GB2513194A

GB2513194A - A valve

Info

Publication number: GB2513194A
Application number: GB1307143.6A
Authority: GB
Inventors: Peter Paul Zilla; Deon Bezuidenhout; Claude Visagie; Harish Appa; Kenneth Stuart Park
Original assignee: Strait Access Tech Holdings Pty Ltd; Strait Access Technologies Holding Pty Ltd
Current assignee: Strait Access Tech Holdings Pty Ltd; Strait Access Technologies Holding Pty Ltd
Priority date: 2013-04-19
Filing date: 2013-04-19
Publication date: 2014-10-22
Also published as: GB201307143D0

Abstract

A tri-leaflet valve 100 for a prosthetic heart valve is provided. The tri-leaflet valve 100 has three leaflets 102 and is made from polymeric material. Each valve leaflet 102 has an attachment edge 104 along which it is attached to a surface of a support stent, a free edge 106 and a belly 108 extending between each free edge 106 and attachment edge 104. The attachment edge 104 of each leaflet 102 is generally arc-shaped wherein the arc-shape is defined by a plane, a cylinder or a cone intersecting a cylinder or a cone, and the length of the free edge 106 of each leaflet 102 is equal to or greater than an arc of radius R between the two points on the attachment edge 104 where the free edge 106 intersects the attachment edge 104, where R is the radius of the tri-leaflet valve 100. The invention extends to a mould and a method for manufacturing a polymeric tri-leaflet valve involving spraying the polymer onto the mould.

Description

A VALVE

FIELD OF THE INVENTION

This invention relates to a replacement valve for use in the human body, more particularly a replacement heart or venous valve having a tn-leaflet configuration.

BACKGROUND TO THE INVENTION

Artificial valves are commonly used to replace damaged, diseased or malfunctioning heart valves or venous valves. Three primary types of artificial valves exist: mechanical valves, bioprosthetic valves, and polymer valves. The term polymer" in this specification shall have its widest meaning and includes plastics materials suitable for use in the human body, such as polyurethanes, and is also includes reinforced polymers, such as fibre reinforced polymers, and composite polymers.

In the case of artificial heart valves, a valve is implanted into an annular opening in the heart of patient, typically after surgical removal of a diseased, damaged or malfunctioning natural valve. Implantation can be carried out by means of a variety of methods, such as surgical implantation or via a valve deployment device.

A polymeric tn-leaflet heart valve typically includes an annular valve body and three flexible leaflets attached thereto. The valve body is commonly known as a stent, and includes an annular base and three leaflet support posts. The valve is attached at the circumference of the annulus. A sewing ring annularly coupled to the periphery of the valve body typically permits attachment means, such as sutures, to be applied when the artificial valve is implanted.

The three flexible leaflets of an artificial tn-leaflet valve mimic natural heart valve leaflet operation. The leaflets are attached to the three shaped posts along an attachment edge and adjacent leaflets typically join at a support post to provide a

I

commissure. Each leaflet includes a free edge extending between two commissures, and the generally curved leaflet area between the free edge and the attachment edge is known as the belly of the leaflet.

When blood flows in the forward direction through the artificial valve, the pressure of the blood flow deflects the three leaflets away from the centre of the annulus into an open position, and allows blood to flow through. When pumping of blood stops during diastole and blood flows in the reverse direction, the free edges of the leaflets abut in a coaptive region, thereby occluding the valve body annulus and preventing the flow of blood.

Artificial leaflets known in the prior art have a wide range of designs, and vary in terms of the geometry of the leaflet, attachment configurations and in thickness of the leaflets.

Existing artificial valve leaflet designs have a number of potential drawbacks.

Designs causing overly close coaptation of the leaflets may limit wash-out of blood during haemodynamic function, particularly in the regions close to the stent support posts at the commissures. These regions, also referred to as regions of stagnation, may encourage local thrombogenesis, and may lead to further restriction of the valve orifice in the longer term.

Another disadvantage of certain existing designs is that the valve leaflets may not fully close in the coaptive region. This may result in excessive regurgitation upon closure of the artificial valve. Furthermore, valve leaflet design may cause high stresses at commissures or in regions of the leaflet belly, which may lead to leaflet damage or valve malfunction.

Some leaflet designs may lead to insufficient orifice size when the artificial valve leaflets are in an open position. This may result in a high pressure drop across the valve, which can in turn limit haemodynamic performance of the artificial valve.

Moulds are commonly used to manufacture artificial polymer heart valve leaflets.

