Patent Publication Number: US-2023146082-A1

Title: Tri-leaflet prosthetic heart valve

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This application claims the benefit of the U.S. Provisional Patent Application No. 62/527,632 filed Jun. 30, 2017, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the manufacture and use of a prosthetic valve for use in the human heart. More specifically, the invention relates to the manufacture and use of a valve that may be surgically implanted into the heart of a patient in order to replace a native tri-leaflet heart valve. 
     BACKGROUND 
     Heart valve replacement is the second most common cardiac operation performed in the United States. Currently, over four million people are diagnosed with heart valve disorder across the world, each year. Moreover, heart disease is prevalent in about 2.5% of the overall United States population, and 10.4% of its elderly population. 
     Typically, prosthetic heart valves used in aortic and mitral heart valve replacement procedures are either mechanical or bioprosthetic. However, these valves introduce significant risk of thromboembolism, requiring the patient to undergo lifelong anticoagulation therapy, or the patient become more prone to valve degeneration and tissue failure, requiring reoperation. It would be useful to produce a prosthetic heart valve that would be durable, while not necessitating anticoagulation therapy. 
     SUMMARY 
     A prosthetic heart valve includes a first upper frame portion and a stent frame connected to the first upper frame portion via at least two stent frame extensions. The stent frame includes a base and at least two stent posts extending upwardly from the base towards the first upper frame portion. The first upper frame portion, the base, and the at least two stent posts each has an inner surface and an outer surface. The prosthetic heart valve also includes at least one sheet of leaflet material configured to weave through the stent frame between the first upper frame portion and the base. 
     A prosthetic heart valve includes a stent frame with a first upper frame portion, a base, and at least two stent posts extending upwardly from the base; wherein the base is connected to the first upper frame portion by the at least two stent posts, and wherein the first upper frame portion, the base, and the at least two stent posts each has an inner surface and an outer surface; and at least one sheet of leaflet material configured to weave through the stent frame from the outer surface to the inner surface between the first upper frame portion and the base of the stent frame. 
     In another embodiment, the at least one sheet of leaflet material is disposed on the outer surface of the base and of the at least two stent posts, and at least a portion of the at least one sheet of leaflet material is tucked under the first upper frame portion between the first upper frame portion and the base and is disposed on the inner surface of the upper frame portion. 
     In another embodiment, the at least one sheet of leaflet material is disposed on the inner surface of the base and of the at least two stent posts, and at least a portion of the at least one sheet of leaflet material is tucked in under the first upper frame portion between the first upper frame portion and the base. 
     In another embodiment, the first upper frame portion has a shape that is substantially similar to an upper edge of the base. 
     In another embodiment, the stent frame further comprises a second upper frame portion connected to the first upper frame portion, and wherein the second upper frame portion has a shape that is substantially similar to an upper edge of the first upper frame portion. The stent frame may also include a third upper frame portion connected to the second upper frame portion, wherein the third upper frame portion has a shape that is substantially similar to an upper edge of the second upper frame portion. Moreover, the at least one sheet of leaflet material weaves through the stent frame between the first upper frame portion and the second upper frame portion and/or between the second upper frame portion and the third upper frame portion. 
     The base may further have a lower edge that is substantially similar to a lower edge of the first upper frame portion. And, the at least two stent posts have at least two heights different from one another. 
     In one embodiment, the at least one sheet of leaflet material is a continuous sheet of leaflet material. In another embodiment, the continuous sheet of leaflet material comprises an upper portion having at least two arches extending upwardly therefrom. In another embodiment, the continuous sheet of leaflet material comprises one or more spacings in the upper portion, wherein each of the one or more spacings is disposed between two of the at least two arches. Moreover, the at least one sheet of leaflet material comprises a polymer material that may be linear low density polyethylene, polytetrafluoroethylene, low-density polyethylene, polyethylene terephthalate, polypropylene, polyurethane, polycaprolactone, polydimethylsiloxane, polymethylmethacrylate, polyoxymethylene, thermoplastic polyurethane, and combinations thereof. The leaflet material may also include hyaluronic acid. And, the at least one sheet of leaflet material may include a bioprosthetic material 
     In one embodiment, the stent frame has a height and an inner diameter, and wherein the ratio of height to diameter is from about 0.5 to about 0.9. The at least two arches may have a height, and wherein the ratio of the height of the at least two arches to the inner diameter of the stent frame is from about 0.05 to about 0.12. 
     Finally, the at least one sheet of leaflet material has a three dimensional curvature and wherein the leaflet material is two dimensional when heated to form a rounded leaflet. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front view of one embodiment of a prosthetic heart valve in an open position; 
         FIG.  2    is a perspective view of the prosthetic heart valve of  FIG.  1   ; 
         FIG.  3    is a front view of one embodiment of a stent frame for use in a prosthetic heart valve; 
         FIG.  4    is a plan view of a rectangular pieces of leaflet material before it is attached to the stent frame; 
         FIG.  5    is a plan view of a piece of leaflet material including an arched upper edge; 
         FIG.  6    is a front view of one embodiment of a clip for use in a prosthetic heart valve; 
         FIG.  7    is an enlarged rear perspective view of one embodiment of the top portion of a clip for use in a prosthetic heart valve; 
         FIG.  8    is a front view of another embodiment of a stent clip and stent frame for use in a prosthetic heart valve; 
