Patent Application
20180335037
n/a
The present invention relates to rotors for use in blood pumps and to blood pumps having such rotors.
In certain disease states, the heart lacks sufficient pumping capacity to maintain adequate blood flow to the body's organs and tissues. For example, conditions such as ischemic heart disease and hypertension may leave the heart unable to fill and pump efficiently. This condition, also called congestive heart failure, may lead to serious health complications, including respiratory distress, cardiac asthma, and even death. In fact, congestive heart failure is one of the major causes of death in the Western World.
The inadequacy of the heart can be alleviated by providing a mechanical blood pump, also referred to as a ventricular assist device (“VAD”), to supplement the pumping action of the heart. VADs may be used to assist the right ventricle, left ventricle, or both. For example, a VAD may assist the left ventricle by mechanically pumping oxygenated blood from the left ventricle into the aorta.
One form of VAD includes an axial flow pump. In an axial flow pump, blood is transported through a chamber from an inlet to an outlet a path substantially parallel to the axis of rotation of a rotor disposed in the chamber. The rotor has blades that perform work on the fluid causing it to flow toward the outlet. As shown, for example, in U.S. Pat. No. 7,959,551 an axial flow rotor may be supported within the chamber by bearings separate from the rotor itself and driven by stator coils mounted to the pump and arrayed around the rotor. The stator coils generate a rotating magnetic field that interacts with the rotor to rotate the rotor around its axis. Another axial flow blood pump, shown in U.S. Pat. No. 7,934,909 uses a system of multiple magnetic bearings and hydrodynamic bearings to support and position the rotor within the chamber. These systems require elements in the flow path additional to the rotor hub and blades. These additional elements can impede the flow of blood through the pump and can cause thrombus to form within the pump.
Another type of blood pump, described in U.S. Pat. No. 7,699,586 (“the '586 Patent), the disclosure of which is hereby incorporated by reference herein, uses a rotor with wide blades having hydrodynamic bearing surfaces on the tip surfaces of the blades. Upon rotation of the rotor, the hydrodynamic interaction between the bearing surfaces on the tips of the blade and the chamber wall suspends the rotor in the chamber and maintains the axis of the rotor coaxial with the chamber. Certain embodiments of the rotor shown in the '586 patent have permanent magnets embedded in the blades of the rotor. These permanent magnets interact with the rotating magnetic field generated by the stator to spin the rotor about its axis. Magnetic interaction between the magnets and a ferromagnetic element incorporated in the stator holds the rotor in a desired position along the axis. However, such an arrangement requires assembly of multiple parts, with precise location of each magnet and precisely equal magnetization of the individual magnets to prevent imbalanced forces on the rotor, which can be challenging. To avoid these challenges, some wide-blade axial flow rotors have been made as a unitary body formed of a ferromagnetic material, which has a permanent magnetization transverse to the rotor's axis. However, the ferromagnetic materials from which such rotors are made must not only be ferromagnetic but also biocompatible and wear resistant. Materials, such as platinum alloys, that can satisfy both of these requirements are expensive and difficult to manufacture. Moreover, a magnetic wide-blade rotor typically is made with an even number of blades, most commonly four blades, to assure balanced operation.
The present invention advantageously provides for a pump rotor including a hub defining a major longitudinal axis. A magnet is disposed within the hub along the major longitudinal axis. A plurality of rotor blades project outwardly from the hub away from the longitudinal axis and are spaced apart from one another in a circumferential direction around the longitudinal axis. Each of the plurality of rotor blades define a hydrodynamic bearing at an outer extremity thereof remote from the hub. The plurality of rotor blades define a plurality of flow channels. Each of the plurality of rotor blades is configured to drive a fluid through the flow channels upon rotation of the rotor around the axis.
In another aspect of this embodiment, the plurality of rotor blades are non-ferromagnetic.
In another aspect of this embodiment, the plurality of rotor blades define a collective area at an outer periphery of the rotor remote from the hub, and wherein the flow channels define a collective area at the outer periphery, and wherein the collective area defined by the plurality of rotor blades at the outer periphery is greater than the collective area defined by the flow channels at the outer periphery.
