Patent Publication Number: US-2021187135-A1

Title: Method for sterilizing heart valves

Description:
This application is a National Stage of International Patent Application No. PCT/US2018/054845, filed Oct. 8, 2018, which claims the benefit of U.S. Patent Application No. 62/572,277, filed Oct. 13, 2017, the entire contents all of which are incorporated into this application by reference for all purposes. 
    
    
     This disclosure relates generally to heart valves and, more particularly, to a method of preparing a sterilized transcatheter heart valve using electron beam sterilization. 
     Transcatheter heart valves are packaged and sterilized at a manufacturing site before they are shipped to an operation site. Currently, a heart valve is crimped at the operation site, whereupon a doctor implants the device. This process of crimping the heart valve at the operation site is inefficient and costly, and it creates opportunities for error. 
     It should be appreciated that there is a need for a method of preparing a transcatheter heart valve that can be crimped, packaged, and sterilized at the manufacturer&#39;s site. The present invention fulfills this need and provides further related advantages. 
     Some embodiments disclosed herein provide methods for preparing a sterilized heart valve. In one embodiment, the method can comprise compressing a compressible frame of a heart valve from an expanded configuration to a crimped configuration, packaging the heart valve within a sealed packaging system while the heart valve is in the crimped configuration, and sterilizing the heart valve packaged within the sealed packaging system with one or more cycles of electron beam radiation. The heart valve can comprise the frame and a plurality of leaflets coupled to the frame. Each of the plurality of leaflets can comprise an unfixed, decellularized, antigen-free biological tissue that has been treated with a solution comprising a polyol or polyhydric alcohol. 
     In one embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15-40 kGy. In another embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15-20 kGy. 
     In one embodiment, the heart valve packaged within the sealed packaging system can be sterilized with two or more cycles of electron beam radiation. In an additional embodiment, the heart valve packaged within the sealed packaging system can be sterilized with three cycles of electron beam radiation. 
     In one embodiment, the polyol or polyhydric alcohol can comprise glycerol. 
     In one embodiment, the method can further comprise coupling the heart valve to a delivery system. 
     In one embodiment, the biological tissue is pericardial tissue. In another embodiment, the biological tissue is pericardial tissue selected from the group consisting of porcine pericardial tissue and bovine pericardial tissue. 
     In one embodiment, the method can further comprise loading the heart valve within a sheath associated with the delivery system. In another embodiment, the loading step can be performed by causing the sheath to move axially over the heart valve. 
     In one embodiment, the frame can be at least partially crimped in the crimped configuration. In another embodiment, the frame can be fully crimped in the crimped configuration. The heart valve can have a first diameter in the expanded configuration and a second diameter in the crimped configuration. In a further embodiment, the second diameter can be smaller than the first diameter. In an additional embodiment, the second diameter can be less than about 50% of the first diameter. In yet another embodiment, the second diameter can be about 10% of the first diameter. 
     In one embodiment, the method can further comprise refrigerating the heart valve and the packaging system before the sterilizing step. In another embodiment, the heart valve does not comprise fluorinated materials. In an additional embodiment, the packaging system does not contain a liquid storage solution. 
     Each feature, concept, or step is independent, but can be combined with any other feature, concept, or step disclosed in this application. 
     In one embodiment, a method of preparing a sterilized heart valve can comprise treating a plurality of leaflets with a solution comprising a polyol or polyhydric alcohol. Each of the plurality of leaflets can comprise a dry, unfixed, decellularized, antigen-free biological tissue. The method can further comprise forming a heart valve, wherein the forming step can comprise coupling each of the plurality of leaflets to a compressible frame. In one embodiment, the method can further comprise compressing the frame from an expanded configuration to a crimped configuration. In another embodiment, the method can further comprise packaging the heart valve within a sealed packaging system while the heart valve is in the crimped configuration. In a further embodiment, the method can further comprise sterilizing the heart valve packaged within the sealed packaging system with one or more cycles of electron beam radiation. 
     In one embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15-40 kGy. In another embodiment, each of the one or more cycles of radiation can comprise a dose of about 15-20 kGy. 
     In one embodiment, the heart valve packaged within the sealed packaging system can be sterilized with two or more cycles of electron beam radiation. In another embodiment, the heart valve packaged within the sealed packaging system can be sterilized with three cycles of electron beam radiation. 
     In one embodiment, the polyol or polyhydric alcohol comprises glycerol. 
     In one embodiment, the method can further comprise coupling the heart valve to a delivery system. 
     In one embodiment, the biological tissue is pericardial tissue. In another embodiment, the biological tissue is pericardial tissue selected from the group consisting of porcine pericardial tissue and bovine pericardial tissue. 
     In one embodiment, the method can further comprise loading the heart valve within a sheath associated with the delivery system. In another embodiment, the loading step can be performed by causing the sheath to move axially over the heart valve. 
     In one embodiment, the frame can be at least partially crimped in the crimped configuration. In another embodiment, the frame can be fully crimped in the crimped configuration. The heart valve can have a first diameter in the expanded configuration and a second diameter in the crimped configuration. In a further embodiment, the second diameter can be smaller than the first diameter. In an additional embodiment, the second diameter can be less than about 50% of the first diameter. In yet another embodiment, the second diameter can be about 10% of the first diameter. 
     In one embodiment, the method can further comprise refrigerating the heart valve and the packaging system before the sterilizing step. In another embodiment, the heart valve does not comprise fluorinated materials. In an additional embodiment, the packaging system does not contain a liquid storage solution. 
     Each feature, concept, or step is independent, but can be combined with any other feature, concept, or step disclosed in this application. 
     In one embodiment, a method of preparing a sterilized heart valve can comprise coupling a heart valve to a delivery system. The heart valve can comprise a compressible frame and a plurality of leaflets coupled to the frame. In another embodiment, each of the plurality of leaflets can comprise a dry, unfixed, decellularized, antigen-free biological tissue. The method can further comprise compressing the frame of the heart valve from an expanded configuration to a crimped configuration. In one embodiment, the method can further comprise packaging the heart valve within a sealed packaging system while the heart valve is in the crimped configuration. In another embodiment, the method can further comprise sterilizing the heart valve packaged within the sealed packaging system with one or more cycles of electron beam radiation. 
     In one embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15-40 kGy. In another embodiment, each of the one or more cycles of radiation can comprise a dose of about 15-20 kGy. 
     In one embodiment, the heart valve packaged within the sealed packaging system can be sterilized with two or more cycles of electron beam radiation. In another embodiment, the heart valve packaged within the sealed packaging system can be sterilized with three cycles of electron beam radiation. 
     In one embodiment, the biological tissue is pericardial tissue. In another embodiment, the biological tissue is pericardial tissue selected from the group consisting of porcine pericardial tissue and bovine pericardial tissue. 
     In one embodiment, the method can further comprise loading the heart valve within a sheath associated with the delivery system. In another embodiment, the loading step can be performed by causing the sheath to move axially over the heart valve. 
     In one embodiment, the frame can be at least partially crimped in the crimped configuration. In another embodiment, the frame can be fully crimped in the crimped configuration. The heart valve can have a first diameter in the expanded configuration and a second diameter in the crimped configuration. In a further embodiment, the second diameter can be smaller than the first diameter. In an additional embodiment, the second diameter can be less than about 50% of the first diameter. In yet another embodiment, the second diameter can be about 10% of the first diameter. 
     In one embodiment, the method can further comprise refrigerating the heart valve and the packaging system before the sterilizing step. In another embodiment, the heart valve does not comprise fluorinated materials. In a further embodiment, the packaging system does not contain a liquid storage solution. 
     Each feature, concept, or step is independent, but can be combined with any other feature, concept, or step disclosed in this application. 
    