         FIG.  9    is a front view of another embodiment of a prosthetic heart valve; 
         FIG.  10    is a perspective valve of the prosthetic heart valve of  FIG.  8   ; 
         FIG.  11    is a front view of another embodiment of a stent frame for use in a prosthetic heart valve; 
         FIG.  12    is a perspective view of the stent frame of  FIG.  11   ; 
         FIG.  13    is a front view of an alternative embodiment of a stent frame for use in a prosthetic heart valve; 
         FIG.  14    is a plan view of the stent frame of  FIG.  13   ; 
         FIG.  15    is top view of the prosthetic heart valve of  FIG.  13    with the leaflets in a closed position; 
         FIG.  16    is a plan view of a piece of leaflet material before it is attached to the stent frame of  FIG.  13   ; 
         FIG.  17    is an exploded view of an alternative embodiment of a stent frame and an outer cover; 
         FIG.  18    is a front view of an alternative embodiment of a stent frame; 
         FIG.  19    is a front view of an alternative embodiment of a stent frame; 
         FIG.  20    is a perspective view of the stent frame of  FIG.  19   ; 
         FIG.  21    is a front view of an alternative embodiment of a stent frame; 
         FIG.  22    is a perspective view of the stent frame valve of  FIG.  21   ; 
         FIG.  23    is a front view of an alternative embodiment of a stent frame; 
         FIG.  24    is a perspective view of the stent frame of  FIG.  23   ; 
         FIG.  25    is a front view of an alternative embodiment of a stent frame; 
         FIG.  26    is a perspective view of the stent frame of  FIG.  25   ; 
         FIG.  27    is an exploded perspective view of an embodiment of a 3D printed model of a prosthetic heart valve; 
         FIG.  28    is a plan view of an embodiment of a 3D printed model of a prosthetic heart valve; 
         FIG.  29    is a graphical representation of a pressure and flow rates over time for prosthetic heart valve Example 5 with a medium profile and a short arch; 
         FIG.  30    is a graphical representation of the normalized flow rate over time for prosthetic heart valve Examples 1-6; 
         FIGS.  31  and  32    are graphical representations of the reverse flow percentages for the closing and regurgitation fractions of Examples 1-6; 
         FIGS.  33  and  34    are high speed camera images of Examples 1-6 taken at four time point throughout a typical cardiac cycle; 
         FIGS.  35  and  36    are graphical representations of averages velocity vectors superimposed by vorticity contours and contours of normalized Reynolds shear stress at two time points throughout the cardiac cycles for Examples 1-6; and 
         FIGS.  37  and  38    are graphical depictions of hemodynamics for prosthetic heart valves having a no arch and varying profiles and varying arch heights, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     A prosthetic heart valve (PHV), including a stent frame and leaflet material, having a tri-leaflet design for use to replace either a failing or damaged native aortic or mitral heart valve in a patient is provided. Although we will refer to a tri-leaflet design, it should be apparent to one of skill in the art that any number of leaflets may be created using the PHV described herein. In one embodiment, the PHV will provide a prosthetic valve with a higher effective orifice compared to other prosthetic valves that are commercially available. The PHV will also provide improved flow characteristics through the geometric design of both the stent frame and the leaflet. 
     In one embodiment, the design of the stent frame in combination with the design of the leaflets enable improved performance over other commercially available prosthetic valves. For example, the design of the leaflet and/or the manner in which the leaflet is disposed on the stent frame may improve durability of the PHV, reduce the number of sutures required to assemble the PHV, and/or improve leaflet coaptation. 
       FIGS.  1  and  2    show illustrate a first embodiment of the PHV  10 . In the embodiment, the PHV  10  includes a suture ring  12 , a stent frame  14 , a plurality of stent clips  16 , and a sheet of leaflet material  32  which may be disposed between the stent frame  14  and the stent clips  16  in order to form at least two leaflets  18 . 
     In one embodiment the stent frame  14  may be formed of a single piece of material, however it should be recognized that multiple pieces of stent material may be used to create a single stent frame  14 . Referring now to  FIG.  3   , the stent frame  14  may be laser cut from a cylindrical tube or pipe. Alternatively, the stent frame  14  may be laser cut from a flat piece of material, rolled into the desired shape, and affixed to hold the shape at either of the free ends (not shown). In another embodiment, the stent frame may be “printed” or molded using additive manufacturing techniques known to those of skill in the art. 
     Generally, the stent frame  14  includes a generally circular base  20  defining the valve orifice of the PHV  10  and at least two, and in one embodiment three, stent posts  22  extending upwardly from the base  20 . The stent frame  14  may also include a plurality of suture openings  24  in order to facilitate attachment of the stent frame  14  to the leaflet material  32  (as shown in  FIG.  1   ). 
     The stent frame  14  may be made of stainless steel, nitinol, cobalt chromium or other suitable material. It should be understood that the base  20  of the frame  14  may be generally circular in nature or it may be elliptical, oval, or other shape suitable to the curvature of the patient&#39;s valve annulus. As shown in  FIGS.  11  and  12   , the base  20  may alternatively have an undulating, rather than straight, shape to better fit the anatomical curvature of a patient&#39;s vessel. It should also be understood that the stent posts  22  that extend from the base  20  of the stent frame  14  may be placed equidistant around the circumference of the stent frame  14  or they may be placed at irregular intervals in order to more closely mimic the natural shape of the patient&#39;s native valve. The stent frame  14  maybe be produced in varying sizes, depending on the size of the patient&#39;s heart. For example, the base  20  of the stent frame  14  may have a diameter of 17, 19, 21, 23, 25, 27, 29, or 31 millimeters (mm). The base of the stent frame  14  may also include an additional plurality of suture openings  26  intended to facilitate attachment of the frame  14  to the suture ring  12  (as shown in  FIGS.  1  and  2   ). 
