Abstract:
A stent may help to reconstruct tissue in a vessel by causing the tissue to re-epithelialize. The stent may include a biodegradable frame and a sheet that coats the frame. The sheet may contain a biological material and may flex in unison with the frame in a radial direction. When placed in a vessel, the stent may at least partially conform to at least a portion of a vessel wall. The stent may be capable of being absorbed over a period of time, such as five years, one year, or six months. The stent may flex as the vessel wall dilates and constricts. The stent may be placed in any type of vessel including an artery and mobile vessels. The biodegradable frame may be made of a poly-lactide and/or magnesium. The sheet may contain a biological material including biologic arterial graft and/or an acellular dermal matrix.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a device for tissue reconstruction. The invention concerns, more particularly, a biodegradable stent having a sheet containing a biological material that is used to reconstruct tissue in blood vessels. 
         [0003]    2. Description of Background Art 
         [0004]    A vessel wall may be damaged in many ways including chronic wear and weakening of the tissue that may eventually lead to weakened ability to dilate and constrict the wall of the vessel (e.g., aneurysm, artherosclerosis, angina, stroke, and other common types of ischemia). Stents are commonly used for repairing vessel walls in patients suffering from chronic and acute vessel tissue injuries. Vessels may also suffer acute trauma-related injuries such as from gunshot wounds, puncturing, bruising, or otherwise damaging the vessel wall by an object. Oftentimes, vessel damage leads to serious medical conditions and may result in long-term injury or even death of a patient. 
         [0005]    When a vessel wall ruptures, gets punctured, cut, or otherwise damaged, blood may leak through the damaged portion of the vessel into the surrounding tissue causing significant damage. Such an injury causes blood pressure through the damaged portion of the vessel to drop and may prevent oxygenated blood from reaching a particular organ or other tissue destination or deoxygenated blood from reaching the lungs. 
         [0006]    Endovascular surgery may offer a solution for repairing damage to the vessels and/or preventing future damage to the vessels. A may provide a reinforcement to a vessel wall to a damaged area. For example, an expandable stent, in its retracted form, may be positioned over a balloon catheter having a guide wire attached at one end. The stent may be delivered to the site of the injury. The stent may be expanded to fit the shape of the vessel wall by controlling the inflation of the balloon catheter. The stent may remain in contact with the vessel wall as a result of the radial pressure from blood flowing through the injured portion of the vessel wall. Examples of commonly known expandable stents include, U.S. Pat. No. 4,655,771 to Wallsten, U.S. Pat. No. 5,061,275 to Wallsten, et al., and U.S. Pat. No. 5,645,559 to Hachtmann, et al. 
         [0007]    Most stents are permanently implanted into the vessel of a patient who suffered a vessel injury. Oftentimes, stents that are permanently implanted within a vessel cause complications over a length of time. This can be especially problematic with some young patients. One common complication that can occur is restonisis which can be caused by surrounding tissue reaction. In addition to the stent gradually blocking up the vessel, it is also possible that the stent can also fracture. 
         [0008]    Endografts are similar to the stents described above but are typically placed in a larger vessels and are typically used to repair damaged tissue or improve an otherwise unhealthy portion of a vessel, which in turn is intended to prevent leakages or ruptures in a vessel wall. The endografts have a stent-like frame and are covered by a synthetic material. The outside of the synthetic material is covered with an adhesive to adhere to the inside of a vessel wall. However, during this procedure, the endograft remains in place for life commonly requiring lifetime follow up to the site. 
       SUMMARY OF THE INVENTION 
       [0009]    Although stents and stent systems exist within the art, there is room for improvement. Accordingly, a stent graft that is partially or completely biodegradable would be a welcomed advancement in the art. Also, a stent that has these capabilities and is capable of expanding across mobile vessels and vessels that extends across a joint would also be beneficial. 
