Implantable Blood Pump Research Articles

Robust Maximum Efficiency Tracking Control of Wirelessly Powered Directly Supplied Heart Pumps

In recent times, wireless power transfer systems have been identified as a reliable option to supply power to medical implants. Up to now, Wireless Power Transfer Systems (WPTS) have only been used to charge batteries of low-power medical implants. However, for medical implants requiring a relatively higher power, such as a ventricular assist device, which is an implanted blood pump in the patient’s abdominal cavity, an external power supply has been used. When WPTS is used for medical implants, it increases the number of required power converter stages and hardware complexity along with the volume, which tends to reduce the overall efficiency. In addition, the existence of uncertainties in WPTS-based medical implants, such as load and mutual inductance variations, can lead to system instability or poor performance. The focus of this paper is to design a WPTS to supply power to the pump motor directly through its inverter based on the requirements of the motor drive system (MDS) without resorting to an additional DC-to-DC converter stage. To this end, the constraints that the drive system imposes upon WPTS have been identified. In addition, to make a reliable closed-loop operation, a µ-synthesis robust controller is designed to make sure the system maintains its stability and performance with respect to the system’s existing uncertainties. A number of experimental results are provided to verify the effectiveness of the adopted WPTS design approach and the corresponding closed-loop controller for WPTS. Furthermore, the experimental findings for the maximum efficiency tracking (MET) approach (to minimize WPTS coil losses) and constant DC link voltage control approach are shown and compared. According to experimental results and system efficiency analysis, the former appears to perform better. The system dynamic performance analysis, on the other hand, demonstrates the latter’s advantage.

Use of 3D anatomical models in mock circulatory loops for cardiac medical device testing.

Mock circulatory loops (MCLs) are mechanical representations of the cardiovascular system largely used to test the hemodynamic performance of cardiovascular medical devices (MD). Thanks to 3 dimensional (3D) printing technologies, MCLs can nowadays also incorporate anatomical models so to offer enhanced testing capabilities. The aim of this review is to provide an overview on MCLs and to discuss the recent developments of 3D anatomical models for cardiovascular MD testing. The review first analyses the different techniques to develop 3D anatomical models, in both rigid and compliant materials. In the second section, the state of the art of MCLs with 3D models is discussed, along with the testing of different MDs: implantable blood pumps, heart valves, and imaging techniques. For each class of MD, the MCL is analyzed in terms of: the cardiovascular model embedded, the 3D model implemented (the anatomy represented, the material used, and the activation method), and the testing applications. MCLs serve the purpose of testing cardiovascular MDs in different (patho-)physiological scenarios. The addition of 3D anatomical models enables more realistic connections of the MD with the implantation site and enhances the testing capabilities of the MCL. Current attempts focus on the development of personalized MCLs to test MDs in patient-specific hemodynamic and anatomical scenarios. The main limitation of MCLs is the impossibility to assess the impact of a MD in the long-term and at a biological level, for which animal experiments are still needed.

Transcutaneous Energy Transfer System for Cardiac-Assist Devices by Use of Inhomogeneous Biocompatible Core Material

A novel magnetic liquid silicone rubber composite core design applicable to wireless power transfer (WPT) for medical applications is presented. As a case study, the integration of WPT, including the proposed cores for the coils, with ventricular-assist devices (VADs) was investigated. This facilitates transferring 4.6 W of power wirelessly through the skin layer, which, thus, allows to disposal of the transcutaneous cable that connects the extracorporal batteries to the implanted blood pump. To enhance the coupling coefficient and consequently increase the WPT efficiency, the geometry of the cores was optimized. This reduces the temperature increase in the implant area. The field and thermal simulations were carried out with CST software. The electrical properties of the proposed design as obtained by simulation were validated by measurements. The simulation results perfectly coincide with the measured results. Finally, a new optimized design with additional high permeability core inserts is introduced to further increase the coupling coefficient. The results indicate that the coupling coefficient is increased from 0.31 to 0.52 with the optimized design compared to the case without cores. Moreover, by fixing the initial temperature as 37 °C, the maximum temperature is decreased from 38.19 °C to 37.27 °C while keeping the transferred power fixed. Its high magnetic conductivity, biocompatibility, low-loss property, flexibility, and Qi-standard compatibility make the proposed WPT design an excellent candidate for the wireless powering of heart-assist devices, such as VADs.

