Patent ID: 12196210

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG.1shows a first embodiment of a centrifugal blood pump with a casing1comprising an upper shell2and a lower shell3. The upper shell2as well as the lower shell3each have a circular recess4accommodating a set of six electromagnetic coils5therein. The number of coils can be different and is preferably dividable by three. The coils5do not have any ferromagnetic core. Preferably, they have an oval shape and may alternatively have a trapezoidal shape, so as to fully exploit the available space within the recess4. The coils5are encapsulated in a polymer matrix directly on a very thin circular ceramic plate6having a thickness of only about 100 μm. The ceramic plate6has a central hole7constituting a blood flow inlet through which blood can enter the blood pump when the blood pump is appropriately connected e.g. to the apex of the left ventricle. The blood will exit the blood pump through the blood flow outlet21. The ceramic plate6with the electromagnetic coils5mounted thereon together form a unitary coil assembly.

FIG.2shows the blood pump ofFIG.1without the coil assembly5,6. As can be seen, the recess4in the upper shell2of the pump casing1has a ledge8on which the ceramic plate6rests. The ledge8defines a step or further recess within the recess4, within which the impeller9is accommodated so that it can rotate about a central axis of the pump casing1. The impeller9comprises an upper magnetic disc10and a lower magnetic disc (not shown) and further a blade rotor11sandwiched between the two magnetic discs10. The upper and lower surfaces of the impeller9and the axially inner surfaces of the upper and lower ceramic plates6of the two coil assemblies define a limited axial clearance within which the impeller9is freely axially movable. The radially outer circumference of the impeller9together with the lower inner surface of the stepped recess4define a radial clearance within which the impeller9is freely radially movable.

The lower wall12of the recess4limiting the radial clearance for the impeller9can be seen better inFIG.3. The wall12is free-standing and has through openings13through which blood being radially propelled by the impeller can pass into a ring diffuser20(FIG.4) arranged peripherally of the wall12. Instead of the wall12having through openings13, the wall may alternatively be composed of axially extending, spaced apart wall sections providing through openings therebetween.

The wall12is further provided with pockets14which are configured to enhance a hydrodynamic radial bearing effect on the impeller9, when the impeller rotates about the pump casing's central axis. In the wall sections of the pockets14, the radial clearance defined between the impeller's9outer circumference and the inner surface of the wall12radially converges, as seen in the direction of rotation of the impeller, which is indicated inFIG.3by an arrow.

FIG.4shows the lower shell3with the blade rotor11, the upper and lower magnetic discs10of the impeller9being removed. As can be seen, the blade rotor11has three radially extending blades15held together by a central circular ring16and two upper and lower circumferential rings17,18. Passages19are defined between the blades15for blood to flow radially from a blood flow inlet, corresponding to the central hole7, to the ring diffuser20arranged peripherally of the blade rotor11and further to a blood flow outlet21of the pump casing. Upon rotation of the impeller9, the upper and lower circumferential rings17,18will slide along the wall12, namely above and below the wall's12through openings13, whereas the radially outer surfaces22of the blade15and the passages19defined there-between will pass along the through openings13of the wall12(seeFIG.3). The distances between two adjacent through openings13in the wall12(or between corresponding axially extending wall sections) are dimensioned so that they are smaller than all distances between the radially outer ends of the blades15of the blade rotor11. In this way, pulsation of the blood flow through the impeller9can be avoided, as the blood flow passages of the impeller are always open in a radially outward direction.

FIG.5shows an alternative upper shell2′ which differs from the upper shell2inFIG.3in that it has a larger number of through openings13and, more importantly, the inner surface of the wall12lacks pockets14. A hydrodynamic radial bearing will nevertheless be established once the impeller9is set rotating. Alternatively (not shown), the wall12may be divided into an upper circular wall section forming part of the upper shell2and a lower circular wall section of the lower shell3, each wall section preferably being provided with the afore-mentioned pockets14, a continuous circular through opening13being formed between the two circular wall sections.

FIG.6shows the lower shell3of the pump casing1with only the lower coil assembly5,6positioned in a recess (not shown) of the lower shell3. The central opening7in the coil assembly5,6can be provided on one or both coil assemblies, thus allowing axial blood inflow from only one side or on both sides of the impeller.

