Intravascular blood pump containing corrosion-resistant permanent magnets

Abstract

The present invention relates to a corrosion-resistant permanent magnet, a method for producing a corrosion-resistant permanent magnet, and an intravascular blood pump comprising such a magnet. The magnet is corrosion-resistant due to a composite coating, which composite coating comprises a metal layer, an optional metal oxide layer, a layer formed of poly(2-chloro-p-xylene), and an adhesion layer between the metal oxide layer and the poly(2-chloro-p-xylene) layer.

Description

[0001] This application is a divisional application of the invention patent application with the application date of October 25, 2017, the application number of 201780068060.9, and the invention name of "Intravascular Blood Pump Containing Corrosion-Resistant Permanent Magnets". Technical Field

[0002] The present invention relates to the corrosion protection of permanent magnets. In particular, the present invention relates to permanent magnets having a protective coating that renders the magnets corrosion-resistant, and to a method for producing corrosion-resistant permanent magnets. The present invention also relates to an intravascular blood pump comprising the corrosion-resistant permanent magnets of the present invention. Although the present invention is applicable to all types of permanent magnets, rare earth permanent magnets are preferred, and neodymium iron boron (NdFeB) permanent magnets are particularly preferred. Background Art

[0003] Intravascular blood pumps maintain blood flow in a patient's blood vessels. They are percutaneously inserted, for example, into the femoral artery and guided through the body's vascular system to their destination, such as the ventricle of the heart.

[0004] Blood pumps generally include a pump housing having a blood flow inlet and a blood flow outlet. To cause blood to flow from the blood flow inlet to the blood flow outlet, an impeller or rotor is rotatably supported within the pump housing about a rotation axis, and the impeller is provided with one or more blades for transporting blood.

[0005] Figure 1 An exemplary blood pump is shown in Figure 1 is a schematic longitudinal sectional view of an exemplary intravascular blood pump 10. The blood pump has a motor section 11 and a pump section 12, which are arranged coaxially one after another, resulting in a rod-shaped configuration. The pump section extends through a flexible suction hose (not shown), which has openings for blood to enter the pump at its end and / or side wall. The end of the blood pump 10 facing away from the suction hose is connected to a catheter 14, which may optionally be combined with a guide wire for guiding the blood pump to its destination.

[0006] Figure 1 The exemplary intravascular blood pump shown in Figure 1In an exemplary blood pump, the stator 24 of the electric motor 21 typically has a number of circumferentially distributed windings and a magnetic circuit 28 in the longitudinal direction. The stator is firmly connected to the motor housing. The stator 24 surrounds the rotor 1 connected to the motor shaft 25, and the rotor 1 consists of permanent magnets magnetized in the effective direction. The motor shaft 25 extends in the longitudinal direction of the total length of the motor housing 20 and protrudes from the housing at the distal side of the motor housing 20. There, it mounts the impeller 34, and the impeller 34 has blades 36 protruding therefrom, or pump blades that rotate within the tubular pump housing 32 firmly connected to the motor housing 20.

[0007] The proximal end of the motor housing 20 has a flexible conduit 14 sealedly connected thereto. In the present disclosure, "proximal" and "distal" indicate positions relative to the doctor inserting the blood pump into the blood vessel, that is, the distal end is on the impeller side. A cable 23 extends through the conduit 14 for supplying power to and controlling the electric motor 21. Additionally, a purge fluid line 29 extends through the conduit 14, and the purge fluid line 29 penetrates the proximal wall 22 of the motor housing 20. Purge fluid (schematically indicated by thick arrows) is supplied into 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 selected purge pressure is higher than the current blood pressure to prevent blood from seeping into the motor housing. Depending on the application, at the motor where pressure accumulates, the pressure of the purge fluid is between 300 and 1400 mmHg.

[0008] A fluid that is very suitable as the purge fluid is a fluid having a viscosity higher than the viscosity of water (η = 0.75 mPa·s at 37°C), particularly a purge fluid having a viscosity of 1.2 mPa·s or higher at 37°C. For example, an aqueous solution of 5% to 40% glucose for injection can be used, but a physiological saline solution is also suitable.

[0009] When the impeller 34 rotates, blood (schematically indicated by unfilled arrows) is sucked in through the end face suction port 37 of the pump housing 32 and is axially conveyed backward within the pump housing 32. Through the outlet opening 38 of the pump housing 32, the blood flows out of the pump section 12 and further flows along the motor housing 20. The pump section can also be operated in the reverse direction of the conveying direction, and blood is sucked in along the motor housing 20 and flows out through the opening 37.

[0010] 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. In addition, the motor shaft 25 is also axially mounted on the axial bearing 40. If the blood pump is also or only used for reverse blood conveyance, the corresponding axial bearing 40 is also / only provided at the proximal end of the motor housing 20 in the corresponding manner.

[0011] It should be emphasized that the above blood pump is merely an example, and the present invention is also applicable to different blood pumps including an electric motor, that is, different blood pumps that require permanent magnets.

[0012] Intravascular blood pumps must meet many requirements. Since they are implanted in the living body, they should be as small as possible. The outer diameter of the smallest blood pump currently in use is about 4 mm. However, the blood pump must deliver a high volume flow of blood in the human blood circulation. Therefore, the micro blood pump must contain a high-performance electric motor.

[0013] In addition, the implantable blood pump must not have an adverse effect on its biological environment, such as the blood to be pumped and the surrounding tissue. Therefore, in a broad sense, the blood pump should be biocompatible, that is, they should not contain or generate any potentially harmful substances or a considerable amount of heat that may damage the body or its components.

[0014] In addition, replacing the blood pump is troublesome for the patient. Of course, there are also financial considerations for the patient. The intravascular blood pump should have a long service life, preferably 180 days or longer.