    
     
       Other features and advantages of the invention should become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
         FIG. 1  is a top perspective view of a transcatheter heart valve in accordance with one embodiment of the present invention. 
         FIG. 2A  is a perspective view of a plurality of leaflets in accordance with one embodiment of the present invention. 
         FIG. 2B  is a perspective view of the plurality of leaflets joined together to form a leaflet assembly for a transcatheter heart valve, in accordance with one embodiment of the present invention. 
         FIG. 3  is bottom perspective view of a transcatheter heart valve in an expanded configuration, in accordance with one embodiment of the present invention. 
         FIG. 4  is a side view of a transcatheter heart valve in a partially crimped configuration, in accordance with one embodiment of the present invention. 
         FIG. 5  is a side view of a transcatheter heart valve in a fully crimped configuration, in accordance with one embodiment of the present invention. 
         FIGS. 6A and 6B  are broken side views of a transcatheter heart valve, in a crimped configuration, coupled to a delivery system, in accordance with one embodiment of the present invention. 
         FIG. 7A  is a broken plan view of a transcatheter heart valve, in a crimped configuration, coupled to a delivery system and partially packaged in a packaging system, in accordance with one embodiment of the present invention. 
         FIG. 7B  is a broken perspective view of a of a fully packaged transcatheter heart valve in a packaging system, in accordance with one embodiment of the present invention. 
         FIG. 8  is a perspective view of the packaging system of  FIGS. 7A and 7B  undergoing sterilization by electron beam radiation, in accordance with one embodiment of the present invention. 
         FIG. 9  illustrates a method of preparing a heart valve in accordance with one embodiment of the present invention. 
         FIG. 10  is a graph illustrating the effects of different sterilization protocols on the tensile strengths of selected sutures. 
     
    
    