Non-parametric dynamical estimation of blood flow rate, pressure difference and viscosity for a miniaturized blood pump.

Blood pumps are becoming increasingly important for medical devices. They are used to assist and control the blood flow and blood pressure in the patient's body. To accurately control blood pumps, information about important hydrodynamic parameters such as blood flow rate, pressure difference and viscosity is needed. These parameters are difficult to measure online. Therefore, an accurate estimation of these parameters is crucial for the effective operation of implantable blood pumps. In this study, in vitro tests with bovine blood were conducted to collect data about the non-linear dependency of blood flow rate, flow resistance (pressure difference) and whole blood viscosity on motor current and rotation speed of a prototype blood pump. Gaussian process regression models are then used to model the non-linear mappings from motor current and rotation speed to the hydrodynamic variables of interest. The performance of the estimation is evaluated for all three variables and shows very high accuracy. For blood flow rate - correlation coefficient ( = 1, root mean squared error () = 0.31 ml min-1, maximal error () = 9.31 ml min-1; for pressure = 1, = 0.09 mmHg, = 8.34 mmHg; and for viscosity = 1, = 0.09 mPa.s, = 0.31 mPa⋅s. The current findings suggest that this method can be employed for highly accurate online estimation of essential hydrodynamic parameters for implantable blood pumps.

Numerical analysis of the effect of the design of axial-flow pump cannula tip on stagnation and recirculation zones in the left ventricle

Objective: to analyze the inflow cannula of an implantable axial-flow blood pump for a long-term left ventricular assist system in order to minimize thromboembolic complications. Materials and methods. Hemodynamics was considered for 4 different designs of the inflow cannula, from 0 mm to 25 mm long. Areas at the base of the cannula received the most attention. Analysis was performed using the OpenFOAM software. Results. It was revealed that sizes of stagnation and recirculation zones directly depended on the length of the cannula when placed in the left ventricle. Accordingly, longer cannula increases the risk of thrombosis. Conclusion. The design of an inflow cannula determines the likelihood of thrombosis in the cannula. Longer inflow cannula increases stagnation and recirculation zones. This provides a basis for a search for other possible modifications.

Cleavage and Re-Supply of von Willebrand Factor in Continuous Flow Blood Pump

Purpose Mechanical circulatory support devices are needed to enable recovery or provide a bridge to decision for patients with heart failure. The effectiveness of extending treatment duration in this therapy was previously reported to increase adverse events, such as acquired von Willebrand disease and gastrointestinal bleeding. Blood-related damage caused by medical devices is one of the most critical parameters needed to determine the performance of medical devices. For the treatment of these complications, we considered that it is very important to analyze the relationship between the cleavage of von Willebrand factor (VWF) due to shear stress and re-supply of VWF from activated platelets during blood pump circulation. We aimed to examine the alterations in the dynamics of VWF multimers in the circulating blood during VAD therapy. Methods In this study, two types (axial and centrifugal) of implantable blood pumps and a disposable blood pump (centrifugal type) for temporary use were used. A simple mock circulation test (5L/min, 100 mmHg) was performed to investigate with both whole-blood samples and platelet-poor plasma (PPP) using fresh bovine blood. Results In an analysis based on SDS-agarose gel electrophoresis and serum VWF values (antigen and activity), high-molecular-weight multimers (HMWMs) in VWF are reduced immediately after the initiation of blood circulation using the axial flow pump, and it had plateaued 60 minutes later. On the other hand, in the study using a centrifugal pump, cleavage of the HMWMs compared to that in the case of using a centrifugal pump was very slight. Moreover, in the whole-blood sample study, HMWMs reduced once, and it had been observed to recover after 60 minutes. However, HMWMs in the PPP sample was observed to reduce continuously during a circulation test. Conclusion In this result, the dynamics of VWF within the blood pump was shown to depend on the type of the blood pump, and this study demonstrated that re-supply of VWF due to platelet activation and cleavage of VWF due to shear stress in the pump occurred at the same time by circulating within the blood pump.

