Patent Publication Number: US-11648122-B2

Title: Techniques for use with prosthetic valve leaflets

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is a Continuation of U.S. patent application Ser. No. 16/756,235 to Harari et al., filed Apr. 15, 2020, and entitled “Techniques for use with prosthetic valve leaflets,” which published as US Pub. 2020/0281723, and which is the US National Phase of PCT application IL2018/050024 to Harari et al., filed Jan. 8, 2018, and entitled “Techniques for use with prosthetic valve leaflets,” which published as WO 2019/077595, and which is a Continuation of U.S. patent application Ser. No. 15/788,407 to Harari et al., filed Oct. 19, 2017, and entitled “Techniques for use with prosthetic valve leaflets” (now U.S. Pat. No. 9,895,226). 
    
    
     FIELD OF THE INVENTION 
     Some applications of the present invention relate in general to prosthetic heart valves. More specifically, some applications of the present invention relate to techniques for testing the flexibility of prosthetic leaflets to be used in prosthetic heart valves. 
     BACKGROUND 
     Prosthetic heart valves may be constructed of a frame to which prosthetic leaflets are attached, the leaflets providing check-valve functionality by opening in response to blood flow in a first direction, and closing in response to blood flow in a second direction. In order to inhibit leakage (“regurgitation”) of blood between the closed leaflets in the second direction, it is important that the leaflets coapt well against each other. 
     SUMMARY OF THE INVENTION 
     Techniques are provided for determining one or more flexibility values of a prosthetic valve leaflet by draping the leaflet over a bar in one or more orientations, and measuring how low the leaflet hangs below the bar. This measurement is made by elevating the bar and measuring an elevation of the bar with respect to a reference. For some applications, the bar is positioned such that the leaflet draped over the bar blocks a light beam, and the bar is then elevated until the leaflet no longer blocks the light beam. The flexibility value is determined responsively to the elevation of the bar at which the leaflet no longer blocks the light beam. 
     Prosthetic valves are constructed using prosthetic valve leaflets that have complementary flexibility values. 
     There is therefore provided, in accordance with an application of the present invention, apparatus for testing a prosthetic heart valve leaflet, the apparatus including: 
     a vertical post, having a longitudinal axis; 
     a horizontal bar having a bar-axis that lies on a vertical bar-plane, the bar being configured to support the leaflet along the bar-axis such that the leaflet drapes over the bar; 
     a linear actuator, movably coupling the bar to the post, actuation of the actuator moving the bar vertically in the bar-plane; 
     a light source, configured to emit a beam of light, and oriented to direct the beam through the bar-plane; 
     a gauge, configured to measure an elevation of the bar above the beam; and 
     a detector, configured and positioned to detect the beam, and to generate a detection-signal indicative of detection of the beam. 
     In an application, the bar extends laterally away from the post. 
     In an application, the light source is disposed laterally from the post. 
     In an application, the light source is oriented to direct the beam horizontally through the bar-plane. 
     In an application, the coupling, by the actuator, of the bar to the post, is such that the moving of the bar vertically in the bar-plane includes moving the bar vertically through the beam. 
     In an application, the light source includes a laser, and the light beam includes a laser beam. 
     In an application, the apparatus further includes a platform having a surface, the platform coupled to the post such that the bar-plane intersects the platform, the actuation of the actuator moving the bar vertically, in the bar-plane, with respect to the platform. 
     In an application, the light source is adjustably coupled to the platform, such that a distance between the beam of light and the surface is adjustable by adjusting a position of the light source with respect to the platform. 
     In an application, the bar has an initial position with respect to the platform, in which the leaflet is placeable across the bar and in contact with the surface. 
     In an application, in the initial position, the bar is disposed below the surface. 
     In an application, the platform has a guide that defines a guide-outline that (i) corresponds to a leaflet-outline of the leaflet, and (ii) has a guide-outline position and a guide-outline orientation that indicate, respectively, a leaflet-outline position and a leaflet-outline orientation in which the leaflet is to be placed when the leaflet is placed across the bar and in contact with the surface. 
     In an application, the platform is coupled to the post such that the bar-plane bisects the guide-outline. 
     In an application, the platform is coupled to the post such that the bar-plane bisects the guide-outline symmetrically. 