     With reference now to  FIG. 1  of the illustrative drawings, there is shown an embodiment of a transcatheter heart valve  100  that is adapted to be implanted in an aortic annulus, although it can be adapted to be implanted in other native annuluses of the heart. In one embodiment, the heart valve  100  can include a compressible frame  110 , a valvular structure  120  comprising a plurality of leaflets  122 , and a skirt  130 . Exemplary transcatheter heart valves are described in U.S. Patent Application Publication No. 2012/0123529, published on May 17, 2012, the entire contents of which are incorporated by reference into this written description. 
     The frame  110  can comprise any suitable plastically-expandable materials (e.g., stainless steel, cobalt-chromium, etc.) or self-expanding materials (e.g., nitinol) as known in the art. The skirt  130  can be positioned on the frame  110  and can be made of any combination of suitable materials, such as a fabric, polyethylene terephthalate (PET), ultrahigh molecular weight polyethylene (UHMWPE), tissue, metal, sponge, or a polymer. In one embodiment, the skirt  130  can be secured to the inside of the frame  110  by sutures  140 , which can comprise any suitable suture, such as polyester (for example, Ethibond PET suture, Ethicon), UHMWPE, polypropylene, and/or PTFE suture. In another embodiment, the sutures  140  track the curvature of a bottom edge, cusp region  125  of the leaflet structure  122 . 
     As described in more detail below, in one embodiment, the heart valve  100 , including the frame  110 , valvular structure  120 , skirt  130 , and sutures  140 , preferably does not comprise fluorinated materials. 
     With reference to  FIGS. 2A and 2B , the leaflet structure  120  comprises a plurality of leaflets  122 . In one embodiment, each of the plurality of leaflets  122  comprises a fixed, dry biological tissue, for example a fixed tissue that has been capped and dried with glycerol. An example of such tissue is referred to as “GLX tissue”, which is described in U.S. Pat. No. 8,748,490, the entire contents which is incorporated by reference. Briefly, capping is believed to reduce calcification of the tissue by chemically modifying at least some of the functional groups that bind calcium or that are degradable to such a functional group, for example, amines, carboxylic acids, or carbonyl groups. In some embodiments, tissue, for example pericardium, is contacted with a capping agent, for example, ethanolamine, then contacted with a reducing agent, for example, sodium borohydride. Exemplary methods for drying tissue include contacting the tissue with glycerol, for example, with a glycerol/ethanol solution. Embodiments of each of the methods for sterilizing tissue disclosed herein are applicable to such tissue. 
     In one embodiment, each of the plurality of leaflets  122  comprises a decellularized, antigen-free, unfixed, dry biological tissue  124  that has been treated with a solution comprising a polyol or polyhydric alcohol. 
     The term “decellularized” means the tissue is substantially free of endogenous cells. Biological tissue includes a collagen skeleton (matrix) supporting cells therein. This extracellular structure supporting the cells is generally referred to as the “extracellular matrix” (ECM). In a “decellularized” tissue, the endogenous cells have been substantially removed from the ECM. For example, in one embodiment, at least about 70%, 80%, 90%, 95%, 99%, or more, of endogenous cellular material has been removed from the extracellular matrix. The presence of endogenous cellular material can be determined using any method known in the art. 
     The term “antigen-free” means the tissue is substantially free of endogenous antigen components (e.g., proteins, lipids, carbohydrates, nucleic acids). With respect to a decellularized tissue, the term refers to a decellularized tissue where the endogenous antigen components have been substantially removed. In one embodiment, at least about 70%, 80%, 90%, 95%, 99%, or more, of endogenous antigen components are removed from the decellularized tissue. In another embodiment, the antigen-free tissue does not elicit a significant immune response against the tissue. The presence of endogenous antigen components can be determined using any method known in the art. Exemplary methods of removing antigens from tissues and decellularized extracellular matrixes produced by such methods are described in U.S. Pat. No. 9,220,733, issued Dec. 29, 2015, the entire contents of which are incorporated by reference into this written description. 
     The term “unfixed” means the tissue has not been treated with a cross-linking fixative solution. Implanted biological tissue is often treated with a cross-linking solution to stabilize the tissue, as well as to reduce the antigenicity thereof. This process of stabilization is known as fixation. Generally, the biological tissue is fixed by cross-linking the amine groups of the proteins of the tissue with an aldehyde fixative solution (e.g., glutaraldehyde). Examples of chemical fixative agents that have been used to cross-link collagenous tissues include: formaldehyde, glutaraldehyde, dialdehyde starch, hexamethylene diisocyanate, and polyepoxy compounds. 