Forming steps may include compression moulding, injection moulding, dip casting, and the like. However, due to the close tolerances that generally need to be achieved, these methods of manufacture may not satisfactorily achieve desirable valve thickness distributions or precise final leaflet geometry.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a tn-leaflet valve made from a polymeric material wherein each leaflet has an attachment edge along which it is attached to a surface and a free edge with a belly extending between each free edge and attachment edge, the leaflets being movable between a coapted condition in which the free edges abut and prevent fluid flow through the valve and an open condition in which fluid flow through the valve is permitted, charactenised in that the attachment edge of each leaflet is generally arc-shaped for attachment to a complementary surface having an arc and a pair of haunches extending therefrom generally outwardly inclined from each other, and in that the free edge of each leaflet is of a length equal to or greater than an arc of radius R between the two points on the attachment edge where the free edge intersects the attachment edge, where R is the radius of the tn-leaflet valve.

A further feature of the invention provides for the arc-shape to be defined by a plane, a cylinder or a cone intersecting a cylinder or a cone.

Further features of the invention provide for the plane, cylinder or cone to intersect the cylinder or cone at an angle theta (9); for the angle theta (9) to be dependent on the height and the radius of the tn-leaflet valve, for an angle 20 to be defined as the central arc angle formed by two radii extending, respectively, to each of the two points on the attachment edge where the free edge intersects the attachment edge; and for the tangent of the angle 0 to be equal to (R -Rcos(Ø))/H, where R is the radius of the tn-leaflet valve and H is the height of the tn-leaflet valve.

Further features of the invention provide for the shape of a leaflet to be defined by an attachment edge function, a plurality of edge functions fitted in the attachment edge function, and a surface lofted between the functions; for the free edge of the leaflet to be defined as a first edge function; and for each remaining edge function to be defined by an equation identical to the first edge function, except for varying amplitude.

Yet further features of the invention provide for the shape of a leaflet to be defined by an attachment edge function, one or more free edge functions fitted in the attachment edge function, one or more belly functions fitted in the attachment edge function, and a surface lofted between the functions; and for one or more of the belly functions to follow a bell-mouth shape.

Still further features of the invention provide for the shape of a leaflet to be defined by an attachment edge function, a plurality of edge functions fitted in the attachment edge function, the edge functions each being defined by a line tangent to a commissure line adjacent the commissure and by a trigonometric function thereafter, and a surface lofted between the functions; for one or more of the edge functions to be smoothed by adding radii at one or more points on the one or more edge functions; and for the attachment edge function to be smoothed by adding radii at one or more points on the attachment edge function.

The invention extends to a mould for making a tn-leaflet valve as defined above, the mould comprising a body portion and three leaflet portions integral with the body portion, and defining a leaflet shape as defined above, the mould being structurally configured to be suitable for either dip coating or spray coating.

Further features of the invention provide for a mould suitable for dip coating to include an inwardly tapered run-off at one or both ends thereof; for a leaflet run-off to be provided at the end of the mould defining the free ends of the leaflets; for a base run-off to be provided at the end of the mould adjacent the attachment edges of the leaflets; for the taper angle of the run-offs to be between 25 and 90 degrees; for the taper angle of the base run-off to be between 25 and 90 degrees, preferably between 45 and 55 degrees; and for the taper angle of the leaflet run-off area to be between 55 and 90 degrees.

Still further features of the invention provide for a mould suitable for spray coating to be shaped to provide increased leaflet height to facilitate cuthng of the free edges of the leaflet from the mould; and for the mould to be manufactured from any one of metal, wood, polymer and glass.

Yet further features of the invention provide for the mould to include a stent holder which secures a stent about the mould in correct orientation relative to the leaflets; for the holder to include a number of clip formations spaced about the mould; and for the holder to maintain the stent a distance of between 0mm and 0.25mm from the surface of the mould.

The invention still further provides a method of manufacturing a tn-leaflet valve as defined above from a polymeric material, the method including the steps of moving a mould and a spraying device relative to one another, spraying a polymer solution onto the mould and permitting the polymer to dry and removing the valve from the mould.

Still further features of the invention provide for the method to further include repeating the steps of spraying a polymer solution onto the mould and permitting the polymer to dry until a desired leaflet thickness is reached; for drying to occur in an environment wherein temperature and optionally humidity is controlled; and for drying to further occur in an environment substantially free of oxygen.

