Abstract:
A blood pump having rotor and/or stator touch down zones to prevent pump failure or hemolysis which can occur if the rotor comes into contact with the stator due to power failure or mechanical shock. The touch down zones can include forming, or coating, portions of adjacent surfaces of the stator and rotor which can come into contact if a rotor touch down occurs. The materials used to form or coat the touch down zones can have properties which ensure that no consequential damage to the contacting surfaces occurs.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is based on U.S. Provisional Patent Application Serial No. 60/275,732, filed Mar. 14, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates generally to blood pumps of the type in which a rotor, having impeller blades, is supported by magnetic bearings within a stator, and more particularly to preventing pump failure or hemolysis if the rotor should come into contact with the stator.  
           [0003]    The number of donor hearts needed for persons having advanced heart failure has not decreased and consequently the need for a long-term alternative to heart transplantation remains. A fully implantable blood pump and system which is smaller than presently available systems and has the high reliability required for long term implantation would be a solution. To address this need, a variety of continuous flow blood pumps have recently been developed to address these requirements.  
           [0004]    Continuous flow pumps generally have a rotor portion that has impeller blades for the pumping of blood and a surrounding stator which has features that mechanically support and turn the rotor to generate flow via the impeller blades. Some of these pumps have a mechanical bearing to support the rotor while others support the rotor in part or whole using a magnetic suspension system. Pumps which have mechanical bearings have the potential to cause hemolysis (blood damage) due to mechanical trauma or to heat generation, both of which are induced by the contact regions of the mechanical bearing. Some pumps employ a hydrodynamic bearing with the blood as the liquid portion of the bearing. Although much work has been done to determine the time duration and shear stress level at which hemolysis occurs, this type of rotor support has unknown long-term effects on blood. Pumps having magnetic suspension have the advantage of rotor-stator interaction that doesn&#39;t require contact or the extremely close tolerance between the rotor and stator of a hydrodynamic bearing, both of which induce mechanical trauma. However, one limitation of magnetic suspension is the control of the rotor during power failure or excessive mechanical shock to the blood pump. In these instances, the rotor may crash into the stator and cause surface damage to both components. In addition, most blood pump rotors use impeller blades for the pumping of blood. The blades are typically thin and consequently provide a small surface area for contact between the rotor and stator. The small surface area provided by the blade tips increases the likelihood of local surface damage. A larger surface area is better than a smaller one since the transfer of energy between the impacting components is spread out to a greater extent and consequently the surface damage will be less. Regardless of the size of the contact area, the touch down event can cause hemolysis and/or damage (scratch or gouge) the contacting surfaces of the rotor and/or stator which may subsequently cause thrombosis (blood clot) by providing a crack or crevice for the blood to begin depositing cells or other blood products.  
           [0005]    One example of a blood pump in which the rotor is entirely supported by magnetic bearings is described in U.S. Pat. No. 4,688,998. When the operation of this blood pump is halted due to a power failure, the rotor shifts toward the inlet of the blood pump to block the backflow of blood through the blood pump. A portion of the rotor, referred to as the valve body, will contact a region of the stator, referred to as the valve seat, during power failure. No provision is made to have the rotor and stator portions designed to tolerate repeated impacts without damage to the blood contacting surfaces. This embodiment is again described in U.S. Pat. No. 4,944,748, which discloses additional embodiments of blood pumps that have magnetically suspended rotors. These embodiments likewise have no unique features for the tolerance of contact between the rotor and stator.  
           [0006]    Another type of magnetically suspended blood pump is described in U.S. Pat. No. 6,050,975. This blood pump is designed to have a textured blood-contacting surface that promotes the growth of a biologic lining from the passing blood. Although this technique has been shown to produce beneficial results from the standpoint of preventing unstable clot formation, contact between the rotor and stator due to a power failure would potentially break loose tissue from the textured surface. Consequently, this pump cannot tolerate rotor-stator contact without causing serious harm to the patient.  
           [0007]    Generally, touch down events may be grouped into two categories: touch down due to power failure; or touch down due to mechanical shock. If a blood pump power failure occurs, the rotor may, in certain designs, be slammed into the stator by the un-powered and consequently unbalanced magnetic bearings. For a well designed blood pump, the chance of a power failure is highly unlikely. However, for the safety of the patient, the blood pump must be designed to survive and correctly function after such a catastrophic event.  
