Search

High-efficiency plasma skimming is hopeful to prevent hemolysis inside spiral groove bearings (SGBs) because it can exclude red blood cells from the ridge gap with a high shear force. However, no study reveals the shape design of SGBs to improve plasma skimming. Therefore, this study proposed and applied a groove design strategy to designing an optimal SGB for enhancing plasma skimming in a rotary blood pump (RBP). Initially, we proposed the design strategy that the shape of the groove for enhancing plasma skimming corresponds to the direction of blood flow in the ridge gap. Second, we visualized the cell flow in a specially designed experimental RBP to determine the direction of blood flow, which was helpful in the subsequent SGB design. Then, we created an SGB to provide superior plasma skimming and applied it to the experimental RBP. We evaluated the plasma skimming effect of SGB at rotational speeds ranging from 2400 to 3000 rpm and hematocrit conditions between 1% and 40%. At a 1% hematocrit, the plasma skimming efficiency for the entire SGB was greater than 95%. In all hematocrit conditions, the efficiency at the inner ridges of the SGB was greater than 80%. The results showed the designed SGB successfully induced excellent plasma skimming within ridge gaps. This study is the first to propose and apply a shape design strategy to generate excellent plasma skimming within an SGB. This study may contribute to the prevention of SGB hemolysis inside SGB for use in RBPs., (© 2023. The Author(s).)

For the practical application of bio-actuators, it is desired to develop a precise control method for skeletal muscles. In this study, a novel model-based control method has been proposed. The control method enables skeletal muscles to exert an arbitrary magnitude of contraction force, rather than just the conventional on/off control. First, we proposed a control system to obtain the optimized electrical stimulation voltage, that can reproduce reference force. In order to actually apply the method, a bio-actuator consisting of a skeletal muscle of a frog was manufactured for a verification experiment. First, muscle contraction model parameters that could reproduce the contractile response of the gastrocnemius muscle were identified from the experimental data. Next, based on this model, the proposed control method was used to calculate the stimulation voltage to exert the reference force. The voltage was applied to the bio-actuator to control the contraction force. As a results, the output of the actuator was able to follow the stepwise reference force. Our proposed control method demonstrates the feasibility of precise control of bio-actuators.Clinical Relevance- If skeletal muscles could be used as actuators for power-assistive suits, it would be possible to develop power-assistive suits that are more compatible with people and reduce the burden on caregivers in the field of nursing care. The method proposed in this study will enable the control of skeletal muscle contraction force by electrical stimulation, bringing skeletal muscle actuators closer to practical application.

Background: Mechanical circulatory support devices, such as left ventricular assist devices, have recently been used in patients with heart failure as destination therapy but the formation of thrombus in blood pumps remains a critical problem. In this study, we propose a mechanical antithrombogenic method by impeller excitation using a magnetically levitated (Maglev) centrifugal pump. Previous studies have shown that one-directional excitation prevents thrombus; however, it is effective in only one direction. In this study, we aimed to obtain a better effect by vibrating it in a circular orbit to induce uniform changes in the shear-rate field entirely around the impeller., Methods: The blood coagulation time was compared using porcine blood. (1) The flow rate was set to 1 L/min, and applied excitation was at a frequency of 280 Hz and amplitude of 3 μm. (2) Moreover, the effect was compared by varying the frequency, amplitude, and direction of the excitation. In this experiment, the flow rate was set to 0.3 L/min., Results: (1) The thrombus formation time was 77 min without excitation and 133 min with excitation, which was 1.7 times longer. (2) The results showed no difference between (280 Hz, 3 μm) and (50 Hz, 16 μm) circular orbital excitations, and no directional difference, with thrombus formation of 2.5 times longer under all conditions than that without excitation., Conclusion: In the case of simple reciprocating excitation, the time was approximately 1.2 times longer. This indicated that the circular orbital excitation is more effective., (© 2022 The Authors. Artificial Organs published by International Center for Artificial Organ and Transplantation (ICAOT) and Wiley Periodicals LLC.)

