Abstract:
An apparatus ( 10 ) for grafting of a blood vessel ( 12 ) and a method of forming the apparatus ( 10 ) is provided. The apparatus ( 10 ) comprises an expandable support member ( 16 ) having inner and outer surfaces ( 36  and  34 ). The outer surface ( 34 ) of the expandable support member ( 16 ) is for engaging and adhering to an inside surface ( 68 ) of the blood vessel ( 12 ). A layer of biological tissue ( 14 ) is attached to the inner surface ( 36 ) of the support member ( 16 ). The layer of biological tissue ( 14 ) has an uninterrupted inwardly facing surface ( 50 ) for extending confluently with the inside surface ( 68 ) of the blood vessel ( 12 ) to provide resistance to thrombosis and platelet deposition.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to an endovascular prosthesis and to a method of forming the endovascular prosthesis.  
         BACKGROUND OF THE INVENTION  
         [0002]    Surgical procedures in which a cardiovascular prosthesis is implanted into a patient&#39;s blood vessel are common in treating many vascular disorders. For example, one common type of cardiovascular prosthesis is an endovascular prosthesis that is used to strengthen a blood vessel wall in the location of an aneurysm, or to open an occlusion in a blood vessel.  
           [0003]    A typical endovascular prosthesis includes a flexible, tubular member, made of fabric or PTFE, that may be anchored with sutures or carried by one or more support structures known as stents. Generally, each stent is formed from a material having an elasticity sufficient to permit radial expansion of the stent and having a strength sufficient to prevent radial collapse or burst. Such stents are typically formed from stainless steel, titanium, Nitinol, or a suitable plastic.  
           [0004]    A common endeavor in the field of cardiovascular prosthetics is to increase the patency rate of prostheses. Thrombosis and platelet deposition on surfaces of a cardiovascular prosthesis reduce the patency rate of the prosthesis. For example, thrombosis and platelet deposition within an endovascular prosthesis may occlude the conduit defined by the endovascular prosthesis.  
           [0005]    Many factors contribute to thrombosis and platelet deposition on the surfaces of known cardiovascular prosthesis. The most common factors are dependent upon the material or materials forming the inner surface of the conduit of the endovascular prosthesis. Typically, thrombosis and platelet deposition begin to occlude the conduit of the endovascular prosthesis when the material or materials forming the conduit of the endovascular prosthesis are foreign to the patient&#39;s body. A thrombus begins to form on the inner surface of the conduit of the endovascular prosthesis and extends annularly about the inner surface of the conduit. Eventually, the thrombus can severely restrict blood flow through the conduit defined by the endovascular prosthesis and, if left untreated, can completely occlude the conduit.  
           [0006]    Additionally, thrombosis and platelet deposition may occur as a result of irregularities on the inner surface of a cardiovascular prosthesis. The irregularities may be formed by the structure of an inner stent that is used to support the cardiovascular prosthesis, or may be formed by the inner surface of the flexible member used for the prosthesis.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is an apparatus for grafting of a blood vessel or other portion of the cardiovascular system. The blood vessel has an inside surface that defines a conduit for directing blood flow. The apparatus comprises an expandable support member having inner and outer surfaces. The outer surface of the expandable support member is for engaging and adhering to the inside surface of the blood vessel. A layer of biological tissue is attached to the inner surface of the support member. The layer of biological tissue has an uninterrupted inwardly facing surface for extending confluently with the inside surface of the blood vessel to provide resistance to thrombosis and platelet deposition as blood flows through the conduit.  
           [0008]    According to one aspect of the invention, the layer of biological tissue is selected from the group consisting of peritoneum, pleura, and pericardium.  
           [0009]    In a further aspect of the invention, a graft for a blood vessel is provided. The blood vessel has an inside surface that defines a conduit for directing blood flow. The graft comprises a layer of biological tissue having an uninterrupted inwardly facing surface for extending confluently with the inside surface of the blood vessel to provide resistance to thrombosis and platelet deposition as blood flows through the conduit.  
           [0010]    According to another aspect of the present invention, the layer of biological tissue comprises an inner lining of a serous membrane that is supported by an outer lining of associated fascia. The outer lining of associated fascia serves as a structural support for the inner lining of serous membrane.  
