Abstract:
A prosthetic heart valve of the bi-leaflet type is provided that includes an annular structure comprised of biocompatible plastic and a pair of bearing blocks and a pair of leaflets equipped with ear-like projections that are all comprised of pyrolytic carbon. The leaflets associate pivotably with the bearing blocks, and, with the bearing blocks and the leaflets being initially held in a connected relationship, the annular structure is molded and formed about perimeter portions of the bearing blocks. The valve has a simple structure, yet is durable and reliable.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to an improved prosthetic heart valve, and more particularly to an improved bi-leaflet prosthetic heart valve made with plastic and pyrolytic carbon.  
       BACKGROUND OF THE INVENTION  
       [0002]     Bi-leaflet or double leaflet prosthetic heart valves are known to the prior art. Such a structure typically incorporates an annular member, also identified as a ring member, and two cooperating leaflets that are intended to open and close the passageway through the ring member responsive to blood flow.  
         [0003]     Prior art bi-leaflet prosthetic heart valve structures typically suffer from various problems. One problem is that in a prior art heart valve structure commonly either the leaflets or the annular member or both must be flexed in order to assemble the valve structure. Flexing can warp, weaken or crack a flexed component of the structure, or make the flexed component susceptible to subsequent unwanted flexing in the assembled valve structure, or result in an assembled valve structure that can have a slight structural deformity owing to a tendency for a warped component not to return completely to its original unflexed configuration or condition. A heart valve structure that has been assembled by a component flexing procedure can display a tendency for the pivot ears of the leaflets to slip or even dislodge from their associated ear bearing recesses resulting in a valve that, when implanted in a patient, has leaflets which do not fully close or fully open, or do not pivot easily, or that even may seize which is a disaster for the involved patient.  
         [0004]     Another problem is that, while it may be desirable to utilize more than one material for fabrication of various prosthetic hear valve components, such as components of pyrolytic carbon and components of plastic, the resulting assembled prosthetic valve may have poor use or structure life characteristics. The typical problem is that the different materials, owing to their formation into respective designed shapes, or their resulting assembled interrelationship relative to other components, may not function very well individually in the assembled prosthetic structure, or may function in combination to produce only an inherently weak or cumbersome prosthetic structure, so that the resulting prosthetic heart valve structure either has an undesirably short use life or functions poorly after implantation.  
         [0005]     These and other considerations indicate the need for an improved heart valve prosthesis of the bi-leaflet type which can avoid such problems and which can incorporate pyrolytic carbon components and plastic components that are structured to work cooperatively and well together for an indefinitely long period of time and that is assembled without any flexing of components. Thereby, a durable, reliable, high quality and high performance prosthetic valve is achieved.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention relates to an improved prosthetic heart valve of the bi-leaflet type which is comprised of biocompatible components of pyrolytic carbon and plastic, which is easy and economical to fabricate and assemble, and which when assembled is durable, reliable, and performs well.  
         [0007]     The inventive heart valve prosthesis incorporates an annular or ring-like structure comprised of a molded plastic, a pair of bearing blocks each comprised of pyrolytic carbon, and a pair of valve leaflets each comprised of pyrolytic carbon.  
         [0008]     The annular structure incorporates two bearing block receiving windows. In each window each bearing block has an edge configuration about its perimeter which cooperatingly associates with the annular structure. Preferably, the windows and the bearing blocks have rectangular configuration.  
         [0009]     Each bearing block has two bearing recesses defined in the flat face thereof. The two leaflets of the prosthesis each have opposed ear-like projections defined therein that are each adapted to pivotably engage a different bearing recess, though all recesses and all ear-like projections are preferably similarly sized. The bearing blocks and the windows in the annular structure are preferably rectangularly configured.  
         [0010]     The leaflets as so engaged with the bearing blocks in the prosthesis are adapted to be disposed in and across the passageway of the annular structure. In the prosthesis, the leaflets can pivot from a valve closed position to a valve open position responsive to blood pressure applied to the passageway.  
         [0011]     After bearing block and leaflet preparation, they are, during prosthesis fabrication, held in a desired relationship while the annular structure is molded in situ about peripheral edge portions of each bearing block. Thereby, the bearing blocks are interlocked with the annular structure with the leaflets remaining pivotable relative to the bearing blocks and the prosthetic heart valve is formed. No bending, flexing, or other distortion of components occurs.  
         [0012]     The product prosthesis is comprised of a minimum number of components and is a relatively simple structure of great durability and reliability. The pyrolytic carbon components comprising the bearing blocks and the leaflets, and the plastic comprising the annular structure are each comprised of physiologically acceptable, non-biodegradable, implantable material.  
         [0013]     The pyrolytic carbon components can be separately and accurately fabricated with conventional processing including use of machine tools.  
         [0014]     Assembly of the components is simple and reliable and is accomplished without any distortion of pyrolytic carbon components.  
         [0015]     The product prosthesis is very reliable, provides excellent service for an extended time period, and is very efficient.  
         [0016]     The pair of pivotable leaflets employed in the prosthesis combination functions to achieve a one-way valve and to control unidirectional blood flow through the passageway of the annular member. In the valve closed position, the edge portions of each leaflets are preferably configured to abut and engage sealingly with and against adjacent surface portions contacted therewith. Each leaflet is preferably flattened and its perimeter includes an arcuately extending outside edge region, a straight inside edge region, and a pair of flattened, ear-like projections each one of which is located between a different pair of the adjacent opposite sides that extend between each end of the arcuate edge region and of the straight edge region.  
         [0017]     Out-turned flanges at opposite ends of the annular member provide rigidity and strength. The bearing recesses achieved in each of the bearing blocks be precisely located and sized.  
