US20190314083A1 - Flexible Multi-Arm Catheter with Diametrically Opposed Sensing Electrodes - Google Patents

Abstract

A medical instrument includes a shaft, multiple flexible spines and multiple electrodes. The shaft is configured for insertion into a body of a patient. The multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored. The spines are bent proximally such that the second ends are more proximal than the first ends. Each of the flexible spines includes a tensile layer configured to cause the flexible spine to bend proximally. The multiple electrodes are disposed over the flexible spines.

Description

FIELD OF THE INVENTION
• The present invention relates generally to medical probes, and particularly to multi-electrode catheters.
BACKGROUND OF THE INVENTION
• Various types of diagnostic-catheters and therapeutic-catheters may be used in cardiac diagnostic procedures. For example, U.S. Patent Application Publication 2016/0081746 describes a catheter adapted for mapping and/or ablation in the atria that has a basket-shaped electrode array with two or more location sensors with a deflectable expander. The catheter comprises a catheter body, a basket electrode assembly at a distal end of the catheter body, and a control handle at a proximal end of the catheter body. The basket electrode assembly has a plurality of electrode-carrying spines and an expander that is adapted for longitudinal movement relative to the catheter body for expanding and collapsing the assembly via a proximal end portion extending past the control handle that can be pushed or pulled by a user. The expander is also adapted for deflection in response to an actuator on the control handle that allows a user to control at least one puller wire extending through the catheter body and the expander.
• As another example, U.S. Pat. No. 6,669,693 describes a device having a retractable and deployable umbrella body. The umbrella body includes ablation elements for circumferentially engaging and ablating a target tissue. The umbrella body is an adjustable, compliant cone-shaped member that may be deployed over a wide range of working diameters. The ablation elements are attached to spines and to a circumferential loop or loop segment attached to the spines. The ablation elements attached to the umbrella body can therefore conform to the geometry of the pulmonary vein ostium and provide circumferential contact, which permits more accurate ablation procedures.
• International Patent Application Publication WO/2016/090175 (PCT/US2015/063807) describes in various embodiments, systems, devices and methods for modulating targeted nerve fibers (e.g., hepatic neuromodulation) or other tissue. The systems may be configured to access tortuous anatomy of or adjacent hepatic vasculature. The systems may be configured to target nerves surrounding (e.g., within adventitia of or within perivascular space of) an artery or other blood vessel, such as the common hepatic artery.
• U.S. Patent Application Publication 2012/0172697 describes a medical device that has a flexible elongated body, a handle connected to the elongated body, at least one spine connected to the elongated body, and a flexible sheet attached to the at least one spine. The flexible sheet has a plurality of electrodes thereon, wherein the flexible sheet and the plurality of electrodes define a mapping assembly for mapping electrical information in tissue, and wherein the at least one spine and the flexible sheet is movable from a collapsed configuration to a deployed configuration.
SUMMARY OF THE INVENTION
• An embodiment of the present invention provides a medical instrument including a shaft, multiple flexible spines and multiple electrodes. The shaft is configured for insertion into a body of a patient. The multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored. The spines are bent proximally such that the second ends are more proximal than the first ends. Each of the flexible spines includes a tensile layer configured to cause the flexible spine to bend proximally. The multiple electrodes are disposed over the flexible spines.
• In some embodiments, the multiple electrodes are disposed over diametrically opposing surfaces of the flexible spines.
• In some embodiments, the flexible spines and the electrodes include circuit board substrates, and metallic elements disposed on the circuit board substrates, respectively.
• In some embodiments, the circuit board substrates are folded so that the multiple electrodes are disposed over diametrically opposing facets of the circuit board substrates.
