Corrosion resistant permanent magnet for intravascular blood pump

Abstract

To provide a corrosion resistant permanent magnet, a method of manufacturing the corrosion resistant permanent magnet, and an intravascular blood pump including a magnet.SOLUTION: A magnet is surrounded by a composite coating comprising, in the order described, a first metal oxide layer, a metal layer, a second metal oxide layer, a linker layer, and a layer formed from poly (2-chloro-p-xylylene). In alternative embodiments, a further metal layer and optionally a further metal oxide layer may be provided between the second metal oxide layer and the linker layer. In a further alternative embodiment, the metal layer may be omitted and a further layer structure comprising at least one metal oxide layer, a linker layer and a layer formed from the poly (2-chloro-p-xylylene) may alternatively be provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to corrosion protection for permanent magnets. In particular, the present invention relates to permanent magnets having a protective coating that renders the magnet corrosion resistant, and to methods for making corrosion-resistant permanent magnets. The present invention also relates to intravascular blood pumps that include the corrosion-resistant permanent magnets of the present invention. While the present invention is applicable to all types of permanent magnets, rare earth permanent magnets are preferred, with neodymium iron boron (NdFeB) permanent magnets being particularly preferred. [Background technology]

[0002] Intravascular blood pumps support blood flow within a patient's blood vessels. They are inserted percutaneously, for example, into the femoral artery, and guided through the body's vascular system to its destination, for example, a ventricle of the heart.

[0003] A blood pump typically includes a pump case having a blood inlet and a blood outlet. An impeller or rotor is rotatably supported within the pump case about an axis of rotation to effect blood flow from the inlet to the outlet, and the impeller has one or more blades for transporting the blood.

[0004] An exemplary blood pump is shown in FIG. 1, which is a schematic longitudinal cross-sectional view of an exemplary intravascular blood pump 10. The blood pump has a motor section 11 and a pump section 12, which are coaxially arranged one behind the other, resulting in a rod-like structural configuration. The pump section is extended by a flexible suction hose (not shown), which has openings at its end and / or side wall through which blood can enter the pump. The end of the blood pump 10 remote from the suction hose is connected to a catheter 14, optionally combined with a guidewire for steering the blood pump to its desired location.

[0005] The exemplary intravascular blood pump shown in FIG. 1 includes a motor section 11 and a pump section 12 rigidly connected to each other. The motor section 11 includes an elongated housing 20 containing an electric motor 21. The electric motor includes a rotor and a stator. The stator is the stationary portion of the motor's electromagnetic circuit, and the rotor is the moving portion. Either the rotor or the stator contains electrically conductive windings, while the other contains permanent magnets. Current flowing through the windings generates an electromagnetic field that interacts with the magnetic field of the permanent magnets, generating a force that rotates the rotor. In the exemplary blood pump of FIG. 1, the stator 24 of the electric motor 21 includes numerous circumferentially distributed windings and a longitudinal magnetic return path 28 in the usual manner. It is rigidly connected to the motor housing. The stator 24 surrounds the motor 1, which is connected to a motor shaft 25 and consists of a permanent magnet magnetized in an active direction. The motor shaft 25 extends the entire length of the motor housing 20 and projects distally therefrom. It carries an impeller 34 having blades 36 or pump blades projecting therefrom, which rotate within a cylindrical pump housing 32 which is rigidly connected to the motor housing 20 .

[0006] The proximal end of the motor housing 20 has a flexible catheter 14 sealingly attached thereto. In this disclosure, "proximal" and "distal" refer to the location relative to the physician inserting the intravascular blood pump, i.e., the distal end is the impeller side. An electrical cable 23 extends through the catheter 14 for powering and controlling the electric motor 21. A purge fluid line 29 also extends through the catheter 14, penetrating the proximal end wall 22 of the motor housing 20. Purge fluid (schematically indicated by a thick arrow) is supplied to the interior of the motor housing 20 through the purge fluid line 29, flows through the gap 26 between the rotor 1 and the stator 24, and exits through the end face 30 at the distal end of the motor housing. The purge pressure is selected to be higher than blood pressure, thus preventing blood from entering the motor housing. Depending on the application, the purge fluid pressure is between 300 and 1400 mmHg in the motor where the pressure increases.

[0007] A suitable purge fluid is one with a viscosity higher than that of water (η = 0.75 mPa·s at 37°C), particularly a viscosity of 1.2 mPa·s or higher at 37°C. For example, a 5% to 40% glucose solution for injection can be used, but saline is also suitable.

[0008] Rotation of the impeller 34 draws blood (schematically indicated by the blank arrow) through an end suction opening 37 in the pump housing 32 and transports it axially rearward inside the pump housing 32. Through an outlet opening 38 in the pump housing 32, the blood leaves the pump section 12 and flows further along the motor housing 20. It is also possible to operate the pump section in the opposite transport direction, with blood being drawn along the motor housing 20 and out through opening 37.

[0009] The motor shaft 25 is mounted in radial bearings 27 and 31, one at the proximal end of the motor housing and the other at the distal end of the motor housing. Furthermore, the motor shaft 25 is also axially mounted in an axial bearing 39. If the blood pump is used to pump blood in the reverse direction as well or only in the reverse direction, a corresponding axial bearing 39 is provided in a corresponding manner also / only at the proximal end of the motor housing 20.

[0010] It is emphasized that the blood pump described above is merely an example and the present invention is also applicable to different blood pumps that include electric motors, i.e., that require permanent magnets. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent No. 3319098 Summary of the Invention [Problem to be solved by the invention]

[0012] Intravascular blood pumps must meet many requirements. Because they are placed inside living organisms, they must be as small as possible. The smallest pumps currently in use have an outer diameter of about 4 mm. Nevertheless, the pump must be able to transport large volumes of flow within the human blood circulation. Therefore, micropumps must be high-performance engines.

[0013] Furthermore, implantable blood pumps must not adversely affect the biological environment, such as the pumped blood and surrounding tissue.

[0014] Pumps therefore need to be biocompatible in the broadest sense, that is, they must not contain or generate harmful substances or significant heat that could damage the body or its components.

[0015] Furthermore, pump replacement is a burden to the patient. For this reason, and of course for economic considerations, intravascular blood pumps must have a long service life.

[0016] The materials and design of the intravascular blood pump must be appropriately selected and specifically adapted to meet these various requirements.

[0017] Importantly, an appropriate permanent magnet for the electric motor must be selected. For pump efficiency and lifespan, the magnet should have a strong magnetic field, i.e., a high residual field, high demagnetization resistance, i.e., a high coercive force, and high saturation magnetization. In this regard, rare earth permanent magnets, particularly those with neodymium as the rare earth metal, and especially neodymium iron boron (NdFeB) permanent magnets, are the magnets of choice. Other rare earth iron boron permanent magnets may also be used.

[0018] The stronger the magnet, the smaller it can be while still generating sufficient rotational force. Thus, the stronger the magnet, the smaller the electric motor can be. NdFeB permanent magnets are the strongest permanent magnets currently available. They are considered ideal for use in intravascular blood pumps.

[0019] It is well known that the magnetic properties of rare earth metal based magnets, such as NdFeB magnets, depend on the specific alloy composition, microstructure, and manufacturing techniques used. NdFeB magnets are available as polymer-bonded magnets and as sintered magnets. Sintered magnets have superior magnetic properties. They are prepared by alloying raw materials, grinding them into powder, compacting, and sintering. During or after preparation, an external magnetic field is applied to magnetize the material. A well-studied magnet is a fine-crystalline sintered material, Nd2Fe 14 The B crystals are surrounded by a thin layer that is particularly rich in neodymium.

[0020] Neodymium iron boron magnets have magnetic properties that make them particularly suitable for use in the electric motors of intravascular blood pumps, but they also have serious drawbacks. Commercially available NdFeB magnets, which are composed primarily of neodymium, iron, and boron, and sintered neodymium iron boron magnets, which have a highly active neodymium-rich phase at their grain boundaries, are highly susceptible to corrosion. Magnets can be corroded, for example, by oxygen and moisture in the air, particularly, but not exclusively, at their grain boundaries. Corrosion results in a significant decrease in magnetic properties, and if corrosion progresses during the magnet's service life, the performance of blood pumps using the magnets will decrease. This phenomenon is exacerbated by the tendency of neodymium iron boron magnets to act as absorbers for corrosion products, leading to structural breakdown, debris flaking from the magnet's surface, and ultimately the magnet's disintegration.

[0021] Unfortunately, corrosion tendency is a common characteristic of all rare earth metals. Therefore, all rare earth metal based permanent magnets have the undesirable tendency to corrode, as discussed above for NdFeB magnets. For currently available magnets, a rule of thumb can be stated: the stronger the magnet, the greater its corrosion tendency.

[0022] In intravascular blood pumps, the magnets must function in a corrosive environment, namely the purge fluid that flows between the rotor and stator (see Figure 1). As mentioned above, the purge fluid is usually an aqueous fluid and may contain chlorides. Chlorides are highly corrosive to rare earth metal-based magnets, but water and the oxygen dissolved in it also cause severe corrosion within a very short time frame of just a few hours.

