U.S. patent application number 10/848898 was filed with the patent office on 2004-11-18 for touch down of blood pump impellers.
Invention is credited to Antaki, James, Borzelleca, David, Burgreen, Greg, Capone, Christopher D., Dempsey, Ruey C., Hebbert, Ralph Scott, Heilman, Marlin S., Holmes, John A., Kolenik, Steve A., Moore, Daniel R., Parisi, Carl M., Prem, Edward K., Sofranko, Richard A., Wu, Zhongjun.
Application Number | 20040228724 10/848898 |
Document ID | / |
Family ID | 26793584 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040228724 |
Kind Code |
A1 |
Capone, Christopher D. ; et
al. |
November 18, 2004 |
Touch down of blood pump impellers
Abstract
A blood pump having rotor and/or stator touch down zones to
prevent pump failure or hernolysis 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.
Inventors: |
Capone, Christopher D.;
(Pittsburgh, PA) ; Dempsey, Ruey C.; (Greensburg,
PA) ; Heilman, Marlin S.; (Sarver, PA) ;
Kolenik, Steve A.; (Leechburg, PA) ; Moore, Daniel
R.; (Gibsonia, PA) ; Parisi, Carl M.;
(Kittanning, PA) ; Prem, Edward K.; (Allison Park,
PA) ; Sofranko, Richard A.; (Pittsburgh, PA) ;
Borzelleca, David; (Wexford, PA) ; Burgreen,
Greg; (Bakerstown, PA) ; Holmes, John A.;
(Wexford, PA) ; Wu, Zhongjun; (Wexford, PA)
; Hebbert, Ralph Scott; (Wexford, PA) ; Antaki,
James; (Allison Park, PA) |
Correspondence
Address: |
BUCHANAN INGERSOLL, P.C.
ONE OXFORD CENTRE, 301 GRANT STREET
20TH FLOOR
PITTSBURGH
PA
15219
US
|
Family ID: |
26793584 |
Appl. No.: |
10/848898 |
Filed: |
May 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10848898 |
May 19, 2004 |
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10097731 |
Mar 14, 2002 |
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6761532 |
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60275732 |
Mar 14, 2001 |
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Current U.S.
Class: |
415/200 |
Current CPC
Class: |
F04D 29/047 20130101;
A61M 60/205 20210101; A61M 60/422 20210101; A61M 60/148 20210101;
F04D 13/064 20130101; A61M 60/824 20210101; A61M 60/82 20210101;
A61M 60/50 20210101 |
Class at
Publication: |
415/200 |
International
Class: |
F01D 001/02 |
Claims
1. A blood pump having inlet and outlet regions, said blood pump
comprising: a. a stator having at least one of first and second
contact portions adjacent at least one of said inlet and outlet
regions, respectively; b. a rotor magnetically supported adjacent
said stator for rotation relative thereto, said rotor having at
least one of third and fourth contact portions adjacent said at
least one of first and second contact portions, respectively; c.
each of said first and second contact portions having properties
resistant to damage resulting from potential touch down of said
rotor against said stator; and d. each of said third and fourth
contact portions having properties resistant to damage resulting
from potential touch down of said rotor against said stator.
2. The blood pump of claim 1 further comprising: a. at least one of
said first and second contact portions being a relatively hard
material; b. at least one of said third and fourth contact portions
being a relatively soft material; c. wherein at least one of said
first and third and said second and fourth contact portions are
soft and hard materials, respectively, such that a soft contact
portion is adjacent a hard contact portion.
3. The blood pump of claim 2 further comprising: a. said relatively
hard materials are at least one of titanium, alloyed titanium, and
a jewel; and b. said relatively soft materials are at least one of
polymer, rubber, and a combination thereof.
4. The blood pump of claim 1 wherein each of said first through
fourth contact portions are relatively hard materials.
5. The blood pump of claim 4 wherein each of said first through
fourth contact portions are at least one of titanium, alloyed
titanium, and a jewel.
6. The blood pump of claim 5 wherein said first through fourth
contact portions are one of titanium and alloyed titanium, and
further comprising said first through fourth contact portions
having one of a crystalline-diamond-like coating, titanium nitride
coating, and graphitic-diamond-like coating.
7. The blood pump of claim 1 wherein each of said first through
fourth contact portions are relatively soft materials.
8. The blood pump of claim 7 wherein each of said first through
fourth contact portions are at least one of polymer, rubber, and a
combination thereof.
9. The blood pump of claim 1 wherein at least one of said second
and third contact portions comprise blade members, and said blade
members being a relatively soft material.
10. The blood pump of claim 9 further comprising at least one of
said first and fourth contact portions adjacent said at least one
of said second and third contact portions being a relatively hard
material.
11. A blood pump having inlet and outlet regions, said blood pump
comprising: a. a stator having at least one of first and second
contact portions adjacent said outlet region; b. a rotor
magnetically supported adjacent said stator for rotation relative
thereto, said rotor having at least one of third and fourth contact
portions adjacent said at least one of first and second contact
portions, respectively; c. each of said first and second contact
portions having properties resistant to damage resulting from
potential touch down of said rotor against said stator; and d. each
of said third and fourth contact portions having properties
resistant to damage resulting from potential touch down of said
rotor against said stator.
