Prosthetic heart valve

Abstract

The present disclosure relates to surgical prosthesis, especially replacement heart valves and more particularly to replacement synthetic aortic valves. The prosthetic heart valves generally comprise a suture ring, a stent cylinder extending from the suture ring, with one or more stent posts extending from the stent cylinder, and one or more leaflets extending around the stent cylinder, wherein the one or more stent posts and one or more leaflets are all formed from a first material, typically a SEES material. In addition, the prosthetic heart valves may include several forms of reinforcement structures and rings formed from a second material, generally a PEEK material.

Description

[0001] PROSTHETIC HEART VALVE

[0002] Description

[0003] Field of the Invention

[0004] The present invention relates to surgical prosthesis, especially replacement heart valves and more particularly to replacement synthetic aortic valves.

[0005] Background to the Invention

[0006] Damaged or diseased human heart valves may be replaced with biological / natural, mechanical or synthetic alternatives. Typical synthetic heart valves will usually be formed from various types of plastics material which mimic the function of a patient’s existing heart valve.

[0007] Prior art synthetic valves may comprise a circular suture ring, from which a generally coronate stent cylinder extends in one direction. Three stent leaflets are provided within the stent cylinder.

[0008] The valves are subject to a significant number of opening / closing working cycles and must be able to withstand different level of share stressing across their different parts. Failure of an artificial valve requires replacement and is best avoided. However, the different parts of the replacement valve are subject to different stress severities and may require deflecting to a greater or lesser degree to enhance durability and function. There is also some choice in how rigid to make the stent posts. The prior art, such as documents W02020 / 174253 and

[0009] WO / 201 5 / 128605, teach the skilled addressee that this problem is best addressed by employing more than one type of polymer for manufacture of the valve.

[0010] This is particularly true if the rigidity of the posts and leaves are to deviate to a significant extent. Whilst it is understood that some deviation of the posts can relieve stress concentrations in the valve leaflets (particularly at the commissures), prior art describes posts which have been made of, or reinforced by, a stiffer material than the leaflets. For example posts are often made of, or incorporate, a metal wire or rigid polymer such as PEEK, or high styrene content SIBS; whilst leaflets can be a more flexible polymer (such as Elast-Eon, Life Polymer, SIBS, Carbosil, POSS-PCU).

[0011] A commonly used material is the styrene-ethylene-butylene-styrene or “SEBS” class of polymers. There are many different types and may be distinguished by the acronym SEBS followed by a number: SEBS20, SEBS60, etc.

[0012] The number ordinarily indicates the styrene percentage by weight in the polymer. SEBS20 has 20% by weight styrene, SEBS29 has 29% by weight styrene, and so on.

[0013] SEBS polymers have multiple uses, and in the scientific paper reference Biomater. Sci. , 2020, 8-4467 it is shown that the SEBS (and related “SEPS” class or polymers) are usually employed for automotive, adhesive and compounding purposes, but experiments were done in making replacement aortic valves from SEBS polymers. The paper considered eight prototype valves which used combinations of SEPS and SEBS polymers to form the valves.

[0014] The paper concluded that the optimum form of valve comprised an over moulded composite of a stiffer support structure (made of SEBS29) and softer leaflets (made of SEBS20), incorporating cylindrically shaped leaflets with a concave leading-edge profile. This is a more complicated manufacturing process than simply injecting moulding a single material.

[0015] The skilled addressee is therefore taught that the optimum valve type must have two or more materials to provide a stiffer support structure and softer leaflets to enable optimum hydrodynamic performance and longevity of the prosthetic valve.

[0016] “In Vitro Evaluation of a Novel Hemodynamically Optimized Trileaflet Polymeric Prosthetic Heart Valve” by Claiborne et al in the Journal of Biomechanical Engineering of February 2013, Vol. 135 discusses prior art heart valves. The paper is not clear whether the heart valves described are reinforced or not and uses a SIBS23 material. There is no mention whether the posts and leaflets are the same material and the skilled addressee may well construe this as having to require different leaflet material. Moreover, there is no indication of durability for this material or the described valve. SIBS23 is a softer material than SEBS29, more akin to SEBS20, and as such may be too soft for such applications. It should also be noted that the finite element modelling discussed in the paper appears to show no post-deflection at all, despite the expectation that a SIBS23 post should display such deflection in use. WO201 3 / 055977 would appear to describe a similar valve as that of the Claiborne et al paper described above and in that paragraph 0029 on page 7 of that document suggests that reinforcement of the posts is necessary and hence some other material has to be used in addition to a SIBS23 material.