Background: Antithrombogenicity of extracorporeal membrane oxygenation (ECMO) devices, particularly oxygenators, is a current problem, with numerous studies and developments underway. However, there has been limited progress in developing methods to accurately compare the antithrombogenicity of oxygenators. Animal experiments are commonly conducted to evaluate the antithrombogenicity of devices; however, it is challenging to maintain a steady experimental environment. We propose an innovative experimental animal model to evaluate different devices in a constant experimental environment in real-time., Methods: This model uses two venous-arterial ECMO circuits attached to one animal (one by jugular vein and carotid artery, one by femoral vein and artery) and real-time assessment of thrombus formation in the oxygenator by indocyanine green (ICG) fluorescence imaging. Comparison studies were conducted using three pigs: one to compare different oxygenators (MERA vs. CAPIOX) (Case 1), and two to compare antithrombotic properties of the oxygenator (QUADROX) when used under different hydrodynamic conditions (continuous flow vs. pulsatile flow) (Cases 2 and 3)., Results: Thrombi, visualized using ICG imaging, appeared as black dots on a white background in each oxygenator. In Case 1, differences in the site of thrombus formation and rate of thrombus growth were observed in real-time in two oxygenators. In Case 2 and 3, the thrombus region was smaller in pulsatile than in continuous conditions., Conclusions: We devised an innovative experimental animal model for comparison of antithrombogenicity in ECMO circuits. This model enabled simultaneous evaluation of two different ECMO circuits under the same biological conditions and reduced the number of sacrificed experimental animals., (© 2022 International Center for Artificial Organ and Transplantation (ICAOT) and Wiley Periodicals LLC.)

Acquired von Willebrand syndrome (AVWS), characterized by reduced von Willebrand factor (VWF) large multimers, has recently been implicated as the principal mechanism underlying bleeding in patients implanted with left ventricular assist devices (LVADs). Hematological severity of AVWS varies among patients, even if an identical device is implanted. We investigated whether this diversity in hematological severity is due to individual variability in VWF fragility, according to responses to incremental shear stress. Whole-blood samples were sheared at 20,000-40,000 s -1 shear rate, an index of shear stress, using a custom-made shear stressor that could generate shear stress compatible with that produced by an LVAD. The degree of VWF large multimers degradation was evaluated using the VWF large multimer index. A significant inverse correlation was observed between the VWF large multimer index and LVAD-compatible magnitudes of shear stress: the VWF large multimer indices were 68.5 ± 18.3, 48.0 ± 13.9, 33.9 ± 12.1, 23.7 ± 7.9, and 18.7% ± 8.7% at 20,000, 25,000, 30,000, 35,000, and 40,000 s -1 of shear rates, respectively ( P < 0.0001). Furthermore, experimental VWF large multimer index values were compatible with those derived from patients with implanted LVADs (median; 28.9%). Finally, reduction in the VWF large multimer index corresponding to shear stress showed individual variation. We demonstrated that the combined use of a novel high shear stress loading device and quantitative evaluation of VWF large multimers may predict risk of bleeding before LVAD implantation., Competing Interests: Disclosure: There are no conflicts of interest to report., (Copyright © ASAIO 2021.)

Plasma skimming can exclude red blood cells from high shear regions in the gaps formed by hydrodynamic bearings in rotary blood pumps. We investigated the effect of the gap size and groove design on the plasma skimming efficiency. Spiral groove bearings (SGBs) were installed into a specially designed test rig for in vitro experiments performed using human blood. The measured gap between the ridges of the bearing and the rotor surface was 17-26 µm at a flow rate of 150 ml/min and a rotor speed of 2400 rpm. Three different patterns of SGBs were designed (SGB-0, SGB-30, and SGB-60) with various degrees of the circumferential component. The hematocrit measured by a high-speed camera was compared with the hematocrit in the circuit, and the plasma skimming efficiency for the three bearing patterns was evaluated at hematocrits of 20%, 25%, and 30%. SGB-60, which had the strongest circumferential component, provided the best plasma skimming efficiency. When the gap size was less than 20 µm, the red blood cells in the gaps between the ridges of the bearing and rotor surface reduced significantly and the efficiency became higher than 90%. The gap size had the strongest effect on producing a significant plasma skimming. The plasma skimming efficiency can be significantly improved by optimizing the bearing gap size and groove design, which facilitates the further development of SGBs for use in applications such as rotary blood pumps., (© 2021. The Japanese Society for Artificial Organs.)

We have been developing an implantable power generation system that uses muscle contraction following electrical stimulation as a permanent power source for small implantable medical devices. However, if the muscle tissue is overloaded for power generation, the tissue may rupture or blood flow may be impaired. In this study, we developed a new muscle-connecting component that solves these problems. The new connection device has three rods attached to the muscle fibers, and the force exerted on the muscle fibers is converted from horizontal to vertical when the muscle contracts. We conducted simulations with a three-dimensional (3D) model, as well as pulse wave muscle measurements and in vivo tests using the actual muscle. The pulse wave in the connecting part and its downstream were optically measured from the muscle surface, and the blood flow was not obstructed. The 3D model simulations revealed that the distribution of stress was preferable compared with the case in which a rod was stuck vertically in the muscle. In the in vivo muscle tests, the metal rod and resin parts were attached to the muscle, and a load of up to approximately 9 N was applied to the connecting part. Consequently, the connecting part was stable and integrated with the muscle, and there was no damage in the muscle. Although no long-term or histological evaluations were conducted, the device may be useful because of the intramuscular power generation owing to the minimal load applied on the part connected with the muscle.