         [0018]     Small, uniform clearances between respective adjacent portions of the leaflet ears and the bearing recesses are achieved by the precise interrelationship between components, such as that between the annular structure and the associated bearing blocks. Free, smooth, self-aligning spherical bearing surfaces are achieved for pivotal hinging-type movements of the leaflets relative to the bearing blocks. End play is adjusted by selective assembly and by precise construction, as those skilled in the art will readily appreciate.  
         [0019]     The ear-like projections of the leaflets are adapted to be held securely in the bearing recesses of the bearing blocks. A minute gap between each leaflet&#39;s ear-like projections and the bearing recesses of the bearing blocks is achieved. There is no possibility of malfunction.  
         [0020]     The provision of pyrolytic carbon particularly in the regions of the bearing surfaces between the respective ears and the associated recesses, and the configuration of the bearing surfaces thus provided, ensures that the leaflet ears do not disengage or slip from bearings in the assembled prosthesis. The pyrolytic carbon in such regions provides a polished and hard surface.  
         [0021]     Other and further features, purposes, objects, aims, advantages, embodiments and the like will be apparent to those skilled in the art from the present description taken with the appended drawings and the following claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     In the drawings:  
         [0023]      FIG. 1  is an isometric view of one embodiment of an annular ring structure for a prosthetic bi-leaflet heart valve of the present invention, some parts thereof being broken away and some parts thereof being shown in phantom;  
         [0024]      FIG. 2  is a plan view of an embodiment of a prosthetic heart valve of the present invention that incorporates the annular structure of  FIG. 1  and is in combination with associated bearing blocks and associated leaflets, some parts thereof being shown in section, this view being generally taken along the line II-II of  FIG. 1 ;  
         [0025]      FIG. 3  is an exploded isometric view of the prosthetic heart valve of  FIG. 2 , some parts thereof being shown in phantom;  
         [0026]      FIG. 4  is an axial sectional view through the prosthetic heart valve of  FIG. 2 , this view being generally taken along the line IV-IV of  FIG. 1 ;  
         [0027]      FIG. 5  is a fragmentary vertical sectional view through a portion of the prosthetic heart valve of  FIG. 2 , this view being generally taken along the line V-V of  FIG. 2  with the leaflets pivoted to a valve open orientation where the leaflets do not show in this Fig.;  
         [0028]      FIG. 5A  is a fragmentary vertical sectional view through another portion of the prosthetic heart valve of  FIG. 2 , this view being generally taken along the line VA-VA of  FIG. 2  where the leaflets are, as shown, pivoted to a valve closed orientation;  
         [0029]      FIG. 6  is an enlarged detailed plan view of the interior flat face of one bearing block, some parts thereof being shown in phantom;  
         [0030]      FIG. 7  is a fragmentary transverse sectional view diagonally taken through a portion of one bearing recess of one bearing block, this view being generally taken through the region VII-VII of  FIG. 6 ;  
         [0031]      FIG. 8  is a longitudinal sectional view transversely taken through the region VIII-VIII of  FIG. 6 ;  
         [0032]      FIG. 9  is a detailed plan view of the upper, flat face of one leaflet;  
         [0033]      FIG. 10  is a fragmentary, transverse sectional view taken through a portion of the leaflet of  FIG. 9 , this view being generally taken through the region X-X of  FIG. 9 ;  
         [0034]      FIG. 11  is a view similar to  FIG. 4  but showing the leaflets in phantom in a valve open configuration;  
         [0035]      FIG. 12  is a transverse sectional view of one embodiment of a combined mold and clamp assembly suitable for use in the in situ forming and molding of an annular ring structure for a heart valve prosthesis of the present invention, this view showing the mold and clamp assembly in association with the heart valve prosthesis after the molding therein of the annular ring structure and before the mold and clamp assembly is separated therefrom, some parts thereof being broken away;  
         [0036]      FIG. 13  is a vertical sectional view taken along the line XIII-XIII of  FIG. 12 , showing the heart valve prosthesis comparably to  FIG. 11 , but here the leaflets are in a valve open position, and the prosthetic heart valve is in association with the combined mold and clamp assembly, some parts thereof being broken away;  
         [0037]      FIG. 14  is a fragmentary vertical, detail, sectional view taken at an edge adjacent region of the assembly of  FIG. 12 , but advanced circumferentially 90 degrees relative to the longitudinal axis and the view shown in  FIG. 13 , showing details of the block clamping arrangement of the combined mold and clamp assembly;  
         [0038]      FIG. 15  is a combined plan view and transverse sectional view of another embodiment of a combined mold and clamp assembly for use in the in situ molding of the annular structure, the mold and clamp assembly as shown being still holding the molded annular structure, and each of the bearing blocks as well as each of the leaflets being in a fixed association and orientation after the annular structure has been formed in the cavity of the mold and clamp assembly; some parts thereof being shown in section and some parts thereof being broken away;  
         [0039]      FIG. 16  is a longitudinal sectional view through the assembly of  FIG. 15  taken generally along the line XVI-XVI of  FIG. 15 ; and  
         [0040]      FIG. 17  is a longitudinal sectional view through the assembly of  FIG. 15  taken generally along the line XVII-XVII of  FIG. 16 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]     A presently preferred embodiment  21  of the inventive heart valve prosthesis is shown in  FIGS. 1-14 . The prosthesis  21  incorporates an annular (or ring) structure  22  which has a generally cylindrical side wall portion  23 , a longitudinal axis  24  (see  FIG. 4 ) and a longitudinal passageway  25  extending about the axis  24 . Respective opposite end portions  26  and  27  of the side wall portion  23  extend circumferentially in longitudinally spaced, parallel relationship relative to each other. Each end portion  26  and  27  is provided with an outwardly and circumferentially extending integral rim flange portion  28  and  29 , respectively. The rim flanges  28  and  29  extend in spaced, parallel relationship relative to each other.  