[0015] The materials and design of the intravascular blood pump must be appropriately selected and specifically adjusted to meet these different requirements.

[0016] Importantly, appropriate permanent magnets must be selected for the electric motor. Considering the efficiency and life of the pump, the magnet should have a strong magnetic field, that is, high remanence, high resistance to demagnetization, that is, high coercivity, and high saturation magnetization. In this regard, rare-earth permanent magnets are the selected magnets, especially those with neodymium as the rare-earth metal, particularly neodymium iron boron (NdFeB) permanent magnets. Other rare-earth element iron boron permanent magnets can also be used.

[0017] The stronger the magnet, the smaller the magnet can be while still generating sufficient rotational force. Therefore, the stronger the magnet, the smaller the electric motor can be. NdFeB permanent magnets are the strongest permanent magnets currently available. Using them in intravascular blood pumps seems to be ideal.

[0018] It is well known that the magnetism of rare-earth metal-based magnets (such as NdFeB magnets) depends on the specific alloy composition, microstructure, and manufacturing technology employed. NdFeB magnets can be used as polymer bonded magnets and sintered magnets. Sintered magnets have excellent magnetism. They are prepared by alloying raw materials, grinding them into powder, pressing, and sintering. During or after the preparation, an external magnetic field is applied to magnetize the material. A well-studied magnet is a fine-grained sintered material in which Nd2Fe 14 B crystals are coated with a thin layer particularly rich in neodymium.

[0019] Although neodymium-iron-boron magnets have magnetic properties that make them particularly suitable for the motors of intravascular blood pumps, they also have serious drawbacks. That is to say, commercially available NdFeB magnets, which consist mainly of neodymium, iron, and boron, especially sintered neodymium-iron-boron magnets with a very active neodymium-rich crystal phase at the grain boundaries, are very prone to corrosion. For example, the magnet can be corroded by oxygen and moisture in the air, especially, but not only, at the grain boundaries. Corrosion leads to a significant reduction in magnetic properties, and if the corrosion continues during the use of the magnet, the performance of the blood pump using the magnet deteriorates. This phenomenon is exacerbated by the following trend: the neodymium-iron-boron magnet forms a spongy material as a corrosion product, which destroys the structure and causes fragments to peel off from the magnet surface, eventually leading to the magnet cracking.

[0020] Unfortunately, susceptibility to corrosion is a characteristic common to all rare-earth metals. Therefore, all rare-earth metal-based permanent magnets have an unfavorable tendency to corrode, as described above for NdFeB magnets. For currently available magnets, it can be said empirically that the stronger the magnet, the more prone it is to corrosion.

[0021] In an intravascular blood pump, the magnet must operate in a corrosive environment, that is, in the purge fluid flowing between the rotor and the stator (see Figure 1 ). As mentioned above, the purge fluid is usually an aqueous fluid, and may be a fluid containing chlorides. Chlorides are highly corrosive to rare-earth metal-based magnets, and water and oxygen dissolved in the water can also cause severe corrosion within just a few hours.

[0022] Obviously, rare-earth metal-based permanent magnets used in intravascular blood pumps, such as NdFeB magnets, need to be protected against corrosion.

[0023] Various measures are known for protecting NdFeB magnets and other rare-earth metal-based magnets from corrosion. For example, the corrosion resistance can be improved by coating the magnet with a protective coating.

[0024] Common coatings are nickel coatings and epoxy resin-based coatings. Especially for blood pumps, titanium coatings and parylene coatings are known. However, these coatings also have drawbacks. Even when biocompatible metals and organic resins are selected separately, such as titanium and parylene, there is a problem that the metal coating must be relatively thick in order to provide sufficient protection. As a result, the gap between the magnet and the windings in the motor of the blood pump must be relatively large. A larger gap has a strong negative impact on the performance of the motor. A large gap requires a higher motor current, and a high motor current generates unwanted heat, which may cause damage to blood and tissue.

[0025] In addition, organic materials such as parylene have a thermal expansion coefficient significantly different from that of the magnet. Therefore, temperature changes during the use of the magnet often cause the coating to crack and / or delaminate.

[0026] Currently, there is no known biocompatible coating for permanent magnets (such as neodymium-iron-boron magnets) that meets all the requirements for an intravascular blood pump. Such a coating must itself have excellent corrosion resistance, must be thin but still dense, must not develop cracks or other defects during use, and must adhere reliably and tightly to the magnet. Of course, the coating must be biocompatible, and it must coat the entire magnet or at least those magnet portions that are exposed to a corrosive environment during magnet use with a uniform thickness. This is particularly demanding because many magnets have porous surfaces and shapes that include edges. Thus, permanent magnets for intravascular blood pumps, such as rare-earth metal-based magnets, such as neodymium-iron-boron magnets, constitute articles that cannot be easily coated with a uniform thickness. Summary of the Invention

[0027] The present invention provides a solution to the above problems.

[0028] The present invention provides a coating for a permanent magnet that reliably protects the magnet from corrosion when used in an intravascular blood pump over a long period of time.

[0029] The subject matter of the present invention relates to a corrosion-resistant permanent magnet having the features described in independent claim 1, a method for producing a corrosion-resistant permanent magnet, the method having the features described in independent claim 21, and an intravascular blood pump having the features described in independent claim 30. Embodiments of the present invention are disclosed in the respective dependent claims.

[0030] If a magnet passes the tests described in the experimental section, then the magnet is corrosion-resistant in the sense of the present invention.

