PCT
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCvr)
`WO 99/12587
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`Jntema.tional Bureau
`
`(51) International Patent Classification 6 :
`A61M 1n2
`
`(11) International Publication Number:
`
`Al
`
`(43) International Publication Date:
`
`18 March 1999 (18.03.99)
`
`(81) Designated States: AL, AM, AT, AU, AZ. BA, BB, BG, BR,
`BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, Fl, GB, GE,
`GH, GM, HR, HU, ID, IL, IS, JP, KE, KG, KP, KR, KZ,
`LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW,
`MX, NO, NZ, PL. PT, RO, RU, SD, SE, SG, SI, SK, SL,
`TJ, TM, TR, TT, UA, UG, US, UZ, YN, YU, ZW, ARIPO
`patent (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent (AT, llE, CH, CY, DE, DK, ES, Fl, FR, GB, GR,
`IE, IT, LU, MC, NL, PT. SE), OAPI patent (BF, BJ, CF,
`CG, Cl, CM, GA, GN, GW, ML, MR. NE, SN, TD, TG).
`
`Published
`With international search report.
`
`(21) International Application Number:
`
`PCf/ A U98/00725
`
`(22) International Filing Date:
`
`7 September 1998 (07.09.98)
`
`(30) Priority Data:
`PO 9027
`
`S September 1997 (05.09.97)
`
`AU
`
`(71) Applicant~ (for ali designated States except US): CORTRONIX
`PTY. LTD. [AU/AU]; II Technology Drive, Labrador, QLD
`4215 (AU). UNIVERSITY OF TECHNOLOGY, SYDNEY
`[AU/AU); I Broadway, Sydney, NSW 2007 (AU).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): WOODARD, John,
`Campbell [AU/AU]; 27 Wareemba Avenue, Thomleigh,
`NSW 2120 (AU). WATTERSON, Peter, Andrew [AU/AU];
`13 Driver Street, West Ryde, NSW 2114 (AU). TANSLEY,
`Geoffrey, Douglas [AU/AU]; 17 Lennox Street, Norman(cid:173)
`hurst, NSW 2076 (AU).
`
`(74) Agent: WALLINGTON- DUMMER; P.O. Box 297, Ry(cid:173)
`dalmere, NSW 1701 (AU).
`
`(54) Title: A ROTARY PUMP WITH HYDRODYNAMICALLY SUSPENDED IMPELLER
`
`(57) Abstract
`
`A pump assembly (1, 33, 200) adapted for
`continuous flow pumping of blood. In a particular fo1m
`the pump (I, 200) is a centrifugal pump wherein the
`impeller (100, 204) is entirely sealed within the pump
`housing (2, 201) and is hydrodynamically suspended
`therein as the impeller rotates within the fluid (105)
`urged by electromagnetic means extemal to the pump
`cavi ty (106, 203). Hydrodynamic suspension is assisted
`by the impeller (100, 204) having deformities therein
`such as blades (8) with tapered surfaces at leading edges
`(102, 223) and trailing edges (1 03, 224) of bottom and
`top edges (221, 222) thereof.
`
`5
`
`I
`
`I~ I
`
`PAGE 1 OF 52
`
`PETITIONERS' EXHIBIT 1112
`
`

`

`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.