         [0042]     The annular structure  22  has defined therein a pair of bearing block windows  31  and  32 . Each window  31  and  32  is medially positioned in and extends radially through the annular structure  22  and each window  31  and  32  is located so as to be generally diametrically opposed to the other across the passageway  25 .  
         [0043]     The prosthesis  21  also incorporates a pair of bearing blocks  33  and  34 . Each block  33  and  34  is adapted and configured to seat in, and engage with, a different one of the windows  31  and  32 . While it is preferred that the pair of windows  31  and  32 , and the pair of bearing blocks  33  and  34 , each be similarly sized and configured, those skilled in the art will appreciate that different configurations can be utilized provided that the size and configuration relationship is such that one bearing block fits into one window. Each block  33  and  34  has a substantially flat interior face  36  and  37 , respectively, and each face  36  and  37  has defined therein a pair of bearing recesses  38  and  39 , respectively, that are circumferentially (relative to the annular structure  22 ) spaced from one another. All bearing recesses  38  and  39  are preferably similarly sized. The exterior face  41  and  42  of each bearing block  33  and  34  can have various configurations, but it is presently preferred to provide each of the exterior faces  41  and  42  with a curvature that generally corresponds with the curvature of the exterior surface of the sidewall portion  23 .  
         [0044]     The perimeter edge region  43  and  44  of each block  33  and  34 , respectively, is configured to engage interlockingly with, and be adjacent to, the corresponding adjacent perimeter edge portions  46  and  47  of the windows  31  and  32 , respectively. The manner of achieving such engagement is explained below. Preferably the edge regions  43  and  44  and the windows  31  and  32  each have a similarly sized rectangular configuration, as shown.  
         [0045]     The prosthesis  21  further incorporates a pair of leaflets  48  and  49 . In the prosthesis  21 , the leaflets  48  and  49  are disposed adjacently relative to each other and transversely relative to the passageway  25 . Each leaflet  48  and  49  has a generally flat body and has approximately the same size and thickness. As shown, for example, in  FIGS. 2, 3  and  9 , each leaflet  48  and  49  has a perimeter that includes an arcuately extending outside edge region  50 , a straight inside edge region  51 , and a pair of straight, transversely spaced (relative to each other) edge regions  53  that extend parallel (relative to each other). Each edge region  53  extends between and interconnects a different adjacent pair of the opposite end regions of each of the outside edge region  52  and the inside edge region  53 . As shown, for example, in  FIG. 9 , the outside edge regions  50  are beveled to better enable the achievement of a close, abutting, preferably matching engagement thereof in the assembled prosthesis  21  with adjacent surface portions of the side wall portion  23  when the leaflets  48 ,  49  are each in a fully valve closed position. Similarly, the inside edge region  51  of each leaflet  48 ,  49  is beveled to enable the achievement of a close fitting, preferably matching, abutting engagement therebetween along a diameter of the annular structure  22  (see, for example,  FIG. 2 ) when the leaflets  48 ,  49  are each in a fully valve closed position. Further, the interconnecting edge regions  53  of each leaflet  48 ,  49  extend perpendicularly to enable the achievement of a close fitting, minute gap or spacing, between each edge region  53  and adjacent surface portions of a bearing block  33  or  34 , as the case may be, in the prosthesis  21  during pivoting movements of the leaflets  48  and  49 .  
         [0046]     As seen, for example, in  FIGS. 3 and 9 , each of the leaflets  48  and  49  has a pair of outwardly extending, integral, peripherally rounded, ear-like projections  88  and  89 . Each projection  88  and  89  is flattened and preferably is about as thick as the associated leaflet  48  or  49 . All projections  88  and  89  are preferably similarly sized. Each ear-like projection  88  and  89  is located medially along a different one of each of the interconnecting edge regions  53 . The outside perimeter curvature of each ear-like projection  88  and  89  corresponds to a spherical segment.  
         [0047]     The interrelationship between the leaflets  48  and  49  and their respective ear-like projections  88  and  89  and the bearing blocks  33  and  34  with their respective bearing recesses  38  and  39  in the prosthesis  21  is such that each of the ear-like projections  88  and  89  is, with close spacing tolerances, receivable in, and pivotably associated with, a different one of the bearing recess pairs  38  and  39  in each of the faces  36  and  37  of the blocks  33  and  34 , respectively, in the prosthesis  21 . Thus, each leaflet  48 ,  49  is pivotable about its own pivot axis  59  (see, for example,  FIG. 2 ) which extends between mid-regions of the ear-like projections on each of the leaflets  48 ,  49 . The recesses  38 ,  39  of each flat interior face  36  of bearing block  33  and flat interior face  37  of bearing block  34  is centered along the predetermined hinging axis  59  that is in aligned relationship with the associated ear-like projection  88  or  89  in the prosthesis  21 . The hinging axis  59  of each leaflet  48 ,  49  is parallel to a diameter of the annular structure  22  and each hinging axis  59  is equally spaced from such diameter by a distance Y (see, for example,  FIG. 2 ) but is located on a different side thereof. In the prosthesis  21 , the flat faces  36  and  37  are in spaced, parallel relationship relative to each other. When each of the leaflets  48  and  49  has its respective ear-like projections  88  and  89  associated with a cooperating respective recess  38  and  39 , a small, uniform clearance preferably exists between each recess  38  and  39  and adjacent portions of the associated ear-like projection  88  and  89 . Preferably, a fluid tight, pivotable joint exists between each bearing block  33  and  34  and its associated leaflets  48  and  49 . Preferably the interrelationship between the bearing blocks  33 ,  34  and the leaflets  48 ,  49  in the prosthesis  21  is such that, when the leaflets  48 ,  49  are in their valve fully closed respective positions, a seal is achieved against the flow of blood through the annular structure  22 . The edge configurations of the leaflets  48 ,  49  prevents leakage in the valve fully closed position, yet jamming of the leaflets  48 ,  49  against adjacent surfaces as a result of back pressure is prevented. Also, the relationship between bearing blocks  33 ,  34  is such that the leaflets  48 ,  49  cannot slip in the prosthesis  21 .  