The blood damage problem inside the narrow hydrodynamic bearing is potentially considered to be solved by applying plasma skimming. However, the consideration of improving plasma skimming has not been included in the design of hydrodynamic bearings. The absence of experimental investigation on revealing the relationship between blood flow and plasma skimming in the bearing gap impedes the design of groove shape for plasma skimming. Thus, the present study was undertaken to evaluate how the blood flow direction and the groove shape affect plasma skimming in the bearing gap. To this end, blood tests using porcine blood were repeated three times with a hematocrit of 0.8%. The bearing gap during the tests was adjusted to 25 µm and the rotational speed was adjusted from 50 rpm to 2500 rpm. The blood flow and plasma skimming effect was evaluated based on image analysis utilizing a high-speed microscope. Results of three tests indicated that the flow direction of RBCs was dominated by the rotating surface in the bearing gap when the rotational speed increased over 1200 rpm. The best plasma skimming effect was observed when the angle between the flow direction of RBCs and the tangent line of the groove was within -10 degrees to 10 degrees. The future study will be conducted with including the consideration of plasma skimming in the bearing shape design. The findings in this study aid the future design and development of hydrodynamic bearing for use in rotary blood pumps.

Biohybrid actuators consisting of skeletal muscle and artificial lattice have unique characteristics such as self-growth and self-repair functions. As a first step for developing model-based design and model-based control methods for the biohybrid actuators, we have developed a muscle contraction model. When the stimulation voltage is applied to the muscle, the electrical charges are stored in the dihydropyridine receptor, and the calcium ions are released. According to the concentration of the ions, the contractile elements generate contraction force. We have modeled this phenomenon with three characteristics in the proposed model-electrical dynamic, physiological, and mechanical dynamic characteristics. Unlike the previous models, the proposed model was verified under the condition of tetanus and incomplete tetanus with the muscle length changed. The simulated contraction force showed good agreement with the experimentally measured contraction force generated by the gastrocnemius muscle of a toad.Clinical Relevance- Biohybrid actuators are expected as a new material for medical and assistive devices having a soft and flexible characteristic. This study provides a basic contraction model for such biohybrid actuators.

Implantable energy harvesting system utilizing contraction of an electrically-stimulated skeletal muscle is proposed for alternative batteries of implantable medical devices. In order to realize high conversion efficiency, we propose a resonance generator utilizing vibration of the skeletal muscle, which is called as incomplete tetanus. Experimental results showed the incomplete tetanus was a suitable form for the energy harvesting and the stimulation at the frequency of 10 Hz was maximized the work of the muscle. Dimensions of the springs of the generator were designed so that its natural frequency was 10 Hz. On the simulation, the maximum generated power was achieved 122.5 μW, which is enough to power the IMDs.Clinical Relevance-The proposed system has a potential to eliminate conventional batteries in the implantable medical devices. It will be beneficial for patients since the periodical surgery for the battery replacement will be avoided.

Extracorporeal membrane oxygenation (ECMO) plays an important role in the coronavirus disease 2019 (COVID-19) pandemic. Management of thrombi in ECMO is generally an important issue; especially in ECMO for COVID-19 patients who are prone to thrombus formation, the thrombus formation in oxygenators is an unresolved issue, and it is very difficult to deal with. To prevent thromboembolic complications, it is necessary to develop a method for early thrombus detection. We developed a novel method for detailed real-time observation of thrombi formed in oxygenators using indocyanine green (ICG) fluorescence imaging. The purpose of this study was to verify the efficacy of this novel method through animal experiments. The experiments were performed three times using three pigs equipped with veno-arterial ECMO comprising a centrifugal pump (CAPIOX SL) and an oxygenator (QUADROX). To create thrombogenic conditions, the pump flow rate was set at 1 L/min without anticoagulation. The diluted ICG (0.025 mg/mL) was intravenously administered at a dose of 10 mL once an hour. A single dose of ICG was 0.25mg. The oxygenator was observed with both an optical detector (PDE-neo) and the naked eye every hour after measurement initiation for a total of 8 hours. With this dose of ICG, we could observe it by fluorescence imaging for about 15 minutes. Under ICG imaging, the inside of the oxygenator was observed as a white area. A black dot suspected to be the thrombus appeared 6-8 hours after measurement initiation. The thrombus and the black dot on ICG imaging were finely matched in terms of morphology. Thus, we succeeded in real-time thrombus detection in an oxygenator using ICG imaging. The combined use of ICG imaging and conventional routine screening tests could compensate for each other's weaknesses and significantly improve the safety of ECMO., (© 2021 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Blood pumps are often used for hemofiltration in patients with renal failure. To design effective centrifugal blood pumps for hemofiltration, it is important to suppress clogging caused by platelet aggregation. However, the optimal conditions for conducting anti-platelet aggregation tests in vitro have not yet been established. This study aimed to quantify the effect of the shear loading value and shear loading time on platelet aggregation and determine the optimal conditions for anti-platelet aggregation testing in vitro. To quantitatively evaluate platelet aggregation in terms of the negative logarithm-platelet aggregation threshold index (NL-PATI), which reflects the propensity of residual platelets to aggregate after shear loading, the following parameters were examined: blood collection method (collected from porcine vein using a syringe or collected from a slaughterhouse), type of anticoagulant (sodium citrate or heparin), shear rate, and shear time. The results showed that platelet aggregation in porcine blood increased under a high shear load applied at shear rates of approximately 20,000 s -1 or higher for 30 s. Platelet aggregation propensity was 2-3 times higher in heparin-anticoagulated blood than in sodium citrate-anticoagulated blood. Moreover, platelet aggregation was 1.5-2 times more in blood collected from the slaughterhouse than in syringe-collected blood. Testing with an integrated shear time of 30 s or less in relation to the total blood volume may be effective for conducting in vitro circulation experiments using hemofiltration blood pumps. The conditions established in this study may be useful for hemocompatibility testing of cardiovascular devices based on NL-PATI.