In another aspect of this embodiment, the magnet is a unitary solid and is coaxial with the hub, the magnet being radially magnetized and defining a plurality of radial poles.
In another aspect of this embodiment, the magnet is cylindrical.
In another aspect of this embodiment, the hub includes tapered end portions and an intermediate portion disposed between the end portions, the intermediate portion houses the magnet and the rotor blades extend from the intermediate portion.
In another aspect of this embodiment, the magnet includes neodymium.
In another aspect of this embodiment, the plurality of rotor blades and the hub are non-ferromagnetic.
In another aspect of this embodiment, the plurality of rotor blades and hub are made from a polymer material.
In another aspect of this embodiment, the plurality of rotor blades and hub are made from a biocompatible material and the magnet includes a non-biocompatible material.
In another embodiment, a blood pump includes a flow chamber defining an axis. A motor stator having stator coils is disposed about the flow chamber. A rotor includes a hub defining a major longitudinal axis. A magnet is disposed within the hub along the major longitudinal axis. A plurality of rotor blades project outwardly from the hub away from the longitudinal axis and are spaced apart from one another in a circumferential direction around the longitudinal axis. Each of the plurality of rotor blades define a hydrodynamic bearing at an outer extremity thereof remote from the hub. The plurality of rotor blades define a plurality of flow channels. Each of the plurality of rotor blades is configured to drive a fluid through the flow channels upon rotation of the rotor around the axis. The stator coils are configured to generate a magnetic field within the flow chamber rotating about the axis of the flow chamber. The rotating magnetic field interacts with the magnet of the rotor to drive the rotor about the axis thereof.
In another aspect of this embodiment, the motor stator includes a back-iron and wherein the magnet and back-iron are passively attracted to each other and cooperate to restrain the rotor from axial displacement within the flow chamber during operation.
In another aspect of this embodiment, the magnet is enclosed within the rotor.
In another aspect of this embodiment, the magnet is sealed within the rotor.
In another aspect of this embodiment, the plurality of rotor blades are non-ferromagnetic.
In another aspect of this embodiment, the plurality of rotor blades define a collective area at an outer periphery of the rotor remote from the hub, and wherein the flow channels define a collective area at the outer periphery, and wherein the collective area defined by the plurality of rotor blades at the outer periphery is greater than the collective area defined by the flow channels at the outer periphery.
In another aspect of this embodiment, the magnet is a unitary solid and is coaxial with the hub, the magnet being radially magnetized and defining a plurality of radial poles.
In another aspect of this embodiment, the plurality of rotor blades and hub are made from a polymer material.
In another aspect of this embodiment, the plurality of rotor blades and hub are made from a biocompatible material and the magnet includes a non-biocompatible material.
In yet another embodiment, a method of operating a blood pump includes generating a rotating magnetic field configured to rotate a rotor of the blood pump. The rotor includes a hub and a magnet disposed within the hub.
A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:
As used in this disclosure, the term “generally helical” refers to a feature which extends in the direction parallel to an axis and which curves in the circumferential direction around the axis over at least 50% of its extent in the direction along the axis. Also, as used herein, the terms “about” and “substantially” are intended to mean that slight deviations from absolute are included within the scope of the term so modified.
Referring now to the drawings in which like reference designators refer to like elements, there is a shown in
The plurality of rotor blades 30 project from the hub 20. In the particular embodiment depicted, the plurality of blades 30 includes exactly three rotor blades 30a-c. Each blade 30 extends outwardly from hub 20 away from hub axis 14 to an outer extremity thereof remote from hub 20. More particularly, each blade 30 extends out of hub 20 in an outward radial or “spanwise” direction perpendicular to the axis 14. Each blade 30 also extends in a lengthwise or axial direction over a portion of the axial extent of hub 20 so that blades 30a-c are coextensive with one another in the axial direction. In the particular embodiment depicted, each blade 30 extends along the length of intermediate portion 22 and terminates adjacent end portions 24 and 26 of hub 20. In other words, blades 30a-c project outwardly from intermediate portion 22. However, in some embodiments, blades 30a-c may partially project outwardly from end portions 24 and 26 as well as from intermediate portion 22.