[0023] Clearly, rare earth metal based permanent magnets, such as neodymium iron boron magnets for intravascular blood pumps, need to be protected against corrosion.

[0024] Various means are known for protecting neodymium iron boron magnets and other rare earth metal based magnets from corrosion. For example, corrosion resistance can be improved by coating the magnets with a protective coating.

[0025] Common coatings are nickel coatings and epoxy resin-based coatings, and titanium and parylene coatings are well-known, especially for blood pumps. However, these coatings also have drawbacks. Even when biocompatible metals and organic resins are selected, such as titanium and parylene, respectively, the metal coating must be relatively thick to provide sufficient protection. As a result, the gap between the magnet and the winding in the electric motor of a blood pump must be relatively large. A large gap has a strong negative effect on the performance of the electric motor. A large gap requires a larger motor current, which generates unwanted heat, which can lead to blood and tissue damage.

[0026] Furthermore, organic materials such as parylene have a coefficient of thermal expansion that differs significantly from that of the magnet, and therefore temperature fluctuations during use of the magnet often result in cracking and / or peeling of the coating.

[0027] EP 3319098 A1 discloses a coating for permanent magnets, which includes a metal oxide layer several nanometers thick that forms spontaneously upon exposure of a metal layer, e.g., aluminum, to air, a linker layer, and a layer of poly(2-chloro-p-xylylene). The coating provides excellent corrosion protection. However, the manufacturing process lacks high reproducibility and, rather, produces an undesirably large number of magnets with insufficient corrosion protection, especially when the coating is thin. Further improvements are desirable.

[0028] Currently, no biocompatible coatings for permanent magnets, such as neodymium-iron-boron magnets, are known that satisfactorily meet all the requirements for use in intravascular blood pumps. Such coatings must have excellent corrosion resistance, be thin yet dense, not develop cracks or other defects during use, and adhere securely and intimately to the magnet. Furthermore, the coating process must produce highly reproducible results, i.e., the fewer magnets that need to be screened, the better. Naturally, the coating must be biocompatible and must coat the entire magnet, or at least the portions of the magnet that will be exposed to a corrosive environment during use, with a uniform thickness. This is particularly required because many magnets have geometries that include porous surfaces and edges. For this reason, permanent magnets, such as rare-earth metal-based magnets for use in intravascular blood pumps, such as neodymium-iron-boron magnets, constitute components that cannot easily be coated with a uniform thickness. [Means for solving the problem]

[0029] The present invention provides a solution to the above problems.

[0030] The present invention provides a permanent magnet with a protective coating that reliably protects the magnet from corrosion during long-term use in an intravascular blood pump, and a method for producing the protective coating with high reproducibility. The protective coating is particularly thin, allowing for the production of very small magnets and, therefore, very small blood pumps.