     The stent posts  22  generally extend upwards from the stent base  20 . In one embodiment, the stent posts  22  have a curved triangular shape, creating scalloped edges  28 , extending between top point  30 ( a ) and top point  30 ( b ), top point  30 ( b ) and top point  30 ( c ), and top point  30 ( c ) and top point  30 ( a ). The stent posts  22 , when wrapped with the leaflet material  32 , define the leaflets  18  (or cusps) of the PHV  10 , as shown in  FIG.  1   . 
     Referring now to  FIGS.  1 ,  4 , and  5   , the leaflets  18  of the PHV  10  may be created using a single piece of polymeric or bioprosthetic (such as porcine or bovine pericardium) material  32 . It will also be understood that the leaflets  18  may also be created using separate pieces of leaflet material affixed between each set of stent posts  22 . 
     As shown in  FIG.  4   , in one embodiment, a continuous sheet of leaflet material  32  may include an upper edge portion  34  and be generally rectangular in shape, or as shown in  FIG.  5   , may include an upper edge portion  34  having at least one arch  36  extending upwardly therefrom. 
     The leaflet material  32  may be made of a polymeric material, such as linear low density polyethylene (LLDPE), polytetrafluoroethylene (PTFE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), polypropylene (PP), polyurethane, polycaprolactone (PCL), polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polyoxymethylene (POM), thermoplastic polyurethane (TPU), and combinations thereof. 
     In one embodiment, the leaflet material  32  may be made of a polymeric material, such as LLDPE, that includes hyaluronic acid to prevent blood clot and thrombosis formation. An example of this material is disclosed in U.S. application Ser. No. 14/381,332, entitled Glycosaminoglycan and Synthetic Polymer Material for Blood-Contacting Applications, which is incorporated herein by reference in its entirety. 
     As shown in  FIG.  1   , the leaflet material  32  may be wrapped about and sutured to the outer circumference of the stent frame  14  through the plurality of suture openings  24  in the stent posts  22 , forming three leaflets  18  resembling the tri-leaflet aortic heart valve in the normally open position. It should be understood that a PHV may also be made having two leaflets to mimic the bi-leaflet mitral heart valve. 
     By using a single continuous piece of leaflet material mounted around the stent frame  14 , the number of sutures required to assemble the leaflets  18  is reduced. However, it should be appreciated that multiple pieces of leaflet material  32  may be mounted about the outer circumference of the stent frame  14 . 
     In one embodiment, the suture ring  12  may be covered in a suitable material, such as Dacron®, disposed atop the leaflet material  32 , and affixed to the stent frame  14  with sutures or other means, such as the use of a suitable adhesive. By covering only the suture ring  12  with Dacron® the outer and inner diameter of the PHV are reduced, allowing for a larger valve area and, consequently, a higher effective orifice area. 
     Referring again to  FIG.  1   , once the leaflet material  32  is affixed to the stent frame  14 , stent clips  16  are affixed to each of the stent posts  22  through the suture openings or with adhesive, such that the leaflet material  32  is disposed there between. The stent clips  16  may be formed of stainless steel, nitinol, or other suitable material. 
     Referring specifically to  FIGS.  6  and  7   , in one embodiment, the stent clips  16  have a facial surface  38  and suture openings  40  that may be laser cut to mimic the shape of the outer surface of stent posts  22 . Referring to  FIG.  7   , the stent clips  16  may also include a top point portion  56  that includes a left flange  42 , right flange  44 , and top flange  46  that extend from the facial surface  38  of the stent clips  16  toward the inner surface (not shown) of the stent frame  14 . 
     In another embodiment, the outer surface of the stent clips  16  may be covered with Dacron® or other suitable material (not shown) in order to provide smooth contact between the stent posts  22  and the vessel wall. 
     As shown in  FIGS.  6  and  7   , in one embodiment, the stent clips  16  may be distinct pieces, formed separately from the stent frame  14 . In another embodiment, as shown in  FIG.  8   , the stent clips  16  may be integrally formed with the stent frame  14 . In this embodiment, the top point portion  56  of each stent clip  16  may be connected to the top point portion  30  of the respective stent post  22 . In this embodiment, the stent clips  16  can be folded at the connection point  58 , with the facial surface  38  of the stent clip  16  facing the outer surface of the stent post  22 . The stent clip  16  is then affixed to the stent posts  22  through the respective suture openings or with adhesive, sandwiching the leaflet material  32  there between, as described above. 
     As shown in  FIG.  2   , the stent clip flanges ( 42 ,  44 ,  46 ) are designed to gather the leaflet material  32  at the stent post  22 , enabling the leaflets  18  to mimic the function of a native aortic heart valve cusp, opening and closing with the flow of blood through the PHV  10 . Specifically, the stent clips  16  provide improved commissure coaptation adjacent to the sent posts and enhance closing dynamics of the leaflets. 
     Referring to  FIGS.  5 ,  9 , and  10   , in another embodiment, the leaflet material  32  may include an upper edge portion  34  with a plurality of arches  36 . It should be understood that the arches  36  may be formed integrally with the single sheet of leaflet material  32  or may be attached to the upper edge portion  34  after the material is formed. The arches  36  on the upper edge portion  34  provide arched leaflets  48  (as shown in  FIG.  9   ), when wrapped around the stent frame  14 . Through the use of arched leaflets  48 , it was discovered that flow reattachment is facilitated and recirculation regions that are directly related to thrombus formation are decreased. In addition, the use of arched leaflets  48  provide an improved leaflet coaptation. 
     In another embodiment, once the sheet of leaflet material  32  is installed onto the stent frame  14 , the leaflets  18  may be further formed by applying a combination of heat and pressure to the once the planar leaflets  18 . This treatment can be used to further change the shape of the leaflets  18  into a three dimensional configuration (as is the case for native valve leaflets). In one embodiment, vacuum pressure is applied to the formed PHV  10  on the upstream side of the PHV to force the leaflets  18  to close and then heat is applied from the downstream side in order to make the polymer (which is a thermoplastic) relax and stretch under the forces exerted by the vacuum. The resulting shape of the leaflets  18  may more closely resemble the patent&#39;s native leaflet shape. 
