Maglev Pump Research Articles

Axial Active–Passive Suspension Electromagnetic System in Radial Air Gap for the Maglev Pump

This paper presents a new type of axial active-passive suspension electromagnetic system for the maglev pump. In industrial applications, the variable residual axial hydraulic force on the impeller may lead to collision and vibration, which need to be compensated. In this paper, a new-type electromagnetic system is constructed with the advantage of providing both active and passive axial force. The designed active magnetic support can generate axial force on diameter magnetized rotor in both positive and negative directions, but it only occupies a small space in the radial air gap. The generated active axial force is proved that it will not change with the rotation angle of the rotor by theoretical derivation. Besides, its control algorithm is also proposed. We designed, simulated and built a prototype, and tested it through the control experiment. And the active force is almost unaffected in the test during rotation and speed step. The prototype system achieves maximum controllable axial force of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 2.0N (0.67N/A), which effectively enhances the axial stiffness. The damping factor of active suspension is 70 times higher than that of passive suspension, which can successfully suppress axial vibration.

Evaluation of real-time thrombus detection method in a magnetically levitated centrifugal blood pump using a porcine left ventricular assist circulation model.

Pump thrombosis induces significant complications and requires timely detection. We proposed real-time monitoring of pump thrombus in a magnetically levitated centrifugal blood pump (mag-lev pump) without using additional sensors, by focusing on the changes in the displacement of the pump impeller. The phase difference between the current and displacement of the impeller increases with pump thrombus. This thrombus detection method was previously evaluated through simulated circuit experiments using porcine blood. Evaluation of real-time thrombus detection in a mag-lev blood pump was performed using a porcine left ventricular assist circulation model in this study. Acute animal experiments were performed five times using five Japanese domestic pigs. To create thrombogenic conditions, fibrinogen coating that induces thrombus formation in a short time was applied to the inner surfaces of the pump. An inflow and an outflow cannula were inserted into the apex of the left ventricle and the carotid artery, respectively, by a minimally invasive surgical procedure that allowed minimal bleeding and hypothermia. Pump flow was maintained at 1L/min without anticoagulation. The vibrational frequency of the impeller (70Hz) and its vibrational amplitude (30μm) were kept constant. The thrombus was detected based on the fact that the phase difference between the impeller displacement and input current to the magnetic bearing increases when a thrombus is formed inside a pump. The experiment was terminated when the phase difference increased by over 1° from the lowest value or when the phase difference was at the lowest value 12hours after commencing measurements. The phase difference increased by over 1° in three cases. The pump was stopped after 12hours in two cases. Pump thrombi were found in the pump in three cases in which the phase difference increased by over 1°. No pump thrombus was found in the other two cases in which the phase difference did not increase. We succeeded in real-time thrombus monitoring of a mag-lev pump in acute animal experiments.

Verification of a thrombus induction method at the target point inside the blood pump using a fibrinogen coating for a thrombus detection study.

Although the magnetically levitated centrifugal blood pump (mag-lev pump) is considered superior to other pumps in antithrombogenicity, thrombotic complications are still reported. Research into thrombus detection inside a mag-lev pump is very important for solving this problem. Our research group has already proposed a method to detect a thrombus inside a mag-lev pump in real time without an additional sensor, which is named the impeller vibration method. To efficiently advance our research with reproducibility, a preconditioning method to induce thrombus inside the pump was thought to be necessary. Therefore, this study aimed to develop a preconditioning method that induces thrombus formation. To verify this method, in vitro experiments for thrombus detection were performed. A mag-lev pump developed at Tokyo Institute of Technology was used. A fibrinogen solution was coated on the inner surfaces of the bottom housing to induce thrombus formation at the target point inside the pump. The thrombus is detected by utilizing the phenomenon that the phase difference between the impeller displacement and input current to the magnetic bearing increases when a thrombus is formed inside a pump. Five hundred mL of porcine blood anticoagulated with heparin sodium was circulated in the mock circuit, and protamine sulfate was administered. Flow rate (1 L/min), impeller vibrational frequency (70 Hz), and vibrational amplitude (30 µm) were set to constant. The experiment was terminated when the phase difference increased by over 2° from the minimum value. The experiments were performed in fibrinogen-coated (group F, n = 5) and non-coated pumps (group N, n = 5). In group F, thrombus formation was observed at the fibrinogen-coated point of the housing. In contrast, a relatively small thrombus was observed in varying locations such as the housing or the impeller in group N. Thrombus formation time (the time from when the phase difference takes the minimum value to when the experiment is terminated) was different between the two groups. The mean time was significantly shorter in group F (44 ± 29 minutes) than in group N (143 ± 38 minutes; p = 0.0019). Therefore, a preconditioning method that induced thrombus formation at the target point inside a blood pump was successfully developed.