     In an application: 
     the platform is a first platform, 
     the guide is a first guide, 
     the guide-outline is a first guide-outline, 
     the apparatus further includes a coupling, 
     the first platform is removably couplable to the post via the coupling 
     when the first platform is coupled to the post via the coupling, the bar-plane bisects the first guide-outline at a first angle, 
     the apparatus further includes a second platform that has a second guide that defines a second guide-outline that corresponds to the leaflet-outline of the leaflet, 
     the second platform is removably couplable to the post via the coupling, and 
     when the second platform is coupled to the post via the coupling, the bar-plane bisects the second guide-outline at a second angle. 
     In an application: 
     the guide is a first guide, 
     the guide-outline is a first guide-outline, 
     the platform has a second guide that defines a second guide-outline that corresponds to the leaflet-outline of the leaflet, 
     the apparatus has a first guide-state in which the bar-plane bisects the first guide-outline, 
     the apparatus has a second guide-state in which the bar-plane bisects the second guide-outline, and 
     the apparatus further includes a coupling via which the platform is movably coupled to the post, such that movement of the platform with respect to the post transitions the apparatus between the first guide-state and the second guide-state. 
     In an application, in the first guide-state, the bar-plane bisects the first guide-outline at a first angle, and in the second guide-state, the bar-plane bisects the second guide-outline at a second angle. 
     In an application, in the first guide-state, the bar-plane bisects the first guide-outline symmetrically, but in the second guide-state, the bar-plane bisects the second guide-outline asymmetrically. 
     In an application, the coupling is a rotating coupling, and rotation of the platform with respect to the post via the rotating coupling transitions the apparatus between the first guide-state and the second guide-state. 
     In an application, the platform defines a longitudinal hollow that lies on the bar-plane, and the bar, in its initial position, is disposed in the hollow. 
     In an application, the apparatus further includes a clamping element, movably coupled to the bar, and configured to clamp the leaflet to the bar. 
     In an application, the clamping element includes a rod, parallel to the bar, and configured to clamp the leaflet against the bar along the bar-axis. 
     In an application, the apparatus further includes a spring that provides a clamping force to clamping element. 
     There is further provided, in accordance with an application of the present invention, apparatus for testing a prosthetic heart valve leaflet, the apparatus including: 
     a bar having a bar-axis, the bar being configured to support the leaflet along the bar-axis such that the leaflet drapes over the bar; 
     a light source, configured to emit a beam of light; 
     a detector, configured to detect the beam, and to generate a detection-signal indicative of detection of the beam; 
     a linear actuator, movably coupling the bar to the light source, actuation of the actuator moving the bar with respect to the beam; 
     a gauge, configured to measure an elevation of the bar above the beam, the elevation changing with the moving of the bar by the actuator; 
     a display, and 
     circuitry, electrically connected to the detector, the gauge, and the display, and configured:
         to receive, from the gauge, the measured elevation,   to receive the detection-signal from the detector, and   in response to the detection-signal, to drive the display to display the elevation that was measured when the detection-signal was received by the circuitry.       

     In an application, the linear actuator is configured such that the actuation of the actuator moves the bar through the beam. 
     In an application, the gauge is configured to continuously measure the elevation, and the circuitry is configured to continuously receive the measured elevation. 
     In an application, the circuitry is configured: 
     while the detection-signal is not received by the circuitry, to continuously drive the display to display the continuously-measured elevation, and in response to the detection-signal, to maintain, on the display, the elevation that was measured at a time that the detection-signal was received by the circuitry. 
     There is further provided, in accordance with an application of the present invention, a method for determining a flexibility of a prosthetic heart valve leaflet, the method including: 
     placing the leaflet across a bar, and positioning the bar such that the leaflet drapes over the bar and blocks a beam of light emitted by a light source; 
     while the leaflet remains draped over the bar, elevating the bar at least until the leaflet stops blocking the beam; 
     identifying an elevation, of the bar from the beam, at which the leaflet stopped blocking the beam; and 
     responsively to the identified elevation, assigning a flexibility value to the leaflet. 
     In an application, elevating the bar at least until the leaflet stops blocking the beam includes moving the bar through the beam. 