[0031] The subject matter of the present invention comprises a corrosion-resistant permanent magnet having the features set forth in independent claim 1, a method for producing a corrosion-resistant permanent magnet having the features set forth in independent claims 13 and 19, and an intravascular blood pump having the features set forth in independent claim 22. The invention is presented below. 1. A corrosion-resistant permanent magnet comprising a magnet body and a composite coating disposed on and covering a surface of the magnet body, the composite coating comprising, in the listed order: a first metal oxide layer in physical contact with the magnet body; metal layer, a second metal oxide layer; a linker layer, and a layer formed from poly(2-chloro-p-xylylene). 2. A magnet having the characteristics described in (1) above, the magnet body being a sintered magnet body. 3. A magnet having the characteristics shown in (1) or (2) above, wherein the magnet body is a rare earth metal-based magnet. 4. A magnet having the characteristics described in (3) above, wherein the rare earth metal is neodymium. 5. A magnet having the characteristics described in any one of (1) to (4) above, wherein the magnet body is a rare earth metal iron boron permanent magnet. 6. A magnet having the characteristics shown in (4) or (5) above, wherein the magnet body is NdFe 14 B crystal and NdFe 14 The sintered magnet body has a neodymium iron boron material surrounding the B crystals, and the neodymium iron boron material is NdFe 14 It is richer in neodymium than B crystal. 7. A magnet having the characteristics described in any one of (1) to (6) above, wherein the magnetic body is rod-shaped with all ends rounded. 8. A magnet having the characteristics described in any one of (1) to (7) above, wherein the linker forming the linker layer is selected from silanes, mercaptans, phosphines, disulfides, and silanes having a thiol, phosphine, or disulfide group. 9. A magnet having the characteristics shown in (8) above, wherein the silanes are selected from alkoxysilanes, or alkoxysilanes having an acryloyloxy or methacryloyloxy functional group, or linkers having bistrimethoxysilyl or bistrimethoxysilyl functional groups. 10. A magnet having the characteristics shown in (9) above, wherein the silane is 3-(trimethoxysilyl)propyl methacrylate. 11. A magnet having the characteristics shown in (8) above, wherein the silane has a hydride functional group. 12. A magnet having the characteristics described in any one of (1) to (11) above, wherein the metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, iridium, platinum, gold, iron, and alloys containing at least one of aluminum, titanium, tantalum, niobium, and zirconium. 13. A magnet having the characteristics described in any one of (1) to (12) above, wherein the metal of the metal layer is aluminum or titanium, or an alloy of aluminum or titanium. 14. A magnet having the characteristics described in any one of (1) to (13) above, wherein the oxide of the first metal oxide layer and / or the second metal oxide layer is an oxide of at least one of aluminum, titanium, tantalum, niobium, zirconium, silicium, iridium, and hafnium. 15. A magnet having the characteristics described in any one of the above (1) to (14), wherein the oxide of the first metal oxide layer is Al2O3 or TiO2, or a mixed oxide of Al2O3 and TiO2. 16. A magnet having the characteristics described in any one of the above (1) to (15), wherein the oxide of the second metal oxide layer is Al2O3 or TiO2, or a mixed oxide of Al2O3 and TiO2. 17. A magnet having the characteristics described in any one of (1) to (16) above, the metal layer is in physical contact with the first metal oxide layer; a second metal oxide layer in physical contact with the metal layer; the linker layer is in physical contact with the second metal oxide layer; The poly(2-chloro-p-xylylene) layer is in physical contact with the linker layer. 18. A magnet having the characteristics described in any one of (1) to (16) above, comprising a further metal layer, and optionally a further metal oxide layer, between the second metal oxide layer and the linker layer; the metal layer is in physical contact with the first metal oxide layer; a second metal oxide layer in physical contact with the metal layer; the additional metal layer is in physical contact with the second metal oxide layer; the further metal oxide layer, if present, is in physical contact with the further metal layer; the linker layer is in physical contact with the further metal layer or, if present, the further metal oxide layer; The poly(2-chloro-p-xylylene) layer is in physical contact with the linker layer. 19. A magnet having the characteristics shown in (18) above, wherein the metal of the further metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, iridium, platinum, gold, iron, and alloys containing at least one of aluminum, titanium, tantalum, niobium, and zirconium. 20. A magnet having the characteristics shown in (18) or (19) above, wherein the metal of the further metal layer is aluminum. 21. A magnet having the characteristics described in any one of (18) to (20) above, which includes an additional metal oxide layer, and the oxide of the additional metal oxide layer is an oxide of at least one of aluminum, titanium, tantalum, niobium, zirconium, silicium, iridium, and hafnium. 22. A magnet having the characteristics shown in (21) above, wherein the oxide of the further metal oxide layer is Al2O3. 23. A magnet having the characteristics described in any one of (18) to (22) above, wherein the linker layer is a linker as described in any one of (8) to (11) above. 24. A magnet having the characteristics described in any one of (18) to (23) above, wherein the linker is selected from mercaptans, phosphines, disulfides, and silanes having a thiol, phosphine, or disulfide group. 25. A magnet having the characteristics shown in (24) above, wherein the linker is selected from 3-(2-pyridylethyl)thiopropyltrimethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane, 2-(diphenylphosphino)ethyltriethoxysilane, bis(2-methacryloyl)oxyethyl disulfide, and dihexadecyl disulfide. 26. A magnet having the characteristics described in any one of (1) to (25) above, wherein the thicknesses of the first metal oxide layer and the second metal oxide layer are the same or different and are in the range of 5 nm to 200 nm, 80 nm to 120 nm, or 50 nm to 100 nm, or the thicknesses of the first and second metal oxide layers are each approximately 100 nm. 27. A magnet having the characteristics described in any one of (20) to (26) above, which includes an additional metal oxide layer, the thickness of which is in the range of 5 nm to 200 nm, 80 nm to 120 nm, or 50 nm to 100 nm, or approximately 100 nm. 28. A magnet having the characteristics described in any one of (1) to (25) above, wherein the second metal oxide layer and / or the further metal oxide layer is a native metal oxide layer. 29. A magnet having the characteristics described in (28) above, wherein the native metal oxide layer has a thickness in the range of 1 nm to 5 nm. 30. A magnet having the characteristics described in any one of (1) to (29) above, wherein the thickness of the metal layer is in the range of 0.1 to 10 μm, 0.5 to 10 μm, or 2 to 6 μm, or is about 4 μm. 31. A magnet having the characteristics described in any one of (20) to (30) above, wherein the thickness of the additional metal layer is a maximum of 29 μm, preferably in the range of 2 μm to 20 μm, or 10 μm to 18 μm, or approximately 15 μm. 32. A magnet having the characteristics described in any one of (1) to (31) above, wherein the linker layer is a single layer, or the thickness of the linker layer is in the range of 20 nm to 150 nm, or 50 nm to 100 nm. 33. A magnet having the characteristics described in any one of (1) to (32) above, wherein the thickness of the layer formed from poly(2-chloro-p-xylylene) is in the range of 3 μm to 20 μm, or 10 μm to 17 μm, or approximately 15 μm. 34. A magnet having the characteristics described in any one of (1) to (33) above, wherein the thickness of the composite coating is 50 μm or less. 35. A magnet having the characteristics described in any one of (1) to (19) above, wherein the metal layer is omitted and the composite coating comprises, in the order described, on a layer formed from poly(2-chloro-p-xylylene): a third metal oxide layer; a further linker layer, and a further layer formed from poly(2-chloro-p-xylylene). 36. A magnet having the characteristics shown in (35) above, comprising an intermediate metal oxide layer between the layer formed from poly(2-chloro-p-xylylene) and the third metal oxide layer. 37. A magnet having the characteristics shown in (35) above, The thickness of each of the first metal oxide layer, the second metal oxide layer, and the third metal oxide layer is in the range of 5 nm to 300 nm. 38. A magnet having the characteristics described in (36) above, wherein the thicknesses of the first metal oxide layer, the second metal oxide layer, the intermediate metal oxide layer, and the third metal oxide layer are each in the range of 5 nm to 200 nm. 39. A magnet having the characteristics described in any one of (35) to (38) above, wherein the thickness of the linker layer and the thickness of the further linker layer are the same or different, and are in the range of 20 nm to 150 nm, or 50 nm to 100 nm, or are essentially monolayer thick. 40. A magnet having the characteristics described in any one of (35) to (39) above, wherein the thickness of the layer formed from poly(2-chloro-p-xylylene) is in the range of 0.5 μm to 4 μm, or 1 μm to 2 μm, and / or the thickness of the further layer formed from poly(2-chloro-p-xylylene) is in the range of 3 μm to 20 μm, or 10 μm to 15 μm, or approximately 13 μm. 41. A magnet having the characteristics described in any one of (35) to (40) above, wherein the thickness of the composite coating is 50 μm or less. 42. A magnet having the characteristics described in any one of (35) to (41) above, wherein the oxide of the first metal oxide layer is Al2O3 and the oxide of the second metal oxide layer is TiO2, or the oxide of the first metal oxide layer is TiO2 and the oxide of the second metal oxide layer is Al2O3, or the oxide of both the first and second metal oxide layers is Al2O3, or the oxide of the first and second metal oxide layers is TiO2. 43. A magnet having the characteristics described in any one of the above (35) to (42), wherein the oxide of the third metal oxide layer is TiO2 or Al2O3, preferably TiO2. 44. A magnet having the characteristics described in any one of (36) to (43) above, wherein the oxide of the intermediate metal oxide layer is Al2O3 or TiO2, preferably Al2O3, and is different from the oxide of the third metal oxide layer. 45. A method for producing a corrosion-resistant permanent magnet, Providing an unmagnetized magnet body; forming a first metal oxide layer on a surface of a magnet body; forming a metal layer on the first metal oxide layer; forming a second metal oxide layer on the metal layer; Optionally, forming at least one further layer on the second metal oxide layer; forming a linker layer on the second metal oxide layer or, if present, on at least one further layer; forming a layer of poly(2-chloro-p-xylylene) on the linker layer; This includes magnetizing the magnetic body. 46. ​​A method having the characteristics shown in (45) above, comprising forming at least one further layer, wherein the at least one further layer is a further metal layer. 47. A method having the characteristics shown in (46) above, further comprising forming a further metal oxide layer on the further metal layer. 48. A method having the characteristics described in any one of (45) to (47) above, wherein the oxide of the first metal oxide layer and / or the oxide of the second metal oxide layer is an oxide described in any one of (14) to (16) above. 49. A method having the characteristics described in any one of the above (46) to (48), wherein the metal of the metal layer is a metal described in the above (12) or (13). 50. A method having the characteristics described in any one of (46) to (49) above, wherein the metal of the further metal layer is a metal described in (21) or (22) above. 51. A method having the characteristics described in any one of the above (47) to (50), wherein the oxide of the further metal oxide layer is an oxide described in the above (23) or (24). 52. A method having the characteristics described in any one of (45) to (51) above, wherein the linker in the linker layer is a linker described in any one of (8) to (11), (17) and (18) above. 53. A method having the characteristics set forth in any one of (45) to (52) above, wherein the first metal oxide layer and / or the second metal oxide layer is formed by a process selected from physical vapor deposition, chemical vapor deposition, sputtering, a sol-gel process, and flame spraying, or by oxidizing the corresponding metal layer. 54. A method having the characteristics as shown in (53) above, wherein the physical vapor deposition process is a plasma-based process, a plasma-free process, or an ion vapor deposition process. 55. A method having the characteristics shown in (53) above, wherein the first metal oxide layer and / or the second metal oxide layer are formed by an atomic layer deposition process, and the atomic layer deposition process is a process using plasma or a process not using plasma. 56. A method having the characteristics described in any one of (45) to (55) above, wherein the metal layer is formed by a process selected from physical vapor deposition, chemical vapor deposition, sputtering, and atomic layer deposition. 57. A method having the characteristics as shown in (56) above, wherein the metal layer is formed by a physical vapor deposition process using plasma, a physical vapor deposition process not using plasma, or an ion vapor deposition process. 58. A method having the characteristics described in any one of (46) to (57) above, wherein the further metal layer is formed by a plating process, a sputtering process, a physical vapor deposition process, or an atomic layer deposition process. 59. A method having the characteristics shown in (58) above, wherein the plating step is a galvanic deposition step from an ionic liquid. 60. A method having the characteristics described in any one of (47) to (59) above, wherein the further metal oxide layer is formed by a step described in any one of (53) to (55) above. 61. A method having the characteristics described in any one of (45) to (60) above, wherein the linker layer is formed by applying the linker by physical vapor deposition using plasma, by physical vapor deposition without plasma, by a wet process, by a plasma deposition process, or by a combination thereof. 62. A method having the characteristics described in any one of (45) to (61) above, wherein the layer of poly(2-chloro-p-xylylene) is formed by a plasma deposition process of dichloro[2.2]paracyclophane. 63. A method having the characteristics described in any one of (45) to (62) above, wherein the layer has a thickness described in any one of (26) to (34) above. 64. A method having the characteristics described in any one of (45) to (63) above, wherein the magnet body is a magnet body described in any one of (1) to (7) above. 65. A method for producing a corrosion-resistant permanent magnet, Providing an unmagnetized magnet body; forming a first metal oxide layer on a surface of a magnet body; forming a second metal oxide layer on the first metal oxide layer; forming a linker layer on the second metal oxide layer; forming a layer of poly(2-chloro-p-xylylene) on the linker layer; optionally forming an intermediate metal oxide layer on the poly(2-chloro-p-xylylene) layer; forming a third metal oxide layer on the poly(2-chloro-p-xylylene) layer or on the intermediate metal oxide layer, if present; forming a further linker layer on the third metal oxide layer; forming a further layer of poly(2-chloro-p-xylylene) on the further linker layer; This includes magnetizing the magnetic body. 66. A method having the characteristics shown in (65) above, wherein the oxide of the first metal oxide layer is Al2O3 and the oxide of the second metal oxide layer is TiO2, or the oxide of the first metal oxide layer is TiO2 and the oxide of the second metal oxide layer is Al2O3, or both of the oxides of the first and second metal oxide layers are Al2O3, or both are TiO2. 67. A method having the characteristics shown in (65) or (66) above, wherein the oxide of the third metal oxide layer is TiO2 or Al2O3, preferably TiO2. 68. A method having the characteristics described in any one of (65) to (67) above, comprising forming an intermediate metal oxide layer, wherein the oxide of the intermediate metal oxide layer is Al2O3 or TiO2, preferably Al2O3, and is different from the oxide of the third metal oxide layer. 69. A method having the characteristics described in any one of (65) to (68) above, wherein the linker of the linker layer and / or the further linker layer is a linker described in any one of (8) to (11) above. 70. A method having the characteristics described in any one of (65) to (69) above, wherein the first metal oxide layer and / or the second metal oxide layer are formed by a process selected from physical vapor deposition, chemical vapor deposition, sputtering, a sol-gel process, flame spraying, and atomic layer deposition. 71. A method having the characteristics described in any one of (65) to (70) above, wherein the third metal oxide layer and / or, if present, the intermediate metal oxide layer are formed by an atomic layer deposition process or a physical vapor deposition process. 72. A method having the characteristics of any one of (65) to (71) above, wherein the linker layer and / or the further linker layer is formed by applying the linker by physical vapor deposition using plasma, by physical vapor deposition without plasma, by a wet process, by a plasma deposition process, or by a combination thereof. 73. A method having the characteristics described in any one of (65) to (72) above, wherein the layer of poly(2-chloro-p-xylylene) is formed by a plasma deposition process of dichloro[2.2]paracyclophane. 74. A method having the characteristics described in any one of (65) to (73) above, wherein the layer has a thickness described in any one of (37) to (41) above. 75. A method having the characteristics described in any one of (65) to (74) above, wherein the magnet body is a magnet body described in any one of (1) to (7) above. 76. An intravascular blood pump including an electric motor, the electric motor including a permanent magnet as shown in any one of (1) to (44) above.