     Glutaraldehyde is one of the most widely used fixative agents for many commercially available bioprosthetic products, but it is known to contribute to calcification, which can result in undesirable stiffening or degradation of the heart valve. This damage to the collagenous tissue of the leaflets can lead to valve failure. 
     Glutaraldehyde solutions are also used as storage and terminal sterilizing solutions for devices that include tissue. The devices are stored and shipped in a jar containing such solutions, which are opened in the operating location. Because glutaraldehyde solutions are toxic to the healthcare workers and the patient, the device is rinsed thoroughly before implantation. Disposal of the glutaraldehyde solution may be regulated in some jurisdictions. The jar of solution also increases shipping weight, as well as limiting shipping flexibility because of the hazardous nature of the solution. Pre-attaching the device to an associated delivery device or system can also be impractical when the device is stored in glutaraldehyde solutions. Any or all of these limitations apply to any liquid storage media. 
     One strategy to avoid glutaraldehyde as a storage solution is to “dry” the biological tissue  124 . Biological tissue comprises free water (between strands of the tissue) and bound water (within the strands of the tissue). The term “dry” refers to tissue that has bound water, but that is substantially devoid of free water. For example, in one embodiment, the plurality of leaflets comprising biological tissue are treated with a solution that causes the free water to be replaced with one or more other compounds (e.g., a polyol, glycerol, propylene glycol, a polyether, polyethylene glycol (PEG), polypropylene glycol, etc.). In another embodiment, the plurality of leaflets is treated with a solution comprising a polyol or polyhydric alcohol. In another embodiment, the polyol or polyhydric alcohol can comprise glycerol. The resulting “dry” tissue remains flexible, and can be stored outside of liquid for extended periods without degradation of functionality. This is contrasted with “dehydrated” tissue, which is substantially completely dry, for example, freeze-dried, such that substantially all of the water, free and bound, is removed. 
     In one embodiment, the biological tissue  124  can be pericardial tissue. In another embodiment, the biological tissue  124  can be pericardial tissue selected from the group consisting of porcine pericardial tissue and bovine pericardial tissue. 
     With continued reference to  FIGS. 2A and 2B , in one embodiment, each of the plurality of leaflets  122  (comprising the biological tissue  124  described above) can include a cusp region  125 , a commissure region  126 , and a free edge region  127 . In another embodiment, the plurality of leaflets  122  can be coupled to each other at the commissure regions  126  so that the free edge regions  127  are aligned. 
     With reference to  FIG. 3 , in one embodiment, each of the plurality of leaflets  122  can be coupled to the compressible frame  110 . In another embodiment, the plurality of leaflets  122  can be coupled to the compressible frame  110  in a configuration that allows the leaflet structure  120  to collapse in a tricuspid arrangement. In a further embodiment, a lower edge of the leaflet structure  120  can have an undulating, curved-scalloped shape (suture line  140  tracks the scalloped shape of the leaflet structure  120 ). 
     With reference to  FIGS. 3-5 , in one embodiment, the compressible frame  110  of the heart valve  100  can be compressed from an expanded configuration ( FIG. 3 ) to a crimped configuration (e.g.,  FIGS. 4 and 5 ). In another embodiment, the frame  110  can be at least partially crimped in the crimped configuration. In a further embodiment, the frame  110  can be fully crimped in the crimped configuration. 
     The heart valve  100  can have a first diameter d 1  in the expanded configuration ( FIG. 3 ) and a second diameter d 2  in the crimped configuration (e.g.,  FIGS. 4 and 5 ). As is shown in  FIGS. 4 and 5 , in one embodiment, the second diameter d 2  can be smaller than the first diameter d 1 . In another embodiment, the second diameter d 2  can be less than about 50% of the first diameter d 1 . In a further embodiment, the second diameter d 2  can be about 10% of the first diameter d 1 . 
     Methods of crimping a compressible frame  110  are known in the art. For example, exemplary loaders for transcatheter heart valves and exemplary methods of crimping transcatheter heart valves are described in U.S. Patent Application Publication No. 2017/0049567, filed Aug. 16, 2016, the entire contents of which are incorporated by reference into this written description. 