Thoracotomy Approach is Associated with Less Right Ventricular Failure and Shorter Length of Stay: An Intermacs Analysis of Nearly 1000 Implants via Thoracotomy

Traditional implantation of Left Ventricular Assist Devices (LVADs) has been performed via median sternotomy. Smaller series of carefully selected patients have suggested a thoracotomy approach may prevent right ventricular failure (RVF) and result in shorter lengths of stay (LOS). We sought to assess the impact of a thoracotomy on outcomes compared to a sternotomy in general clinical use as reported to Intermacs. Retrospective analysis of continuous flow primary LVAD implants from Intermacs between 6/2/2014-12/31/2018 were identified. Logistic regression for moderate/severe RVF at 1 and 3 months by surgical approach was performed. Primary endpoints of time to first RVF and median LOS were analyzed in aggregate, by pump flow type (axial, centrifugal, Full MagLev), and by surgical approach (sternotomy v. thoracotomy). Secondary analysis of survival was performed. Total of 11185 patients were identified (10207 sternotomy, 978 thoracotomy). After multivariate regression, in aggregate thoractomy was independently associated with less for RVF at 1 month (p=0.01) and trended toward less RVF at 3 months (p=0.06). Time to first RVF was significantly different based on pump type with centrifugal pump having significantly less RVF with thoracotomy approach. Time to first RVF was not significantly different based on surgical approach for axial and Full MagLev pumps. LOS was shorter for thoracotomy patients (17 vs 19 days, p<0.0001). Survival did not differ based on surgical approach. Less-invasive, thoracotomy approach to LVAD placement is associated with less RVF in short term follow up and has a shorter post-operative LOS. Pump type significantly influences the advantage of thoracotomy approach with only centrifugal flow pumps benefiting. Randomized trials to further investigate are needed.

磁気浮上型人工心臓

The magnetic bearing and self-bearing motor are promising technologies to achieve long device durability and good blood compatibility of the blood pumps. Active position control of the levitated impeller provides safer operation of the blood pumps in the whole driving range of the pumps. Several types of the magnetically suspended blood pumps have been developed at Ibaraki University. An implantable thin ventricular device for mild heart disease patients has been developed with a self-bearing motor suspended in the radial direction. An extracorporeal maglev blood pump has been developed for acute heart disease patients. It indicates powerful pump performance over a flow rate of 20 L/min and ability to regulate the load of the natural heart by synchronizing the pump speed with the heartbeat. A total artificial heart with rotary blood pumps driven by a single maglev motor has a small size to implant it enough in patients. The magnetic suspension mechanism and pump features of these maglev pumps are described in the paper.

Magnetically suspended motor system applied to artificial hearts and blood pumps

Magnetic levitation technology, for magnetic bearings and magnetically suspended motors, is a cutting edge technology to produce artificial hearts and higher performance blood pumps. A wider blood gap and the elimination of the contacting parts in the device based on the maglev technology provide better blood compatibility and higher durability of the device. Several maglev pumps developed at Ibaraki University are introduced in this article. Maglev pumps have been designed for different medical requirements and for different magnetic suspension systems. All pumps have sufficient suspension and pump performance as blood pumps. The axial suspension system with a double biased hybrid magnetic bearing is explained in detail as one example of maglev blood pumps.

回転数周期的変動時の磁気浮上型血液ポンプの浮上安定性と溶血性能の検討

A novel blood pump with magnetically levitated impeller has been developed to recover cardiac function of acute heart failure patients. The pump assists patients' heart and the impeller's rotational speed are changed based on synchronizing with heart beat in order to increase coronary flow of patients' heart. Impeller levitation stability of the pump operated in pulsatile mode was evaluated with a mock circuit filled with water. In the pulsatile mode, the rotational speed was changed from 800 rpm to 1800 rpm with a beat rate of 60 bpm. Maximum axial displacement of the impeller is 22 % of the blood gap between the impeller and casing. Characteristics of hemolysis of the pump were examined within in-vitro hemolysis tests. NIH value of the maglev pump is about half time of it of a commercial based extracorporeal pump in constant speed operation. Even NIH value operated in the pulsatile mode is about two times of the commercial based pump's one and it is acceptable range for clinical usage. The developed maglev pump indicates sufficient impeller levitation stability and hemolysis property.