Flow-Rate–Pressure Characteristics of a Disk Blood Pump

An experimental model of a disk pump for pumping a liquid has been designed and fabricated. This model was tested on a special stand with the use of a 40% aqueous solution of glycerin whose hydrodynamical characteristics most closely correspond to those of blood. The results obtained lend credence to the view that an implantable blood pump can be developed on the basis of the disk pump.

COMPUTER SIMULATION OF PLATELET ACTIVATION IN A PULSATILE VENTRICULAR ASSIST DEVICE, THROUGH FINITE ELEMENTS AND A SIMPLIFIED GEOMETRY

Ventricular assist devices are a technological solution for patients who suffer from cardiac insufficiency and await a transplant. In this work, a new design of an implantable pulsatile blood pump is analyzed in terms of blood damage, by means of finite elements on a simplified geometry. It is a double effect volumetric pump, which has a noncontact driven piston and four active valves. The analysis is done by means of blood flow simulation into the pump and the prediction of platelets activation. The last is a measure of the pump compatibility with human life. The platelet activation state is evaluated by an equivalent or representative shear stress and compared with bibliographic data corresponding to other VAD kinds and cardiac prosthetic valves. The results show that, for the complementary blood flow rate supplied by the simulated VAD, the predicted platelet damage is in the same levels of current cardiac devices, particularly other VADs.

Left Ventricular Assist Device Malfunctions: It Is More Than Just the Pump.

Reports of left ventricular assist device (LVAD) malfunction have focused on pump thrombosis. However, the device consists of the pump, driveline, and peripherals, all of which are potentially subject to failure. Prospectively collected data were reviewed for all LVAD device malfunctions (DMs) occurring in rotary LVADs implanted at a single center between April 2004 and May 2016. Durable LVADs included 108 Heartmate II (HM II) and 105 HeartWare VAD (HVAD). DM data were categorized according to device type and into categories related to the component that failed: (1) controller, (2) peripheral components, and (3) implantable blood pump or its integral electric driveline. Pump-related events were analyzed as pump-specific (suspected or confirmed thrombosis) or nonpump-specific (driveline failure). DM rates were reported as events per 1000 patient-days, and Cox proportional hazard models were used for time-to-event analyses. Cumulative rates of malfunction were examined for the main components of each type of LVAD. Types of DM included controller failure (30%), battery failure (19%), or patient cable failure (14%), whereas only 13% were because of pump failure. DMs were more common in the HM II device (3.73 per 1000 patient-days versus 3.06 per 1000 patient-days for the HVAD, P<0.01). A higher rate of pump-specific malfunctions was discovered in those implanted with an HM II versus an HVAD (0.55 versus 0.39, respectively; P<0.01) and peripheral malfunctions (2.32 versus 1.78 for the HM II and HVAD, respectively; P<0.01); no difference occurred in the incidence of controller DM between the 2 LVADs. Patients with HVAD were 90% free of a pump-specific malfunction at 3 years compared with 56% for the HM II (log-rank P<0.003). Only 74% of the patients with HM II were free of pump thrombosis at 3 years compared with 90% of the patients with HVAD. Freedom from failure of the integrated driveline was 79% at 3 years for the HM II but 100% for the HVAD (log-rank P<0.02). Device malfunction is much broader than pump failure alone and occurs for different components at different rates based on the type of LVAD.

Machinability and Optimization of Shrouded Centrifugal Impellers for Implantable Blood Pumps

This paper describes the use of analytical methods to determine machinable centrifugal impeller geometries and the use of computational fluid dynamics (CFD) for predicting the impeller performance. An analytical scheme is described to determine the machinable geometries for a shrouded centrifugal impeller with blades composed of equiangular spirals. The scheme is used to determine the maximum machinable blade angles for impellers with three to nine blades in a case study. Computational fluid dynamics is then used to analyze all the machinable geometries and determine the optimal blade number and angle based on measures of efficiency and rotor speed. The effect of tip width on rotor speed and efficiency is also examined. It is found that, for our case study, a six- or seven-bladed impeller with a low blade angle provides maximum efficiency and minimum rotor speed.