     In other set of embodiments, the stent frame  14  may have various other designs, while the leaflet material  32  may be secured to the stent frame  14  in generally the same or similar manner as set forth above. In one embodiment, as shown in  FIGS.  11  and  12   , the base  20  of the stent frame  14  may have an undulating, rather than straight, shape to better fit the anatomical curvature of a patient&#39;s vessel. 
     In another embodiment, as shown in  FIG.  17   , an outer cap  166  may be used to secure the leaflet material to the stent frame  114 . In this embodiment, the outer cap  166  may be disposed to fit over the outer surface of the stent frame  114 , sandwiching the leaflet material between the frame  114  and the cap  166 . 
     In another set of embodiments, as shown in  FIGS.  13 - 16 , and  18 - 24   , the PHV  10  may have a stent frame that includes an upper frame portion, a base, and at least two stent posts (e.g., two stent posts, three stent posts, etc.). Referring to  FIG.  13    for example, the stent frame  114  includes an upper frame portion or a first upper frame portion  160 , a base  120 , and stent posts  122  (e.g., at least two stent posts  122 ). Generally, the upper frame portion  160  has a shape that mimics that of the upper edge  162  of and between the stent posts  122 . The upper frame portion  160  connects to the stent posts  122  only at each of the top points  130 ( a )-( c ) by stent frame extensions  164 ( a )-( c ), respectively. 
     In this embodiment, the leaflet material may be attached to the stent frame  114  as described above with the use of stent clips. However, in an alternative embodiment, as shown in  FIGS.  13 ,  14  and  15    the leaflet material may be attached to the stent frame  114  by weaving the single piece of leaflet material  132  between the stent frame  114  and the upper frame portion  160  such that either the bottom portion of the leaflet material (as shown in  FIGS.  4  and  5   ) is disposed against the inner surface of the stent frame  114  and the upper portion of the leaflet material is disposed against the outside surface of the upper frame portion  160  or the bottom portion of the leaflet material is disposed against the outer surface of the stent frame  114  and the upper portion is disposed against the inner surface of the upper frame portion  160 . The leaflet material may then be further secured to the stent frame  114  using sutures or adhesives, as described above. 
     While reducing the number of sutures needed to secure the leaflet material to the frame  114 , this embodiment also protects the formed leaflets (not shown) from possible tearing as they expand and contract over the top of the upper frame portion  160 . Moreover, in embodiments that the leaflet material  132  is woven through the stent frame  114  as shown in  FIGS.  13  and  15   , the upper frame portion  160  gathers the leaflet material  132  and enables the leaflets  118  to mimic the function of a native aortic heart valve cusp, opening and closing with the flow of blood through the PHV  10 . As such, the stent clip may be eliminated. The leaflet material  132  may be further adhered to the outside of the stent frame  114  by using a minimal amount of sutures. 
     In another embodiment of the leaflet material, as shown in  FIG.  16   , the continuous sheet of leaflet material  132  may include one or more spacings or notches  137  in the upper edge portion  134 . This embodiment of leaflet material is particularly useful with the stent frames shown and described in  FIGS.  13 - 15   . For example, each of the one or more spacing or notches  137  is between every two directly adjacent arches  136 . The one or more spacings  137  may improve coaptation of the leaflets  118  when wrapped around stent frame extensions  164 . For example, the one or more spacing  137  may help accommodating the opening and closing motions of the leaflets  118 , such that the commissures  119  meet with better conformity to achieve better coaptation and ensure minimal reverse flow of the blood when the leaflets  118  are closed, as shown in  FIG.  15   . 
     As shown in  FIGS.  18 - 20   , the stent frame  114  may include multiple upper frame portions (as discussed in  FIG.  13   ). For example, as shown in  FIG.  18   , the stent frame  114  may include a first, second, and third upper frame portions  160 ,  168 , and  170 . Using the weaving technique described above, a single or multiple pieces of leaflet material may be applied to the stent frame  114 . For example, in one embodiment, three separate pieces of leaflet material may be applied to the stent frame  114  by including leaflet extensions that extend from the leaflet material body and may be woven through the various upper frame portions  160 ,  168 , and  170 , in order to secure the leaflet material to the frame  114 . This technique may reduce the number of sutures needed to secure the material to the frame. 
     As shown in  FIGS.  21 - 26   , in yet other embodiments, a stent frame  214  may be made so that a minimal amount of stent material is needed. In this embodiment, the leaflet material may be woven through the stent frame  214  and an upper frame portion  260 , as described above, however when multiple pieces of leaflet material are employed, the leaflet extensions may be disposed though slots  272  formed through the stent frame  214 . 
     Referring now to  FIGS.  25  and  26   , like the stent frame  214  described above, a stent frame  314  is made of a minimal amount of material. In this embodiment, however, the stent frame  314  may be customized to fit individual patients by varying the height of stent posts  322  and the depth of a stent base  320 . 
     The PHV may be implanted into a patient using known surgical techniques. However, it should be appreciated that modifications may be made to the PHV to enable implantation using known trans-catheter methods. 
     Examples 
     In order to assess the commissure coaptation and fluid dynamics of the PHV in the ascending aorta, six 3D printed models of the stent and corresponding leaflets were produced to mimic the performance of the PHV. As shown in  FIGS.  27  and  28   , the models included a stent base  50 , a stent clip portion  52 , and a sheet of LLDPE leaflet material  54  wrapped around the stent base  50  and disposed between the base  50  and the stent clip portion  52 . As shown in  FIG.  28   , the aspect ratio between stent height and diameter (H/D) was varied for three different PHVs with ratios listed in Table 1, below: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Height (H) to Diameter (D) Aspect Ratio 
               