[0032] A magnet is corrosion resistant in the sense of the present invention if it passes the following test: The coated magnets are subjected to a corrosion test in an aqueous solution containing 0.9% by weight of sodium chloride at 60°C (accelerated corrosion test). Corrosion of the magnetic material results in lifting or deformation of the coating. Thus, the formation of lifting or blisters on the surface of the test specimen indicates corrosion of the magnetic material. The formation of blisters 0.1 mm high and lifting of the coating are defined as indicating failure of the magnet. A magnet passes the test if the time to failure is at least 30 days.

[0033] In accordance with the present invention, a powerful permanent magnet includes a coating that either completely surrounds the magnet body or covers at least those surfaces of the magnet body that are exposed to fluid when the magnet is operating in an intravascular blood pump. The coating renders the magnet corrosion resistant during use in the intravascular blood pump. The preferred magnet body is a sintered magnet, as described above, composed primarily of neodymium, iron, and boron, with fine tetragonal magnetic NdFe 14 It consists of B crystals and a neodymium-rich non-magnetic phase surrounding the crystals. Usually, the main phase is NdFe 14 The B crystals have an average crystal size in the range of 1 to 80 μm. The non-magnetic neodymium-rich phase accounts for 1% to 50% by volume of the magnet body. These magnets are readily commercially available. They are preferred because of their high magnetic properties and because they are particularly strong, i.e., have a high magnetic flux density. For the above reasons, particularly powerful magnets are required for intravascular blood pump applications. However, in principle, the corrosion-resistant coating of the present invention can be applied to any material requiring protection against corrosion, such as different rare earth iron-boron magnetic materials, or any other magnetic material.

[0034] The coating of the present invention is a composite coating applied to the surface of a magnet body, i.e., an actual magnetic material. According to a first embodiment, the composite coating includes a first metal oxide layer on the surface of the magnet body, a metal layer on the first metal oxide layer on its exposed surface, a second metal oxide layer on the metal layer, a layer formed from poly(2-chloro-p-xylylene), and a linker layer between the second metal oxide layer and the poly(2-chloro-p-xylylene) layer. The first metal oxide layer, the metal layer, and the second metal oxide layer together form an inorganic layer.

[0035] According to a second embodiment, a further metal layer is provided between the second metal oxide layer and the linker layer, in which the first metal oxide layer, the metal layer, the second metal oxide layer and the further metal layer together form an inorganic layer.

[0036] In a preferred variant, a further metal oxide layer is provided on the further metal layer. In this particular embodiment, the first metal oxide layer, the metal layer, the second metal oxide layer, the further metal layer, and the further metal oxide layer together form an inorganic layer. The further metal oxide layer may be artificially formed or may be a natural oxide layer, i.e., an oxide layer that is formed automatically when the further metal layer is exposed to air. This also applies to the second metal oxide layer in the first and second embodiments.

[0037] According to a third embodiment, the composite coating includes a first layer structure and a second layer structure. The first layer structure is provided on the surface of the magnet body, and the second layer structure is provided on the first layer structure. The first layer structure includes a first metal oxide layer (on the surface of the magnet body), a second metal oxide layer on the first metal oxide layer, a layer formed from poly(2-chloro-p-xylylene), and a linker layer between the second metal oxide layer and the poly(2-chloro-p-xylylene) layer. The metal oxide layers together form an inorganic layer. The second layer structure includes a third metal oxide layer (on the first layer structure), a layer formed from poly(2-chloro-p-xylylene), and a linker layer between the third metal oxide layer and the poly(2-chloro-p-xylylene) layer. The third metal oxide layer forms an inorganic layer.

[0038] An additional (intermediate) metal oxide layer may be provided between the first layer structure and the third metal oxide layer. In this case, the second layer structure includes the intermediate metal oxide layer (on the first layer structure), the third metal oxide layer on the intermediate metal oxide layer, a layer formed from poly(2-chloro-p-xylylene), and a linker layer between the third metal oxide layer and the poly(2-chloro-p-xylylene) layer. The metal oxide layers together form an inorganic layer. In this case, the second layer structure includes the intermediate metal oxide layer (on the first layer structure), the third metal oxide layer on the intermediate metal oxide layer, a layer formed from poly(2-chloro-p-xylylene), and a linker layer between the third metal oxide layer and the poly(2-chloro-p-xylylene) layer.

[0039] The poly(2-chloro-p-xylylene) layer constitutes an organic layer. Thus, in each embodiment, the composite coating comprises at least one inorganic layer and at least one organic layer.

[0040] The metal oxides in the first layer structure and the second layer structure may be the same or different.

[0041] Rare earth metal-based magnets purchased from suppliers are typically protected by a phosphate coating. This phosphate coating can be removed, for example, by washing with acid, before applying the composite coating. However, the phosphate coating may remain on the magnet body, as it does not adversely interfere with the coating or coating process according to the present invention. Preferably, the phosphate coating is not removed. Not removing the phosphate coating eliminates a step and avoids the introduction of impurities during such a process. However, it is desirable to wash the magnet before applying the first metal oxide layer. Washing is preferably performed by washing the magnet with an organic solvent, such as alcohol. Particularly preferred cleaning agents are isopropanol and a mixture of isopropanol and ethanol. After washing with the organic solvent, the magnet is dried, for example, in a vacuum or airflow.

[0042] After washing and drying, a first metal oxide layer is applied to the surface of the magnet body. In this invention, it is essential that the metal oxide layer be applied directly to the magnet surface, i.e., in physical contact with the magnet (contact with a phosphate-coated magnet is considered direct contact with the magnet). The metal oxide adheres well to the relatively rough magnet surface, preventing it from easily peeling off even under the harsh operating conditions of an intravascular blood pump. As a result, the corrosion resistance of the magnet is significantly improved, allowing intravascular blood pumps containing magnets to operate without damage for extended periods of time. Furthermore, it is recommended that the composite coating of this invention be applied to an unmagnetized magnet body, and that the magnet body be magnetized only after the coating has been applied. Applying the coating after magnetizing the magnet body is not appropriate.

[0043] In the first and second embodiments, the metal oxides forming the first and second metal oxide layers may be the same or different. Preferably, the oxide of the first and / or second metal oxide layer is an oxide of at least one of aluminum, titanium, tantalum, niobium, zirconium, silicium, iridium, and hafnium. Particularly preferred oxides for the first and / or second metal oxide layer are Al2O3, TiO2, and mixtures thereof. The same applies to the further metal oxide layer optionally present in the second embodiment.

[0044] In the third embodiment, the composition of the first metal oxide layer is typically different from that of the second metal oxide layer, and the composition of the third metal oxide layer is typically different from that of the intermediate metal oxide layer, if present. The oxide of the first inorganic layer may be the same as or different from the metal oxide(s) of the second inorganic layer. The metal oxides suitable for forming the first, second, third, and intermediate metal oxide layers are the same as in the first and second embodiments. Preferably, the oxide of the first metal oxide layer is Al2O3 and the oxide of the second metal oxide layer is TiO2, or the oxide of the first metal oxide layer is TiO2 and the oxide of the second metal oxide layer is Al2O3. The oxide of the third metal oxide layer is preferably TiO2 or Al2O3, with TiO2 being particularly preferred. If an intermediate metal oxide layer is present, the oxide of the intermediate metal oxide layer is preferably Al2O3 or TiO2, with Al2O3 being particularly preferred.

[0045] The oxides of the first and second metal oxide layers can also be the same. In this case, the first and second metal oxide layers are applied by the same or different processes. This also applies to the third and intermediate metal oxide layers.

[0046] In the first and second embodiments, a metal layer is provided between the first metal oxide layer and the second metal oxide layer. Exemplary metals for forming the metal layer include aluminum, titanium, tantalum, niobium, zirconium, iron, iridium, platinum, gold, and alloys containing at least one of aluminum, titanium, tantalum, niobium, and zirconium. Particularly preferred metals are aluminum and titanium. Specifically, in the second embodiment, iron is also preferred.