           [0008]    In contrast to touch down caused by a power failure, touch down due to mechanical shock is more difficult to account for, given the difficulty to predict the shock loading a patient may see if they are involved in an accident. One important consideration for determining the required magnetic suspension strength is the capability of the magnetic suspension to withstand the mechanical shock loading from everyday activity. In addition, there are considerations regarding the natural frequency of the magnetic suspension as a function of impeller rotational speed. Both of these issues tend to encourage a stiff magnetic bearing for rotor suspension. A stiffer suspension will enable larger shock loads to be tolerated without touch down occurring. Unfortunately, a stiffer suspension can also result in higher touch down loading if a power failure occurs.  
           [0009]    It should be noted that touch down resulting from a mechanical shock will normally occur for a brief time period, typically only for an instant. In contrast, touch down resulting from a power failure can potentially bring the rotor to a complete stop, since the magnets will hold the rotor in place while the rotational energy is dissipated.  
           [0010]    Accordingly, there is a need for a blood pump designed to eliminate surface damage that can occur if the rotor should come into contact with the stator.  
         SUMMARY  
         [0011]    A blood pump is provided according to the invention wherein portions of the rotor and/or stator are designed to eliminate surface damage if the rotor and stator should come into contact with each other. This can be accomplished generally by specially designing the portions of the rotor and stator which are likely to come into contact as a result of power failure or mechanical shock. In particular, likely touch down contact surfaces of the rotor and/or stator can be made from materials having properties such that generally even the highest touch down forces would not cause any surface damage. Alternatively, the geometry of the likely touch down contact surfaces of the rotor and/or stator can be designed such that the touch down forces are spread across the largest possible surface area to reduce the contact stresses. Moreover, a combination of the choice of materials and the design of the geometry of the likely touch down contact surfaces can be employed to achieve the desired results of eliminating surface damage in the event of rotor touch down against the stator.  
           [0012]    Other details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying figures of certain embodiments thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0013]    A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 is a side cross section view of an exemplary embodiment of an single gap axial flow blood pump according to the invention.  
         [0015]    [0015]FIG. 2 is a view of a single gap axial flow pump similar to FIG. 1, except illustrating more details of such a pump.  
         [0016]    [0016]FIG. 3 is a side cross section view of an exemplary embodiment of a dual gap centrifugal blood pump according to the invention.  
         [0017]    [0017]FIG. 4 is a side cross section view of an exemplary embodiment of a dual gap axial flow blood pump according to the invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Referring now to the drawing figures, like reference numbers refer to similar parts throughout the several views. Except for FIG. 2, generally only the rotor and stator members of the blood pump are illustrated since it is those components which are pertinent to understanding the details of the invention. The invention is primarily concerned with adjacent regions of the rotor and stator which are most likely to come into contact with each other in the case of a rotor touch down event. In particular, as will be described in greater detail hereinafter, the material composition and geometry of such adjacent regions of the rotor and/or stator can be designed to generally eliminate any surface damage resulting from contact due to touch down events. The materials chosen can have properties such that touch down contact will not result in damage to the contacting rotor and stator surfaces. The geometry of the portions of the adjacent surfaces of the rotor and stator can be designed to spread the force of contact over a larger area, and can further be designed to simultaneously account for touch downs in both the axial and radial directions.  
         [0019]    In accordance with the foregoing, FIGS. 1, 3 and  4  are generally simplified depictions of blood pumps, showing a rotor housed within a stator, wherein portions of adjacent regions of the rotor and stator have “touch down zones.” In each Figure, the rotor is magnetically suspended and rotated within the stator, although the details of the magnetic suspension and rotation system are not shown. In FIG. 1, the touch down zones are designated A 1 , B 1 , C 1 , and D 1 , wherein A 1  designates a first, or fore, touch down zone portion of the rotor and B 1  designates a corresponding fore touch down zone portion of the stator which, in the event of rotor touch down, will be contacted by touch down zone A 1 . Similarly, C 1  designates a second, or aft, touch down zone portion of the rotor, and D 1  designates a corresponding aft touch down zone portion of the stator which, in the event of rotor touch down, will be contacted by touch down zone C 1 .  