`
`AL
`AM
`AT
`AU
`AZ
`BA
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`CI
`CM
`CN
`cu
`cz
`DE
`DK
`EE
`
`Albania
`Annenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Herzegovina
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cote d'Tvoire
`Cameroon
`China
`Cuba
`Czech Republic
`Gennany
`Denmark
`Estonia
`
`ES
`FI
`FR
`GA
`GB
`GE
`GH
`GN
`GR
`HU
`IE
`IL
`IS
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LC
`LI
`LK
`LR
`
`Spain
`Finland
`France
`Gabon
`United Kingdom
`Georgia
`Ghana
`Guinea
`Greece
`Hungary
`Ireland
`Israel
`Iceland
`Italy
`Japan
`Kenya
`Kyrgyzstan
`Democratic People's
`Republic of Korea
`Republic of Korea
`Kazakstan
`Saint Lucia
`Liechtenstein
`Sri Lanka
`Liberia
`
`LS
`LT
`LU
`LV
`MC
`MD
`MG
`MK
`
`ML
`MN
`MR
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`so
`SE
`SG
`
`Lesotho
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`'Tite former Yugoslav
`Republic of Macedonia
`Mali
`Mongolia
`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`
`SI
`SK
`SN
`sz
`TO
`TG
`TJ
`TM
`TR
`TT
`UA
`UG
`us
`uz
`VN
`YU
`zw
`
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Turkmenistan
`Turkey
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`VietNam
`Yugoslavia
`Zimbabwe
`
`PAGE 2 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`A ROTARY PUMP WITH HYDRODYNAMICALLY SUSPENDED IMPELLER
`
`FIELD OF THE INVENTION
`This invention relates to rotary pumps adapted, but not
`exclusively, for use as artificial hearts or ventricular
`assist devices and,
`in particular, discloses in preferred
`forms a seal-less shaft-less pump featuring open or closed
`(shrouded) impeller blades with the edges of the blades used
`as hydrodynamic thrust bearings and with electromagnetic
`torque provided by the interaction between magnets embedded
`in the blades and a rotating current pattern generated in
`wires fixed relative to the pump housing.
`
`BACKGROUND ART
`This
`invention relates to the art of continuous or
`pulsatile
`flow
`rotary
`pumps
`and,
`in particular,
`to
`electrically driven pumps suitable for use although not
`exclusively as an artificial heart or ventricular assist
`device. For permanent implantation in a human patient, such
`pumps should ideally have the following characteristics: no
`leakage of fluids into or from the bloodstream; no wearing
`parts; minimum residence time of blood in pump to avoid
`thrombosis (clotting) ; minimum shear stress on blood to avoid
`blood cell damage such as haemolysis; maximum efficiency to
`maximise battery duration and minimise blood heating; and
`absolute reliability.
`Several of these characteristics are very difficult to
`meet in a conventional pump configuration including a seal,
`i.e. with an impeller mounted on a shaft which penetrates a
`wall of the pumping cavity, as exemplified by the blood pumps
`referred to in U.S. Pat. No. 3,957,389 to Rafferty et al.,
`U.S. Pat. No. 4,625,712
`to Wampler, and U.S. Pat. No.
`5,275,580 to Yamazaki. Two main disadvantages of such pumps
`are firstly that the seal needed on the shaft may leak,
`especially after wear, and secondly that the rotor of the
`motor providing the shaft torque remains to be supported, with
`mechanical bearings such as ball-bearings precluded due to
`
`5
`
`10
`
`15
`
`2 0
`
`25
`
`30
`
`35
`
`PAGE 3 OF 52
`
`

`

`wo 99/12587
`
`PCT/AU98/00725
`
`-2-
`
`Some designs, such as U.S. Pat. No. 4,625,712 to
`wear.
`Wampler and U.S. Pat. No. 4, 908, 012 to Moise et al., have
`overcome these problems simultaneously by combining the seal
`and the bearing into one hydrodynamic bearing, but in order
`to prevent long residence times they have had to introduce
`means to continuously supply a blood-compatible bearing purge
`fluid via a percutaneous tube.
`In seal-less designs, blood is permitted to flow through
`the gap in the motor, which is usually of the
`DC
`type, i.e. comprising a rotor including permanent magnets and
`a stator in which an electric current pattern is made to
`rotate synchronously with the rotor.
`Such designs can be
`classified according to the means by which the rotor is
`suspended: contact bearings, magnetic bearings or hydrodynamic
`bearings, though some designs use two of these means.
`Contact or pivot bearings, as exemplified by U.S. Pat.