Further features of the invention provide for the step of moving the mould and the spraying device relative to one another to include one or more of the steps of rotating the mould horizontally about its central axis, rotating the mould vertically about its central axis, rotating the mould about its central axis while holding the mould in an inclined position, and holding the mould in a fixed position whilst moving the spraying device around the mould.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-Figure 1 illustrates a tn-leaflet valve according to the invention; Figure 2 illustrates a tn-leaflet valve according to the invention, where the valve is attached to a stent; Figure 3 illustrates a tn-leaflet valve according to the invention, where the leaflets are in a coapted condition; Figure 4 illustrates a tn-leaflet valve according to the invention, where the leaflets are in an open condition; Figure 5 illustrates a scallop shape produced by cutting a cylinder with a plane at an angle 0; Figure 6A illustrates a front view of a cylinder, showing the angIe 9 formed by cutting the cylinder with a plane; Figure 6B illustrates a top view of the cylinder shown in Figure 6; Figure 7 is a top view of a first embodiment of a valve leaflet in accordance with the invention; Figure 8 is a top view of a second embodiment of a valve leaflet in accordance with the invention; Figure 9 is an isometric view of a third embodiment of a valve leaflet in accordance with the invention; Figure 10 illustrates the addition of coaptation height to the top of a valve leaf let; * Figure 11 is an isometric view of a fourth embodiment of a valve leaflet in accordance with the invention; Figure 12 is a three-dimensional view of a spray coating mould in accordance with the invention; and Figure 13 is a three-dimensional view of a dip coating mould in accordance with the invention.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A polymeric tn-leaflet valve (100) is shown in Figure 1 and includes three valve leaflets (102) arranged in a ring-like configuration and extending integrally from a tubular body (101). Each valve leaflet (102) has an attachment edge (104) and a free edge (106) with a belly (108) extending between each free edge (106) and attachment edge (104).

In use, each attachment edge (104) is attached to a complementary shaped surface (202) provided by a stent (200) as shown in Figure 2. The shape of the stent forms the subject of a co-pending patent application. However, the use of stents as a support structure for replacement valves is known in the art and it will be apparent to those skilled in the art that the tn-leaflet valves of the present invention are to be used with suitable stents.

The leaflets (102) mimic natural heart valve leaflet operation. They are movable between a coapted (closed) condition in which the free edges (106) abut and prevent fluid flow through the valve, as shown in Figure 3, and an open condition in which fluid flow through the valve is permitted as shown in Figure 4. The directional arrow (400) in Figure 4 shows the direction of blood flow which causes leaflets (102) to move into the open condition. Pressure of the blood flow deflects the three leaflets (102) into an open position, and allows blood to flow through.

Importantly, the free edges (106) of the leaflets should define a circle in the open condition, as illustrated in Figure 4. In this condition the free edges have the same circumference as the valve and there is thus minimal impedance to fluid flow and thus maximum efficiency. It is, however, provided that the circumference of the free edges in the open condition may be larger than that of the valve. This design feature is explained in greater detail below.

The attachment edge (104) is arc-shaped for attachment to a surface having an arc with a pair of haunches extending therefrom outwardly inclined from each other. The attachment edge can be defined by an attachment edge function. The shape of the belly (108) of the leaflet (102) is then defined by fitting one or more edge curves, also referred to as edge functions, in the attachment edge function.

The complete leaflet shape is produced by lofting, or meshing, a surface between the individually defined curves.

Figures 5 and 6A illustrate an arc-shape (500) forming the attachment edge produced by a cylinder (502) intersecting a plane (504) at an angle theta (e). The angle 0 is dependent on the height (H) and the radius (R) of the tn-leaflet valve and more clearly shown in Figure 6A. The shape produced shall be referred to herein as a "scallop shape" and the function defining such shape as a "scallop function". In Figures 6A and GB, R refers to the radius of the tn-leaflet valve and H refers to the height of the tn-leaflet valve.

Figure 6B shows a top view of the cylinder of Figure 6A. An angle phi (0) is shown, where 20 is defined as the central arc angle formed by radii extending to each of the two points on the attachment edge where the free edge intersects the attachment edge. The tangent of the angle e is equal to (R -Rcos(ø))/H.

It should be noted that the scallop shape may also be defined by a plane intersecting a cone at a certain angle, or by a cylinder or a cone intersecting a cylinder or a cone at a certain angle.

The scallop shape can, in one embodiment of the invention, be defined by the following set of parametric equations: x = Rt(t) y = I? cos U) 1?-BRcos(t)

C

where R is the inner radius of the artificial tn-leaflet valve and B, C and 0 are constants obtained in determining the equation of the plane which cuts the 2m cylinder. The parameter t is varied and spans a range of 0 to T for one valve leaflet.