         [0020]    The touch down zones of the various blood pump embodiments illustrated in FIGS. 2 through 4 are similarly labeled, in regard to fore and aft touch down zones of the rotor and stator. For example, in FIG. 2, touch down zones A 2 , B 2 , C 2 , and D 2  correspond to touch down zones A 1 , B 1 , C 1 , and D 1  in FIG. 1. Likewise, touch down zones A 3 , B 3 , C 3  and D 3  in FIG. 3, and touch down zones A 4 , B 4 , C 4  and D 4  in FIG. 4, each also correspond to touch down zones A 1 , B 1 , C 1 , and D 1  in FIG. 1. In accordance with the invention, each of the touch down zones in any of FIGS. 1 through 4, on either the rotor or the stator, can be smooth or may have blades. However, adjacent touch down zones of the rotor and stator will generally be smooth-to-smooth or blade-to-smooth, but not blade-to-blade.  
         [0021]    Referring now particularly to FIG. 1, a simplified drawing of an axial flow pump  10  is depicted showing only the rotor  13  magnetically supported within the stator  16 . In this configuration, the blood pump has a single blood flow path  19 . As shown, axial motion of the rotor  13  is restrained within the stator  16  by portions  22 ,  24  of the stator wall at inlet (fore)  28  and outlet (aft)  31  sides of the blood pump. Touch down zones A 1 -B 1  are provided at the fore end  28  of the pump  10  and touch down zones C 1 -D 1  are provided at the aft end  31 . In the pump inlet  28  region, impeller blades  34  are provided on the rotor  13  which rotate in close proximity to the adjacent wall portion  22  of the stator. At the inlet side  28  of the pump  10 , the tips of the impeller blades  34  constitute touch down zone A 1  and the adjacent wall portion  22  of the stator  16  constitutes corresponding touch down zone B 1 . Due to the geometry of the impeller blades  34  and the stator wall portion  22 , excessive axial motion of the rotor  13  towards the pump inlet  28  can result in touch down between zones A 1  and B 1 .  
         [0022]    Consideration must also be given for axial motion of the rotor  13  toward the pump outlet  31 . In the pump inlet region  28 , the bladed touch down zone A 1 , is on the rotor  13  whereas in the pump outlet region  31 , the bladed touch down zone D 1  is part of the stator  16 . The blades  37  on the stator  16  can be inwardly pointing, which serves to straighten the flow of blood as it exits the pump outlet  31 . Corresponding rotor touch down zone C 1  constitutes the  40  portion of the rotor  13  surface adjacent the stator touch down zone D 1 . Although a particular configuration of the rotor  13  and stator  16  is shown, it is to be understood that other configurations can be designed by those skilled in the art.  
         [0023]    Rotor touch down, is not limited to the axial direction, but can also occur in the radial direction. Moreover, a rotor touch down may have both axial and radial components. Consequently, at both the pump inlet  28  and pump outlet  31  regions, the touch down zones A 1  through D 1  can be designed to accommodate rotor touch down from radial or axial directions, or a combination thereof. This can be achieved by controlling the geometry of the fore and aft touch down zone portions of the rotor  13  and stator  16 , and/or by forming the cooperating fore and aft touch down zones over a large surface area. In particular, this can be accomplished by making on or both touch adjacent down zone portions extend axially along the length of the rotor and/or stator sufficiently to ensure that a rotor touch down, from generally any direction, will result in contact between only the adjacent touch down zone portions. Thus, the rotor  13  can be constrained within the stator  16  both radially and axially, such as by bladed touch down zones A 1  and D 1  at the pump inlet  28  and by the smooth touch down zones B 1  and C 1  at the pump outlet  31 .  
         [0024]    At the pump inlet  28  area, the impeller blades  34 , or the tips thereof, (touch down zone A 1 ) and the adjacent portion  22  of the stator  16  wall (touch down zone B 1 ) may be formed from, or coated to a sufficient thickness with, a variety of specially selected materials. The materials chosen for adjacent touch down zones can be generally categorized into three groups: hard surface to hard surface; soft surface to hard surface; or soft surface to soft surface. As an example, a hard surface on stator touch down zone B could be provided using pure titanium, an alloyed titanium, a crystalline-diamond-like coated pure or alloyed titanium, a titanium nitride coated pure or alloyed titanium, a graphitic-diamond-like coated pure or alloyed titanium, or a jewel, like sapphire. Likewise, the blade tips of touch down zone A may be a pure titanium, an alloyed titanium, a crystalline-diamond-like coated pure or alloyed titanium, a titanium nitride coated pure or alloyed titanium, a graphitic-diamond-like coated pure or alloyed titanium, or a jewel, like sapphire. Other hard materials like ceramics could also be used.  