     With reference to  FIGS. 6A and 6B , in one embodiment, the heart valve  100  can be coupled to a delivery system  150 . Expandable heart valves are known in the art, and the illustrated valve  100  is representative of a number of such valves that can be converted from a narrow, crimped configuration to a wider, expanded configuration. Typically, the valves are balloon expanded into position at a target annulus after having been advanced through the vasculature. The most common delivery routes commence at the femoral or carotid arteries, though other more direct routes through chest ports are also known. One particularly successful expandable prosthetic heart valve is the Edwards SAPIEN Transcatheter Heart Valve, available from Edwards Lifesciences of Irvine, Calif. The Edwards SAPIEN valve may be placed either through a transfemoral (RetroFlex 3 Transfemoral Delivery System from Edwards Lifesciences) or transapical (Ascendra Transapical Delivery System from Edwards Lifesciences) approach.  FIG. 6A  illustrates a system much like the RetroFlex 3 Transfemoral Delivery System from Edwards Lifesciences. 
     In one embodiment, the delivery system  150  can include an elongated catheter  151  having an expansion balloon  152  near a distal end of the catheter. The heart valve  100  can mount around the balloon  152  and be expanded by it. The system can further include proximal connectors  153 , for example, Luer connectors, for delivery of balloon inflation fluid, passage of a guide wire, or other such functions. As described in more detail below, in another embodiment, the delivery system  150  preferably does not comprise fluorinated materials. 
     With particular reference to  FIG. 6B , in a further embodiment, the heart valve  100  can be loaded within a sheath  154  associated with the delivery system  150 . For example, the heart valve  100  can be compressed to a crimped configuration such that the second diameter d 2  is smaller than the inner diameter of the sheath  154 . In this configuration, the loading step can be performed by causing the sheath  154  to move axially over the heart valve  100 . In some embodiments, the heart valve  100  is at least partially self-expanding. 
     With reference to  FIGS. 7A and 7B , in one embodiment, the heart valve  100  can be packaged within a sealed packaging system  160  while the heart valve  100  is in the crimped configuration. In another embodiment, the packaging system  160  does not contain a liquid storage solution. In a further embodiment, the packaging system  160  can comprise a primary storage container  161  and a secondary storage container  167 . As described in more detail below, in an additional embodiment, the packaging system  160  preferably does not comprise fluorinated materials. 
     For example,  FIG. 7A  illustrates a heart valve  100  and delivery system  150  packaged in an exemplary packaging system  160 . In one embodiment, the packaging system  160  can comprise a primary storage container  161  and a secondary storage container  166 . In another embodiment, the primary storage container  161  can include a primary storage container  161  in the form of a tray  162  and a sheet-like lid  164 . In one embodiment, the tray  162  features a cavity  163 , which retains and stabilizes the heart valve  100  within the primary storage container  161 . The cavity  163  can be sized and configured to retain the heart valve  100  by itself, the heart valve  100  coupled to a delivery system  150 , or the heart valve  100  loaded within a sheath  154  associated with the delivery system  150 . In an additional embodiment, the lid  164  can adhere to an upper rim  165  of the tray  162 . 
       FIG. 7B  is a perspective view of a secondary storage container  166  in the form of a pouch  167 . In one embodiment, the storage pouch  167  can receive the primary storage container  161 . During packaging, the primary storage container  161  is placed within the pouch  167  and a seal  168  is closed to seal the packaging system  160 . With the seal  168  closed, the sealed packaging system  160  provides a barrier against contamination from oxygen, moisture, or other contaminants. 
     With reference to  FIG. 8 , in one embodiment, the heart valve  100  packaged within the sealed packaging system  160  can be sterilized with one or more cycles of electron beam (e-beam) radiation  170 . For example, in one embodiment, the heart valve  100  in the sealed packaging system  160  can pass under a linear accelerator  172 , which accelerates electrons from an electrical source. It is believed that the accelerated, high-energy electrons  170  interact with molecules in the sealed packaging system  160  and induce breaks in the DNA double helix of living organisms such as bacteria, which creates a sterile environment. 
     In some embodiments, one cycle of electron beam radiation consists of coverage on both the top side and bottom side of the packaging system  160 . In one embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15-40 kGy. In another embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15-20 kGy. In a further embodiment, each of the one or more cycles of electron beam radiation can comprise a dose of about 15 kGy, about 16 kGy, about 17 kGy, about 18 kGy, about 19 kGy, or about 20 kGy. 
