Abstract:
A blood pump can include a pump housing, an impeller, and a hub. The pump housing can be configured to move blood from an inlet to an outlet thereof. The impeller can be housed in the pump housing, have a plurality of blades joined by a central ring, and be radially supported at the central ring by a bearing. The hub can transmit torque to the impeller using a radial magnetic coupling.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/973,593, which is a continuation of U.S. patent application Ser. No. 12/899,748, filed Oct. 7, 2010, and issued as U.S. Pat. No. 9,227,001, the entirety of each of which is hereby incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to implantable rotary blood pumps. 
       BACKGROUND OF INVENTION 
       [0003]    Some blood pumps mimic the pulsatile flow of the heart and have progressed to designs that are non-pulsatile. Non-pulsatile or continuous flow pumps are typically rotary and propel fluid with impellers that span the spectrum from radial flow centrifugal type impellers to axial flow auger type impellers. 
         [0004]    A common issue encountered by blood pumps is blood damage. The causes of blood damage are mostly attributed to shear stress and heat generated by the bearings supporting the impeller and/or shaft seals of externally driven impellers. Shear stress and/or heat may cause hemolysis, thrombosis, and the like. 
         [0005]    A great deal of effort has been devoted to reducing or eliminating blood damage in rotary blood pumps. One solution to minimizing/eliminating blood damage is to provide total hydrodynamic support of the impeller. For example, ramp, wedge, plain journal, or groove hydrodynamic bearings may be utilized to provide hydrodynamic support in blood pumps. 
         [0006]    Additionally, passive permanent magnetic and active controlled magnetic bearings can be utilized to provide impeller support in blood pumps. Magnetic bearings may be combined with hydrodynamic bearings to provide total impeller support in blood pumps. 
         [0007]    Some blood pumps provide blood flow utilizing a motor that has a shaft mechanically connected to an impeller. Shaft seals may be utilized to separate the motor chamber from the pump chamber. However, shaft seals can fail and generate excess heat allowing blood to enter the motor and/or produce blood clots. Some blood pumps incorporate electric motors into the pumping chamber, rather than providing separate motor and pumping chambers. For example, a stator may be provided in the pump housing and magnets can be incorporated into an impeller to provide a pump impeller that also functions as the rotor of the electric motor. 
         [0008]    Heart pumps that are suitable for adults may call for approximately 5 liters/min of blood flow at 100 mm of Hg pressure, which equates to about 1 watt of hydraulic power. Some implantable continuous flow blood pumps consume significantly more electric power to produce the desired amount of flow and pressure. 
         [0009]    High power consumption makes it impractical to implant a power source in the body. For example, size restrictions of implantable power sources may only allow the implantable power source to provide a few hours of operation. Instead, high power consumption blood pumps may provide a wire connected to the pump that exits the body (i.e. percutaneous) for connection to a power supply that is significantly larger than an implantable power source. These blood pumps may require external power to be provided at all times to operate. In order to provide some mobility, external bulky batteries may be utilized. However, percutaneous wires and external batteries can still restrict the mobility of a person with such a blood pump implant. For example, such high power consumption blood pumps have batteries that frequently require recharging thereby limiting the amount of time the person can be away from a charger or power source, batteries that can be heavy or burdensome thereby restricting mobility, percutaneous wires that are not suitable for prolonged exposure to water submersion (i.e. swimming, bathing, etc.), and/or other additional drawbacks. 
         [0010]    The various embodiments of blood pumps discussed herein may be suitable for use as a ventricular assist device (VAD) or the like because they cause minimal blood damage, are energy efficient, and can be powered by implanted batteries for extended periods of time. Further, these pumps are also beneficial because they may improve the quality of life of a patient with a VAD by reducing restrictions on the patient&#39;s lifestyle. 
       SUMMARY OF THE INVENTION 
       [0011]    The discussion herein provides a description of a high efficiency blood pump that is energy efficient, causes minimal blood damage, and improves quality of life. 
         [0012]    An embodiment of a blood pump includes a pump housing, wherein the pump housing provides an inlet and outlet. The blood pump also includes an impeller housed in the pump housing, wherein the impeller is radially supported by a first hydrodynamic bearing that provides at least one row of flow inducing pattern grooves. 