Route Chart to Stabilizing Permanent Maglev Rotator

Permanent maglev has been since long recognized to be unstable because of Earnshaw's theory, which theoretically proved that permanent maglev can not achieve stable equilibrium in static state. How about that in dynamic state, for example, about a rotator, nobody has given an answer until now actually. A permanent maglev pump and a permanent maglev turbine have been developed, by using a patented permanent magnetic bearing developed by the author. Experiments demonstrated, there is a critic speed either in the pump or in the turbine, under which the rotors in the pump and the turbine have a maximal eccentricity being possible to reach the gap between the rotor and the stator. That means the rotors have contact with the stators occasionally, and thus the rotor is not suspended. In case the rotating speed is higher than this critic speed, the rotors' eccentricity will be remarkably smaller than the gap between the rotor and the stator, that is to say the rotor is stably levitated. Further investigation exhibtes that at the critic speed a so-called gyro-effect is generated which stabilizes the rotor, just like a gyro standing over a ball, if the rotating speed is large enough it can be stable over the ball. The critic speed, essentially to be minimal stable speed of the rotor, depends on the rotating inertia of the rotor and the bearing force, the larger the inertia and the larger the force, the lower the critic speed. Conclusively, a route chart to stabilization of permanent maglev rotator has been clear: in static state, permanent maglev is unstable (Earnshaw's theory); as the rotating speed gradually increases but not up to a critic speed, the permanent maglev rotator is also unstable; in case that the speed equals or is larger than this critic speed, the permanent maglev rotator is suspended stably because of gyro-effect; the critic speed is affected by rotating inertia of the rotor and the bearing force, by larger inertia and larger bearing force, the critic speed will be smaller.

Hemocompatibility of a Fully Magnetically Levitated Centrifugal LVAD: Results from the DuraHeart Pivotal Trial

Purpose The DuraHeart LVAD is a CF pump with centrifugal design with active magnetic levitation for impellor positioning and passive magnetic coupling of motor and impellor. This design allows for large gaps (250 microns), reducing the potential for high shear stress and blood trauma. The objective of this study was to evaluate the biocompatibility and durability and of this unique centrifugal design. Methods and Materials The DuraHeart Pivotal trial was a multicenter, prospective, observational, single-arm study for BTT. 63 patients were enrolled and follow up was complete in 100%. Results Median duration of support was 204 (range 10-1156) days with a total support time of 45 patient-years. Mean LDH values peaked at day 4 and significantly decreased during support (435 ±236 and 297±142 on day 3 and day 180, respectively) Mean plasma-free hg peaked to 14.8 mg/dl (±10) at day 4 and remained low during the period of support. There were no hemolysis AEs and no de-novo pump thrombosis. 3 cases of pump thrombus “in transit” occured based on current waveform analysis (0.06 events/ patient-year support). Overall 50 pumps were available for analysis and confirmed no pump thrombus. There were 6 (10%) cases of Mag-Lev failure, all secondary to cable wire fractures (0.12 events/ patient-year support). In all cases the patients were hemodynamically stable with the back-up hydrodynamic mode. Five patients underwent successful device exchange and 1 was transplanted. Conclusions The first trial of a fully magnetically-levitated centrifugal pump demonstrated excellent hemocompatibility assessed by a very low incidence of hemolysis and de-novo pump thrombosis. The Mag-Lev system was reliable and failure was associated with cable fractures. Future designs in full Mag-Lev pumps require improvement in durability of the cable. Full magnetic levitation may have improved blood compatibility compared to existing axial designs with bearing technology or centrifugal designs that rely on primary hydrodynamic levitation.

Computational Fluid Dynamics-Based Design Optimization for an Implantable Miniature Maglev Pediatric Ventricular Assist Device

Computational fluid dynamics (CFD)-based design optimization was applied to achieve the finalized design of the PediaFlow® PF4, a magnetically levitated rotodynamic pediatric ventricular assist device. It features a streamlined blood-flow path with a single annular fluid passage between the rotor and the stationary housing. The resulting impeller is composed of a first-stage mixed-flow section having four blades at the conical nose region followed by a second-stage fully axial-flow section with three blades within the annular gap region. A stator with three inwardly-directed vanes is provided at the conical tail region to recover pressure and straighten the flow. CFD predictions of head and efficiency characteristics agreed remarkably well with the validation experimental data: with overprediction of head by &lt;7 mmHg over the entire operational range and a slight overprediction in best efficiency by ∼1%. The new optimized PF4 extended the maximum flow range of the previous PF3 device by more than 100% to over 2.3 liter per minute (LPM) for the same range of operating speeds, and doubled the maximum hydraulic efficiency to ∼27%. Evaluation of hemolysis was performed by a Lagrangian particle-tracking technique with analysis of regional contributions to the overall blood damage. The simulation revealed that hemolysis increases with an increase in both the flow rate and rotor speed but not necessarily with just an increase in flow rate at a constant rotor speed. At the flow rate of 1.0 LPM and a head of 138 mmHg, PF4 has a hemolysis index of 0.0032 compared to 0.0058 produced by PF3 at the same flow rate with a head of 48 mmHg. Numerical simulation of radial fluid forces performed by the CFD model with an eccentric rotor revealed the presence of negative fluid stiffness that was monotonically related to both flow and speed. Finally, conjugate heat transfer analysis predicted temperature rise adjacent to the motor to be inversely proportional to the length, but not exceeding ∼2 °C over the intended range of operation. In conclusion, CFD-based design optimization greatly expedited and facilitated the completion of the PediaFlow® flow path and contributed to the system-wide optimization to produce a miniature maglev pump with exceptional hemocompatibility.