[0047] In a second embodiment, a further metal layer is provided on the second metal oxide layer. Exemplary metals for forming the further metal layer are the same as for the metal layer, with aluminum being the preferred metal.

[0048] In all embodiments, the method for forming the metal oxide layer is not particularly limited, but atomic layer deposition (ALD) is preferred. In particular, the third metal oxide layer, and if present, the intermediate metal oxide layer of the third embodiment, are preferably formed by an ALD process.

[0049] ALD is a thin film deposition method in which thin films are grown on a substrate by alternately exposing the substrate surface to gaseous substances, called precursors, which are introduced into a reactor containing the substrate to be coated in a series of consecutive, non-overlapping pulses, meaning that the precursors are never present in the reactor at the same time.

[0050] In each pulse, a precursor introduced into the reactor is adsorbed onto the surface of the substrate to be coated until all available reactive sites on the surface are consumed. The excess precursor is then removed from the reactor. A second precursor, different from the first precursor, is then introduced into the reactor, adsorbed onto the substrate surface, and chemically reacts with the previously adsorbed first precursor. Again, the excess precursor and gaseous reaction products are then removed from the reactor. Depending on the type of layer being deposited, additional precursors different from the first and second precursors may be introduced into the reactor, adsorbed and reacted, and the excess precursor and reaction products removed from the reactor.

[0051] A single exposure to all precursors is called one ALD cycle. Ideally, each ALD cycle produces a monolayer of coating material. Thus, ALD allows atomic-level control of layer thickness and composition. It allows large substrates with complex geometries to be coated with uniform, conformal coatings free of defects, which may constitute sites that make the composite coating susceptible to attack by corrosive agents.

[0052] When forming an aluminum oxide layer, preferred precursor materials for performing an ALD process are AlX3 and water (gaseous). In AlX3, X represents a lower alkyl group (which may be the same or different), or a lower alkyl group (which may be the same or different) and hydrogen, or a halogen atom (which may be the same or different). Particularly preferred AlX3 compounds are trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), dimethylaluminum (DMAlH), and aluminum trichloride (AlCl3).

[0053] In an exemplary ALD process for producing an aluminum oxide layer, a magnet is placed in a reaction chamber, and AlX3 is introduced into the reaction chamber in a suitable inert carrier gas, such as argon, at a suitable temperature, such as about 300°C. The AlX3 almost instantly adsorbs onto the surface of the magnet or onto a coating already formed on the magnet, and the excess AlX3 and carrier gas are removed by evacuation, for example, to about 0.1-0.01 Pa. Moist air is then introduced. The water contained therein adsorbs onto the surface and reacts with the AlX3, producing aluminum oxide and HX on the surface. The air, excess AlX3, and HX are then removed by again evacuating the reaction chamber to about 0.1-0.01 Pa.

[0054] A complete ALD cycle takes approximately 10-12 seconds to produce an aluminum oxide coating layer approximately 0.1 nm thick, which means that producing an aluminum oxide layer approximately 100 nm thick requires an ALD process time of approximately 3 hours.

[0055] ALD is also the preferred method for forming titanium oxide (TiO2), however, ALD is not available for every metal oxide due to the lack of suitable precursors for each metal oxide.

[0056] Other methods well suited for forming the various metal oxide layers of embodiments of the present invention are, for example, physical vapor deposition, chemical vapor deposition, sputtering, sol-gel processing, flame spraying, or oxidation of a previously applied metal layer. If the metal layer is oxidized, the metal of the metal oxide will, of course, be the same as the metal of the underlying metal layer; otherwise, the metal of the metal oxide layer and the metal of the underlying metal layer may be different.

[0057] Physical vapor deposition can be a plasma-based or plasma-free process, or an ion deposition process. Similarly, ALD can be performed with or without a plasma.

[0058] As a particularly suitable method for applying niobium oxide, the sol-gel process can be mentioned, and as a particularly suitable method for applying tantalum oxide, the application of tantalum metal by physical vapor deposition followed by oxidation in a plasma or oven can be mentioned. When using zirconium oxide, it is recommended to stabilise it, for example with yttrium oxide.

[0059] Methods such as physical vapor deposition and sputtering can be carried out with or without a bias. A bias is advantageous insofar as it promotes the formation of a uniform coating even on irregularly shaped surfaces.

[0060] In the first and second embodiments, the thicknesses of the first metal oxide layer, the second metal oxide layer, and the additional metal oxide layer (if present) may be the same or different and may range from 5 nm to 200 nm, preferably from 80 nm to 120 nm, more preferably from 50 nm to 100 nm, and most preferably about 100 nm. The second metal oxide layer and the additional metal oxide layer may be native oxide layers, i.e., they may be formed naturally when the underlying metal layer is exposed to air and allows the formation of a native oxide. The native oxide layer preferably has a thickness in the range of 1 nm to 5 nm.

[0061] In the third embodiment, the total thickness of the first metal oxide layer, the second metal oxide layer, the third metal oxide layer, and, if present, the intermediate metal oxide layer, is preferably in the range of 20 nm to 800 nm. Thus, in the case of four metal oxide layers, the thickness of each metal oxide layer is preferably in the range of 5 nm to 200 nm, and in the case of only three metal oxide layers, the thickness of each metal oxide layer is preferably in the range of 5 nm to 300 nm.

[0062] In the first and second embodiments, the methods for forming the metal layer and the further metal layer are respectively a dry deposition method for the metal layer and a wet deposition method or a dry deposition method for the further metal layer.

[0063] Exemplary dry processes include chemical vapor deposition, physical vapor deposition (PVD), ion vapor deposition (IVD), stoppering, as well as plasma coating and atomic layer deposition (ALD). IVD produces a metal layer with a columnar structure. Peening is preferably performed before depositing additional layers. Such metal layers also lack the desired quality. PVD, particularly Arc-PVD, is a preferred method for producing the metal layer of the composite coating of the present invention. PVD can produce metal layers with the desired quality and thickness within a reasonable time and at a reasonable cost. In particular, PVD produces homogeneous metal layers. Therefore, the composite coatings of the first and second embodiments of the present invention preferably include a metal layer deposited by PVD, optimally by Arc-PVD. Preferred metals for forming the metal layer are aluminum and / or titanium.

[0064] Exemplary reaction conditions for the PVD process are a temperature in the range of about 200° C. to 260° C. and an inert gas atmosphere, such as an argon gas atmosphere.

[0065] Exemplary metal layers have thicknesses of 0.1 μm to 10 μm, or 0.5 μm to 10 μm. While a thicker metal layer is desirable from the standpoint of providing optimal corrosion protection, the thicker the layer, the more time it takes to apply (the more expensive the process becomes), and as noted above, thick coatings have the disadvantage of increasing the distance between the magnet body and the windings in the electric motor of the blood pump. Therefore, a preferred thickness is 10 μm or less. From the standpoint of corrosion protection, the metal layer should be at least 0.5 μm thick, although thinner layer thicknesses may be sufficient in some cases. A more preferred thickness for the metal layer is 2 μm to 6 μm, with a thickness of approximately 4 μm being particularly preferred.

[0066] According to a second embodiment, the composite coating includes an additional metal layer. The additional metal layer is applied by the same or a different method as the metal layer, preferably by a different method. This is because dry methods such as physical vapor deposition provide coatings with good reproducibility and long-term stability, whereas wet methods such as galvanic deposition (ion plating) apparently provide denser, i.e., better quality, metal layers. Therefore, the second embodiment of the present invention combines a metal layer preferably formed by a physical vapor deposition process with an additional metal layer preferably formed by a plating process. However, wet deposition may not be feasible. For example, gold is preferably applied by sputtering. The additional metal layer preferably has a thickness in the range of 2 μm to 20 μm, more preferably in the range of 10 μm to 18 μm, and most preferably about 15 μm. The thickness of the plating layer is up to 29 μm.

[0067] The preferred metal for forming the further metal layer is aluminum. The galvanic deposition of aluminum is carried out from an ionic liquid by methods conventional in the art, for example, using a mixture of aluminum chloride and 1-ethyl-3-methylimidazolium chloride. The aluminum is preferably pure, for example at least 99% pure, particularly preferably at least 99.9% pure.

[0068] To enhance the corrosion protection provided by the metal / metal oxide layer(s), in all embodiments of the present invention, the metal / metal oxide layer(s) are combined with a poly(p-xylylene) polymer layer. Poly(p-xylylene) polymers are well known under the trade name Parylene. Parylenes are known to react with surfaces containing hydroxyl groups to form thin, pinhole-free coatings. Furthermore, they have a low dielectric constant (approximately 3), which is advantageous for implantable blood pumps. Composite coatings comprising metal oxide layer(s) and / or metal / metal oxide layer(s) and a parylene layer, such as those according to the present invention, are biocompatible and also provide corrosion protection. However, the adhesion of the parylene layer to the metal or metal oxide layer is not strong enough under the operating conditions of an intravascular blood pump. The parylene layer begins to peel off in an unacceptably short time, exposing the metal or metal oxide layer. The metal layer(s) and / or metal oxide layer(s) do not provide sufficient protection for the magnetic body, which causes the magnetic body to start to corrode.