         [0013]    Another embodiment of a blood pump includes a pump housing, wherein the pump housing provides an inlet and outlet. The blood pump also includes an impeller housed in the pump housing, wherein the impeller is axially supported by a first hydrodynamic bearing that provides at least one row of flow inducing pattern grooves. 
         [0014]    Yet another embodiment of a pump includes a pump housing providing an inlet and outlet and a motor housing, wherein the motor housing houses a motor. The pump also includes an impeller housed in the pump housing that is radially supported by a hydrodynamic bearing that provides at least one row of pattern grooves. The pump also provides a magnetic coupling between the motor and the impeller, wherein the magnetic coupling causes the impeller to rotate when the motor rotates. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a top view of an illustrative embodiment of a pump; 
           [0016]      FIG. 2  is a cross-sectional side view of an illustrative embodiment of a pump; 
           [0017]      FIG. 3  is a cross-sectional top view of an illustrative embodiment of a pump; 
           [0018]      FIG. 4  is a close up cross-sectional view of an area of an illustrative embodiment of a pump; 
           [0019]      FIG. 5  is a cross-sectional view of an illustrative embodiment of an impeller; 
           [0020]      FIG. 6  is a cross-sectional view of an illustrative embodiment of a pump housing; 
           [0021]      FIG. 7  is a cross-sectional view of an illustrative embodiment of a motor housing of a pump; 
           [0022]      FIG. 8  is an isometric view of an illustrative embodiment of an impeller; 
           [0023]      FIG. 9A-9K  are illustrative embodiments of various types of pattern grooves; 
           [0024]      FIG. 10A-10D  are cross-sectional views of various shapes of pattern grooves; 
           [0025]      FIG. 11  is a cross-sectional side view of an illustrative embodiment of a pump with an axial hydrodynamic bearing; 
           [0026]      FIGS. 12A and 12B  are top views of illustrative embodiments of impellers with spiral herringbone grooves and spiral grooves; 
           [0027]      FIG. 13  is a close up cross-sectional view of an area of an illustrative embodiment of a pump with an axial hydrodynamic bearing; 
           [0028]      FIGS. 14A and 14B  are isometric views of illustrative embodiment of impellers with spiral herringbone grooves and spiral grooves; 
           [0029]      FIG. 15  is a cross-sectional side view of an illustrative embodiment of a pump with a conically shaped impeller; 
           [0030]      FIG. 16A-16E  are isometric views of illustrative embodiments of conically shaped impellers; 
           [0031]      FIG. 17  is a close up cross-sectional view of an area of an embodiment of a pump with a conically shaped impeller; 
           [0032]      FIG. 18  is a cross-sectional side view of an illustrative embodiment of a pump with passive magnetic axial bearings; 
           [0033]      FIG. 19  is a cross-sectional top view of an illustrative embodiment of a pump with passive magnetic axial bearings; and 
           [0034]      FIG. 20  is a close up cross-sectional view of an area of an illustrative embodiment of a pump with passive magnetic axial bearings. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
         [0036]    The following detailed description provides an implantable, energy efficient, small, seamless, and magnetically driven blood pump. The blood pump is capable of operating for extended periods of time on a single charge. For example, the energy efficient blood pump may be suitable for use with an implanted rechargeable power source or the like. The pump can be installed pericardially (i.e. near the heart) with less complex surgical procedures. Those skilled in the art will appreciate that the various features discussed below can be combined in various manners, in addition to the embodiments discussed below. The scope of the claims is in no way limited to the specific embodiments discussed herein. 
         [0037]      FIG. 1  is a top view of an illustrative embodiment of pump  10 . Pump  10  is formed from pump housing  15  providing inlet  20  and outlet  25  and motor housing  35 . Pump housing  15  is composed of two or more pieces and may be joined by welding. However, in other embodiments, pump housing  15  may be joined by fusing, press fit, threading, screw and elastomeric sealing, bonding, fasteners, and/or any other suitable joining method or combinations of joining methods. Motor housing  35  may be joined to pump housing  15  by welding, fusing, press fit, threading, screw and elastomeric sealing, bonding, fasteners, and/or any other suitable joining method or combinations of joining methods. Line A-A passing through pump housing  15  indicates the plane from which the cross-sectional view in  FIG. 2  is provided. 
