| Method and apparatus for thermal spray processing of medical devices -> Monitor Keywords |
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Method and apparatus for thermal spray processing of medical devicesRelated Patent Categories: Stock Material Or Miscellaneous Articles, Hollow Or Container Type Article (e.g., Tube, Vase, Etc.), Polymer Or Resin Containing (i.e., Natural Or Synthetic), Open-ended, Self-supporting Conduit, Cylinder, Or Tube-type ArticleMethod and apparatus for thermal spray processing of medical devices description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070166496, Method and apparatus for thermal spray processing of medical devices. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] This invention relates to medical devices and more particularly, the invention relates to methods of manufacturing and coating medical devices utilizing thermal spray processing (TSP). [0002] Several interventional treatment modalities are presently used for heart disease, including balloon and laser angioplasty, atherectomy, and by-pass surgery. In typical coronary balloon angioplasty procedures, a guiding catheter having a distal tip is percutaneously introduced through the femoral artery into the cardiovascular system of a patient using a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated at the ostium of the coronary arteries. A guide wire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. [0003] The guide wire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guide wire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy over the previously introduced guide wire until the balloon of the dilatation catheter is properly positioned across the lesion. [0004] Once in position across the lesion, the balloon is inflated to compress the plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then deflated so that blood flow can be resumed through the dilated artery and the dilatation catheter can be removed therefrom. Further details of dilatation catheters, guide wires, and devices associated therewith for angioplasty procedures can be found in U.S. Pat. No. 4,323,071 (Simpson-Robert); U.S. Pat. No. 4,439,185 (Lindquist); U.S. Pat. No. 4,516,972 (Samson); U.S. Pat. No. 4,538,622 (Samson, et al.); U.S. Pat. No. 4,554,929 (Samson, et al.); U.S. Pat. No. 4,616,652 (Simpson); U.S. Pat. No. 4,638,805 (Powell); U.S. Pat. No. 4,748,982 (Horzewski, et al.); U.S. Pat. No. 5,507,768 (Lau, et al.); U.S. Pat. No. 5,451,233 (Yock); and U.S. Pat. No. 5,458,651 (Klemm, et al.), which are hereby incorporated herein in their entirety by reference thereto. [0005] One problem that can occur during balloon angioplasty procedures is the formation of intimal flaps which can collapse and occlude the artery when the balloon is deflated at the end of the angioplasty procedure. Another problem characteristic of balloon angioplasty procedures is the large number of patients who are subject to restenosis in the treated artery. In the case of restenosis, the treated artery may again be subjected to balloon angioplasty or to other treatments such as by-pass surgery, if additional balloon angioplasty procedures are not warranted. However, in the event of a partial or total occlusion of a coronary artery by the collapse of a dissected arterial lining after the balloon is deflated, the patient may require immediate medical attention, particularly in the coronary arteries. [0006] A focus of recent development work in the treatment of heart disease has been directed to endoprosthetic devices referred to as stents. Stents are generally cylindrically shaped intravascular devices which are placed within an artery to hold it open. The device can be used to reduce the likelihood of restenosis and to maintain the patency of a blood vessel immediately after intravascular treatments. In some circumstances, they can also be used as the primary treatment device where they are expanded to dilate a stenosis and then left in place. Further details of stents can be found in U.S. Pat. No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,338 (Balko et al.); U.S. Pat. No. 4,553,545 (Maass et al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gianturco); U.S. Pat. No. 4,856,516 (Hillstead); U.S. Pat. No. 4,886,062 (Wiktor); U.S. Pat. No. 5,421,955 (Lau); and U.S. Pat. No. 5,569,295 (Lam), which are hereby incorporated herein in their entirety by reference thereto. [0007] One method and system developed for delivering stents to desired locations within the patient's body lumen involves crimping a stent about an expandable member, such as a balloon on the distal end of a catheter, advancing the catheter through the patient's vascular system until the stent is in the desired location within a blood vessel, and then inflating the expandable member on the catheter to expand the stent within the blood vessel. The expandable member is then deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel, holding open the passageway thereof. [0008] Commercially available 316L stainless steel tubing contains average grain sizes ranging from approximately 0.0025 inch (64 microns), ASTM grain size 5 to around 0.00088 inch (22 microns), ASTM grain size 8. These grain sizes result in anywhere from two to five grains across the