The research on the influence of kinetic parameters on the vibration of blood pump in viscoelastic implantation environment

The implantable axial flow blood pump would be vibrated when in actual use because of the viscoelastic implantation environment, unbalanced driven force, high speed rotor and so on. The blood pump researched in the paper was designed to be implanted in ascending aortic and driven by external magnetic force. The kinetic equation of blood pump worked in viscoelastic implantation environment was built, and then the blood pump’s vibration influenced by viscoelasticity of implantation environment, running speed of blood pump, weight of blood pump were studied. Appropriate damping coefficient of implantation environment, running speed of blood pump and weight of blood pump for blood pump’s more stable working were found in the paper. The paper could provide theoretical basis and research method for blood pump’s structure parameters and work performance improving.

The Effect of Geometry on the Efficiency and Hemolysis of Centrifugal Implantable Blood Pumps.

The application of centrifugal pumps as heart assist devices imposes design limitations on the impeller geometry. Geometry and operating parameters will affect the performance and the hemocompatibility of the device. Among all the parameters affecting the hemocompatibility, pressure, rotational speed, blade numbers, angle, and width have significant impact on the blood trauma. These parameters directly (pressure, speed) and indirectly (geometry) affect the efficiency of the pump as well. This study describes the experimental investigation on geometric parameters and their effect on the performance of small centrifugal pumps suitable for Mechanical Circulatory Support (MCS) devices. Experimental and numerical techniques were implemented to analyze the performance of 15 centrifugal impellers with different characteristics. The effect of each parameter on the pump performance and hemolysis was studied by calculating the normalized index of hemolysis (NIH) and the shear stress induced in each pump. The results show five and six blades, 15-35° outlet angle, and the lowest outlet width that meets the required pressure rise are optimum values for an efficient hemocompatible pump.

Vortical flow characteristics of mechanical cavopulmonary assistance: Pre- and post-swirl dynamics.

Surgical optimization of the cavopulmonary connection and pharmacological therapy for dysfunctional Fontan physiology continue to advance, but these treatment approaches only slow the progression of decline to end-stage heart failure. The development of a mechanical cavopulmonary assist device will provide a viable therapeutic option in the bridging of patients to transplant or to stabilization. We hypothesize that rotational blood flow, delivered by an implantable axial flow blood pump, could effectively assist the venous circulation in Fontan patients by mimicking vortical blood flow patterns in the cardiovascular system. This study investigated seven new models of mechanical cavopulmonary assistance (single and dual-pump assist), created combinations of pump designs that deliver counter rotating vortical flow conditions, and analyzed pump performance, velocity streamlines, swirling strength, and energy augmentation in the cavopulmonary circuit for each support scenario. The model having an axial clockwise-oriented impeller in the inferior vena cava and an axial counterclockwise-oriented impeller rotating in the superior vena cava outperformed all of the support scenarios by enhancing the energy of the cavopulmonary circulation an average of 10.3% over the entire flow range and a maximum of 27.4% at %the higher flow rates. This research will guide the development of axial flow blood pumps for Fontan patients and demonstrated the high probability of %a cardiovascular benefit using counter rotating pumps in a dual support scenario, but found that this is dependent upon the patient-specific cavopulmonary anatomy.

The Effects of Ambulatory Accelerations on the Stability of a Magnetically Suspended Impeller for an Implantable Blood Pump

This article describes the effects of ambulatory accelerations on the stability of a magnetically suspended impeller for use in implantable blood pumps. A magnetic suspension system is developed to control the radial position of a magnetic impeller using coils in the pump casing. The magnitude and periodicity of ambulatory accelerations at the torso are measured. A test rig is then designed to apply appropriate accelerations to the suspension system. Accelerations from 0 to 1 g are applied to the suspended impeller with ambulatory periodicity while the radial position of the impeller and power consumption of the suspension system are monitored. The test is carried out with the impeller suspended in air, water, and a glycerol solution to simulate the viscosity of blood. A model is developed to investigate the effects of the radial magnetic suspension system and fluid damping during ambulatory accelerations. The suspension system reduces the average displacement of the impeller suspended in aqueous solutions within its casing to 100 µm with a power consumption of below 2 W during higher magnitude ambulatory accelerations (RMS magnitude 0.3 g). The damping effect of the fluid is also examined and it is shown that buoyancy, rather than drag, is the primary cause of the damping at the low displacement oscillations that occur during the application of ambulatory accelerations to such a suspension system.