           [0011]    The present invention also provides a method for forming a graft for insertion in a blood vessel. The blood vessel has an inside surface that defines a conduit for directing blood flow. According to the inventive method, an expandable support member having inner and outer surfaces is provided. The outer surface of the support member is for engaging and adhering to the inside surface of the blood vessel. A layer of biological tissue having an uninterrupted inwardly facing surface for extending confluently with the inside surface of the blood vessel to provide resistance to thrombosis and platelet deposition as blood flows through the conduit is also provided. The layer of biological tissue is molded into a desired shape. The layer of biological tissue is attached to the inner surface of the support member.  
           [0012]    In yet another aspect of the present invention, a method for preparing a patch for insertion in a blood vessel is provided. The blood vessel has an inside surface that defines a conduit for directing blood flow. According to the method, a layer of biological tissue comprising an inner lining of a serous membrane supported by an outer lining of associated fascia is harvested. The inner lining of serous membrane has an uninterrupted inwardly facing surface for extending confluently with the inside surface of the blood vessel to provide resistance to thrombosis and platelet deposition as blood flows through the conduit. The layer of biological tissue is molded into a desired shape. The layer of biological tissue is packaged in a sterile, biological medium and stored within a vacuum-packed container. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 is a perspective view of an apparatus constructed in accordance with the present invention;  
         [0015]    [0015]FIG. 2 is a view along line  2 - 2  in FIG. 1;  
         [0016]    [0016]FIG. 3 is a view along line  3 - 3  in FIG. 2;  
         [0017]    [0017]FIGS. 4 a - 4   f  illustrate the method of forming the apparatus of FIG. 1;  
         [0018]    [0018]FIG. 5 is a sectional view illustrating the apparatus of FIG. 1 implanted in a blood vessel;  
         [0019]    [0019]FIG. 6 is a longitudinal sectional view of a second embodiment of an apparatus constructed in accordance with the present invention;  
         [0020]    [0020]FIG. 7 is a longitudinal sectional view of a third embodiment of an apparatus constructed in accordance with the present invention;  
         [0021]    [0021]FIG. 8 is a longitudinal sectional view of a fourth embodiment of an apparatus constructed in accordance with the present invention;  
         [0022]    [0022]FIG. 9 is a longitudinal sectional view of a fifth embodiment of an apparatus constructed in accordance with the present invention;  
         [0023]    [0023]FIG. 10 is a longitudinal sectional view of a sixth embodiment of an apparatus constructed in accordance with the present invention;  
         [0024]    [0024]FIG. 11 is a perspective view of a seventh embodiment of an apparatus constructed in accordance with the present invention;  
         [0025]    [0025]FIG. 12 is a perspective view of an eighth embodiment of an apparatus constructed in accordance with the present invention; and  
         [0026]    [0026]FIG. 13 is a perspective view of a ninth embodiment of an apparatus constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    [0027]FIG. 1 is a perspective view of an apparatus  10  constructed in accordance with the present invention. The apparatus  10  is a cardiovascular graft for grafting of a blood vessel  12  (FIG. 5). The apparatus  10  includes a layer of biological tissue  14  and an expandable support member  16  or stent.  
         [0028]    The layer of biological tissue  14  includes an inner lining  18  and an outer lining  20  (FIGS. 2 and 3). The inner lining  18  is a serous membrane and the outer lining  20  is fascia associated with the serous membrane. The biological tissue  14  is autogenous tissue. Alternatively, cadaveric tissue or xenogeneic tissue may be used. According to one embodiment, the layer of biological tissue  14  is harvested from the peritoneum. Alternatively, the biological tissue may be harvested from the pericardium or from the pleura. As an alternative to a layer of biological tissue  14 , a layer of artificial tissue that mimics the characteristics of peritoneal, pleural, or pericardial membrane may be used. The artificial tissue may be constructed from collagen scaffolding that is seeded with tissue cells, such as human keratinocytes. The artificial tissue may also include a basement membrane. The basement membrane may be a fascia lining or another known artificial lining.  
         [0029]    The biological tissue  14  is harvested in sheets of appropriate size. Conventional techniques are used for harvesting the biological tissue  14 . The sheet of biological tissue  14  is fixed or preserved with alcohol, glutaraldehyde, and/or another biological solution. After being fixed, the biological tissue  14  is trimmed or cut into the desired shape and size. It is noted that the biological tissue  14  may shrink slightly when fixed. Thus, the biological tissue  14  should be fixed prior to being trimmed to the desired shape and size. Preferably, the biological tissue  14  is trimmed into a rectangular shape. After being trimmed, the biological tissue may be bathed in the biological solution.  