         [0038]      FIG. 2  is a cross-sectional side view of an illustrative embodiment of pump  10 . Pump housing  15  provides impeller chamber  30  for impeller  75 . Impeller chamber  30  has inlet  20  for connection to a fluid source and outlet  25  for providing fluid to a desired location. Impeller chamber  30  is sealed and pressure tight to prevent fluid from entering/exiting impeller chamber  30  from locations other than inlet  20  and outlet  25 . 
         [0039]    Motor housing  35  is attached to pump housing  15  to form a fluid and/or pressure tight chamber for motor  40 . While motor housing  35  is shown as a separate component from pump housing  15 , in other embodiments, pump housing  15  and motor housing  35  may be combined to form a single combined housing. A cross-sectional view of an illustrative embodiment of motor  40  and motor housing  35  of pump  10  is shown in  FIG. 7 . In particular, motor housing  35  is shown separate from pump  10 . Motor  40  is entirely contained between pump housing  15  and motor housing  35 . A high efficiency electric motor can be utilized, such as an electric motor with efficiency of about 85% or greater. However, in other embodiments, any other suitable driving means can be utilized. Motor  40  provides shaft  45  with hub  50  mounted to shaft  45 . Hub  50  contains one or more permanent magnets and/or magnetic materials  55 . Motor  40  rotates shaft  50  causing permanent magnets  55  placed in hub  50  to rotate. In some embodiments, a motor with a useful life of greater than 10 years is utilized. Further, the motor may utilize hydrodynamic bearings with fluid support provided by a fluid other than blood. 
         [0040]    A cross-sectional view of an illustrative embodiment of pump housing  15  without impeller  75  is shown in  FIG. 6 . Pump housing  15  may provide a non-ferromagnetic and/or non-electrically conductive diaphragm  60  separating impeller chamber  30  from the chamber housing motor  40 . Diaphragm  60  defines cavity  70  providing a region for hub  50  to rotate within. Additionally, diaphragm  60  may provide cylindrical bearing surface  65  for impeller  75  to rotate around with hydrodynamic radial support. Impeller  75  includes one or more permanent magnets and/or magnetic materials  80 . Permanent magnets  80  allow impeller  75  to be magnetically coupled to hub  50 . This magnetic coupling allows motor  40  to cause impeller  75  to rotate when motor  40  rotates hub  50 . 
         [0041]    Line B-B passing through pump housing  15  indicates the plane from which the cross-section view in  FIG. 3  is provided.  FIG. 3  is a cross-sectional top view of an illustrative embodiment of pump  10 . Impeller  75  is composed of an array of arc shaped segments  90  joined by central ring  95 . Pump housing  15  has volute  110  feeding the outlet  25 . In other embodiments, volute  110  could be omitted from pump housing  15  and outlet  25  could have any suitable orientation and shape. Pump housing  15  is designed in a manner where impeller  75 , when rotated, pressures and moves fluid received from inlet  20  to outlet  25 . 
         [0042]    Permanent magnets  55  in hub  50  and permanent magnets  80  in central ring  95  of impeller  75  form a magnetic coupling between the impeller  75  and hub  50 . In contrast to radial magnetic bearings that are arranged to repel each other, permanent magnets  55  and  80  are arranged so that they are attracted to each other. In order to minimize radial loads, permanent magnets  55  and  80  provide a minimal magnetic coupling or just enough of a magnetic coupling to rotate impeller  75  under load. The attractive force of the magnetic coupling of permanent magnets  55  and  80  also provides axial restraint of impeller  75 . For example, axial movement of impeller  75  would misalign permanent magnets  55  and  80 . The magnetic forces of permanent magnets  55  and  80  would restrain and re-align the magnets. Because of the magnetic forces caused by permanent magnets  55  and  80 , axial movement of impeller  75  may cause axial force to be exerted on shaft  45  and hub  50  of motor  40 , which is then transferred to bearing(s) (not shown) of motor  40 . 