Each blade 30 defines generally helical surfaces 36, 38 that intersect the outer surface or floor surface 23 of intermediate portion 22 of hub 20. These helical surfaces 36, 38 are referred to as a pressure surface 36 and a suction surface 38, as shown in
Rotor blades 30a-c are evenly spaced apart from one another around axis 14 in forward and rearward circumferential directions. Thus, blades 30a-c define a plurality of flow channels 12 that extend between blades 30a-c and likewise in an axial direction along rotor axis 14. Such channels 12 are bounded by outer surface 23 of intermediate portion 22 and the pressure and suction surfaces 36, 38 of adjacent blades 30. In this regard, flow channels 12 are generally helical to correspond to the helical profile of pressure and suction surfaces 36 and 38.
Each blade 30 has a tip surface 35 intersecting with and extending between the pressure surface and suction surface 36, 38. Each tip surface 35 faces outwardly away from axis 14 and defines the outermost extremity or outer periphery of both blade 30 and the rotor 10 itself. These tip surfaces 35 define a collective surface area that is larger than a collective area defined by flow channels 12 at the outer periphery of rotor 10. In other words, each tip surface 35 of blades 30a-c is large as compared to empty space of flow channels 12 such that in the aggregate, the surface area defined by tip surfaces 35 is more extensive than the aggregate area of flow channels 12 taken at the periphery of rotor 10. In this regard, rotor 10 is characterized as a wide-blade or large-area rotor. Other exemplary wide-blade rotors are described in the heretofore referenced '586 Patent; U.S. Pat. Nos. 7,972,122; 8,007,254; 8,419,609 and U.S. Publication No. 2015/0051438, the entirety of which are all incorporated by reference herein. The wide-blade configuration of rotor 10 allows rotor blades 30a-c to have hydrodynamic bearing surfaces at blade tips 35 that are capable of suspending rotor 10 within a pump housing during operation without the need for mechanical supports. Also, such a wide-blade configuration of rotor 10, particularly in combination with hydrodynamic bearings at blade tips 35, allows it to be extraordinarily compact. For example, the maximum diameter of rotor 10 at blades 30a-c may be about 0.5 inches (12.7 mm) and have an overall length of about 0.86 inches (21.8 mm).
In the configuration shown in
Each hydrodynamic bearing surface 32, 34 extends in the rearward circumferential direction from pressure surface 36 of its respective blade 30 and is bounded by and recessed radially relative to land surface 33. The recess of bearing surfaces 32, 34 is at a maximum at the forward edge of such surfaces where bearing surfaces 32, 34 meet pressure surface 36 of the blade 30. The recess of each bearing surface 32, 34 diminishes progressively in the rearward circumferential direction, so that each bearing surface 32, 34 merges smoothly into land surface 33 at the rearward edge of each bearing surface 32, 34.
Referring now to
As best shown in
Magnet 40 is a permanent magnet made from ferromagnetic materials that may or may not be biocompatible. However, the biocompatibility magnet 40 is of no import when implanted within a patient because such magnet 40 is embedded within rotor 10 which itself has a biocompatible exterior. In addition to having a biocompatible exterior, rotor 10 is non-ferromagnetic. As discussed above, magnet 40 may be the only magnetic component within rotor 10. In other words, hub 20 and rotor blades 30a-c are made from non-ferromagnetic materials and are either made from a biocompatible material or made from a non-biocompatible material with a biocompatible coating. For example, rotor 10 may be made from a biocompatible polymer material, such as silicone polymers, fluoroalkylsiloxane polymers or polyphosphazenes. Such polymer material can be molded over magnet 40. Alternatively, a polymeric rotor 10 can be molded separately from magnet 40 and machined so as to form the interior space within hub 20 for magnet 40. A separately molded end portion 24, such as that shown in
Rotor 10 can also be made from non-ferromagnetic metals, such as nonmagnetic stainless steel or titanium, or non-ferromagnetic ceramics, such as pyrolytic carbon, aluminum oxide, and zirconium oxide, for example. Furthermore, rotor 10 may have a biocompatible coating, such as a parylene, silicone, chromium nitride, or titanium nitride coating, for example. Rotor 10 can be made from a combination of the materials described above, but overall the rotor itself, regardless of the materials selected, is non-ferromagnetic. In this regard, the selection of materials is numerous and can be selected to control costs and/or optimize performance without the additional concern of providing magnetization as such is provided by center magnet 40.