         [0030]    The expandable support member  16  is tubular and extends axially from a first end  22  (FIG. 2) to a second end  24 . The expandable support member  16  illustrated in FIG. 1 is a mesh structure that includes a plurality of support beams  26  and a plurality of axially extending support rods  27 .  
         [0031]    Each support beam  26  has a generally sinusoidal shape. The wavelength of each of the support beams  26  is identical or nearly identical to the wavelength of adjacent support beams. Circumferentially adjacent support beams  26  are 180° out of phase from one another. Connector bars  28  (FIG. 1) connect the peaks  30  of each support beam  26  to the associated troughs  32  (FIG. 1) of the adjacent support beam. The amplitude (or height) of each support beam  26  is designed so that a whole number of support beams forms the circumference of the expandable support member  16 .  
         [0032]    Each of the axially extending support rods  27  extends parallel to axis A. The support rods  27  add additional support to the expandable support member  16 . One embodiment of the apparatus  10  includes eight support rods  27  that are equally spaced about the circumference of the expandable support member  16 . In the embodiment illustrated in FIG. 1, two support beams  26  are located between adjacent support rods  27 .  
         [0033]    The expandable support member  16  also includes a plurality of eyelets  29 , four of which are shown in FIG. 1. Each eyelet  29  extends from one of the support rods  27 . The eyelets  29  illustrated in FIG. 1 are circular, however other shapes may be used. The eyelets  29  provide a means for suturing the layer of biological tissue  14  to the outer support member  16 .  
         [0034]    The expandable support member  16  is formed from an expandable metal, such as Nitinol. Alternatively, the expandable support may be formed from a fabric layer such as Dacron® or a plastic material such as polytetraflouroethylene (PTFE).  
         [0035]    The expandable support member  16  includes an outer surface  34  and an inner surface  36  (FIG. 2). The outer surface  34  is generally cylindrical and extends axially along axis A. The inner surface  36  is also generally cylindrical and is coaxial with the outer surface  34 .  
         [0036]    Alternatively, the expandable support member  16  may include any known stent structure that is expandable and that defines inner and outer surfaces  36  and  34 , respectively. Although the apparatus  10  is illustrated as being cylindrical with a circular cross-sectional shape, the cross-sectional shape of the apparatus may alternatively be elliptical, polygonal, or cone-shaped.  
         [0037]    [0037]FIGS. 4 a - 4   f  illustrate a method for forming the apparatus  10  of the present invention. The method begins at FIG. 4 a  with a dowel  38  and a sheet of biological tissue  14  that has been fixed and trimmed into a rectangular shape. The dowel  38  is formed from glass. The dowel  38  illustrated in FIG. 4 a  is cylindrical and has an outer surface  40  with a circular cross-sectional shape. Alternatively, the dowel  38  may be cone-shaped. A circumference of the outer surface  40  of the dowel  38  is equal to a width of the biological tissue  14 . The width of the biological tissue  14  is defined as the distance between a first side surface  42  and a second side surface  44 . FIG. 4 a  illustrates the biological tissue  14  being wrapped or rolled around the dowel  38 .  
         [0038]    [0038]FIG. 4 b  illustrates the biological tissue  14  completely wrapped around the dowel  38 . When completely wrapped around the dowel  38 , the first side surface  42  of the biological tissue  14  abuts, rather than overlaps, the second side surface  44  of the biological tissue  14 . An axially extending seam  46  is defined at the location where the first side surface  42  and the second side surface  44  meet. The seam  46  extends along an axial length of the biological tissue  14 . The axial length of the biological tissue  14  is defined as a distance between a first axial end  58  and a second axial end  60 .  
         [0039]    The first side surface  42  abuts the second side surface  44  such that the inner surface  48  (FIGS.  1 - 3 ) of the apparatus  10 , which is defined by an inner surface  50  (FIGS.  1 - 3 ) of the inner lining  18  of the biological tissue  14 , is smooth, continuous, and uninterrupted. Since the inner surface  48  of the apparatus  10  has no projections or irregularities, such as would be present if the biological tissue  14  were overlapped, thrombosis and platelet deposition at the seam  46  are resisted. An additional benefit of abutting the first and second side surfaces  42  and  44  of the biological tissue  14  together is that the smooth, continuous, and uninterrupted inner surface  48  of the apparatus  10  does not create turbulent flow through the apparatus.  