     In an application, the bar is movably coupled to a post via a linear actuator, and elevating the bar includes actuating the linear actuator. 
     In an application, the light source is a laser, and the beam of light is a laser beam, and: 
     positioning the bar such that the leaflet blocks the beam of light includes positioning the bar such that the leaflet blocks the laser beam; and 
     elevating the bar at least until the leaflet stops blocking the beam includes elevating the bar at least until the leaflet stops blocking the laser beam. 
     In an application, the method further includes clamping the leaflet to the bar. 
     In an application, determining the flexibility of the leaflet includes determining the flexibility of a first leaflet, and the method further includes: 
     determining a flexibility of a second prosthetic heart valve leaflet; 
     identifying that the flexibility of the first leaflet and the flexibility of the second leaflet are within a threshold flexibility difference of each other; and 
     in response to the identifying, assembling a prosthetic heart valve by attaching the first leaflet and the second leaflet to a frame. 
     In an application: 
     positioning the bar such that the leaflet blocks the beam includes positioning the bar such that the leaflet blocks the beam from reaching a detector configured to detect the beam, 
     elevating the bar at least until the leaflet stops blocking the beam includes elevating the bar at least until the detector detects the beam, and 
     identifying the elevation includes identifying the elevation, from the beam, at which the bar was disposed when the detector detected the beam. 
     In an application, placing the leaflet across the bar includes placing the leaflet on a surface of a platform. 
     In an application, elevating the bar at least until the leaflet stops blocking the beam includes elevating the bar at least until a gap forms between the leaflet and the platform, and the beam passes through the gap. 
     In an application, the method further includes, prior to elevating the bar, adjusting a distance between the beam and the surface by adjusting a position of the light source with respect to the platform. 
     In an application, placing the leaflet on the surface of the platform includes placing the leaflet on the surface of the platform while the bar is disposed below the surface of the platform. 
     In an application, placing the leaflet across the bar includes placing the leaflet across the bar in a first orientation of the leaflet with respect to the bar, the elevation is a first elevation, and assigning the flexibility value to the leaflet includes assigning a first flexibility value to the leaflet, and the method further includes: 
     placing the leaflet across the bar in a second orientation of the leaflet with respect to the bar, and positioning the bar such that the leaflet drapes over the bar in the second orientation and blocks the beam; 
     while the leaflet remains draped over the bar in the second orientation, elevating the bar at least until the leaflet stops blocking the beam; 
     identifying a second elevation, of the bar from the beam, at which the leaflet in the second orientation stopped blocking the beam; and 
     responsively to the identified second elevation, assigning a second flexibility value to the leaflet. 
     In an application, in the first orientation, the leaflet is draped symmetrically over the bar, and in the second orientation, the leaflet is draped asymmetrically over the bar. 
     In an application, placing the leaflet across the bar in the first orientation includes placing the leaflet within a first guide defined by a surface of a platform, and placing the leaflet across the bar in the second orientation includes placing the leaflet within a second guide defined by the surface of the platform. 
     In an application: 
     placing the leaflet across the bar in the first orientation includes placing the leaflet within the first guide while the first guide is aligned with the bar; 
     placing the leaflet across the bar in the second orientation includes placing the leaflet within the second guide while the second guide is aligned with the bar; and 
     the method further includes, prior to placing the leaflet across the bar in the second orientation, aligning the second guide with the bar by rotating the platform with respect to the bar. 
     There is further provided, in accordance with an application of the present invention, apparatus for testing a prosthetic heart valve leaflet, the apparatus including: 
     a platform having a surface; 
     a bar:
         movably coupled to the platform,   having an initial position with respect to the platform, in which the leaflet is placeable across the bar and in contact with the surface, and   being movable out of the initial position and away from the surface, so as to lift the leaflet away from the surface;       

     a gauge, coupled to the platform and the bar, and configured to measure an elevation between the bar and the platform; and 
     a sensor, configured to detect a gap between the leaflet and the surface, and to generate a detection-signal indicative of detection of the gap. 
     In an application, the detection-signal is an audio signal, and the sensor is configured to generate the audio signal. 
     In an application, the detection-signal is a visual signal, and the sensor is configured to generate the visual signal. 