For simplicity all functions and leaflet designs in accordance with the invention are described for a tn-leaflet valve with a diameter of 23mm. It will be appreciated, however, that the principles and designs may be applied to a valve of any diameter. For example, the values of the constants are described for a valve with a diameter of 23mm and will necessarily change if a different diameter valve is desired.

The scallop shape can, in another embodiment of the invention, be defined by the following set of parametric equations: x =RsinU) y=RcosU) 2 = 1sin(3t)+ where P is equal to the valve radius and J is equal to the valve height. The Zir parameter I is varied and spans a range of 0 to T for one valve leaflet.

In a preferred embodiment of the invention, the free edge of the valve leaflet is defined by the following equation: y = -Ecoso'x(Gcst(Kx +©1 The value of constant E is in the range of 0.5 to 2.5, preferably in the range of 1 to 2, and more preferably in the range of 1.2 to 1.6. The value of constant F is in the range of 0.05 to 1, preferably in the range of 0.05 to 0.5, and more preferably in the range of 0.1 to 0.2. The value of constant G is in the range of 0.5 to 2.5, preferably in the range of ito 2.5 and more preferably in the range of 1.5 to 2.

The value of constant H is in the range of 0.05 to 1.5, preferably in the range of* 0.2 to 1, and more preferably in the range of 0.6 to 0.7.

In another embodiment of the invention, the free edge of the leaflet is defined by the following: y = mx for -Ca«= X C -Cb + Xx y = .iCcozUx)+ tier -Cb g «= X <4-y = -inxior c -x3 «= x «= c where Ct is defined as end-points (or commissure points) of the leaflet function.

The variable x is a function of the length of the straight line portion of the leaflet and may vary according to leaflet design. In this case, therefore, one or more edge functions are defined by a line tangent to a commissure line, such as a straight line, adjacent the commissure and by a trigonometric function thereafter.

This reduces the degree of folding adjacent the commissures and thus reduces the possibilities of blood coagulating in those areas. This also reduces pooling of the polymer at the commissures during manufacture of the valve.

The value of constant m is in the range of 0.1 to 1, preferably in the range of 0.3 to 0.8, and more preferably in the range of 0.55 to 0.75. The value of constant K is in the range of -3 to 0, preferably in the range of -3 to -2 and more preferably in the range of -2.7 to -2.3. The value of constant L is in the range of 0.05 to 1.5, preferably in the range of 0.2 to 1, and more preferably in the range of 0.5 to 0.6.

The value of t is such that it ensures the end points of the curves represented by the three equations above always meet one another.

The junctions between the different equations of this embodiment may be smoothed by adding a fillet of radius Rf. The value of this constant is in the range of 0.5 to 3, preferably in the range of 0.5 to 1.5 and more preferably in the range of 0.8 to 1.2.

The free edge of each leaflet is of a length equal to or greater than an arc of radius R between the two points on the attachment edge where the free edge intersects (extends from) the attachment edge, where R is the radius of the tn-leaflet valve. The free edge of each leaflet should also be equal to or greater than the length of an element spanning between two commissure points and which is folded inward to the center of the valve, thereby forcing a closed or coapted portion of the valve. Furthermore, the height of the valve should always be greater than the radius of the valve.

In one embodiment of the invention, the free edge of each leaflet is defined by the following equations: 5i = Pcos(Qz)-fScodTx)-v y = U.cos(Tx)(j' cos(Qx) + Scos[(Tx)) -Constant P is in the range of 0.2 to 1.5, preferably in the range of 0.4 to 0.8, and more preferably in the range of 0.6 to 0.7. Constant Q is in the range of 0.5 to 3.5, preferably in the range of 1.5 to 2.5, and more preferably in the range of 2.1 to 2.25. Constant S is in the range of 0.1 to 0.5, preferably in the range 0.15 to 0.3, and more preferably in the range of 0.23 to 0.26. Constant T is in the range of 0.05 to 0.3, preferably in the range of 0.1 to 0.2 and more preferably in the range of 0.15 to 0.18. Constant LI is in the range of 0.5 to 3, preferably in the range of I to 2 and more preferably in the range of 1.2 to 1.3. Value v is calculated such that the end points of the curve always intersect the points (-Rsin(rr/3);Rcos(rr/3)) and (Rsin(rrI3);Rcos(Tr/3)).

End points of the edge functions may be rounded to allow better opening characteristics at the commissures and also to ease manufacturability of the leaflet. Commissure boundaries can be rounded by replacing data points at the edge of the cosine function with the data points of a quarter circle of radius Rc.

The value of Re is in the range of 0.05 to 1, preferably in the range of 0.2 to 0.8, and more preferably in the range of 0.45 to 0.55.