         [0010]    Aspects of the present invention involve a biodegradable stent graft for reconstructing tissue in a vessel. The stent may comprise a biodegradable frame and a sheet containing a biological material. The sheet may coat the biodegradable frame and may be capable of flexing in cooperation with the frame. The biodegradable frame and the sheet may be capable of flexing in a radial direction to at least partially conform to at least a portion of a wall of the vessel. 
         [0011]    In another aspect of the invention, a biodegradable stent graft may comprise a biodegradable frame and a sheet that may contain a biological material. The frame may have a plurality of discrete expandable elements. The sheet may coat at least a portion of the discrete expandable elements. The sheet may also be capable of adhering to the interior surface of a wall of a vessel. The frame and the sheet may be capable of expanding in cooperative engagement with each other to adhere to the shape of the interior surface of the wall of the vessel. 
         [0012]    In another aspect of the invention, a method of reconstructing tissue in a vessel includes positioning a delivery device at a site of damage in a vessel of a patient. The delivery device including a biodegradable frame and a sheet containing a biological material. The delivery device is affixed to a wall of the vessel at the site of damage, and is left in the vessel to permit the biodegradable frame to completely dissolve and be carried off in the blood stream. 
         [0013]    The advantages and features of novelty characterizing aspects of the present invention are pointed out with particularity in the appended claims. To gain an improved understanding of the advantages and features of novelty, however, reference may be made to the following descriptive matter and accompanying drawings that describe and illustrate various embodiments and concepts related to the invention. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    The foregoing Summary of the Invention, as well as the following Detailed Description of the Invention, will be better understood when read in conjunction with the accompanying drawings. 
           [0015]      FIG. 1  is a perspective view of a biodegradable stent graft, in accordance with aspects of the invention. 
           [0016]      FIG. 2  is a perspective view of an alternative embodiment of a biodegradable stent frame, in accordance with aspects of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The following discussion and accompanying figures disclose a biodegradable stent graft in accordance with various aspects of the present invention. Example embodiments of the stent graft is depicted in the figures and discussed below as having a configuration that is suitable for use in human vessels. The concepts disclosed with respect to human vessels may, however, be applied to any non-human vessel or other flexible tubular structure for a wide range of other utilities, including veterinary applications, for example, and may also be applied to various non-medical (non-health related) uses. Accordingly, one skilled in the relevant art will recognize that the concepts disclosed herein may have a wide range of applications and are not limited to the specific embodiments discussed below and depicted in the figures. 
         [0018]    In general, and according to an embodiment, a stent graft is provided for reconstructing tissue in a vessel may include a biodegradable frame and a sheet containing a biological material. The sheet coats the biodegradable frame. The sheet may be capable of flexing in unison with the frame. The frame and the sheet may be capable of flexing in a radial direction to at least partially conform to at least a portion of a wall of the vessel. 
         [0019]      FIG. 1  illustrates a first arrangement of a stent graft  100 . The stent graft  100  includes a biodegradable frame  104  and a sheet  102 . The sheet  102  surrounds and may coat the biodegradable frame  104  throughout at least a significant portion of the longitudinal length of the biodegradable frame  100 . In the depicted embodiments of  FIG. 1 and 2 , the sheet  102  does not extend to the longitudinal ends of the frame  104  and therefore leaves the end sections  103  of the frame  104  exposed. However, the sheet  102  can extend to the ends of the frame if desired. As assembled, the biodegradable frame  104  and the sheet  102  are capable of flexing in a radial direction to at least partially conform to at least a portion of a wall of a vessel to be repaired. 
         [0020]    It is understood that the biodegradable frame  104  may have the properties of any desired stent structure. Additionally, the biodegradable frame  104  is tubular shaped and is capable of sufficient flexing under desired conditions. In a first arrangement, as shown, the biodegradable frame  104  is made from an expandable wire form. In an alternate arrangement, the biodegradable frame is made from a perforated tube. If a wire form design is used, as shown, any desirable wire form configuration may be used. For example, as shown, the wire form may be made from a series of circumferential frame elements  105  that are longitudinally joined together by joining members  106 . According to this arrangement, the frame elements  105  are more flexible than the joining members  106  along the longitudinal direction of the stent graft  100 . 
