Patent Application
20180303643
The invention relates generally to methods of making medical devices, and more particularly to a method of making stents using additive manufacturing.
A wide range of medical treatments exist that utilize medical devices such as 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 without limitation: 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, and often more specifically, for implantation within the blood vessels of the body.
Stents have been made by a variety of methods, including forming a wire into 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 a 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, also known as rapid prototyping methods and three-dimensional printing, 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 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 U.S. Pat. No. 9,114,032 assigned to Medtronic Vascular, Inc., incorporated by reference herein in its entirety, connectors are formed between all crowns of a stent by additive manufacturing. Some of the connectors are then removed by laser removal, chemical etching, or other methods. In particular embodiments, the connectors configured to be removed are formed from a different material than the connectors configured to remain. Then, the precursor stent is exposed to a chemical etchant that dissolves/removes the connectors configured to be removed without adversely affecting the stent components configured to remain. However, changing materials during additive manufacturing may complicate the process. Further, mechanical removal of connectors may be difficult if the connectors to be removed are the same as the connectors to remain.
Accordingly, it would be desirable to build a medical device such as a stent by additive manufacturing with only the desired connectors between portions of the medical device.
Embodiments hereof relate to a method of making a medical device using additive manufacturing. In an embodiment, the medical device includes a plurality of portions disposed adjacent to each other and at least one connector connecting each portion to an adjacent portion. In the method, a plurality of layers of a first portion of the plurality of portions are formed by additive manufacturing. A removable masking plate is placed over the first portion. The removable masking plate includes at least one opening aligned with a point of the first portion. At least one layer of a first connector is formed on the first portion in the at least one opening of the removable masking plate. A plurality of layers of a second portion of the plurality of portions are formed. A first layer of the plurality of layers of the second portion is formed partially on the first connector and partially on the removable masking plate. The removable masking plate is then removed.
The foregoing and other features and advantages of the invention will be apparent from the following description of embodiments hereof as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale.
Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements.
Accordingly,
Thus, the object 218 (in this embodiment a precursor stent as described below), is built layer-by-layer. However, in order for a subsequent layer of powder material 208 to be fused, it must be supported. Typically, support is provided by the preceding layer of fused material as the object is formed vertically. However, with certain medical devices, such as certain 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, as will be described in greater detail below. However, in many embodiments, these portions cannot be excluded during additive manufacturing because the following layers need support upon which to build. Thus, when building such a stent vertically by additive manufacturing, it may be necessary 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. As noted above, some of the connectors are not desirable in the final stent and therefore must be removed.
Therefore, in accordance with embodiments hereof and as described in more detail below, a removable masking plate is disposed between adjacent bands (portions) of the precursor stent to mask the areas that are not to be connected between the adjacent bands. The removable masking plate provides the underlying support for the following layers of material. The method of
In an embodiment, in step 101 of the method 100 of
Step 102 of the method 100 of
Once the first band 310a is formed, in step 104 a first removable masking plate 340a is placed over the first band 310a of the precursor stent 300, as shown in
The removable masking plate 340 may be in the form of a sheet, foil, tape, or other suitable form for use herein. The particular dimensions of the removable masking plate 340, such a length, width, thickness and/or diameter may be determined by the particular stent design. For example, the desired length of the connectors 324 between each band 310 may determine the thickness of the removable masking plate 340. Similarly, the diameter of the bands 310 may determine the diameter of the removable masking plates 340. In the embodiment of
In the embodiment of the additive manufacturing system 200 of
In the next step 106, the additive manufacturing system 200 lays down at least one layer of the powder material 208 of the desired material to build the first connector 324a, as shown in
Once the first connector 324a is formed through the opening 342 of the first masking plate 340a, in the following step 108 the additive manufacturing system 200 lays down successive layers of the powder 208 to build the second band 310b from a series of cross sections, as shown in
Once the second band 310b is formed, in step 110 a second removable masking plate 340b is placed over the second band 310b of the precursor stent 300, as shown in
In the next step 112, the additive manufacturing system 200 lays down at least one layer of the powder material 208 of the desired material to build the second connector 324b, as shown in
The steps of forming a band 310 on a removable masking plate 340, placing another removable masking plate 340 thereon, and forming a connector 324 therethrough may be repeated until the desired precursor stent 300 is achieved.
As explained above, each crown 314 of a band 310 is connected to a corresponding crown 314 of an adjacent band 310 by a connector 324 or separated therefrom by a removable masking plate 340. The crowns 314 of a band 310 desired to be independent of or not connected to the corresponding crown 314 of an adjacent band 310 are therefore separated by one of the removable masking plates 340. As further explained above, each removable masking plate 340 is needed to support the following band 310 of the precursor stent 300. However, the removable masking plates 340 are not desired as part of the finished stent. Accordingly, step 114 of the method 100 of
For example, in one non-limiting example, the bands 310 and the connectors 324 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316SS), cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)), or nickel-titanium alloys. The removable masking plates 340 may be made of a brittle material, such as, but not limited to, a ceramic material. The removable masking plates 340 may be removed by physical methods such as shattering the brittle ceramic material using a hammer, tweezers, dropping-off, etc. without damaging the more ductile (i.e., less brittle) bands 310 and connectors 324.