`No. 5527159 to Bozeman et al. and U.S. Pat. No. 53990.74 to
`Nose et al., have potential problems due to wear, and cause
`very high localised heating and shearing of the blood, which
`can cause deposition and denaturation of plasma proteins, with
`the risk of embolisation and bearing seizure.
`Magnetic bearings, as exemplified by U.S. Pat. No.
`5,350,283 to Nakazeki et al., U.S. Pat. No. 5,326,344 to Bramm
`et al. and U.S. Pat. No. 4,779,614 to Moise et al., offer
`contactless suspension, but require rotor position measurement
`and active control of electric current for stabilisation of
`the position
`in at
`least one direction, according
`to
`Earnshaw's theorem. Position measurement and feedback control
`introduce significant complexity, increasing the failure risk.
`Power use by the control current implies reduced overall
`efficiency. Furthermore, size, mass, component count and cost
`are all increased.
`US Pat. No. 5,507,629 to Jarvik claims to have found a
`configuration circumventing Earnshaw's Theorem and
`thus
`requiring only passive magnetic bearings, but this is doubtful
`and contact axial bearings are
`included
`in any case.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 4 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-3-
`
`Similarly, passive radial magnetic bearings and a pivot point
`are employed in U.S. Pat. No. 5,443,503 to Yamane.
`employing
`Prior
`to
`the present
`invention,
`pumps
`hydrodynamic suspension, such as US Pat. No. 5,211,546 to
`Isaacson et al. and US Pat. No. 5,324,177 to Golding et al.,
`have used journal bearings, in which radial suspension is
`provided by the fluid motion between two cylinders in relative
`rotation, an inner cylinder lying within and slightly off axis
`to
`a
`slightly
`larger diameter outer cylinder.
`Axial
`suspension is provided magnetically in US Pat. No. 5,324,177
`and by either a contact bearing or a hydrodynamic thrust
`bearing in US Pat. No. 5,211,546.
`A purging flow is needed through the journal bearing, a
`high shear region, in order to remove dissipated heat and to
`prevent long fluid residence time.
`It would be inefficient
`to pass all the fluid through the bearing gap, of small
`cross-sectional area, as this would demand an excessive
`pressure drop across the bearing.
`Instead a leakage path is
`generally provided from the high pressure pump outlet, through
`the bearings and back to the low pressure pump inlet, implying
`a small reduction in outflow and pumping efficiency. US Pat.
`No. 5,324,177 provides a combination of additional means to
`increase the purge flow, namely helical grooves in one of the
`bearing surfaces, and a small additional set of impellers.
`US Pat. No. 5,211,546 provides 10 embodiments with
`various locations of cylindrical bearing surfaces. One of
`these embodiments,
`the third,
`features a single
`journal
`bearing and a contact axial bearing.
`Embodiments of the present invention offer a relatively
`low cost and/or relatively low complexity means of suspending
`the rotor of a seal-less blood pump,
`thereby overcoming or
`ameliorating the problems of existing devices mentioned above.
`
`SUMMARY OF THE INVENTION
`According to one aspect of the present invention, there
`is disclosed a rotary blood pump with impeller suspended
`hydrodynamically by thrust forces generated on the edges of
`
`5
`
`10
`
`15
`
`2 0
`
`25
`
`30
`
`35
`
`PAGE 5 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-4-
`
`the impeller blades. The blade edges are shaped such that the
`gap between the edges and the housing at the leading edge is
`greater than at the trailing edge and thus the fluid which is
`drawn through the gap experiences a wedge shaped restriction
`which generates a thrust away from the housing, as described
`in Reynold's theory of lubrication.