The curves of this embodiment are fifted between two commissure boundaries.

A first commissure boundary is defined as the point where a line of length R (the radius of the valve), drawn at an angle of 30 degrees with the horizontal would intersect a circle of radius R. A second commissure boundary lies 120 degrees from that point on a circle of radius P. A third commissure boundary then lies another 120 degrees from that point. The x and y coordinates of the first commissure point would then be (Roose; Rsin6).

Various functions may be used to define the other edge functions fitted in the scallop function. In one embodiment, edge functions are defined by an equation identical to the free edge function, except for varying amplitude.

Different methods also exist for producing a shape function for the belly extending between each free edge and attachment edge and which preferably has a bell-mouth shape. In one embodiment of the invention, the belly function or belly curve is defined by: / ______ z = tA,e Zo2 J (-As co$(B,y) 4-AC)] The value of constant 1b is in the range of I to 10, preferably in the range of 4 to 8, and more preferably in the range of 6.5 to 7.5. The value of constant p is in the range of 5 to 10, preferably in the range of 7 to 9, and more preferably in the range of 7.8 to 8.3. The value of p is dependent on the length of the belly curve and has a direct relation to that length.

The value of constant a is in the range of 10 to 15, preferably in the range of 11 to 13, and more preferably in the range of 12 to 12.5. Constant A is in the range of 0.1 to 0.6, preferably in the range of 0.3 to 0.5, and more preferably in the range of 0.33 to 0.4. Constant L is in the range of 0.25 to 0.5, preferably in the range of 0.3 to 0.45, and more preferably in the range of 0.35 to 0.4. The value of B, is also dependent on the length of the belly curve.

In a further embodiment, the belly function or belly curve is defined by: I Cv-u)\ z = tAb e 2ó ) (-Ar sin(By) B) The value of constant Ab is in the range of 1 to 5, preferably in the range of 2 to 4, and more preferably in the range of 3 to 3.5. The value if constant p is in the range of 10 to 20, preferably in the range of 12 to 16, and more preferably in the range of 14.5 to 15.5. The value of p is dependent on the length of the belly curve and has a direct relation to that length.

The value of constant a is in the range of 5 to 10, preferably in the range of 7 to 9, and more preferably in the range of 7.5 to 8.5. Constant A is in the range of 0.5 to 5, preferably in the range of 1 to 3, and more preferably in the range of 1.5 to 2.5. Constant B is in the range of 0.05 to 0.3, preferably in the range of 0.1 to 0.25, and more preferably in the range of 0.15 to 0.2. The value of B, is also dependent on the length of the belly curve.

The length of the free edge of a leaflet can be calculated by the following equation: Free Edge Length = (Jit dx Zg where In a preferred embodiment, the free edge length is equal to or slightly larger than the arc length of a segment defined by the angle 120 degrees and radius of the valve. This free edge length ensures that the free edge is long enough to fully open the valve and it also ensures that there is sufficient Iadditional free edge length for full valve leaflet coaptation.

S Figure 7 illustrates an embodiment of the invention wherein the shape of the leaflet (700) is produced by a scallop function (702) and a plurality of edge functions (704) within the scallop function (702), including a free edge function (706). A surface (708) is lofted, or meshed, between the functions so as to define the shape of the leaflet (700).

In this embodiment, the free edge (706) has the same length as an arc between the two points on the scallop (702) where the free edge (706) intersects it. In alternative embodiments, the length of the free edge (706) may be slightly larger than an arc between the two points on the scallop (702) where the free edge (706) intersects it.

Multiple edge curves are used to define the geometry of the leaflet (700) along the height of the valve. The length of each edge curve can be chosen individually to ensure specific features are incorporated into the valve to facilitate, for example, better opening or closing characteristics or reduced stress on the valve.

It should be noted that the curvature of each edge curve does not have to be in the same direction, for example, the free edge (706) may be curved inversely to the other curves (704) to produce a desired belly shape of the valve.

Figure 8 illustrates a further embodiment of the invention wherein the shape of the leaflet (800) is produced by a scallop function (802) and a free edge function (804). A surface (806) is lofted between the functions so as to define the shape of the leaflet (800). The free edge (804) is approximately 15% longer than the diameter of the tn-leaflet valve in this case.

This type of design ensures that the valve not only opens completely for minimal pressure differentials, but also provides redundancy in leaflet length when the valve is in a closed position. The redundancy may also prevent leakage even if the valve is slightly over-deployed, that is, expanded to a greater diameter than the one it was designed for. If greater redundancy or less redundancy is required, the scallop function and the free edge function may be altered accordingly.

