <NUM> includes making portions of the precursor stent <NUM> radiopaque, as will be described in more detail below. The term "radiopaque" refers to the ability of a substance to absorb X-rays. Few substances will transmit <NUM>% of X-rays and few substances will absorb <NUM>% of X-rays. For the purposes of this disclosure, "radiopaque" will refer to those substances or materials which have suitable visibility for stent procedures when being imaged by an X-ray imaging device such as but not limited to a fluoroscope.

The first connectors <NUM> and the second connectors <NUM> are distinguished from each other in that the first connectors <NUM> are configured to remain connecting the adjacent crowns <NUM> to each other, while the second connectors <NUM> are configured to be removable from the precursor stent <NUM>. Similarly, the stilts <NUM> are configured to be removable from the precursor stent <NUM> such that the band 310a closest to the substrate <NUM> is not damaged when separating the precursor stent <NUM> from the substrate <NUM>. Although a particular precursor stent <NUM> embodiment is shown in <FIG>, different precursor stents may be formed using the micro-cladding manufacturing process. For example, and not by way of limitation, additional connectors may be utilized, the bands may be slanted, different bands may have different features (such as different thicknesses), additional features such as surface features, notches, etc. may be added, and other stent design differences may be utilized which are capable of being made using the micro-cladding manufacturing process.

As explained above, each crown <NUM> of a band <NUM> is connected to a corresponding crown <NUM> of an adjacent band <NUM> by a first connector <NUM> or a second connector <NUM>. However, as also explained above, for certain applications it would be desirable for some of the crowns <NUM> of a band <NUM> to be independent or not connected to the corresponding crown <NUM> of an adjacent band <NUM>. As also explained above, the second connectors <NUM> cannot simply be excluded from the precursor stent <NUM> when forming the precursor stent <NUM> by micro-cladding because excluding such second connectors <NUM> when building a precursor stent vertically on the substrate <NUM> would result in instability between the adjacent bands <NUM> during the micro-cladding manufacturing process. For example, and not by way of limitation, if only one first connector <NUM> were included between the first band 310a and the second band 310b of <FIG>, the second band 310b would tend to move towards the first band 310a at the crowns <NUM> without a connector due to gravity. Such a tendency would negatively impact the ability to build a stent with the desired characteristics.

Accordingly, step <NUM> of the method <NUM> of <FIG> is to process the precursor stent <NUM> to remove the plurality of second connectors <NUM> between crowns <NUM> of adjacent bands <NUM>. In the particular embodiment of <FIG>, the second connectors <NUM> are selected to be removed such that only a single first connector <NUM> is disposed between each band <NUM> and its adjacent band <NUM>. However, the number and type of second connectors <NUM> to be removed can be selected depending on various factors including, but not limited to, the desired flexibility of the resulting stent.

As explained above, it is desirable to minimize difficulty in removing the second connectors. Therefore, in embodiments of the present application, the second connectors <NUM> are formed by either abruptly transitioning from the first material to the second material or by functionally grading a first material and a second material such that the second connectors <NUM> are more brittle than the first connectors <NUM> and the bands <NUM> of the precursor stent <NUM>. Similarly, the stilts <NUM> may be formed by similar methods. With the second connectors <NUM> and the stilts <NUM> more brittle than the bands <NUM> and the first connectors <NUM>, the second connectors <NUM> and the stilts <NUM> may be easily removed by mechanical, chemical, or other suitable methods.

Functional grading is the variation in structure of two materials over a volume. Stated more plainly, functional grading is changing the ratio or mix of the first material to the second material. Functional grading results in corresponding changes in the properties of the final material. Therefore, specific properties may be imparted on specific areas of structures formed by the micro-cladding manufacturing process using functional grading. For example, and not by way of limitation, functional grading may be utilized to increase strength, rigidity, radiopacity, embrittlement, or corrosion resistance over the first, or base material or alloy. As an example, in the embodiment of the method of <FIG>, it would be desirable to embrittle, or make more brittle the second connectors <NUM> of the precursor stent <NUM> such that the second connectors <NUM> may be easily removed from the precursor stent <NUM> during the processing of step <NUM>. Therefore, each second connector <NUM> may be embrittled by functional grading such that each second connector <NUM> may be easily removed without adversely affecting the bands <NUM> and the plurality of first connectors <NUM>. Provided below are embodiments of materials and methods to make the second connectors <NUM> brittle and embodiments to make portions of the precursor stent <NUM> radiopaque.