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 1 L/min without anticoagulation. The vibrational frequency of the impeller (70 Hz) and its vibrational amplitude (30 μm) 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 12 hours after commencing measurements. The phase difference increased by over 1° in three cases. The pump was stopped after 12 hours 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., (© 2021 International Center for Artificial Organs and Transplantation and Wiley Periodicals LLC.)

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., (© 2020 International Center for Artificial Organs and Transplantation and Wiley Periodicals LLC.)

The use of contactless support technology for the impeller has led to an increase in the durability of ventricular assist devices (VADs), and these have been in clinical use worldwide. However, pump thrombosis and stroke are still issues to be solved. We have developed a method for detecting the thrombosis in a magnetically levitated blood pump without the need for additional sensors or other equipment. In the proposed method, a sinusoidal current is applied to the electromagnets used for the magnetic bearing, resulting in vibration of the impeller. The phase difference between the current and displacement of the impeller increases with pump thrombosis. First, we describe the principle by which the pump thrombosis is detected. Pump thrombosis reduces the narrowest fluid gap in the pump and this gives rise to a change in the phase difference. Second, we report on experiments in which we changed the narrowest fluid gap using oriented polypropylene tape and showed that decreasing the narrowest fluid gap resulted in an increase in phase difference. For these experiments, the measurements were repeated three times for each condition. Third, we examine the relationship between the pump thrombosis and the phase difference evaluated by observations of the underside of the impeller when operating the pump with porcine blood. Since light was unable to penetrate the blood layer, the erythrocytes were removed for this observation. Only one observation was made. The results showed the phase difference rapidly increased at the same moment when the pump thrombosis was observed. This implies the proposed method has the potential to detect the early stages of pump thrombosis. Finally, in vitro experiments to detect thrombosis when using whole porcine blood in the pump were conducted. The experiment was carried out five times. To intentionally form a thrombus inside the pump, the activated clotting time was controlled to be less than 200 s. In every case, the phase difference increased by more than one degree after tens of minutes. Then, the pump was disassembled and a small amount of pump thrombosis was observed. We conclude that real-time diagnosis of pump thrombosis may be realized by measuring the phase difference without the need for additional sensors., (© 2020 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Mechanical circulatory support devices have been used clinically for patients with heart failure for over 10 years. However, thrombus formation inside blood pumps remains a risk to patient life, causing pump failure and contributing to neurological damage through embolization. In this article, we propose a method for preventing thrombus formation by applying vibrational excitation to the impeller. We evaluate the ability of this method to enhance the antithrombogenic properties of a magnetically levitated centrifugal blood pump and ensure that the impeller vibration does not cause undue hemolysis. First, 3 vibrational conditions were compared using an isolated pump without a mock circulation loop; the vibrational excitation frequencies and amplitudes for the impeller were set to (a) 0 Hz-0 μm, (b) 70 Hz-10 μm, and (c) 300 Hz-2.5 μm. The motor torque was measured to detect thrombus formation and obtain blood coagulation time by calculating the derivative of the torque. Upon thrombus detection, the pump was stopped and thrombi size were evaluated. The results showed an increase in the blood coagulation time and a decrease in the rate of thrombus formation in pumps with the impeller vibration. Second, an in vitro hemolysis test was performed for each vibrational condition to determine the effect of impeller vibration on hemolysis. The results revealed that there was no significant difference in hemolysis levels between each condition. Finally, the selected vibration based on the above test results and the non-vibration as control were compared to investigate antithrombogenic properties under the continuous flow condition. The blood coagulation time and thrombi size were investigated. As a result, vibrational excitation of the impeller at a frequency of 300 Hz and amplitude of 2.5 μm was found to significantly lengthen clotting time, decreasing the rate of pump thrombus compared to the non-vibration condition. We indicate the potential of impeller vibration as a novel mechanical antithrombogenic mechanism for rotary blood pumps., (© 2019 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Mouthguard type sensors have been developed to monitor the healthcare-related information, which is expected to be used for pre-illness and preventive medicine. However, a method for supplying the power to these sensors is still an issue to be solved. In this paper, we propose an electrostatic oral cavity generator driven by occlusal force to supply the power for mouthguard type sensors. The proposed generator is a sheet form and consists of the lamination of the electret, dielectric elastomer and copper electrode. In this paper, we estimated the power generation with a piezoelectric generator and the proposed electrostatic generator. Then, the generators were designed and fabricated. The generated power of the prototype electrostatic generator was 18.0 μW. It was about 560 times larger than that of a piezoelectric generator with the area equivalent to four pairs of molars. Although the generated power was still smaller than the required power to drive the mouthguard sensor, we considered they can be comparable with each other by optimizing the design parameters of the generator.