     In an application, the gauge is configured to measure an elevation-difference between (i) a present elevation between the bar and the platform, and (ii) an initial-position elevation between the bar and the platform when the bar is in the initial position. 
     In an application, the platform is shaped such that the surface is a horizontal surface, the bar is a horizontal bar, the apparatus further includes a vertical post that is coupled to and extends upward from the platform, and the bar is movably coupled to the platform by being coupled to the post and vertically slidable along the post. 
     In an application, the sensor: 
     includes at least one electrode positioned on the platform to be in contact with the leaflet, 
     is configured to detect electrical contact between the leaflet and the electrode, and 
     is configured to detect the gap by detecting a reduction in the electrical contact. 
     In an application, the apparatus further includes a controller, and: 
     the controller includes:
         a display; and   circuitry that interfaces with the display, the gauge and the sensor, and the circuitry, upon receipt of the detection-signal, drives the display to display the elevation.       

     In an application, the circuitry drives the gauge to measure the elevation upon receipt of the detection-signal. 
     In an application, the gauge is configured to generate an elevation-signal indicative of the measured elevation, and the apparatus further includes a controller, the controller including circuitry configured to: 
     receive the detection-signal and the elevation-signal, and 
     responsively to the detection-signal and the elevation-signal, to provide an output indicative of an elevation, between the bar and the platform, at which the gap is detected. 
     In an application, the circuitry is configured to, in response to the detection-signal, drive the gauge to generate the elevation-signal. 
     In an application, the gauge is configured to generate the elevation-signal independently of the circuitry receiving the detection-signal. 
     In an application, the apparatus further includes a display, and: 
     the circuitry is configured to drive the display to display the elevation independently of the circuitry receiving the detection-signal, and 
     the circuitry is configured to provide the output by maintaining, on the display, the elevation that was measured at a time that the detection-signal was received by the circuitry. 
     In an application, the sensor includes: 
     a laser, configured to emit a laser beam, and positioned to direct the laser beam to pass across the surface; and 
     a detector, configured to detect that the laser beam has passed across the surface. 
     In an application, the laser is positioned to direct the laser beam to pass across the surface within 2 mm of the surface. 
     In an application, the laser is positioned to direct the laser beam to pass across the surface between 0.4 and 0.6 mm of the surface. 
     In an application: 
     the platform is shaped such that the surface is a horizontal surface, 
     the bar is a horizontal bar, 
     the laser is positioned to direct the laser beam horizontally, 
     the apparatus further includes a vertical post that is coupled to and extends upward from the platform, and 
     the bar is movably coupled to the platform by being coupled to the post and vertically slidable along the post. 
     In an application, sliding of the bar vertically along the post moves the bar through the laser beam. 
     In an application, the laser beam is orthogonal to the bar. 
     In an application, the platform defines a guide that indicates an orientation in which the leaflet is to be placed on the surface. 
     In an application, the leaflet has a size and a shape, and the guide has a size and a shape that match the size and the shape of the leaflet. 
     In an application, the guide is a marking on the surface. 
     In an application, the guide is a depression in the surface. 
     In an application, the guide is a first guide, the orientation is a first orientation, and the platform further defines a second guide that indicates a second orientation that is different to the first orientation. 
     In an application, the platform is movable between a first-guide state and a second-guide state, such that: 
     in the first-guide state, the first guide is at a location with respect to the sensor, and is in the first orientation, and 
     in the second-guide state, the second guide is at the location in the second orientation. 
     In an application, the second orientation is orthogonal to the first orientation. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 ,  2 A -E, and  3  are schematic illustrations of a system for testing prosthetic heart valve leaflets, in accordance with some applications of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is made to  FIGS.  1 ,  2 A -E, and  3 , which are schematic illustrations of a system  20  for testing a prosthetic heart valve leaflet  10 , in accordance with some applications of the invention.  FIG.  1    shows system  20  alone, and  FIGS.  2 A-E  show the system being used to test leaflet  10 , in accordance with some applications of the invention. Prosthetic heart valve leaflets  10  are typically cut from animal tissue such as bovine pericardium, whose flexibility naturally varies between animals, and even between regions of the tissue within the same animal Typically, system  20  is used to determine the flexibility of leaflets  10 . For example, the system may be used to determine one or more flexibility values of the leaflet. The leaflet may be categorized according to the one or more flexibility values. Such categorization is hypothesized by the inventors to facilitate construction of prosthetic valves comprising such leaflets in order to reduce or eliminate regurgitation of blood between the prosthetic leaflets of the prosthetic valve. For example, for an individual prosthetic valve, prosthetic leaflets would be selected having similar or otherwise complementary flexibility values to one other. 