[0031] According to the present invention, a strong permanent magnet comprises a coating that completely surrounds the magnet or at least covers those surfaces that are exposed to fluid when the magnet is operating in an intravascular blood pump. When used in an intravascular blood pump, the coating renders the magnet resistant to corrosion. Preferred magnets are sintered magnets mainly composed of neodymium, iron, and boron, having excellent tetragonal magnetic Nd2Fe 14 B crystals and a neodymium-rich non-magnetic phase surrounding the crystals, as described above. Generally, the average crystal diameter of the Nd2Fe 14 B crystals forming the main phase is in the range of 1 - 80 μm. The non-magnetic neodymium-rich phase accounts for 1% to 50% of the magnet volume. These magnets are readily available on the market. They are preferred because they have high magnetic properties and because they are particularly strong, i.e., have a high magnetic flux density. Due to the above reasons, applications in intravascular blood pumps require particularly strong magnets. However, in principle, the corrosion-resistant coating of the present invention can be applied to any material that requires corrosion protection, such as different rare-earth iron-boron magnetic materials or any other magnetic material.

[0032] The coating of the present invention is a composite coating provided on the surface of a magnet, i.e., the actual magnetic material. The composite coating comprises a metal layer on the surface of the magnet, optionally a metal oxide layer on the metal layer at its exposed surface, a layer formed from poly(2-chloro-p-xylene), and a linking layer between the metal layer or metal oxide layer and the poly(2-chloro-p-xylene) layer.

[0033] Rare earth metal-based magnets purchased from suppliers are usually protected by a phosphate coating. Before applying the metal layer, this phosphate coating can be removed, for example, by washing with an acid. However, the phosphate coating does not adversely interfere with the coating or coating method according to the present invention and can thus remain on the magnet. Preferably, the phosphate coating is not removed. Not removing the phosphate coating saves a process step and avoids introducing impurities in such a process step. However, it is preferred to clean the magnet before applying the metal layer. The cleaning is preferably carried out by washing the magnet with an organic solvent (such as an alcohol). A particularly preferred cleaner is isopropyl alcohol and a mixture of isopropyl alcohol and ethanol. After washing with the organic solvent, the magnet is dried, for example, in a vacuum or air stream.

[0034] After cleaning and drying, the metal layer is applied to the surface of the magnet. The metal used to form the metal layer is not particularly limited. The term "metal" used herein must be understood to include metal alloys. Suitable for forming the metal layer are any metals (metal alloys) that can form a dense layer and are biocompatible. Similarly, the method of applying the metal layer is not particularly limited. Exemplary coating methods include dry methods, such as physical vapor deposition, especially ion vapor deposition, plasma coating, and atomic layer deposition, and wet methods, such as electrodeposition (ion plating). Plasma deposition and ion vapor deposition are rather fast and cost-effective methods, but it seems that wet deposition produces a metal layer of better quality, i.e., a metal layer with enhanced density. However, layers deposited by ion vapor deposition or other dry methods have excellent long-term stability.

[0035] A preferred metal for forming the metal layer is aluminum. The electrodeposition of aluminum from an ionic liquid is carried out in a manner commonly used in the art, for example, by using a mixture of aluminum chloride and 1-ethyl-3-methylimidazolium chloride salt. The aluminum is preferably pure, for example, at least 99% pure, particularly preferably at least 99.9% pure.

[0036] When exposed to air, aluminum forms a passivating oxide layer. This naturally formed (native) oxide layer is only a few nanometers thick and adheres well to the underlying metal. Other metals that form a natural oxide layer are also suitable. Exemplary metals include titanium, tantalum, niobium, zirconium, and alloys of two or more of these metals, for example, aluminum alloys and niobium-titanium alloys. In the present invention, the oxide layer is formed by oxidizing a metal coated on the magnet, which oxidizes automatically when exposed to air or is oxidized artificially, for example, by anodization. In any case, the oxide layer is only a few nanometers thick, for example, about 2 to 5 nm. However, the present invention can also work well without an oxide layer, and biocompatible metals without an oxide layer can be advantageously used. These metals and metal alloys are, for example, noble metals such as platinum and gold.

[0037] The thickness of the metal layer and the combined metal / metal oxide layer is preferably small, i.e., about 20 μm or less. A thickness of 10 μm or less is particularly preferred.

[0038] To enhance the corrosion protection provided by the metal layer or the metal / metal oxide layer, the metal layer or the metal / metal oxide layer is combined with a poly(p-xylene) polymer layer. Poly(p-xylene) polymers are known under the trade name Parylene. Poly-p-xylene can react with a hydroxyl-containing surface and is known to form a pinhole-free coating at low layer thicknesses. In addition, they have a low dielectric constant (about 3), which is advantageous in implantable blood pumps. The composite coating comprising the metal layer or the metal / metal oxide layer and the parylene layer is biocompatible and also provides corrosion protection. However, under the operating conditions in an intravascular blood pump, the adhesion of the parylene layer to the metal layer or the metal oxide layer is insufficient. After an unacceptably short time, the parylene layer begins to delaminate, thus exposing the metal or the metal oxide layer. The metal layer or the metal / metal oxide layer cannot adequately protect the magnet, and thus corrosion of the magnet begins.

[0039] According to the present invention, this is prevented by a combination of two measures: providing an interface layer connecting the metal layer or the metal oxide layer and the parylene layer, and using a specific parylene compound.

[0040] The compound forming the interface layer, i.e., the linking compound, must be bifunctional. Bifunctional means that the linking compound must have two types of functional groups or molecular moieties with different functional groups (reactivity), one functional group or molecular moiety bonding to the metal layer or the metal oxide layer, for example, by reacting with the surface hydroxyl groups of the metal or the metal oxide layer, and the other functional group or molecular moiety bonding to the parylene, thereby firmly connecting the inorganic metal layer or the metal oxide layer and the organic parylene layer. The connection can be provided by a covalent bond or other bonds (e.g., by van der Waals forces).