     In one embodiment, the heart valve  100  packaged within the sealed packaging system  160  can be sterilized with two or more cycles of electron beam radiation. In an additional embodiment, the heart valve  100  packaged within the sealed packaging system  160  can be sterilized with three cycles of electron beam radiation. In a further embodiment, the method can further comprise refrigerating the heart valve and the packaging system before the sterilizing step. 
     Electron beam sterilization of biological tissue is known in the art. For example, exemplary methods of sterilizing a biological tissue by exposing the tissue in saline solution to a beam of accelerated electrons are described in U.S. Pat. No. 6,203,755, filed Mar. 4, 1994, the entire contents of which are incorporated by reference into this written description. 
     With reference now to  FIG. 9 , some embodiments provide methods for preparing a sterilized heart valve. In one embodiment, the method comprises treating or contacting  610  a plurality of leaflets with a solution comprising a polyol or polyhydric alcohol. As described above, each of the plurality of leaflets comprises an unfixed, decellularized, antigen-free biological tissue. The treatment  610  with a solution comprising a polyol or polyhydric alcohol produces a “dry” biological tissue, as is understood in the art. In another embodiment, the method can further comprise forming a heart valve, wherein the forming step can comprise coupling  620  each of the plurality of leaflets to a compressible frame. In a further embodiment, the method can further comprise coupling  630  the heart valve to a delivery system. In an additional embodiment, the method can further comprise compressing  640  the frame from an expanded configuration to a crimped configuration. In yet another embodiment, the method can further comprise packaging  650  the heart valve within a sealed packaging system while the heart valve is in the crimped configuration. In one embodiment, the method can further comprise sterilizing  660  the heart valve packaged within the sealed packaging system with one or more cycles of electron beam radiation. 
     It should be understood that each feature, concept, or step is independent, and can be combined with any other feature, concept, or step disclosed in this application. Moreover, certain steps can be omitted entirely, as will be understood by a person of ordinary skill in the art. 
     For example, another embodiment comprises compressing  640  a compressible frame of a heart valve from an expanded configuration to a crimped configuration, packaging  650  the heart valve within a sealed packaging system while the heart valve is in the crimped configuration, and sterilizing  660  the heart valve packaged within the sealed packaging system with one or more cycles of electron beam radiation. In this embodiment, the heart valve can comprise the frame and a plurality of leaflets coupled to the frame. In one embodiment, each of the plurality of leaflets can comprise an unfixed, decellularized, antigen-free biological tissue that has been treated with a solution comprising a polyol or polyhydric alcohol. In an alternative embodiment, each of the plurality of leaflets can comprise a dry, unfixed, decellularized, antigen-free biological tissue. 
     Dry heart valves are commonly sterilized with ethylene oxide (EO, ETO). However, EO sterilization does not work well on heart valves in a compressed configuration. When the heart valve is pre-crimped, the EO gas is unable to penetrate and effectively sterilize the surfaces of the heart valve. One method for working around this limitation is contacting the uncrimped device with EO, following by contacting the partially crimped device with EQ. Each round of EO potentially damages the tissue and/or changes the leaflet shape. 
     Leaflet structures  120  comprising the biological tissues  124  described above are able to undergo a more efficient electron beam sterilization process while in a compressed configuration. 
     It should be appreciated from the foregoing description that the present invention provides a method of preparing a transcatheter heart valve that can be crimped, packaged, and sterilized at the manufacturer&#39;s site. The heart valve processed according to these methods minimizes crimping error and, as suggested by the examples below, exhibits advantageous mechanical properties as well as favorable biological and histological responses. 
     Other objectives, features, and advantages of the present embodiments will become apparent from the following specific examples. The specific examples, while indicating specific embodiments, are provided by way of illustration only. Accordingly, the present invention also includes those various changes and modifications within the spirit and scope of the invention that may become apparent to those skilled in the art from this detailed description. The following examples are illustrative only, and are not limiting of the disclosure in any way whatsoever. 