         [0040]    In FIG. 4 c , the first side surface  42  of the biological tissue  14  is attached to the second side surface  44  of the biological tissue  14  using sutures  52 . The sutures  52  extend radially inwardly through the biological tissue  14  and generally circumferentially between areas adjacent the first and second side surfaces  42  and  44 . The biological tissue  14  remains on the dowel  38  while the sutures  52  are sewn in place. A layer of biological glue  54  may be placed over the seam  46  on an outer surface  56  of the biological tissue  14 . The biological glue  54  helps to ensure that the inner surface  48  of the apparatus  10  remains smooth, continuous, and uninterrupted. The biological glue  54  also aids in completely sealing the seam  46  to prevent any leakage through the seam  46 .  
         [0041]    [0041]FIG. 4 d  illustrates the expandable support member  16  being placed over the biological tissue  14 . The expandable support member  16  forms an outer support for the biological tissue  14 . The expandable support member  16  forms the radially outermost component of the apparatus  10 . The radially innermost component of the apparatus  10  is formed by the serous membrane lining  18  of the layer of biological tissue  14 .  
         [0042]    To place the expandable support member  16  over the biological tissue  14 , the expandable support member  16  is expanded. Any known method for expanding the expandable support member  16  may be used, such as heating or balloon dilation of the expandable support member. The dowel  38  and the biological tissue  14  that is being held on the dowel  38  are inserted into the first end  22  of the expandable support member  16 , as shown in FIG. 4 d . The expandable support member  16  and the dowel  38  are moved relative to one another until an equivalent amount of biological tissue  14  extends axially outwardly of both the first and second ends  22  and  24  of the expandable support member  16 .  
         [0043]    The expandable support member  16  is then constricted until the inner surface  36  of the expandable support member  16  engages the outer surface  56  of the biological tissue  14  equally about the circumference of the outer surface  56  of the biological tissue  14 . Next, the biological tissue  14  is attached to the expandable support member  16 . Preferably, sutures (not shown) are used to attach the biological tissue  14  to the expandable support member  16 . Each suture extends through the biological tissue  14  and a portion of the suture is threaded through one of the eyelets  29  of the expandable support member  16 . The suture is then tied outside of the expandable support member  16  and around the respective eyelet  29 . The suture holds the biological tissue  14  to the inner surface  36  of the expandable support member  16 . The sutures are sufficiently small so that turbulent flow will not result from the interaction of blood flow with the sutures. Alternately, the outer surface  56  of the biological tissue  14  may be glued to the inner surface  36  of the expandable support member  16  using biological glue. When biological glue is used to attach the biological tissue  14  to the expandable support member  16 , the support beams  26  and the support rods  27  must have an inner surface area large enough for adhesion of the biological tissue  14 .  
         [0044]    After the biological tissue  14  is attached to the expandable support member  16 , the first and second axial ends  58  and  60  of the biological tissue  14  are folded over the first and second ends  22  and  24 , respectively, of the expandable support member  16 , as is shown in FIG. 4 e . The first axial end  58  of the biological tissue  14  is stretched and folded over the first end  22  of the expandable support member  16  to form a first folded portion  62 . The first folded portion  62  is then attached to the outer surface  34  of the expandable support member  16  using sutures (not shown). A second axial end  60  of the biological tissue  14  is stretched and folded over the second end  24  of the expandable support member  16  to form a second folded portion  64 . The second folded portion  64  is also attached to the expandable support member  16  using sutures (not shown).  
         [0045]    The apparatus  10 , including the dowel  38 , is stored in a sterile environment until it is time for implantation into a patient. Preferably, the apparatus  10  is submersed in a biological solution and is stored in a sterile, vacuum-packed container (not shown). Alternatively, the dowel  38  may be removed from the apparatus  10  prior to storing the apparatus. FIG. 4 f  illustrates the dowel  38  being removed from the apparatus  10 . Preferably, the dowel  38  and the apparatus  10  are placed in biological or fixing solution to facilitate removal of the dowel  38  from inside the apparatus  10 . The solution will sufficiently lubricate the dowel  38  and the biological tissue  14  so that the dowel may be removed from the apparatus  10  without tearing or weakening the biological tissue  14 . As a result, the inner surface  48  of the apparatus  10  remains smooth, continuous, and uninterrupted. Alternatively, the apparatus  10  may be expanded and the dowel  38  removed from the expanded apparatus  10 .  