         [0048]     Each recess  38  and  39  is further configured to provide a bearing surface upon which and relative to which an associated ear-like projection  88  and  89  is self-aligning. Each leaflet  48  and  49  with its ear-like projections  88  and  89  in the prosthesis  21  is allowed to swing pivotally and independently with restricted rotary oscillatory movements between a fully open and a fully closed position inclusive, and these oscillatory movements occur along the pivot axis of each leaflet  48  and  48  between its respective pair of ear-like projections  88  and  89 . As those skilled in the art will readily appreciate, varying pivot excursional movements can occur during leaflet oscillations responsive to applied differential fluid (blood) pressure in a surgically implanted prosthesis  21  with the direction of blood flow being shown by illustrative arrow  70  in  FIG. 11 . It will be appreciated that the bearing blocks  33 ,  34  and the cooperatively associated leaflets  48 ,  49  make use of the well-established principle of “self-aligning spherical bearing.” The flattened ear-like projections  87 ,  89  reduce frictional losses relative to adjacent surface portions of the recesses  38 ,  39 . Smooth pivotal movements are achieved with least effort, and with minimal loss of energy during leaflet  48 ,  49  oscillations. Close tolerances are achieved and are much preferred. The bell-type mouth associated with the annular structure  22  for inlet and outlet achieves smooth entry and exit for blood passage.  
         [0049]     Each recess  38  and  39  has a region of internal surface curvature that corresponds to a spherical segment and these recesses  38  and  39  cooperate with each other and with the ear-like projections  88  and  89  for free and smooth pivotal movement of each leaflet  48  and  48  in the prosthesis  21 . Each recess  38  and  39  (as illustrated, for example, in  FIG. 6 ) has opposed side portions  98  and  99  which define side regions that act as stop means for limiting pivotal travel of the ear-like projections  88  and  89 , thereby providing for the leaflets  48  and  49  desired end positions for maximum opening and closing movements. Also, inside surface portions of the annular structure  22  in the passageway  25  that are adjacent to outside regions  50  of each leaflet  48  and  49  serve as additional stop means when the leaflets  48  and  49  are in their respective fully valve closed positions. The edge regions  53  of each leaflet  48 ,  49  extend generally perpendicularly to the hinging axis of the associated leaflet  48  and  49 . These chordal edge regions  53  function to clean blood on the adjacent flat facial regions  36  and  37  of the bearing blocks  33  and  34  during oscillations of the leaflets  48  and  49 . The spherically curved edge regions of each ear-like projection  88  and  89  sweep adjacent internal spherical surfaces of each bearing recess  38  and  39 . The opposed side portions  98  and  99  also serve to avoid potential stagnation of blood which might otherwise occur in what would otherwise be unused portions of the cavities of the bearing recesses  38  and  39  due to restricted pivotal movements of the leaflets  48  and  49 .  
         [0050]     The bearing blocks  33  and  34  and the leaflets  48  and  49  are comprised of pyrolytic carbon which is characteristically a hard, physiologically acceptable, non-biodegradable, implantable material. Various methods known to the prior art can be used to fabricate components comprised of pyrolytic carbon for employment in the present invention. Typically, a component with a carbon surface is heated to beyond 1,000° C. to achieve a hard and naturally polished surface. Higher temperatures give greater hardness depth relative to the surface. See, for example, Bokros U.S. Pat. Nos. 3,298,921; 3,399,969; 3,526,005; 3,547,676; and 3,676,179. For example, in one process, carbon black powder is pressed under high pressure to make bearing block and leaflet shapes. The shapes are machined and articles (components) are produced. In the present situation, the leaflets  48  and  49  and the bearing blocks  48  and  49 , for example, are produced. These articles are then heated in a controlled atmosphere to 1,200° C. or above, the temperature selected being influenced by the desired structure. Thus, the resulting pyrolytic carbon components of an inventive prosthesis embodiment, such as the leaflets  48  and  49 , for example, are characteristically heat treated and hardened but not coated using conventional technology. Typically, pyrolytic carbon components are inert and relatively light in weight and density.  
         [0051]     The annular member  22  is comprised of a moldable, physiologically acceptable, non-biodegradable, implantable plastic. Various such plastics are known and can be used, as those skilled in the art will appreciate. Examples include polymethylmethacrylate and other acrylate polymers that incorporate acrylic acid or methacrylic acid; polyethylene and polypropylene including ultra high molecular weight polyethylene; polyvinylchloride (usually with stabilizers and plasticisers); polytetrafluoroethylene (PTFE or Teflon); polyesters, especially polyethylene terephthalate (PET); polyamides (including Nylon and Kelvar, especially as a reinforcing fiber in composites); polycarbonates; polyurethanes, particularly as elastomeric additives or components; certain polyaromatic semicrystalline polymers (such as “Peek Optima” and the like); silicone polymers developed for medical usage, certain ceramics, and the like.  