`In preferred embodiments of the invention, the pump is
`of centrifugal or mixed flow type with impeller blades open
`on both the front and back faces of the housing. At least one
`face of the housing is made conical, in order that the thrust
`perpendicular to it has a radial component, which provides a
`radial restoring force
`to a
`radial displacement of
`the
`impeller axis. Similarly, an axial displacement toward either
`the front or the back face increases the thrust from that face
`and reduces the thrust from the other face. Thus the sum of
`the forces on the impeller due to inertia (within limits),
`gravity and any bulk radial or axial hydrodynamic force on the
`impeller can be countered by a restoring force from the thrust
`bearings after a small displacement of the impeller within the
`housing relative to the housing in either a radial or axial
`direction.
`In the preferred embodiment, the impeller driving torque
`derives
`from
`the magnetic
`interaction between permanent
`magnets within the blades of the impeller and oscillating
`currents in windings encapsulated in the pump housing.
`In a second embodiment of the invention, the principle
`is applied in a pump of axial
`type. Within a uniform
`cylindrical section of the pump housing, tapered blade edges
`form a radial hydrodynamic bearing.
`If the pump housing is
`made with reducing radius at the two ends,
`then the end
`hydrodynamic thrust forces have an axial component which can
`provide the axial bearing. Alternatively, magnetic forces or
`other means can provide the axial bearing.
`In a
`further broad form of
`the
`invention there is
`provided a rotary blood pump having an impeller suspended
`hydrodynamically by thrust forces generated by the impeller
`during movement in use of the impeller.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`3 0
`
`3 5
`
`PAGE 6 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-5-
`
`Preferably said thrust forces are generated by blades of
`said impeller or by deformities therein.
`More preferably said thrust forces are generated by edges
`of said blades of said impeller.
`Preferably said edges of said blades are tapered.
`In an alternative preferred form said pump is of axial
`type.
`Preferably within a uniform cylindrical section of the
`pump housing, tapered blade edges form a radial hydrodynamic
`bearing.
`Preferably the pump housing is made with reducing radius
`at the two ends, and wherein the end hydrodynamic thrust
`forces have an axial component which can provide the axial
`bearing.
`Preferably magnetic forces or other means can provide the
`axial bearing.
`In a further broad form invention there is provided a
`rotary blood pump having a housing within which an impeller
`acts by
`rotation about an axis
`to cause
`a pressure
`differential between an inlet side of a housing of said pump
`and an outlet side of the housing of said pump; said impeller
`suspended hydrodynamically by thrust forces generated by the
`impeller during movement in use of the impeller.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`invention will now be
`Embodiments of
`the present
`described, with reference
`to
`the accompanying drawings,
`wherein:
`longitudinal cross-sectional view of a
`Fig. 1 is a
`preferred embodiment of the invention;
`Fig. 2 is a cross-sectional view taken generally along
`the line z-z of Fig. 1;
`Fig. 3A is a cross-sectional view of an impeller blade
`taken generally along the line A-A of Fig. 2;
`Fig. 3B is an enlargement of the blade-pump housing
`interface portion of Fig. 3A;
`Fig. 3C is an alternative impeller blade shape;
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 7 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-6-
`
`Figs. 4A, B, C illustrate various possible locations of
`magnet material within a blade;
`Fig. 5 is a left-hand end view of a possible winding
`geometry taken generally along the line 8-8 of Fig. 1;
`Fig. 6 is a diagrammatic cross sectional view of an
`alternative embodiment of the invention as an axial pump;
`Fig .. 7 is an exploded, perspective view of a centrifugal
`pump assembly according to a
`further embodiment of
`the
`invention;
`Fig. 8 is a perspective view of the impeller of the
`assembly of Fig. 7;
`Fig. 9 is a perspective, cut away view of the impeller
`of Fig. 8 within the pump assembly of Fig. 7;
`Fig. 10 is a side section indicative view of the impeller
`of Fig. 8;
`Fig. 11 is a detailed view in side section of edge
`portions of the impeller of Fig. 10;
`Fig. 12 is a block diagram of an electronic driver
`circuit for the pump assembly of Fig. 7;
`Fig. 13 is a graph of head versus flow for the pump
`assembly of Fig. 7;
`Fig.. 14 is a graph of pump efficiency versus flow for the
`pump assembly of Fig. 7;
`Fig. 15 is a graph of electrical power consumption versus
`flow for the pump assembly of Fig. 7;
`Fig. 16 is a plan, section view of the pump assembly
`showing
`a volute arrangement according
`to a preferred
`embodiment;
`Fig. 17 is a plan, section view of a pump assembly
`showing an alternative volute arrangement;
`Fig. 18 is a plan view of an impeller according to a
`further embodiment of the invention;
`Fig. 19 is a plan view of an impeller according to a
`further embodiment of the invention;
`Fig. 20 is a perspective view of an impeller according
`to a further embodiment of the invention.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 8 OF 52
`
`

`

`wo 99/12587
`
`PCT/AU98/00725
`
`-7-
`
`DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
`The pump assemblies according
`to various preferred
`embodiments
`to be described below all have particular,
`although not exclusive, application for implantation in a
`mammalian body so as to at least assist, if not take over, the
`function of
`the mammalian heart.