         [0046]    [0046]FIG. 5 illustrates the apparatus  10  of the present invention implanted in a blood vessel  12 . The blood vessel  12  includes an outside surface  66  and an inside surface  68 . The inside surface  68  of the blood vessel  12  forms a conduit for directing blood flow. The apparatus  10  is delivered and positioned in the blood vessel  12  using methods that are known in the art. Once the apparatus  10  is positioned in the desired location in the blood vessel  12 , the expandable support member  16  is expanded, by a balloon (not shown) or through self-expansion as is known in the art. When the expandable support member  16  expands, a first end  70  of the apparatus  10  engages the blood vessel  12  such that an interference fit is created between the first folded portion  62  and the inside surface  68  of the blood vessel  12 . Similarly, a second end  72  of the apparatus  10  engages the blood vessel  12  such that an interference fit is created between the second folded portion  64  and the inside surface  68  of the blood vessel  12 . An interference fit is also created between the expandable support member  16  and the inner surface  68  of the blood vessel  12  along the axial length of the apparatus  10  that extends between the first and second ends  70  and  72 . In addition to the interference fit between the expandable support member  16  and the blood vessel  12 , sutures can also used to anchor the expandable support member  16  to the blood vessel  12 .  
         [0047]    When the apparatus  10  engages and adheres to the inside surface  68  of the blood vessel  12  in the above manner, the inner lining  18  of serous membrane forms the outermost surface at the first and second folded portions  62  and  64 . The inner lining  18  bonds to the inside surface  68  of the blood vessel  12  in a normal tissue-healing fashion and prevents the ingrowth of inflammatory tissue. As a result, the bond between the serous membrane of the inner lining  18  at the first and second folded portions  62  and  64  and the inside surface  68  of the blood vessel  12  prevents restenosis or occlusion. Additionally, the healing bond between the serous membrane of the inner lining  18  at the first and second folded portions  62  and  64  and the inside surface  68  of the blood vessel  12  forms more quickly than a bond between the fascia lining  20  and the inside surface  68  of the blood vessel  12 .  
         [0048]    When implanted in the blood vessel  12 , the conduit formed by the inner surface  50  of the biological tissue  14  is confluent with the inside surface  68  of the blood vessel  12 . The transition between the inside surface  68  of the blood vessel  12  and the inner surface  50  of the biological tissue  14  is smooth so that thrombosis and platelet deposition is resisted and that blood flow is not restricted when passing through the apparatus  10 . The expandable support member  16  provides sufficient support against the internal pressure caused by the blood flow through the apparatus  10 , and also resists radial collapse of the blood vessel.  
         [0049]    [0049]FIG. 6 is a longitudinal sectional view of a second embodiment of an apparatus  10   a  constructed in accordance with the present invention. Structures of the embodiment shown in FIG. 6 that are similar to structures of FIGS.  1 - 3  have the same reference numbers with the suffix “a” added. The apparatus  10   a  is identical to apparatus  10  of FIGS.  1 - 3  with the exception that the layer of biological tissue  14   a  in the embodiment of FIG. 6 includes only a layer  18   a  of serous membrane.  
         [0050]    The layer of biological tissue  14   a  is harvested to include only the layer  18   a  of serous membrane. The method for harvesting only a layer  18   a  of serous membrane is known in the art  
         [0051]    The assembly of apparatus  10   a  is identical to the assembly of apparatus  10  that is illustrated in FIGS. 4 a - 4   f . When trimmed into the desired shape, the layer of biological tissue  14   a  includes first and second side surfaces  42   a  and  44   a , respectively, and first and second axial ends  58   a  and  60   a , respectively.  
         [0052]    The assembled apparatus includes a seam  46   a  that is formed from abutting the first and second side surfaces  42   a  and  44   a . The assembled apparatus  10   a  also includes first and second folded portions  62   a  and  64   a . The first folded portion  62   a  is formed by folding the first axial end  58   a  of the layer of biological tissue  14   a  over the first end  22   a  of the expandable support member  16   a . The second folded portion  64   a  is formed by folding the second axial end  60   a  of the layer of biological tissue  14   a  over the second end  24   a  of the expandable support member  16   a.    
         [0053]    The inner surface  48   a  of the assembled apparatus  10   a  is defined by the inner surface  50   a  of the layer  18   a  of serous membrane. The inner surface  148   a  of the apparatus  10   a  is smooth, continuous, and uninterrupted. The smooth, continuous, and uninterrupted inner surface  48   a  of the apparatus  10   a  resists thrombosis and platelet deposition.  