tube thickness, and the stent subsequently manufactured from the tubing depending on the tube and stent strut thicknesses. Part of the limitation in achieving a finer grain size in this material arises from the number of draws and anneals the tubing must go through to achieve its final size. The potential for reducing the grain size exists by reducing the required number of heat-processing steps by reducing the starting size of the raw product that is then processed down into the tubing. [0009] Lowering the grain size and increasing the number of grains across the strut thickness of a stent allows the grains within the stent to act more as a continuum and less as a step function. The ideal result of processing the material to a smaller grain size would result in an average grain size of between approximately 1 and 10 microns, with a subsequent average number of grains across the strut thickness about eight or greater. Likewise, other medical devices will benefit from a reduction in grain size such as guide wires, ring markers, defibrillator lead tips, delivery system devices such as catheters, and the like. SUMMARY OF THE INVENTION [0010] The present invention relates to methods of manufacturing and coating medical devices utilizing thermal spray processing (TSP). The process includes producing a coating having an average grain size of between 1 and 64 microns and providing a thin walled structure having a wall thickness of about eight or more grains. While the grain size for thin walled structures (such as stents) has been referred to herein as about eight or more grains, the number of grains does vary depending on wall thickness. Thus, for very thin walled structures the wall thickness may be between four and eight grains, but for most (but not all) stent applications it is desirable to have at least eight or more grains comprising the wall thickness. [0011] The invention involves the use of TSP for the manufacture of fine grained tubing for subsequent use as a medical device such as a stent or other tubular or ring-based implant, the manufacture of intermediate size tube that may then be drawn into final size tubing, and for the coating of a stent or other medical device. Medical devices which will benefit from the present invention include stents, guide wires, ring markers, tubular or wire based implants, defibrillator lead tips, and catheters and other delivery system devices. While the present invention TSP is utilized for the medical devices described herein, stents will be used as an example of the inventive manufacturing process and coating process disclosed and claimed herein. [0012] Thermal spray is a generic term for a broad class of related processes in which molten droplets of metals, ceramics, glasses, and/or polymers are sprayed onto a surface to produce a coating, to form a free-standing near-net-shape, or to create an engineered material with unique properties (e.g., strain-tolerant ceramics, metallic glasses, cermets, or metal/polymer composites). [0013] In principle, any material with a stable molten phase can be thermally sprayed, and a wide range of pure and composite materials are routinely sprayed for both research and industrial applications. Deposition rates are very high in comparison to alternative coating technologies. Deposit thicknesses of 0.1 to 1 mm are common, and thicknesses greater than 1 cm can be achieved with some materials. [0014] With regard to manufacturing, the invention relates to the overall manufacturing of tube stock and coatings, creating layered material and other materials through powder consolidation during spraying, with the additional potential of creating composite materials. [0015] As mentioned above, commercially available 316L stainless steel tubing contains average grain sizes ranging from approximately 0.0025 inch (64 microns), ASTM grain size 5 to around 0.00088 inch (22 microns), ASTM grain size 8. These grain sizes result in anywhere from two to five grains across the tube thickness, and the stent subsequently manufactured from this tubing depending on the tube and stent strut thicknesses. Part of the limitation in achieving a finer grain size in this material arises from the number of draws and anneals the tubing must go through to achieve its final size. The potential for reducing the grain size exists by reducing the required number of heat-processing steps by reducing the starting size of the raw product that is then processed down into the tubing. [0016] Lowering the grain size and increasing the number of grains across the strut thickness allows the grains within the stent to act more as a continuum and less as a step function. For example, the result of processing the material to a smaller grain size in a stent would result in an average grain size of between approximately 1 and 64 microns, with a subsequent average number of grains across the strut thickness about eight or greater. The average number of grains in a cross-section of a medical device depends upon the size of the device and the diameter of the grains. [0017] In one embodiment, the manufacturing process includes thermal spray processing. Thermal spray processing can be generally defined as a group of processes in which finely divided metallic or nonmetallic