In the examples explained below, cobalt is used as the first powder material <NUM> and tantalum is used as the second powder material <NUM>. However, this is not meant to be limiting. Cobalt is used in the examples as the first powder material <NUM> because cobalt is the primary metal in cobalt-chromium alloys, such as MP35N. However, as would be understood by those skilled in the art the properties of MP35N are not identical to cobalt. Further, tantalum is used in the examples as the second powder material <NUM> because it is an example of a radiopaque material used in medical devices. Further, cobalt and tantalum are used in the examples due to the cobalt-tantalum phase diagram (<FIG>). As would be understood by those skilled in the art, the principles explained below can be used with other materials, such as those listed above and below. With the materials selected as the first powder material <NUM> and the second powder materials <NUM>, a phase diagram of the two materials selected, similar to the phase diagram in <FIG> for cobalt-tantalum, may be referenced to utilize the principles discussed below to functionally grade the two materials for embrittlement and/or radiopacity, as described in more detail below.

In an example for making the second connectors <NUM> easy to remove, the first powder material <NUM> is cobalt or a cobalt alloy, as described above. The second powder material <NUM> is tantalum. The bands <NUM> and the first connectors <NUM> of the precursor stent <NUM> are formed of the first powder material <NUM>. In an example, the plurality of second connectors <NUM> of <FIG> are formed by abruptly transitioning from the first powder material <NUM> to the second powder material <NUM>. Thus, as the substrate <NUM> of the micro-cladding system <NUM> is moved to form layers of the bands <NUM> and the first connectors <NUM>, the first powder material <NUM> is dispensed from the first hopper <NUM>. When a layer of one of the second connectors <NUM> is to be formed, the second powder material <NUM> is dispensed from the second hopper <NUM>. This is an abrupt or stepwise transition from the first powder material <NUM> to the second powder material <NUM>, as shown in the transition profile chart of <FIG>. The hash marks <NUM> of <FIG> indicate the relative level of the first material (cobalt or cobalt alloy) and the second material (tantalum). Thus, in the example of <FIG>, hash marks <NUM> that are spaced apart are the first material (cobalt) and hash marks that are close together are the second material (tantalum). The abrupt transition from <NUM>% cobalt to <NUM>% tantalum causes embrittlement in that area. Similarly, the abrupt transition from <NUM>% tantalum back to <NUM>% cobalt causes embrittlement in that area. In an embodiment, these transition areas are at the transition from the crowns <NUM> to the second connectors <NUM>, as shown in <FIG>. Thus, the connection between the second connectors <NUM> and the adjacent crowns <NUM> is brittle, making the connection easy to break. Thus, the second connectors <NUM> may be removed mechanically by breaking the connection between the second connectors <NUM> and the adjacent crowns <NUM>. Further, because the second connectors <NUM> in this example do not include any of the first powder material <NUM>, the second connectors <NUM> may be removed by other methods such a chemical etching, as described in <CIT>. The stilts <NUM> may be formed in the same manner for easy removal from the first band 310a.

In another example shown in <FIG>, the plurality of second connectors <NUM>' are embrittled by forming each second connector <NUM>' by functionally grading the first powder material <NUM> and the second powder material <NUM> to form detrimental second phase intermetallic compounds. By "detrimental second phase intermetallic compounds", it is meant that the second phase intermetallic compounds of sufficient size and quantity to embrittle each second connector <NUM>'. Such detrimental intermetallic compounds are larger than nano-sized. Second phase intermetallic compounds are crystal structures of an intermediate phase, formed through functionally grading the first material and the second material in specific ratios at specific temperature ranges. Second phase intermetallic compounds are different from either base material. They include fixed composition and are similar to alloys, however the bonding between the different atoms of a second phase intermetallic compound is partly ionic. This leads to different properties and characteristics than traditional alloys. Thus, second phase intermetallic compounds have their own crystal structure and are almost always brittle.

