Patent Publication Number: US-9429160-B2

Title: Centrifugal pump and method of manufacturing centrifugal pump

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese patent application 2012-068398, filed Mar. 23, 2012, which is hereby incorporated by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a centrifugal pump and a method of manufacturing a centrifugal pump. 
     2. Background Art 
     In the prior art, a blood pump for transporting blood includes a turbo-type pump for delivering blood by a centrifugal force, the pump being provided with a hollow housing, an impeller rotatably encased in the housing, and a rotation shaft being in the rotation center of the impeller (for example, see U.S. Pat. No. 5,575,630). In the blood pump disclosed in U.S. Pat. No. 5,575,630, the housing, the impeller, and the rotation shaft are constituted of separate members which are assembled to manufacture the blood pump. In assembling the blood pump, the rotation shaft and a magnet are first assembled onto the pre-existing impeller, and then the assembled components are encased in the housing. At least one of the rotation shaft or a pivot bearing that receives the shaft is made of a relatively hard material such as metal or ceramic in order to provide sufficient durability to the constant wear that occurs during rotation of the impeller. 
     Desirable properties of the impeller include compatibility with blood, easy moldability, and transparency. Due to these different considerations, the preferred materials for the impeller are different from the preferred materials for the shaft member. Consequently, the two components have been separately fabricated and then assembled together. 
     Since the blood pump disclosed in U.S. Pat. No. 5,575,630 has a structure in which the rotation shaft is assembled to the impeller by inserting it into a pre-existing bore formed in the impeller, a slight (minute) gap is unavoidably present between the rotation shaft and the impeller because of manufacturing tolerances and the requirement to make the shaft member insertable. During the use of the blood pump, blood enters into the gap between the rotation shaft and the impeller due to a capillary phenomenon or a pressure difference, which can result in blood clotting and hemolysis during pump operation. 
     SUMMARY OF THE INVENTION 
     The invention provides a centrifugal pump, which reliably prevents blood from entering between a centrifugal force applying member and a shaft member, and a method of manufacturing the centrifugal pump. 
     According to the present invention, a shaft member and a centrifugal force applying member (i.e., impeller) are formed integrally with each other. Consequently, it is possible to prevent a gap from being formed between the centrifugal force applying member and the shaft member, that is, at a boundary portion between the centrifugal force applying member and the shaft member. Blood flowing into a housing through a blood inlet is prevented from entering the boundary portion, and thus it is possible to prevent blood clotting and hemolysis at the boundary portion during the use of the centrifugal pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view showing a shaft member. 
         FIG. 2  is a vertical cross-sectional view showing the shaft member in a die during insert molding of a spacer member of an impeller. 
         FIG. 3  is a vertical cross-sectional view showing the shaft member and spacer member after insert molding. 
         FIG. 4  is a vertical cross-sectional view showing the shaft member and spacer member after inserting magnets. 
         FIG. 5  is a vertical cross-sectional view showing the product of  FIG. 3  in a die during insert molding of a cover member. 
         FIG. 6  is a vertical cross-sectional view showing the product resulting from  FIG. 5 . 
         FIG. 7  is a vertical cross-sectional view showing an assembled blood pump according to a first embodiment. 
         FIG. 8  is a perspective view of a state shown in  FIG. 3 . 
         FIG. 9  is a perspective view of a state shown in  FIG. 4 . 
         FIG. 10  is a perspective view of the state shown in  FIG. 6 . 
         FIG. 11  is a vertical cross-sectional view showing a second embodiment of a centrifugal pump according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, a centrifugal pump and a method of manufacturing a centrifugal pump according to the invention will be described in detail based on preferred embodiments shown in the accompanying drawings. 
       FIGS. 1 to 7  are vertical cross-sectional views sequentially showing a method of manufacturing a centrifugal pump according to a first embodiment of the invention. In the following description, the upper sides of  FIGS. 1 to 10  will be referred to as “upper” and their lower sides as “lower” for convenience of explanation. 
     A centrifugal pump  1  shown in  FIG. 7  is provided with a housing  2  constituted of a hollow body, an impeller  3  rotatably encased in the housing  2 , and a support mechanism  4  supporting the impeller  3  rotatably with respect to the housing  2 . Hereinafter, the configuration of each component will be described. 