12. The blood pump of claim 11 further comprising: a. at least one
of said first and second contact portions being a relatively hard
material; b. at least one of said third and fourth contact portions
being a relatively soft material; c. wherein at least one of said
first and third and said second and fourth contact portions are
soft and hard materials, respectively, such that a soft contact
portion is adjacent a hard contact portion.
13. The blood pump of claim 12 further comprising: a. said
relatively hard materials are at least one of titanium, alloyed
titanium, and a jewel; and b. said relatively soft materials are at
least one of polymer, rubber, and a combination thereof.
14. The blood pump of claim 11 wherein each of said first through
fourth contact portions are relatively hard materials.
15. The blood pump of claim 14 wherein each of said first through
fourth contact portions are at least one of titanium, alloyed
titanium, and a jewel.
16. The blood pump of claim 15 wherein said first through fourth
contact portions are one of titanium and alloyed titanium, and
further comprising said first through fourth contact portions
having one of a crystalline-diamond-like coating, titanium nitride
coating, and graphitic-diamond-like coating.
17. The blood pump of claim 11 wherein each of said first through
fourth contact portions are relatively soft materials.
18. The blood pump of claim 17 wherein each of said first through
fourth contact portions are at least one of polymer, rubber, and a
combination thereof.
19. The blood pump of claim 11 wherein at least one of said third
and fourth contact portions comprise blade members, and said blade
members being a relatively soft material.
20. The blood pump of claim 19 further comprising at least one of
said first and second contact portions being a relatively hard
material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on U.S. Provisional Patent
Application Ser. 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'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] 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] 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] FIG. 3 is a side cross section view of an exemplary
embodiment of a dual gap centrifugal blood pump according to the
invention.
[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 A1, B1, C1,
and D1, wherein A1 designates a first, or fore, touch down zone
portion of the rotor and B1 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 A1. Similarly, C1
designates a second, or aft, touch down zone portion of the rotor,
and D1 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 C1.
[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 A2, B2, C2, and D2 correspond
to touch down zones A1, B1, C1, and D1 in FIG. 1. Likewise, touch
down zones A3, B3, C3 and D3 in FIG. 3, and touch down zones A4,
B4, C4 and D4 in FIG. 4, each also correspond to touch down zones
A1, B1, C1, and D1 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 A1-B1 are
provided at the fore end 28 of the pump 10 and touch down zones
C1-D1 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 A1 and the adjacent wall portion 22
of the stator 16 constitutes corresponding touch down zone B1. 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 A1 and B1.
[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 A1, is on the rotor 13 whereas in the
pump outlet region 31, the bladed touch down zone D1 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 C1 constitutes the
40 portion of the rotor 13 surface adjacent the stator touch down
zone D1. 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 A1 through D1 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 A1 and D1 at the pump
inlet 28 and by the smooth touch down zones B1 and C1 at the pump
outlet 31.
[0024] At the pump inlet 28 area, the impeller blades 34, or the
tips thereof, (touch down zone A1) and the adjacent portion 22 of
the stator 16 wall (touch down zone B1) 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 A1 or the stator touch down zone
B1. 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 A1 and B1 are also possible on the
outlet end 31 of the blood pump 10 regarding touch down zones D1
and C1, respectively. The portion 40 of the rotor 13 at the pump
outlet 31 can have a smooth touch down zone C1. The stator 16
blades 37 forming touch down zone D1 and the rotor 13 touch down
zone C1 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 A2-B2 are provided at
the pump inlet 64 and touch down zones C2-D2 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 A2 and the adjacent portion of the
stator wall can constitute adjacent touch down zone B2. Due to the
geometry of touch down zones A2 and B2, excessive axial motion of
the rotor 42 towards the pump inlet 64 will result in touch down
between zones A2 and B2. 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 D2. The region of the
rotor 42 adjacent the blades 72 can constitute touch down zone C2.
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 A2-B2 and aft C2-D2 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 B3, and D3, are much closer to the rotor
89 touch down zones A3 and C3, they may still be defined as fore,
A3-B3, and aft, C3-D3, touch down zones, respectively. Likewise,
the fore touchdown zones can instead be situated closer to the
inlet end of the blood pump. Zones A3' and B3' can be used as
opposed to zones A3 and B3. 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 A3 through D3, as well as A3' and B3',
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 A4-B4 and aft C4-D4 touch
down zones. The fore touch down zones A4-B4 at the inlet 223 of the
pump 100 includes rotor 202 touch down zone A4 and stator 205 touch
down zone B4, and is very similar to the fore touch down zones
AL-B1 at the inlet 28 of the single gap axial flow pump 10 shown in
FIG. 1. However, the aft touch down zones C4-D4 at the outlet 214
of the pump 100 can be configured somewhat differently than the aft
touch down zones C1-D1, 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 C4 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 D4 can
be provided on the correspondingly tapering larger end 217 of the
central shaft 109, which is adjacent rotor touch down zone C4.
[0032] In the dual gap axial blood pump 100 shown, aft touch down
zones C4-D4 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.
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