     EXAMPLE 1 
     One study compared the effect of sterilization methods on crimped tissue. In the study, valves were constructed from GLX tissue leaflets as described in U.S. Pat. No. 8,748,490 mounted in Edwards Sapien 3 valve-frames. The resulting devices were crimped onto expansion balloons and sterilized either with ethylene oxide (EO or electron-beam. The heart valves sterilized with the EO process were subjected to a dosage from about 436 to about 558 mg/L of gas over 6 hours and a temperature of from about 48° C. to about 54° C. The heart valves sterilized with the e-beam process were subjected to a maximum dose of about 30 kilogray (kGy). A control valve was sterilized by the e-beam process in an expanded configuration. 
     The valves were then aged and expanded to the labeled size. After eight weeks, the crimped tissue sterilized by the EO process exhibited a deformed leaflet structure, with a triangular opening and a yellow discoloration. It is believed that cross-linking, and possibly heat generated in the EO process caused the leaflets to shape-set and to deform in the crimped configuration. 
     The tissue in the valves that were pre-crimped and sterilized with e-beam was more flexible and did not exhibit the same level of shape deformity or discoloration. The shape, color, and pliability of these valves was much closer to that of the control valve, which was e-beam sterilized in the expanded configuration. 
     In hydrodynamic testing, all of the valves exhibited good coaptation with either no or a very small central hole. All valves exhibited some mismatch and puckering. 
     Each of the leaflets was then removed from each of the heart valves, and three dimensions of each leaflet measured: a width at the top or free edge; a width at a mid-height; and a height. The dimensions of the EO and e-beam sterilized crimped leaflets were similar. 
     EXAMPLE 2 
     One study analyzed the effect of e-beam sterilization on the tensile strengths of materials commonly used in heart valves. In the study, cloth materials (i.e., knitted polyester, PET woven 70 mm, and PET woven ribbon 65 HD) and suture materials (i.e., PET (Ethibond 4-0 suture, Ethicon), UHMWPE (Force Fiber suture, Teleflex Medical), PTFE, and PTFE round) underwent e-beam sterilization at a maximum dose of about 30 kilogray. The tensile strength of each of the various materials was tested against the tensile strength of the respective control that underwent EO sterilization under the conditions described in Example 1. 
     With reference to  FIG. 10 , e-beam sterilization degraded PTFE suture tensile strength by at least 50%, while the tensile strengths of the non-fluorinated sutures materials were unaffected. Similarly, e-beam exposure did not degrade the tensile strengths of the fabrics. 
     Current valves often include components, such as suture, that comprise PTFE. It is believed that contacting these materials with an electron beam cleaves the fluorinated polymers, which changes the material properties of the plastic, causing embrittlement. This problem is not present with non-fluorinated materials under the experimental conditions, such as ultra-high molecular weight polyethylene materials. 
     EXAMPLE 3 
     The effect of e-beam sterilization on tissue calcification was studied in rabbits using the experimental conditions of Example 3 of U.S. Pat. No. 8,748,490, the disclosure of which is incorporated by reference. In this study, dry, fixed bovine pericardium (GLX) and dry, unfixed, decellularized, antigen-free bovine pericardium (“unfixed”) were sterilized by e-beam or by EO as described in Example 1. Control samples were bovine pericardium fixed with glutaraldehyde and stored in a glutaraldehyde terminal sterilization solution. 
     Histological analysis of the sterilized unfixed tissue showed that the e-beam-sterilized pericardium retained a collagen “crimp” structure, but that the EO sterilization eliminated this structure. EO-sterilized unfixed tissue was not dimensionally stable, instead curling and crimping on itself, behavior which was not observed in the e-beam sterilized unfixed tissue. No microstructural differences were observed between the e-beam- and EO-sterilized GLX pericardium. 
     The samples were implanted in rabbits and the calcification levels were measured in the explanted tissue. In general, the more calcified a tissue becomes, the less durable it is. With reference to Table 1, which tabulates the mean calcium in μg per mg of dry tissue, electron beam sterilization did not increase the calcification in the GLX or in the unfixed tissue. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 N 
                 Calcium (μg/mg) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Control 
                 22 
                 170.41 
               