`In practice this is
`performed by placing the pump assembly entirely within the
`body of the mammal and connecting the pump between the left
`ventricle and the aorta so as to assist left side heart
`function. It may also be connected to the right ventricle and
`pulmonary artery to assist the right side of the heart.
`In this instance the pump assembly includes an impeller
`which is fully sealed within the pump body and so does not
`require a shaft extending through the pump body to support it.
`The impeller is suspended, in use, within the pump body by,
`at least, the operation of hydrodynamic forces imparted as a
`result of the interaction between the rotating impeller, the
`internal pump walls and the fluid which the impeller causes
`to be urged from an inlet of the pump assembly to an outlet
`thereof.
`the
`is
`invention
`the
`embodiment of
`A preferred
`centrifugal pump 1, as depicted in Figs. 1 and 2, intended for
`implantation into a human, in which case the fluid referred
`to below is blood. The pump housing 2, can be fabricated in
`two parts, a front part 3 in the form of a housing body and
`a back part 4 in the form of a housing cover, with a smooth
`join therebetween, for example at 5 in Fig. 1. The pump 1 has
`an axial inlet 6 and a tangential outlet 7. The rotating part
`100 is of very simple form, comprising only blades 8 and a
`support cone 9 to hold those blades fixed relative to each
`other. The blades may be curved as depicted in Fig. 2, or
`straight, in which case they can be either radial or tilted,
`i.e. at an angle to the radius. This rotating part 100 will
`hereafter be called the impeller 100, but it also serves as
`a bearing component and as the rotor of a motor configuration
`as to be further described below whereby a torque is applied
`by electromagnetic means to the impeller 100. Note that the
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 9 OF 52
`
`

`

`WO 99/12587
`
`PCT/AU98/00725
`
`-8-
`
`impeller has no shaft and that the fluid enters the impeller
`from the region of its axis RR.
`Some of the fluid passes in
`front of the support cone 9 and some behind it, so that the
`pump 1 can be considered of two-sided open type, as compared
`to conventional open centrifugal pumps, which are only open
`on the front side. Approximate dimensions found adequate for
`the pump 1 to perform as a ventricular assist device, when
`operating at speeds in the range 2,000 rpm to 4,000 rpm, are
`outer blade diameter 40 mm, outer housing average diameter 60
`mm, and housing axial length 40 mm.
`As the blades 8 move within the housing, some of the
`fluid passes through the gaps, much exaggerated in Figs. 1 and
`3, between the blade edges 101 and the housing front face 10
`and housing back face 11.
`In all open centrifugal pumps, the
`gaps are made small because this leakage flow lowers the pump
`hydrodynamic efficiency.
`In the pump disclosed in this
`embodiment,
`the gaps are made slightly smaller
`than is
`conventional in order that the leakage flow can be utilised
`to create a hydrodynamic bearing. For the hydrodynamic forces
`to be sufficient, the blades must also be tapered as depicted
`in Figs. 3A and 3B 1
`so that the gap 104 is larger at the
`leading edge 102 of the blade 8 than at the trailing edge 103.
