Abstract:
A method of making a prosthetic heart valve may include providing an annular stent having a plurality of annularly spaced commissure portions having tips, covering each of the tips with a first fabric cover, covering the first fabric covers and the remainder of the stent with a second fabric cover, covering the second fabric cover with a first tissue membrane, and covering the outside of the first tissue membrane with a second tissue membrane, the second tissue membrane forming leaflet portions that extend inwardly between the commissure portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. application Ser. No. 12/004,170, filed Dec. 19, 2007 which claims the benefit of Provisional Application No. 60/875,921 filed Dec. 19, 2006, the disclosures of which are hereby incorporated by reference herein in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to prosthetic heart valves, and more particularly to the type of prosthetic heart valves that use tissue material for the leaflets of the valve. The invention also relates to methods of making such valves. 
         [0003]    There is increasing interest in artificial, prosthetic heart valves that use tissue material for the leaflets of the valve. Such valves tend to be less thrombogenic than mechanical prosthetic heart valves. This can reduce or eliminate the need for a patient who has received such a prosthesis to take anti-coagulant medication on a long-term basis. Tissue-based heart valves may also have other advantages, such as quieter operation. Because of the interest in such valves, improvements to them are greatly desired. Improved methods of making such valves are also sought. 
       SUMMARY OF THE INVENTION 
       [0004]    In accordance with certain aspects of the invention, a prosthetic heart valve includes an annular stent having a plurality of annularly spaced commissure portions, each of which has a tip. A fabric cover may be provided over each tip. An additional fabric covering may be provided over the fabric tip covers and the remainder of the stent. Tissue may be provided over the fabric covering. Additional tissue is provided around the outside of the previously mentioned components. This additional tissue includes leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. 
         [0005]    In accordance with certain other aspects of the invention, a method of making a prosthetic heart valve includes providing an annular stent having a plurality of annularly spaced commissure portions, each of which has a tip. The method may further include covering each of the tips with a fabric tip cover. The method may still further include covering the tip covers and the remainder of the stent with an additional fabric cover. The method may further include covering the fabric cover with a tissue cover. The method may still further include wrapping additional tissue around the radially outer surface of the tissue cover, the additional tissue including leaflet portions that extend inwardly between annularly adjacent ones of the commissure portions. 
         [0006]    Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a simplified perspective view of a component of an illustrative embodiment of a prosthetic heart valve in accordance with the invention; 
           [0008]      FIG. 2  is a simplified perspective view of a representative portion of  FIG. 1  with another representative component added in accordance with the invention; 
           [0009]      FIG. 3  is a simplified elevational view of another component prior to assembly with other components in accordance with the invention; 
           [0010]      FIG. 4  is a simplified elevational view of yet another component prior to assembly with other components in accordance with the invention; 
           [0011]      FIG. 5  is a simplified perspective view of an assembly of the components from  FIGS. 1-4  in accordance with the invention; 
           [0012]      FIGS. 6 and 7  are respectively simplified perspective top and bottom views of the  FIG. 5  assembly with another component added in accordance with the invention; 
           [0013]      FIG. 8  is a simplified perspective view of another component prior to assembly with the other components in accordance with the invention; 
           [0014]      FIG. 9  is a simplified perspective view of a tool that is useful at a certain stage in the manufacture of heart valves in accordance with the invention; 
           [0015]      FIG. 10  is a simplified elevational view of a representative portion of an assembly of components in accordance with the invention; 
           [0016]      FIG. 11  is a simplified perspective view of an assembly in accordance with the invention on a tool like that shown in  FIG. 9 ; and 
           [0017]      FIG. 12  is a simplified perspective of an illustrative embodiment of a completed prosthetic heart valve in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    An illustrative embodiment of a first component  100  of an artificial heart valve in accordance with the invention is shown in  FIG. 1 . Component  100  is a hollow, annular, stent-like structure (sometimes referred to for convenience herein simply as a stent). Stent  100  is referred to as “hollow” because the interior that is bounded by its annular structure is open. Stent  100  is typically made of metal such as titanium (e.g., Ti 6Al-4V ELI Grade 5). A typical technique for making stent  100  is to cut it from a tube using a laser. Stent  100  is then typically electro-polished. 