• In an embodiment, each of the tensile layers includes one or more tensile fibers configured to cause the flexible spine to bend proximally. In another embodiment, a tensile strength of the layer is greater than that of a Nitinol alloy layer of same dimensions. In one example, the tensile strength of the layer is greater than the ultimate tensile strength of fully annealed Nitinol (at approximately 895 MPa) and greater than the tensile strength of work hardened Nitinol (at approximately 1900 MPa).
• There is additionally provided, in accordance with an embodiment of the present invention, a manufacturing method, including producing multiple flexible spines having multiple electrodes disposed thereon. The multiple flexible spines are mounted at a distal end of a shaft. The multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, and the spines are bent proximally such that the second ends are more proximal than the first ends.
• There is also provided, in accordance with an embodiment of the present invention, a manufacturing method, including patterning electrodes and conductive lines on multiple flexible circuit boards. Pairs of the flexible circuit boards are laminated with a layer of tensile material sandwiched between the circuit boards of each pair, so as to form flexible spines. The multiple flexible spines are mounted at a distal end of a shaft. The multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, and the spines are bent proximally such that the second ends are more proximal than the first ends. A tensile layer included in each of the flexible spines is configured to cause the flexible spines to bend proximally.
• There is further provided, in accordance with an embodiment of the present invention, a manufacturing method, including patterning electrodes and conductive lines on multiple flexible circuit boards. The flexible circuit boards are folded along respective longitudinal axes of the circuit boards, over one or more fibers made of a tensile material, such that the fibers become sandwiched between two diametrically opposing facets of the patterned flexible boards, so as to form flexible spines. The multiple flexible spines are mounted at a distal end of a shaft. The multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, and the spines are bent proximally such that the second ends are more proximal than the first ends. A tensile layer included in each of the flexible spines is configured to cause the flexible spines to bend proximally.
• The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic, pictorial illustration of a catheter-based electro-anatomical mapping system, in accordance with an embodiment of the present invention;
• FIG. 2 is a schematic, pictorial view of a soft multi-arm catheter, in accordance with an embodiment of the present invention;
• FIGS. 3A-3D are schematic views that exemplify manufacturing stages of flexible spines comprising diametrically opposed electrodes, in accordance with some embodiments of the present invention; and
• FIG. 4 is a schematic, detailed pictorial view of the soft multi-arm catheter ofFIG. 2, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTSOverview
• Electrical signals in the myocardium may be recorded by sensing electrodes disposed on diagnostic cardiac catheters. Such sensing electrodes may be disposed at a catheter distal end comprising a rigid backbone structure, or over stiff arms. A rigid backbone structure may be made, for example, of spines that are secured at both their ends to a shaft, e.g., assembled into a basket catheter. Alternatively, arms that are stiff enough can be held at one end only.
• In some cases, however, a rigid distal end may be problematic. For example, while mapping the myocardium to acquire electrical signals, diagnostic catheters made of rigid structures or stiff members can trigger ectopic heartbeats (i.e., irregular heart rhythm due to a premature heartbeat) by mechanical contact with the tissue. There is also a risk of perforation of the myocardium by, for example, the edge of a stiff spine.
• Embodiments of the present invention that are described hereinafter provide a multi-arm catheter comprising multiple flexible spines, referred to hereinafter as a ‘flexible multi-arm catheter.’ The flexible spines comprise a high density of diametrically opposing sensing electrode-pairs. The multiple flexible spines extend outward from a center of the distal end of the shaft that the soft catheter is fitted at and then curve inward towards the shaft and backwards in the proximal direction over the distal end of the shaft. Each flexible spine bends without being anchored at its other end, e.g., by embedding tensile material in the spine.
• In other words, a given flexible spine has a respective first end that is connected to the distal end of the shaft and a respective second end that is free-standing and unanchored, wherein the spine is bent proximally such that the second end is more proximal than the first end.