`The fluid 105 which passes through the gap thus experiences
`a wedge shaped restriction which generates a
`as
`thrust 1
`described
`in Reynolds'
`theory of
`lubrication
`(see,
`for
`example 1 "Modern Fluid Dynamics, Vol. 1 Incompressible Flow",
`by N. Curle and H.J. Davies, Van Nostrand, 1968). The thrust
`is proportional to the square of the blade thickness at the
`edge, and
`thus thick blades are favoured, since if the
`proportion of the pump cavity filled by blades is constant,
`then the net thrust force will be inversely proportional to
`the number of blades. However, the blade edges can be made
`to extend as tails from thin blades as depicted in Fig. 3C in
`order to increase the blade area adjacent the walls.
`In one particular form, the tails join adjacent blades
`so as
`to form a complete shroud with wedges or tapers
`incorporated therein. An example of a shroud design as well
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 10 OF 52
`
`

`

`wo 99/12587
`
`PCT/AU98/00725
`
`-9-
`
`as other variations on the blade structure will be described
`later in this specification.
`For manufacturing simplicity, the housing front face 10
`can be made conical, with an angle of around 45° so that
`provides both axial and radial hydrodynamic forces. Other
`angles are suitable that achieve the functional requirements
`of this pump including the requirements for both axial and
`radial hydrodynamic forces.
`Other curved surfaces are possible provided both axial
`and radial hydrodynamic forces can be produces as a res~lt of
`rotation of the blades relative to the housing surfaces.
`The housing back face 11 can include a roughly conical
`extension 12 pointing into the pump cavity 106, to eliminate
`or minimise the effect of the flow stagnation point on the
`axis of the back housing.
`Alternatively extension 12 can resemble an impeller eye
`to make the flow mixed.
`for manufacturing
`embodiment,
`In
`this preferred
`simplicity and for uniformity in the flow axial direction RR,
`the housing back face 11 is made flat over the bearing
`surfaces, i.e. under the blade edges. With this the case, a
`slacker tolerance on the alignment between the axes of the
`front part 3 and back part 4 of the housing 2 is permissible.
`An alternative is to make the back face 11 conical at the
`bearing surfaces, with taper in the opposite direction to the
`front face 10, so that the hydrodynamic forces from the back
`face will also have radial components. Tighter tolerance on
`the axes alignment would then be required, and some of the
`flow would have to undergo a reversal in its axial direction.
`Again a roughly conical extension (like 12) will be needed.
`There may be some advantage in making the housing surfaces and
`blade edges non-straight, with varying tangent angle, although
`this will impose greater manufacturing complexity.
`There are several options for the shape of the taper, but
`in the preferred embodiment the amount of material removed
`simply varies linearly or approximately linearly across the
`blade. For the back face, the resulting blade edges are then
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 11 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-10-
`
`planes at a slight inclination to the back face.
`For the
`front face, the initial blade edges are curved and the taper
`only removes a relatively small amount of material so they
`still appear curved. Alternative taper shapes can include a
`step in the blade edge, though the corner in that step would
`represent a stagnation line posing a thrombosis risk.
`For a given minimum gap, at the trailing blade edge, the
`hydrodynamic force is maximal if the gap at the leading edge
`is approximately double that at the trailing edge. Thus the
`taper, which equals the leading edge gap minus the trailing
`edge gap, should be chosen to match a nominal minimum gap,
`once the impeller has shifted towards that edge. Dimensions
`which have been found to give adequate thrust forces are a
`taper of around 0.05 mm for a nominal minimum gap of around
`0.05 mm, and an average circumferential blade edge thickness
`of around 5 mm for 4 blades. For the front face, the taper
`is measured within the plane perpendicular to the axis. The
`axial length of the housing between the front and back faces
`at any position should then be made about 0.2 mm greater than
`the axial length of the blade, when it is coaxial with the
`housing,· so that the minimum gaps are both about 0. 1 mm
`axially when the impeller 100 is centrally positioned within
`the housing 2.