         [0052]     To assemble and fabricate the prosthesis  21 , the bearing blocks  33  and  34  are positioned with their respective bearing recess pairs  38  and  39  of blocks  33  and  34  engaged with the respective ear-like projection pairs  88  and  89  of the leaflets  48  and  49 . The projections  88  and  89  are pivotably associated with the recesses  38  and  39 . Close tolerances between adjacent surfaces are desired and preferably selected. An initial desired connected relationship between blocks  33 ,  34  and leaflets  48 ,  49  is maintained with an assembly that clamps, holds, and positions the pyrolytic carbon components (bearing blocks  33  and  34  and the leaflets  48  and  49 ), but that does not appreciably bend, flex, distort, or otherwise affect or mark them. With these components so held, the annular structure  22  is molded in situ by any convenient means or procedure and so is thereby formed with the edge portions  43 ,  44  of the bearing blocks  33 ,  34 , respectively, being seated in the windows  31  and  32  and as now explained and illustrated. As formed, the annular structure  22  holds, positions, retains, and is in fluid tight association with, the bearing blocks  33  and  34 .  
         [0053]     The annular structure  22  is unitarily molded as a single piece component around perimeter edge portions of the bearing blocks  33 ,  34  with the windows  31 ,  32  of the annular structure  22  being formed about and defined by the perimeter edge portions  43 ,  44  of the bearing blocks  33 ,  34  respectively. The perimeter edge portions  46 ,  47  of each window  31 ,  32  are interlockingly engaged with, and effectively bonded to, the perimeter edge portions  43 ,  44  of the bearing blocks  33 ,  34 , and the bearing blocks  33 ,  34  are held in engaged relationship with the leaflets  48 ,  49 , respectively.  
         [0054]     As those skilled in the art will readily appreciate, any suitable and convenient holding and molding assembly can be utilized in the practice of this invention. For present illustration and disclosure purposes, one illustrative clamping assembly  52  is shown in  FIGS. 12-14 . Also, as those skilled in the art will also readily appreciate, any suitable and convenient mold assembly and molding procedure can be employed. For present illustration and disclosure purposes, one illustrative mold assembly  54  is also shown in  FIGS. 12-14 . A present preference, as shown in  FIGS. 12-14 , is for the mold assembly  54  to be in combination with the clamp assembly  52 .  
         [0055]     The mold assembly  54  is here shown in a simplified form. The formation and usage of molds for plastics is well known to those skilled in the art. The mold assembly  54  includes a lower mold portion  55  which cooperatively associates with an upper mold portion  56  along a transversely (relative to the mold assembly  54 ) extending joint or parting line  57 . Located between inner peripheral edge portions of the upper portion  56  and the lower portion  55  is a split ring structure  60  that is provided with upper and lower ridge ribs  69   a  and  69   b  that cooperatively engage receiving pockets defined in each of the inner peripheral edge portions of the upper portion  56  and the lower portion  55 . The upper portion  56  and the lower portion  56  together with the split ring structure  60  define a mold cavity  58  for the annular structure  22 .  
         [0056]     The split ring structure  60  is divided into a half  60   a  and a half  60   b.  As seen, for example, in  FIG. 12 , a medial opposed outside edge region of each half  60   a  and  60   b  of the split ring structure  60  is fixed by welding (preferred) or the like to a different retaining arm  100   a  and  100   b  (four separate arms in all). The arms  100   a  and  100   b  are each preferably hemi-cylindrical and are adapted abut against one another lengthwise along a diameter to define a combined cylindrical configuration when abutting. When the arms  100   a  and  100   b  in the assembled mold assembly  54  are clamped together in such an abutting relationship, the split ring  60  is locked (held) in a fixed relationship as is needed to complete the definition of the cavity  58 . Conventional holding and clamping means (not shown) are employed to hold in assembled combination the lower portion  55 , the upper portion  56 , and the split ring structure  60 .  
         [0057]     For present illustration and disclosure purposes, the cavity  58  is assumed to be completely defined and is shown holding (after being fully charged and filled with a fluid moldable plastic) a molded annular structure  22  in  FIGS. 12-14 . Thus, the annular structure  22  is formed in the cavity  58  of the assembled mold assembly  54  around perimeter edge portions  43  and  44  of each of the bearing blocks  33  and  34 . For simplicity, the conventional location(s) are not shown in the mold assembly  54  where a moldable plastic in a fluid, usually melted, state is introduced during molding into the cavity  58  of the assembled and operable mold assembly  54  using a convenient, selected, conventional casting or injection molding procedure. Also, for simplicity, conventional means that may be employed for removing air and avoiding air pockets or heat sinks in the molded annular structure  22  molded in the mold assembly  54  are not shown.  
         [0058]     After the molding of an annular structure  22  in the cavity  58 , the clamping assembly  52  is separated from the bearing blocks  33  and  34  and the leaflets  48  and  49 , and in the mold assembly  54  then the upper portion  56  and the lower portion  55  of the mold assembly  54  are separated and the split ring  60  is separated into halves  60   a  and  60   b,  thereby to enable separation and removal of the molded annular ring structure  22  from the cavity  58  together the components now associated with the annular structure  22  including the blocks  33  and  34  and the leaflets  48  and  49 . The annular structure  22  as thus formed (molded) is associated and connected with the bearing blocks  33  and  34  and the leaflets  48  and  49 , thereby to obtain a completed prosthesis  21 .  
         [0059]     The lower portion  55  of the mold assembly  54  is associated with the clamping assembly which is generally designated as  52 . The clamping assembly  52  includes a pair of C-clamp-type structures  61  (see  FIGS. 13 and 14 , for example). Each C-clamp structure  61  includes a base leg  62  that has arms  63  and  64  at each opposite end thereof. The arms  63  and  64  here are integrally formed with the base leg  62  and the arms  63 ,  64  upstand relative to base leg  62  with arms  63 ,  64  being in an aligned planar relationship (relative to each other). Each arm  63 ,  64  has a terminal outer end region. The arm  63  is provided at its outer terminal end region with a terminally generally flat faced foot  65  whose flat face is oriented so as to be generally opposed to the outer terminal end region of the arm  64 . Arm  64  is engaged at its outer terminal end region with a transversely extending, threadably engaged, elongated, adjustable screw  66 . Screw  66  has at its forward end a loosely journaled and affixed, self-angle-adjusting, flat faced foot  67  that, taken with screw  66 , is orientable so as to be generally opposed to the outer terminal region and the flat face of foot  65  of the arm  63 . At its rearward end, the screw  66  is affixed to a finger engageable, wing-like head  68  for enabling the screw  66  to be manually turned, thereby to enable adjustment of the spatial position of the foot  67  relative to and between the outer terminal end regions of the arms  64  and  63 .  
