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Fiber reinforced composite stentsRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Stent Structure, Having Multiple Connected BodiesFiber reinforced composite stents description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070038290, Fiber reinforced composite stents. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to radially expandable implantable medical devices such as stents for implantation into a bodily lumen. In particular, the invention relates composite stents reinforced with fibers. [0003] 2. Description of the State of the Art [0004] This invention relates to radially expandable endoprostheses, which are adapted to be implanted in a bodily lumen. An "endoprosthesis" corresponds to an artificial device that is placed inside the body. A "lumen" refers to a cavity of a tubular organ such as a blood vessel. [0005] A stent is an example of such an endoprosthesis. Stents are generally cylindrically shaped devices, which function to hold open and sometimes expand a segment of a blood vessel or other anatomical lumen such as urinary tracts and bile ducts. Stents are often used in the treatment of atherosclerotic stenosis in blood vessels. "Stenosis" refers to a narrowing or constriction of the diameter of a bodily passage or orifice. In such treatments, stents reinforce body vessels and prevent restenosis following angioplasty in the vascular system. "Restenosis" refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty, stenting, or valvuloplasty) with apparent success. [0006] The treatment of a diseased site or lesion with a stent involves both delivery and deployment of the stent. "Delivery" refers to introducing and transporting the stent through a bodily lumen to a region, such as a lesion, in a vessel that requires treatment. "Deployment" corresponds to the expanding of the stent within the lumen at the treatment region. Delivery and deployment of a stent are accomplished by positioning the stent about one end of a catheter, inserting the end of the catheter through the skin into a bodily lumen, advancing the catheter in the bodily lumen to a desired treatment location, expanding the stent at the treatment location, and removing the catheter from the lumen. [0007] In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter. Mounting the stent typically involves compressing or crimping the stent onto the balloon. The stent is then expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be secured to the catheter via a retractable sheath or a sock. When the stent is in a desired bodily location, the sheath may be withdrawn which allows the stent to self-expand. [0008] The stent must be able to satisfy a number of mechanical requirements. First, the stent must be capable of withstanding the structural loads, namely radial compressive forces, imposed on the stent as it supports the walls of a vessel. Therefore, a stent must possess adequate radial strength. Radial strength, which is the ability of a stent to resist radial compressive forces, is due to strength and rigidity around a circumferential direction of the stent. Radial strength and rigidity, therefore, may also be described as, hoop or circumferential strength and rigidity. [0009] Once expanded, the stent must adequately maintain its size and shape throughout its service life despite the various forces that may come to bear on it, including the cyclic loading induced by the beating heart. For example, a radially directed force may tend to cause a stent to recoil inward. Generally, it is desirable to minimize recoil. [0010] In addition, the stent must possess sufficient flexibility to allow for crimping, expansion, and cyclic loading. Longitudinal flexibility is important to allow the stent to be maneuvered through a tortuous vascular path and to enable it to conform to a deployment site that may not be linear or may be subject to flexure. Finally, the stent must be biocompatible so as not to trigger any adverse vascular responses. [0011] The structure of a stent is typically composed of scaffolding that includes a pattern or network of interconnecting structural elements often referred to in the art as struts or bar arms. The scaffolding can be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. Conventional methods of constructing a stent from a polymer material involve extrusion, blow molding, or injection molding a polymer tube based on a single polymer or polymer blend and then laser cutting a pattern into the tube. The scaffolding is designed so that the stent can be radially compressed (to allow crimping) and radially expanded (to allow deployment). A conventional stent is allowed to expand and contract through movement of individual structural elements of a pattern with respect to each other. [0012] Additionally, a medicated stent may be fabricated by coating the surface of either a metallic or polymeric scaffolding with a polymeric carrier that includes an active or bioactive agent or drug. Polymeric scaffolding may also serve as a carrier of an active agent or drug. [0013] Furthermore, it may be desirable for a stent to be biodegradable. In many treatment applications, the presence of a stent in a body may be necessary for a limited period of time until its intended function of, for example, maintaining vascular patency and/or drug delivery is accomplished. Therefore, stents fabricated from biodegradable, bioabsorbable, and/or bioerodable materials such as bioabsorbable polymers should be configured to completely erode only after the clinical need for them has ended. [0014] In general, there are several important aspects in the mechanical behavior of polymers that affect stent design. Polymers tend to have lower strength