[0017] “A New Nanocomposite Copolymer Based On Functionalised Graphene Oxide for Development of Heart Valves” by Ovcharenko et al (Scientific Reports also discusses prior art heart valves. There is no technical description of how the valve was made or how it performs, it does not seem much more than a valve shaped piece of plastic from the literature.

[0018] Summary of the Invention

[0019] According to the present invention there is provided a prosthetic heart valve comprising a suture ring, a stent cylinder extending from the suture ring, with one or more stent posts extending from the stent cylinder, and one or more leaflets extending around the stent cylinder, wherein the one or more stent posts and one or more leaflets are all formed from a first material.

[0020] In a typical valve, there will be three leaflets and three stent posts.

[0021] The suture ring may also be made from the first material.

[0022] The stent cylinder may also be made from the first material.

[0023] The suture ring, the stent cylinder, the one or more stent posts and one or more leaflets are all formed from the first material. The stent cylinder may be a generally coronate shape i.e. crown shaped, with the stent posts atop three high points on the stent cylinder i.e. the three points on the stent cylinder the greatest distance from the stent ring.

[0024] The first material may be a styrene-ethylene-butylene-styrene (“SEBS”) class of block copolymer.

[0025] The first material may be a cylinder forming SEBS block copolymer with a styrene fraction in the range of 25% to 32%.

[0026] The first material may be a cylinder forming SEBS block copolymer with a styrene fraction in the range of 27% to 32%.

[0027] The first material may be selected from the group comprising: SEBS25, SEBS26, SEBS27, SEBS28, SEBS29, SEBS30, SEBS31 and SEBS32._

[0028] The first material may be SEBS29.

[0029] The first material may have a Young’s modulus at 20% strain in the range of 5.2 - 9.3 MPa.

[0030] The first material may have a Young’s modulus at 20% strain of 7.43 MPa.

[0031] The suture ring may be reinforced with a reinforcement ring of a second material.

[0032] The second material may be stiffer than the first material. The second material may have a higher a Young’s modulus than the first material.

[0033] The reinforcement ring may form part of a reinforcement structure.

[0034] The reinforcement structure may include reinforcement leaflets.

[0035] The reinforcement leaflets may project from the reinforcement ring.

[0036] The reinforcement ring may be encapsulated within the SEBS structure.

[0037] The second material may be Polyether Ether Ketone (“PEEK”).

[0038] According to a second aspect of the present invention there is provided a method of surgery wherein one or more valves according to the present invention is implanted in a patient.

[0039] Brief Description of the Drawings

[0040] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

[0041] Fig. 1 is a side elevation of a first embodiment prosthetic heart valve according to the present invention;

[0042] Fig. 2 is a plan view of the prosthetic heart valve of Fig. 1 ;

[0043] Fig. 3 is an end elevation of the prosthetic heart valve of Fig. 1 ; Fig. 4 is a perspective view of the prosthetic heart valve of Fig. 1 ;

[0044] Fig. 5 is a chart showing the predicted durability of an all SEBS29 prosthetic valve according to the present invention;

[0045] Fig. 6 is a chart showing the predicted durability of an all SEBS29 prosthetic valve, an all SEBS20 prosthetic valve and a prosthetic valve using both SEBS20 and SEB29 in its construction;

[0046] Fig. 7 is a sectional end elevation of the prosthetic heart valve of Fig. 1 with sutures added;

[0047] Fig, 8 is a perspective view of a second embodiment prosthetic heart valve according to the present invention;

[0048] Fig. 9 is a plan view of the prosthetic heart valve of Fig. 8;

[0049] Fig. 10 is a chart showing the updated predicted durability of an all SEBS29 prosthetic valve and a prosthetic valve using both PEEK and SEB29 in its construction;

[0050] Fig, 11 is a perspective view of a third embodiment prosthetic heart valve according to the present invention;

[0051] Fig. 12 is a plan view of the prosthetic heart valve of Fig. 11 ;

[0052] Fig. 13 is a perspective view of a reinforcement ring of the prosthetic heart valve of Fig. 11 ; Fig. 14 is a perspective view of the reinforcement ring of Fig. 13 attached to the prosthetic heart valve of Fig. 11 ;