FIG.7shows a cross-sectional view of the blood pump described above with all elements accordingly numbered. As can be seen, the upper and lower coil assemblies5,6are identical in size and structure. The lower ceramic plate6can be supported on the free end of the wall12of the upper shell2. The blade rotor11of the impeller9carrying a magnetic disc10on each side, as shown in the cross-sectional view inFIG.7, is cut at one side through a blade15and at the other side through a passage19defined between two blades15. As further becomes apparent from the cross-sectional view inFIG.7, the cross section of the ring diffuser20increases in the circumferential direction of the blood pump in this embodiment.

Upon rotation of the impeller9, blood flows radially through the passages19and also above and below the impeller's9magnetic discs10between the discs10and the ceramic plates6. Their mutual contact surfaces are planar. Alternatively, one or both of these surfaces may have ramps extending in a circumferential direction so as to create a hydrodynamic lifting effect on the impeller. Although the lower ceramic plate6is shown as having a central hole, similar to the central hole7of the upper ceramic plate6, the lower ceramic plate6preferably has no central hole but completely seals against blood leakage.

FIG.8shows the blade rotor11separately, including the blades15and their radially outer surfaces22, the through openings13defined between the blades15, the central circular ring16as well as the upper and lower circumferential outer rings17and18connecting the blades15to form an integral piece, which is preferably injection molded. The blades15of the impeller9have an axially extending leading edge23, as seen in the direction of rotation of the impeller, which is curved or tapered in order to enhance the hydrodynamic effect of the radially outer surfaces22and reduce blood damage. The number of blades15can be more than three, e.g. four, five or six. Likewise, the angular extension a of the blades may be larger or smaller than shown inFIG.8. Also, the inner diameter of the blades may be larger or smaller than shown inFIG.8.

FIGS.9,10and11show a first, a second and a third variant of the blade rotor11. The blade rotor11inFIG.9differs from the blade rotor11inFIG.8in that the upper and lower circumferential rings17,18are interrupted. The hydrodynamic radial bearing for the impeller9is achieved with this variant of the blade rotor11mainly by the radially outer surfaces22of the blades15. Alternatively, the magnetic disc10(not shown inFIG.9) may be formed such that it fills the space of the missing sections of the upper and lower circumferential rings17,18. Here, too, it is advantageous if the blades15of the impeller have an axially extending leading edge, as seen in the direction of rotation of the impeller, which is curved or tapered in order to increase the hydrodynamic effect for the hydrodynamic radial bearing of the impeller and in order to reduce blood damage.

FIG.10shows a second variant of the blade rotor11in which the blades15are formed as straight bars, so that the passages19defined between adjacent blades15are accordingly increased.

The blade rotor11inFIG.11is formed from a polymeric washer-like disc having a number of radially extending passages19which may overlap in a central area of the blade rotor11. The radial passages19may have a constant cross section or, as shown at19.1, may have a cross section which increases towards the outer circumference.

In the embodiments described so far and in all variants thereof, the magnetic discs10are magnetized in sections in opposite directions. Each section has a first pole at the upper side of the disc and the respective opposite pole on the lower side of the disc. The number of magnetized sections is preferably eight but may likewise be four or twelve and should be different from the number of coils5. Furthermore, instead of the upper and lower circumferential rings17,18, the radial dimensions of the circular magnetic discs10may be such that the outer circumferential radial surfaces of the magnetic discs replace the upper and lower circumferential rings17,18. In this case, the blades15are interconnected only by the central circular ring16. The advantage is that more magnetic material is present, so that the maximum torque provided by the impeller may accordingly be increased.

FIG.12shows a further variant of an impeller that can be used in connection with the blood pump according to the first embodiment. Here the impeller is entirely made from permanently magnetized ferromagnetic material, i.e. not only the upper and lower magnetic discs10but also the radially extending blades15are magnetic. Again, the blades15have an axially extending leading edge23, as seen in the direction of rotation of the impeller, which is curved or tapered in order to reduce blood damage. To reduce the likelihood of corrosion and increase the hemo-compatibility, the rotor may be encapsulated or shielded by a polymeric or metal housing. The encapsulation can be provided in a polymeric molding process or by galvanic metal deposition.

The blade rotor11may have more than three blades15, and the form of the blades15need not be triangular or trapezoidal or straight.FIG.13schematically shows top views of various blade rotor forms. Among these forms, blade rotors with curved blades are preferred. It is particularly preferred when the leading surface22bof the impeller blades15, as seen in the direction of rotation of the impeller, is convex with respect to its radial extension.