Estimation of changes in dynamic hydraulic force in a magnetically suspended centrifugal blood pump with transient computational fluid dynamics analysis

The effect of the hydraulic force on magnetically levitated (maglev) pumps should be studied carefully to improve the suspension performance and the reliability of the pumps. A maglev centrifugal pump, developed at Ibaraki University, was modeled with 926 376 hexahedral elements for computational fluid dynamics (CFD) analyses. The pump has a fully open six-vane impeller with a diameter of 72.5 mm. A self-bearing motor suspends the impeller in the radial direction. The maximum pressure head and flow rate were 250 mmHg and 14 l/min, respectively. First, a steady-state analysis was performed using commercial code STAR-CD to confirm the model's suitability by comparing the results with the real pump performance. Second, transient analysis was performed to estimate the hydraulic force on the levitated impeller. The impeller was rotated in steps of 1 degrees using a sliding mesh. The force around the impeller was integrated at every step. The transient analysis revealed that the direction of the radial force changed dynamically as the vane's position changed relative to the outlet port during one circulation, and the magnitude of this force was about 1 N. The current maglev pump has sufficient performance to counteract this hydraulic force. Transient CFD analysis is not only useful for observing dynamic flow conditions in a centrifugal pump but is also effective for obtaining information about the levitation dynamics of a maglev pump.

A Mini Axial and a Permanent Maglev Radial Heart Pump§

The implantability and durability have been for decades the focus of artificial heart R&D. A mini axial and a maglev radial pump have been developed to meet with such requirements.The mini axial pump weighing 27g (incl.5g rotor) has an outer diameter of 21mm and a length of 10mm in its largest point, but can produce a maximal blood flow of 6l/min with 50mmHg pressure increase. Therefore, it is suitable for the patients of 40-60kg body weight. For other patients of 60-80kg or 80-100kg body weight, the mini axial pumps of 23mm and 25mm outer diameter had been developed before, these devices were acknowledged to be the world smallest LVADs by Guinness World Record Center in 2004.The permanent maglev radial pump weighing 150g is a shaft-less centrifugal pump with permanent magnetic bearings developed by the author. It needs no second coil for suspension of the rotor except the motor coil, different from all other maglev pumps developed in USA, Japan, European, etc. Thus no detecting and controlling systems as well as no additional power supply for maglev are necessary. The pump can produce a blood flow up to as large as 10l/min against 100mmHg pressure.An implantable and durable blood pump will be a viable alternative to natural donor heart for transplantation.

Gyro-effect Stabilizes Unstable Permanent Maglev Centrifugal Pump

According to Earnshaw's Theorem (1839), the passive maglev cannot achieve stable equilibrium and thus an extra coil is needed to make the rotor electrically levitated in a heart pump. The author had developed a permanent maglev centrifugal pump utilizing only passive magnetic bearings, to keep the advantages but to avoid the disadvantages of the electric maglev pumps. The equilibrium stability was achieved by use of so-called "gyro-effect": a rotating body with certain high speed can maintain its rotation stably. This pump consisted of a rotor (driven magnets and an impeller), and a stator with motor coil and pump housing. Two passive magnetic bearings between rotor and stator were devised to counteract the attractive force between the motor coil iron core and the rotor driven magnets. Bench testing with saline demonstrated a levitated rotor under preconditions of higher than 3,250 rpm rotation and more than 1 l/min pumping flow. Rotor levitation was demonstrated by 4 Hall sensors on the stator, with evidence of reduced maximal eccentric distance from 0.15 mm to 0.07 mm. The maximal rotor vibration amplitude was 0.06 mm in a gap of 0.15 mm between rotor and stator. It concluded that Gyro-effect can help passive maglev bearings to achieve stabilization of permanent maglev pump; and that high flow rate indicates good hydraulic property of the pump, which helps also the stability of passive maglev pump.