In another non-limiting example, the bands 310 and the connectors 324 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316SS), cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)), or nickel-titanium alloys. The removable masking plates 340 may be made from aluminum or an aluminum alloy (such as an aluminum sheet). The aluminum will be preferentially etched by sodium hydroxide (NaOH) such that immersing the precursor stent 300 in NaOH will remove the aluminum masking plates 340 while leaving the bands 310 and the connectors 324 unharmed.
In another non-limiting example, the removable masking plates 340 may be a magnesium sheet and the bands 310 and the connectors 324 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316SS) or cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)). Immersing the precursor stent 300 in an acidic solution will lead to preferential removal of the magnesium masking plates 340 while leaving the bands 310 and the connectors 324 unharmed. In another example, a potential (voltage) can be applied to the precursor stent 300 to promote and/or hasten the reaction. In the example above, the magnesium masking plates 340 can be preferentially removed by immersing the precursor stent 300 in water (or an acidic solution) and applying a positive potential to the precursor stent 300, thereby removing the magnesium masking plates 340.
In another non-limiting example, the precursor stent 300 is exposed to a hot oxidizing environment to consume the removable masking plates 340. For example, the removable masking plates 340 of the precursor stent 300 may each be a magnesium sheet and the bands 310 and the connectors 324 of the precursor stent 300 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316SS) or cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)). Exposing the precursor stent 300 to oxygen above the autoignition temperature (approximately 473° C.) of magnesium will cause the magnesium masking plates 340 to rapidly oxidize without adversely affecting the bands 310 and the connectors 324.
In another non-limiting example, the removable masking plates 340 may be made of polyetherimide, and the bands 310 and the connectors 324 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316SS), cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)), or nickel-titanium alloys. Immersing the precursor stent 300 in chloroform will dissolve the polymer masking plates 340 without adversely affecting the bands 310 and the connectors 324.
In another non-limiting example, the precursor stent 300 may be formed with zinc sheets as the removable masking plates 340, and the bands 310 and the connectors 324 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316SS), Cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)), or nickel-titanium alloys. Exposing the precursor stent 300 to temperatures between the melt temperature (about 420° C.) and the boiling temperature (about 907° C.) for zinc, and thus below the melt temperature for the material of the bands 310 and the connectors 340, will cause the zinc masking plates 340 to melt without adversely affecting the bands 310 and the connectors 324.
In another non-limiting example, the precursor stent 300 may be formed with a zinc sheet as the removable masking plates 340, and the bands 310 and the connectors 324 may be formed of materials commonly used in a stent such as stainless steel (e.g. 316DD), Cobalt-chromium alloys (e.g. cobalt-nickel-chromium alloys (MP35N, MP20N, MP35NLT), chromium-nickel-tungsten-cobalt alloys (L605)), or nickel-titanium alloys. Exposing the precursor stent 300 to temperature and pressure conditions in excess of the boiling point for zinc, while below the boiling point for the material of the bands 310 and the connectors 324, will sublimate the zinc removable masking plates 340 without adversely affecting the bands 310 and the connectors 324. In a particular example, heating the precursor stent 300 in a vacuum will reduce the energy required to sublimate the zinc removable masking plates 340.
The above examples are not comprehensive. Further non-limiting examples of materials used for the bands 310, the connectors 324, and the removable masking plates 340, and examples of processes to remove the removable masking plates 340 are provided in the chart below. These examples are not exhaustive and other materials and processes may be used to remove the masking plates 340 without adversely affecting the bands 310 and connectors 324.
With method 100 completed and the removable masking plates 340 removed, the precursor stent 300 has been transformed to the stent 400 shown in
Further processing of the stent 400 may be performed after the removal of the masking plates 340. For example, and not by way of limitation, electropolishing, laser micro-machining, or other processes to smooth the surfaces of the stent 400 may be performed, if necessary and or desired. Accordingly, the struts 312 and the crowns 314 of the bands 310, and the first connectors 324, of the precursor stent 300 may be slightly thicker than the final desired thickness of these elements to account for processes to smooth or otherwise finish the stent since such processes may be subtractive processes. Further, processes to remove the stilts 330, if used, or other materials between the first band 310a and the substrate 212 may also be performed. Other finishing processes may be performed on the stent 400 to prepare the stent 400 for use in a body, such as, but not limited to, passivation and sterilization. Further processing may also include steps such as adding coatings to the stent, adding radiopaque markers, adding biologically or pharmaceutically active substances to the stent, and/or adding surface features (such as recesses) to the stent. Some of this described further processing may be performed on the precursor stent 300 prior to removal of the removable masking plates 340. Further, some of the described further processing may be included in steps of forming the precursor stent. For example, and not by way of limitation, surface features such as recesses may be formed in the stent as part of the additive manufacturing process.
While the embodiments shown and described herein refer to a crown connected to a corresponding crown of an adjacent band on the precursor stent by a connector, other connections between adjacent bands may be utilized. 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 connectors 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 connector and at least one removable masking plate 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. More specifically, a precursor medical device may include a first portion coupled to a second portion by at least one connector and a removable masking plate disposed between the first portion and the second portion. The precursor medical device may be processed to remove the masking plate, thereby forming a medical device including a first portion coupled to a second portion by at least one connector.
While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.