`Then, for example, if the impeller shifts
`axially by 0.05 mm,
`the minimum gaps will be 0.05 mm at one
`face and 0.15 mm at the other face. The thrust increases with
`decreasing gap and would be much larger from the 0.05 mm gap
`than from the 0.15 mm gap, about 14 times larger for the above
`dimensions. Thus there is a net restoring force away from the
`smaller gap.
`Similarly, for radial shifts of the impeller the radial
`component of the thrust from the smaller gap on the conical
`housing front face would offer the required restoring radial
`force or from the hub. The axial component of that force and
`its torque on the impeller would have to be balanced by an
`axial force and torque from the housing back face, and so the
`impeller will also have to shift axially and tilt its axis to
`be no longer parallel with the housing axis.
`Thus as the
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 12 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-11-
`
`person moves and the pump is accelerated by external forces,
`the
`impeller will continually shift
`its position and
`alignment, varying the gaps in such a way that the total force
`and torque on the impeller 100 match that demanded by inertia.
`The gaps are so small, however,
`that
`the variation in
`hydrodynamic efficiency will be small, and the pumping action
`of the blades will be approximately the same as when the
`impeller is centrally located.
`While smaller gaps imply greater hydrodynamic efficiency
`and greater bearing thrust forces, smaller gaps also demand
`tighter manufacturing tolerances, increase frictional drag on
`the impeller, and impose greater shear stress on the fluid.
`Taking these points in turn, for the above 0.05 mm
`and
`gaps, tolerances of around ±0. 015 mm are needed, which imposes
`some cost penalty but is achievable. A tighter tolerance is
`difficult, especially if the housing is made of a plastic,
`given the changes in dimension caused by temperature and
`possible absorption of fluid by plastic. The frictional drag
`for the above gaps produces negligible torque compared to the
`typical motor torque. Finally, to estimate the shear stress,
`consider a rotation speed of 3,000 rpm and a typical radius
`of 15 mm, at which the blade speed is 4.7 ms- 1 and the average
`velocity shear for an average gap of 0.075 mm is 6.2 x 10 4
`For blood of dynamic viscosity 3. 5 x 10- 3 kgm- 1 s- 1
`the average
`shear stress would be 220 Nm- 2
`• Other prototype centrifugal
`blood pumps with closed blades have found that slightly larger
`gaps, e.g. 0.15 mm, are acceptable for haemolysis. A major
`advantage of the open blades of the present invention is that
`a fluid element that does pass through a blade edge gap will
`have very short residence time in that gap, around 2 x 10- 3 s,
`and the fluid element will most likely be swept though the
`pump without passing another blade edge.
`To minimise the net force required of the hydrodynamic
`bearings, the net axial and radial hydrodynamic forces on the
`impeller from the bulk fluid flow should be minimised, where
`"bulk" here means other than from the bearing thrust surfaces.
`One method of minimising the bulk radial hydrodynamic
`
`,
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 13 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-12-
`
`force is to use straight radial blades so that pressure acting
`on the blade sides has virtually no radial component.
`The
`radial force on the impeller depends critically on the shape
`of the output flow collector or volute 13. The shape should
`be designed to minimise the radial impeller force over the
`desired range of
`pump speeds, without excessively lowering
`the pump efficiency. The optimal shape will have a roughly
`helical perimeter between the "tongue" and out
`The radial
`force can also be reduced by the introduction of an internal
`division in the volute 13 to create a second output flow
`collector passage, with tongue approximately diametrically
`opposite to the tongue of the first passage.
`An indicative plan view of impeller 100 relative to
`housing 2 is shown having a concentric volute 13.