We propose an energy harvesting device driven by a contraction of an electrically-stimulated skeletal muscle for an alternative battery of implantable medical devices. In order to realize a durable generator, we proposed a contactless plucking mechanism utilizing parallel leaf springs and magnets, with which the generator can be driven without friction. By utilizing this mechanism, the generator can be driven not only in a contraction phase, but also a relaxant phase. We optimized the stiffness of the parallel leaf springs, air gap between the magnets, and magnetic circuit in order to maximize generated power of the generator. The generated power of the prototype in nonliving environment was evaluated. The result showed the protype could achieve 35.8 μW, the value of which is enough to drive the implantable medical devices. Finally, the generated power was evaluated in the ex-vivo experiment using a gastrocnemius muscle of a toad with a weight of 193.4 g. In this experiment, the generator achieved 18.1 μW from only 3.5 g of the skeletal muscle. Also, we confirmed that the generated power exceeded the power consumption of the electrical stimulation on the skeletal muscle. Hence, we concluded the results showed the feasibility of the energy harvesting system with proposed mechanism.

Plasma skimming is the phenomenon whereby the discharge hematocrit is lower than feed hematocrit naturally occurring in the microvessels with Poiseuille flow. It has been studied in Poiseuille flow extensively. Besides, plasma skimming has also been observed and investigated in blood pumps due to its potential to prevent hemolysis by skimming blood cells out of the small gap. However, whether plasma skimming occurs in blood pumps with whole blood has not been verified. Additionally, the independent influence of rotational speed and gap size has not been clarified. Therefore, in order to lay the foundation of applying plasma skimming to the development of blood pumps and also investigate the influence of rotational speed and gap size on plasma skimming respectively, we designed a simplified geometric device which not only imitates the flow inside clearances of blood pumps, but also provides different rotational speed and gap size conditions. We first conducted the verification tests of plasma skimming using whole blood with an initial hematocrit of 44% and the gap size was varied from 10 μm to 240 μm with 10 μm interval. The plasma skimming was verified occurring when the gap was less than 70 μm at a rotational speed of 800 rpm. Since plasma skimming was confirmed, we employed 30% hematocrit blood and performed the following tests to evaluate the influence of rotational speed of 600 rpm, 700 rpm, and 800 rpm respectively. As a result, the hematocrit of sampled blood declined as the rotational speed increased from 600 rpm to 800 rpm. And there was the lowest hematocrit of 16% when the gap was adjusted to 50 μm gap size at 800 rpm. This study further promotes the possibility of applying plasma skimming to the blood pumps with higher hemocapability.

Ventricular assist devices assist in blood circulation and form a crucial component of artificial hearts. While it is important to measure parameters such as the flow rate, pressure head and viscosity of the blood, implanting additional devices to do such measurements is inadvisable. To this end, we demonstrate the adaptation of a ventricular assist device for the purpose of measuring blood viscosity. Such an approach eliminates the need for additional dedicated viscometers in artificial hearts. In the proposed method, the blood viscosity is measured by applying radial vibrational excitation to the impeller in a ventricular assist device using its magnetic levitation system. During the measurement, blood is exposed to a combination of a low shear rate (≈100/s) generated by the radial vibration of the impeller and a high shear rate (>10,000/s) generated by the impeller's rotation. The apparent viscosity of blood depends on the shear rate, so we determined which shear rate was the dominant one in the proposed method. The measurement results showed that the viscosity measured by the proposed method was in good agreement with the reference viscosity measured with a high shear rate. The mean absolute deviation in the measurements using the proposed method and those obtained using a concentric cylindrical viscometer at a high shear rate was 0.12 mPa s for four samples of porcine blood, with viscosities ranging from 2.32 to 2.75 mPa s.