In a yet further embodiment, as shown in Figures 9 and 10, to construct a final portion of the leaflet (900), an additional coaptation edge (902) is added to the top of the leaflet (900). The coaptation edge (902) is orthogonal to the top plane of the leaflet (900), with a radius tangent to the scallop (904). Figure 9 also indicates the free edge function (906) and other edge functions (908).

Figure 10 shows the edge function for a similar embodiment to Figure 9 and displays the scallop (1000), a radiused corner (1002) tangent to the scallop (1000), and a straight coaptation edge (1004) added to the top of the leaflet. The coaptation edge (1004) as well as the coaptation edge (1002) of Figure 9 serves to ensure proper valve leaflet coaptation. In one embodiment of the invention, the coaptation edge (1004) has a height of approximately 1mm.

In another embodiment of an artificial valve leaflet (1100), which is shown in Figure 11, the free edge (1102) has a longer length than an arc of radius R at that height location. Two other edges (1104) are also shown. These edges have a length equal to an arc of radius R between its two corresponding end-points on the scallop. The direction of curvature of the free edge (1102) is different to the direction of curvature of the other edges (1104). This introduces a belly into the shape of the leaflet (1100) which is a function of the individual fibre" lengths.

The shape of the scallop (1106) is similar to those discussed above.

Moulds for making valves as defined above are shown in Figures 12 and 13. The mould (1200) in Figure 12 is spray coated to produce a valve, while the mould (1300) in Figure 13 is a dip coating mould.

The moulds (1200, 1300) may be manufactured from any suitable material, including metal, wood, polymer and glass. The outer surface of the mould (1200, 1300) may, in some embodiments, also be coated with any appropriate material so asto enhance desired surface properties of the mould (1200, 1300).

The spray coating mould (1200) of Figure 12 has a body portion (1202) and three leaflet portions (1204) integral with the body portion (1202) which are complementary to the shape of the valve as described above.

The spray coating mould (1200) further has a top portion (1206) providing additional height which results in the valve leaflets having increased height. This ensures that the leaflets have adequate height when removed from the mould.

The free edges may be cut from the mould at the correct position (1208) using, for example, a blade or a laser.

In order to manufacture the leaflets, the mould (1200) may be rotated horizontally about its longitudinal axis and then sprayed with a polymer solution and the solution is allowed to dry with the mould still rotating. This spraying and drying process may be repeated a plurality of times until a desired valve leaflet thickness is achieved.

Drying can take place in ambient conditions. However, it may be preferable to dry the coated mould (1200) in a chamber in which the temperature and the humidity is controlled. The coated mould (1200) may also be dried in a chamber which is substantially free of oxygen to avoid oxygen interaction with the polymer.

The polymer solution sprayed onto the mould may contain a relatively low concentration of polymeric material. In preferred embodiments, the polymer solution is 2% to 5% m/m polymer.

In one embodiment, a small amount of solution, preferably ranging between 0.lmL and 2mL, is sprayed on the mould (1200). Spraying may take place for 5 to 10 seconds, depending on the volume of solution sprayed on the mould (1200). The mould (1200) is sprayed while it is rotating horizontally. The sprayed mould is then dried, while still rotating horizontally, until all solvents are evaporated. This may take 5 to 20 minutes depending on the solvent used and the volume sprayed. The mould is then sprayed again and the process is repeated until the desired leaflet thickness is achieved.

Spray coating in this manner has been found to produce highly uniform valves. It appears as if problems with droplets collecting on one area are avoided by both the spraying and rotation of the mould.

It should be noted that various other methods of spray coating may be employed without departing from the scope of the invention. For example, the mould may be sprayed while it is rotated in a vertical or an inclined position. Alternatively, the mould may remain in a fixed position while a spraying device is moved relative to the mould in order to carry out the spraying operation, or both the mould and spraying device moved at the same time.

The dip coating mould (1300) shown in Figure 13 includes inwardly tapered run-offs at either end. A leaflet run-off (1302) is provided at the end (1304) of the mould defining the free ends of the leaflets and a base run-off (1306) is provided at the end (1308) of the mould adjacent the attachment edges of the leaflets.

The run-offs (1302,1306) act to prevent pooling of a polymer solution which can take place while the polymer solution is allowed to dry on the mould after dip coating in the polymer solution. Typically the mould is hung with either the free edge side facing downward or the body portion facing downward, depending on the run-off configuration. Alternatively, the mould can be made to stand on one of its ends on a surface during drying. The polymer solution flows under gravity down the mould and pools at the lowermost end. The run-offs ensure that the polymer solution is diverted away from the ends of the mould defining the valve.