     The overall shape of the housing  2  is a flat cylindrical shape and is constituted of an upper member  27  and a lower member  28 . The upper member  27  has a top plate  21  and a side wall  23  provided at an edge of the top plate  21  so as to have an annular shape in a circumferential direction of the top plate  21 . The lower member  28  has a bottom plate  22  and a rib  29  provided near the edge of the top plate  21  so as to have an annular shape in the circumferential direction of the top plate  21 . The rib  29  is fitted in a liquid-tight manner to the side wall  23  onto its outer periphery, whereby the upper member  27  and the lower member  28  are assembled. A flat space surrounded by the top plate  21 , the bottom plate  22 , and the side wall  23  defines a pump chamber  24 . 
     The housing  2  has a blood inlet  25  through which blood Q flows in and a blood outlet  26  through which the blood Q flows out. The blood inlet  25  and the blood outlet  26  each communicate with the pump chamber  24 . The blood Q flowing in through the blood inlet  25  can flow out through the blood outlet  26  via the pump chamber  24 . 
     The blood inlet  25  is formed to protrude in a tubular form from the central portion of the top plate  21  of the upper member  27 . A tube constituting a blood circuit of a perfusion system can be connected to the blood inlet  25 , for example. 
     The blood outlet  26  is formed to protrude in a tubular form from an outer periphery  231  of the side wall  23 . The blood outlet  26  extends in a tangential direction from the outer periphery  231  of the side wall  23 . 
     In the pump chamber  24  of the housing  2 , the disk-shaped impeller  3  is disposed concentrically. The impeller  3  is a centrifugal force applying member which rotates to apply the centrifugal force to the blood Q. 
     The impeller  3  has a cover member  35 , a spacer member  36  encased in the cover member  35 , and a magnet  34  encased in the cover member  35  along with the spacer member  36 . 
     The cover member  35  consists of a disk-shaped hollow body having a hollow  351  which can collectively encase the spacer member  36  and the magnet  34  together. 
     As shown in  FIG. 10 , the impeller formed by cover member  35  and spacer member  36  has a plurality of blood flow paths  31  (e.g., six in this embodiment) through which the blood Q passes. The blood flow paths  31  are radially formed beginning at the center of the cover member  35 . The respective portions of the blood flow paths  31  on the center side of the cover member  35  are joined to (intersected with) each other and open in the upper surface  32  of the cover member  35 . Meanwhile, the respective portions of the blood flow paths  31  on the opposite side to the center side of the cover member  35  open in an outer periphery  33  of the cover member  35 . A gap  241  is formed between the outer periphery  33  of the cover member  35  and an inner periphery  232  of the side wall  23  of the housing  2  ( FIG. 7 ). 
     When the cover member  35  rotates in a clockwise direction in  FIG. 10 , the blood Q flowing in through the blood inlet  25  enters each of the blood flow paths  31  from the center side portion of the cover member  35  to receive a centrifugal force, and, thus, to flow down in the blood flow paths  31 . The blood Q, which has flowed down, flows out into the gap  241 . Then, when the blood Q receives rotational force in the clockwise direction in the gap  241  and reaches the blood outlet  26 , the blood Q is discharged from the blood outlet  26 . 
     The spacer member  36  is disposed in the hollow  351  of the cover member  35 . As shown in  FIGS. 8 and 9 , the spacer member  36  has a disk-shaped base  361 , a plurality of fan-shaped portions  362  (six in the illustrated configuration) arranged above the base  361  and having a fan shape in plan view, and an annular connection  363  connecting the base  361  and each of the fan-shaped portions  362 . 
     Fan-shaped portions  362  have corners  364 , each with a central angle facing toward the center of the base  361  and arranged at equal angular intervals around the central axis of the base  361 . The fan-shaped portions  362  adjacent to each other are spaced apart from each other, and the single blood flow path  31  is constituted between the fan-shaped portions  362 . 