Thrombus is one of the major problems in ventricular assist devices (VADs). However, method for detecting thrombus in early stage has not been established yet. In this study, we propose an intelligent function that the VAD itself can detect thrombus automatically and alert it to medical staffs. In the proposed method, thrombus formation inside a blood pump is detected by monitoring blood viscosity. This viscosity measurement is performed by using magnetic levitation system for the impeller. Hence, it can be implemented without any additional sensors or mechanisms in principle. For verification of the method, at first, we visualized inside of the pump during thrombus formation with measuring blood viscosity by using erythrocytes removed porcine blood. The result showed that the viscosity of the blood increased as blood coagulation progressed. Then, we conducted in vitro principle verification experiments with three different whole porcine blood. In all experiments, the measured blood viscosity increased and small thrombus was observed inside the pump. From these results, we confirmed that the proposed method has a possibility to detect and predict the thrombus in early stage.

We propose a contactless energy harvesting system driven by the contraction of an electrically-stimulated skeletal muscle to be used to supply electrical energy to implantable medical devices. In order to realize a durable generator, the one proposed here has a contactless clutch mechanism with parallel leaf springs, with which the generator can be driven without friction. In this system, the muscle connected to the parallel leaf spring is intentionally contracted by electrical stimulation. The generator can be driven not only in the contraction phase of the muscle, but also relaxation phase. The result an evaluation showed that the prototype could generate 26.1 $\mu \mathrm{W}$ with an efficiency of 13.7%. Finally, we conducted an animal experiment using the gastrocnemius muscle of a toad with a weighing of200 g The generator was driven in the contraction phase generating 1.37 $\mu \mathrm{W}$ of power from the energy supplied by the muscle.

An implantable power generation system driven by muscle contractions for supplying power to active implantable medical devices, such as pacemakers and neurostimulators, is proposed. In this system, a muscle is intentionally contracted by an electrical stimulation in accordance with the demands of the active implantable medical device for electrical power. The proposed system, which comprises a small electromagnetic induction generator, electrodes with an electrical circuit for stimulation and a transmission device to convert the linear motion of the muscle contractions into rotational motion for the magneto rotor, generates electrical energy. In an ex vivo demonstration using the gastrocnemius muscle of a toad, which was 28 mm in length and weighed 1.3 g, the electrical energy generated by the prototype exceeded the energy consumed for electrical stimulation, with the net power being 111 µW. It was demonstrated that the proposed implantable power generation system has the potential to replace implantable batteries for active implantable medical devices., (© IMechE 2016.)

A sliding planar motion table system that can be used for the lens driving actuator of a laser cutting machine was developed. The system uses magnetic fluid as the lubricant to avoid the leakage of lubricating oil under the table and reduce environmental pollution. The motion table is suspended from the guide surface by an attractive force generated by electromagnets to reduce the contact and frictional forces between the table and the guide surface. The table is capable of movement in one rotational and two translational directions over the guide surface using six electromagnets and three non-contact displacement sensors. Experimental results showed that the magnetic suspension of the table reduced the friction by 82.1% compared to the friction that would otherwise be generated by the dead weight of the table. Circular motion within a diameter of 2 mm was achieved with resolutions of 5 μm and 20 μrad in the translational and rotational directions, respectively. A bandwidth of higher than 100 Hz was also achieved in the three movement directions.

