INTRAVASCULAR BLOOD PUMP COMPRISING CORROSION RESISTANT PERMANENT MAGNET

Abstract

This invention is directed to a corrosion resistant permanent magnet, to a method for producing a corrosion resistant permanent magnet, and to an intravascular blood pump comprising the magnet. The magnet is corrosion resistant due to a composite coating comprising a metal layer, optionally a metal oxide layer, a layer formed from poly(2-chloro-p-xylylene), and a linker layer between the metal oxide layer and the poly(2-chloro-p-xylylene) layer.

Claims

1.-30. (canceled)

31. An intravascular blood pump comprising: a motor section; and a pump section connected to the motor section, wherein the motor section comprises an electric motor, wherein the electric motor comprises a permanent magnet comprising: a magnet body; and a composite coating provided on and covering surfaces of the magnet body, the composite coating comprising: a metal layer on the magnet body, optionally a metal oxide layer on the metal layer at the surface facing away from the magnet body, a linker layer on the metal layer or the metal oxide layer, and a layer formed from poly(2-chloro-p-xylylene) on the linker layer.

32. The intravascular blood pump of claim 31, wherein the magnet body is a sintered magnet body.

33. The intravascular blood pump of claim 31, wherein the magnet body comprises a rare earth metal.

34. The intravascular blood pump of claim 33, wherein the rare earth metal is neodymium.

35. The intravascular blood pump of claim 31, wherein the magnet body is a rare earth metal iron boron permanent magnet.

36. The intravascular blood pump of claim 35, wherein the magnet body is a sintered magnet body having Nd2Fe.sub.14B crystals and a neodymium iron boron material surrounding the Nd2Fe.sub.14B crystals, the neodymium iron boron material being richer in neodymium than the Nd2Fe.sub.14B crystals.

37. The intravascular blood pump of claim 31, wherein the magnet body is rod-shaped with all edges being rounded.

38. The intravascular blood pump of claim 31, wherein a linker forming the linker layer is selected from silanes, mercaptans, phosphines, disulfides, and silanes having a thiol, phosphine or disulfide group.

39. The intravascular blood pump of claim 38, wherein the silanes are selected from trimethoxysilanes and triethoxysilanes having an acryloyloxy or methacryloyloxy functional group and linker having bis-trimethoxysilyl or bis-triethoxysilyl functional group.

40. The intravascular blood pump of claim 38, wherein the silanes comprise a hydride functional group.

41. The intravascular blood pump of claim 38, wherein the linker is selected from 3-(2-pyridylethyl)thiopropyl trimethoxysilane, 3-(4-pyridylethyl)thiopropyl trimethoxysilane, 2-(diphenylphosphino)ethyl triethoxysilane, bis(2-methacryloyl)oxyethyldisulfide, and dihexadecyldisulfide.

42. The intravascular blood pump of claim 31, wherein a metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium, platinum, gold, and a metal alloy comprising at least one of: aluminum, titanium, tantalum, niobium, and zirconium.

43. The intravascular blood pump of claim 31, wherein a metal of the metal layer is selected from aluminum, titanium, tantalum, niobium, zirconium and a metal alloy thereof, and a surface of the metal layer facing away from the magnet body is covered by an oxide layer formed by oxidation of the metal or the metal alloy.

44. The intravascular blood pump of claim 31, wherein a metal of the metal layer is selected from platinum, titanium, and zirconium.

45. The intravascular blood pump of claim 31, wherein a metal of the metal layer is gold.

46. The intravascular blood pump of claim 31, wherein the composite coating completely extends over all surfaces of the magnet body.

47. The intravascular blood pump of claim 31, wherein a thickness of the metal layer or a combined thicknesses of the metal layer and the metal oxide layer is in a range from 5 μm to 20 μm.

48. The intravascular blood pump of claim 31, wherein a thickness of the linker layer is in a range from 20 nm to 150 nm.

49. The intravascular blood pump of claim 31, wherein a thickness of the layer formed from poly(2-chloro-p-xylylene) is in a range from 5 μm to 20 μm.

50. The intravascular blood pump of claim 31, wherein a thickness of the composite coating is no more than 200 μm.

51. The intravascular blood pump of claim 31, wherein a thickness of the composite coating is no more than 50 μm.

52. The intravascular blood pump of claim 31, wherein the permanent magnet is a corrosion resistant permanent magnet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will be further explained with reference to the accompanying drawings, wherein

[0061] FIG. 1 is a schematic longitudinal section of an exemplary embodiment of an intra-vascular blood pump,

[0062] FIG. 2A is a schematic representation of an exemplary single-piece magnet according to the present invention,

[0063] FIG. 2B is a partial sectional view showing a detail of the magnet illustrated in FIG. 2A, and

[0064] FIG. 3 is a schematic top view of an exemplary segmented magnet according to the present invention.