            
           
           
               
               
               
               
            
               
                   
                 Low profile (LP) 
                 Medium profile (MP) 
                 High profile (HP) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 H/D 
                 0.6 
                 0.7 
                 0.88 
               
               
                   
               
            
           
         
       
     
     Also, the arch height to diameter aspect ratio, herby referred to as h/D, was varied as shown in Table 2, below: 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Parameters used to design leaflets 
               
            
           
           
               
               
               
               
            
               
                   
                 No arch (NA) 
                 Short arch (SA) 
                 Long arch (LA) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 h/D 
                 0 
                 0.081 
                 0.116 
               
               
                   
                   
               
            
           
         
       
     
     Those examples having configurations providing full commissure coaptation were studied further, including models with a low profile/no arch (LPNA), low profile/short arch (LPSA), low profile/long arch (LPLA), medium profile/no arch (MPNA), medium profile/short arch (MPSA), and high profile/no arch (HPNA). 
     Examples 1-6 had a diameter of about 21.5 mm. The stent base  50  had a cylindrical end, which serves to keep the leaflets in place and three stent posts to form the three cusps of the valve. The rectangular piece of LLDPE  54  was cut and wrapped around the stent base  50 , creating a cylinder. The LLDPE  54  was fixed to the three stent posts to ensure a symmetric geometry in closed position of the leaflets. Fixing was performed by connecting the stent base  50  to an air vacuum and fixing the LLDPE  54  by matching the three cusps. 
     In order to mimic the PHV  10 , the stent clip portion  52  was placed on top of the LLDPE  54  in a way that created three cusps resembling the tri-leaflet PHV in the normally closed position. The stent base  50  and the stent clip portion  52  were secured together using three orthodontic rubber bands.  FIG.  26    shows the assembling process for each of the Examples 1-6. 
     Flow Loop Setup 
     Each example valve was inserted into a transparent acrylic aortic chamber machined to mimic the outer walls of an aorta. The chamber was then placed in the aortic position of a left heart simulator that was controlled by an in-house LabVIEW program. The parameters of the left heart simulator were adjusted to simulate the physiological flow and pressure conditions of the aortic valve in the in vitro setup, which were measured using ultrasonic flow probes (Transonic Inc., Ithaca, N.Y.), and the pressure upstream and downstream of the valve was measured with Validyne pressure transducers (Validyne Engineering Corp., Northridge, Calif.). 
     An ensemble average of flow curves was obtained over 20 cycles at an average resting condition (Heart Rate (HR)=60 bpm, Mean Aortic Pressure (MAP)=100 mmHg, Cardiac Output (CO)=5 L/min) using the aforementioned LabVIEW program. The working fluid for the flow loop was a mixture of water/glycerin with 38% glycerin concentration to produce a Newtonian blood analog of similar kinematic viscosity and density (v=3.5 cSt, p=1080 kg/m 3 ). 
     High Speed Imaging 
     The example valves&#39; dynamic models were evaluated using high speed imaging and particle image velocimetry (PIV). Both of these were done using the same aortic chamber, obtaining data from front viewing window and lateral side. High speed videos were captured to analyze the overall performance of the designed PHVs and to evaluate leaflet closure. To do this, an acrylic dog-leg chamber was added to the downstream of aortic chamber and a high-speed CMOS camera (FASTCAM SA3, 60 kfps, 1024×1024 px, Photron, Tokyo, Japan) was positioned in front of the dog-leg window. Images were acquired at 1000 fps. 
     Particle Image Velocimetry 
     To visualize particle movement during the PIV process, the flow was seeded with PMMA-Rhodamine B seeding particles (microParticles GmbH, Berlin, Germany) with particle sizes ranging from 1 to 20 μm. A laser sheet cut through the center plane of one leaflet and illuminated the particles. The laser sheet was created using a Nd:YLF single-cavity diode-pumped solid-state, high-repetition-rate laser (Photonic Industries, Bohemia, N.Y.) coupled with external spherical and cylindrical lenses and an orange filter. The high-speed camera was placed on the side of aortic chamber to view the laser sheet. Measurements were phase-locked with acquisition of 250 double-frame images at each time point. Commercial PIV software, DaVis (LaVision, Germany), was used for data acquisition and processing. 
     Velocity vectors were calculated using an advanced PIV cross-correlation method with a 50% overlap multi-pass approach with an initial interrogation window of 64×64 pixels which progressively reduced to 8×8 pixels interrogation window passes. No pre-processing was done, but post-processing was performed using a median filter that rejected vectors outside 2 standard deviations of the neighbor vector. The effective spatial resolution was 27 μm/(pixel) and the temporal resolution was 1000 Hz. Particle seeding density was approximately 0.02 particles per pixel and the particle displacement was around 0-10 pixels per frame (average 5 pixels). The number of particles per interrogation window averaged 20.5 which are acceptable for high-quality PIV. Velocity vectors and vorticity contours were ensemble averaged across  5  trials. 
     Definition of the Calculated Parameters 
     The following parameters are used to characterize fluid dynamics in the valve and the flow chamber used as model of the ascending aorta: 
     Regurgitation fraction: In order to make a comparison between regurgitant fractions that occur in each example valve, flow diagrams obtained from LabVIEW program assigned to the flow loop were analyzed. The regurgitation fraction is the ratio between reverse flow during the time the valve is closed to the total flow in the loop. Leakage percentage is defined as the ratio between the sum of the reverse flows that occur both during valve closure (closing fraction) and the duration of the time the valve is closed to the total flow in the loop (regurgitation fraction). 
     Effective Orifice Area (EOA): The effective orifice area (EOA) is another parameter to evaluate valve&#39;s hemodynamic performance. EOA was calculated using Gorlin equation, in which it is a function of both flow rate and transvalvular pressure gradient. 
       EOA= Q   rms /(51.6√(Δ P   mean ))  (1)
 
