Patent Publication Number: US-2017348122-A1

Title: Expandable stent having a constant length

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/213,668, filed Mar. 14, 2014, which claims the benefit of the U.S. Provisional Application No. 61/794,924, filed Mar. 15, 2013. Each of these applications are incorporated by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates generally to stents and, more particularly, to stents that maintain a substantially constant length when moved from a collapsed position to a deployed position. 
     Related Art 
     Stents are commonly used to treat vessel diseases such as stenoses, strictures, thrombosis, and aneurysms. Stents can be configured to perform a variety of different functions such as, for example and without limitation, reinforcing vessel walls and increasing cross sectional area and, thus, volumetric flow. Typically, stents are employed to restore or maintain healthy blood flow. 
     Various types of stent architectures are known in the art. One shortcoming of conventional stents is that they may have deficiencies described collectively as “edge effects.” In one aspect, the overall length of the stent shortens as the stent is moved from a collapsed configuration to a deployed configuration. Edge effects due to stent shortening can lead to unpredictability of stent placement. In aspects where a balloon is used to deploy the stent, if the overall length of the stent decreases during deployment and the balloon is exposed, the balloon can over expand at one or both end of the stent. Edge effects due to balloon over expansion can lead to injury of the vessel wall. 
     Accordingly, a need exists for stents configured to maintain a substantially constant length between a collapsed and a deployed configuration. 
     SUMMARY 
     It is to be understood that this summary is not an extensive overview of the disclosure. This summary is exemplary and not restrictive, and it is intended to neither identify key or critical elements of the disclosure nor delineate the scope thereof. The sole purpose of this summary is to explain and exemplify certain concepts of the disclosure as an introduction to the following complete and extensive detailed description. 
     Aspects of the present invention comprise an expandable stent for placement in a blood vessel comprising a plurality of spring members and a plurality of biasable couplings connecting adjacent spring members. Here, the plurality of spring members defines a stent having a longitudinal axis, wherein the plurality of spring members can be configured to move between a collapsed position and a deployed position. Each spring member can comprise a plurality of integrally connected wave members formed in a ring shape that can be positioned in a ring plane substantially perpendicular to the longitudinal axis. Further, each wave member can comprise a plurality of curved segments having a plurality of substantially straight segments disposed therebetween. In other aspects, the plurality of biasable couplings have opposing ends  122 ,  124 , wherein one end of one biasable coupling can be joined to a portion of the respective curved segment of a select wave member of a selected spring member and the other opposing end of the one biasable coupling can be joined to a portion of the respective curved segment of another select wave member of an adjacent spring member. It is contemplated that the plurality of biasable couplings can be adapted to elongate upon movement of the stent from the collapsed position to the deployed position to proportionally compensate for the decrease in amplitude of the plurality of wave members of the plurality of spring members such that the stent maintains a substantially constant length. 
     Additional features and advantages of exemplary aspects of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of such exemplary aspects. The features and advantages of such aspects may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features will become more fully apparent from the following description and appended claims, or may be learned by the practice of such exemplary aspects as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects and together with the description, serve to explain the principles of the methods and systems. 
         FIG. 1  illustrates one implementation of a stent of the present disclosure, where the stent has been cut longitudinally and laid flat. 
         FIG. 2  illustrates a detailed view of one implementation of a biasable coupling of the present disclosure. 
         FIG. 3  illustrates a perspective view of one implementation of a stent of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention can be understood more readily by reference to the following detailed description, examples, drawing, and claims, and their previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that this invention is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. 
     The following description of the invention provided as an enabling teaching of the invention in its best, currently known aspect. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the invention described herein, while still obtaining the beneficial results described herein. It will also be apparent that some of the desired benefits described herein can be obtained by selecting some of the features described herein without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances and are a part described herein. Thus, the following description is provided as illustrative of the principles described herein and not in limitation thereof. 
     Reference will be made to the drawings to describe various aspects of one or more aspects of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of one or more aspects, and are not limiting of the present disclosure. Moreover, while various drawings are provided at a scale that is considered functional for one or more aspects, the drawings are not necessarily drawn to scale for all contemplated aspects. The drawings thus represent an exemplary scale, but no inference should be drawn from the drawings as to any required scale. 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding described herein. It will be obvious, however, to one skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well known aspects of stent technology have not been described in particular detail in order to avoid unnecessarily obscuring aspects of the disclosed aspects. 
     As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. 
     Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers or steps. “Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal aspect. “Such as” is not used in a restrictive sense, but for explanatory purposes. 
