Patent Application
20180303642
The invention relates generally to methods of making a medical device, and more particularly to a method of making stents using rapid form prototyping or additive manufacturing.
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 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.
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 a medical device, 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 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, removal by chemical etching is not always desirable. Still 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 connectors between portions of the medical device that can be more easily, efficiently, and effectively removed without adversely affecting the remaining medical device.
Embodiments hereof relate to a method of making a medical device using additive manufacturing. The method includes forming a precursor medical device. The precursor medical device comprises a first portion, a second portion, a first connector connecting the first portion to the second portion, and a second connector connecting the first portion to the second portion. The first connector is configured to remain. The second connector is configured to be removed. The second connector is formed such that the second connector is less ductile/more brittle than the first portion, the second portion, and the first connector. The precursor medical device is processed to remove the second connector without adversely affecting the first portion, the second portion, or the first connector. In an embodiment, the medical device is a stent.
Embodiments hereof are directed to methods of making the second connector less ductile/more brittle than the first portion, the second portion, and the first connector. Embodiments for embrittlement include incomplete fusion of particles of the second connector, material selection to form intermetallics in the second connector, material selection to form a ceramic second connector, and selection of materials such that exposure to hydrogen in a heated environment causes the second connector to be less ductile than the first connector.
Embodiments hereof also relate to a precursor medical device including a first portion, a second portion, a first connector connecting the first portion to the second portion, and a second connector connecting the first portion to the second portion. The first connector is configured to remain. The second connector is configured to be removed and is less ductile than the first portion, the second portion, and the first connector. In an embodiment, the precursor medical device is a precursor stent.
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,
The method of
Step 104 of the method of
The first connectors 324 and the second connectors 326 are distinguished from each other in that the first connectors 324 are configured to remain connecting the adjacent crowns 314 to each other and the second connectors 326 are configured to be removable from the precursor stent 300. Similarly, the stilts 330 are configured to be removable from the precursor stent 300 such that the band 310a closest to the substrate 212 is not damaged when separating the precursor stent 300 from the substrate 212. Although a particular precursor stent 300 embodiment is shown in
As explained above, each crown 314 of a band 310 is connected to a corresponding crown 314 of an adjacent band 310 by a first connector 324 or a second connector 326. However, as also explained above, for certain applications it would be desirable for some of the crowns 314 of a band 310 to be independent or not connected to the corresponding crown 314 of an adjacent band 310. As also explained above, the second connectors 326 may not be able to be excluded from the precursor stent 300 during the additive manufacturing process because excluding such second connectors 326 when building the precursor stent 300 vertically on the substrate 212 would result in instability between the bands 310. For example, and not by way of limitation, if only one first connector 324 were included between the first band 310a and the second band 310b, the second band 310b would tend to move towards the first band 310a at the crowns 314 without a connector due to gravity. Such a tendency would negatively impact the ability to build a stent with the desired characteristics.
Accordingly, step 106 of the method 100 of
In an embodiment described in U.S. Pat. No. 9,114,032 the connectors configured to be removed may be made from a different material than the connectors configured to remain. The precursor stent is then processed, such as by chemical etching, such that the material of the connectors configured to be removed is removed but the material of the connectors configured to remain and the material of the bands is unharmed. However, switching materials during the additive manufacturing process may not be easy in certain additive manufacturing methods. The above-noted patent also describes some mechanical methods for removing some of the connectors. However, mechanically removing connectors that are constructed in the same manner of connectors configured to be removed may be difficult.
Therefore, in an embodiment of the present application, as shown in step 104 of the method 100 of
As explained above, in the additive manufacturing process, the powder material 208 is deposited over the substrate 212 and fused by the energy source 206 in the shape of a particular layer of the object 208 being formed. In an embodiment, when forming the bands 310 and the first connectors 324, the particles of the powder material 208 are completely fused. However, when forming second connectors 326 and the stilts 330, the particles of the powder material 208 are incompletely or suboptimally fused. Incomplete fusion of the powder material 208 of the second connectors 326 and the stilts 330 keeps the material particles largely unmelted (intact) with fusion of the particles mostly on the surface. This incomplete or suboptimal fusing of the powder material 208 of the second connectors 326 and the stilts 330 results in the second connectors 326 and the stilts 330 being more brittle than the bands 310 and the first connectors 324.
In an embodiment, when forming the bands 310 and the first connectors 324 (i.e., the portions of the precursor stent 300 configured to remain), a first energy per unit area is applied to the powder material 208 of each layer to completely fuse the particles of the powder material 208 to each other and to adjacent layers. When fusing the powder material 208 of the second connectors 326 and optional stilts 330 (i.e., portions of the precursor stent configured to be removed), however, a second energy per unit area is applied to the powder material of each layer to incompletely or suboptimally fuse the particles of the powder material 208 to each other and to adjacent layers. The second energy per unit area is lower than the first energy per unit area such that the second energy per unit area incompletely or suboptimally fuses the powder material 208 of the second connectors 326 and the stilts 330.
Several methods may be utilized to vary the energy applied to the material layers, either individually or in combination. More specifically, the speed of travel of the energy source, the power of the energy source, the distance of the energy source from the powder material, and the pattern of the energy source over the powder material may be varied to affect the energy per unit area applied to the powder material.