         [0043]    Permanent magnets  80  may be sufficiently small in size that they have no impact on the main fluid flow paths of impeller  75 , thereby allowing the design of impeller  75  to focus on fully optimizing pump efficiency. These benefits can allow pumping efficiencies of greater than 50% to be achieved. 
         [0044]    Impeller internal surface  100  of central ring  95  is utilized to form a hydrodynamic bearing between cylindrical bearing surface  65  and impeller internal surface  100 . Impeller  75  is configured to rotate within impeller chamber  30  with full radial hydrodynamic support from the hydrodynamic bearing formed by cylindrical bearing surface  65  and impeller internal surface  100 . A cross section view of an illustrative embodiment of impeller  75  is shown in  FIG. 5  and an isometric view of an illustrative embodiment of impeller  75  is shown in  FIG. 8 , which more thoroughly illustrate the hydrodynamic bearing. 
         [0045]    Pattern grooves on impeller internal surface  100  of impeller  75  create a high pressure zone when impeller  75  is rotated, thereby creating a hydrodynamic bearing. For example, symmetrical herringbone grooves create a high pressure zone where the two straight lines of the V-shape grooves meet or the central portion of the symmetrical herringbone grooves. The pressure created by the pattern grooves on impeller internal surface  100  acts as a radial stabilizing force for impeller  75  when it is rotating concentrically. While the embodiment shown provides symmetrical herringbone grooves on internal surface  100  of impeller  75 , a variety of different groove patterns may be utilized on impeller internal surface  100  to provide a hydrodynamic bearing, which is discussed in detail below. Because low loads are exerted on impeller  75 , the radial hydrodynamic bearing formed between cylindrical bearing surface  65  and impeller internal surface  100  can provide stable radial support of impeller  75 . 
         [0046]    Impeller  75  may be an open, pressure balanced type impeller to minimize axial thrust. Impeller  75  is considered to be open because there is no endplate on either side of arc shaped segments  90 . Further, impeller  75  is considered to be pressure balanced because it is designed to minimize axial thrust during the rotation of impeller  75 . However, other types of impellers may be suitable in other embodiments. Impeller  75  could be any other suitable blade shape, rotate in the opposite direction, or non-pressure balanced. For example, other suitable impellers may be semi-open type (i.e. end plate on one side of impeller) or closed type (i.e. end plate on both sides of impeller). 
         [0047]      FIG. 4  is a close up cross-sectional view of an area C (see  FIG. 2 ) of an illustrative embodiment of pump  10 . The magnetic coupling transmits torque from shaft  45  of the motor  40  to impeller  75 . In the embodiment shown, permanent magnets  55  and  80  are radially distributed around hub  50  and impeller  75 . The poles of permanent magnets  55  and  80  are arranged to attract to each other. The attractive force of the magnetic coupling of permanent magnets  55  and  80  provides axial restraint of impeller  75 . While permanent magnets  55  and  80  are shown as arc shaped like quadrants of a cylinder, it should be recognized that permanent magnets  55  and  80  may be shaped in a variety of different manners to provide the magnetic coupling. For example, one or more ring shaped magnets polarized with arc shaped magnetic regions, square/rectangular shaped, rod shaped, disc shaped, or the like may be utilized. In the magnetic coupling arrangement shown, permanent magnets  80  are shown in the internal portion of impeller  75 . Internal magnetic couplings, similar to the arrangement shown, can be more efficient than face or external type magnetic couplings that place the magnets in the blades of an impeller or rotor because they have a smaller diameter and less eddy current losses. Diaphragm  60 , intermediate the coupling, is non-ferromagnetic and/or non-electrically conductive to minimize eddy current losses. For example, couplings with non-electrically conducting diaphragms such as bio-compatible ceramic, glass or the like, would exhibit less eddy current losses than those with electrically conducting diaphragms. 
         [0048]    In one embodiment, motor  40  is of the brushless DC, sensorless, iron core type electric motor with fluid dynamic bearings. However, in other embodiments, any suitable type of motor including one or more features such as, but not limited to, brushed, hall-effect sensored, coreless, and Halbach array or any type of bearing such as ball or bushing may be used. Motor housing  35  may include motor control circuitry or be configured to operate with remotely located control circuits. 