[0069] This scenario is prevented by a combination of two measures: providing an interface layer connecting the metal or metal oxide layer to the parylene layer, and using a specific parylene compound.

[0070] The compound forming the interfacial layer, i.e., the linker compound, must be bifunctional. Bifunctionality means that the linker compound must have two functional groups or molecular moieties with different functionalities (reactivities), one of which binds to the metal or metal oxide layer, for example, by reacting with hydroxyl groups on the surface of the metal or metal oxide layer, and another functional group or molecular moiety which binds to the parylene, thereby ensuring a bond between the inorganic metal or metal oxide layer and the organic parylene layer. The bond can be provided by a covalent bond or another bond, such as van der Waals forces.

[0071] Linkers having functional groups or moieties that bind to metals or metal oxides and functional groups or moieties that bind to parylene are well known. Exemplary linkers include silane compounds, mercaptans, phosphines, disulfides, and silanes with thiol, phosphine, or disulfide groups. Depending on the metal, different linker compounds are preferred.

[0072] For aluminum, titanium, tantalum, niobium, zirconium, iridium, silicium, hafnium, and oxides of these metals, the linkers for the metal and metal oxide layers are preferably alkoxysilanes, such as methoxysilanes and ethoxysilanes, e.g., silanes having the formula (HCO)Si-R, where R is, for example, methacrylate, alkylamine, phenylamine, or epoxyalkyl. For bonding to parylene, the linker preferably has an acryloyloxy or methacryloyloxy functional group. The length of the carbon chain between the silyl and (meth)acryloyloxy moieties of the linker is typically 1 to 16 carbon atoms (e.g., methyl, ethyl, propyl, butyl, pentyl, etc.). The hydrocarbon chain is typically saturated but may contain one or more unsaturated bonds. A particularly preferred linker is 3-(trimethoxysilyl)propyl methacrylate (A-174) from Silquest, although other silane compounds such as G-170 (a vinyl-functional silane coupling agent) from Silquest are also suitable. Additionally, linkers with bis-trimethoxysilyl or bis-triethoxysilyl functionality can also be used, such as bis(trimethoxysilylethyl)benzene.

[0073] Linkers with hybrid functional groups such as trihydrosilane work well, especially for titanium, zirconium, and platinum. 10-Undecenylsilane and n-octadecylsilane are particularly noteworthy. Silanes are preferably applied at room temperature from the gas phase or from aprotic solutions. In addition, the above-mentioned alkoxysilanes with (meth)acryloyloxy groups and compounds with bis-trimethoxysilyl or bis-triethoxysilyl functional groups are also suitable.

[0074] Linkers suitable for attaching the parylene layer to the gold layer are typically mercaptans, phosphines, or disulfides, preferably alkyl disulfides or dialkyl disulfides with longer hydrocarbon chains, e.g., alkyl groups with 10 to 16 carbon atoms. Such alkyl groups form dense, well-ordered layers on the metal or metal oxide surface. However, alkyl groups with only 1 to 9 carbon atoms can also be used.

[0075] Equally suitable for the gold layer are silane linker compounds containing thiol, phosphine, or disulfide groups. Particularly preferred examples are 3-(2-pyridylethyl)thiopropyltrimethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane, 2-(diphenylphosphino)ethyltriethoxysilane, bis(2-methacryloyl)oxyethyl disulfide, and dihexadecyl disulfide.

[0076] The bifunctional linker is preferably applied to the metal or metal oxide surface by a plasma coating process, by physical vapor deposition without plasma, or by applying an aprotic, alcoholic, or aqueous solution of the bifunctional linker compound to the metal or metal oxide surface. Dry coating of the silane compound in a plasma chamber produces a glassy layer that is oriented substantially parallel to the metal oxide surface and contains Si-O-Si-O- chains bonded to the surface via oxygen atoms. The organic residues face away from the surface and are available for bonding with parylene. Physical vapor deposition and wet application produce interfacial layers with similar structure but without the glassy appearance.

[0077] Plasma deposition produces dense layers with acceptable adhesion to parylene. Physical vapor deposition without plasma produces less dense layers that adhere better to parylene than plasma-deposited layers. Wet application produces a very dense monolayer with a random network structure, a high degree of cross-linking, and a high proportion of silicon-bonded oxygen. This layer also adheres very well to the parylene layer. Therefore, wet application is particularly preferred.

[0078] Alternatively, plasma application can be combined with physical vapor deposition (without plasma) or wet application processes, i.e., a glassy interfacial layer is first formed by plasma deposition, followed by physical vapor deposition or wet application of a second linker layer to form a composite linker layer, in which silicon atoms of the glassy layer are covalently bonded to oxygen atoms of the second layer, and organic residues (such as methacrylate, alkylamine, or epoxyalkyl) of the second layer can be used to bond to parylene, either covalently or otherwise, for example, via van der Waals forces.

[0079] The interfacial layer typically has a thickness in the range of 20 to 150 nm, preferably 50 to 100 nm. Alternatively, only a monolayer can be applied. A monolayer can be obtained by applying a solution of the linker compound and evaporating the solvent.

[0080] A parylene layer, i.e., a poly(p-xylylene) polymer layer, is formed on the interfacial layer, or in a third embodiment, on the interfacial layers of both the first and second layer structures. The poly(p-xylylene) polymer has the following structural formula: [ka] In the formula, n is the degree of polymerization.

[0081] The precursors of poly(p-xylylene) compounds are [2.2]paracyclophanes having the following structural formula: [ka] Dimeric compounds are commercially available and are precursors to, for example, Parylene N, Parylene C, Parylene D, and Parylene F. In Parylene N, X and all of R1-R4 are hydrogen; in Parylene C, one of R1-R4 is chlorine and the other residues R and X are hydrogen; in Parylene D, two of R1-R4 are chlorine and the other residues are hydrogen; and in Parylene F, residue X is fluorine and residues R1-R4 are hydrogen. Parylene layers are typically used as moisture and dielectric barriers.

[0082] At high temperatures (above about 500°C, depending on the particular parylene) under vacuum, the dimers decompose to form the corresponding p-xylylene radicals. The monomers polymerize to form poly(p-xylylene) polymers, which on the one hand bond to the interfacial layer via their functional groups, e.g., methacrylate groups, on the other hand. Alternatively, they may simply attach to the hydrophobic parts of the interfacial layer.

[0083] Parylene C, in which one of R1-R4 is chlorine, has been found to form a coating that provides corrosion resistance to magnetic materials under conditions encountered in intravascular blood pumps when applied as a cover layer for composite layers according to the first and second embodiments, or as a cover layer for first and second layer structures according to the third embodiment. The parylene layer is preferably applied by plasma deposition, and the thickness of the top layer is preferably in the range of 3 μm to 20 μm, more preferably 10 μm to 17 μm, and most preferably about 15 μm. In the third embodiment, the parylene layer of the first layer structure preferably has a thickness in the range of 0.5 μm to 4 μm, more preferably 1 μm to 2 μm.

[0084] When Parylene C is applied directly to the surface of a magnetic material, cracking and delamination of the protective Parylene C layer and corrosion of the magnetic material are observed within a few days. Similarly, when Parylene C is applied over a metal or metal / metal oxide layer, corrosion of the magnetic material is observed within an unacceptably short time due to delamination under the conditions found in intravascular blood pumps. In addition, parylene compounds other than Parylene C do not provide sufficient corrosion protection when an adhesion promoter is used, even when applied over a silane-based interface layer, for example.

[0085] The composite coating of the present invention has good adhesion to the magnet body and, because it has a structure consisting of both inorganic and organic components, it provides an effective barrier against both inorganic and organic substances. Furthermore, the glassy interfacial layer also has barrier properties.

[0086] In a particularly preferred embodiment of the present invention, corrosion protection of the magnetic material is further enhanced by the fact that the shape of the magnet body is specially adapted to allow the formation of a coating that covers the magnet body with a uniform thickness. For this purpose, the magnet body has no sharp edges, but rather a rounded shape with gentle edges. Preferably, the magnet body is rod-shaped and has a channel extending therethrough in the longitudinal direction for receiving the motor shaft of the intravascular blood pump, the opposing front faces of the magnet body being inclined toward the channel. The channel does not need to be coated with the composite coating, since in the intravascular blood pump, the channel receives and is fixed to the motor shaft. Of course, the channel may still be coated for safety reasons.