[0053] Fig. 15 is a perspective transparent view of the heart valve of Fig. 11 ;

[0054] Fig. 16 is a detailed perspective transparent view of the heart valve of Fig. 11 ;

[0055] Fig. 17 is a perspective view of a fourth embodiment prosthetic heart valve according to the present invention;

[0056] Fig. 18 is a side elevation of the prosthetic heart valve of Fig. 17;

[0057] Fig. 19 is a perspective view of a fifth embodiment prosthetic heart valve according to the present invention; and

[0058] Fig. 20 is a perspective view of a PEEK frame of the prosthetic heart valve of Fig. 19.

[0059] Referring to the drawings, and initially to Fig. 1 a first embodiment prosthetic heart valve is depicted generally referred to with the numeral 10. The prosthetic heart valve comprises a suture ring 12, a generally coronate shaped stent cylinder 20 extending from the suture ring 12, one or more stent posts 14 positioned on the stent cylinder 20, and one or more leaflets 16 extending around the stent cylinder. There are several suture holes 18 formed through the thickness of the suture ring 12 to enable surgical attachment to the aorta. In the present example embodiment, the valve 10 is a 21 .0mm diameter valve, the diameter being the internal diameter not including the stent cylinder 20 thickness. The external diameter including the stent cylinder 20 thickness is 25.2mm. The length of the valve 10 excluding the stent posts 14 but including the suture ring 12 is 13.0mm, with the suture ring 12 being 3.2mm in length.

[0060] The design represents a somewhat typical synthetic leaflet-type synthetic valve.

[0061] In the present embodiment, the entire valve 10 is formed from the injection moulding of styrene-ethylene-butylene-styrene 29 or SEBS29. This has a Young’s modulus at 20% strain of 7.43 MPa. This represents a significant simplification of the manufacturing process for such valves since different types of polymers are not required to be formed into a single valve.

[0062] In an alternative second embodiment depicted in Figs 8 and 9 generally referred to as 110, the suture ring 112, the stent posts 114, stent leaflets 116 and stent cylinder 120 are all made from SEBS29.

[0063] The suture ring 112 in the second embodiment 110 is reinforced with a reinforcement ring 122 made of a second material. The second material is stiffer than the first material. The second material may have a higher a Young’s modulus than the first material. In the present embodiment, the second material is Polyether Ether Ketone (“PEEK”). The reinforcement ring 122 may simply be over-moulded onto the suture ring 112 during manufacture. The suture ring 112 is also provided as a flange or lip structure projecting outwardly from the stent cylinder.

[0064] The reinforcement ring 122 is also provided with suture holes 118 for surgical attachment. The main purpose of the reinforcement ring 122 is to maintain the circularity of the suture ring 112 and mitigate any tendency for the suture ring 112 (and by extension the entire valve 110) to deform in vivo.

[0065] Figs 11 to 16 depict a third embodiment valve is depicted, generally referred to as 210. The third embodiment is largely similar to the second embodiment, being provided with a reinforcement ring 222 over the suture ring 212.

[0066] In addition, there are three pins 219 which extend from the lower surface of the reinforcement ring 222, and three corresponding sockets 217 which are provided on the suture ring 212. These interlock in order to fit the two parts together, and subsequent suturing in vivo assists in fitting the two parts together.

[0067] A fourth embodiment valve is depicted in Figs 17 and 18, generally referred to as 310. The fourth embodiment is broadly similar to the previous embodiments, albeit the reinforcement ring is replaced with an internal reinforcement structure 321 formed from PEEK. The internal reinforcement structure or PEEK insert 321 comprises a lower undulating reinforcement ring 322 from which extend support leaflets 324. The lower undulating reinforcement ring 322 is positioned beneath, and attached to, the suture ring 312. Suture holes 328 are provided through the lower undulating reinforcement ring 322. The support leaflets 324 are positioned within the stent leaflets 316, with the internal reinforcement structure 321 supporting the other components of the valve 310. The PEEK insert 321 may be formed from any suitable manufacturing process, and in small numbers this may be CNC-milling, and in larger numbers may be from injection moulding. In the current embodiment the SEBS component and the PEEK component are formed separately, and are joined by suturing together in vivo.