     As shown in  FIGS. 6, 7, and 9 , the annular magnet  34  is mounted between the base  361  and each of the fan-shaped portions  362  of the spacer member  36  by press fitting, for example. In the mounted state, the magnet  34  fills the entire hollow  351  of the cover member  35  in cooperation with the spacer member  36 . 
     For operating the centrifugal pump  1 , the centrifugal pump is first installed in external driving means (not shown). The external driving means has, for example, a motor and a permanent magnet connected to the motor, and the permanent magnet attracts the magnet  34  built in the centrifugal pump  1  by a magnetic force. When the motor rotates in this state, the rotational force is transmitted through the magnets attracted to each other, whereby the impeller  3  can be rotated in the housing  2 . 
     Although the diameter of the impeller  3  is not particularly limited, the diameter may preferably be from 20 to 200 mm, for example, and more preferably 30 to 100 mm. Although the thickness of the impeller  3  is not particularly limited, the thickness may preferably be from 3 to 40 mm, for example, and more preferably 5 to 30 mm. Although a maximum rotation speed of the impeller  3  is not particularly limited, the rotation speed may preferably be up to about 2000 to 6000 rpm, and more preferably 2500 to 5000 rpm, for example. 
     Although materials for the cover member  35 , the spacer member  36 , and the housing  2  are not particularly limited, polycarbonate and acrylic resin are preferably used since these resins are excellent in compatibility with blood Q, transparency, and moldability. 
     As shown in  FIG. 7 , the impeller  3  is supported rotatably with respect to the housing  2  through the support mechanism  4 . The support mechanism  4  has a shaft member  41  constituted of a rod-shaped body, a first bearing  42  rotatably supporting an upper end (one end) portion  411  of the shaft member  41 , and a second bearing  43  rotatably supporting a lower end (the other end) portion  412  of the shaft member  41 . The shaft member  41  is installed so as to be inserted through the center rotation axis of the impeller  3 . The first bearing  42  is installed in and fixed to a first bearing installation portion  254  recessed in the inner peripheral portion of the blood inlet  25  of the housing  2 . The second bearing  43  is installed in and fixed to a position different from the position of the first bearing installation portion  254  (first bearing  42 ) of the housing  2 , that is, a second bearing installation portion  221  recessed in the central portion of the bottom plate  22 . Although a method of fixing the first and second bearings  42  and  43  to the housing  2  is not particularly limited, there are, for example, a method using press fitting, a method using adhesion (with an adhesive or a solvent), a method using fusion bonding (such as thermal fusion bonding, high-frequency fusion bonding, and ultrasonic fusion bonding), and a method using insert molding. 
     Because of their contact with rotating shaft member  41 , first and second bearings  42  and  43  are preferably formed of a material having a higher hardness and resistance to wear than the material forming impeller  3  and housing  2 . 
     The shaft member  41  is a solid body having a constant outer diameter in the longitudinal direction. The upper end surface  413  and the lower end surface  414  of the shaft member  41  are rounded and have a semi-spherical shape. In the shaft member  41 , at least the upper end surface  413  and the lower end surface  414  may be coated with diamond-like carbon (DLC) or titanium, for example. 
     In the centrifugal pump  1  shown in  FIG. 7 , the cover member  35  and the spacer member  36  are formed integrally with the shaft member  41 . According to this construction, it is possible to prevent a gap from being formed between the cover member  35  and the shaft member  41 , that is, at the boundary portion  11 . It is also possible to prevent a gap from being formed between the spacer member  36  and the shaft member  41 , that is, at the boundary portion  12 . It is further possible to prevent the blood Q in the pump chamber  24  from entering the boundary portions  11  and  12  and prevent clotting of the blood Q and hemolysis at the boundary portions  11  and  12  during the use of the centrifugal pump  1 . 
     The integral formation of the cover member  35  and the shaft member  41  and the integral formation of the spacer member  36  and the shaft member  41  can be realized by insert molding as described below. By using the technique of insert molding, members can be integrally molded, and thus it is possible to prevent the blood Q from entering into a spacing and prevent or suppress occurrence of thrombus and hemolysis. Because of the unitary structure of the integrally formed impeller and shaft member, a gap between members is not formed. Since blood cannot enter between the members, sterilization before molding can be omitted. 