• Some disclosed embodiments utilize a flexible circuit board to construct spines that have electrodes on both the top-side and under-side (i.e., over diametrically opposing surfaces of the flexible circuit board). Such a geometry enables measuring signals from two opposing directions per each electrode-pair location. When the flexible spines are fully extended, the electrodes that face the shaft will typically not be in contact with tissue. These electrodes may be clinically significant when the spines are still partially advanced out of the sheath, when these ‘interior’ electrodes are still on the exterior side, and sensing may commence while the catheter is still in a compact form, being partially folded in the sheath.
• In some embodiments, the circuit board is made of a flexible material that allows the circuit board to be tightly folded, in order to form the electrodes on two opposing sides. A thin material with high tensile strength, such as Vectran® or Ultra High Molecular Weight Polyethylene (UHMWPE), can be sandwiched between the two facets of the folded circuit board to force the flexible circuit board to bend. The resulting spine geometry provides additional structural and clinical safety, by avoiding contact of sharp edges with the myocardium.
• Alternatively, or additionally, the flexible spine may include one or more high-tensile-strength fibers to control its bending, such as ones made of Liquid Crystal Polymer (LCP), Carbon Fiber, Fiberglass, and/or UHMWPE. In some embodiments, the flexible circuit has the electrodes conductive lines patterned as thin films and/or as an embedded yarn, in a way that maintains the structural flexibility of the flexible spine.
• In some embodiments, the tensile strength of the material used for forcing the flexible circuit board to bend is greater than that of Nitinol alloys. Namely, for a same layer or a same fiber-thickness, the tensile force exerted by the layer or a fiber using one of the above listed materials, is higher than if made of one of Nitinol alloys. An example of catheter arms that are made of a Nitinol alloy, are the arms of a Pentaray® sensing-catheter, made by Biosense Webster, Irvine, Calif.
• The disclosed flexible multi-arm catheter, whose arms are self-bending proximally and inwardly while being suspended from the distal end of the shaft, can accommodate any anatomy with high flexibility and with minimum stiffness. This design allows the physician to safely maneuver the catheter within a cardiac chamber and collect signals from tissue with less risk of ectopic beats or perforation. The soft multi-arm catheter thus expands the capabilities of a physician to diagnose certain cardiac disorders, especially in patients who are more vulnerable to side-effects described above of cardiac catherization. Moreover, the flexible multi-arm design can increase the accessibility to mapping of anatomy parts hard to access with existing designs.
System Description
• FIG. 1 is a schematic, pictorial illustration of a catheter-based electro-anatomical mapping system20, in accordance with an embodiment of the present invention.System20 comprises acatheter21, wherein ashaft22 of the catheter is inserted into aheart26 of a patient28 through asheath23. The proximal end ofcatheter21 is connected to acontrol console31. In the embodiment described herein,catheter21 may be used for any suitable diagnostic purposes, such as electrophysiological mapping and/or electro-anatomical mapping of tissue inheart26.
• Console31 comprises aprocessor38, typically a general-purpose computer, with suitable front end.Console31 comprises also aninterface circuitry41 for receiving signals fromcatheter21, as well as for connecting to other components ofsystem20 thatprocessor38 controls.
• Aphysician30inserts shaft22 through the vascular system ofpatient28 lying on a table29. As seen in aninset25,catheter21 comprises a softmulti-arm sensing catheter40 fitted at the distal end of shaft22 (after being advanced outside sheath23). During the insertion ofshaft22, softmulti-arm catheter40 is maintained in a collapsed configuration bysheath23. By containingcatheter40 in a collapsed configuration,sheath23 also serves to minimize vascular trauma along the way to target location.Physician30 navigates softmulti-arm catheter40 to a target location inheart26 by manipulatingshaft22 using amanipulator32 near the proximal end of the catheter and/or deflection from thesheath23. Once the distal end ofshaft22 has reached the target location,physician30 retractssheath23, or advancesshaft22, letting softmulti-arm sensing catheter40 expand. The physician then operatesconsole31 so as sense signals using electrodes24 (seen inFIG. 2) from tissue at the target location.