A pump 50 according to one embodiment of the present invention includes a pump housing 60, motor stator 70, and rotor 10 as discussed hereinabove with reference to
In operation, with pump 50 implanted in the body of mammalian subject, and with housing 60 connected into the circulatory system, for example, in the conventional manner for a VAD, coils 72 are actuated to provide a magnetic field directed transverse to rotor axis 14 to cause such field to rotate rapidly around axis 14. Such magnetic field interacts with the radial poles of magnet 40 disposed within rotor 10 to rotate magnet 40 and, consequently, rotor 10 itself along with the magnetic field.
Rotor 10 also passively interacts with back-iron 74 of motor stator 70. In this regard, the permanent magnetism of back-iron 74 and center magnet 40 results in a magnetic attraction that resists axial displacement of rotor 10 within flow channel 62 that may be caused by pressure head gravity, or both. Also, while rotor 10 is rotated, a thin film of blood between hydrodynamic bearing surfaces 32, 34 and interior surface 64 of housing 60 is formed which maintains rotor 10 coaxial with housing 60 so that rotor 10 does not contact interior surface 64 due to radial movement, transverse to the axis 14 of rotor 10, or due to tilting of axis 14 relative to housing 60. Thus, hydrodynamic bearings 32, 34 of blades 30a-c in conjunction with the axial alignment provided by the attraction of center magnet 40 and back-iron 74 eliminate the need for mechanical suspension systems to stabilize rotor 70 during operation. This allows flow channel 62 to be free and clear of obstructions other than rotor 10 itself.
The rotor 10 as discussed above offers significant advantages. For example, because the blades 30 of the rotor 10 are formed from non-ferromagnetic materials, the blades 30 do not introduce imbalanced magnetic forces, and the rotor 10 can operate stably with three blades 30. A rotor 10 with three blades 30 and three channels having a given aggregate cross-sectional area, provides better flow conditions than a comparable four bladed rotor with four channels having the same aggregate cross-sectional area. Precise alignment between the axis of the magnet 40 and the axis 14 of the rotor is achieved in common manufacturing techniques. For example, the magnet can be formed to a body of revolution of precise dimensions by techniques such as machining or centerless grinding. The interior surface 29 of the wall surrounding the interior space can be formed to a surface of revolution having precise dimensions and precisely coaxial with the axis and with the land surfaces 33 of the blades, by machining or molding the interior surface.
Other alternative embodiments of the aforementioned devices are contemplated. For example,
Another rotor 210 is shown in
In the rotor embodiment depicted in
In the embodiments discussed above, the rotor is constrained against axial movement relative to the pump chamber by magnetic attraction between the magnet and the back-iron incorporated in the stator. In other embodiments, the hydrodynamic bearing surfaces of the rotor may include hydrodynamic bearing surfaces arranged to provide axial thrust and thus constrain the rotor against axial movement relative to the pump chamber and stator. For example, as disclosed in U.S. Published Patent Application No. 2011/0311383, the entirety of which is incorporated by reference herein, hydrodynamic bearing surfaces facing in a direction oblique to the axis may be provided on the blades so as to provide axial thrust in one direction. To provide full axial constraint, the oblique surfaces may include oblique surfaces facing in opposite axial directions.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as described in the claims below.
This application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 62/508,543, filed May 19, 2017, entitled CENTER ROD MAGNET, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62508543 | May 2017 | US |