In the example shown in <FIG>, the first powder material <NUM> is cobalt and the second powder material <NUM> is tantalum. As with the embodiment described above, the bands <NUM>, including the struts <NUM> and crowns <NUM>, the first connectors <NUM>, and the second connectors <NUM>' may be formed by using the micro-cladding system <NUM>. As the substrate <NUM> is moved to form layers of the bands <NUM> and the first connectors <NUM>, the first powder material <NUM> is dispensed from the first hopper <NUM>. At locations of the second connectors <NUM>', both the first powder material <NUM> and the second powder material <NUM> are dispensed in the ratios shown in <FIG>. Thus, in the example, the crown <NUM> adjacent the second connector <NUM>' is <NUM>% cobalt. The initial layers of each second connector <NUM>' are formed with <NUM>% cobalt and <NUM>% tantalum as shown in <FIG>. Then, the middle portion of each second connector <NUM>' is formed with <NUM>% cobalt and <NUM>% tantalum, as also shown in <FIG>. Then, the end portion adjacent to another crown <NUM> is formed with <NUM>% cobalt and <NUM>% tantalum, as shown in <FIG>.

<FIG> is a cobalt-tantalum phase diagram. As can be seen at <NUM>, using <NUM>% cobalt and <NUM>% tantalum under certain conditions forms a second phase intermetallic Co<NUM>Ta<NUM>. Similarly, as shown at <NUM>, using <NUM>% cobalt and <NUM>% tantalum under certain conditions forms a second phase metallic CoTa<NUM>. Each of these second phase intermetallic compounds is hard and brittle. Thus, each second connector <NUM>' is made brittle by forming each second connector <NUM>' from combinations of the first powder material <NUM> and the second powder material <NUM> to form two detrimental second phase intermetallic compounds as shown in the transition profile of <FIG>. Alternatively, each second connector <NUM>' may be formed of only one detrimental second phase intermetallic compound. The hash marks <NUM> to the left of the functional grading ratios in the transition profile of <FIG> indicate the relative ratio of cobalt and tantalum. Hash marks <NUM> that are spaced apart are mostly or all cobalt and as the hash marks <NUM> move closer together, the ratio of tantalum increases relative to cobalt.

As explained above, step <NUM> of the method <NUM> of <FIG> is to process the precursor stent <NUM> to remove the plurality of second connectors <NUM> between the crowns <NUM> of the adjacent bands <NUM> and the plurality of stilts <NUM> without adversely affecting the adjacent bands <NUM> and the plurality of first connectors <NUM>. In the example of the second connector <NUM> of <FIG>, wherein the second connectors <NUM> are formed by abrupt material transitions, the plurality of second connectors <NUM> may be removed by methods such as, but not limited to chemical dissolution or chemical etching. However, in the example of <FIG>, wherein the second connectors <NUM>' are made brittle by functional grading to form detrimental second phase intermetallic compounds, the second connectors <NUM>' may be removed by mechanical methods such as, but not limited to laser ablation, electrical discharge machining (EDM), water jet, electron beam, focused ion beam (FIB), micromachining, and other similar methods. Additionally, the stilts <NUM> may be removed by methods similar to the methods for removing the second connectors <NUM>, <NUM>'.

As described previously, some materials generally used for stents are not radiopaque. Thus, radiopaque bands or other radiopaque devices are sometimes added to stents to aid in visually detecting the stent. In an embodiment of the present application, functional grading of the first powder material <NUM> and the second powder material <NUM> may be used to impart radiopacity on portions of a medical device such as a stent. In particular, functional grading may be used to add radiopacity to portions of the precursor stent <NUM> configured to remain. In some embodiments, radiopacity may be added to low-stress components of the precursor stent <NUM>, such as the struts <NUM> and/or the plurality of first connectors <NUM> using functional grading.