     System  20  comprises a horizontal bar  22 , a sensor  23 , and a gauge  28 . Sensor  23  typically comprises a light source  24  and a detector  26 . Bar  22  has a bar-axis ax 1  that lies on a bar-plane  30 . Bar  22  is movable with respect to light source  24 , and bar-plane  30  is defined by the movement of axis ax 1  when bar  22  is moved, as described hereinbelow. Typically, bar  22  is movable vertically, so bar-plane  30  is typically a vertical plane, as shown. Bar  22  is configured to support, along bar-axis ax 1 , the leaflet being tested such that the leaflet drapes over the bar. This draping is visible in  FIGS.  2 D-E . 
     Light source  24  is configured to emit a beam  32  of light, and is oriented to direct the beam through bar-plane  30 . It is to be noted that, in this context, the term “light” (including in the specification and the claims) includes frequencies that are invisible to the human eye, but that are blocked by leaflet  10 . Typically, light source  24  is a laser, configured to emit a laser beam. 
     Detector  26  is configured and positioned to detect beam  32 , and is configured to generate a detection-signal indicative of detection of the beam. For example, detector  26  may be directly opposite light source  24 , facing the light source. Alternatively, and as shown, system  20  may comprise a reflector  36  that reflects beam  32  toward detector  26 , e.g., to facilitate more convenient positioning of detector  26 . For some applications, and as shown, light source  24  and detector  26  are integrated within a housing  34 , and reflector  36  reflects beam  32  back toward the housing from which the beam originated. 
     Gauge  28  is configured to measure a distance between bar  22  and beam  32  (e.g., an elevation of bar  22  above beam  32 ). It is to be noted that in this patent application, including in the specification and the claims, this includes measuring a distance that is indicative of the elevation of the bar above the beam, e.g., without directly measuring the specific distance between the bar and the beam. For example, if there is a fixed distance between beam  32  and another element of system  20 , gauge  28  may measure the distance between bar  22  and the other element. 
     Bar  22  is movable with respect to light source  24  and beam  32 , the movement of the bar defining bar-plane  30 . Typically, this is achieved by bar  22  being movably coupled to a post (e.g., a vertical post)  38 , to which light source  24  is coupled (e.g., fixedly coupled). For some applications, this is achieved by bar  22  being coupled to post  38  via a linear actuator  40 , actuation of which moves the bar with respect to the post and within bar-plane  30 . Actuator  40  may be mechanical, electronic, or any suitable type. Post  38  has a longitudinal axis ax 2 . 
     There is therefore provided, in accordance with some applications of the invention, apparatus for testing a prosthetic heart valve leaflet, the apparatus comprising:
         a vertical post, having a longitudinal axis;   a horizontal bar having a bar-axis that lies on a vertical bar-plane, the bar being configured to support the leaflet along the bar-axis such that the leaflet drapes over the bar;   a linear actuator, movably coupling the bar to the post, actuation of the actuator moving the bar vertically in the bar-plane;   a light source, configured to emit a beam of light, and oriented to direct the beam through the bar-plane;   a gauge, configured to measure an elevation of the bar above the beam; and   a detector, configured and positioned to detect the beam, and to generate a detection-signal indicative of detection of the beam.       

     For some applications, and as shown, bar  22  extends laterally away from post  38  (e.g., such that the post lies on bar-plane  30 ). For some applications, and as shown, light source  24  is disposed laterally from post  38 . Typically, light source  24  is oriented to direct beam  32  through the bar-plane horizontally (e.g., such that the beam is perpendicular to the bar-plane). For some applications, the movement of bar  22  in the bar-plane, described hereinabove, includes movement of the bar through (e.g., vertically through) beam  32 . That is, for some applications, bar  22  is coupled to post  38  such that the bar is movable, within the bar-plane, through (e.g., vertically through) the beam. It is to be noted that, in practice, leaflet  10  may block beam  32  from reaching bar  22  as the bar moves through the beam. 