[0065] The drawings are not to scale. They should not be construed as limiting the invention in any manner.

DETAILED DESCRIPTION

[0066] The intravascular blood pump 10 illustrated in FIG. 1 has been described above. The pump is conventional in construction, but comprises a corrosion resistant permanent magnet 1 according to the present invention. In the pump of FIG. 1, the magnet 1 is rod-shaped, the opposing front faces being flat and parallel to each other. While the composite coating according to the present invention may effectively protect a mag-net body having sharp edges as illustrated in FIG. 1 against corrosion over an extended period of time, it is preferred in the present invention to use a magnet body having a shape as illustrated in FIGS. 2A and 3. The individual layers of the composite coating completely extend over each previously applied composite coating layer.

[0067] FIG. 2A shows a single-piece magnet 1 having a rod shape and a bore or channel extending therethrough in a longitudinal direction. During use of the magnet in an intravascular blood pump 10 as illustrated in FIG. 1, the channel receives the motor shaft 25. The opposing front faces 4 of the magnet are tapered towards the channel. The magnet 1 is provided with a composite coating according to the invention at the outer surfaces 2 exposed to the fluid flowing in gap 26 and the tapered front faces 4. The inner surfaces 3 adjacent to the motor shaft 25 may or may not be coated. Edge 5 at the transition between the outer surface 2 and the front surface 4, as well as edge 6 at the transition between front surface 4 and the inner surface 3, are coated. The edges are soft, thus facilitating the formation of a well-adhering uniform coating. “N” and “S” indicate the north pole and the south pole of the magnet.

[0068] FIG. 2B is a partial sectional view along the dash-dot line in FIG. 2A. FIG. 2B shows the region of the magnet within the loop in FIG. 2A. FIG. 2B clearly shows the soft edges 5, 6.

[0069] FIG. 3 shows a segmented magnet 7. The magnet illustrated in FIG. 3 has four segments 8, 8′. Segments 8, which are opposite to one another, have the same magnetic polarity, as indicated by “N” in the top view of FIG. 3, and segments 8′, which are also opposite to one another, have the same magnetic polarity, as indicated by “S” in the top view of FIG. 3. As a result, adjacent segments 8, 8′ have opposite magnetic polarity.

[0070] Segments 8, 8′ have, analogously to the single-piece magnet shown in FIG. 2A, inner surfaces, outer surfaces, opposing front faces, edges at the transition between the outer surfaces and the front surfaces, and edges at the transition between the front surfaces and the inner surfaces. Front faces are designated 4′, and the edges are designated 5′ and 6′, respectively, in correspondence to the designations in FIG. 2A. In addition, segments 8, 8′ have side surfaces 9, 9′, separated by gaps in the drawing. Of course, when the magnet is in use, side surfaces 9, 9′ contact each other. All sur-faces of each segment of the magnet may be completely covered by the inventive composite coating, but side surfaces 9, 9′ which are not exposed because they con-tact each other, and the inner surfaces which are not exposed because they contact the motor shaft, do not need to be coated. Preferably all edges of all segments are soft edges.

[0071] Table 1 illustrates the results of corrosion testing of niobium iron boron magnets coated with different coatings. Twelve identical cylindrical non-magnetized Nd2Fe.sub.14B sintered magnet bodies having a length of 12 mm and a diameter of 2.8 mm were coated as described below, and subjected to corrosion testing in an aqueous solution containing 0.9 weight % sodium chloride at 60° C. Test specimens were inspect-ed daily until day 60, and thereafter inspected once a week. Corrosion of the magnetic material results in lifting or deformation of the coating. Thus, lifting of the coating or formation of a bulge at a surface of a test specimen indicates corrosion of the magnetic material. Formation of a bulge having a height of 0.1 mm as well as lifting of the coating were defined as being indicative of magnet failure.

[0072] Test specimens were prepared in the following manner:

[0073] All specimens: Non-magnetized neodymium iron boron magnet bodies (with phosphate passivation as purchased) were cleaned with isopropanol and then dried in an air stream. Then, coatings were applied, and after application of the coatings, the coated magnets were subjected to magnetization in a magnetic field. Magnetizing the magnet bodies before applying the inventive composite coating is not appropriate. Coating thicknesses were about 7 μm for the aluminum layer, about 100 nm for the silane layer, and about 10 μm for the Parylene layer, where applicable.

[0074] Specimens 1 and 2: the dry magnet bodies were coated with aluminum by ion vapor deposition. Upon exposure to air, an aluminum oxide layer (native aluminum oxide layer) formed. Then, Parylene C was plasma coated thereon.

[0075] Specimens 3 and 4: the dry magnet bodies were coated with aluminum by ion vapor deposition. Upon exposure to air, a native aluminum oxide layer formed at the exposed surface of the aluminum layer. No further coating was applied.