In an example, the plurality of first connectors <NUM>' are made radiopaque by functionally grading a first powder material <NUM>, cobalt, with a radiopaque second powder material <NUM>, tantalum, in a transition profile as shown in <FIG>. In the example of <FIG>, the functional grading is performed to minimize the formation of second phases of cobalt-tantalum described above (i.e., minimize the formation of Co<NUM>Ta<NUM>, Co<NUM>Ta<NUM>, CoTa<NUM>). By minimizing the formation of second phase intermetallic compounds, it is meant that the second phase intermetallic compounds are of sufficiently small quantity and size (nano-sized or smaller) to not cause embrittlement. Thus, the plurality of first connectors <NUM>' may be made radiopaque without being made brittle. In the embodiment shown in <FIG>, each first connector <NUM>' adjacent to a corresponding crown <NUM> of a corresponding band <NUM> is generally <NUM>% cobalt. As each first connector <NUM>' is formed layer by layer by the micro-cladding manufacturing process, the ratio of the second powder material <NUM> to the first powder material <NUM> is increased. In the example of <FIG>, a middle portion of the first connector <NUM>' is <NUM>% tantalum. As the first connecter <NUM>' is formed such that the layers move away from the middle portion toward a corresponding crown <NUM> of an adjacent band <NUM>, the ratio of the second powder material <NUM> to the first powder material <NUM> is decreased such that adjacent the corresponding crown <NUM> of the adjacent band <NUM>, first connector is <NUM>% of the first powder material (cobalt). The hash marks <NUM> to the left of the functional grading profile ratios in <FIG> indicate the ratio of the first material and the second material, and also the radiopacity of the material compound in comparison to the radiopacity of the first material. Thus, the hash marks <NUM> spaced far apart are <NUM>% of the first material (Cobalt) and the resulting material is not radiopaque. As the hash marks <NUM> move closer together, the ratio of the second material increases and the ratio of the first material decreases. Further, as the hash marks move closer together, radiopacity of the resulting material increases.

<FIG> shows another example of functional grading that can be used at the plurality of first connectors <NUM>' configured to remain such that the first connectors <NUM>' are radiopaque. As with the embodiment of <FIG>, the functional grading is performed to minimize the formation of second phases of the first and second materials, in this case cobalt and tantalum (i.e., minimize the formation of Co<NUM>Ta<NUM>, Co<NUM>Ta<NUM>, CoTa<NUM>). Thus, the plurality of first connectors <NUM>' may be made radiopaque without being made brittle. In the embodiment shown in <FIG>, each first connector <NUM>' adjacent to a corresponding crown <NUM> of a corresponding band <NUM> is generally <NUM>% cobalt. As each first connector <NUM>' is formed layer by layer by the micro-cladding manufacturing process, the ratio of the second powder material <NUM> to the first powder material <NUM> is increased. In the example of <FIG>, a middle portion of the first connector <NUM>' is about <NUM>% cobalt and <NUM>% tantalum. As the first connecter <NUM>' is formed such that the layers move away from the middle portion toward a corresponding crown <NUM> of an adjacent band <NUM>, the ratio of the second powder material <NUM> to the first powder material <NUM> is decreased such that adjacent the corresponding crown <NUM> of the adjacent band <NUM>, the first connector is <NUM>% of the first powder material (cobalt). The hash marks <NUM> to the left of the functional grading profile ratios in <FIG> indicate the ratio of the first material and the second material, and also the radiopacity of the material compound in comparison to the radiopacity of the first material. Thus, the hash marks <NUM> spaced far apart are <NUM>% of the first material (Cobalt) and the resulting material is not radiopaque. As the hash marks <NUM> move closer together, the ratio of the second material increases and the ratio of the first material decreases. Further, as the hash marks move closer together, radiopacity of the resulting material increases.