• Although the pictured embodiment relates specifically to the use of a softmulti-arm sensing catheter40 for electrophysiological sensing of heart tissue, the elements ofsystem20 and the methods described herein may additionally be applied in controlling multi-electrode ablation devices, such as circular ablation catheters, balloon ablation catheters, and multi-arm ablation devices.
• FIG. 2 is a schematic, pictorial view of softmulti-arm sensing catheter40, in accordance with an embodiment of the present invention. As seen, softmulti-arm catheter40 is fitted on a distal end ofshaft22.Catheter40 is made of multiple flexible spines that extend diagonally outward from a center of the distal end ofshaft22. The spines then bend inwardly, in the proximal direction, over the distal end ofshaft22, with their other end free-standing and unanchored. A multiplicity of metallic elements in the form ofrectangular sensing electrodes24 are patterned over the two facets offlexible spines27 so as to allow detection of signals from opposing directions.
• Electrodes24 that are facing the shaft after the spines fully expand may still be clinically significant prior tospines27 being fully advanced out of the sheath. Whenspines27 are partially advanced out, such interior electrodes are on the exterior side, and sensing may commence while the catheter is still in a compact form, being partially folded in the sheath.
• Flexible spines27 are practically semi-floating so as to gently accommodate an anatomy that the spines may come in contact with. The edges ofspines27 are pointing towardshaft22 so as to avoid sharp contact of an edge of a spine with tissue.
• Spines27 are designed to apply elastic opposing force when pressed inward, for example when pressed against a surface of tissue. The strength of the elastic opposing force can be tuned during design and/or manufacturing, so as to optimize the flexibility ofcatheter40. In an embodiment, the opposing elastic force is made strong enough to ensure firm contact ofelectrodes24 with tissue, but still weak enough to minimize undesired events such as ectopic heartbeats upon mechanical contact of one ormore spines27 ofcatheter40 with myocardium tissue.
• The example illustration shown inFIG. 2 is chosen purely for the sake of conceptual clarity. Other configurations of flexible spines are possible. Alternative or additional patterns are possible, such as circular electrodes, as well as fitting additional types of patterned sensors or electrodes, e.g., ablative, strain, ultrasound, or any other suitable type of sensor or electrode. The cross-section offlexible spines27 may vary in shape. The distribution and number of electrodes that may encompass the flexible spines may vary. For example, ring shaped electrodes may be disposed over flexible spines having a circular cross-section.
• FIGS. 3A-3D are schematic views that exemplify manufacturing stages offlexible spines27 comprising diametrically opposed electrodes, in accordance with some embodiments of the present invention. In general, the flexible spines and the electrodes comprise circuit board substrates, and metallic elements disposed on the circuit board substrates, respectively.
• FIG. 3A shows aflexible circuit board52 before being folded to form aspine27.Sensing electrodes24aand24bare patterned overcircuit board52 with afolding line51 separating them physically and electrically. Onceflexible circuit board52 will be folded along foldingline51,electrodes24aand24bwill form the diametrically opposing electrodes geometry, as further described below.
• FIG. 3B shows a foldedspine27, which was made by foldingcircuit board52 to achieve the diametrically opposing electrodes disposed onspine27. The foldedcircuit board52 wraps one or moretensile fibers54 that run along the interior of the spine and provide the required structural strength and the tendency ofspine27 to bend as it is fixed on one of its ends.
• FIG. 3C shows another embodiment, in whichflexible spine27 is made of a layer of atensile material50, such as Liquid Crystal Polymer (LCP), Ultra High Molecular Weight Polyethylene (UHMWPE), para-aramid, carbon fiber, or glass fiber, which is laminated in between twoflexible circuit boards52aand52b(that were made, for example, by cuttingcircuit board52 into two along line51).Sensing electrodes24 are patterned overboards52aand52bto face opposite directions.