     The first bearing  42  is constituted of a cup-shaped member having a semi-spherical concave  421 . The upper end surface  413  of the shaft member  41  can slide on the concave  421 . 
     Similarly to the first bearing  42 , the second bearing  43  is constituted of a cup-shaped member having a semi-spherical concave  431 . The lower end surface  414  of the shaft member  41  can slide on the concave  431 . 
     In a preferred embodiment, the shaft member  41  is made of a metal material, and the first and second bearings  42  and  43  are each made of a resin material. 
     The metal material is not particularly limited and includes, for example, stainless steel. In addition to the metal material, ceramics or the like may be used. The hardness (Vickers hardness, Hv) of such metal or ceramic material is not particularly limited, and may preferably be not less than about 50 and more preferably not less than about 100, for example. 
     The resin material for bearings  42  and  43  is not particularly limited and may include a thermoplastic resin, for example. As the thermoplastic resin, ultrahigh molecular weight polyethylene and polypropylene can be used, for example. 
     Next, a method of manufacturing the centrifugal pump  1  by assembling the housing  2 , the impeller  3 , and the support mechanism  4 , namely by encasing the impeller  3  and the support mechanism  4  in the housing  2  will be described with reference to  FIGS. 1 to 7 . The manufacturing method is characterized in that the shaft member  41  and the impeller  3  are formed integrally with each other before the impeller  3  and the support mechanism  4  are encased in the housing  2 . 
     Prior to the description of the manufacturing method, a molding die  20  for molding the spacer member ( FIG. 2 ) and a molding die  30  for molding the cover member  30  ( FIG. 5 ) that are used in the manufacturing process will be described. 
     As shown in  FIG. 2 , the molding die  20  is used for molding the spacer member  36 . The molding die  20  has an upper molding die  201  and a lower molding die  202  so that they can be vertically opened and closed. When the upper molding die  201  and the lower molding die  202  are closed, a cavity  203  for molding the spacer member  36  can be formed. The upper molding die  201  has a communication hole  204  communicating with the cavity  203 . The cavity  203  can be filled with a resin material  36 ′ as a constituent material of the spacer member  36  in the liquid state through the communication hole  204 . The resin material  36 ′ is cooled to become the spacer member  36 . 
     The upper molding die  201  has a recess  206  into which an upper end side portion of the shaft member  41  is inserted, and the lower molding die  202  has a recess  207  into which a lower end side portion of the shaft member  41  is inserted. In such a state that the shaft member  41  is inserted through the recesses  206  and  207 , the recesses  206  and  207  each are sealed in a liquid-tight manner. 
     As shown in  FIG. 5 , the molding die  30  is used to form the cover member  35 . The molding die  30  has an upper molding die  301  and a lower molding die  302  so that they can be vertically opened and closed. The molding die  30  further has a core  305  removably mounted on the inside of the upper molding die  301 . When the upper molding die  301  on which the core  305  is mounted and the lower molding die  302  are closed, a cavity  303  for molding the cover member  35  can be formed. Core  305  corresponds to openings in cover member  35  for providing blood flow paths  31 . The upper molding die  301  has a communication hole  304  communicating with the cavity  303 . The cavity  303  can be filled with a resin material  35 ′ as a constituent material of the cover member  35  in the liquid state through the communication hole  304 . The resin material  35 ′ is cooled to become the cover member  35 . 
     The upper molding die  301  has a recess  306  into which the upper end side portion of the shaft member  41  is inserted, and the lower molding die  302  has a recess  307  into which the lower end side portion of the shaft member  41  is inserted. 
     According to the sequence of the method of the invention beginning with  FIG. 1 , the shaft member  41  constituting the support mechanism  4  is provided. 
     Next, as shown in  FIG. 2 , the molding die  20  is provided, and the upper molding die  201  and the lower molding die  202  are brought into the mold opening state. The shaft member  41  is disposed between the upper and lower molds, and these molds are then brought into the mold closing state. Accordingly, the molding die  20  is in such a state that the shaft member  41  is disposed in the cavity  203 . 