         [0054]    [0054]FIG. 7 is a longitudinal sectional view of an apparatus  10   b  constructed in accordance with a third embodiment of the present invention. Structures of the embodiment shown in FIG. 7 that are similar to structures of FIGS.  1 - 3  have the same reference numbers with the suffix “b” added.  
         [0055]    The apparatus  10   b  illustrated in FIG. 7 includes a layer of biological tissue  14   b  and an expandable support member  16   b . The layer of biological tissue  14   b  includes a serous membrane lining  18   b  and associated fascia lining  20   b . The expandable support member  16   b  has a structure similar to that illustrated in FIG. 1. The layer of biological tissue  14   b  forms the innermost component of the apparatus  10   b.    
         [0056]    The layer is biological tissue  14   b  is formed into a tubular portion by abutting first and second side surfaces  42   b  and  44   b  of the biological tissue  14   b  at a seam  46   b . Preferably, the first and second side surfaces  42   b  and  44   b  are sutured together at the seam  46   b  and biological glue (not shown) is applied to an outer surface  56   b  of the biological tissue  14   b.    
         [0057]    The outer surface  56   b  of the layer of biological tissue  14   b  is attached to the inner surface  36   b  of the expandable support member  16   b . The expandable support member  16   b  is placed over the biological tissue  14   b  such that equal amounts of biological tissue  14   b  extend from the first and second ends  22   b  and  24   b  of the expandable support member  16   b . Instead of folding the first and second axial ends  58   b  and  60   b  of the biological tissue  14   b  over the expandable support member  16   b  as discussed above with regard to the embodiment of FIGS.  1 - 3 , the first and second axial ends  58   b  and  60   b  of the biological tissue  14   b  extend axially beyond the first and second ends  22   b  and  24   b  of the expandable support member  16   b . Thus, in assembling the apparatus  10   b , the step illustrated in FIG. 4 e  is omitted.  
         [0058]    When implanted into a blood vessel of a patient, the first and second axial ends  58   b  and  60   b  of the tissue  14   b  engage and are adhered to the inside surface of the blood vessel by the expansion of the expandable support member  16 . The extension of the first and second axial ends  58   b  and  60   b  of the biological tissue  14   b  axially beyond the first and second ends  22   b  and  24   b  of the expandable support member  16   b  allows the first and second axial ends of the biological tissue to be sutured directly to the inside surface of the blood vessel.  
         [0059]    [0059]FIG. 8 is a longitudinal sectional view of a fourth embodiment of an apparatus  10   c  constructed in accordance with the present invention. Structures of the embodiment shown in FIG. 8 that are similar to structures of FIG. 7 have the same reference numbers with the suffix “c” replacing the suffix “b”. The apparatus  10   c  is identical to apparatus  10   b  of FIG. 7 with the exception that the layer of biological tissue  14   c  in the embodiment of FIG. 8 includes only a layer  18   c  of serous membrane.  
         [0060]    The assembly of apparatus  10   c  is identical to the assembly of apparatus  10   b . When trimmed into the desired shape, the layer of biological tissue  14   c  includes first and second side surfaces  42   c  and  44   c , respectively, and first and second axial ends  58   c  and  60   c , respectively.  
         [0061]    The assembled apparatus includes a seam  46   c  that is formed from abutting the first and second side surfaces  42   c  and  44   c . The inner surface  48   c  of the assembled apparatus  10   c  is defined by the inner surface  50   c  of the layer  18   c  of serous membrane. The inner surface  48   c  of the apparatus  10   c  is smooth, continuous, and uninterrupted. The smooth, continuous, and uninterrupted inner surface  48   c  of the apparatus  10   c  resists thrombosis and platelet deposition.  
         [0062]    [0062]FIG. 9 illustrates a longitudinal sectional view of a fifth embodiment of an apparatus  10   d  constructed in accordance with the present invention. Structures of the embodiment shown in FIG. 9 that are similar to structures of FIG. 7 have the same reference numbers with the suffix “d” replacing the suffix “b”.  