[0041] Linkers having functional groups or moieties bonded to a metal or metal oxide and functional groups or moieties bonded to parylene are known. As exemplary linkers, silane compounds, thiols, phosphines, disulfides and silanes having thiol, phosphine or disulfide groups can be mentioned. Depending on the metal, different linking compounds are preferred.

[0042] In the case of aluminum, titanium, tantalum, niobium, zirconium and oxides of these metals, the linker for the metal layer and the metal oxide layer is preferably a siloxane, such as methoxysilane and ethoxysilane, for example a silane having the formula (H3CO)3Si-R, where R is, for example, methacrylate, alkylamine, aniline or epoxyalkyl. For bonding to parylene, the linker preferably has acryloxy or methacryloxy functional groups. The carbon chain length between the silyl part and the (meth)acryloxy part of the linker usually has 1-16 carbon atoms (methyl, ethyl, propyl, butyl, pentyl...). The hydrocarbon chain is usually saturated, but may also contain one or more unsaturated bonds. A particularly preferred linker is 3-(trimethoxysilyl)propyl methacrylate (A-174) from Silquest, but other silane compounds such as G-170 (vinyl-functional silane coupling agent) from Silquest are also suitable. Additionally, linkers having bis-trimethoxysilyl or bis-triethoxysilyl functional groups, such as bis(trimethoxysilylethyl)benzene, can be used.

[0043] Particularly for titanium, zirconium and platinum, linkers having hydrogenation functional groups such as trihydrosilane work well. 10-Undecenylsilane and n-octadecylsilane can be specifically mentioned. The silane is preferably coated from the gas phase or an aprotic solution at room temperature. Additionally, the above-mentioned alkoxysilanes having (meth)acryloxy and compounds having bis-trimethoxysilyl or bis-triethoxysilyl functional groups are also suitable.

[0044] Linkers suitable for connecting a parylene layer to a gold layer are usually thiols, phosphines or disulfides, preferably having a longer hydrocarbon chain, such as an alkyl-disulfide or dialkyl-disulfide having an alkyl with 10-16 carbon atoms. Such alkyls form a dense and ordered layer on the metal or metal oxide surface. However, alkyls having only 1 to 9 carbon atoms can also be used.

[0045] Also applicable to the gold layer are silane linker compounds having thiol, phosphine or disulfide groups. Particularly preferred examples are 3-(2-pyridylethyl)thiopropyltrimethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane, 2-(diphenylphosphino)ethyltriethoxysilane, bis(2-methacryloyloxy)ethyl disulfide and bis(hexadecyl) disulfide.

[0046] The bifunctional linker is applied to the metal surface or the metal oxide surface, preferably by a plasma coating process or by plasma-free physical vapor deposition or by applying a non-protic or alcoholic or aqueous solution of the bifunctional linker compound to the metal or metal oxide surface. Drying the applied silane compound in a plasma chamber produces a glassy layer that contains Si-O-Si-O-chains arranged substantially parallel to the metal oxide surface and bonded to the surface by oxygen atoms. The organic residues are away from this surface and can be used to bond parylene. Physical vapor deposition and wet coating form an interfacial layer with a similar structure but without a glassy appearance.

[0047] Plasma deposition produces a dense layer that has acceptable adhesion to parylene. Plasma-free physical vapor deposition produces a less dense layer that has better adhesion to parylene than the plasma-deposited layer. Wet coating produces a very dense monolayer that has an irregular network and a high degree of crosslinking and a high percentage of oxygen bonded to silicon. These layers also adhere very well to the parylene layer. Therefore, wet coating is particularly preferred.

[0048] As an alternative, the plasma coating and physical vapor deposition (without plasma) or wet coating process can be combined, that is, first a glassy interfacial layer is formed by plasma deposition, and then a second linker layer is formed by physical vapor deposition or wet coating, thus forming a composite linker layer. In such a composite linker layer, the silicon atoms of the glass layer are covalently connected to the oxygen atoms of the second layer, and the organic residues (such as methacrylate, alkylamine or epoxyalkyl) of the second layer can be used to bond parylene, either covalently or in a different way, such as by van der Waals forces.

[0049] The thickness of the interfacial layer is generally 20 - 150 nm, preferably 50 - 100 nm.

[0050] Finally, a parylene layer is formed on the interfacial layer, that is, a poly(parylene) polymer layer, and the poly(parylene) polymer has the structural formula

[0051]

[0052] where n is the degree of polymerization.

[0053] The precursor of the poly(parylene) compound is a [2.2]paracyclophane having the following structural formula:

[0054]

[0055] Dimer compounds are commercially available, for example, precursors of Parylene N, Parylene C, Parylene D, and Parylene F. In Parylene N, X and R1 to R4 are all hydrogen. In Parylene C, one of R1 to R4 is chlorine, and the other residues R and X are hydrogen. In Parylene D, two of the residues R1 to R4 are chlorine, and all other residues are hydrogen. In Parylene F, the residue X is fluorine, and the residues R1 to R4 are hydrogen. Poly(parylene) layers are commonly used as moisture barriers and dielectric barriers.

[0056] At a high temperature in a vacuum (above about 500 °C, depending on the specific parylene), the dimer cracks to form the corresponding p-xylylene. The monomers polymerize on the one hand to form a poly(parylene) polymer and bond to the interface layer through their functional groups such as methacrylate groups on the other hand. Alternatively, they can simply adhere to the hydrophobic part of the interface layer.

[0057] According to the present invention, it has been found that Parylene C, in which one of R1 to R4 is chlorine, when used as a covering layer of the composite layer as described above, forms a coating such that the magnetic material is corrosion-resistant under the conditions encountered by an intravascular blood pump. The Parylene C layer is preferably coated by plasma deposition, and the coating thickness is preferably 5 - 20 μm, more preferably 10 - 16 μm.