`Fig. 17 illustrates the alternative volute arrangement
`comprising a split volute created by volute barrier 107 which
`causes volute 108 in a first hemisphere of the housing 2 to
`split into first half volute 109 and second half volute 110
`over the second hemisphere.
`The hemispheres are defined
`respectively on each side of a diameter of the housing 2 which
`passes through or near exit point 111 of outlet 7.
`In alternative forms concentric volutes can be utilised,
`particularly where specific speed is relatively low.
`In a further particular form a vaneless diffuser may also
`reduce the radial force.
`In regard to the bulk axial hydrodynamic axial force, if
`the blade cross-section is made uniform in the axial direction
`along the retational axis, apart from the conical front edge,
`then the pressure acting on the blade surface (excluding the
`bearing edges) will have no axial component.
`This also
`simplifies the blade manufacture. The blade support cone 9
`must then be shaped to minimise axial thrust on the impeller
`and minimise disturbance to the flow over the range of speeds,
`while maintaining sufficient strength to prevent relative
`blade movement. The key design parameter affecting the axial
`force is the angle of the cone. The cone is drawn in Fig. 1
`as having the same internal diameter as the blades, which may
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 14 OF 52
`
`

`

`wo 99/12587
`
`PCT I A U98/00725
`
`-13-
`
`aid manufacture. However, the cone could be made with larger
`or smaller internal diameter to the blades. There may be
`advantage in using a non-axisymmetric support "cone", e.g.
`with larger radius on the trailing surface of a blade than the
`radius at the leading surface of the next blade.
`If the
`blades are made with non-uniform cross section to increase
`hydrodynamic efficiency,
`then any bulk hydrodynamic axial
`force on them can be balanced by shaping the support cone to
`produce an opposite bulk hydrodynamic axial force on it.
`Careful
`design
`of
`the
`entire
`pump,
`employing
`computational fluid dynamics, is necessary to determine the
`optimal shapes of the blades 8, the volute 13, the support
`cone 9 and the housing 2, in order to maximise hydrodynamic
`efficiency while keeping the bulk fluid hydrodynamic forces,
`shear and residence times
`low. All edges and the joins
`between .the blades and the support cone should be smoothed.
`The means of providing the driving torque on the impeller
`100 of
`the preferred embodiment of
`the
`invention is to
`encapsulate permanent magnets 14
`in the blades 8 of the
`impeller 100 and to drive them with a rotating magnetic field
`pattern from oscillating currents in windings 15 and 16, fixed
`relative to the housing 2. Magnets of high remanence such as
`sintered rare-earth magnets should be used to maximise motor
`efficiency.
`The magnets should be aligned axially or
`approximately axially, with alternating polarity for adjacent
`blades. Thus there must be an even number of blades. Since
`low blade number is preferred for the bearing force, and since
`two blades would not have sufficient bearing stiffness to
`rotation about an axis through the blades and perpendicular
`to the pump housing (unless the blades are very curved), four
`blades are recommended.
`A higher number of blades, for
`example 6 or 8 will also work.
`Some possible options for locating the magnets 14 within
`the blades 8 are shown in Fig. 4. The most preferred which
`is depicted in Fig. 4A,
`for the blade to be made of magnet
`material apart from a biocompatible shell or coating to
`prevent fluid corroding the magnets and to prevent magnet
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`PAGE 15 OF 52
`
`

`

`wo 99/12587
`
`PCT/AU98/00725
`
`-14-
`
`thickness
`
`is approximately 1
`
`material (which is toxic for rare earth magnets) entering the
`blood stream. The coating should also be sufficiently durable
`especially at blade corners to withstand rubbing during
`start-up or during inadvertent bearing touch down.
`In one particular form the inside walls of the pump
`housing 2 are also coated with a biologically compatible and
`wear resistant material such as diamond coating or titanium
`nitride so that wear on both of the touching surfaces is
`minimised.
`An acceptable coating
`micron.
`A suitable impeller manufacturing method is to die-press
`the ent