[0068] A fifth embodiment valve is depicted in Figs. 19 and 20, generally referred to as 410. The fifth embodiment is broadly similar to the fourth embodiment, having a PEEK insert reinforcing structure 421. The PEEK insert 421 of the fifth embodiment, has a more lightweight, web-like structure, with three support leaflets 424 formed as triangles with internal apertures 425. The reinforcement ring 422 sits within the confines of the SEBS suture ring 412. Three attachment lugs 423 extend from the reinforcement ring 422 which form part of the suture ring 412. In this embodiment, the PEEK insert 421 may be manufactured from processes such as CNC milling, typically in low volume, or injection moulding, typically in higher volume. The SEBS part is then over-moulded onto the PEEK insert.

[0069] In line with the summary of invention and claims, further embodiments exist in which the entire valve may be formed from a material that is a cylinder forming SEBS block copolymer with a styrene fraction in the range of 25% to 32%.

[0070] The material may be a cylinder forming SEBS block copolymer with a styrene fraction in the range of 27% to 32%.

[0071] The material may be selected from the group comprising SEBS25, SEBS26, SEBS27, SEBS28, SEBS29, SEBS30, SEBS31 and SEBS32.

[0072] The material may have a a Young’s modulus at 20% strain in the range of 5.2 - 9.3 MPa. Data

[0073] Since it is not possible to practically test a prosthetic heart valve for the number of cycles it will have to withstand in real life (e.g. potentially 20- 30 years or longer), so experimental data is obtained and lifespan may then be modelled from that data.

[0074] Table 1 below shows experimental data obtained for hydrodynamic performance for a reference 21 mm SEBS29 valve after 250 million cycles in a wear tester against a Biological Edwards Perimount reference valve and the minimum ISO 5840 standard:

[0075] Table 1

[0076] This demonstrates that the SEBS29 valve exceeds the ISO standard for EOA / cm3and REG / % and compares favourably with the reference valve on all criteria.

[0077] Table 2 below shows current durability test data under the ISO 5840 standard for four prototype versions: two (V1 (row 1) and V2 (row 2)) being fully SEBS 29 valves with flexible posts; and two (R 24 (row 3) and R 25 (row 4)) having rigid posts. The rigid post valves are designed to fail relatively rapidly, since constraining the post motion concentrates stress at the leaflet commissures.

[0078] This allows cycles to valve failure to be measured in a more tractable period of time, than for the flexible post version (which is the prototype intended for use) - although to date, we have yet to observe failure even in the rigid post valves for single material SEBS29 valves. Combined with crack propagation experiments on planar samples and finite element modelling, the lifetime of the flexible post valves can be predicted from the time to failure of the rigid post ones (Figure 6)

[0079] Table 2 The ISO 5840 standard dictates a minimum of 400 million cycles being achieved. Both flexible and rigid SEBS 29 valves comfortably exceed the standard and notably the flexible post versions do so by some margin.

[0080] Modelling Data

[0081] Fig. 5 shows a predicted durability plot of number of cycles until failure (exponential on Y-axis) against maximum strain energy density in MPa (exponential on X-axis) for a SEBS29 valve being 21 mm in diameter with a leaflet thickness of 0.2mm.

[0082] Durability prediction is based on rigid post valve lifetime as of 1 st Feb 2023 (450 million cycles) at which point the rigid post valves have still not failed. As measured rigid post lifetime goes up, flexible post prediction goes up in proportion.

[0083] The model algorithm for the plot is:

[0084] Where:

[0085] SAMPLE 1 SAMPLE 2 Average

[0086] B 0.000102938 0.0001149 0.000108917

[0087] F 2.22620679 2.14713825 2.186672519 N_f No. of Cycles until failure

[0088] F Model Parameter

[0089] B Model Parameter k Constant of Proportionality 2<k<3

[0090] W SED Function Quadratic Function a_o Initial Crack Size

[0091] The SEBS29 valve prediction line is shown as the straight uninterrupted dark line with the ISO standard showing as the horizontal dotted line. B and F come from crack propagation experiments; Wfrom finite element modelling; aO from the rigid post experiment.

[0092] The SEBS29 observed rigid post durability is shown as the hollow diamond and the flexible post prediction as the solid diamond. Again, this comfortably exceed the standard.

[0093] In fact, the modelling predicts a flexible post SEBS29 valve having a durability of 3.76 billion cycles from the 450 million observed (and as yet not failed) rigid post durability.