     Calculations were acquired over 10 cardiac cycles and then averaged to provide the representative values in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Calculated values for the Effective Orifice Area and normalized RSS of each valve model. 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 LPNA 
                 LPSA 
                 LPLA 
                 MPNA 
                 MPSA 
                 HPNA 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 EOA 
                 2.57 ± 0.087 
                 1.99 ± 0.007 
                 2.01 ± 0.415 
                 2.74 ± 0.02 
                 1.72 ± 0.031 
                  1.89 ± 0.013 
               
               
                 Normalized RSS 
                 0.14 ± .008  
                 0.023 ± 0.0029 
                 0.016 ± 0.0014 
                 0.040 ± 0.005 
                 0.017 ± 0.0001 
                 0.029 ± 0.002 
               
               
                   
               
            
           
         
       
     
     The coordinate system used to calculate different parameters are defined so that X direction is along the center plane of the heart valve and Z-direction is perpendicular to our interrogation window. U and V are velocity components respectively along X and Y directions with u′ and v′ as the velocity fluctuations in each direction. 
     Vorticity (ω z ): Regions of high vorticity indicate high tendency of fluid elements swirling and rotating along one axis. Even though flow field in aorta is three-dimensional, the vorticity along z-direction is dominant. 2D PIV results along X-Y plane provide vorticity field along Z axis which is defined as follows: 
       ω z =(∂ V/∂x )−(∂ U/∂y )  (2)
 
     Principal Reynolds Shear Stress (RSS): It is known that high shear stress results in destruction of red blood cells (hemolysis). One method to evaluate the performance of designed PHVs is to calculate RSS to obtain the optimal design for minimal blood damage. RSS is a component of total shear stress calculated from Reynolds decomposition of Navier-Stokes equation. RSS is defined as: 
       RSS=ρ√((((   u′u ′ )−(   v′v ′ ))/2) 2 +(   u′v ′ ) 2 )  (3)
 
     Turbulent Kinetic Energy (TKE): This parameter represents the kinetic energy per unit mass for eddies in a turbulent flow. The physiological effect of high TKE is extended exposure of cells to high shear stress and will result in cell membrane rapture, platelet activation and thrombosis. For a 2D PIV, TKE is expressed as: 
       TKE=½(   u′   2   +   v′   2   )  (4)
 