surfacing materials are deposited in a molten or semi-molten condition on a substrate to form a spray deposit. Cold spray thermal processing, to be discussed herein, is considered a thermal spray process although the materials projected onto a surface are not necessarily molten or semi-molten. TSP includes several variants such as cold spraying, combustion spraying, arc spraying, high velocity oxy-fuel spraying, and plasma spraying. Currently sprayed materials include elements, metallic alloys, ceramics, composites and polymers. TSP can be considered to be a net or near net shaped process. This means that the product that comes out of the thermal spray process is close to or at the desired size and shape of the final product. This process can be used not only to coat a stent but also to manufacture tube stock that is used in place of gun drilled or extruded rod or subsequent tube manufacturing. Some factors to consider when spray forming include the grain size, porosity, and dimensional tolerances of the sprayed part. Post-processing can assist when one or more of these factors is not as desired for the final product. Thus TSP processing is presented here both with and without post-processing of the material. [0018] Some advantages of thermal processing include the versatility with respect to feed materials (metals, ceramics, and polymers in the form of wires, rods, or powders); the capacity to form barrier and functional coatings on a wide range of substrates; the ability to create freestanding structures for net-shape manufacturing of high-performance ceramics, composites, and functionally graded materials; and the rapid-solidification synthesis of specialized materials. [0019] TSP may be used to spray-form tube stock on top of a removable mandrel. The thickness of the tube may be varied by spraying more or less material, and the inner diameter dimensions may be varied by changing the size of the mandrel. The inner mandrel may be made of a substance that melts out or that is coated with a substance that allows easy removal of the finished sprayed tube. If the grain size, porosity, and dimensional tolerances (including wall runout, wall thickness, concentricity and surface roughness) are as desired, the mandrel may be removed and the sprayed tube is ready for further processing into a stent or other tubular or ring-shaped product. To create a ring-shaped product from a tube product, the tube is sprayed to the desired dimensions and then sliced in the transverse direction to result in rings of the desired size. [0020] There are several potential post-processing operations that may take place on a sprayed tube. Grain size, porosity, and final dimensions are a few of the incentives for performing post processing. [0021] Grain size of the finished tube depends on numerous factors, including the size of the particles being sprayed, the formation, impact and rate of solidification of the sprayed material, and the length of time the material is heated above a temperature that allows significant grain growth. For a metallic tube, if the grain size is larger than desired, the tube may be swaged to introduce heavy dislocation densities, then heat treated to recrystallize the material into finer grains. Alternatively, different material forms may be taken through a drawing or other working and heat treat processes to recrystallize the tubing. The type and amount of working allowed depends on the material, e.g., ceramics may require a high temperature working step while metals and composites may be workable at room temperature. Grain-size strengthening is where there is an increase in strength of a material due to a decrease in the grain size. The larger grain-boundary area more effectively blocks dislocation movement. The outer diameter of the tube usually requires a machining step of some sort to smooth the surface after the swaging process, and the same may be true before the tubing can be properly drawn. [0022] By the very nature of the spray processing itself, the sprayed material may contain porosity, or small voids. These may be minimized or eliminated through control of the TSP parameters. The potential exists that the tube may need to be post-processed to eliminate this feature. One potential method of post processing involves a traveling ring furnace, where the material is melted and re-solidified as the ring travels down the length of the tube. This method requires close control to prevent preferential segregation of elements along with the melt pool. Another method is to process the material under high mechanical pressure to sinter the grains together; this method is generally used for powder processing. As porosity is difficult to remove from a material, however, the best form of elimination is to ensure that the TSP parameters are such that the porosity is not present in the first place. Continue reading about Method and apparatus for thermal spray processing of medical devices... Full patent description for Method and apparatus for thermal spray processing of medical devices Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and apparatus for thermal spray processing of medical devices patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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