• FIG. 3D provides a zoom-in cross-sectional view of a patterning scheme ofelectrode24 on aflexible board65. In an embodiment,electrode layer61 is made of copper deposited on an insulatingpolyimide layer64. Nickel is next deposited then onto the copper, and finally gold is deposited onto the nickel. In an alternative embodiment,electrode layer61 is made of a Titanium Tungsten (TiW) seed layer sputtered onto insulatingpolyimide layer64. Gold is next sputtered onto the seed layer, and then a final layer of gold is added in a plating process. Aconductive trace63 forelectrode24 is embedded underneathpolyimide layer64 so as to connectelectrode24 tosystem20, wherein thepolyimide insulating layer64 isolates trace63 from theelectrode layer61. In an embodiment,conductive trace63 is made of copper encapsulated in alayer66 of gold. A via62 (a through hole) is formed (e.g., by etching or drilling through printed board52) and plated with gold, so as to electrically connectelectrode24 withconductive trace63. In an embodiment, via62 extends deeper and all the way throughflexible board65, to connect the diametrically opposing electrodes (FIG. 3D shows only the one facet coated with an electrode, while for connecting the opposing electrode the via extends much deeper to reach the other electrode on the other facet of flexible board65).
• Anadhesive layer66bonds polyimide layer64 toflexible board65 so as to provide additional endurance and aid in manufacturing the multiple layers.
• The examples of manufacturing designs shown inFIGS. 3A-3D are chosen purely for the sake of conceptual clarity. In alternative embodiments, the patterned designs may include different number and types of electrodes. The processing technologies of the different parts and layers offlexible spines27 may vary.
• In an embodiment, a flexible multi-arm catheter is provided, having up to thirty-two sensing electrodes24 (e.g., sixteen opposing pairs) patterned on eachflexible spine27.Cather40 is made of eight spines, making the total number of sensing-electrodes disposed atcatheter40 up to 256 electrodes.
• FIG. 4 is a schematic, detailed pictorial view of the soft multi-arm catheter ofFIG. 2, in accordance with an embodiment of the present invention. For example,catheter42 inFIG. 4 shows 12 electrode pairs24 on eachspine27, eachelectrode pair24 having anelectrode24athat faces away from alongitudinal axis100 and anelectrode24bthat faces thelongitudinal axis100. Thespine27 is configured such that when thespines27 are fully extended fromtubular shaft22, a radius of curvature R can be conformed onto a portion of theinterior surface27bof the spine. As seen,spines27 extend outward and then bend proximally and inwardly, relative to alongitudinal axis100 ofshaft22. In an embodiment,tensile material50 is configured to causeflexible spines27 to bend freely at a preset radius of curvature R (i.e., the radius of the approximately circular arc shape thatflexible spines27 have) of about 0.40 inches with respect to alongitudinal axis100, so as to haveflexible spines27 fit into a curved anatomy having similar typical size, such as of an ostium of a pulmonary vein.
• In general, aftercatheter40 is fully deployed, at least part ofelectrodes24awill come in physical contact with tissue.Electrodes24b, on the other hand, will typically not be in contact with tissue (rather, with blood only).Electrodes24bmay be clinically significant when the spines are still partially advanced out of the sheath, when these ‘interior’ electrodes are still on the exterior side, and sensing may commence while the catheter is still in a compact form, being partially folded in the sheath. Additionally,electrodes24bmay be used for the collection of background (e.g., far-field) electrophysiological signals, whichprocessor41 may utilize for the analysis of tissue electrophysiological signals fromrespective electrodes24a.
• In an embodiment, the size ofelectrodes24aand24bis both about 0.040 by about 0.027 inches, in width times length, respectively. The length ofgap34 between neighboringelectrodes24 is about 0.030 inches. The size of electrodes and gaps is designed such that it provides the medically required spatial resolution of intra-cardiac measured electrophysiological signals. The exemplary configurations described and illustrated herein allow for the elimination of a rigid backbone member such as a Nitinol wire in the spine while allowing detection of signals from both side ofspine27 viaouter electrode24aandinner electrode24b(FIG. 4) for eachelectrode pair24. This can be achieved by configuring each spline to have a flexible circuit substrate. The substrate has conductive surfaces on the outer surface of the substrate as electrodes. By using the thin flexible circuit with a suitable tensile member (e.g., polymeric fiber) disposed between the surfaces, a physician can maneuver thespines27 in the heart and collect signals regardless of the orientation of thespines27 as well as a lower risk of complications due to the spine members.
• Although the embodiments described herein mainly address cardiac electrophysiological mapping and/or electroanatomical mapping, the methods and systems described herein can also be used in other applications, such as otolaryngology or neurology procedures.
• It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.