         [0060]     The base  62  of each C-clamp  61  (pair)is positioned to extend along a bottom region  76  of the lower portion  55  adjacent to an outer edge region thereof. The position of the base  62  for each C-clamp  61  is such that, when viewed in plan from along the axis  24  (which in  FIG. 13  is a center point, not shown, but which is seen, for example, in the  FIG. 11  view), the base  62  is generally aligned with and lies in a hypothetical, vertically oriented (relative to prosthesis  21 ) plain that passes generally through the axis  24  of the annular structure  22  that is being formed (molded) in the cavity  58  of the mold assembly  54 . Each base  62  is preferably fastened by conventional disengageable mechanical fastening means, such as machine screws (not shown), to the bottom region  76 . As shown in  FIG. 14 , for example, the outer (relative to lower portion  55 ) arm  64  projects perpendicularly upward along and in radially outwardly spaced relationship from lower portion  55 . The inner (relative to lower portion  55 ) arm  63  projects upwardly through a hole in the bottom region  76  of the lower portion  55  and extends adjacent to an inside surface region of the lower portion  55 . Preferably (as shown in, for example,  FIG. 14 ), the inner arm  63  projects upwardly at a slight inclination angle to adapt the arm  63  to the local contour of the adjacent inside surface region of lower portion  55 .  
         [0061]     The spacing between, and the orientation of, the arms  63  and  64  is preferably such that the foot  65 , the axis of the screw  66  and the foot  67  (that is associated with the screw  66 ) lie approximately in and along along the above indicated transverse diameter hypothetical plain. Thus, each of the bearing blocks  33 ,  34 , as the case may be, can be positioned by a different C-clamp structure  61  between the foot  65  on arm  63  and the foot  67  on screw  66  with the flat face if foot  67  being medially adjacent to a different exterior face  41 ,  42  and each foot  65  being adjacent to a different interior face  36 ,  37 . Each bearing block  33 ,  34  is thus locatable at, and positionable in, a window  31 ,  32 , respectively, of the annular structure  22  defined by the cavity  58 . Auxiliary mechanical positioning and measuring means (not shown) may be employed, if desired, as those skilled in the art will readily appreciate, to achieve precise positioning and spacing of the pyrolytic carbon components, within selected tolerances, preferably before these components are clamped by clamping assembly  52  components in desired positions prior to molding of the annular ring structure  22 . Thus, by adjustment of the position of the foot  67  of an associated clamp  61 , each of the bearing blocks  33  and  34  is positioned, held and clamped in a desired position between the outer terminal end portions of each arm  63  and  64  of a C-clamp structure  61  with the exterior face  41  and  42  adjacent the foot  67  and the interior face  36  and  36  adjacent foot  65 , respectively.  
         [0062]     The cavity  71  provided in upper portion  56  and the cavity  72  provided in lower portion  55  become abuttingly aligned in the assembled mold assembly  54  and cooperate to define windows in cavity  58  in the mold assembly  54  that correspond to each of the respective opposed bearing block windows  31  and  32  in the cylindrical side wall portion  23  of the annular structure  22 . The interrelationship between each pair of windows  31 ,  32  thus defined by the combined cavities  71  and  72  for each bearing block  33 ,  34  is such that each of the bearing blocks  33 ,  34 , as held by one of the C-clamps  61 , is seated in a different one of the windows  31 ,  32 . The respective perimeter edge regions  43 ,  44  of each bearing block  33 ,  34  forms portions of the wall surfaces defining the cavity  58  in the mold assembly  54 . Thus, the relationship between each bearing block  33 ,  34  as held by a C-clamp structure  61 , taken with the lower portion  55 , the upper portion  56 , and the split ring  60 , is such that, when the upper portion  56  is assembled with the lower portion  55 , the walls of the mold cavity  58  are fully defined except for the windows in cavity  58 , as above explained.  
         [0063]     The configuration and position of each of the perimeter edge regions  43  and  44  of the bearing blocks  33  and  34 , respectively, is such that the bearing blocks  33  and  34  are held and fixed in place by the annular structure  22  after molding. Various configurations for the perimeter edge regions  43  and  44  can be employed. A present preference is for each block  33  and  34  to have a generally rectangular perimeter configuration (see, for example,  FIG. 3 ). Preferably (as shown) there is defined in each lateral opposed short end of each edge  43 ,  44  of each block  33 ,  34  a groove  85  (see, for example,  FIG. 3 ) which, as illustrated in, for example,  FIGS. 2, 8  and  11 , is sized to fit within the thickness of the cylindrical sidewall portion  23  of annular structure  22 . Thus, during the molding of annular structure  22 , the grooves  85  (four) each become filled with the plastic comprising the annular structure  22  to achieve a rib-like structure  86  in windows  31 ,  32  of sidewall portion  23  (see, for example,  FIG. 3 ).  