The resultant valves have been found to have excellent uniformity. In particular, run-offs reduce pooling at the base end, the free edge of the leaflets, commissures and folds in the free edges and lower the risk of uneven leaflet thickness.

Either end of the mould can be used to support the mould during drying. Often it is desirable to use alternate ends after each dip coating to ensure an even distribution of the polymer solution on the mould. For this reason run-offs are provided at both ends. It will be appreciated, however, that the dip coating mould may have a run-off at one end only if desired.

The taper angle of the leaflet run-off area is between 25 and 90 degrees, preferably between 55 and 90 degrees. The taper angle of the base run-off is between 25 and 90 degrees, preferably between 45 and 55 degrees. The taper angles and other dimensions of the run-off areas can, however, be altered to achieve a desired valve thickness taking into account the properties of the polymer solution used.

To ensure that the leaflets are not damaged or torn when removed from the moulds (1200, 1300), the moulds (1200, 1300) may further be provided with rounded edges (1210, 1310) in the areas defining the leaflets (1204, 1304).

The moulds (1200, 1300) can also be provided with a stent holder for securing a stent on an outer surface thereof in the correct orientation relative to the leaflets.

Is As indicated above, the stent is an artificial annular body which provides structural support to the valve. Such a body typically includes an annular base and three leaflet support posts.

In this embodiment the holder includes a number of clip formations (1212, 1312) spaced about the mould. The holder facilitates securing a stent on a mould before or during polymer coating operation so that the stent is also coated with the polymer solution and the valve becomes attached to the stent during the coating process. To this end, the holders maintain the stent a distance of between 0mm and 0.25mm from the surface of the mould.

By placing a stent onto the mould before, during or after the process of manufacturing the valve, a complete artificial tn-leaflet valve fitted onto a stent, ready for insertion into a heart of a patient, can then be assembled on the mould itself.

Polymeric valves, moulds for manufacturing the valves, as well as a method for manufacturing the valves are therefore provided.

The shape of each leaflet is controlled by each edge function having a specified shape and length. In certain embodiments, each edge function is defined in such a way that its length is equal to an arc contained in that specific segment of the valve between its two corresponding end-points on the scallop.

This ensures that when the valve is fully open it closely approximates the profile of a cylinder of the specific valve radius. This, in turn, leads to a valve with a low pressure drop across the valve created by a large orifice when the valve is open.

This results in improved haemodynamic performance.

The provision of additional height to leaflets may also ensure that there is sufficient coaptation upon closure of the valve to result in a proper seal and a non-regurgitant valve.

In alternative embodiments, certain edge functions have a length that is larger than the arc length contained in that segment. This aids in closure of the valve.

Other edge functions for the same leaflet may then still have a length equal to an arc contained in that segment. This valve leaflet design may lower the risk of high stresses at commissures or in regions of the leaflet belly.

A further advantage of embodiments of the invention is that free edge length can be defined exactly. This allows, for example, for a known "redundancy" to be allowed in the length of a leaflet, such as the 15% redundancy described. This may allow leaflets to still close fully when the valve is over-deployed (or over-distended). Furthermore, it makes one particular leaflet design useable for different annular opening sizes in different patients, for example, the same design may be applied to two aortic valves of slightly varying radii.

In addition to the above-mentioned advantages, the manner in which the free edge is defined at the commissure boundaries also results in better coaptation and minimal regurgitation upon closure of the valve.

The dip coating mould allows for the mould to be dipped in either direction during manufacturing. This may allow for the cutting of the free edge to be eliminated during the manufacturing process, ensuring final dimensions that accurately correspond to leaflet design. Furthermore, the shape of the run-off of the mould may be altered to control the thickness distribution of the valve. By providing a holder for placing a stent on the mould during manufacturing, pooling of the polymer is reduced.

A further advantage of the described method for designing polymeric leaflets is that leaflet geometries can be optimised or near-optimised in terms of haemodynamic function and stress distribution, for example, by using finite element modelling. These optimised or near-optimised designs can then be implemented. This may lead to reduced manufacturing costs.

It is foreseen that the tn-leaflet valve as described will be used with a stent that may be crimped and deployed via, for example, transcatheter techniques, or that the tn-leaflet valve can be surgically implanted.

The above description is by way of example only and it will be understood that numerous variations may be made to the implementation of the invention that is described above without departing from the scope hereof, for example, it should be apparent to those skilled in the art that the valve as described is not limited to heart valves and could also be used in, for example, veins.