         [0025]    As for soft materials, PEEK (polyetheretherkeytone) is preferred, but any similar polymer, rubber, a combination thereof, or other relatively soft materials having similar properties, could also be used. The soft material could be used for either the impeller blades of touch down zone A 1  or the stator touch down zone B 1 . The exact configuration of materials can depend on the particular application and related considerations. Additionally, other material combinations will also be apparent to those skilled in light of this disclosure.  
         [0026]    Similar configurations as described above regarding materials for touch down zones A 1  and B 1  are also possible on the outlet end  31  of the blood pump  10  regarding touch down zones D 1  and C 1 , respectively. The portion  40  of the rotor  13  at the pump outlet  31  can have a smooth touch down zone C 1 . The stator  16  blades  37  forming touch down zone D 1  and the rotor  13  touch down zone C 1  can have material selections/breakdowns as described above.  
         [0027]    Referring now to FIG. 2, a presently preferred embodiment of a single gap axial flow blood pump  40  is shown, which can be similar to the blood pump  10  shown in FIG. 1, except that a more detailed illustration is provided, including details of the magnetic suspension and rotation systems. In particular, the rotor  42  can be supported radially within the stator  44  by cooperating magnetic radial bearing members  46 ,  48  on the rotor  42  and the stator  44 , respectively. The rotor  42  can be magnetically supported in the axial direction by cooperating Lorentz force axial bearing members  50 ,  52  on the stator  44  and rotor  42 , respectively. The rotor  42  can be rotated via magnetic drive members  54 ,  56  on the stator  44  and rotor  42  respectively. The magnetic drive members  54 ,  56  can comprise a toroidally wound motor. An axial position sensor can be also provided via cooperating stator  44  sensor portion  58  and rotor  42  sensor portion  60 .  
         [0028]    In the single gap axial flow pump  40 , the rotor  42  can be entirely magnetically supported and rotated within the stator  44 . Thus, as in the blood pump  10  shown in FIG. 1, axial movement of the rotor  42  can be restrained within the stator  44  by portions of the stator  44  at inlet (fore)  64  and outlet (aft)  66  sides of the blood pump  40  Therefore, touch down zones A 2 -B 2  are provided at the pump inlet  64  and touch down zones C 2 -D 2  are provided at the pump outlet  66 . In the pump inlet  64  region, impeller blades  68  on the rotor  42  sweep in close proximity to the adjacent stator wall surface. Thus, the impeller blades  68 , or the tips thereof, can constitute touch down zone A 2  and the adjacent portion of the stator wall can constitute adjacent touch down zone B 2 . Due to the geometry of touch down zones A 2  and B 2 , excessive axial motion of the rotor  42  towards the pump inlet  64  will result in touch down between zones A 2  and B 2 . Also like the blood pump  10  shown in FIG. 1, separate consideration is given for axial motion of the rotor  42  toward the pump outlet  66 . At the pump outlet  66 , blades  72  can be provided on the stator  44  to straighten the blood flow as it exits the pump  40 . The blades  72  can be inwardly pointing, for the same reason explained in connection with FIG. 1. The flow straightening blades  72  can constitute aft touch down zone D 2 . The region of the rotor  42  adjacent the blades  72  can constitute touch down zone C 2 . Although a particular configuration of the rotor  42  and stator  44  is shown, it is to be understood that other configurations can be designed by those skilled in the art.  
         [0029]    As described in connection with FIG. 1, there are likewise a number of different types of materials, and combinations of materials, for adjacent touch down zones which can be selected to eliminate damage that can result from rotor  42  touch down against the stator  44 . In particular, the fore A 2 -B 2  and aft C 2 -D 2  touch down zones can be made of hard and/or soft materials, and various combinations thereof, depending on design requirements.  