         [0063]    The apparatus  10   d  of FIG. 9 is also a cardiovascular graft. The apparatus  10   d  includes a layer of biological tissue  14   d  that includes an inner lining  18   d  of serous membrane and an outer lining  20   d  of fascia associated with the serous membrane. The layer of biological tissue  14   d  is rectangular and includes first and second side surfaces  42   d  and  44   d , respectively, and first and second axial ends  58   d  and  60   d , respectively. The inner lining  18   d  of serous membrane includes an inner surface  50   d . The outer lining  20   d  of fascia includes an outer surface  56   d.    
         [0064]    The apparatus  10   d  illustrated in FIG. 9 is cylindrical and is formed by the layer of biological tissue  14   d . The first and second side surfaces  42   d  and  44   d  of the layer of biological tissue  14   d  are abutted and secured together to define a seam  46   d . Sutures  52   d  attach the first and second side surfaces  42   d  and  44   d  at the seam  46   d . A layer of biological glue (not shown) is applied to the outer surface  56   d  of the outer lining  20   d  over the seam  46   d . The biological glue aids in completely sealing the seam  46   d  to prevent any leakage through the seam.  
         [0065]    To form the apparatus  10   d , the steps illustrated in FIGS. 4 a  to  4   c  and discussed in detail with regards to apparatus  10  of FIGS.  1 - 3  are followed. After the step shown in FIG. 4 c , the apparatus  10   d  is stored in a sterile environment until it is time for implantation into a patient. Prior to implantation into the patient, the dowel is removed from the apparatus.  
         [0066]    The outer surface  56   d  of the outer lining  20   d  forms the outermost component of the apparatus  10   d . The inner surface  50   d  of the inner lining  18   d  of serous membrane forms the innermost component of the apparatus  10   d . The inner surface  50   d  of the inner lining  18   d  is smooth, continuous, and uninterrupted. As a result, the inner surface  48   d  of the apparatus  10   d  is smooth, continuous, and uninterrupted and resists thrombosis and platelet deposition.  
         [0067]    When surgically implanted in a patient, the apparatus  10   d  is attached using sutures. For example, when used within a blood vessel, the apparatus  10   d  is sutured to the inside surface of the blood vessel. As a result, the continuous and uninterrupted inner surface  50   d  of the inner lining  18   d  is confluent with the inside surface of the blood vessel.  
         [0068]    Since the apparatus  10   d  includes no support structures, the apparatus adapts or conforms to the shape of the blood vessel into which it is attached. Thus, if the inside surface of the blood vessel has an elliptical cross-sectional shape, the apparatus  10   d , when attached to the inside surface of the blood vessel, has an elliptical cross-sectional shape.  
         [0069]    [0069]FIG. 10 is a longitudinal sectional view of a sixth embodiment of an apparatus  10   e  constructed in accordance with the present invention. Structures of the embodiment shown in FIG. 10 that are similar to structures of FIG. 9 have the same reference numbers with the suffix “e” replacing the suffix “d”. The apparatus  10   e  is identical to apparatus  10   d  of FIG. 9 with the exception that the layer of biological tissue  14   e  in the embodiment of FIG. 10 includes only a layer  18   e  of serous membrane.  
         [0070]    The assembly of apparatus  10   e  is identical to the assembly of apparatus  10   e . When trimmed into the desired shape, the layer of biological tissue  14   e  includes first and second side surfaces  42   e  and  44   e , respectively, and first and second axial ends  58   e  and  60   e , respectively.  
         [0071]    The assembled apparatus includes a seam  46   e  that is formed from abutting the first and second side surfaces  42   e  and  44   e . The inner surface  48   e  of the assembled apparatus  10   e  is defined by the inner surface  50   e  of the layer  18   e  of serous membrane. The inner surface  48   e  of the apparatus  10   e  is smooth, continuous, and uninterrupted. The smooth, continuous, and uninterrupted inner surface  48   e  of the apparatus  10   e  resists thrombosis and platelet deposition.  
         [0072]    [0072]FIG. 11 illustrates a perspective view of a seventh embodiment of an apparatus  100  constructed in accordance with the present invention. The apparatus  100  in FIG. 11 is a patch for repairing a portion of a blood vessel or other membrane within the cardiovascular system of the human body.  
         [0073]    The patch  100  includes a layer of biological tissue  102  and an outer support member  104 . The layer of biological tissue  102  includes a serous membrane lining  106  and associated fascia lining  108 . The serous membrane lining  106  forms an inner surface (not shown) of the biological tissue  102  and the associated fascia  108  forms an outer surface  110  of the biological tissue  102 . The layer of biological tissue  102  is illustrated as being rectangular but may be of any desired shape.  