[0094] Fig. 6 again shows a predicted durability plot of number of cycles until failure (exponential on Y-axis) against maximum strain energy density in MPa (exponential on X-axis) for a SEBS29 valve being 21 mm in diameter and with a leaflet thickness of 0.18mm.

[0095] The right-hand solid line is the same from Fig. 5 showing the fully SEBS29 durability line and the left-hand solid line showing a durability for a SEBS20 / SEBS29 valve as discussed in the scientific paper reference Biomater. Sci., 2020, 8-4467. The right-hand line has observed durability of a SEBS20 rigid post valve shown as a hollow diamond (below the ISO 5840 standard) and being 43 million cycles and a hollow diamond plotting the predicted durability of SEBS20 / SEBS29 flexible post prediction (below the ISO 5840 standard) 212 million cycles predicted.

[0096] However, there is also shown on the graph (as a solid circle between the two lines) the actual observed experimental durability data for a SEBS20 / SEBS29 valve of some 1.3 billion cycles, which as can be seen comfortably exceeds the ISO standard.

[0097] This may suggest that the modelling for durability is somewhat conservative, but if so that would suggest that the actual observed experimental durability of the SEBS29 valve should comfortably exceed both the predicted value and the ISO standard.

[0098] Fig. 8 provides updated experimental and predicted durability data for both the SEBS29 only embodiment and the PEEK reinforced embodiment showing both to comfortably exceed the relevant standard.

[0099] Discussion

[0100] The experimental and modelling data all suggest that, contrary to the teaching of the prior art, not only is SEBS29 a suitable form of material for producing a uniformly moulded prosthetic heart valve such as the described embodiment 10, but also that there is a profound improvement on measured and predicted durability of such a valve. The skilled addressee is both not likely to choose a solely SEBS29 material for such nor would they expect such a marked improvement in durability over the known art.

Claims

Claims1 . A prosthetic heart valve comprising a suture ring, a stent cylinder extending from the suture ring, with one or more stent posts extending from the stent cylinder, and one or more leaflets extending around the stent cylinder, wherein the one or more stent posts and one or more leaflets are all formed from a first material.

2. A prosthetic heart valve according to claim 1 wherein the suture ring is also made from the first material.

3. A prosthetic heart valve according to claim 1 or 2 wherein the stent cylinder may also be made from the first material.

4. A prosthetic heart valve according to any preceding claim wherein the suture ring, the stent cylinder, the one or more stent posts and one or more leaflets are all formed from the first material.

5. A prosthetic heart valve according to any preceding claim wherein the first material may be a cylinder forming SEBS block copolymer with a styrene fraction in the range of 25% to 32%.

6. A prosthetic heart valve according to any preceding claim wherein the first material may be a cylinder forming SEBS block copolymer with a styrene fraction in the range of 27% to 32%.

7. A prosthetic heart valve according to any preceding claim wherein the first material may be selected from the group comprising SEBS25, SEBS26, SEBS27, SEBS28, SEBS29, SEBS30, SEBS31 and SEBS32.

8. A prosthetic heart valve according to any preceding claim wherein the first material is SEBS29.

9. A prosthetic heart valve according to any preceding claim wherein the first material may have a Young’s modulus at 20% strain in the range of 5.2 - 9.3 MPa.

10. A prosthetic heart valve according to any preceding claim wherein the first material may have a a Young’s modulus at 20% strain of 7.43 MPa.

11. A prosthetic heart valve according to any preceding claim wherein the suture ring is reinforced with a reinforcement ring of a second material.

12. A prosthetic heart valve according to claim 11 wherein the second material is stiffer than the first material.

13. A prosthetic heart valve according to any of claims 11 or 12 wherein the second material has a higher a Young’s modulus than the first material.

14. A prosthetic heart valve according to any of claims 11 to 13 wherein the second material is Polyether Ether Ketone (“PEEK”).

15. A prosthetic heart valve according to any of claims 11 to 14 wherein the reinforcement ring forms part of a reinforcement structure.

16. A prosthetic heart valve according to claim 15 wherein thereinforcement structure includes reinforcement leaflets.

17. A prosthetic heart valve according to claim 16 wherein the reinforcement leaflets project from the reinforcement ring.

18. A prosthetic heart valve according to claims 11 to 17 wherein the reinforcement ring may be encapsulated within the SEBS structure.

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