         [0049]    Separating motor  40  from impeller chamber  30  may allow a high efficiency motor to be utilized. For example, incorporating components into a pump impeller to form the rotor of an electric motor may compromise the design of the pump impeller resulting in reduced efficiency. Further, designing a rotor and stator that is incorporated into the design of a pump may result in an electric motor with large gaps between components of the rotor and stator, thereby decreasing the efficiency of the motor. The magnetic coupling arrangements utilized in the embodiments discussed herein allow a highly efficient motor design to be utilized without compromising the design of an efficient pump impeller. 
         [0050]    As shown in  FIGS. 4-5 , a maximum height  320  of the plurality of blades  90  overlaps with the internal surface  100 , having a height  312 , the maximum height  320  being in a direction of an axis  350  of impeller rotation. As shown in  FIG. 4 , a topmost extent  330  of the plurality of blades  90  is axially closer to the inlet  20  than is (a) a topmost extent  340  of the hydrodynamic bearing and (b) a bottom  332  of the plurality of blades  90 . As shown in  FIGS. 12A and 12B , a maximum cross-sectional dimension  304  of a shape  302  inscribed by all radially innermost edges  300  of the plurality of blades  90  is greater than a maximum cross-sectional dimension  310  of the impeller internal surface  100 . 
         [0051]      FIGS. 9A-9K and 10A-10D  illustrate various embodiments of pattern grooves that may be implemented on impeller internal surface  100 . As discussed previously, impeller internal surface  100  provides a hydrodynamic journal bearing. For example, impeller internal surface  100  may utilize patterned grooves. The pattern grooves may be of any type including, but not limited to, half herringbone ( FIG. 9A ), dual half herringbone ( FIG. 9B ), symmetrical herringbone ( FIG. 9C ), dual symmetrical herringbone ( FIG. 9D ), open symmetrical herringbone ( FIG. 9E ), open dual symmetrical herringbone ( FIG. 9F ), asymmetrical herringbone ( FIG. 9G ), continuous asymmetrical dual herringbone ( FIG. 9H ), asymmetrical dual herringbone ( FIG. 9I ), asymmetrical open herringbone ( FIG. 9J ), asymmetrical open dual herringbone ( FIG. 9K ), or the like. Flow inducing pattern grooves, such as half herringbone patterns and asymmetrical herringbone patterns, have the added benefit of producing a substantial secondary flow, particularly along the axis of impeller rotation between cylindrical bearing surface  65  and impeller  75 , thereby minimizing stagnant flow between cylindrical bearing surface  65  and impeller  75 . Because stagnant areas may cause blood clots to form in blood pumps, the secondary flow reduces the chances of blood clots forming. Further, asymmetrical herringbone patterns have the additional benefit over half herringbone patterns in that they provide similar radial stiffness as symmetrical herringbone patterns. As shown in  FIG. 10A-10D , each of the pattern grooves of internal surface  100  can be shaped in a variety of different manners, such as, but not limited to, rectangular grooves, rectangular grooves with a bevel, semi-circular grooves, elliptical grooves, or the like. In other embodiments, impeller internal surface  100  may also be a plain journal bearing without pattern grooves or a multi-lobe shape that creates a hydrodynamic bearing. In alternative embodiments, the pattern grooves or multi-lobe shapes may be located on the surface of cylindrical bearing surface  65  facing impeller  75  rather than impeller internal surface  100  or the pattern grooves may be located on an outer radial surface of impeller  75  or internal radial surface of pump housing  15  facing the impeller  75 . 
         [0052]      FIG. 11  provides a cross-sectional side view of an illustrative embodiment of housing  150  for pump  120 . Similar to the embodiment shown in  FIG. 2 , pump  120  provides pump housing  150 , impeller  125 , shaft  130 , hub  132 , permanent magnets  135  and  140 , motor housing  142 , motor  145 , and impeller chamber  160 , which all provide a similar function to the components discussed previously. These common elements may operate in substantially the same manner as previously described. The substantial differences in the embodiments are discussed below. 