<FIG> shows another example of functional grading that can be used at the plurality of first connectors <NUM>' configured to remain such that the first connectors <NUM>' are radiopaque. As with the embodiment of <FIG> and <FIG>, the functional grading is performed to minimize the formation of second phases of the first and second materials, in this case cobalt and tantalum (i.e., minimize the formation of Co<NUM>Ta<NUM>, Co<NUM>Ta<NUM>, CoTa<NUM>). Thus, the plurality of first connectors <NUM>' may be made radiopaque without being made brittle. In the embodiment shown in <FIG>, each first connector <NUM>' adjacent to a corresponding crown <NUM> of a corresponding band <NUM> is generally <NUM>% cobalt. As each first connector <NUM>' is formed layer by layer by the micro-cladding manufacturing process, the ratio of the second powder material <NUM> to the first powder material <NUM> is increased. In the example of <FIG>, a middle portion of the first connector <NUM>' is about <NUM>% tantalum. As the first connecter <NUM>' is formed such that the layers move away from the middle portion toward a corresponding crown <NUM> of an adjacent band <NUM>, the ratio of the second powder material <NUM> to the first powder material <NUM> is decreased such that adjacent the corresponding crown <NUM> of the adjacent band <NUM>, the first connector is <NUM>% of the first powder material (cobalt). The embodiment of <FIG> is generally similar to the embodiment of <FIG> except that the transition from <NUM>% of the first material (cobalt) to <NUM>% of the second material (tantalum) is more gradual. The hash marks <NUM> to the left of the functional grading profile ratios in <FIG> indicate the ratio of the first material and the second material, and also the radiopacity of the material compound in comparison to the radiopacity of the first material. Thus, the hash marks <NUM> spaced far apart are <NUM>% of the first material (Cobalt) and the resulting material is not radiopaque. As the hash marks <NUM> move closer together, the ratio of the second material increases and the ratio of the first material decreases. Further, as the hash marks move closer together, radiopacity of the resulting material increases.

The embodiments of <FIG> have been described with respect to making radiopaque at least some of the plurality of first connectors <NUM>' configured to remain. However, these embodiments are not limited to the plurality of first connectors. In other embodiments, other portions of the precursor stent <NUM> that are configured to remain may be made radiopaque. For example, as shown in <FIG>, at least some of the struts <NUM>' of the precursor stent <NUM> may be radiopaque in the same manner described above with respect to <FIG>. <FIG> shows an example band <NUM> in flattened for simplified viewing. The example band <NUM> can be any or all of the bands <NUM> of <FIG>. In some instances, it may be desirable for all or some of the struts <NUM>' of some or all of the bands <NUM> to be radiopaque. For example, and not by way of limitation, it may desirable for the struts of the end bands (bands 310a and <NUM>) to be radiopaque such that the ends of the stent may be seen under fluoroscopy. In an embodiment to form the struts <NUM>' to be radiopaque, referring to <FIG>, as the substrate <NUM> moves such that the crowns 314a are being formed, the first powder material <NUM> is deposited on a previous layer and fused by the laser <NUM>. This occurs for each layer of the crowns 314a. As the layers are being built upon one another and the struts <NUM>' are beginning to be formed, the second powder material <NUM> is gradually added and the amount of the first powder material <NUM> is gradually decreased to form layers of the struts <NUM>'. The gradual increase/decrease can be according to any of the embodiments of <FIG>. Upon reaching approximately the center of each strut <NUM>', the amount of second powder material <NUM> is decreased and the amount of the first powder material <NUM> is increased for layers towards the crowns 314b until the layers at the crowns 314b are <NUM>% the first powder material. This gradual decrease/increase may also be according to the embodiments of <FIG>. The resulting struts <NUM>' are radiopaque without detrimentally affecting the strength, rigidity and overall performance of the precursor stent <NUM>.