Development and Canned Pump Application of Wide-Gap Magnetic Bearings

Maglev pump is widely requested for artificial heart or chemical industries. Hybrid magnetic bearing is recognized as high efficient one even with wide airgap and suitable for such applications. This paper proposes two types of hybrid magnetic bearings for canned maglev pump. One is the standard (STD) type and another is the internal permanent magnet (IPM) type. Both types are analyzed using the finite element package and designed. Then the experimental setups are made and their fundamental characteristics are explained. The results show stable levitation and promising characteristics for the practical use.

OPTIMAL DESIGN FOR THE MAGNETIC SUSPENDED CENTRIFUGAL BLOOD PUMP

An optimal design method for the maglev system is devised to develop a miniature and high performance maglev pump. There are trade-off problems on the maglev artificial heart design. For example, the device should be small enough for implantation. But, the small device has limited performance for force generation to suspend an impeller with the magnetic circuit. For another example, the gap between the levitated impeller and a pump casing is a main factor to determine the efficiency of the magnetic system. Narrow gap is suitable for the efficiency, but is not good for hemolysis property. For optimal design, a theoretical design model for a maglev centrifugal blood pump with a self-bearing motor is constructed based on the magnetic circuit theory. The self-bearing motor consists of the magnetic stator at the center of the pump, outer rotor ring with an impeller at the circumferential space of the stator. Relationships among model parameters are defined as restriction conditions. The thickness of magnets, the diameter of the stator and the turn number of electromagnet coils are optimized to achieve the small size and high efficient performance with pre-determined stiffness. As a result, the diameter of the stator could be reduced from 60 mm to 55 mm with no deterioration of the generated force. Also, the energy consumption was reduced from 16 W to 11 W against a head of 100 mm Hg with a flow rate of 5 L/min. Developed design method is useful to optimize the maglev pump and the optimized pump indicated sufficient performance as a ventricular assist device.

DEVELOPMENT OF A NOVEL HYBRID TYPE MAGNETIC BEARING AND APPLICATION TO SMALL IMPELLER CENTRIFUGAL PUMP FOR ARTIFICIAL HEARTS

We have developed a new hybrid magnetic(HM)bearing system for durable and small size artificial hearts. A prototype maglev pump was also developed to verify the feasibility of the developed HM bearing system. A small impeller centrifugal pump was combined with the HM bearing for the prototype pump. The impeller is levitated by a set of HM bearings at both sides of the impeller. A motor stator is set at the center of the device to rotate the levitated impeller. Maximum rotating speed with complete levitation in the air is15, 000rpm. Maximum oscillation amplitude in the radial direction is 0. 04mm with a target rotating number of5, 000rpm. The developed HM bearing system indicated sufficient levitation performance for the artificial heart and the magnetically levitated centrifugal pump with small impeller also displayed good pump performance as a ventricular assist system.

Dynamic fluid force estimation with the maglev pump

Dynamic fluid force estimation with the maglev pump

Novel Maglev Pump With a Combined Magnetic Bearing

The newly developed pump is a magnetically levitated centrifugal blood pump in which active and passive magnetic bearings are integrated to construct a durable ventricular assist device. The developed maglev centrifugal pump consists of an active magnetic bearing, a passive magnetic bearing, a levitated impeller, and a motor stator. The impeller is set between the active magnetic bearing and the motor stator. The active magnetic bearing uses four electromagnets to control the tilt and the axial position of the impeller. The radial movement of the levitated impeller is restricted with the passive stability dependent upon the top stator and the passive permanent magnetic bearing to reduce the energy consumption and the control system complexity. The top stator was designed based upon a magnetic field analysis to develop the maglev pump with sufficient passive stability in the radial direction. By implementing this analysis design, the oscillating amplitude of the impeller in the radial direction was cut in half when compared with the simple shape stator. This study concluded that the newly developed maglev centrifugal pump displayed excellent levitation performance and sufficient pump performance as a ventricular assist device.

509 人工心臓用ラジアル型磁気浮上遠心ポンプの最適化(GS-07 : 人工臓器)

509 人工心臓用ラジアル型磁気浮上遠心ポンプの最適化(GS-07 : 人工臓器)

K17 回転型人工心臓血液ポンプの開発状況(基調講演)

This article introduces the state-of-art of the artificial rotary blood pump. Aiming at a small blood pump with a levitated rotor, several types of maglev pumps are introduced and reported. Among them we proposes to use a self-bearing motor for combined fuctions of AC motor and magnetic bearing. The proposed pump is one of the smallest blood pump with non-contact nature which is essential for the artificial heart pump.