         [0053]    The embodiment shown in  FIG. 2  provided radial support of impeller  75  utilizing a hydrodynamic bearing. However in  FIG. 11 , in addition to a radial hydrodynamic bearing, one or more external planar surfaces or top surfaces  165  of impeller  125  include pattern grooves providing partial axial hydrodynamic support. 
         [0054]      FIG. 13  is a close up cross-sectional view of an area D of an illustrative embodiment of pump  120 . Each arc shaped segment  127  of impeller  125  includes one or more pattern grooves on top surfaces  165 . The pattern grooves on top surface  165  of impeller  125  and internal surface  155  of housing  150  form a hydrodynamic bearing providing partial axial hydrodynamic support that prevents or minimizes contact between impeller  125  and housing  150 . The pattern grooves on top surface  165  are considered to be interrupted because they are separated by the flow channels of impeller  125 . 
         [0055]    Pattern grooves on top surface of impeller  125  may be any suitable type of grooves including, but not limited to, spiral herringbone and spiral grooves shown in  FIGS. 12A and 12B .  FIGS. 14A and 14B  respectively provide an isometric view of impeller  125  with spiral herringbone and spiral grooves. The arrangement of the pattern grooves on top surfaces  165  is balanced so that instability during rotation of impeller  125  is prevented or minimized. For example, all of the top surfaces  165  have pattern grooves in the embodiment shown. However, it should be recognized that in other embodiments a balanced arrangement of top surfaces  165  that have pattern grooves and do not have pattern grooves may be utilized. A balanced arrangement of top surfaces  165  prevents or minimizes the instability of impeller  125 . Examples of balanced arrangements for the embodiment shown may include, but are not limited to, all top surfaces  165  with grooves or three alternating top surfaces  165  with grooves and three without grooves. Flow inducing pattern grooves, such as spiral and spiral herringbone grooves, have the added benefit of producing a substantial secondary flow, particularly between top surface  165  of impeller  75  and internal surface  155  of housing  150 . Additionally, various pattern groove types including symmetrical, asymmetrical, open, and/or dual groove patterns and various groove shapes including rectangular, rectangular with a bevel, semi-circular, and elliptical shown in  FIGS. 9A-9K and 10A-10D  may be utilized. An additional benefit of the hydrodynamic bearing on top surface  165  of impeller  125  is that it increases impeller stability during rotation by restraining angular motion along axes normal to the axis of impeller rotation. 
         [0056]      FIG. 15  is a cross-sectional side view of an illustrative embodiment of pump  170  with a conically shaped impeller  175 . Many of the components of pump  170  are substantially similar to the components of the previously discussed illustrative embodiments. These similar components may operate in substantially the same manner as previously described. As in the previously discussed embodiments, impeller  175  is magnetically coupled to shaft  180  of motor  182 . Permanent magnets  185  and  190  couple motor  182  to impeller  175 . However, in the embodiment shown, impeller  175  is formed in a generally conical shape. Top surfaces  195  of impeller  175  facing internal surface  200  of the pump housing  202  are shaped in a manner that provides a hydrodynamic bearing between impeller top surfaces  195  and internal surface  200 . 
         [0057]      FIG. 17  is a close up cross-sectional view of an area E of an illustrative embodiment of pump  170 . As in the other embodiments previously discussed, internal surface  205  of impeller  175  may include pattern grooves for a hydrodynamic bearing providing radial support. Top surfaces  195  of impeller  175  are angled to provide a generally conical shaped impeller  175 .  FIGS. 16A-16E  are views of various embodiments of impeller  175 . Impeller  175  has multiple blade segments  210  that each have a top surface  195 . Top surfaces  195  of blade segments  210  may be linear ( FIG. 16A ), convex ( FIG. 16B ), or concave ( FIG. 16C ) surfaces. Additionally,  FIGS. 16D-16E  are views of impeller  175  with convex and concave top surfaces  195 . 