     Results 
     Hemodynamics Results 
     Pressure and flow data were acquired for all six examples from LabVIEW. As shown in  FIG.  29   , the pressure and flow curve for the MPSA PHV was plotted (series  401  corresponds an aortic pressure cure, series  402  corresponds to a ventricular pressure curve, and series  403  corresponds to a flow rate curve). The flow loop was adjusted to match physiological conditions and the pressure curves for the four valves, except the LPNA, were found to have the same general shape. 
     However, the LPNA valve failed to maintain the desired 120/80 mm Hg pressures. Flow was normalized by the maximum flow rate for each valve model and the normalized flow curves for all six valves are presented in  FIG.  30   . The comparison between flow curves obtained for each valve indicates an improvement in commissure coaptation based on the reduction in back flow as profile length increased or when leaflet arches were added. The regurgitation fraction is further quantified for both H/D and h/D aspect ratios.  FIGS.  31  and  32    show a decrease in regurgitation fraction with the increment in H/D and h/D respectively. The error bars in  FIGS.  31  and  32    represent the calculated standard deviation for each value. 
     Leaflet Kinematics 
     Coaptation kinematics were further studied using high-speed camera images of each valve in the flow loop. Images were acquired during four time points throughout the cardiac cycle: Early Systole (ES), Peak Systole (PS), Late Systole (LS) and Diastole. The first set of experiments were carried out using the three valve model examples without arches to evaluate the effect of H/D ( FIG.  33   ). The second set were for the medium and short profile valves with short and long arch added to their leaflets to study the effect of h/D ( FIG.  34   ). As observed in  FIGS.  33  and  34   , the large gap at the center of commissures in the LPNA valve is diminished as either the stent profile or the arch length increase. This observation indicates the increment in commissural contact as the aspect ratio and arch height increase. 
     The LPLA valve in  FIG.  34    shows warping of commissures at diastole and small amount of asymmetry at PS.  FIG.  33    also indicates that obtaining a symmetrical leaflet opening is easier when the leaflets have no arch added. MPSA had an asymmetric leaflet opening with a lag time for one leaflet to open all the way which can result in undesired fluid motion during early systolic phase. 
     Quantitative Flow Results 
     High resolution PIV was used to capture turbulent characteristics through the aortic valve and ascending aorta. Ensemble averaged velocity vectors superimposed by vorticity contours are shown at two time points (ES and PS) throughout the cardiac cycle for each PHV in the left panels of  FIG.  35    and  FIG.  36    to show the effect of stent height and leaflet arch respectively. As illustrated, the averaged velocity vectors for the six example PHVs are plotted based on the scale bar representing vorticity in a unit of inverse seconds (s −1 ). At early systole (ES) the examples with an arch result in an asymmetric velocity profile skewed toward the top along the centerline of the chamber. No significant difference was observed in the values for velocity for each example. The maximum velocity during ES was ranged from 1.3 m/s for MPNA to 1.8 m/s for LPLA. The flow streamlines for LPLA and MPSA were curved, showing a downward motion towards lower part of the flow chamber and then upward motion to obtain a straight streamline through the rest of the measurement plane. 
     The central orifice jet in short profile valves initiated perfectly symmetric during ES, however during PS the central jet for LPNA showed an upward motion at the trailing edge of the leaflet and resulted in larger separation region in the lower portion of the chamber. Except for LPSA, the other PHVs produced separation zone only on the lower part of the flow chamber, corresponding to the side of the valve with the stent post, as opposed to a free leaflet edge. No reattachment point was observed for the HPNA PHV in the measurement plane; while the rest of the PHVs showed reattachment points in 1-2 diameters downstream of the annulus (e.g., the distance from the annulus to the reattachment point is between 1 to 2 times the diameter of the respective valve size), as observed in  FIGS.  37  and  38   . Maximum velocity during PS is assigned to LPNA and was measured 3.1 m/s. 
     Maximum peak velocity for the other PHVs ranged between 1.8 m/s to 2.2 m/s. The velocities downstream of the trailing edge of the leaflet during diastole were typically less than 0.1 m/s for all the examples except for LPNA and MPNA which were measured 0.35 m/s and 0.17 respectively. The reason for higher diastolic velocity in these two PHVs was the presence of a leakage jet at the center of the commissural region. The velocity for this leakage jet was 0.7 m/s and 0.2 m/s for LPNA and MPNA models respectively. 
     RSS and TKE Distribution 
     Reynolds shear stress (RSS) is a critical parameter in predicting blood damage and calcification in heart valves. Contours of normalized RSS near PHV leaflets and inside the ascending aorta are provided in the right panels in  FIGS.  35  and  36   , for varying stent profile and arch length to study the propensity of blood cell damage in each of the six examples. Normalized values were calculated to take the difference in peak velocity for each example into account. As illustrated, the normalized RSS for the six PHVs are plotted based on the scale bar representing RSS (e.g., a unitless number). The highest value for RSS is observed in the LPNA during PS, which is 1940 dyne/cm2 with normalized RSS value of 0.14±0.008. Adding leaflet arches as well as increasing aspect ratio decreased RSS one order of magnitude. However, MPNA showed higher normalized RSS values in comparison to the other four valve, and was measured to be 0.04±0.004. The LPLA valve configuration resulted in the smallest value of normalized RSS, which was 0.016±0.0014. The measured valued for normalized RSS is presented in Table 3, above. Generally high regions of RSS were observed in the shear layer region between the central orifice jet and at the trailing edge of the leaflets. As shown in  FIGS.  35  and  36   , regions of high RSS values were diminished when arches were added to the leaflets. 
     Contours of TKE bear a resemblance to RSS plots shown in  FIGS.  35  and  36   . LPNA had highest magnitudes of TKE, corresponding to higher levels of kinetic energy for turbulent eddies. Similar to RSS, TKE was also decreased with the addition of leaflet arches and increment in aspect ratio. 
     Discussion 
     Effect of Heart Valve Profile 
     Hemodynamics and Kinematics of Leaflets 
     One major parameter that needs to be taken into account for the AV hemodynamics is to ensure a negligible regurgitation fraction during diastole to minimize the work of the heart and avoid a high shear stress jet that can induce platelet activation and hemolysis. Appropriate sealing of the leaflets is obtained through a proper aspect ratio or a modified leaflet design. Generally, short profile heart valves are more desirable due to the reduced dead space by diminishing the blockage of coronary ostium and aortic sinuses. The dead space created in higher profile PHVs supports coagulation and will increase the risk for thromboembolic complications. 
     The high-speed camera snapshots shown in  FIG.  33    indicate that the aspect ratio of LPNA and MPNA models was not large enough to cover the central gap, which leads to flow regurgitation throughout diastole. The regurgitant flow in these two valve models can be detected in the diastolic phase of the cardiac cycle. 
     All designed models were able to withstand the physiological flow and pressure condition except for the LPNA model which showed higher pressure drops across the PHV during systolic phase. This is due to the increment in the peak flow rate to maintain an average flow rate compensating for regurgitation. 
     Based on the EOA values provided in Table 3, the highest value for EOA was achieved in the MPNA valve. A decrement in EOA was observed in the HPNA valve, which is likely due to the fact that the larger leaflets take more time to fully open. The EOA for LPNA valve is shown to be relatively high, and this is likely due to the fact that LPNA valve configuration was not able to withstand normal pressure gradient of 80-120 mmHg. 