[0087] The magnetic body may be a single piece or may consist of several segments, each of which is provided with the coating of the invention in a uniform thickness, either completely surrounding it or at least on its exposed surfaces, and preferably with gentle edges. [Brief explanation of the drawings]

[0088] The invention will be further explained with reference to the accompanying drawings. [Figure 1] 1 is a schematic longitudinal cross-sectional view of an exemplary embodiment of an intravascular blood pump. [Figure 2] 1 is a schematic cross-sectional view of a portion of a magnet according to a first embodiment of the present invention. [Figure 3a] FIG. 4 is a schematic cross-sectional view of a portion of a magnet according to a second embodiment of the present invention. [Figure 3b]5 is a schematic cross-sectional view of a portion of another magnet according to a second embodiment of the present invention. [Figure 4a] FIG. 4 is a schematic cross-sectional view of a portion of a magnet according to a third embodiment of the present invention. [Figure 4b] FIG. 10 is a schematic cross-sectional view of a portion of another magnet according to a third embodiment of the present invention. [Figure 5a] 1 is a schematic diagram of an exemplary single-piece magnet according to the present invention. [Figure 5b] FIG. 5b is a partial cross-sectional view showing a detail of the magnet shown in FIG. 5a. [Figure 6] FIG. 2 is a schematic top view of an exemplary segmented magnet according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0089] The drawings are not to scale and they should not be construed as limiting the invention in any way.

[0090] The intravascular blood pump 10 shown in Figure 1 has been described above. The pump is of conventional construction but includes a corrosion-resistant permanent magnet 1 according to the present invention.

[0091] In the pump of Figure 1, the magnet 1 is rod-shaped, with opposite flat front faces that are parallel to each other. While the composite coating of the present invention can effectively protect sharp-edged magnet bodies, such as that shown in Figure 1, from corrosion over a long period of time, the present invention preferably uses magnet bodies having shapes such as those shown in Figures 5 and 6. Each individual layer of the composite coating extends completely over the previously applied composite coating layer.

[0092] FIG. 2 is a schematic cross-sectional view of a portion of a magnet 1 having a composite coating 15 according to a first embodiment of the present invention. For the exemplary magnet shown in FIG. 2, the composite coating 15 is formed on the surface 19' of an unmagnetized magnet body 19. The composite coating 15 includes a first aluminum oxide layer 42 formed by atomic layer deposition on the surface 19' of the magnet body 19. An aluminum layer 43 is deposited on the surface 42' of the aluminum oxide layer 42 by physical vapor deposition. A second aluminum oxide layer 44 is deposited on the surface 43' of the aluminum layer 43 by atomic layer deposition. The first aluminum oxide layer 42, the aluminum layer 43, and the second aluminum oxide layer 44 combine to form the inorganic layer 41 of the composite coating 15. A linker layer 46 is formed on the surface 44' of the second aluminum oxide layer 44 to securely bond the organic layer 47 to the second metal oxide layer 44. The organic layer 47 of the composite coating 15 is made of Parylene C and covers the surface 46' of the linker layer 46.

[0093] For the exemplary magnet shown in Figure 2, the first and second aluminum oxide layers are each 100 nm thick, the aluminum layer is 4 μm thick, the layer formed from Parylene C is 15 μm thick, and the linker layer is a single layer.

[0094] FIG. 3a is a schematic cross-sectional view of a portion of a magnet 1 having a composite coating 16 according to a second embodiment of the present invention. For the exemplary magnet shown in FIG. 3a, the composite coating 16 is formed on the surface 19' of an unmagnetized magnet body 19. The composite coating 16 includes a first metal oxide layer 52 made of titanium oxide. The first metal oxide layer 52 is deposited by atomic layer deposition on the surface 19' of the magnet body 19 to a thickness of 100 nm. A metal layer 53 made of titanium is deposited by physical vapor deposition on the surface 52' of the first metal oxide layer 52 to a thickness of 4 μm. A second metal oxide layer 54 is deposited by atomic layer deposition on the surface 53' of the metal layer 53 to a thickness of 100 nm. The second metal oxide layer is made of a mixture of aluminum oxide and titanium oxide. A plating layer 55 is provided on the surface 54' of the second metal oxide layer 54. The plating layer 55 is an aluminum metal layer and has a thickness of approximately 15 μm. The first metal oxide layer 52, the metal layer 53, the second metal oxide layer 54, and the further metal layer 55 combine to form the inorganic layer 51. The linker layer 56 is formed on the surface 55' of the further metal layer 55 and securely bonds the organic layer 57 to the further metal layer 55. The organic layer 57 of the composite coating 16 is made of Parylene C and covers the surface 56' of the linker layer 56.

[0095] Figure 3b shows a magnet 1 similar to that shown in Figure 3a, but with an additional metal oxide layer 58 provided on the aluminum metal layer 55. In the embodiment shown in Figure 3b, the additional metal oxide layer 58 is a native aluminum oxide layer having a thickness of about 3 nm, i.e., a passivation layer formed by exposing the aluminum metal layer to air.

[0096] Figure 4a is a schematic cross-sectional view of a portion of a magnet 1 having a composite coating 18 according to a third embodiment of the present invention. For the exemplary magnet shown in Figure 4a, the composite coating 18 includes a first layer structure 17 and a second layer structure 17'.

[0097] The first layered structure 17 includes an inorganic layer 61 consisting of a first metal oxide layer 62 and a second metal oxide layer 64, an organic layer 67, and a linker layer 66 provided between the second metal oxide layer 64 and the organic layer 67. The second layered structure 17′ is provided on the first layered structure 17, and includes an inorganic layer 71 consisting of a third metal oxide layer 74, an organic layer 77, and a linker layer 76 provided between the third metal oxide layer 74 and the organic layer 77.

[0098] The first metal oxide layer is a 100 nm thick aluminum oxide layer formed on the surface 19' of the magnet body 19 by atomic layer deposition. The second metal oxide layer is a 10 nm thick titanium oxide layer formed on the surface 62' of the first metal oxide layer by atomic layer deposition. The linker layer 66 is a monolayer formed on the surface 64' of the second metal oxide layer, and the organic layer 67 is a layer of parylene C formed on the surface 66' of the linker layer 66. The thickness of the parylene C layer is in the range of 1 to 2 μm.

[0099] The third metal oxide layer 74 is a 10 nm thick titanium oxide layer formed by atomic layer deposition on the surface 67' of the first organic layer 67. A linker layer 76 is provided on the surface 74' of the titanium oxide layer, and a further Parylene C layer 77 is formed on the surface 76' of the linker layer 76. This outermost Parylene C layer is approximately 13 μm thick.

[0100] FIG. 4b shows a magnet 1 similar to that shown in FIG. 4a, but with an additional (intermediate) metal oxide layer 72 between the organic layer 67 and the third metal oxide layer 74. The second layer structure 17′ thus comprises an inorganic layer 71 consisting of the intermediate metal oxide layer 72 and the third metal oxide layer 74, an organic layer 77, and a linker layer 76 between the third metal oxide layer 74 and the organic layer 77. The intermediate metal oxide layer 72 is a 20 nm thick aluminum oxide layer formed by atomic layer deposition. The rest is similar to the embodiment shown in FIG. 4a above. The first and second layer structures comprise layers made of the same material (although in other embodiments the materials may be different), but with different thicknesses.

[0101] In the embodiment shown in Figures 4a and 4b, all linker layers are monolayers and identical.

[0102] FIG. 5a shows a single-piece magnet 1, rod-shaped and with a longitudinal hole or channel therethrough. During use of the magnet in an intravascular blood pump 10 such as that shown in FIG. 1, the channel receives a motor shaft 25. The opposing front faces 4 of the magnet taper toward the channel. The magnet 1 includes a composite coating according to the present invention on the outer surface 2 exposed to fluid flowing in the gap 26 and on the tapered front face 4. The inner surface 3 adjacent the motor shaft 25 may or may not be coated. The transition edges 5 between the outer surface 2 and the front face 4 are coated, as are the transition edges 6 between the front face 4 and the inner surface 3. The edges are gradual, which facilitates the formation of a uniform, adherent coating. "N" and "S" refer to the north and south poles of the magnet.

[0103] Figure 5b is a partial cross-sectional view taken along the dashed line in Figure 5a, showing the area of ​​the magnet within the circle in Figure 5a, and clearly showing the soft edges 5, 6.

[0104] Figure 6 shows a segmented magnet 7. The magnet shown in Figure 6 has four segments 8, 8'. The segments 8 face each other and have the same magnetic polarity, as indicated by an "N" in the top view of Figure 6, and the segments 8' also face each other and have the same magnetic polarity, as indicated by an "S" in the top view of Figure 6. As a result, adjacent segments 8, 8' have opposite magnetic polarities.

[0105] Segments 8, 8', like the single-piece magnet shown in FIG. 5, have an inner surface, an outer surface, opposing front faces, a transition edge between the outer and front faces, and a transition edge between the front and inner surfaces. Corresponding to the designations in FIG. 5, the front faces are designated 4', and the edges are designated 5' and 6', respectively. Additionally, segments 8, 8' have side faces 9, 9', separated by a gap in the figure. Of course, the side faces 9, 9' will contact each other while the magnet is in use. While all surfaces of each segment of the magnet may be completely covered by the composite coating of the present invention, the side faces 9, 9' not exposed to contact each other and the inner surface not exposed to contact the motor shaft need not be coated. Preferably, all edges of all segments are gradual.