[0058] When Parylene C is directly coated onto the surface of the magnetic material, crack formation and delamination of the protective Parylene C layer and corrosion of the magnetic material are observed within a few days. Similarly, if Parylene C is coated onto a metal layer or a metal / metal oxide layer, corrosion of the magnetic material due to delamination is observed within an unacceptably short time under the conditions of an intravascular blood pump. In addition, parylene compounds different from Parylene C cannot provide sufficient corrosion protection, even when using an adhesion promoter, for example, if applied to a silane-based interface layer.

[0059] The composite coating of the present invention adheres well to the magnet, and since it has a structure composed of inorganic and organic components, it provides an effective barrier against inorganic and organic substances. In addition, the glassy interface layer also has barrier properties.

[0060] In a particularly preferred embodiment of the present invention, the corrosion protection of the magnetic material is further enhanced by specifically shaping the magnet to allow the formation of a coating covering the magnet with a uniform thickness. For this purpose, the magnet does not have sharp edges, but rather a rounded shape such as a softened edge. Preferably, the magnet is rod-shaped and has a channel extending longitudinally therethrough for receiving the motor shaft of an intravascular blood pump, and the opposite positive end faces of the magnet are beveled towards the channel. The channel does not need to be coated with the composite coating because in an intravascular blood pump, this channel receives the motor shaft and is fixed thereto. Of course, for safety reasons, the channel can be coated.

[0061] The magnet can be a single piece or can be composed of multiple segments. In the latter case, each segment is provided with the coating of the present invention, either with a uniform thickness or completely around it or at least around its exposed surface. Preferably, each segment has a softened edge. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The present invention will be further explained with reference to the accompanying drawings, in which

[0063] Figure 1 is a longitudinal sectional view of an exemplary embodiment of an intravascular blood pump,

[0064] Figure 2 a is a schematic view of an exemplary single-piece magnet according to the present invention,

[0065] Figure 2 b is a partial cross-sectional view showing the details of the magnet shown in Figure 2 a,

[0066] Figure 3 is a schematic top view of an exemplary segmented magnet according to the present invention.

[0067] The drawings are not drawn to scale. They should not be construed as limiting the present invention in any way. DETAILED DESCRIPTION

[0068] The intravascular blood pump 10 shown in Figure 1 has been described above. The pump is conventional in construction but includes a corrosion-resistant permanent magnet 1 according to the present invention. In the pump of Figure 1 , the magnet 1 is rod-shaped and the opposite positive end faces are flat and parallel to each other. Although the composite coating according to the present invention can effectively protect a magnet with sharp edges as shown in Figure 1 from being corroded over a long period of time, in the present invention, a magnet having a shape as shown in Figure 2 and 3 is preferred. The individual layers of the composite coating extend completely over each previously coated composite coating.

[0069] Figure 2a shows a one-piece magnet 1 having a rod shape and a hole or passage extending longitudinally therethrough. During use of the magnet in an intravascular blood pump 10 as shown in Figure 1 the channel receives the motor shaft 25. The opposite positive end faces 4 of the magnet are tapered towards the channel. The magnet 1 is provided with a composite coating according to the present invention at the outer surface 2 exposed to the fluid flowing in the gap 26 and the tapered positive end face 4. The inner surface 3 adjacent to the motor shaft 25 may or may not be coated. The edges 5 at the transition between the outer surface 2 and the front surface 4 and the edges 6 at the transition between the front surface 4 and the inner surface 3 are coated. The edges thereof are softened, thus facilitating the formation of a uniform coating with good adhesion. "N" and "S" represent the north and south poles of the magnet.

[0070] Figure 2 b is a partial cross-sectional view along the Figure 2 dash-dotted line in a. Figure 2 b shows Figure 2 the area within the ring of the magnet in a. Figure 2 b clearly shows the softened edges 5, 6.

[0071] Figure 3 shows a segmented magnet 7. Figure 3 The magnet shown in has four segments 8, 8'. The segments 8 opposite to each other have the same magnetic polarity, as shown by "N" in the top view of Figure 3 and the segments 8' opposite to each other have the same magnetic polarity, indicated by "S" in the top view of Figure 3 . As a result, the adjacent segments 8, 8' have opposite magnetic polarities.

[0072] Similar to Figure 2 the one-piece magnet shown in, the segments 8, 8' have an inner surface, an outer surface, opposite positive end faces, an edge at the transition between the outer surface and the front surface, and an edge at the transition between the front surface and the inner surface. The positive end faces are marked 4', and the edges are denoted 5' and 6' respectively, corresponding to the markings in Figure 2 . Additionally, the segments 8, 8' have side faces 9, 9' which are separated by a gap in the drawing. Of course, when the magnet is in use, the side faces 9, 9' are in contact with each other. All surfaces of each segment of the magnet may be completely covered with the composite coating according to the present invention, but the side faces 9, 9' which are not exposed due to their contact with each other and the inner surface which is not exposed due to its contact with the motor shaft do not need to be coated. Preferably, all edges of all segments are softened edges.

[0073] Table 1 shows the corrosion test results of neodymium-iron-boron magnets coated with different coatings. Twelve identical cylindrical non-magnetized Nd2Fe with a length of 12 mm and a diameter of 2.8 mm were coated as described below 14B sintered magnets were subjected to a corrosion test in an aqueous solution of 0.9 wt% sodium chloride at 60 °C. The test samples were inspected daily until the 60th day and then once a week. Corrosion of the magnetic material results in the lifting or deformation of the coating. Therefore, the lifting or formation of protrusions on the surface of the test sample indicates corrosion of the magnetic material. The formation of protrusions with a height of 0.1 mm and the lifting of the coating were determined as indicators of magnet failure.