Controlling the flow rate in an implantable rotary blood pump based on the physiological demand made by the body is important. Even though various methods to estimate the flow rate without using a flow meter have been proposed, no adequate method for measuring the blood viscosity, which is necessary for an accurate estimate of the flow rate, without using additional sensors or mechanisms in a noninvasive way, has yet been realized. We have developed a sensorless method for measuring viscosity in magnetically levitated rotary blood pumps, which requires no additional sensors or mechanisms. By applying vibrational excitation to the impeller using a magnetic bearing, we measured the viscosity of the working fluid by measuring the phase difference between the current in the magnetic bearing and the displacement of the impeller. The measured viscosity showed a high correlation (R(2)  > 0.992) with respect to a reference viscosity. The mean absolute deviation of the measured viscosity was 0.12 mPa·s for several working fluids with viscosities ranging from 1.18 to 5.12 mPa·s. The proposed sensorless measurement method has the possibility of being utilized for estimating flow rate., (Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Last year, we reported in vitro pump performance, low hemolytic characteristics, and initial in vivo evaluation of a disposable, magnetically levitated centrifugal blood pump, MedTech Dispo. As the first phase of the two-stage in vivo studies, in this study we have carried out a 2-week in vivo evaluation in calves. Male Holstein calves with body weight of 62.4–92.2 kg were used. Under general anesthesia, a left heart bypass with a MedTech Dispo pump was instituted between the left atrium and the descending aorta via left thoracotomy. Blood-contacting surface of the pump was coated with a 2-methacryloyloxyethyl phosphorylcholine polymer. Post-operatively, with activated clotting time controlled at 180–220 s using heparin and bypass flow rate maintained at 50 mL/kg/min, plasma-free hemoglobin (Hb), coagulation, and major organ functions were analyzed for evaluation of biocompatibility. The animals were electively sacrificed at the completion of the 2-week study to evaluate presence of thrombus inside the pump,together with an examination of major organs. To date, we have done 13 MedTech Dispo implantations, of which three went successfully for a 2-week duration. In these three cases, the pump produced a fairly constant flow of 50 mL/Kg/min. Neurological disorders and any symptoms of thromboembolism were not seen. Levels of plasma-free Hb were maintained very low. Major organ functions remained within normal ranges. Autopsy results revealed no thrombus formation inside the pump. In the last six cases, calves suffered from severe pneumonia and they were excluded from the analysis. The MedTech Dispo pump demonstrated sufficient pump performance and biocompatibility to meet requirements for 1-week circulatory support. The second phase (2-month in vivo study) is under way to prove the safety and efficacy of MedTech Dispo for 1-month applications., (© 2010, Copyright the Authors. Artificial Organs © 2010, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

To enhance the durability and reduce the blood trauma of a conventional blood pump with a cone-shaped impeller, a magnetically levitated (MagLev) technology has been applied to the BioPump BPX-80 (Medtronic Biomedicus, Inc., Minneapolis, MN, USA), whose impeller is supported by a mechanical bearing. The MagLev BioPump (MagLev BP), which we have developed, has a cone-shaped impeller, the same as that used in the BPX-80. The suspension and driving system, which is comprised of two degrees of freedom, radial-controlled magnetic bearing, and a simply structured magnetic coupling, eliminates any physical contact between the impeller and the housing. To reduce both oscillation of the impeller and current in the coils, the magnetic bearing system utilizes repetitive and zero-power compensators. In this article, we present the design of the MagLev mechanism, measure the levitational accuracy of the impeller and pressure-flow curves (head-quantity [HQ] characteristics), and describe in vitro experiments designed to measure hemolysis. For the flow-induced hemolysis of the initial design to be reduced, the blood damage index was estimated by using computational fluid dynamics (CFD) analysis. Stable rotation of the impeller in a prototype MagLev BP from 0 to 2750 rpm was obtained, yielding a flow rate of 5 L/min against a head pressure in excess of 250 mm Hg. Because the impeller of the prototype MagLev BP is levitated without contact, the normalized index of hemolysis was 10% less than the equivalent value with the BPX-80. The results of the CFD analysis showed that the shape of the outlet and the width of the fluid clearances have a large effect on blood damage. The prototype MagLev BP satisfied the required HQ characteristics (5 L/min, 250 mm Hg) for extracorporeal circulation support with stable levitation of the impeller and showed an acceptable level of hemolysis. The simulation results of the CFD analysis indicated the possibility of further reducing the blood damage of the prototype MagLev BP.

MedTech Dispo, a disposable maglev centrifugal blood pump with two degrees of freedom magnetic suspension and radial magnetic coupling rotation, has been developed for 1-month extracorporeal circulatory support. As the first stage of a two-stage in vivo evaluation, 2-week evaluation of a prototype MedTech Dispo was conducted. In in vitro study, the pump could produce 5 L/min against 800 mm Hg and the normalized index of hemolysis was 0.0054 +/- 0.0008 g/100 L. In in vivo study, the pump, with its blood-contacting surface coated with biocompatible 2-methacryloyloxyethyl phosphorylcholine polymer, was implanted in seven calves in left heart bypass. Pump performance was stable with a mean flow of 4.49 +/- 0.38 L/min at a mean speed of 2072.1 +/- 64.5 rpm. The maglev control revealed its stability in rotor position during normal activity by the calves. During 2 weeks of operation in two calves which survived the intended study period, no thrombus formation was seen inside the pump and levels of plasma free hemoglobin were maintained below 4 mg/dL. Although further experiments are required, the pump demonstrated the potential for sufficient and reliable performance and biocompatibility in meeting the requirements for cardiopulmonary bypass and 1-week circulatory support.