         [0064]     The windows  31  and  32  are, as shown, for example, in  FIGS. 1 and 3 , so that each is preferably so located in the sidewall  23  as to have an upper side thereof located adjacent to the upper flange  28  of the annular structure  22 . The top side surface of the edge  43 ,  44  of each block  33 ,  34  is as shown preferably flattened and configured to extend beneath and adjacent to the contiguous lower surface portions of the upper flange  28  of the annular structure  22 . Thus, the upper portion each edge  43 ,  44  of each window  31 ,  32  is defined by the plastic that comprises the annular structure  22  and comprises a relatively broad expanse that radially extends (relative to the annular structure  22 ) from the upper edge of the flat interior face  36 ,  37  of each block  33 ,  34  to the contiguous adjacent outer arcuate edge portion of the upper flange  28  of the annular structure  22 . Such broad expanse, in addition to improving the fixed association desired between each block  33 ,  34  and the annular structure  22 , is believed to strengthen the association and also to provide each block  33 ,  34  with the capacity to resist possible tilting movement of blocks  33 ,  34  relative to the axis  24  that might otherwise weaken or even dislodge the desired fixed association between the annular structure  22  and each block  33 ,  34 . Optionally, the flattened top surface of each block  33 ,  34  can be roughened or otherwise shaped, if desired (not shown), to achieve a desired surface for formation of an annular structure  22 .  
         [0065]     The back exterior face  41 ,  42  and adjacent surface portions of the perimeter edge  43 ,  44  of each block  33 ,  34  is as shown (see for example  FIG. 3 ) preferably formed with an outwardly projecting flange portion  91  and whose outside face extends arcuately and parallel to the adjacent face  41 ,  42 . Owing to the cooperative association between the respective blocks  33 ,  34  and the lower portion  55  of mold assembly  54 , the cavity  58  is configured so that, along the bottom edge of the perimeter  46 ,  47  of each window  31 ,  32 , a mating upstanding shoulder  93  is provided which has a terminal outwardly extending flange  95  (relative to each window  31 ,  32 , as shown in  FIGS. 5A and 14 , for example). Thus, when the annular structure  22  is molded in the cavity  58 , the annular structure  22  includes this shoulder  93  and flange  95  at the backside edge region of each block  33 ,  34 . This interrelationship between the bottom edge and adjacent backside regions of each block  33 ,  34  and each window  31 ,  32  in annular structure  22  is believed to provide a desirable locking inter-engagement between adjacent respective portions of each block  33 ,  34  and the annular structure  22 .  
         [0066]     Other arrangements and configurations for the edge surfaces  43 ,  44  of the blocks  33 ,  34  and of the windows  31 ,  32 , respectively, can be employed, if desired.  
         [0067]     As part of the clamping assembly  52 , the upper surface of the central bottom region of the lower portion  55  of mold assembly  54  is provided with a raised (vertically thickened) platform region  73 . A pair of diametrically (relative to the annular structure  22 ) spaced channels  74 ,  75  is defined in platform  73  so that each channel  74 ,  75  extends straight lengthwise, transversely relative to a hypothetical cord structure extending across portions of the annular structure  22 , and downwardly into platform  73  from the upper central surface thereof so that, with increasing channel depths, the channel  74  slightly diverges from, and is somewhat inclined relative to, the channel  75  (see, for example,  FIG. 12 ). Cross-sectionally, each channel  74 ,  75  extends in a generally spaced, parallel relationship relative to the other, and each channel  74 ,  75  is generally equally spaced from the longitudinal axis  24  (see  FIG. 11 ) of the annular structure  22  as defined by the cavity  58 . Each channel  74 ,  75  is adapted to receive therein a medial region along an edge  50  of each leaflet  48 ,  49  with the ear like projections  88 ,  89  of each leaflet  48 ,  49  being concurrently positioned for pivotal movement in bearing recesses  38 ,  39  of each bearing block  33 ,  34  (as such is held by a C-clamp  61  as above described; see, for example,  FIG. 14 ) To hold each of the leaflets  48 ,  48  in a fixed position so as to achieve a desired close tolerance between the adjacent respective surface portions of the bearing blocks  33 ,  34  and the bearing recesses  38 ,  39 , the leaflets  48 ,  49 , as associated with the projections  88 ,  89 , are clamped in a desired position by respective ones of a pair of relatively small C-clamp assemblies  77  that are each associated with the platform  73 .  
         [0068]     Each C-clamp assembly  77  includes a foot member  78  that is mounted on the platform  73  so as to be adjacent to, but equally spaced from, the longitudinal axis  24  of annular structure  22  as defined by the cavity  58 . Each foot member  78  is parallel to the other. Each foot member  78  is also adjacent to a different channel  74 ,  75  (see  FIG. 12 ). Each foot member  78  has an upstanding leg  79 , each leg  79  being slightly inclined to conform to the slope established by the adjacent channel  74 ,  75 . Along opposed outside edge portions of the platform region  73  a post  83  upstands. Through an upper end region of each post  83  an elongated screw  80  threadably extends generally horizontally.  
         [0069]     Each screw  80  has its forward end loosely journaled and affixed to a self-angle-adjusting, flat faced foot  81  that, taken with screw  80 , is oriented so as to be generally opposed to an upper end region of the each leg  79 . At its rearward end, the screw  80  is affixed to a finger engageable, wing-like head  82  for enabling the screw  80  to be manually turned, thereby to adjust the spatial position of the foot  81  relative to and between the outer terminal end regions of the leg  79  and the post  83 .  
         [0070]     The spacing between, and the orientation of, the terminal end regions of the leg  79  and the bracket  85  is such that each one of the leaflets  48  and  49  can be positioned, oriented and held by a different leg  79  and an adjacent foot  81 , the foot  81  being adjustable by screw  80 . Thus, by adjustment of the position of the foot  81 , each of the leaflets  48 ,  49 , with their respective projections  88 ,  89  engaged with the bearing recesses  38 ,  39 , can be positioned and held in a desired position between the bearing blocks  33 ,  34 , as desired, by a different C-clamp assembly  77 .  