[0074] The test specimens were prepared in the following manner:

[0075] All specimens: The unmagnetized neodymium-iron-boron magnets (purchased, with phosphate passivator) were cleaned with isopropyl alcohol and then dried in an air stream. Then, the coating was applied, and after applying the coating, the coated magnet was magnetized in a magnetic field. It is not appropriate to magnetize the magnet before applying the composite coating of the present invention. Where applicable, the coating thickness of the aluminum layer is about 7 μm, the coating thickness of the silane layer is about 100 nm, and the coating thickness of the parylene layer is about 10 μm.

[0076] Specimens 1 and 2: The dried magnet was coated with aluminum by ion vapor deposition. When exposed to air, an aluminum oxide layer (natural aluminum oxide layer) was formed. Then, Parylene C was plasma-coated thereon.

[0077] Specimens 3 and 4: The dried magnet was coated with aluminum by ion vapor deposition. When exposed to air, a natural aluminum oxide layer was formed at the exposed surface of the aluminum layer. No further coating was applied.

[0078] Specimen 5: The dried magnet was coated with aluminum by ion vapor deposition. When exposed to air, a natural aluminum oxide layer was formed. Then, 3-(trimethoxysilyl)propyl methacrylate (silane A-174) was applied by plasma coating, and subsequently Parylene F was applied by plasma coating.

[0079] Specimens 6 and 7: The dried magnet was coated with aluminum by ion vapor deposition. When exposed to air, a natural aluminum oxide layer was formed. Then, an ethanol solution containing silane A-174 (water / ethanol; acetic acid to reach a pH of about 5 to 6; silane concentration of about 1%; reaction time of about 5 minutes) was applied and the ethanol was evaporated. Finally, Parylene C was applied by plasma coating.

[0080] Specimen 8: The dried magnet was coated with aluminum by ion vapor deposition. When exposed to air, a natural aluminum oxide layer was formed. Then, silane A-174 was applied by plasma coating, and subsequently Parylene C was applied by plasma coating.

[0081] The ion vapor deposition of Specimens 1 to 8 was carried out at about 10 -3It is carried out in argon at mbar with a potential of about 1000 volts and 1500 amperes DC. Generally, about 400 to 1000 volts and about 500 to 1500 amperes DC are suitable.

[0082] Specimens 9 and 10: A copolymer of ethylene and chlorotrifluoroethylene was coated on the dried magnet by spraying. The coated magnet was baked and then cooled.

[0083] Specimens 11 and 12: The dried magnet was sprayed with polyphenylene sulfide resin and baked at 135 °C for 30 minutes.

[0084] Table 1

[0085]

[0086]

[0087] Test results of Nd2Fe 14 B magnets

[0088] When the coating lift or buckling reaches 0.1 mm, the magnet fails.

[0089] When the time until failure is at least 6 months (1 month = 30 days), the magnet passes the test.

[0090] When passing the test, that is, when the time until failure is at least 180 days, the magnet is corrosion-resistant in terms of the present invention.

[0091] Specimen samples 9, 10, 11, and 12 each had a resin coating directly coated onto the neodymium iron boron magnet according to the prior art and failed in less than 3 days in a sodium chloride solution at 60 °C. Specimen samples 1 to 5 with a protective aluminum / aluminum oxide layer were used for a longer time. Specimen samples 3 and 4 were protected from corrosion by the aluminum / aluminum oxide layer without any additional protective layer and failed in less than 1 month. The same results were obtained when a coating consisting of Parylene C was directly coated onto the aluminum oxide layer, i.e., without a silane-based interface layer (specimen samples 1 and 2). Additionally, the same results were achieved when there was a silane-based interface layer between the aluminum oxide layer and the parylene layer but the parylene layer was not composed of Parylene C (specimen sample 5).

[0092] Specimen sample 8 has substantially the same coating composition as specimen sample 5 and the individual layers of the composite coating are applied in the same manner. However, Parylene C is used in specimen sample 8 instead of Parylene F of specimen sample 5. Surprisingly, this slight change results in specimen sample 8 not failing even after 6 months, while specimen sample 5 failed in less than 1 month.

[0093] The coating compositions of specimen samples 6 and 7 are the same as that of specimen sample 8. However, in specimen sample 8, the interface layer is applied by plasma coating, while wet coating is used for the interface layer in specimen samples 6 and 7. As a result, specimen samples 6 and 7 still showed no signs of corrosion when the testing was stopped after one year, while specimen sample 8 could not be used in the corrosive environment for 12 months.

[0094] The above test results clearly show that a neodymium iron boron permanent magnet with a composite coating (the composite coating includes a metal layer, a connecting layer, and an outer layer formed of poly(2-chloro-p-xylene)) has excellent corrosion resistance even in an aggressive environment, and the permanent magnet can be advantageously used in an intravascular blood pump.

[0095] The test results also show that the coating method of the connecting layer affects the corrosion resistance. When the connecting layer is applied by wet coating, particularly excellent corrosion resistance is achieved.

[0096] To achieve optimal corrosion protection, it is recommended to apply the composite coating of the present invention to a non-magnetized magnet and magnetize the magnet only after the coating is applied.

[0097] Specimen samples 6, 7, and 8 simultaneously meet the above two conditions. A non-magnetized magnet is coated with the composite coating of the present invention and magnetized after the complete composite coating is applied. As a result, specimen samples 6, 7, and 8 showed no coating lifting and the buckling was less than 0.1 mm when immersed in a 0.9 wt% NaCl solution at 60 °C for at least 180 days. Therefore, specimen samples 6, 7, and 8 are corrosion-resistant magnets.