               
                 GLX, EO 
                 22 
                 101.5 
               
               
                 GLX, e-beam 
                 22 
                 103.3 
               
               
                 Unfixed, EO 
                 20 
                 6.81 
               
               
                 Unfixed, e-beam 
                 22 
                 3.1 
               
               
                   
               
            
           
         
       
     
     Explanted EO-sterilized pericardium exhibited significantly greater degradation compared with the e-beam sterilized samples. 
     It should be appreciated from the foregoing description that the present disclosure provides a method of preparing a transcatheter heart valve that can be crimped, packaged, and sterilized at the manufacturer&#39;s site. A heart valve processed according to these methods minimizes crimping error and exhibits advantageous mechanical properties as well as favorable biological and histological responses. 
     Specific methods, devices, and materials are described, although any methods, devices, and materials similar or equivalent to those described can be used in the practice or testing of the present embodiment. Unless defined otherwise, all technical and scientific terms used in this written description have the same meanings as commonly understood by one of ordinary skill in the art to which this embodiment belongs. 
     The terms “a,” “an,” and “at least one” encompass one or more of the specified element. That is, if two of a particular element are present, one of these elements is also present and thus “an” element is present. The terms “a plurality of” and “plural” mean two or more of the specified element. 
     The term “or” used between the last two of a list of elements means any one or more of the listed elements. For example, the phrase “A, B, or C” means “A, B, and/or C,” which means “A,” “B,” “C,” “A and B,” “A and C,” “B and C,” or “A, B, and C.” 
     The term “coupled” generally means physically coupled or linked and does not exclude the presence of intermediate elements between the coupled items absent specific contrary language. 
     Without further elaboration, it is believed that one skilled in the art, using the proceeding description, can make and use the same to the fullest extent. Persons skilled in the art will appreciate that various modifications of the embodiments described herein can be made without departing from the teachings of this disclosure, the scope of which is defined only by the following claims.