A magnetically levitated centrifugal blood pump (MedTech Dispo) has been developed for use in a disposable extracorporeal system. The design of the pump is intended to eliminate mechanical contact with the impeller, to facilitate a simple disposable mechanism, and to reduce the blood-heating effects that are caused by motors and magnetic bearings. The bearing rotor attached to the impeller is suspended by a two degrees-of-freedom controlled radial magnetic bearing stator, which is situated outside the rotor. In the space inside the ringlike rotor, a magnetic coupling disk is placed to rotate the rotor and to ensure that the pump head is thermally isolated from the motor. In this system, the rotor can exhibit high passive stiffness due to the novel design of the closed magnetic circuits. The disposable pump head, which has a priming volume of 23 mL, consists of top and bottom housings, an impeller, and a rotor with a diameter of 50 mm. The pump can provide a head pressure of more than 300 mm Hg against a flow of 5 L/min. The normalized index of hemolysis of the MedTech Dispo is 0.0025 +/- 0.0005 g/100 L at 5 L/min against 250 mm Hg. This is one-seventh of the equivalent figure for a Bio Pump BPX-80 (Medtronic, Inc., Minneapolis, MN, USA), which has a value of 0.0170 +/- 0.0096 g/100 L. These results show that the MedTech Dispo offers high pumping performance and low blood trauma.

Mechanical shaft seal bearing incorporated in the centrifugal blood pumps contributes to hemolysis and thrombus formation. In addition, the problem of durability and corrosion of mechanical shaft seal bearing has been recently reported from the safety point of view. To amend the shortcomings of the blood-immersed mechanical bearings, a magnetic levitated centrifugal rotary blood pump (MedTech Dispo Model 1; Tokyo Medical and Dental University, Tokyo, Japan) has been developed for extracorporeal disposable application. In this study, the hemolytic performance of the MedTech Dispo Model 1 centrifugal blood pump system was evaluated, with special focus on the narrow blood path clearance at the magnetic bearing between rotor and stator, and on the pump housing surface roughness. A pump flow of 5 L/min against the head pressure of 100 mm Hg for 4 h was included in the hemolytic test conditions. Anticoagulated fresh porcine blood was used as a working fluid. The clearance of blood path at the magnetic bearing was in the range of 100-250 micro m. Pump housing surface roughness was controlled to be around Ra = 0.1-1.5 micro m. The lowest hemolytic results were obtained at the clearance of 250 micro m and with the polished surface (Ra = 0.1 micro m) yielding the normalized index of hemolysis (NIH) of less than 0.001 g/100 L, which was 1/5 of the Biopump BP-80 (Medtronic Inc., Minneapolis, MN, USA, and 1/4 of the BPX-80. In spite of rough surface and narrow blood path, NIH levels were less than clinically acceptable level of 0.005 g/100 L. The noncontact, levitated impeller system is useful to improve pump performance in blood environment.

The magnetically levitated (Mag-Lev) centrifugal rotary blood pump (CRBP) with two-degrees-of-freedom active control is promising for safe and long-term support of circulation. In this study, Mag-Lev CRBP controllability and impeller behavior were studied in the simulated heart failure circulatory model. A pneumatically driven pulsatile blood pump (Medos VAD [ventricular assist device]-54 mL) was used to simulate the left ventricle (LV). The Mag-Lev CRBP was placed between the LV apex and aortic compliance tank simulating LV assistance. The impeller behavior in five axes (x, y, z, theta, and phi) was continuously monitored using five eddy current sensors. The signals of the x- and y-axes were used for feedback active control, while the behaviors of the other three axes were passively controlled by the permanent magnets. In the static mock circuit, the impeller movement was controlled to within +/-10-+/-20 microm in the x- and y-axes, while in the pulsatile circuit, LV pulsation was modulated in the impeller movement with the amplitude being 2-22 microm. The amplitude of impeller movement measured at 1800 rpm with the simulated failing heart (peak LV pressure [LVP] = 70 mm Hg, mean aortic pressure [AoP(mean)] = 55 +/- 20 mm Hg, aortic flow = 2.7 L/min) was 12.6 microm, while it increased to 19.2 microm with the recovered heart (peak LVP = 122 mm Hg, AoP(mean) = 100 +/- 20 mm Hg, aortic flow = 3.9 L/min). The impeller repeated the reciprocating movement from the center of the pump toward the outlet port with LV pulsation. Angular rotation (theta, phi) was around +/-0.002 rad without z-axis displacement. Power requirements ranged from 0.6 to 0.9 W. Five-axis impeller behavior and Mag-Lev controller stability were demonstrated in the pulsatile mock circuit. Noncontact drive and low power requirements were shown despite the effects of LV pulsation. The impeller position signals in the x- and y-axes reflected LV function. The Mag-Lev CRBP is effective not only for noncontact low power control of the impeller, but also for diagnosis of cardiac function noninvasively.