Patent Publication Number: US-2015073544-A1

Title: Superabsorbent coated stents for vascular reduction and for anchoring valve replacements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims priority to U.S. Provisional Patent Application No. 61/606,599, filed Mar. 5, 2012. The content of that patent application is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to stents for insertion into vascular spaces including veins and arteries as well as in the right ventricular outflow tract of the heart and, more particularly, to stents including superabsorbent material that slowly expands to the size of the dilated right ventricular outflow tract or blood vessel in which a stent is to be mounted, thereby facilitating anchoring of the stent and preventing leakage. 
     BACKGROUND 
     Stents are widely used to treat diseased blood vessels and to help to anchor valve replacements in the heart. However, such stents have limited use in large or dilated blood vessels or in large areas such as the right ventricular outflow tract where chronic regurgitation results in dilation and distortion of the target area to the point where it is too large to allow proper mounting of conventional valved stents. This makes it very difficult to mount replacement pulmonary or tricuspid valves using stents as the anchoring mechanism. Also, since the stents are typically uniform in shape, they may permit leakage around the stent due to non-uniformities at the mounting site. A vascular reduction mechanism is desired that permits the stent to mount more firmly in dilated vascular spaces (such as veins, arteries, valve annuli) and to prevent leakage around the stent. The present invention addresses these needs in the art. 
     SUMMARY 
     The present inventors have addressed the above needs in the art by providing a stent-based platform adapted for percutaneous delivery to and anchoring in a pulmonary or tricuspid valve annulus. Implantation of this platform creates a uniform landing zone for subsequent percutaneously delivered valved-stent implantation into the pulmonary or tricuspid valve annulus. The platform includes an at least partially self-expanding stent and a cuff comprising an absorbent material disposed at least partially circumferentially around the outer and inner surfaces of the stent-based platform. Upon placement at an implantation site such as the pulmonary or tricuspid valve annulus, the absorbent material expands by absorption of a fluid to create a substantial seal between the vessel wall/annulus and the outer portion of the stent. The inner layer of superabsorbent material will expand to create a zone that is uniform in diameter and shape, thereby creating a customizable landing zone for subsequent valved-stent implantation. Preferably, the expansion of the superabsorbent material is delayed for a time sufficient to permit positioning of the stent at the implantation site. 
     The above needs in the art are also met by providing a vascular reducer comprising an at least partially self-expanding stent and a sealing cuff comprising an absorbent material disposed at least partially circumferentially around the outer and inner surface of the stent. Upon installation in the blood vessel, the absorbent material expands by absorption of a fluid to substantially adhere the stent at an implantation site. The cuff expansion is preferably delayed for a time sufficient to permit positioning of the stent at the implantation site. 
     In exemplary embodiments, the absorbent material is implemented as a bi-layer system in which an outer layer is a hydrophobic material that prevents the absorbent material from expanding while the stent is being placed. The outer layer is also adapted to elute off slowly to allow underlying absorbent material to expand to permit positioning of the stent. The absorbent material may be based on poly(acrylic acid) that is cross-linked with poly(ethylene glycol) diacrylate where the swelling volume and softness of the absorbent material is varied by manipulating the extent of cross-linking. Also, the hydrophobic material may comprise a water proof polymer barrier deposited on the absorbent material using initiated chemical vapor deposition. 
     Embodiments within the scope of the invention as described in the following detailed description and claimed in the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various novel aspects of the invention will be apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings, of which: 
         FIG. 1  illustrates a vascular stent that is covered on both the inside and outside with a cuff of superabsorbent (SA) material. 
         FIG. 2  illustrates the device of  FIG. 1  compressed for insertion into an angioplasty balloon for delivery to the implantation site. 
         FIG. 3  illustrates the compressed vascular stent of  FIG. 2  prior to deployment at the implantation site. 
         FIG. 4  illustrates the deployed device of  FIG. 1  where the superabsorbent material has expanded in a pulmonary annulus for anchoring. 
         FIG. 5  illustrates the hour-glass shape formed by the expanded internal cuff of the device of  FIG. 1 . 
         FIG. 6  illustrates the deployed device of  FIG. 1  with a deployed valved stent mounted therein. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The invention will be described in detail below with reference to  FIGS. 1-6 . Those skilled in the art will appreciate that the description given herein with respect to those figures is for exemplary purposes only and is not intended in any way to limit the scope of the invention. All questions regarding the scope of the invention may be resolved by referring to the appended claims. 
     The invention broadly addresses the problem of deploying devices in dilated body lumens and/or in large cavities by reducing the diameter to an appropriate and uniform size/dimension for subsequent implantation of a stent, a valved stent, or some other device. The superabsorbent coated stent can also provide a platform for accepting a pulmonary or tricuspid valve prosthesis. 