[0106] Identical cylindrical unmagnetized NdFe with a length of 12 mm and a diameter of 2.8 mm 14 Sintered magnet bodies B were coated with different coatings (after washing but without removing the phosphate coating), magnetized, and subjected to a corrosion test at 60°C in an aqueous solution containing 0.9% by weight of sodium chloride. In this test, corrosion proceeds approximately 3.75 times faster than in an injectable 5% to 40% by weight glucose solution at room temperature.

[0107] The following coatings have proven particularly advantageous with respect to the desirable combination of excellent corrosion resistance and minimal reject rates.

[0108] Magnets according to the first embodiment had first and second metal oxide layers formed by ALD to a thickness of 100 nm, a metal layer formed by PVD to a thickness of 4 μm, and a Parylene C coating formed to a thickness of 15±2 μm. The best magnets had (a) Al2O3 as the first and second metal oxide layers and aluminum as the metal layer, (b) Al2O3 as the first and second metal oxide layers and titanium as the metal layer, (c) TiO2 as the first and second metal oxide layers and titanium as the metal layer, (d) Al2O3 as the first metal oxide layer, a mixture of Al2O3 and TiO2 as the second metal oxide layer, and titanium as the metal layer, and (e) TiO2 as the first metal oxide layer, a mixture of Al2O3 and TiO2 as the second metal oxide layer, and titanium as the metal layer. Applying a bias during PVD appeared to improve coating quality.

[0109] A magnet according to a second embodiment having a first metal oxide layer formed by ALD to a thickness of 100 nm, a second metal oxide layer formed by ALD to a thickness of 100 nm, a metal layer formed by PVD to a thickness of 4 μm, a further metal layer (aluminum) formed by plating to a thickness of 15±3 μm, and a Parylene C coating formed to a thickness of 15±2 μm.

[0110] The best magnets had (a) Al2O3 as the first and second metal oxide layers and aluminum as the metal layer, (b) TiO2 as the first metal oxide layer, a mixture of Al2O3 and TiO2 as the second metal oxide layer, and titanium as the metal layer, and (c) TiO2 as the first and second metal oxide layers and iron as the metal layer.

[0111] A magnet according to a third embodiment having Al2O3 as a first metal oxide layer formed by ALD to a thickness of 100 nm, TiO2 as a second metal oxide layer formed by ALD to a thickness of 10 nm, a Parylene C coating formed to a thickness of 1-2 μm, Al2O3 as a middle metal oxide layer formed by ALD to a thickness of 200 nm, TiO2 as a third metal oxide layer formed by ALD to a thickness of 10 nm, and a Parylene C coating formed to a thickness of 13±2 μm.

[0112] In both cases, the linker layer and the additional linker layer, if applicable, were formed from an alcohol solution containing Silane A-174 (water / ethanol, acetic acid to achieve a pH of approximately 5-6, approximately 1% silane concentration, approximately 5 minutes of reaction time). Evaporation of the alcohol resulted in essentially a monolayer. The Parylene C coating was formed by plasma deposition.

Claims

1. 1. A corrosion-resistant permanent magnet comprising a magnet body and a composite coating disposed on and covering a surface of the magnet body, the composite coating comprising, in the listed order: a first metal oxide layer in physical contact with the magnetic body; metal layer, Second Metal Oxide Layer a linker layer, wherein the linker forming said linker layer is a bifunctional compound; and a layer formed from poly(2-chloro-p-xylylene), Corrosion resistant permanent magnet.

2. 2. The magnet of claim 1, wherein the linker compound has one functional group or molecular moiety that binds to the second metal oxide layer and another functional group or molecular moiety that binds to the poly(2-chloro-p-xylylene).

3. 3. The magnet of claim 1, wherein the magnetic body is a rare earth iron boron permanent magnet.

4. The magnet body is Nd ２ Fe １４ B crystal and the Nd ２ Fe １４ and a neodymium iron boron material surrounding the Nd B crystals, ２ Fe １４ 4. The magnet of claim 3, which is richer in neodymium than the B crystal.

5. 5. The magnet according to claim 1, wherein the metal of the metal layer is aluminum or titanium, or an alloy of aluminum or titanium.

6. The oxide of the first metal oxide layer is Al ２ O ３ or TiO ２ , or Al ２ O ３ and TiO ２ 6. The magnet according to claim 1, wherein the mixed oxide is:

7. The oxide of the second metal oxide layer is Al ２ O ３ or TiO ２ , or Al ２ O ３ and TiO ２ 7. The magnet according to claim 1, wherein the mixed oxide is:

8. a further metal layer and optionally a further metal oxide layer between said second metal oxide layer and said linker layer; the metal layer is in physical contact with the first metal oxide layer; the second metal oxide layer is in physical contact with the metal layer; the further metal layer is in physical contact with the second metal oxide layer; said further metal oxide layer, if present, being in physical contact with said further metal layer; the linker layer is in physical contact with the further metal layer, or the further metal oxide layer, if present, and the linker compound has one functional group or molecular moiety that bonds to the further metal layer, or the further metal oxide layer, if present, and another functional group or molecular moiety that bonds to the poly(2-chloro-p-xylylene); the poly(2-chloro-p-xylylene) layer is in physical contact with the linker layer; The magnet according to any one of claims 1 to 7.

9. 9. The magnet of claim 8, wherein the metal of the further metal layer is aluminum.

10. The metal layer is omitted and the composite coating is formed in the order listed above on a layer formed from the poly(2-chloro-p-xylylene). a third metal oxide layer; a further linker layer, wherein the linkers forming said further linker layer are bifunctional compounds; and A magnet according to any one of claims 1 to 6, further comprising a further layer formed from poly(2-chloro-p-xylylene).

11. 11. The magnet of claim 10, wherein the linker compound forming the further linker layer has one functional group or molecular moiety that binds to the third metal oxide layer and another functional group or molecular moiety that binds to the poly(2-chloro-p-xylylene).

12. 12. A magnet according to claim 10 or 11, comprising an intermediate metal oxide layer between the layer formed from poly(2-chloro-p-xylylene) and the third metal oxide layer.

13. The oxide of the first metal oxide layer is Al ２ O ３ and the oxide of the second metal oxide layer is TiO ２ or the oxide of the first metal oxide layer is TiO ２ and the oxide of the second metal oxide layer is Al ２ O ３ or the oxide of the first and second metal oxide layers is Al ２ O ３ or the oxide of the first and second metal oxide layers is TiO ２ and / or the oxide of the third metal oxide layer is Al ２ O ３ or TiO ２ The magnet according to any one of claims 10 to 12, wherein

14. The oxide of the intermediate metal oxide layer is Al ２ O ３ or TiO ２ and is different from the oxide of the third metal oxide layer.

15. 1. A method for producing a corrosion-resistant permanent magnet, comprising: providing a magnet body; forming a first metal oxide layer on a surface of the magnet body; forming a metal layer on the first metal oxide layer; forming a second metal oxide layer on the metal layer; Optionally, forming at least one further layer on said second metal oxide layer; forming a linker layer on said second metal oxide layer or, if present, on said at least one further layer; forming a layer of poly(2-chloro-p-xylylene) on the linker layer; method.

16. 16. The method of claim 15, comprising forming the at least one further layer, the at least one further layer being a further metal layer.

17. 17. The method of claim 16, further comprising forming a further metal oxide layer over the further metal layer.

18. The method according to any one of claims 15 to 17, wherein the oxide of the first metal oxide layer and / or the oxide of the second metal oxide layer is an oxide as defined in claim 5 or 6.

19. The method according to any one of claims 15 to 18, wherein the metal of the metal layer is a metal as defined in claim 5.

20. The method according to any one of claims 16 to 19, wherein the metal of the further metal layer is aluminium.

21. 1. A method for producing a corrosion-resistant permanent magnet, comprising: providing a magnet body; forming a first metal oxide layer on a surface of the magnet body; forming a second metal oxide layer on the first metal oxide layer; forming a linker layer on the second metal oxide layer; forming a layer of poly(2-chloro-p-xylylene) on the linker layer; optionally forming an intermediate metal oxide layer on said poly(2-chloro-p-xylylene) layer; forming a third metal oxide layer on said poly(2-chloro-p-xylylene) layer and, if present, on said intermediate metal oxide layer; forming a further linker layer on the third metal oxide layer; forming a further layer of poly(2-chloro-p-xylylene) on said further linker layer; method.

22. The oxide of the first metal oxide layer is Al ２ O ３ and the oxide of the second metal oxide layer is TiO ２ or the oxide of the first metal oxide layer is TiO ２ and the oxide of the second metal oxide layer is Al ２ O ３ or the oxides of the first and second metal oxide layers are both Al ２ O ３ or both are TiO ２ and / or the oxide of the third metal oxide layer is TiO ２ or Al ２ O ３ 22. The method of claim 21, wherein:

23. forming the intermediate metal oxide layer, wherein the oxide of the intermediate metal oxide layer is Al ２ O ３ or TiO ２ and is different from the oxide of the third metal oxide layer.

24. An intravascular blood pump comprising an electric motor, said electric motor comprising a permanent magnet as claimed in any one of claims 1 to 14.

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