         [0071]     Another suitable holding and molding assembly embodiment  101  is illustrated in  FIGS. 15-17 . In assembly  101 , the components coact to provide both the cavity  102  in which the plastic annular structure  22  is molded and the holding, retaining and positioning function for the pyrolytic carbon components blocks  33 ,  34  and leaflets  48 ,  49 .  
         [0072]     The assembly  101  incorporates upper and lower cap plates  103 A and  103 B each with interior peripheral surface portions that abuttingly engage an adjacent side edge region of each of an upper and lower forming ring  104  and  105 , respectively. The medial region of each ring  104  and  105  is fitted with an upper and lower circular forming plate  107  and  108 . The middle peripheral region of the assembly  101  is provided with a split ring  109  that defines outside wall portions of the cavity  102  and that is located radially in, and fitted between, the upper and lower forming rings  104  and  105 . The lower forming plate  108  includes an integral, upstanding, central, plateau-like region  110  which is provided with a relatively large central aperture  111  that longitudinally extends therethrough and downwardly into forming plate  108 . In combination with lower portions of the forming plate  107 , the outside circumferential wall portions of the region  110  define inside wall portions of the cavity  102 . The split ring  109  is comprises of half  109   a  and half  109   b.  A medial, outside, opposed region of each half  109   a  and  109   b  is attached, preferably by welding, to a clamping arm  113   a  and  113   b  (four separate arms in all) which are comparable to the arms  100   a  and  100   b  (above) and which function similarly so that the split ring can be held in a closed position as needed to define the cavity  102  yet permit separation of a molded annular structure  22  from the apparatus  101 , as those skilled in the art will readily appreciate. To retain the components in association, allen bolts  112 , preferably four, extend vertically through each plate  102  and  103  into threaded engagement with the adjacent ring  104  and  105 , respectively.  
         [0073]     Inside facial portions of the ring  109  and outside facial portions of the region  110  cooperate to define at opposed locations the bearing block windows  31  and  32  provided in the cylindrical side wall portion  23  of the annular structure  22  that is defined by the cavity  102 . Each bearing block  33  and  34  is positioned in a window  31  and  32 , respectively. Edge portions of each of the ring  109  and the region  110  that are adjacent to the apertures defined by ring  109  and region  110  that provide each window  31  and  32  are sized so as to slightly overlie edge portions of each of the bearing blocks  33  and  34 . Thus, in the assembled assembly  101 , each bearing block  33  and  34  is held in position at each window  31  and  32  defined by the ring  109  and region  110 .  
         [0074]     Prior to positioning of the bearing blocks  33  and  34  in the assembly  101 , the leaflets  48  and  49  are associated with the bearing blocks  33  and  34  with each projection  88  and  89  being located in a different bearing recess  38  and  39  as above explained. The lower surface region of the forming plate  107  and the upper central surface region of the lower forming plate  108  are each provided with a cavity  114  and  115 , respectively, as shown. Thus, when the assembly  101  is assembled with the bearing blocks  33  and  34 , and edge portions of the bearing blocks  33  and  34  are held by portions of the region  110  and the ring  109 , as above explained, and the leaflets  48  and  49  are associated with the bearing blocks  33  and  34 , the leaflets  48  and  49  extend unimpeded but inclined through the aperture  111  and into the respective cavities  114  and  115  defined in the forming plates  107  and  108 . The annular structure  22  can then be molded after which a completed prosthesis  21  is separated from the assembly  101  by disassembly of assembly  101 .  
         [0075]     The assembly  101  is here shown in a simplified form. The formation and usage of molds for plastics is well known to those skilled in the art. The assembly  101 , if desired, like the mold assembly  54 , may include additional portions and features. For present illustration and disclosure purposes, the cavity  102  is assumed to be completely defined by the assembly  101  and is shown holding (after being fully charged and filled with a fluid moldable plastic) a molded annular structure  22 . Thus, the annular structure  22  is formed in the cavity  102  of the assembly  101  around perimeter edge portions  43  and  44  of each of the bearing blocks  33  and  34 . For simplicity, the conventional location(s) are not shown in the assembly  101  where a moldable plastic in a fluid, usually melted, state is introduced during molding into the cavity  102  of the assembly  101  using a convenient, selected, conventional casting or injection molding procedure. Also, for simplicity, conventional means that may be employed for removing air and avoiding air pockets or heat sinks in the molded annular structure  22  molded in the mold assembly  54  are not shown.  
         [0076]     The assembly  101  illustrates an alternative arrangement for the annular structure  22  in the vicinity of the bearing blocks  33 ,  34 . After molding of an annular structure  22  in an assembly  101 , the assembly is disassembled by removing the alien bolts  112  and separating the split ring  109 , as those skilled in the art will appreciate.  
         [0077]     If desired, for example, the bottom outside region of each block  33 ,  34  may be provided with a different configuration from that shown, for example, in  FIGS. 3, 5A ,  14  and  17  and also the radial thickness of the sidewall portion  23  of the annular structure  22  may be provided with a different thickness. Because the inside surface portions of the sidewall  23  are cylindrical while the respective interior faces  36 ,  37  of the blocks  33 ,  34  are flat, as described above, the configuration of the sidewall  23  in the vicinity of the blocks  33 ,  34  can be adjusted so as to have, for example, a maximum thickness that corresponds to the medial thickness of a bearing block  33 ,  34  or a minimum thickness that corresponds to the average radial thickness of the sidewall  23 . In the latter situation, the mid-region of each bearing block  33 ,  34  projects radially into the passageway  25  as those skilled in the art will readily appreciate. Various relationships between the bearing blocks  33 ,  34  and the sidewall  23  can be utilized without departing from the spirit and scope of the invention.  
         [0078]     Various other and further embodiment applications, structures and the like will be apparent to those skilled in the art from the teachings herein provided and no undue limitations are to be drawn therefrom.