Claims

1. A corrosion-resistant permanent magnet, comprising - a magnet, and - a composite coating provided on and covering the surface of the magnet, the composite coating comprising (a) a metal layer on the magnet, (b) a connecting layer on the metal layer, wherein the binder forming the connecting layer is a bifunctional compound, and (c) a layer formed of poly(2-chloro-p-xylene) on the connecting layer.

2. A corrosion-resistant permanent magnet, comprising - a magnet, and - a composite coating provided on and covering the surface of the magnet, the composite coating comprising (a) a metal layer on the magnet, (b) a metal oxide layer on the surface of the metal layer facing away from the magnet, wherein the metal oxide layer is formed by oxidation of the metal layer, (c) a connecting layer on the metal oxide layer, wherein the binder forming the connecting layer is a bifunctional compound, and the connecting layer is formed by wet coating, and (d) a layer formed of poly(2-chloro-p-xylene) on the connecting layer.

3. The corrosion-resistant permanent magnet according to claim 1, wherein the bifunctional compound has a molecular moiety bonded to the metal layer and another molecular moiety bonded to poly(2-chloro-p-xylene).

4. The corrosion-resistant permanent magnet according to claim 3, wherein, The molecular moiety bonded to the metal layer is a functional group.

5. The corrosion-resistant permanent magnet according to claim 2, wherein the bifunctional compound has a molecular moiety bonded to the metal oxide layer and another molecular moiety bonded to poly(2-chloro-p-xylene).

6. The corrosion-resistant permanent magnet according to claim 5, wherein, The molecular moiety bonded to the metal oxide layer is a functional group.

7. The corrosion-resistant permanent magnet according to claim 3 or 5, wherein, The other molecular moiety bonded to poly(2-chloro-p-xylene) is a functional group.

8. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the magnet is a sintered magnet.

9. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the magnet is based on rare earth metals.

10. The corrosion-resistant permanent magnet according to claim 9, wherein the rare earth metal is neodymium.

11. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the magnet is a rare earth metal iron boron permanent magnet.

12. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the magnet is a sintered magnet having Nd2Fe 14 B crystals and a neodymium iron boron material surrounding the Nd2Fe 14 B crystals, the neodymium iron boron material being richer in neodymium than the Nd2Fe 14 B crystals.

13. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein, The magnet is rod-shaped with all edges rounded.

14. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the binder forming the connecting layer is selected from silanes, thiols, phosphines, disulfides.

15. The corrosion-resistant permanent magnet according to claim 14, wherein the silane has a thiol, phosphine or disulfide group.

16. The corrosion-resistant permanent magnet according to claim 14, wherein the silane is selected from trimethoxysilanes and triethoxysilanes having acryloyloxy or methacryloyloxy functional groups, or a binder having a bis-trimethoxysilyl functional group.

17. The corrosion-resistant permanent magnet according to claim 14, wherein the silane has a hydride functional group.

18. The corrosion-resistant permanent magnet according to claim 13, wherein the coupling agent is selected from 3-(2-pyridylethyl) thiopropyltrimethoxysilane, 3-(4-pyridylethyl) thiopropyltrimethoxysilane, 2-(diphenylphosphino) ethyltriethoxysilane, bis(2-methacryloyloxy) ethyldisulfide, and bishexadecyldisulfide.

19. The corrosion-resistant permanent magnet according to claim 1, wherein the metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, platinum, gold, and alloys of aluminum, titanium, tantalum, niobium, and zirconium.

20. The corrosion-resistant permanent magnet according to claim 2, wherein the metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, and their alloys, and the surface of the metal layer facing away from the magnet is covered by an oxide layer formed by oxidation of the metal or metal alloy.

21. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the metal of the metal layer is selected from platinum, titanium, and zirconium.

22. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the metal of the metal layer is gold.

23. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein all layers of the composite coating completely extend to cover all surfaces of the magnet.

24. The corrosion-resistant permanent magnet according to claim 1, wherein the thickness of the metal layer is in the range of 5 μm to 20 μm.

25. The corrosion-resistant permanent magnet according to claim 2, wherein the combined thickness of the metal layer and the metal oxide layer is in the range of 5 μm to 20 μm.

26. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the thickness of the coupling layer is in the range of 20 nm to 150 nm.

27. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the thickness of the layer formed of poly(2-chloro-p-xylene) is in the range of 5 μm to 20 μm.

28. The corrosion-resistant permanent magnet according to claim 1 or 2, wherein the thickness of the composite coating is not greater than 200 μm.

29. The corrosion-resistant permanent magnet according to claim 28, wherein the thickness of the composite coating is not greater than 50 μm.

30. A method for producing a corrosion-resistant permanent magnet, the method comprising: - providing a magnet, - forming a metal layer on the surface of the magnet, - forming a coupling layer on the metal layer, and - forming a poly(2-chloro-p-xylene) layer on the coupling layer.

31. The method according to claim 30, wherein the magnet is a sintered magnet having Nd2Fe 14 B crystals and a neodymium iron boron material surrounding the Nd2Fe 14 B crystals, the neodymium iron boron material being richer in neodymium than the Nd2Fe 14 B crystals.

32. The method according to claim 30 or 31, wherein the metal is coated by ion vapor deposition or plasma deposition or atomic layer deposition to form the metal layer.

33. The method according to claim 30 or 31, wherein the metal is coated by electroplating deposition from an ionic liquid to form the metal layer.

34. The method according to claim 30 or 31, wherein the metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, platinum, gold, and alloys of aluminum, titanium, tantalum, niobium, and zirconium.

35. The method according to claim 30 or 31, wherein the connection layer is formed by physical vapor deposition using plasma to coat the connector, or by physical vapor deposition without using plasma, or by wet method, or by a combination thereof.

36. The method according to claim 35, wherein the connector for forming the connection layer is selected from silanes, thiols, phosphines, and disulfides.