         [0030]    Referring now to FIGS. 3 and 4, other pump concepts which have touch down zones are depicted. In particular, FIG. 3 depicts a simplified illustration of a dual gap centrifugal pump  80 , including a rotor  89  housed within a stator  92  and separated therefrom by a magnetic suspension gap  83 . The magnetic suspension gap  83  forms a secondary blood flow path in addition to the main blood flow path  86 . Provision of two gaps  83 ,  86  can enable provision of a narrower suspension gap  83  between the magnets of the bearing suspension system, which lowers the amount of energy required to suspend the pump rotor  89  radially within the stator  92 . The touch down zones are labeled in a manner similar to that of the blood pump  10  shown in FIG. 1. Specifically, although the stator  92  touch down zones B 3 , and D 3 , are much closer to the rotor  89  touch down zones A 3  and C 3 , they may still be defined as fore, A 3 -B 3 , and aft, C 3 -D 3 , touch down zones, respectively. Likewise, the fore touchdown zones can instead be situated closer to the inlet end of the blood pump. Zones A 3 ′ and B 3 ′ can be used as opposed to zones A 3  and B 3 . Like the axial flow pump  10  shown in FIG. 1, there are a number of potential different types of materials, and combinations of material in adjacent touch down zones, which can be selected to eliminate damage from rotor touch down. The touch down zones A 3  through D 3 , as well as A 3 ′ and B 3 ′, at the inlet (fore)  95  and outlet (aft)  98  ends of the rotor  89  and stator  92  can be made of hard and/or soft materials and various combinations thereof as described above in connection with FIG. 1, depending on the design requirements.  
         [0031]    Referring now to FIG. 4, there is shown a simplified illustration of an axial flow blood pump  100  having primary  103  and secondary blood flow gaps  106 , and in which there is provided a central shaft  109  which constrains a rotor  202  internally within a stator  205 . The narrow secondary, i.e., magnetic suspension, gap  106  is the gap between an inner surface of a bore  208  through the center of the rotor  202  and an outer surface of the central shaft  109  which extends through the bore  208 . The end  211  of the bore  208  at the outlet side  214  of the pump  100  can have an outwardly tapering opening, and the central shaft  109  can have a correspondingly tapering larger end  217 , which serves to provide an axial support for the rotor  202 . Blades  220  can be provided on the rotor  202  at the inlet side  223  of the pump  100  which cooperate with a portion  226  of the stator  205  to provide corresponding axial restraint on the inlet side  223  of the pump  100 . As with the previously described embodiments of blood pumps  10 ,  80 , the dual gap axial flow pump  100  can have fore A 4 -B 4  and aft C 4 -D 4  touch down zones. The fore touch down zones A 4 -B 4  at the inlet  223  of the pump  100  includes rotor  202  touch down zone A 4  and stator  205  touch down zone B 4 , and is very similar to the fore touch down zones A 1 -B 1  at the inlet  28  of the single gap axial flow pump  10  shown in FIG. 1. However, the aft touch down zones C 4 -D 4  at the outlet  214  of the pump  100  can be configured somewhat differently than the aft touch down zones C 1 -D 1 , owing to the central shaft  109  extending through the bore  208  in the rotor  202 . In particular, the pump outlet  214  can have aft rotor touch down zone C 4  provided on the inner surface of the bore  208 , and particularly on the outwardly tapering end  211  of the bore  208 . Aft stator touch down zone D 4  can be provided on the correspondingly tapering larger end  217  of the central shaft  109 , which is adjacent rotor touch down zone C 4 .  
         [0032]    In the dual gap axial blood pump  100  shown, aft touch down zones C 4 -D 4  can both be smooth surfaces. Moreover, as explained in connection with FIG. 3, there are a number of potential different types of materials, and combinations of material in adjacent touch down zones, which can be selected to eliminate damage from rotor touch down, as described in connection with FIG. 1. Thus, the fore and aft touch down zones of the rotor  202  and stator  205  can be made of hard and/or soft materials and various combinations thereof as described above in connection with FIG. 1, depending on design requirements.  
         [0033]    In general, with any particular embodiment of a blood pump with touch down zones, a key factor to be considered is the geometric orientation of the touch down zone. The touch down zones, as shown in all of the drawing figures, can be configured such that the zones can simultaneously account for both axial and radial touch down. This can be accomplished through design of the specific geometry of the rotor and stator, particularly in the regions which are to be touch down zones. The size of the touch down zones can also affect this aspect of the invention, since the various touch down zone may need to extend sufficiently inwards from both the inlet and the outlet of the blood pump in order to accommodate radially directed touch downs, or a combination of radially and axially directed touch down events. Moreover, the size of the touch down zones can also be important in that a relatively large surface area can be desired, over which the force of touch down events can be spread. Spreading the force of touch down impact over a larger area will reduce imposed stresses and thereby lessen the likelihood of damage to either the rotor or the stator as a result of a touch down event.  
         [0034]    Although certain embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications to those details could be developed in light of the overall teaching of the disclosure. Accordingly, the particular embodiments disclosed herein are intended to be illustrative only, and not limiting to the scope of the invention which should be awarded the full breadth of the following claims and any and all embodiments thereof.