Novel photoreactive phospholipid polymers for preparing a stable biocompatible surface with a smart process

Event Abstract Back to Event Novel photoreactive phospholipid polymers for preparing a stable biocompatible surface with a smart process Tomozumi Noda1*, Masaru Matsuda1*, Nobuyuki Sakamoto1*, Shigeru Kitano1*, Yuuki Inoue2*, Kyoko Fukazawa2* and Kazuhiko Ishihara2* 1 NOF Corporation, Life Sciences Products Division, Japan 2 The University of Tokyo, Department of Materials Engineering, School of Engineering, Japan Introduction: 2-Methacryloyloxyethyl phosphorylcholine (MPC) [1] polymers have been widely applied to some medical devices, including implantable blood pumps, cardiovascular stents and other medical goods. Stabilization of the MPC polymer layer on the substrate is essential issue to solve to have conventional surface treatment. In this study, in order to react the MPC polymer layer to the substrate, we have newly synthesized photoreactive MPC polymers to modify the plastic surface, and evaluated fundamental properties regarding biocompatibility, that is, protein adsorption and cell adhesion. By using these photoreactive MPC polymers, surface treatment is conducted very easy way, such as, coating of the MPC polymer by solvent dipping and after that irradiation light. Materials and Methods: Two types of photoreactive MPC polymers bearing n-butyl methacrylate (BMA) and benzophenone group or phenylazide group were synthesized in a conventional free-radical copolymerization. The presence of benzophenone group (7.20-8.00 ppm ) or phenylazide group (7.10-7.35 ppm and 7.90-8.25ppm) was confirmed by Proton NMR. Each MPC polymer was used for surface modification on various substrates, such as polyethylene and polystyrene, by dip or cast coating, and following the photoirradiation of UV light at 254nm for 7 min. After photoirradiation, all substrates were soaked in ethanol more than 16 h to evaluate reactivity of MPC polymers. The hydrophilic characteristics of the substrates modified with photoreactive MPC polymers were evaluated contact angle measurement by air under water. Then the 96-well polystyrene plates treated with photoreactive MPC polymers were used for examining protein adsorption using peroxidase conjugated antibody and cell adhesion of NIH3T3 cells. Result: Novel photoreactive MPC polymers possessing MPC unit, BMA unit and photoreactive groups were successfully synthesized. The monomer unit fraction of the MPC unit was 60 mol %, BMA unit was 30 mol % and photoreactive group was about 10 mol %. The photoreactive groups were confirmed by 1H-NMR. These polymers can be dissolved in alcohol. Regardless of the kind of the MPC polymers, the treatment resulted in high contact angles of air on the surfaces under water (100 o to 140 o). In addition, protein adsorption and cell adhesion were suppressed. On the other hand, those of the substrates without photoirradiation were equivalent to non-treated substrates in all examinations. Discussion: The substrates treated with the MPC polymers coating and photoirradiation were demonstrated good hydrophilicity even after washing process with ethanol. At this substrate, we observed reduced protein adsorption and cell adhesion. These are one of the fundamental characteristics for making blood-contacting medical devices and implantable devices. These results were due to formation of covalent bonds between the MPC polymers and the substrates and stable surface modification layer was constructed. Conclusion: We developed a smart process to obtain stable and biocompatible surface using photoreactive MPC polymers. The surfaces of various substrates modified with the photoreactive MPC polymer showed super-hydrophilic character, reduction of protein adsorption and inhibition of cell adhesion. Also, the photoreaction with the MPC polymer will be applied to treat a microspace of the substrate. Thus, this excellent anti-biofouling nature will be important to make biocompatible medical devices and biodevices. This research was supported by S-innovation from Japan Agency for Medical Research and Development (AMED)

動圧軸受を用いた小型遠心血液ポンプ羽根車の運動特性

An implantable Left Ventricular Assist Device (LVAD) is used as a Right Ventricular Assist Device (RVAD) because there is no implantable blood pump specialized for a right ventricular assist. As a demanded pump head of the implantable RVAD is different from that of LVAD, LVAD used as RVAD is operated at off-design points. In the operation of blood pumps at off-design points, hemolysis (destruction of blood cells) and thrombosis (formation of blood clots) can occur. As a realization of the implantable RVAD specialized for a right ventricular assist has been expected due to these backgrounds, the implantable RVAD has been developed by our research group. In the present study, motions of the impeller in a developed RVAD were investigated to clarify a floating mechanism of the impeller supported by dynamic pressure bearings. In experiments, performance tests of RVAD were carried out and motions of the impeller were measured by using two laser displacement sensors. As a result, it was confirmed that a main motion of the impeller was a whirling motion and its frequency was a rotational frequency of the impeller. The amplitude of the whirling motion was about 0.2 times as large as a mean radial clearance of bearings.

