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  Expandable medical device with locking mechanismUSPTO Application #: 20060030931Title: Expandable medical device with locking mechanism Abstract: According to the present invention there is provided an expandable medical device having, a plurality of elongated beams, the plurality of elongated beams joined together to form a substantially cylindrical device which is expandable from a cylinder having a first diameter to a cylinder having a second diameter. A plurality of hinges connecting the elongated beams have a hinge width, wherein the hinge width is smaller than the beam width. A pawl is disposed adjacent to and substantially parallel to the hinge prior to expansion of the medical device and a plurality of teeth are adapted to receive the pawl. The present invention additionally provides the benefit of limiting the amount of recoil of an expandable device by engaging a locking mechanism, thereby retaining the expanded diameter of the device. (end of abstract) Agent: Cindy A. Lynch Conor Medsystems, Inc. - Menlo Park, CA, US Inventor: John F. Shanley USPTO Applicaton #: 20060030931 - Class: 623001150 (USPTO) Related Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Stent Structure The Patent Description & Claims data below is from USPTO Patent Application 20060030931. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIM OF PRIORITY [0001] The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/266,805 filed Feb. 5, 2001, the entirety of which is hereby incorporated by reference. FIELD OF THE INVENTION [0002] This invention relates to expandable medical devices, more particularly to an expandable medical device including a locking mechanism and low recoil after expansion from one diameter to a greater second diameter. SUMMARY OF THE RELATED ART [0003] In the past, permanent or biodegradable devices have been developed for implantation within a body passageway to maintain patency of the passageway. These devices are typically introduced percutaneously, and transported transluminally until positioned at a desired location. These devices are then expanded either mechanically, such as by the expansion of a mandrel or balloon positioned inside the device, or expand themselves by releasing stored energy upon actuation within the body. Once expanded within the lumen, these devices, called stents, become encapsulated within the body tissue and remain a permanent implant. [0004] Known stent designs include monofilament wire coil stents (U.S. Pat. No. 4,969,458); welded metal cages (U.S. Pat. Nos. 4,733,665 and 4,776,337); and, most prominently, thin-walled metal cylinders with axial slots formed around the circumference (U.S. Pat. Nos. 4,733,665, 4,739,762, and 4,776,337). Known construction materials for use in stents include polymers, organic fabrics and biocompatible metals, such as, stainless steel, gold, silver, tantalum, titanium, and shape memory alloys such as Nitinol. [0005] U.S. Pat. Nos. 4,733,665, 4,739,762, and 4,776,337 disclose expandable and deformable intraluminal vascular grafts in the form of thin-walled tubular members with axial slots allowing the members to be expanded radially outwardly into contact with a body passageway. After insertion, the tubular members are mechanically expanded beyond their elastic limit and thus permanently fixed within the body. [0006] Many of the known stents display a large elastic recovery, known in the field as "recoil," after expansion inside a lumen. Large recoil necessitates over-expansion of the stent during implantation to achieve the desired final diameter. Over-expansion is potentially destructive to the lumen tissue and is known to cause higher rates of restenosis. Known stents of the type described above experience recoil of up to about 9 to 21% from maximum expansion. [0007] Large recoil also makes it very difficult to securely crimp most known stents onto delivery catheter balloons. As a result, slippage of stents on balloons during intralumenal transportation, final positioning, and implantation has been an ongoing problem. Many ancillary stent securing devices and techniques have been advanced to attempt to compensate for this basic design problem. Some of the stent securing devices include collars and sleeves used to secure the stent onto the balloon. [0008] Some materials have intrinsic properties that are beneficial in some aspects of stent design, and undesirable in other aspects. U.S. Pat. No. 5,545,210, for example, discloses a thin-walled tubular stent geometrically similar to those discussed above, but constructed of a nickel-titanium shape memory alloy ("Nitinol"). Martensitic Nitinol has a very low Young's Modulus, and a low, nearly horizontal "de-twinning" stress plateau that provide an exceptionally large strain range before plastic deformation commences. When incorporated into conventional stent designs, these properties produce stents that have unusually good flexibility, deliverability, conformability and radiopacity, but also unacceptably high recoil and poor radial strength. For example, recoil of a typical design Nitinol stent ranges from 10% to 25%, typically about 12% to 16%. [0009] One approach to remedying material-based recoil and radial strength problems is to employ locking or detent features in the stent design. A number of such locking stent designs have been proposed for conventional materials like stainless steel, but none has proven workable in practice. Many of the designs are simply impossible to manufacture on a small scale. More fundamentally, most of the designs fail to provide the basic mechanical requirements of a ratchet or detent. mechanism: 1) two degree-of-freedom differential motion between the engaging elements, and 2) a restoring or spring force between the elements. It is relatively easy to provide these two elements in larger mechanisms comprised of discrete components, but much more difficult to provide this functionality while cutting all features into a very small, continuous, cylindrical surface. [0010] FIG. 1 shows a typical prior art "expanding cage" stent design. The stent 10 includes a series of axial slots 12 formed in a cylindrical tube 14. Each axial row of slots 12 is displaced axially from the adjacent row by approximately half the slot length providing a staggered slot arrangement. The material between the slots 12 forms a network of axial struts 16 joined by short circumferential links 18. The cross section of each strut 16 remains constant or varies gradually along the entire length of the strut and thus the rectangular moment of inertia and the elastic and plastic section moduli of the cross section also remain constant or vary gradually along the length of the strut. Such a strut 16 is commonly referred to as a prismatic beam. Struts 16 in this type of design are typically 0.005 to 0.006 inches (0.127-0.1524 