37. The method according to claim 36, wherein the silane has a thiol, phosphine, or disulfide group.

38. The method according to claim 30 or 31, wherein the poly(2-chloro-p-xylene) layer is formed by plasma deposition of dichloro[2.2]paracyclophane.

39. The method according to claim 30 or 31, wherein the thickness of the metal layer is in the range of 5 μm to 20 μm, and / or the thickness of the connection layer is in the range of 20 nm to 150 nm, and / or the thickness of the layer formed of poly(2-chloro-p-xylene) is in the range of 5 μm to 20 μm, and / or the thickness of all the layers formed on the magnet is not greater than 200 μm.

40. A method for producing a corrosion-resistant permanent magnet, the method comprising: - providing a magnet, - forming a metal layer on the surface of the magnet, - forming a metal oxide layer on the surface of the metal layer facing away from the magnet by oxidation of the metal layer, - forming a connection layer on the metal oxide layer by wet coating, and - forming a poly(2-chloro-p-xylene) layer on the connection layer.

41. The method according to claim 40, wherein the magnet is a sintered magnet having Nd2Fe 14 B crystals and a neodymium iron boron material surrounding the Nd2Fe 14 B crystals, the neodymium iron boron material being richer in neodymium than the Nd2Fe 14 B crystals.

42. The method according to claim 40 or 41, wherein the metal is coated by ion vapor deposition or plasma deposition or atomic layer deposition to form the metal layer.

43. The method according to claim 40 or 41, wherein the metal is coated by electroplating deposition from an ionic liquid to form the metal layer.

44. The method according to claim 40 or 41, wherein the metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, and their alloys, and the surface of the metal layer facing away from the magnet is covered by an oxide layer formed by oxidation of the metal or metal alloy.

45. The method according to claim 40 or 41, wherein the connector for forming the connection layer is selected from silanes, thiols, phosphines, and disulfides.

46. The method according to claim 45, wherein the silane has a thiol, phosphine, or disulfide group.

47. The method according to claim 40 or 41, wherein the poly(2-chloro-p-xylene) layer is formed by plasma deposition of dichloro[2.2]paracyclophane.

48. The method according to claim 40 or 41, wherein the combined thickness of the metal layer and the metal oxide layer is in the range of 5 μm to 20 μm, and / or the thickness of the connection layer is in the range of 20 nm to 150 nm, and / or the thickness of the layer formed of poly(2-chloro-p-xylene) is in the range of 5 μm to 20 μm, and / or the thickness of all the layers formed on the magnet is not greater than 200 μm.

49. A corrosion-resistant permanent magnet, comprising - a magnet in the state as purchased from a supplier, and - a composite coating provided on and covering the surface of the magnet, the composite coating comprising (a) a metal layer on the magnet, (b) a metal oxide layer on the surface of the metal layer facing away from the magnet, wherein the metal oxide layer is formed by oxidation of the metal layer, (c) a connection layer on the metal oxide layer, and the connection layer is formed by wet coating, and (d) a layer formed of poly(2-chloro-p-xylene) on the connection layer.

50. A corrosion-resistant permanent magnet, comprising - a magnet, and - a composite coating provided on and covering the surface of the magnet, the composite coating having a uniform thickness and comprising (a) a metal layer on the magnet, (b) a connection layer on the metal layer, and (c) a layer formed of poly(2-chloro-p-xylene) on the connection layer.

51. A corrosion-resistant permanent magnet, comprising - a magnet, and - a composite coating provided on and covering the surface of the magnet, the composite coating having a uniform thickness and comprising (a) a metal layer on the magnet, (b) a metal oxide layer on the surface of the metal layer facing away from the magnet, wherein the metal oxide layer is formed by oxidation of the metal layer, (c) A connection layer on the metal oxide layer, wherein, the connection layer is formed by wet coating, and (d) a layer formed of poly(2-chloro-p-xylene) on the connection layer.

52. A corrosion-resistant permanent magnet, comprising - a magnet, and - a composite coating provided on and covering the surface of the magnet, the composite coating comprising (a) a metal layer on the magnet, (b) a metal oxide layer on the surface of the metal layer facing away from the magnet, the metal oxide of the metal oxide layer being a natural oxide, and the metal oxide layer is formed by oxidation of the metal layer, (c) A connection layer on the metal oxide layer, wherein, the connection layer is formed by wet coating, and (d) a layer formed of poly(2-chloro-p-xylene) on the connection layer.

53. A method for producing a corrosion-resistant permanent magnet, the method comprising: - providing an unmagnetized magnet, - washing the magnet with an organic solvent, - forming a metal layer on the surface of the magnet, - forming a connection layer on the metal layer, - forming a poly(2-chloro-p-xylene) layer on the connection layer, and - magnetizing the magnet.

54. A method for producing a corrosion-resistant permanent magnet, the method comprising: - providing an unmagnetized magnet, - washing the magnet with an organic solvent, - forming a metal layer on the surface of the magnet, - forming a metal oxide layer on the surface of the metal layer facing away from the magnet by oxidation of the metal layer, - forming a connection layer on the metal oxide layer by wet coating, - forming a poly(2-chloro-p-xylene) layer on the connection layer, and - magnetizing the magnet.

55. A method for producing a corrosion-resistant permanent magnet, the method comprising: - providing an unmagnetized magnet, - forming a metal layer on the surface of the magnet, - forming a metal oxide layer by exposing the metal layer to air, - forming a connection layer on the metal oxide layer by wet coating, - A poly(2-chloro-para-xylene) layer is formed on the connection layer, and - The magnet is magnetized.

56. An intravascular blood pump, comprising an electric motor, wherein the electric motor comprises a corrosion-resistant permanent magnet according to any one of claims 1 to 29 or 49 to 52.

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