     Velocity and Vorticity Results 
     The Velocity and vorticity pattern observed in the center orifice jet shows a great dependence to the PHV geometry. LPNA and MPNA models created jets with higher systolic peak velocity throughout the ascending aorta. The higher downstream velocity present in these models is to compensate for the regurgitating flow during diastole and keep the average flow rate at the desired value of 5 L/s. No reattachment points were observed for the lower part of the HPNA model in our view plane. The reason for delayed reattachment appears to be the presence of longer stent posts act as a barrier and create a larger turbulent shear zone which delays reattachment ( FIG.  37   ). This implies leaflet coaptation does not necessarily correlate to an optimum PHV geometry. 
     Comparing all three examples together shows that the central orifice jet for the MPNA valve models achieved unidirectional flow sooner than the other two models by creating reattachment points in the 1D downstream of the trailing edge of the leaflets. 
     Effect of RSS and TKE 
     High values of RSS are strongly correlated to hemolysis and blood damage. The RSS values reduced dramatically as a result of an enhanced leaflet coaptation. The high values of RSS and TKE were more dominantly observed in the LPNA and MPNA valve models, which shows the contribution of the leakage jet in increasing the risk of blood damage. The HPNA model also resulted in larger values of RSS and TKE throughout the ascending aorta. The values measured for RSS in these examples is well below the results found previously, however they still are above the reported values for RSS threshold (˜400 dyne/cm 2 ) suggested by previous studies which can cause hemolysis and platelet activation. 
     Effect of Leaflet Arch 
     Leaflet Kinematics 
     The results indicate that leaflet arch dramatically improves commissure coaptation. The leakage flow percentage reduced from 150% in the LPNA model to 5.6% in the LPLA configuration. As a result the maximum PS downstream velocity reduced to 58% of its value in LPNA to 1.8 m/s in LPSA valve model. Additionally, maximum RSS value reduced 40% from the LPNA to LPLA model. Increments in leaflet arch length resulted in warping in the leaflet tips during diastole, which can increase the chance of fatigue. Warping was observed in the LPLA and became more noticeable for the MPSA, which also resulted in reduced EOA. An asymmetric leaflet opening and closing seen for MPSA example ( FIG.  34   ) is associated with the warping of the leaflets in their closed position. Long leaflet arches resulted in one leaflet being pushed underneath the other two which is another reason of the asymmetric opening and closing of the MPSA example. 
     Additionally, the EOA value for the MPSA is lower than LPSA and LPLA and this can be due to the larger size of leaflets and the lag in the opening time compared to the other two. 
     Velocity and Vorticity Results 
       FIG.  37    shows jets of fluid through PHVs with different stent profiles (e.g., low profile, medium profile, high profile) and  FIG.  38    shows jets of fluid through PHVs with different leaflet arch (e.g., no arch, arch). In  FIG.  37   , the blue, red, and green profiles correspond to jets of fluid for the LPNA, MPNA, and HPNA models, respectively. In  FIG.  38   , the blue and red profiles correspond to jets of fluid for the LPNA and LPSA models, respectively. In both figures the black arrows indicate where reattachment points to the aortic wall occur for the respective valve design. Earlier reattachment points were observed in both top and bottom sections of the ascending aorta for LPLA and MPNA models. The flexible arches may create a wider opening for the jet of fluid exiting through the PHV. As shown in the schematic drawing in  FIG.  37   , due to Coanda effect the fluid jet stays attached to the arch surface and this attachment deviates flow from the straight path guiding the flow to a higher point in the sinus area. Moreover, increasing the exit diameter as the starting flow develops results in higher-energy vortex ring structures with peak vorticity located further from the axis of symmetry relative to a static nozzle case. The flexible arches facilitate transfer of impulse to a greater volume of fluid and result in an enhanced turbulent mixing as well as helping the flow to slow down. This reveals the critical role that leaflet arches play in damping velocity fluctuations and initiates sooner reattachment. Hence, reduces the residence time in recirculation zones and decreases the chance of platelet activation and blood damage. 
     Even though arches provided earlier reattachment to the ascending aorta, the added arch increases leaflet area, requiring more pressure to open the leaflet all the way. The delayed opening of flaps during early systolic pushes the fluid towards the center of the chamber, resulting in vortex rings in the trailing edge of the leaflets ( FIG.  36   ). Viscous Shear Stress (VSS) data presents much lower values for all six valve models in comparison to mechanical heart valves, indicating a much lower blood damage potential. 
     Effect of RSS and TKE 
     The RSS values reduced dramatically, since the reduced leakage associated with coaptation resulted in reduced peak flow to maintain an average cardiac output. Additionally, the presence of arches at leaflet tips could act as damping mechanism by providing a variable exit diameter for the orifice jet and reduce RSS and TKE values. 
     Combined Effects and Interactions 
     Comparison of coaptation in MPNA and LPSA indicates commissural contact is more easily accomplished by the addition of leaflet arches. The combination of leaflet arch and increased profile height observed in MPSA design led to better overall hemodynamic performance. This is due to the fact that longer arches increase asymmetric leaflet opening due to warping; therefor, making short arches preferable. 
     Generally, it was demonstrated that leaflet arches and higher heart valve profile provide several advantages such as: 1) resulting in a dramatic decrease in the RSS, 2) yielding to better leaflet coaptation, and 3) minimizing regurgitation percentage. However, high stent profile may delay reattachment of flow in the aorta and slightly increases RSS. This increment can potentially escalate hemolysis and blood damage. Leaflet arches result in great enhancement of leaflet kinematics and PHV hemodynamics by optimizing the low profile design of the heart valve. 
     To the extent that the term “includes” or “including” is used in the specification or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term “or” is employed (e.g., A or B) it is intended to mean “A or B or both.” When the applicants intend to indicate “only A or B but not both” then the term “only A or B but not both” will be employed. Thus, use of the term “or” herein is the inclusive, and not the exclusive use. See Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into” are used in the specification or the claims, it is intended to additionally mean “on” or “onto.” To the extent that the term “substantially” is used in the specification or the claims, it is intended to take into consideration the degree of precision available or prudent in manufacturing. To the extent that the term “operably connected” is used in the specification or the claims, it is intended to mean that the identified components are connected in a way to perform a designated function. As used in the specification and the claims, the singular forms “a,” “an,” and “the” include the plural. Finally, where the term “about” is used in conjunction with a number, it is intended to include ±10% of the number. In other words, “about 10” may mean from 9 to 11. 
     As stated above, while the present application has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art, having the benefit of the present application. Therefore, the application, in its broader aspects, is not limited to the specific details, illustrative examples shown, or any apparatus referred to. Departures may be made from such details, examples, and apparatuses without departing from the spirit or scope of the general inventive concept.