For example, in an embodiment, the energy source is a laser. In order to fuse the powder material 208 together and to the previous layer of material, the beam from the laser is moved over the powder material 208 in a pattern, thereby moving the laser focal zone 216 (see
In another embodiment, the energy source includes a first power for the first energy and a second power for the second energy. The second power is lower than the first power. The first power is utilized when the powder material 208 of the layers of the bands 310 and the first connectors 324 are being fused. The second power is utilized when the powder material 208 of the layers of the second connectors 326 and the stilts 330 are being fused. Thus, with the rate of travel of the energy source over the powder material, the distance from the energy source to the powder material 208, and the pattern of travel of the energy source over the powder material all constant, the energy source will apply less energy per unit area to form the second connectors 326 and the stilts 330 than to form the first connectors 324 and the bands 310. The second power is selected such that the energy per unit area applied to the powder material 208 to form the second connectors 326 and the stilts 330 results in incomplete or suboptimal fusion of the powder material.
In another embodiment, the energy source is positioned a first distance from the powder material 208 when applying energy to fuse the first connectors 324 and the bands 310 and a second distance from the powder material 208 when applying energy to fuse the second connectors 326 and the stilts 330. The second distance is greater than the first distance. Thus, with the rate of travel of the energy source across the powder material, the power of the energy source, and the pattern of travel of the energy source over the powder material all constant, the energy source will apply less energy per unit area at the second distance to form the second connectors 326 and the stilts 330 than to form the first connector 324 and the bands 310. The second distance is selected such that the energy per unit area applied to the powder material 208 to form the second connectors 326 and the stilts 330 results in incomplete or suboptimal fusion of the powder material 208.
In another embodiment shown in
In the embodiments described above regarding incomplete or suboptimal fusion of the second connectors 326 and the stilts 330, the powder material 208 for the second connectors 326 and the stilts 330 may be the same as the powder material 208 for the bands 310 and the first connectors 324. This may simplify the additive manufacturing process by not requiring a change in materials for different parts for the precursor stent 300. The powder material 208 used to form the precursor stent 300 is the material desired from the finished stent 400 (
In another embodiment, in step 104 of the method of
For example, in an embodiment, stainless steel alloy particles (e.g., 316SS) are used to form the bands 310 and the first connectors 324. In the locations of the second connectors 326 and the stilts 330, a mixture of the stainless steel particles and aluminum particles is used. When the mixture of stainless steel particles and aluminum particles is fused, the resulting fused material is more brittle than when stainless steel particles alone are fused. Thus, the second connectors 326 and the stilts 330 will be more brittle than the first connectors 324 and the bands 310. The chart below shows other examples of materials that can be used to form intermetallics at the location of the second connectors 326 and the stilts 330. These example materials are associated with the “Embrittlement Process” labeled “Intermetallics” in the chart.
In another embodiment, the second connectors 326 and the stilts 330 may be made from a ceramic material formed when the particles of the powder material are fused, while the first connectors 324 and the bands 310 are made from materials commonly used for stents, such as but not limited to 316SS, MP35N, NiTi, or L605. For example, and not by way of limitation, the second connectors 326 and the stilts 330 may be made from aluminum oxide particles that when fused by the energy source form a ceramic material which is low in ductility (i.e. brittle). The chart below shows other examples of materials that can be used to form brittle ceramics at the location of the second connectors 326 and the stilts 330. These example materials are associated with the “Embrittlement Process” labeled “Ceramics” in the chart.
In another embodiment, the second connectors 326 and the stilts 330 may be made from a material that is more susceptible to hydrogen embrittlement than the material used to make the first connectors 324 and the bands 310. For example, and not by way of limitation, the second connectors 326 and the stilts 330 may be formed from tantalum, while the first connectors 324 and the bands 310 are formed from stainless steel (e.g., 316SS). The precursor stent 300 is exposed to hydrogen gas in a heated environment. The exposure forms detrimental hydrides in the tantalum, decreasing ductility of the second connectors 326 and the stilts 330. The chart below shows other examples of materials that can be used at the location of the second connectors 326 and the stilts 330 such that when exposed to hydrogen gas in a heated environment, the second connectors 326 and the stilts 330 become less ductile/more brittle than the first connectors 324 and the bands 310. These example materials are associated with the “Embrittlement Process” labeled “Hydrogen Exposure” in the chart.
In the examples above, different materials are used for the portions of the precursor stent 300 configured to remain (the first connectors 324 and the bands 310) and the portions of the precursor stent configured to be removed (the second connectors 326 and the stilts 310). To change materials for different portions of the precursor stent 300, instead of using a powder bed with the blade 210 spreading material, as shown in
Thus, as explained in detail above, step 104 of the method 100 for forming a precursor stent 300 by additive manufacturing includes forming the second connectors 326 and the stilts 330 such that the second connectors 326 and the stilts 330 are less ductile (more brittle) than the bands 310 and the first connectors 324. Several methods of forming the second connectors 326 and the stilts 330 such that they are more brittle than the first connectors 324 and the bands 310 are disclosed above. Further, when using the terms “more brittle” or “less brittle” or “more ductile” or “less ductile”, it is meant that the parts discussed are “more brittle” or “less ductile” per unit volume of the part.
With the precursor stent 300 made, step 106 of the method of
With method 100 completed and the second connectors 326 and the stilts 330 removed, the precursor stent 300 has been transformed to the stent 400 shown in
Although 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 instead. 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 324 and the second connectors 326 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, a 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. More specifically, a precursor medical device may include a first portion coupled to a second portion by a first connector and a plurality of second connectors, the precursor medical device processed to form a medical device.
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.