Claims (15)

1. A medical instrument, comprising:

a shaft for insertion into a body of a patient;

multiple flexible spines, having respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, wherein the spines are bent proximally such that the second ends are more proximal than the first ends, and wherein each of the flexible spines comprises a tensile layer configured to cause the flexible spine to bend proximally; and

multiple electrodes disposed over the flexible spines.

2. The medical instrument according toclaim 1, wherein the multiple electrodes are disposed over diametrically opposing surfaces of the flexible spines.

3. The medical instrument according toclaim 1, wherein the flexible spines and the electrodes comprise circuit board substrates, and metallic elements disposed on the circuit board substrates, respectively.

4. The medical instrument according toclaim 3, wherein the circuit board substrates are folded so that the multiple electrodes are disposed over diametrically opposing facets of the circuit board substrates.

5. The medical instrument according toclaim 1, wherein each of the tensile layers comprises one or more tensile fibers configured to cause the flexible spine to bend proximally.

6. The medical instrument according toclaim 1, wherein a tensile strength of the tensile layer is greater than that of a Nitinol alloy layer of same dimensions.

7. A manufacturing method, comprising:

producing multiple flexible spines having multiple electrodes disposed thereon; and

mounting the multiple flexible spines at a distal end of a shaft, wherein the multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, wherein the spines are bent proximally such that the second ends are more proximal than the first ends, and wherein each of the flexible spines comprises a tensile layer configured to cause the flexible spine to bend proximally.

8. The manufacturing method according toclaim 7, wherein producing the spines comprises disposing multiple electrodes over diametrically opposing surfaces of the flexible spines.

9. The manufacturing method according toclaim 7, wherein producing the spines comprises disposing the electrodes on circuit board substrates.

10. The manufacturing method according toclaim 9, wherein producing the spines comprises folding the circuit board substrates so that the multiple electrodes are disposed over diametrically opposing facets of the circuit board substrates.

11. The manufacturing method according toclaim 7, wherein producing the spines comprises fitting one or more tensile fibers in each of the spines, so as to cause the flexible spine to bend proximally.

12. The manufacturing method according toclaim 7, wherein producing the spines comprises including a tensile layer with tensile strength that is greater than that of a Nitinol alloy layer of same dimensions.

13. A manufacturing method, comprising:

patterning electrodes and conductive lines on multiple flexible circuit boards;

laminating pairs of the flexible circuit boards, with a layer of tensile material sandwiched between the circuit boards of each pair, so as to form flexible spines; and

mounting the multiple flexible spines at a distal end of a shaft, wherein the multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, wherein the spines are bent proximally such that the second ends are more proximal than the first ends, and wherein a tensile layer included in each of the flexible spines is configured to cause the flexible spines to bend proximally.

14. A manufacturing method, comprising:

patterning electrodes and conductive lines on multiple flexible circuit boards; and

folding the flexible circuit boards along respective longitudinal axes of the circuit boards, over one or more fibers made of a tensile material, such that the fibers become sandwiched between two diametrically opposing facets of the patterned flexible boards, so as to form flexible spines; and

mounting the multiple flexible spines at a distal end of a shaft, wherein the multiple flexible spines have respective first ends that are connected to a distal end of the shaft and respective second ends that are free-standing and unanchored, wherein the spines are bent proximally such that the second ends are more proximal than the first ends, and wherein a tensile layer included in each of the flexible spines is configured to cause the flexible spines to bend proximally.

15. A medical instrument, comprising:

a catheter shaft extending along a longitudinal axis from a proximal end to a distal end;

multiple flexible spines extending out of the catheter shaft toward the distal end, each flexible spine includes:

a respective first end that is connected to the distal end of the catheter shaft and respective second end that is free-standing and unanchored;

a first plurality of electrodes disposed on a surface of the spine facing the longitudinal axis; and

a second plurality of electrodes disposed on a surface of the spine facing away from the longitudinal axis; and

a tensile member disposed between the first and second plurality of electrodes having tensile strength greater than 895 MPa.

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