mm) wide in the circumferential direction. Strut thicknesses in the radial direction are typically about 0.0025 inches (0.0635 mm) or less to keep expansion forces within acceptable levels. However, most stent materials must be approximately 0.005 inches (0.127 mm) thick for good visibility on conventional fluoroscopic equipment. This high ratio of strut width to thickness, combined with the relatively high strut length and the initial curvature of the stent tubing combine to cause the instability and bucking often seen in this type of stent design. When expanded, the stent structure of FIG. 1 assumes the roughly diamond pattern commonly seen in expanded sheet metal. [0011] Another stent described in PCT publication number WO 96/29028 uses struts with relatively weak portions of locally-reduced cross sections that on expansion of the stent act to concentrate deformation at these areas. However, as discussed above non-uniform expansion is even more of a problem when smaller feature widths and thicknesses are involved because manufacturing variations become proportionately more significant. The locally-reduced cross section portions described in this document are formed by pairs of circular holes. The shape of the locally reduced cross section portions undesirably concentrates the plastic strain at the narrowest portion. This concentration of plastic strain without any provision for controlling the level of plastic strain makes the stent highly vulnerable to failure. [0012] U.S. Pat. No. 6,241,762, entitled "EXPANDABLE MEDICAL DEVICE WITH DUCTILE HINGES" filed Oct. 10, 1998 and assigned to Conor Medsystems Inc., is incorporated herein by reference in its entirety. This patent discloses a stent design that provides a stent with large, non-deforming strut and link elements, which can contain holes without compromising the mechanical properties of the strut or link elements, or the device as a whole. Further, these holes may serve as large, protected reservoirs for delivering various beneficial agents to the device implantation site. [0013] In view of the drawbacks of prior art stents, it would be advantageous to have an expandable medical device with low radial recoil and high radial force (circumferential crush strength) independent of the intrinsic properties of the material of fabrication. [0014] It would further be advantageous to have a tissue-supporting device that could be expanded to a range of final diameters independent of the means of expansion or the force levels applied. [0015] It would also be desirable to control the maximum material strain to a desired level wherein when the expandable medical device is deployed the material remains below its elastic limit, and may be expanded to a greater diameter if necessary without plastically deforming the material. SUMMARY OF THE PRESENT INVENTION [0016] The present invention makes novel use of hinges to provide both the spring force and two degrees-of-freedom motions required for a true self-locking expandable medical device design. In addition to that above the present invention provides a novel expandable medical device that is capable of self-expansion or expansion through the use of a balloon catheter or similar device. Further still, the expandable medical device according to the present invention may be utilized to deliver a beneficial agent to the area adjacent to the expanded medical device. [0017] In accordance with one aspect of the present invention there is provided an expandable medical device including a plurality of elongated beams. The plurality of elongated beams are joined together to form a substantially cylindrical device. The cylindrical device is expandable from a cylinder having a first diameter to a cylinder having a second diameter, the plurality of the elongated beams having a beam width in a circumferential direction. A plurality of hinges connecting the elongated beams have a hinge width, wherein the hinge width is smaller than the beam width. A pawl is disposed adjacent to and substantially parallel to the hinge prior to expansion of the medical device and a plurality of teeth are adapted to receive the pawl. [0018] In accordance with another aspect of the present invention there is provided an expandable medical device including a cylindrical tube and a plurality of axial slots formed in the cylindrical tube in an arrangement to define a network of elongated struts, wherein each of the elongated struts are radially displaced from adjacent struts, and each elongated strut further includes at least one tooth disposed thereupon. A pawl formed between the elongated struts has a distal end adapted to be received by the tooth. A plurality of hinges formed between the elongated struts allow the cylindrical tube to be expanded from a first diameter to a second diameter by bending of the hinges and engaging the distal end of the pawl with the tooth. [0019] In accordance with another aspect of the present invention there is provided an expandable medical device including, a cylindrical expandable body of Nitinol and a locking feature for locking the expanded body in an expanded position, wherein the locking mechanism prevents recoil of the expanded body of greater than 5 percent. [0020] In accordance with another aspect of the present invention there is provided a method of processing an expandable medical device, the method including the steps of fabricating a cylindrical expandable medical device from martensitic Nitinol, where the expandable medical device is fabricated with a first unexpanded diameter. Expanding the cylindrical expandable medical device to an expanded second diameter, wherein deformation during expansion is confined to a hinge and the deformation is below the elastic limit of the material. Processing the expandable medical device, and restoring the expandable medical device to the unexpanded first diameter by applying heat to the expandable medical device. Continue reading... Full patent description for Expandable medical device with locking mechanism Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Expandable medical device with locking mechanism 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 Expandable medical device with locking mechanism or other areas of interest. ### Previous Patent Application: Thin-layered endovascular silk-covered stent device and method of manufacture thereof Next Patent Application: Flap-cover aneurysm stent Industry Class: Prosthesis (i.e., artificial body members), parts thereof, or aids and accessories therefor ### FreshPatents.com Support Thank you for viewing the Expandable medical device with locking mechanism patent info. IP-related news and info Results in 0.17165 seconds Other interesting Feshpatents.com categories: Accenture , Agouron Pharmaceuticals , Amgen , AT&T , Bausch & Lomb , Callaway Golf |
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