     As shown in  FIGS. 1-3 , aspects of the present invention comprise an expandable stent  100  for placement in a blood vessel comprising a plurality of spring members  102  and a plurality of biasable couplings  118  connecting adjacent spring members, wherein the stent is adapted to maintain a substantially constant length when moved between a collapsed position and a deployed position. In certain aspects, the stent  100  can be adapted to be balloon-expandable. In certain other aspects, the stent can be adapted to have a deployed radial strength sufficient to overcome the recoil forces applied by the blood vessel and, optionally, the plaque layer, within which it is deployed. In certain other aspects, the stent is configured not to develop strains greater than about 45% in the stent material upon movement from the collapsed position to the deployed position. It is also contemplated that the stent  100  can be formed from conventional stent materials, for example and without limitation, stainless steel, Cobalt Chromium alloy and the like. 
     In certain aspects, the plurality of spring members  102  defines a stent  100  having a longitudinal axis  101 , wherein the plurality of spring members can be configured to move between a collapsed position and a deployed position. It is contemplated that each spring member  102  can comprise a plurality of integrally connected wave members formed in a ring shape that can be positioned in a ring plane substantially perpendicular to the longitudinal axis of the stent  100 . In other aspects, each wave member  104  can comprise a plurality of curved segments having a plurality of substantially straight segments  116  disposed therebetween. 
     In another aspect, the plurality of curved segments of each wave member  104  can have a radius  114 . In certain aspects, the radius  114  can be from about 0.05 to about 0.15 mm and, more preferably, can be about 0.1 mm. In other aspects, the radius should be sufficiently large so that the change in the radius due to deployment will not result in strains greater than 45% in the stent  100  material. Conversely, in additional or alternative aspects, the radius should be sufficiently small so that the stem can be crimped sufficiently tight over a balloon. 
     In another aspect, the plurality of substantially straight segments  116  of each wave member  104  can further comprise a width and a thickness. In one aspect, the width and thickness are substantially equal such that the cross-section of the plurality of substantially straight segments is substantially square. In some aspects, the width of the substantially straight segment can be about 0.05 inches and, in additional or alternative aspects, the thickness of the substantially straight segment can be about 0.05 inches. 
     In other aspects, each adjacent pair of straight segments  116  in each wave member  104  can define a wave angle. In one aspect, the wave angle  110  can be an acute angle when the stent  100  is in a collapsed position. In another aspect, the wave angle can be about 90 degrees when the stent is in a deployed position. In light of the present disclosure, one skilled in the art will appreciate that the radial force exerted by the stent  100  can depend on both the stent diameter and the wave angle and increases as the stent is moved from the collapsed to the deployed position. It is contemplated that the stent can be adapted to have a deployed radial strength sufficient to overcome the recoil forces applied by the blood vessel and, optionally, the plaque layer, within which it is deployed. 
     In other aspects, the plurality of interconnected wave members  104  of each spring member can comprise from about  4  to about  12  wave members, more preferably, from about  6  to about  10  wave members and, most preferably, about  8  wave members. In other aspects, the wave amplitude  108  and wave angle  110  can determine the number of wave members of a spring member. 
     In one aspect, each wave member  104  of the spring member  102  can have an amplitude  108 . In operation, when the stent  100  is moved from the collapsed position to the deployed position, the radii  114  of each curved segment  106  and the wave angle  110  of each wave member  104  increases, while the wave amplitude  108  decreases. Here, the wave amplitude  108  determines the moment applied on each of the plurality of curved segments and can affect the pressure at which the stent begins to expand. In one aspect, the stent  100  can be configured to expand at a relatively low pressure, i.e., between about 3 to about 5 ATM. In light of the present disclosure, one skilled in the art will appreciate the wave amplitude should not be too small and, conversely, if the wave amplitude is too high, the wave angle will not increase enough rendering the stent with insufficient radial force to withstand the recoil forces of the blood vessel and any plaque layer upon deployment. In light of the foregoing, in sonic aspects, the amplitude can be from about 1 to about 2 mm and, more preferably, can be about 1.5 mm. 
     In other aspects, the plurality of biasable couplings  118  have opposing ends  122 ,  124 , wherein one end of one biasable coupling can be joined to a portion of the respective curved segment  106  of a select wave member  104  of a selected spring member  102  and the other opposing end of the one biasable coupling can be joined to a portion of the respective curved segment  106  of another select wave member  104  of an adjacent spring member. It is contemplated that the plurality of biasable couplings can be adapted to elongate upon movement of the stent  100  from the collapsed position to the deployed position to proportionally compensate for the decrease in amplitude of the plurality of wave members of the plurality of spring members  102  such that the stent maintains a substantially constant length. 