     A brief, general description of a use of system  20  is as follows: Leaflet  10  is placed across bar  22 , and the bar is positioned such that the leaflet drapes over the bar and blocks beam  32  ( FIGS.  2 B-D ). While leaflet  10  remains draped over bar  22 , the bar is elevated at least until the leaflet stops blocking the beam ( FIG.  2 E ). An elevation of the bar from the beam at which the leaflet stopped blocking the beam is identified, and responsively to the identified elevation, a flexibility value is assigned to the leaflet. It is hypothesized by the inventors that, a leaflet which is more flexible about the bar-plane will drape more steeply, and therefore further down, from bar  22 , thereby requiring a higher elevation above beam  32  before the leaflet stops blocking the beam. 
     For some applications, and as shown, system  20  comprises a platform  60  that has a surface  62  (e.g., an upper surface that is typically horizontal). Bar-plane  30  intersects platform  60 , and the movement of bar  22  (e.g., via actuation of actuator  40 ) is with respect to the platform. Bar  22  has an initial position in which leaflet  10  is placeable across the bar and in contact with the surface. For some applications, in the initial position, bar  22  is disposed at least partly (e.g., completely) below the surface, as shown in  FIG.  2 A . 
     Typically, leaflets  10  that are to be tested using system  20  are cut from an animal tissue such as bovine pericardium. Further typically, leaflets  10  are cut to have consistent shape and size, the shape and size defining a leaflet-outline. For some applications, platform  60  has a guide  64  that defines a guide-outline  65  that corresponds to the leaflet-outline. Guide-outline  65  has a guide-outline position and a guide-outline orientation that indicate the position and orientation in which leaflet  10  is to be placed across the bar and in contact with the surface. Bar-plane  30  bisects guide-outline  65 . 
     For some applications, system  20  has a plurality of guides  64 , e.g., comprising a first guide  64   a , a second guide  64   b , and a third guide  64   c , each of the guides at a defining a respective guide-outline  65   a ,  65   b , and  65   c . System  20  has a respective guide-state in which bar-plane  30  bisects a respective guide  64  (e.g., the guide-outline  65  thereof). For example, system  20  may have a first guide-state in which bar-plane  30  bisects guide  64   a , a second guide-state in which the bar-plane bisects guide  64   b , and a third guide-state in which the bar-plane bisects guide  64   c . In its respective guide-state, each guide  64  is bisected by bar-plane  30  at a different angle. Typically, bar-plane  30  bisects at least one of the guides symmetrically when system  20  is in the corresponding guide-state, and bisects at least one of the other guides asymmetrically when the system is in the guide-state that corresponds to that guide. 
     For some such applications, and as shown, platform  60  defines the plurality of guides  64 , and is movably (e.g., rotatably) coupled to post  38  via a coupling  70 . System  20  is transitioned between its guide-states via movement (e.g., rotation) of platform  60 , the movement bringing the respective guides  64  into alignment with bar-plane  30 .  FIG.  2 A  shows system  20  in a first guide-state, in which bar-plane  30  bisects first guide  64   a  (e.g., first guide-outline  65   a ) symmetrically.  FIG.  3    shows system  20  in a second guide-state, following rotation of platform  60 , in which bar-plane  30  bisects the second guide  64   b  (e.g., second guide-outline  65   b ) asymmetrically. 
     Alternatively, system  20  comprises more than one platform  60 , each platform defining a respective guide, and being removably couplable to a coupling (e.g., couplable to post  38  via the coupling). For such applications, each guide-state is achieved by coupling the corresponding platform to the coupling. 
     As described hereinabove, for some applications, in the initial position, bar  22  is disposed at least partly (e.g., completely) below the surface. To achieve this, platform  60  typically defines a longitudinal hollow  66  that lies on bar-plane  30 . When bar  22  is in its initial position, it is disposed in hollow  66 . Hollow  66  is shown as a groove in platform  60 , but may alternatively be a slot cut all the way through the platform. Irrespective of whether platform  60  defines hollow  66 , the initial position of bar  22  may be such that the placement of leaflet  10  across the bar places the leaflet in contact with the bar. Alternatively, the initial position of bar  22  (facilitated by the depth of hollow  66 ) may be such that the leaflet spans the hollow but does not actually touch the bar. In this context, the leaflet being “placed across the bar” includes such a configuration. 