than metals on a per unit mass basis. Therefore, polymeric stents typically have less circumferential strength and radial rigidity than metallic stents of the same or similar dimensions. Inadequate radial strength potentially contributes to a relatively high incidence of recoil of polymeric stents after implantation into vessels. [0015] Another potential problem with polymeric stents is that their struts or bar arms can crack during crimping and expansion, especially for brittle polymers. The localized portions of the stent pattern subjected to substantial deformation tend to be the most vulnerable to failure. Furthermore, in order to have adequate mechanical strength, polymeric stents may require significantly thicker struts than a metallic stent, which results in an undesirably larger profile. [0016] Additionally, another factor to consider in stent design is radiopacity. In addition to meeting the mechanical requirements described above, it is desirable for a stent to be radiopaque, or fluoroscopically visible under x-rays. "Radiopaque" refers to the ability of a substance to absorb x-rays. Accurate stent placement is facilitated by real time visualization of the delivery of a stent. A cardiologist or interventional radiologist can track the delivery catheter through the patient's vasculature and precisely place the stent at the site of a lesion. This is typically accomplished by fluoroscopy or similar x-ray visualization procedures. For a stent to be fluoroscopically visible it must be more absorptive of x-rays than the surrounding tissue. Radiopaque materials in a stent may allow for its direct visualization. [0017] A significant shortcoming of polymers as compared to metals (and polymers generally composed of carbon, hydrogen, oxygen, and nitrogen) is that they are radiolucent with no radiopacity. Polymers tend to have x-ray absorption similar to body tissue. [0018] Additionally, there are manufacturing difficulties in placing small markers on stents as well as challenges in keeping very small markers attached to the stent. If the maximum permissible size of the marker is too small to be visible on a fluoroscope, multiple markers may be necessary. This makes manufacturing even more challenging. [0019] Therefore, it would be desirable to have methods of making biodegradable polymeric stents that are both strong and flexible. SUMMARY OF THE INVENTION [0020] Certain embodiments of the present invention are directed to a method of making a stent that may include forming a mixture having a matrix polymer and a plurality of short fibers such that fibers include a material having a melting temperature greater than a melting temperature of the matrix polymer. The method may further include disposing the mixture in a tube or sheet forming apparatus to form a tube or a sheet such that the apparatus is heated so that a temperature of the mixture in the apparatus is greater than the melting temperature of the matrix polymer and less than the melting temperature of the material of the fibers. At least a portion of the matrix polymer may be a polymer melt. A stent may be fabricated from the tube or sheet including the matrix polymer and the short fibers. [0021] Further embodiments of the present invention are directed to a method of making a stent that may include forming a tube having at least one fiber layer and at least one polymer film layer such that fibers of at least one fiber layer include a material having a melting temperature greater than a melting temperature of at least one polymer film layer. The method may further include heating the tube to a temperature greater than the melting temperature of at least one polymer film layer and less than the melting temperature of the material of the fibers to melt at least a portion of the polymer of at least one polymer film layer. At least a portion of at least one fiber layer may become embedded within at least a portion of the melted polymer of at least one polymer film layer. The heated tube may then be cooled and a stent fabricated from the cooled tube. [0022] Additional embodiments of the present invention are directed to a method of making a stent that may include forming a layered sheet having at least one fiber layer and at least one polymer film layer such that fibers of at least one fiber layer include a material having a melting temperature greater than a melting temperature of at least one polymer film layer. The method may further include heating the layered sheet to a temperature greater than the melting temperature of at least one polymer film layer and less than the melting temperature of the material of the fibers to melt at least a portion of the polymer of at least one polymer film layer. At least a portion of the fibers may become embedded within at least a portion of the melted polymer of at least one polymer film layer. The heated layered sheet may then be cooled and a stent fabricated from the cooled sheet. Continue reading about Fiber reinforced composite stents... Full patent description for Fiber reinforced composite stents Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fiber reinforced composite stents 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. Start now! - Receive info on patent apps like Fiber reinforced composite stents or other areas of interest. ### Previous Patent Application: Electromagnetic resonant circuit sleeve for implantable medical device Next Patent Application: Intralumenally-implantable frames Industry Class: Prosthesis (i.e., artificial body members), parts thereof, or aids and accessories therefor ### FreshPatents.com Support Thank you for viewing the Fiber reinforced composite stents patent info. 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