         [0074]    The outer support member  104  has the same shape as the biological tissue  102  but is slightly smaller is size. The outer support member  104  may have a curved profile, as is illustrated in FIG. 11, for fitting to a curved surface such as the inside or outside surfaces of a blood vessel.  
         [0075]    The outer support member  104  in FIG. 11 is rectangular and includes an outer frame  112  and inner support beams  114 . The outer frame  112  defines the shape of the outer support member  104  and provides support near the periphery of the biological tissue  102 . The inner support beams  114  of the outer support member  104  provide support for an interior portion of the biological tissue  102 . Eyelets  118  are provided through which sutures (not shown) may be threaded when attaching the biological tissue  102  to the outer support member  104 .  
         [0076]    The outer surface  110  of the biological tissue  102  is attached to the outer support member  104 . Preferably, the biological tissue  102  is sutured to the outer support member  104 . The peripheral portion of the biological tissue  102  extends outwardly from the outer support member  104 . Alternatively, the peripheral portion of the biological tissue  102  may be folded over the outer frame  112  of the outer support member  104 .  
         [0077]    When implanted in a blood vessel, an outer surface  116  of the outer support member  104  of the patch  100  is placed over an aneurysm or a weakened portion of the blood vessel. The size of the outer support member  104  is preferably larger than the aneurysm or weakened portion of the blood vessel such that the outer frame  112  of the outer support member  104  contacts healthy portions of the inside surface of the blood vessel. The outer periphery of the biological tissue  102  is then attached to the inside surface of the blood vessel, preferably by suturing. The patch  100  may alternatively be placed over the outside surface of the blood vessel or be used on another membrane of the cardiovascular system.  
         [0078]    [0078]FIG. 12 is a view of an eighth embodiment of an apparatus  100   a  constructed in accordance with the present invention. Structures of the embodiment shown in FIG. 12 that are similar to structures of FIG. 11 have the same reference numbers with the suffix “a” added.  
         [0079]    The apparatus  100   a  of FIG. 12 is also a patch for repairing a portion of a blood vessel or other membrane within the cardiovascular system of the human body. The patch  100   a  includes a layer of biological tissue  102   a . The patch  100   a  of FIG. 12 does not include a support structure such as the outer support structure  104  illustrated in FIG. 11.  
         [0080]    The layer of biological tissue  102   a  includes a serous membrane lining  106   a  and associated fascia lining  108   a . The serous membrane lining  106   a  forms an inner surface (not shown) of the biological tissue  102   a  and the associated fascia  108   a  forms an outer surface  110   a  of the biological tissue  102   a . The inner surface of the biological tissue  102   a  is smooth, continuous, and uninterrupted. The layer of biological tissue  102   a  is illustrated as being rectangular but may be of any desired shape.  
         [0081]    When implanted in a blood vessel, an outer surface  110   a  of the associated fascia  108   a  of the layer of biological tissue  102   a  is placed over an aneurysm or a weakened portion of the blood vessel. The biological tissue  102   a  is then attached to the inside surface of the blood vessel, preferably by suturing. Since the patch  100   a  does not include structural support, the patch  100   a  easily adapts to the shape of the blood vessel or membrane to which it is attached to ensure a sufficient area of contact between patch  100   a  and the blood vessel or membrane. The patch  100   a  may alternatively be placed over the outside surface of the blood vessel or be used on another membrane of the cardiovascular system.  
         [0082]    [0082]FIG. 13 is a perspective view of a ninth embodiment of an apparatus  100   b  constructed in accordance with the present invention. Structures of the embodiment shown in FIG. 13 that are similar to structures of FIG. 12 have the same reference numbers with the suffix “b” replacing the suffix “a”. The apparatus  100   b  is identical to apparatus  100   a  of FIG. 12 with the exception that the layer of biological tissue  102   b  in the embodiment of FIG. 13 includes only a layer  106   b  of serous membrane.  
         [0083]    The outer surface  110   b  of the biological tissue  102   b  is formed by an outer surface of the layer  106   b  of serous membrane. The inner surface (not shown) of the biological tissue is formed by an inner surface of the layer  106   b  of serous membrane and is smooth, continuous and uninterrupted.  
         [0084]    From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, a layer of artificial tissue, which mimics the characteristics of the layer of biological tissue, may be used in any of the embodiments discussed above. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.