     For applications in which system  20  has more than one guide  64  (e.g., applications in which platform  60  defines more than one guide), each guide typically has a corresponding hollow  66  appropriately aligned with the corresponding guide-outline  65 . For example, and as shown, platform  60  may define a hollow  66   a , a hollow  66   b , and a hollow  66   c . Transitioning of the system into a given guide-state aligns the corresponding hollow  66  with bar-plane  30 . 
     For some applications, and as shown, each guide-outline  65  is defined by a ridge  68  that facilitates correct placement of leaflet  10 , e.g., by at least partially inhibiting movement of the leaflet. For some such applications, and as shown, platform  60  defines each guide  64  as a depression, ridge  68  being the boundary of the depression. Alternatively, guide-outline  65  may simply be a marking. 
     For some applications, light source  24  is adjustably coupled to platform  60 , such that a distance between the beam of light and the surface is adjustable by adjusting a position of the light source with respect to the platform. For some applications, light source  24  is positioned (or is positionable via adjustment) such that beam  32  passes across surface  62  within 2 mm of the surface, e.g., 0.1-1.5 mm (such as 0.1-1 mm, e.g., 0.1-0.5 mm, or such as 0.4-1.5 mm, e.g., 0.4-1 mm, such as 0.4-0.6 mm, such as about 0.46 mm) from the surface. For some applications, light source  24  is positioned such that beam  32  in effect skims surface  62 . For such applications, system  20  is therefore configured to detect a gap between leaflet  10  and surface  62 , and is used to determine the distance (e.g., elevation) between bar  22  and platform  60  at which the gap is formed. For such applications, there is therefore provided apparatus comprising:
         a platform having a surface;   a bar:
           movably coupled to the platform,   having an initial position with respect to the platform, in which the leaflet is placeable across the bar and in contact with the surface, and   being movable out of the initial position and away from the surface, so as to lift the leaflet away from the surface;   
           a gauge, coupled to the platform and the bar, and configured to measure a distance between the bar and the platform; and   a sensor, configured to detect a gap between the leaflet and the surface, and to generate a detection-signal indicative of detection of the gap.       

     For some applications, detection of the gap is achieved through means other than detecting the unblocking of a beam of light. For example, instead of light source  24  and detector  26 , sensor  23  may comprise at least one electrode positioned on platform  60  such that the electrode is in contact with leaflet  10  when the leaflet is placed across the bar and in contact with the platform. Via the electrode, the sensor detects electrical contact between the leaflet and the electrode, and detects the gap by detecting a reduction in (e.g., loss of) the electrical contact. 
       FIG.  2 A  shows system  20 , in a first guide-state, with bar  22  in its initial position. Bar  22  is disposed in hollow  66 , and is completely below surface  62  of platform  60 . Leaflet  10  is positioned within guide-outline  65   a  of guide  64   a , thereby placing the leaflet across bar  22  ( FIG.  2 B ). 
     For some applications, and as shown, system  20  further comprises a clamping element  72 , movably coupled to bar  22 , and configured to clamp leaflet  10  to the bar.  FIG.  2 C  shows a step in which clamping element is moved toward the bar in order to clamp the leaflet to the bar, to prevent the leaflet from slipping off the bar when the bar is elevated. As shown, the clamping element may comprise a rod, parallel to the bar, and configured to clamp the leaflet against the bar along bar-axis ax 1 . For some applications, system  20  comprises a spring that provides a clamping force to element  72 , the clamping force having a magnitude sufficiently great to secure leaflet  10 , but sufficiently small to avoid damaging the leaflet. 
     Bar  22  is positioned such that leaflet  10  drapes over the bar and blocks beam  32 . For some applications, in the initial position of bar  22 , the bar is positioned in this manner. Alternatively, and as shown in  FIG.  2 D , bar  22  is positioned in this manner by elevating the bar. 
     While leaflet  10  remains draped over bar  22 , the bar is elevated at least until the leaflet stops blocking beam  32  ( FIG.  2 E ). Detector  26  detects beam  32 , and responsively generates a detection-signal, indicative of detection of the beam. For some applications, the detection-signal is an audio signal. For some applications, the detection signal is a visual signal. 