         [0021]    The biodegradable frame  104  may be made of any suitable material. For example, in a first embodiment, the frame  104  is made from a magnesium alloy. In a second embodiment, the frame  104  is made from a poly-lactide which is a biodegradable, thermoplastic, aliphatic polyester derived from renewable resources, such as corn starch. In another embodiment, the frame  104  is made from an iron alloy. Biodegradable magnesium stents and poly-lactide stents are known in art and have been used as unshrouded devices to treat blockages in coronary arteries. By biodegradable, as used herein, it is meant that the frame substantially dissolves into small pieces, loses its shape, and is substantially carried off in the blood stream. In the blood stream, and based on the composition of the frame  104 , the broken off molecular sized pieces are hydrolyzed and filtered according to the body&#39;s normal processes. The biodegradable frame  104  is biodegradable in a blood vessel of an average human under standard conditions in a period of 5 years or less, 1 year or less, and/or 6 months or less based on the composition of the frame  104 . 
         [0022]    The sheet  102  is preferably made from materials and is configured to be incorporated into the natural tissue such that a vessel wall will grow into it. That is, the sheet  102  will be bioabsorbed in the patient. The sheet  102  is configured such that the vessel wall will fully grow into it under standard conditions in a period of 1 year or less, 6 months or less, and/or 2 months or less based on the material properties of the sheet  102 . In one arrangement, the sheet  102  is collagen-based such as a protein-based biologic collagen matrix. In another arrangement, the sheet may be an acellular dermal matrix. Alternatively, the sheet material can be derived from a biologic source, such as a pig intestine. In other embodiments, the sheet  102  may be made of any material suitable for tissue reconstruction including donated human skin, which may be skin from the patient himself. Accordingly, under such an approach, the skin would be taken from elsewhere on the patient&#39;s body and applied to outside of the frame  104 . The frame  104 /sheet  102  combination would be utilized as described below. 
         [0023]    In a first embodiment, the outer surface of the sheet  102  is adhesive free and the vessel wall will grow into it aided by the force applied to it from the frame  104  once deployed. The sheet  102 , and more specifically the outer surface of the sheet  102 , may include seeding cells (not shown) coupled to it. The seeding cells may be endothelial cells or stem cells from the patient or a matching donor. The seeding cells help promote cell ingrowth from the inner vessel wall to the sheet  102 . 
         [0024]    The sheet  102  is attached to the frame  104  in any desirable manner. In a first arrangement, the sheet  102  is sewn to the frame  104  at selected points along the length and circumference of the frame  104  based on the design of the frame  104 . Element  108  depicts sewing points  108  between the sheet  102  and the frame  104 . Alternatively, or in addition, the sheet  102  may be joined to the frame  104  by suitable body-compatible adhesives such as fibrin glue. In a third embodiment, not shown, the stent graft has a sheet inside the frame in addition to the outer sheet  102 . The inner and outer sheets are compressed or are heat sealed with the frame  104  therebetween. 
         [0025]      FIG. 2  depicts an alternative embodiment to  FIG. 1 . More specifically, the embodiment of  FIG. 2  differs from that of  FIG. 1 , in that the frame is not a unitary element. Rather, the frame is constructed of at least two longitudinally spaced independent frame sections. In the depicted embodiment of  FIG. 2 , the frame is formed from at least four frame sections  104   a,    104   b,    104   c,  and  104   d.  Flexibility along the longitudinal axis is enhanced by the gap sections  107  of the stent graft  100   a  where there is a circumferential gap in the frame as the flexibility is based on the characteristics of the sheet  102 . 