         [0019]    Because the valve of the illustrative embodiment being discussed is a tricuspid valve (e.g., for use in replacing a patient&#39;s aortic valve), stent  100  has three commissure portions or regions  110   a,    110   b,  and  110   c  that are equally spaced from one another around the circumference of the stent. Each commissure portion stands up from the annularly continuous base portion of the stent. The base portion includes a lower-most, blood-inflow edge portion  120 . This blood-inflow edge portion is scalloped as one proceeds around the stent to approximately match the natural scallop of the native valve annulus. In particular, this scallop rises in the vicinity of each commissure region, and it falls between each annularly adjacent pair of commissures. 
         [0020]    Stent  100  also includes an annularly continuous blood-outflow edge portion  130  (which merges with and becomes part of each commissure region  110  at the commissures). Outflow edge portion  130  is much more deeply scalloped than the inflow edge portion. In particular, outflow edge portion  130  rises adjacent each commissure  110  (actually merging into each commissure as noted above), and falls between each annularly adjacent pair of commissures. 
         [0021]    The inflow edge  120 , outflow edge  130 , and flexibility of stent  100  are designed to help ensure proper opening and coaptation of the finished valve in use. (Coaptation is the coming together of the outflow portions of the valve leaflets when the valve is closed.) Stent  120  is further designed to decrease maximum stresses in the stent in use, which gives the finished valve an increased safety factor. 
         [0022]    Although titanium is mentioned above as a typical material from which stent  100  can be made, other materials are also possible. Some examples of other materials that may be suitable for use in making stent  100  include Elgiloy MP35N or polymers such as PEEK or acetal. 
         [0023]      FIG. 2  illustrates a subsequent possible step in the manufacture of the illustrative embodiment being described. This is the addition of a sleeve-like fabric covering  200  over the top of each commissure post. Fabric commissure tip covers  200  help reduce the possibility that the stent commissure tips may poke through subsequently added components. An illustrative fabric that is suitable for use in making coverings  200  is reemay fabric, which is a spun form of polyester. Each tip cover  200  may be secured to the associated commissure tip with sutures. 
         [0024]      FIGS. 3-5  illustrate further possible components and steps in the manufacture of the illustrative embodiment being described.  FIG. 3  shows an illustrative embodiment of a polyester fabric tube  300 ;  FIG. 4  shows an illustrative embodiment of a silicone cuff filler ring  400 ; and  FIG. 5  shows an assembly  500  that includes stent  100  (with post tip coverings  200 ) and silicone cuff filler ring  400  covered inside and out by fabric tube  300 . For example, stent  100  (with coverings  200 ) and ring  400  may be placed coaxially around the outside of a lower portion of fabric tube  300 . Ring  400  may be located outside inflow edge portion  120 . The upper portion of sleeve  300  may then be pulled down over the outside of components  100  and  400  and pulled tightly enough to conform to outflow edge portion  130  as shown in  FIG. 5 . Sutures may be used to hold the above-described components together in the condition shown in  FIG. 5 . In particular, all of components  100 ,  200 , and  400  are completely covered inside and out by fabric  300 . Ring  400  is located adjacent inflow edge portion  120  and follows the scalloping of inflow edge portion  120  all the way around assembly  500 . The upper portion of fabric  300  conforms closely to stent  100  above ring  400 , and in particular, the upper portion of the fabric follows the scalloped outflow edge portion  130  all the way around assembly  500 . 
         [0025]      FIGS. 6 and 7  illustrate still further possible components and steps in the manufacture of the illustrative embodiment being described. In particular, these FIGS. illustrate the addition of porcine pericardium tissue  600  over assembly  500 , both inside and out, to produce assembly  700 . One of the purposes of this is to enhance durability of the finished valve. Another purpose is to reduce thrombogenicity of the finished valve. Sutures may be used to secure tissue  600  to assembly  500  as shown in  FIGS. 6 and 7 . Apart from somewhat thickening assembly  700  as compared to assembly  500 , the addition of tissue  600  does not significantly change the shape of any portion of the structure. 
         [0026]    Although porcine pericardium is mentioned above for component  600 , other types of tissue may be used instead if desired. Examples of such other possible tissue for component  600  include any mammalian pericardium (e.g., equine or bovine pericardium). 