     For some applications, the operator stops elevating bar  22  (e.g., actuating actuator  40 ) upon perceiving the detection-signal, reads the elevation measured by gauge  28 , and responsively assigns a flexibility value to the leaflet. 
     For some applications, system  20  is at least partly automated, e.g., by electronically coupling sensor  23  to gauge  28 . This is represented by a cable  86  connecting housing  34  to controller  80 , but it is to be understood that the scope of the invention includes other means, both wired and wireless, of electronically coupling the sensor to the controller. For example, system  20  may comprise a controller  80  that comprises a display  82 , and circuitry  84  that interfaces with the display, gauge  28 , and sensor  23  (e.g., detector  26  thereof). Controller  80  (e.g., circuitry  84 ) is configured to receive the detection-signal, and to responsively drive display  82  to display the elevation of bar  22 , with respect to beam  32 , at which the beam was detected. 
     For example, gauge  28  may continuously (or repeatedly) measure the elevation of bar  22  with respect to beam  32 , e.g., continuously providing an elevation-signal. Upon receipt of the detection-signal, controller  80  (e.g., circuitry  84 ) drives display  82  to display the elevation at which the beam was detected (i.e., the elevation measured at the time that the detection-signal was received by the controller), and continues to display that elevation even if bar  22  is moved further. Alternatively, gauge  28  may only measure the elevation in response to the detection-signal (e.g., controller  80  may be configured to, in response to receiving the detection-signal, drive gauge  28  to measure the elevation). 
     There is therefore provided, in accordance with some applications of the invention, apparatus comprising:
         a bar having a bar-axis, the bar being configured to support a prosthetic heart valve leaflet along the bar-axis such that the leaflet drapes over the bar;   a light source, configured to emit a beam of light;   a detector, configured to detect the beam, and to generate a detection-signal indicative of detection of the beam;   a linear actuator, movably coupling the bar to the light source, actuation of the actuator moving the bar with respect to the beam;   a gauge, configured to measure an elevation of the bar above the beam, the elevation changing with the moving of the bar by the actuator;   a display, and   circuitry, electrically connected to the detector, the gauge, and the display, and configured:
           to receive, from the gauge, the measured elevation,   to receive the detection-signal from the detector, and   in response to the detection-signal, to drive the display to display the elevation that was measured when the detection-signal was received by the circuitry.   
               

     It is to be understood that display  82  is merely an example of an output that controller  80  (e.g., circuitry  84  thereof) may provide in response to receipt of the detection-signal, and that the scope of the invention includes the controller providing other outputs, such as an electronic output signal that is received by a computer system. 
     As described hereinabove, the flexibility of animal tissue from which leaflets  10  are typically cut is naturally variable. Moreover, such tissue may have anisotropic flexibility, and therefore each leaflet  10  may be more flexible on one axis than on another. It is hypothesized by the inventors that testing the flexibility of leaflets on more than one axis advantageously improves matching of complementary leaflets for use within a single prosthetic valve. Therefore, as described hereinabove, for some applications system  20  has a plurality of guides  64  and a plurality of guide-states, for testing the flexibility of leaflet  10  in different orientations (e.g., rotational orientations) with respect to bar  22 . In the example shown, system  20  has three guides  64  and three guide-states.  FIG.  3    shows system  20  after it has been transitioned into another guide-state by rotating platform  60  such that guide  64   b  is aligned with (and bisected by) bar-plane  30 . The steps described with reference to  FIGS.  2 B-E  are typically repeated for each guide state. When in its corresponding guide-state, guide  64   b  is disposed with respect to bar-plane  30  at an orientation that is orthogonal to that of guide  64   a  in its corresponding guide-state. When in its corresponding guide-state, guide  64   c  is disposed with respect to bar-plane  30  at an orientation that is between that of guide  64   a  in its corresponding guide-state, and that of guide  64   b  in its corresponding guide state. 
     For some applications, for one or more of the guide states, leaflet  10  is tested one side up and the other side up. 
     For some applications, system  20  does not comprise post  38 , and another mechanism is used to movably couple bar  22  to light source  24 . 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.