         [0058]    One or more of the top surfaces  195  of impeller  175  may incorporate interrupted pattern grooves of any type including, but not limited to, spiral or spiral herringbone grooves. For example, the interrupted pattern grooves may be similar to the pattern grooves shown in  FIGS. 12A and 12B . The arrangement of the pattern grooves on top surfaces  195  is balanced so that instability during rotation of impeller  175  is prevented or minimized. For example, all of the top surfaces  195  have pattern grooves in the embodiment shown. However, it should be recognized that in other embodiments a balanced arrangement of top surfaces  195  that have pattern grooves and do not have pattern grooves may be utilized. Flow inducing pattern grooves, such as spiral and spiral herringbone grooves, have the added benefit of producing a substantial secondary flow, particularly between top surface  195  of impeller  175  and internal surface  200  of pump housing  202 . Additionally, various pattern groove types including symmetrical, asymmetrical, open, and/or dual groove patterns and various groove shapes including rectangular, rectangular with a bevel, semi-circular, and elliptical may alternatively be utilized as shown in  FIGS. 9A-9K and 10A-10D . In some embodiments, top surfaces  195  of impeller  175  do not utilize pattern grooves. For example, the conical shaped impeller  175  may be a pressure balanced type impeller where the magnetic coupling formed by magnets  185  and  190  provides sole axial restraint of impeller  175 . 
         [0059]    In addition to the axial restraint provided by the magnetic coupling discussed previously, the hydrodynamic bearing provided by top surfaces  195  of impeller  175  partially restrains axial movement in the direction along the axis of rotation. Because top surfaces  195  are angled, the hydrodynamic bearing of top surfaces  195  also partially restrains radial motion of impeller  175 . Thus, the hydrodynamic bearing of top surfaces  195  provides partial radial and axial support for impeller  175 . The hydrodynamic bearings of top surface  195  and impeller internal surface  205  and the partial restraint provided by the magnetic coupling increase impeller stability during rotation by restraining axial and radial motion. 
         [0060]      FIG. 18  is a cross-sectional side view of an illustrative embodiment of pump housing  215  for pump  212 . Many of the components of pump  212  are substantially similar to the components of the previously discussed illustrative embodiments. These similar components may operate in substantially the same manner as previously described. As in the previously discussed embodiments, impeller  220  is magnetically coupled to shaft  225 . Permanent magnets  230  and  235  couple the motor to impeller  220 . 
         [0061]    Impeller  220  contains permanent magnets  240  and pump housing  215  contains permanent magnets  245 ,  250  thereby forming a magnetic thrust bearing for minimizing axial movement of impeller  220 . Permanent magnets  245 ,  250  in housing  215  may be one or more magnets formed into a ring.  FIG. 20  is a close up cross-sectional view of an area H of an illustrative embodiment of pump  212 . Permanent magnets  240  in impeller  220  and permanent magnets  245  in the top portion of pump housing  215  are arranged to provide a repulsive force between impeller  220  and pump housing  215 . Permanent magnets  240  in impeller  220  and permanent magnets  250  in the bottom portion of pump housing  215  are also arranged to provide a repulsive force between impeller  220  and pump housing  215 . The axial restraint forces generated by magnets  240 ,  245 ,  250  are significantly greater than the attractive forces generated by the permanent magnets  230  and  235  and thereby provide sole axial support with greater stiffness for impeller  220  during rotation. Magnets  240  in impeller  220  and magnets  245 ,  250  in pump housing  215  provide large axial restraint forces to allow for increased clearances between impeller  220  and pump housing  215  during rotation. The increased clearances reduce damage to blood and allow for increased flow through the clearances during impeller rotation. 
         [0062]      FIG. 19  is a cross sectional top view of an illustrative embodiment of pump  212 . Magnets  240  are arranged radially around impeller  220 . Each blade segment  255  of impeller  220  may provide an opening/region for receiving one or more magnets  240 . Additionally, in some embodiments, the top and/or bottom surfaces of impeller  220  may incorporate various pattern groove types including spiral, spiral herringbone, symmetrical, asymmetrical, open, and/or dual groove patterns. Further, various groove shapes including rectangular, rectangular with a bevel, semi-circular, and elliptical may also be utilized as shown in  FIGS. 9A-9K and 10A-10D . 
         [0063]    While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations can be made to those embodiments without departing from the scope of the appended claims.