     Next, the entire cavity  203  is filled with the resin material  36 ′ in the liquid state through the communication hole  204  of the upper molding die  201 . 
     Next, the resin material  36 ′ is cooled together with the molding die  20  low enough to solidify the resin material  36 ′ in the cavity  203 . 
     Next, the molding die  20  is opened, and a molded product is released from the molding die  20 , whereby a molded body (first molded body)  40  molded by insert molding is obtained as shown in  FIG. 3 . Thus, the molded body  40  is obtained by integrally forming the spacer member  36  onto the shaft member  41 . 
     Next, as shown in  FIG. 4 , the magnet  34  is affixed on the spacer member  36  of the molded body  40 , whereby an assembly  50  is obtained. For mounting the magnet, adhesion or press fitting is appropriately selected. 
     Next, as shown in  FIG. 5 , the molding die  30  is provided, and the upper molding die  301  mounted with the core  305  and the lower molding die  302  are brought into the mold opening state. The assembly  50  is disposed between the upper and lower molds, and these molds are then brought into the mold closing state. According to this constitution, the molding die for molding the cover member  30  is in such a state that the assembly  50  is disposed in the cavity  303 . 
     Then, the entire cavity  303  is filled with the resin material  35 ′ in the liquid state through the communication hole  304  of the upper molding die  301 . 
     Next, the resin material  35 ′ is cooled together with the molding die for molding the cover member  30  low enough to solidify the resin material  35 ′ in the cavity  303 . 
     Next, the molding die  30  is opened, and a molded product is released from the molding die  30 , whereby a molded body (second molded body)  60  molded by insert molding is obtained as shown in  FIG. 6 . The molded body  60  is obtained by further integrally forming the shaft member  41  with the cover member  35 . 
     Next, the housing  2  is provided. In the housing  2 , the first and second bearings  42  and  43  each are previously fixed to the housing  2 . 
     Then, as shown in  FIG. 7 , in such a state that the housing  2  is separated into the upper member  27  and the lower member  28 , the molded body  60  is disposed between the upper member  27  and the lower member  28 , and thereafter, the upper member  27  and the lower member  28  are connected, whereby the centrifugal pump  1  is obtained. As described above, in the centrifugal pump  1 , the shaft member  41 , the cover member  35 , and the spacer member  36  are formed integrally with each other to prevent the blood Q from entering the boundary portions  11  and  12 . 
     The shaft member  41  is preferably made of a metal material to obtain strength, hardness and durability. The cover member  35  and the spacer member  36  are preferably made of a resin material to obtain ease of molding. Alternatively, the shaft member  41  may be constituted of a resin material and coated with a material (metal or resin) with a greater hardness than the material used for housing  2  and impeller  3 . 
       FIG. 11  is a vertical cross-sectional view showing a second embodiment of a centrifugal pump according to the invention. Only the points different from the first embodiment will be described, and descriptions of similar matters will not be repeated. 
     The embodiment is similar to the first embodiment, except that the configuration of a support mechanism is different. In the centrifugal pump  1  of the embodiment shown in  FIG. 11 , a support mechanism  4 A includes a second (lower) bearing  43  but lacks the first or upper bearing  42  of the previous embodiment. Shaft member  41  does not fully penetrate through impeller  3 , so that its upper portion  411  is located within spacer member  36  of the impeller  3 . Accordingly, the shaft member  41  is rotationally supported only on one side (the lower side), instead of being rotatably supported on the both sides (upper and lower sides) as in the first embodiment. 
     When the centrifugal pump  1  having the above configuration is operated, the impeller  3  can be stably rotated by its own centrifugal force. 
     Hereinabove, although the illustrated embodiments of the centrifugal pump and the method of manufacturing a centrifugal pump according to the invention have been described, the invention is not limited thereto, and each component constituting the centrifugal pump can be replaced with one having any configuration which can exhibit similar functions. Further, any component may be added to the centrifugal pump. 
     The centrifugal pump and the method of manufacturing a centrifugal pump according to the invention may be a combination of two or more arbitrary configurations of the above embodiments. 
     Although the shaft member is a solid body in the above embodiments, the invention is not limited thereto, and the shaft member may be a hollow body.