Simulation of Blood Flow Dynamics Changes through Implantable Axial Flow Pump

In this work, changes in the dynamics of blood flow through a pump were simulated using a mathematical model of an implantable axial blood pump. To describe these changes, indices derived from the mathematical model of the pump are used. Analysis of the index dynamics when changing pump speed allowed defining the modes of pump operation: mode of reverse blood flow through the pump, mode of partial unloading of the ventricle, mode of complete unloading of the ventricle, modes of partial and complete collapse of the ventricular wall.

The CentriMag centrifugal blood pump as a benchmark for in vitro testing of hemocompatibility in implantable ventricular assist devices.

Implantable ventricular assist devices (VADs) have proven efficient in advanced heart failure patients as a bridge-to-transplant or destination therapy. However, VAD usage often leads to infection, bleeding, and thrombosis, side effects attributable to the damage to blood cells and plasma proteins. Measuring hemolysis alone does not provide sufficient information to understand total blood damage, and research exploring the impact of currently available pumps on a wider range of blood cell types and plasma proteins such as von Willebrand factor (vWF) is required to further our understanding of safer pump design. The extracorporeal CentriMag (Thoratec Corporation, Pleasanton, CA, USA) has a hemolysis profile within published standards of normalized index of hemolysis levels of less than 0.01 g/100 L at 100 mm Hg but the effect on leukocytes, vWF multimers, and platelets is unknown. Here, the CentriMag was tested using bovine blood (n = 15) under constant hemodynamic conditions in comparison with a static control for total blood cell counts, hemolysis, leukocyte death, vWF multimers, microparticles, platelet activation, and apoptosis. The CentriMag decreased the levels of healthy leukocytes (P < 0.006), induced leukocyte microparticles (P < 10−5), and the level of high molecular weight of vWF multimers was significantly reduced in the CentriMag (P < 10−5) all compared with the static treatment after 6 h in vitro testing. Despite the leukocyte damage, microparticle formation, and cleavage of vWF multimers, these results show that the CentriMag is a hemocompatible pump which could be used as a standard in blood damage assays to inform the design of new implantable blood pumps.

A new design and computational fluid dynamics study of an implantable axial blood pump

Considering small thoracic space, using implantable ventricular assist device requires reduction in a pump size. Among many available blood pumps, axial blood pumps have attracted greatly because of their small size. In this article, a new miniature axial blood pump has been designed and studied which can be easily implanted in the human body. In this design, the pump overall length decreased by a little increasing in the pump diameter, and new blade geometry is used to produce a streamlined, idealized, and nonobstructing blood flow path in the pump. By means of computational fluid dynamic, the flow pattern through the pump has been predicted and overall pump performance and efficiency has been computed. Also, to ensure a reliable VAD design, two methods for checking wall shear stress were used to confirm that this pump wouldn't cause serious blood damage.

The simulation of multiphase flow field in implantable blood pump and analysis of hemolytic capability

The numerical simulation of the axial flow impeller blood pump NIVADIII is carried out by using a CFD multiphase flow model. The hydrodynamic performance of the pump and the flow field in the pump are analyzed, and the shear stress distribution is obtained. A hemolytic prediction model based on the shear stress is built based on the calculation results, and it can be used for qua- ntitative predictions of the hemolytic behavior of a blood pump. Hemolysis tests in vitro were performed 6 times with fresh bovine blood. At each time, the flow of the pump NIVADIII is 5 L/min and the outflow tract pressure is 100 mmHg. According to the tests, the plasma free hemoglobin (FHB) content and the hematocrit (HCT) are measured after 0 s, 0.5 s, 1 s, 1.5 s, …4 s. At the end of each experiment Normal Index of Hemolysis (NIH) of NIVADIII is calculated. The average of NIH is 0.0055 g/100L, almost identical with that obtained from the hemolytic prediction model. This method can be applied in the selection stage of a blood pump.