         [0026]    The biodegradable stent graft  100 ,  100   a  may be used to perform a repair to any desired vessel such as an artery or a vein. More specifically, the biodegradable stent graft  100 ,  100   a,  can be used to deliver a sheet or layer of biological material to a location in a vessel or other tubular structure for tissue ingrowth. The vessel that can be repaired with the biodegradable stent graft  100  can be a vessel in any desired location of a body, including, but not limited to, arms, shoulders, legs, a chest, a neck, and an abdomen. Particular vessels that would gain benefit from using the biodegradable stent graft  100 ,  100   a  include, but are not limited to the distal subclavian artery, the brachial artery, the axillary artery, the proximal femoral artery, the popliteal artery, the carotid artery, and the iliac artery. Additional benefits can also be obtain by use in repairing vessels that tend to be mobile and/or vessels that extend through or across at least a portion of a joint. 
         [0027]    Like known deployment approaches for stents, the biodegradable stent graft  100 ,  100   a  may be designed to be expanded by the dilation of a balloon catheter. Alternatively, the frame  104  may be designed to have properties to be self-expandable. By way of example, the deployment of the biodegradable stent graft  100 ,  100   a  is described below as if performed a balloon catheter. This balloon catheter deployment process includes steps similar to existing methods for deploying a permanent stent with a balloon catheter. 
         [0028]    In one procedure method, the first end of guide wire may be inserted into a femoral artery. It can then be maneuvered through the vessels in the body to and past the location of the damaged portion of the desired vessel. The balloon catheter (in a deflated state) is guided over the guide wire. The balloon catheter preferably has the biodegradable stent graft  100 ,  100   a  positioned on it so it can be centered at the location of the damaged portion of the vessel. The balloon catheter is inflated from outside the patient&#39;s body at or near the opposing end of the guide wire. The biodegradable stent graft  100 ,  100   a  expands in the radial direction due to the inflation of the balloon. This therefore results in the biodegradable stent graft  100 ,  100   a  expanding at the site of the damaged vessel. The sheet  102  adheres to the interior surface of the vessel wall and remains in the expanded state due to the geometry and properties of the frame  104 . The balloon catheter may be deflated and removed. The biodegradable stent graft  100  remains in the vessel at the site of damage and supports and patches the vessel wall. 
         [0029]    Based on the materials used, over a period of time, such as 5 years or less, 1 year or less, or 6 months or less, the frame  104  biodegrades into small pieces and is substantially carried off in the blood stream. In the blood stream, and based on the composition of the frame  104 , the broken off molecular sized pieces are hydrolyzed and filtered in the body&#39;s normal processes. The sheet  102  may be bioabsorbed in the vessel wall within preferably shorter limits of time such as a year or less, 6 months or less, or 2 months or less. Effectively, the frame  104  serves as a delivery system for the grafting sheet  102 . It initially supports the sheet  102  and applies a radial force to aid in the ingrowth. Over time, the after the ingrowth is effected, the frame  104  will biodegrade in the patient and the sheet  102  will be bioabsorbed. This ends up leaving an ideal result—a permanently patched vessel wall with a bioabsorbed patch and no residual stenting structure. This also eliminates situations of permanent stresses and strains to the repaired vessel. The biodegradability and the bioabsorption of the stent graft  100 ,  100   a  also provides other advantages such as enabling the endovascular therapy rather than more invasive alternatives when a patient has a damaged vessel in a location that is subject to a high degree of movement such as at or near a joint. This type of endovascular therapy would result in a lower surgical risk for the patient, and a faster recovery time. 
         [0030]    The above discussion details the structure and configuration of biodegradable stent grafts, as depicted in the figures. Various modifications may be made to these biodegradable stent grafts without departing from the intended scope of the present invention. For example, the biodegradable frame and the sheet may be made of any suitable material that may not be currently known in the art. 
         [0031]    The present invention is disclosed above and in the accompanying drawings with reference to a variety of embodiments. The purpose served by the disclosure, however, is to provide an example of the various features and concepts related to the invention, not to limit the scope of the invention. One skilled in the relevant art will recognize that numerous variations and modifications may be made to the embodiments described above without departing from the scope of the present invention, as defined by the appended claims.