| Method of fabricating an implantable medical device with biaxially oriented polymers -> Monitor Keywords |
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Method of fabricating an implantable medical device with biaxially oriented polymersRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Made Of Synthetic MaterialMethod of fabricating an implantable medical device with biaxially oriented polymers description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060020330, Method of fabricating an implantable medical device with biaxially oriented polymers. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to methods of fabricating implantable medical devices such as stents. [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 implantable medical device that is placed inside the body. A "lumen" refers to a cavity of a tubular organ such as a blood vessel. A stent is an example of these endoprostheses. 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 or valvuloplasty) with apparent success. [0005] Stents have been made of many materials including metals and polymers. Polymer materials include both nonbioerodable and bioerodable plastic materials. The cylindrical structure of stents is typically composed of a scaffolding that includes a pattern or network of interconnecting structural elements or struts. The scaffolding can be formed from wires, tubes, or planar films of material rolled into a cylindrical shape. In addition, a medicated stent may be fabricated by coating the surface of either a metallic or polymeric scaffolding with a polymeric carrier. The polymeric carrier can include an active agent or drug. Furthermore, the pattern that makes up the stent allows the stent to be radially expandable and longitudinally flexible. Longitudinal flexibility facilitates delivery of the stent and rigidity is needed to hold open a body lumen. The pattern should be designed to maintain the longitudinal flexibility and rigidity required of the stent. A stent should also have adequate strength in the circumferential direction. [0006] A number of techniques have been suggested for the fabrication of stents from tubes and planar films or sheets. One such technique involves laser cutting or etching a pattern onto a material. Laser cutting may be performed on a planar film of a material which is then rolled into a tube. Alternatively, a desired pattern may be etched directly onto a tube. Other techniques involve cutting a desired pattern into a sheet or a tube via chemical etching or electrical discharge machining. Laser cutting of stents has been described in a number of publications including U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005 to Richter and U.S. Pat. No. 5,906,759 to Richter. [0007] A treatment involving 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 requiring 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. 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 allowing the stent to self-expand. [0008] It is desirable for a stent to have certain mechanical properties to facilitate delivery and deployment of a stent. For example, longitudinal flexibility is important for successful delivery of the stent. In addition, circumferential strength and rigidity and are vital characteristics in deployment and for holding open a body lumen. As indicated above, the pattern of the stent may be designed to provide longitudinal flexibility and rigidity. [0009] However, the characteristics of the material of which a stent is composed also affects the mechanical properties of the stent. An advantage of stents fabricated from polymers is that they tend to possess greater flexibility than metal stents. Other potential shortcomings of metal stents include adverse reactions from the body, nonbioerodability, and non-optimal drug-delivery. However, a potential shortcoming of polymer stents compared to metal stents, is that polymer stents typically have less circumferential strength and rigidity. Inadequete circumferential strength potentially contributes to relatively high recoil of polymer stents after implantation into vessels. Furthermore, another potential problem with polymer stents is that struts can crack during crimping, especially for brittle polymers. Therefore, methods of manufacturing polymer stents that improve circumferential strength and rigidity are desirable. The embodiments of the present invention address the issue of improving circumferential strength and rigidity in polymer stents. SUMMARY OF THE INVENTION [0010] The present invention is directed to methods for fabricating an implantable medical device, such as a stent, from a tube, with desirable mechanical properties, such as improved circumferential strength and rigidity. Improved circumferential strength and rigidity may be obtained by inducing circumferential molecular orientation in materials for use in manufacturing an implantable medical device. Various embodiments of the present invention include methods for inducing circumferential molecular orientation in a material. [0011] Certain embodiments of methods of manufacturing an implantable medical device include introducing a polymer into a forming apparatus. The forming apparatus may include a first annular member disposed within a second annular member. The polymer may be conveyed through an annular chamber as an annular film between the annular members. Some embodiments may include radially expanding the annular film. Expansion may be performed after the annular film exits the apparatus. The method may further include forming a tube from the expanded annular film. The method may also include fabricating an implantable medical device from the tube. [0012] Other embodiments of the present invention may include a method including introducing a polymer into a forming apparatus. The forming apparatus may include a first annular member disposed within a second annular member. The polymer may be conveyed through an annular chamber as an annular film between the annular members. The method may further include inducing circumferential flow in the annular film. The method may also include forming a tube from the annular film. Some embodiments may include fabricating an implantable medical device from the tube. [0013] Some embodiments of the present invention may include a method of fabricating an implantable medical device that includes radially expanding a tube about a cylindrical axis of the tube from a first diameter to a second diameter. The method may further include fabricating an implantable medical device from the expanded tube that has a second diameter greater than the first diameter. [0014] Certain embodiments of the present invention may include a method of manufacturing an implantable medical device that includes stretching a film along a first axis of stretching and stretching a film along a second axis of stretching. The method may further include fabricating an implantable medical device from the stretched film. [0015] The present invention may further include an apparatus for manufacturing an implantable medical device that includes a first zone and a second zone. The first zone may include a first annular member and a second annular member. The first annular member may be disposed within the second annular member so as to provide for an annular chamber between the first and second annular members. The annular chamber may be configured to receive a material and dispense the material as an annular film to a second zone. The second zone may include a space for allowing radial pressure to be applied to the annular film to expand the material from a first film diameter to a second, larger film diameter. BRIEF DESCRIPTION OF THE DRAWINGS [0016] FIG. 1 depicts a tube. [0017] FIG. 2 depicts a three-dimensional rendering of an implantable medical device with a pattern. [0018] FIG. 3 depicts a system and method of manufacturing an implantable medical device. [0019] FIG. 4A depicts a radial cross-section of a forming apparatus. [0020] FIGS. 4B-7 depict an axial cross-section of a forming apparatus. [0021] FIGS. 8A and 8B depict a method of expanding a tube. 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