FIG.14shows a first variant of an impeller9of a second embodiment of a blood pump. The pump casing1, upper shell2, lower shell3, recesses4, coil assemblies comprising the coils5and ceramic plates6, wall12or wall sections within the pump casing1, through openings13extending through the wall12or between corresponding wall sections, ring diffuser20and blood flow outlet21in the second embodiment are identical to those of the first embodiment described above. The only difference in the second embodiment is the impeller9, which comprises only one disc10with a central opening7, rather than two magnetic discs10. The disc10in the second embodiment is centrally arranged, as seen in an axial direction, and may or may not be magnetic. The blades15of the impeller9extend axially from both axial sides of the disc10and are formed as magnets or may have magnetic regions. Blood flow passages19are defined between adjacent blades15.

In addition, in a variant of the second embodiment, the wall12or wall sections arranged within the pump casing may be formed as a radially inward extending wall arranged horizontally, so as to form together with the circular radially outer surface of the central disc10the afore-described hydrodynamic radial bearing.

In the first variant of the second embodiment shown inFIG.14, both the blades15and the disc10of the impeller9are made from magnetized material. The borders between adjacent magnetized regions are indicated by dotted lines. The direction of rotation of the impeller9is indicated by an arrow. Here again, the axially extending leading edges of the blades15are rounded or tapered so as to enhance the radial hydrodynamic bearing effect and reduce blood damage. In addition, the horizontal leading edges24of the blades15are also rounded or tapered to enhance the axial hydrodynamic bearing effect and reduce blood damage. Further in addition, although not easy to recognize from the drawing, the upper and lower axial surfaces25of the blades are slightly tapered so as to provide a circumferentially extending ramp to create a hydrodynamic axial force lifting the impeller from the respective adjacent wall (not shown) upon rotation of the impeller. Similarly, as has already been explained in connection with the first embodiment, the radially outer surfaces22of the blades15may likewise change from a smaller radius to a larger radius, as seen in the direction of rotation of the impeller, so as to form, together with the circular wall12or circularly arranged wall sections in the pump casing1, radially converging clearance sections, so as to enhance the radial hydrodynamic bearing effect on the impeller.

FIG.15shows a second variant of the impeller9similar to that shown inFIG.14, except that the disc10and the blades15are composed of two semi-shells26,27within which the magnets are housed. The semi-shells26,27may be injection molded.

FIG.16shows a third variant of the impeller9of the second embodiment, similar to the variant shown inFIG.15. Here, two magnets are housed within each of the blades15, the alternation of the north and south poles of the respective magnets being indicated with N and S. Again, alternatively both the blades15and the disc10may be integrally formed from ferromagnetic material and magnetized in sections, as described above in relation toFIG.14.

Finally, a fourth variant of the impeller9of the second embodiment is shown inFIG.17. This variant is similar to the variant shown inFIG.14, except that the disc10is not necessarily made from a magnetized material. Here the disc10may instead be made of a polymer and has a plurality of circularly arranged axial through openings into which the blades15are inserted so that they extend from one axial side of the disc10to the other axial side thereof.

In all variants of the second embodiment described above, the blades15may have a different axial cross section, similar to one of those schematically shown inFIG.13. However, since only the upper and lower axial surfaces of the blades15contribute to the hydrodynamic axial bearing in the second embodiment, blades15with a large axial cross section are preferred.

FIG.18shows an alternative upper shell2″ which differs from the upper shell2′ inFIG.5in that the free-standing wall12has a greater thickness and the openings13are diverging in a radially outward direction. Alternatively (not shown), the free-standing wall12may be divided into an upper circular wall section forming part of the upper shell2and a lower circular wall section of the lower shell3, a continuous circular through opening being formed between the two circular wall sections. The continuous circular through opening also may have a diverging or increasing cross-section in a radial outward direction. The increasing cross section is illustrated inFIG.19showing a cross sectional view of the wall ofFIG.18in an axial direction. The blood flows in the direction of the arrow. It is noted that, in case a wall with circumferentially spaced apart openings13is provided, the openings preferably also diverge as seen in a radial cross-sectional view. The opening angle is 7° or less in order to avoid detachment of the flow. In this variant the openings13or the circular opening serve as a first diffuser providing a pressure increase, i.e. an additional pump effect. The first diffuser may also stabilize the radial hydrodynamic bearing of the impeller by keeping the pressure along the circumference of the impeller constant. For this purpose, the deceleration of the blood in the first diffuser may either be constant or may vary along the circumference of the circular wall12, for instance by varying the height, width and/or diameter of the openings13and/or the wall thickness (i.e., the length of the openings13).