     In accordance with this embodiment of the invention, a successful percutaneously placed “vascular reducer” has the following characteristics:
         1. Deliverable using established stenting techniques;   2. Low profile for delivery via standard vascular sheath sizes;   3. Upon expansion, it should be large enough in diameter for secure deployment into dilated right ventricle outflow tracts; and   4. Provide an appropriate “landing zone” (“hourglass shaped”) for subsequent deployment and secure anchoring of a pulmonary valved-stent.       

     A device meeting these requirements is shown in  FIG. 1 . The device of  FIG. 1  includes a vascular stent  10  (e.g., stainless steel, Cobalt, chromium or Nitinol) covered on both the inside and outside with a cuff  20  of superabsorbent (SA) material. The interior covering of the stent is a tailored cuff filled with superabsorbent material that is engineered to blossom into a firm, hourglass shape upon expansion; making the lumen of the stent circumferentially uniform. This hourglass shaped lumen serves as an ideal landing site for valved-stent deployment and anchoring. 
     As shown in  FIG. 2 , the device of  FIG. 1  compresses for insertion into an angioplasty balloon  30  for delivery, for example, to a pulmonary valve annulus ( FIG. 3 ).  FIG. 4  shows the device once the superabsorbent material begins to expand in the pulmonary valve annulus. As illustrated, the superabsorbent material of the cuff  20  expands to fit the contours of the mounting site.  FIG. 5  illustrates the hour-glass shape formed by the expanded superabsorbent cuff  20 , and  FIG. 6  illustrates the device with a deployed valved stent  40  mounted therein. 
     The outside covering of the cuff  20  on the stent  10  expands when the stent is deployed into the deployment position, for example, the right ventricle outflow tract (RVOT). This outer covering of the cuff  20  serves to fill in potential gaps between the stent  10  and the vascular walls thus improving apposition and preventing leakage around the stent  10 . The superabsorbent material is preferably implemented as a bi-layer system in which the outer layer is a hydrophobic material that will prevent the super absorbent material from expanding while the stent  10  is being placed. This layer is designed to elute off slowly to ultimately allow the underlying superabsorbent material to expand. In this way, a low profile covered stent  10  can be advanced through the vasculature and then deployed using standard stenting techniques. The device will then “morph” into its predetermined shape as the SA material expands to fill the vascular space. 
     In an exemplary embodiment, the super-absorbent material best suited for this application is based on poly(acrylic acid) that is cross-linked with poly(ethylene glycol) diacrylate. The cross-linking can be controlled by a photopolymerization mechanism. The overall swelling volume and softness can be optimized by manipulating the extent of cross-linking of the material. In addition, the expansion of the superabsorbent material needs to be delayed while the device is being placed. To achieve this, the hydrophobic outer layer in an exemplary embodiment incorporates a coating technology called initiated chemical vapor deposition (iCVD) to place a water proof polymer barrier on the surface of the cuff fabric. iCVD is a proven technique that can synthesize and integrate polymer coatings on complex 3D structures like the cuff fabric. The polymer is based on copolymerization of hydrophilic (N-vinyl-2-pyrrolidone/methacrylic acid) and hydrophobic (alkyl acrylate) components that are designed to harmlessly elute off after a given amount of time thus allowing the super absorbent material to expand and seal. The water absorption delay can be engineered by manipulating the structure and properties of the coating polymer through control of iCVD processing, and will be dictated by device placement time which should be approximately 30 minutes. 
     Those skilled in the art will appreciate that the invention is particularly useful in specific circumstances where vascular occlusion and/or flow reduction is necessary (e.g., pulmonary artery banding, PDA occlusion, or aneurysm/pseudoaneurysm treatment). However, the device of this embodiment also has multiple applications for patients with pulmonary valve incompetence following surgical and/or catheter-based intervention. The majority of these patients would benefit from pulmonary valve replacement; however, most are not eligible for the minimally invasive approach due to the limitations in the current technology. Surgical valve replacement is an option, but it is associated with significant morbidity. Thus, definitive therapy is often delayed subjecting patients to chronic pulmonary insufficiency, leaving them at risk for right ventricular failure. This embodiment can be used to limit such valve incompetence. 
     Those skilled in the art will further appreciate that the invention has several advantages. Firstly, it can be implanted into the RVOT using standard stenting techniques, with which all interventional cardiologists are familiar. Secondly, the device maintains a low profile for percutaneous delivery, minimizing vascular trauma. Thirdly, the engineered superabsorbent cuff forms the ideal landing zone (size, shape and firmness) for percutaneous valved-stent implantation. Other advantages will be apparent to those skilled in the art. 
     Those skilled in the art will also appreciate that the invention may be applied to other applications and may be modified without departing from the scope of the invention. For example, those skilled in the art will appreciate that the devices and techniques of the invention may be used to replace the tricuspid valve as well as the pulmonary valve. Also, the devices and techniques of the invention may be used to provide a vascular reducer when a reduced vessel diameter is desired, as when mounting a stent. Accordingly, the scope of the invention is not intended to be limited to the exemplary embodiments described above, but only by the appended claims.