Claims

CLAIMS1. A tn-leaflet valve made from a polymeric material, wherein each valve leaflet has an attachment edge along which it is attached to a surface; a free edge; and a belly extending between each free edge and attachment edge; wherein the leaflets are movable between a coapted condition in which the free edges abut and prevent fluid flow through the valve and an open condition in which fluid flow through the valve is permitted; charactenised in that the attachment edge of each leaflet is generally arc-shaped for attachment to a complementary surface having an arc and a pair of haunches extending therefrom generally outwardly inclined from each other; and in that the free edge of each leaflet is of a length equal to or greater than an arc of radius R between the two points on the attachment edge where the free edge intersects the attachment edge, where R is the radius of the tn-leaf let valve.
2. A tn-leaflet valve as claimed in claim 1 in which the arc-shape is defined by a plane, a cylinder or a cone intersecting a cylinder or a cone.
3. A tn-leaflet valve as claimed in claim 2 in which the plane, cylinder or cone intersects the cylinder or cone at an angle e and wherein the tangent of the angle e is equal to (R -Rcos(ø))IH, where R is the radius of the tn-leaflet valve and H is the height of the tn-leaflet valve, and where 20 is defined as the central arc angle formed by radii extending to each of the two points on the attachment edge where the free edge intersects the attachment edge.
4. A tn-leaflet valve as claimed in any one of the preceding claims in which the shape of a leaflet is defined by an attachment edge function; a plurality of edge functions fitted in the attachment edge function; and a surface lofted between the functions.
5. A tn-leaflet valve as claimed in claim 4 in which the free edge of the leaflet is defined as a first edge function and each remaining edge function is defined by an equation identical to the first edge function, except for varying amplitude.
6. A tn-leaflet valve as claimed in any one of claims 1 to 3 in which the shape of a leaflet is defined by an attachment edge function; is one or more free edge functions fitted in the attachment edge function; one or more belly functions fitted in the attachment edge function; and a surface lofted between the functions.
7. A tn-leaflet valve as claimed in claim 6 in which one or more of the belly functions follow a bell-mouth shape.
8. A tn-leaflet valve as claimed in any one of claims 1 to 3 in which the shape of a leaflet is defined by an attachment edge function; a plurality of edge functions fitted in the attachment edge function, the edge functions each being defined by a line tangent to a commissure line adjacent the commissure and by a trigonometric function thereafter; and a surface lofted between the functions.
9. A tn-leaflet valve as claimed in any one of claims 4 to 8 in which the attachment edge function or one or more of the edge functions fitted in the attachment edge function are smoothed by adding radii at one or more points along the attachment edge function or the one or more edge functions fitted in the attachment edge function.
1O.A mould for making a tn-leaflet valve as claimed in any one of the preceding claims, the mould defining the inner surface of a tn-leaflet valve, wherein each valve leaflet has an attachment edge along which it is attached to a surface; a free edge; and a belly extending between each free edge and attachment edge; and characterised in that the attachment edge of each leaflet is generally arc-shaped for attachment to a complementary surface having an arc and a pair of haunches extending therefrom generally outwardly inclined from each other; and in that the free edges of the leaflets are of length equal to or greater than an arc of radius R between the two points on the attachment edge where the free edge intersects the attachment edge, where R is the radius of the tn-leaf let valve.
11.A mould as claimed in claim 10 which includes a stent holder capable of securing a stent about the mould in correct orientation relative to the leaflets.
12.A mould as claimed in claim 11 in which the stent holder secures a stent between 0mm and 0.25mm away from the mould.
13.A mould as claimed in any one of claims 10 to 12 which is shaped to provide increased leaflet length to facilitate cuffing of the free edges of the leaflet from the mould.
14.A mould as claimed in any one of claims 10 to 12 which includes an inwardly tapered run-off at one or both ends thereof.
15. A mould as claimed in claim 14 in which a leaflet run-off is provided at the end of the mould defining the free ends of the leaflets with the taper angle of the leaflet run-off being between 55 and 90 degrees.
16. A mould as claimed in claim 14 or claim 15 in which a base run-off is provided at the end of the mould adjacent the attachment edges of the leaflets with the taper angle of the base run-off being between 25 and 90 degrees.
17.A method of manufacturing a tn-leaflet valve from a polymeric material, which includes moving a mould and a spraying device relative to one another; spraying a polymer solution onto the mould; permitting the polymer to dry; optionally repeating one or more of the above steps until a desired leaflet thickness is reached; and removing the valve from the mould.