Discussed above were various embodiments for making the precursor stent <NUM>. As also described above with respect to step <NUM> of the method of <FIG>, the plurality of second connectors <NUM>, <NUM>' and the optional stilts <NUM> are removed from the precursor stent <NUM>. With the plurality of second connectors <NUM>, <NUM>' and the stilts <NUM> removed, the precursor stent <NUM> becomes the stent <NUM> shown in <FIG>. The stent <NUM> includes a plurality of ring-shaped elements or portions or bands <NUM>. In the embodiment of <FIG>, the stent <NUM> includes eight bands <NUM> corresponding to the eight bands <NUM> of the precursor stent <NUM>. However, more or fewer bands <NUM> may be utilized. Each band <NUM> is disposed adjacent to another band <NUM> along a central longitudinal axis LA to form a tube or cylinder. Each band <NUM> is a waveform formed from a plurality of struts <NUM> connected together by bends or crowns <NUM>. At least one crown <NUM> of each band <NUM> is connected to a corresponding crown <NUM> of an adjacent band <NUM> by a first connector <NUM>. <FIG> shows a close-up illustration of one first connector <NUM> connecting the crowns <NUM> of adjacent bands <NUM> to each other. At other crowns, a gap <NUM> is disposed between the crown <NUM> and the corresponding crown <NUM> of the adjacent bands <NUM>, as shown in <FIG>. It is understood that the stent <NUM> shown in <FIG> may have radiopaque first connectors <NUM> if the methods used as described above were used to make first connectors <NUM>' radiopaque. Similarly, at least some of the struts <NUM> of the stent <NUM> may be radiopaque if the methods used as described above were used to make the corresponding struts <NUM>' of the precursor stent <NUM> radiopaque.

The specific embodiments described above for functionally grading a first material and a second material to make connectors brittle or to make connectors or struts radiopaque used cobalt and tantalum as the first and second materials, respectively. However, these are examples and other materials may be used in keeping with the present disclosure. For example, and not by way of limitation, the first material may be stainless steel and stainless steel alloys (e.g. SS316L), cobalt-chromium alloys, nickel titanium alloys (e.g. NITINOL), magnesium and magnesium alloys, or combinations thereof. The term "cobalt-chromium" alloys as used herein includes alloys with cobalt and chromium. Generally, materials such as, but not limited to, cobalt-nickel-chromium alloys (e.g. MP35N, MP20N, and MP35NLT) and chromium-nickel-tungsten-cobalt alloys ("L605") are the types of materials included in the term "cobalt-chromium alloys" as used herein. Further, the second material may be platinum, gold, tantalum, and other radiopaque materials known to those skilled in the art. Moreover, the exemplary functional grading ratio profiles and transition rates provided with the method of manufacturing the precursor stent <NUM> are examples only and are not meant to be limiting. Other functional grading systems, system ratio profiles and transition rates may be utilized based upon the application.

While the embodiments shown and described herein refer to a crown connected to a corresponding crown of an adjacent band on the precursor stent, other connections between adjacent bands may be used. For example, and not by way of limitation, a crown of one band may be connected to a strut of an adjacent band, or struts of adjacent bands may be connected. Further, the first connectors <NUM> and the second connectors <NUM> may be angled with respect to the longitudinal axis LA or may be curved.

Although the embodiments shown and described herein refer to a precursor stent with bands, at least one first connector, and a plurality of second connectors, the precursor stent processed to form a stent, this is not meant to limit the method, and other medical devices may be manufactured utilizing the method described herein.

Claim 1:
A method of making a stent (<NUM>) comprising the steps of:
forming a precursor stent (<NUM>) using micro-cladding, wherein the precursor stent (<NUM>) comprises a plurality of bands (<NUM>) made of a first material disposed adjacent to each other, wherein each band (<NUM>) is attached to an adjacent band by a plurality of first connectors (<NUM>, <NUM>') configured to remain and a plurality of second connectors (<NUM>, <NUM>') configured to be removed, wherein the plurality of second connectors (<NUM>, <NUM>') are made by functionally grading the first material with a second material to create embrittlement in the plurality of second connectors (<NUM>, <NUM>');
processing the precursor stent (<NUM>) to remove the plurality of second connectors (<NUM>, <NUM>') without adversely affecting the bands (<NUM>) and the plurality of first connectors (<NUM>, <NUM>').