         [0027]      FIG. 8  illustrates a further possible component and steps in the manufacture of the illustrative embodiment being described. As shown in  FIG. 8 , component  800  is a sheet of bovine pericardium that has been die cut to a shape that can be used to form all three leaflets of a finished valve. Note that the lower edge of sheet  800  (as viewed in  FIG. 8 ) is scalloped to conform to the blood-inflow edge (like  120  in  FIG. 1 ) of the finished valve. The upper portion of sheet  800  (as viewed in  FIG. 8 ) will form the three leaflets of the valve. There are shallow downward cuts  802  between the individual leaflet portions adjacent the upper edge of sheet  800 , but sheet  800  remains intact so that this single sheet of tissue can be used to form all three leaflets in the finished valve. 
         [0028]    Although bovine pericardium is mentioned above for component  800 , other types of tissue may be used instead if desired. Examples of such other possible tissue for component  800  include any mammalian pericardium (e.g., equine or porcine pericardium). 
         [0029]      FIG. 9  illustrates a tool  900  that can be used in further steps in manufacturing the illustrative embodiment being described. Tool  900  is a mounting mandrel which can be inserted coaxially into assembly  700 . In particular, this is done so that each of the commissure portions  910   a - c  of mandrel  900  is angularly or rotationally aligned with a respective one of the commissure portions  710  of assembly  700 . In addition, each of the scalloped edge portions  930  of mandrel  900  is adjacent a corresponding scalloped outflow edge portion  730  of assembly  700 . 
         [0030]    With mandrel  900  positioned inside assembly  700  as described in the preceding paragraph, tissue  800  is wrapped around the outside of assembly  700  above the sewing cuff portion of assembly  700 . The sewing cuff portion is the portion that includes ring  400  in its interior. This wrapping is done with the scalloped lower edge ( FIG. 8 ) of tissue  800  just above and conformed to the scalloped sewing cuff of assembly  700 . In addition, each of cuts  802  is adjacent a respective one of two of commissures  710 , and the extreme left and right edges of tissue  800  come together adjacent the third one of commissures  710 . The portion of tissue  800  above each of outflow edge scallops  730 / 930  is pressed radially inwardly so that it resets on the adjacent concave surface  940  of mandrel  900 . Tissue  800  is stitched to assembly  700  (but not to mandrel  900 ) in this condition. For example,  FIG. 10  shows stitching  1002  that is used to hold the initially free, left and right edges of tissue  800  together adjacent one of the commissures  710  of assembly  700 . Other stitching  1004  in  FIG. 10  is used to stitch tissue  800  to assembly  700  annularly all the way around assembly  700  just above the sewing ring portion of assembly  700 . The valve structure shown in  FIG. 10  may be referred to as assembly  1000 . 
         [0031]      FIG. 11  illustrates a possible further step in manufacturing the illustrative embodiment being described.  FIG. 11  shows an assembly  1000  still on a mandrel  900  as described in the immediately preceding paragraphs. Note in particular that the portion of tissue  800  above each of outflow edge scallops  730  remains pressed in against the adjacent concave surface  940  of mandrel  900 . With assembly  1000  in this condition on mandrel  900 , assembly is subject to fixation of the tissue. Such fixation of the tissue may be by any conventional and suitable means and may include cross-linking of the tissue by exposing it to cross-linking agents such as glutaraldehyde or epoxides such as TGA triglcidyl amine). Such fixation of the tissue stabilizes the tissue and renders it substantially biologically inert and bio-compatible. Such fixation of the tissue in contact with shaped surfaces  940  also gives the tissue a bias to return to that shape when it is not subjected to external forces. On the other hand, the fixation still leaves the tissue sufficiently flexible that the leaflet portions of tissue  800  above outflow edge scallops  730  can deflect outwardly to open the valve and let blood flow out when a ventricular contraction pressurizes the blood in the ventricle below the valve. When that ventricular pressure ceases, however, the leaflet portions above outflow edge scallops  730  come together again (coapt) and close the valve. 
         [0032]    After the tissue of assembly  1000  has been subjected to fixation as described above, assembly  1000  can be removed from mandrel  900 . The result is a finished valve  1200  as shown in  FIG. 12 . In use, valve  1200  has the operating characteristics described in the preceding paragraphs. 
         [0033]    It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. For example, the shapes and/or sizes of various components can be different from the shapes and sizes shown herein. As another example, the materials used for various components can be different from those mentioned specifically herein.