     In further aspects, the plurality of biasable couplings  118  can further comprise a plurality of flexible struts, each having a central axis  120  that is rotationally offset from the longitudinal axis of the stent  100 . In other aspects, the plurality of flexible struts comprises a plurality of flexible S-shaped struts, each having a central axis  120  that is rotationally offset from the ring plane and, thus the longitudinal axis of the stent. In even further aspects, the plurality of flexible struts can be rotationally offset from either the longitudinal axis of the stent or the ring plane at a selected angle. In even further aspects, a selected plurality of flexible struts can be offset in a first direction by the selected angle while each adjacent plurality of flexible struts is offset in a second direction by the selected angle, where the first direction is opposite to the second direction. In operation, rotationally offsetting the central axes of the plurality of flexible struts from the longitudinal axis of the stent can improve the longitudinal flexibility of the stent as compared to a configuration where the plurality of flexible struts each have a central axis  120  aligned with the longitudinal axis of the stent  100  and, thus, increase the resistance to longitudinal bending of the stent. 
     In other aspects, where each of the plurality of biasable couplings  118  comprises one end joined to a portion of the respective curved segment  106  that is spaced apart from and lies to a first side of the apex  112  of a selected wave member  104  of a selected spring member  102 and the opposing end of the one biasable coupling is joined to a portion of the respective curved segment  106  that is spaced apart from and to a second side of the apex  112  of another select wave member  104  of an adjacent spring member. In even further aspects, the portions of the respective curve segments to which the opposing ends  122 ,  124  of the biasable couplings  118  are joined can be selected to be the that portion of the respective curve segment that adjoins the straight segment. In light of the present disclosure, one skilled in the art will appreciate that one end of a selected biasable coupling (or one apex of a select wave member of a spring member) can be stretched relative to the second end of the biasable coupling (or the apex of another select wave member of an adjacent wave member) during movement of the plurality of spring members  102  from a collapsed position to a deployed position. In other aspects, it is contemplated that plurality of biasable couplings elongate to proportionally compensate for the decrease in amplitude of the plurality of wave members of the plurality of spring members such that the stent  100  maintains a substantially constant length. 
     In other aspect, stents of the present disclosure can be designed such that each curved segment  106  of the wave member  104  of the two adjacent spring members  102  jointed via a biasable coupling can be configured so as not to substantially change their respective circumferential positions during movement of the stent  100  between the collapsed and the deployed positions. 
     In alternate aspects, stents of the present disclosure can be designed such that each curved segment  106  of the wave member  104  of the two adjacent spring members  102  joined via a biasable coupling can be configured to selectively change their respective circumferential positions during movement of the stent  100  between the collapsed and the deployed positions. Here, due to the friction between the spring members and the balloon, the plurality of biasable couplings  118  can elongate while the stent  100  expands and the wave amplitude  108  decreases, thus maintaining the overall length of the stent. In even further aspects, while the spring members  102  expand at both sides of a given biasable coupling, they apply a moment on the biasable coupling operable to open the biasable coupling and assist in elongation thereof. 
     It is further contemplated that the stents described herein can be designed to selectively elongate along the stent axis. 
     In light of the present disclosure, one skilled in the art will appreciate that the number of biasable couplings  118  joining adjacent spring members  102  can impact the longitudinal flexibility of the stent  100  and, in turn, the ability of the stent to conform to the blood vessel curvature. I.e., the fewer biasable couplings joining adjacent spring members, the more longitudinally flexible the stent can be. Conversely, longitudinal stability can be beneficial during crimping, expansion and when expanded in the artery. Accordingly, the number of biasable couplings between adjacent spring members can be from about 2 to about 8 and, more preferably, from about 3 to about 4. 
     In yet other aspects, each of the plurality of biasable couplings  118  can have at least one of a width and a thickness thinner than that of each of the plurality of spring members  102  in order to facilitate elongation of the plurality of biasable couplings. In one exemplary embodiment where the each of the plurality of biasable couplings comprises an flexible S-shaped strut, at least one of the width and the thickness of each of the plurality of struts can be about 0.003″, the internal radius  114  of the strut can be about 0.07 mm and the distance between the internal radii of the strut can be about 0.4 mm. 
     In yet other aspects, the length of the connection joining the biasable couplings  118  to the spring members  102  can be minimized so as to avoid thickening of the curved segment  106  of the respective wave member  104  sufficient to materially increase the material strain during movement of the stent  100  between the collapsed and deployed positions. 
     The present invention can thus be embodied in other specific forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.