[0076] Specimen 5: the dry magnet body was coated with aluminum by ion vapor deposition. Upon exposure to air, a native aluminum oxide layer formed. Then, 3-(trimethoxysilyl)propyl methacrylate (silane A-174) was applied by plasma coating, followed by application of Parylene F by plasma coating.

[0077] Specimens 6 and 7: the dry magnet bodies were coated with aluminum by ion vapor deposition. Upon exposure to air, a native aluminum oxide layer formed. Then, an alcoholic solution (water/ethanol; acetic acid to achieve a pH of about 5 to 6; concentration of silane about 1%; reaction time about 5 minutes) containing silane A-174 was applied, and the alcohol evaporated. Finally, Parylene C was applied by plasma coating.

[0078] Specimen 8: the dry magnet body was coated with aluminum by ion vapor deposition. Upon exposure to air, a native aluminum oxide layer formed. Then, silane A-174 was applied by plasma coating, followed by application of Parylene C by plasma coating.

[0079] Ion vapor deposition for specimen 1 to 8 was performed in argon gas at about 10-.sup.3 mbar at a potential of about 1000 volts and 1500 amperes DC. Generally, from about 400 to 1000 volts and from about 500 to 1500 amperes DC are suitable.

[0080] Specimens 9 and 10: the dry magnet bodies were coated with a copolymer of ethylene and chlorotrifluoroethylene by spray coating. The coated magnets were subjected to baking, and then cooled.

[0081] Specimens 11 and 12: the dry magnet bodies were spray coated with polyphenylene sulfide resin and baked at 135° C. for thirty minutes.

TABLE-US-00001 TABLE 1 Time t until failure Specimen # 3 days ≤ t < 1 invention comparative t < 3 days month t ≥ 6 months 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x 10 x 11 x 12 x Test results of coated Nd.sub.2Fe.sub.14B magnets in 0 9% NaCl solution at 60° C. Magnet fails when coating lifts or buckling reaches 0.1 mm Magnets pass the test when time until failure is at least 6 months (1 month = 30 days) A magnet is corrosion resistant in terms of this invention when it passes the test, i.e., time until failure is at least 180 days

[0082] Specimen samples 9, 10, 11, and 12, each having a resin coating according to the state of the art directly applied to the neodymium iron boron magnet body, failed within less than 3 days in sodium chloride solution at 60° C. Specimen samples 1 to 5 comprising protective aluminum/aluminum oxide layers survived for a longer time. Specimen samples 3 and 4 which were corrosion protected by aluminum/aluminum oxide layers without any additional protective layers failed within less than 1 month. The same result was achieved when a coating consisting of Parylene C was applied directly onto the aluminum oxide layer, i.e., without a silane-based interface layer (specimen samples 1 and 2). Additionally, the same result was achieved when a silane-based interface layer was present between the aluminum oxide layer and the Parylene layer, but the Parylene layer did not consist of Parylene C (specimen sample 5).

[0083] Specimen sample 8 had essentially the same coating composition as specimen sample 5, and the individual layers of the composite coating were applied in the same manner. However, in specimen sample 8 Parylene C was used rather than the Parylene F of specimen sample 5. Surprisingly, this slight modification had the consequence that specimen sample 8 did not fail even after 6 months, while specimen sample 5 already failed within less than 1 month.

[0084] The coating compositions of specimen samples 6 and 7 were identical to the coating composition of specimen sample 8. However, in specimen sample 8 the interface layer was applied by plasma coating, while in specimen samples 6 and 7 a wet process was used for applying the interface layer. As a result, specimen samples 6 and 7 were still without any sign of corrosion when the test was stopped after one year, while specimen sample 8 did not survive twelve months in a corrosive environment.

[0085] The above test results provide a clear indication that a neodymium iron boron permanent magnet having a composite coating comprising a metal layer, a linker layer and an outer layer formed from poly(2-chloro-p-xylylene) has excellent corrosion resistance even under aggressive conditions, and may be advantageously used in an intravascular blood pump.

[0086] The test results also indicate that the application method of the linker layer influences the corrosion resistance. A particularly excellent corrosion resistance was achieved when the linker layer was applied by a wet process.

[0087] In order to achieve optimum corrosion protection, it is advisable to apply the inventive composite coating to the non-magnetized magnet bodies, and to magnetize the magnet bodies only after the coating is applied.

[0088] Specimen samples 6, 7 and 8 fulfilled both the above conditions. Non-magnetized magnet bodies were coated with the inventive composite coating, and magnetized after application of the complete composite coating. As a result, specimen samples 6, 7 and 8 did not show any coating lifting, and buckling was less than 0.1 mm in 0.9 weight % NaCl solution at 60° C. for at least 180 days. Therefore, specimen samples 6, 7 and 8 are corrosion resistant magnets.