Development of Inspired Therapeutics Pediatric VAD: Benchtop Evaluation of Impeller Performance and Torques for MagLev Motor Design

Abstract

Despite the availability of first-generation extracorporeal mechanical circulatory support (MCS) systems that are widely used throughout the world, there is a need for the next generation of smaller, more portable devices (designed without cables and a minimal number of connectors) that can be used in all in-hospital and transport settings to support patients in heart failure. Moreover, a system that can be universally used for all indications for use including cardiopulmonary bypass (CPB), uni- or biventricular support (VAD), extracorporeal membrane oxygenation (ECMO) and respiratory assist that is suitable for use for adult, neonate, and pediatric patients is desirable. Providing a single, well designed, universal technology could reduce the incidence of human errors by limiting the need for training of hospital staff on a single system for a variety of indications throughout the hospital rather than having to train on multiple complex systems. The objective of this manuscript is to describe preliminary research to develop the first prototype pump for use as a ventricular assist device for pediatric patients with the Inspired Universal MCS technology. The Inspired VAD Universal System is an innovative extracorporeal blood pumping system utilizing novel MagLev technology in a single portable integrated motor/controller unit which can power a variety of different disposable pump modules intended for neonate, pediatric, and adult ventricular and respiratory assistance. A prototype of the Inspired Pediatric VAD was constructed to determine the hemodynamic requirements for pediatric applications. The magnitude/range of hydraulic torque of the internal impeller was quantified. The hydrodynamic performance of the prototype pump was benchmarked using a static mock flow loop model containing a heated blood analogue solution to test the pump over a range of rotational speeds (500 - 6000 RPM), flow rates (0 - 3.5 L/min), and pressures (0 to ~420 mmHg). The device was initially powered by a shaft-driven DC motor in lieu of a full MagLev design, which was also used to calculate the fluid torque acting on the impeller. The pediatric VAD produced flows as high as 4.27 L/min against a pressure of 127 mmHg at 6000 RPM and the generated pressure and flow values fell within the desired design specifications. The empirically determined performance and torque values establish the requirements for the magnetically levitated motor design to be used in the Inspired Universal MagLev System. This next step in our research and development is to fabricate a fully integrated and functional magnetically levitated pump, motor and controller system that meets the product requirement specifications and achieves a state of readiness for acute ovine animal studies to verify safety and performance of the system.

Introduction

Pediatric heart failure (HF) patients have historically been an underserved population and have the highest mortality rate at 17% of any population awaiting heart transplantation [1]. Due to this great clinical need, Inspired Therapeutics (Merritt Island, FL) and the University of Louisville (Louisville, KY) have been developing the Inspired Pediatric VAD, a rotary blood pump to be used with the Inspired Universal MagLev System. As seen in Table 1 below, the vision for this system is a universal controller/motor which can be paired with a variety of different single-use pumps for different indications for use (neonate, pediatric and adult) providing up to 30-days of circulatory or respiratory support. The development goals for the system are to produce a product that is smaller, less expensive, and wearable to allow for patient ambulation during treatment. The first single-use pump for the system, the Inspired Pediatric VAD, is intended to provide extracorporeal left, right, or biventricular support for neonate and pediatric patients up to 40 Kg. The design criteria for the Pediatric VAD include providing flows ranging from 0.5 – 3.5 L/min against pressures of 40 – 150 mmHg using clinically available arterial and venous pediatric cannula (30 to 40 cm in length). Figure 1 represents a schematic illustration of the basic components of the Inspired System and Pediatric VAD, including the pump (impeller/rotor and pump housing), MagLev motor, and controller interface. The pump design, including the impeller, and an initial CFD analysis for the Pediatric VAD concept have been previously described by the authors [2]. The next phase in the development process will focus on the design of the novel MagLev motor that will be integrated into the Universal MagLev System to levitate and rotate the Pediatric VAD impeller/rotor. This article describes the methodology and presents the results of in vitro testing (static mock flow loop model) to characterize pump pressure and flow performance and hydraulic torques acting on the pump impeller/rotor. These results will be used to guide completion of the design of the novel MagLev motor.

Table 1.

Potential advantages of the Inspired Pediatric VAD and Universal MagLev System.

Advantages of the Inspired Pediatric VAD and Universal MagLev System
MagLev	Fully magnetically levitated impeller/rotor means no contacting parts, greatly reducing wear, potential thrombus formation, and increasing pump lifespan
Size	System (pump, motor, controller) fits into a single enclosure the size of a 7.5 oz soda can
Weight	Less than 2 lbs.
Reduced Priming Volume	30% lower than commercial devices (e.g. PediMag)
Compatible with Commercially Available Cannulae	¼ inch connectors
Single Controller for Multiple Indications	Pediatric VAD;Adult VAD;Respiratory Assist Device;ECMO;CPB
Wearable	Patients able to ambulate to accelerate recovery
Improved Quality of Life	Not bedridden and tethered to a stationary console
Reduces Risk of Human Errors	Caretakers trained on one system that can be used in any hospital setting (OR, ICU, Stepdown Units)

Figure 1.

A) Components of the Thoratec CentriMag/PediMag system (pump, motor, controller) (Top) compared to the Inspired Pediatric VAD and Universal MagLev System (Bottom). The Inspired Universal System combines all extracorporeal components into one small, universal package allowing for greater ease of use, quality of care, and possible patient ambulation, B) Basic components of the Inspired Universal MagLev system and removable Pediatric VAD pump.

Motor designs for rotary blood pumps (RBP) have many unique requirements. Not only do these motors need to be compact and demonstrate long-term reliability, they also require relatively large gaps between rotor and stator components (compared to traditional motors) to accommodate channels for adequate blood flow and the use of contactless bearings to prevent blood damage [3]. Modern RBPs typically use electric motors with an external motor stator, pump housing, internal rotating element (typically a combination impeller and motor rotor), and bearings to allow for rotation and impeller/rotor stability (Figure 1B). The driving portion of the motor that rotates the impeller/rotor uses a combination of permanent- and electromagnets, which may also serve to levitate the impeller/rotor within the pump casing.

To stabilize the impeller/rotor and provide a point of rotation, several RBP designs, including the Medtronic Biopump BP-50, Maquet RotaFlow, and Medos Deltastream DP3, use a shaft and mechanical bearing attached to the center of the rotor [4]-[6]. Although these designs use small bearings with minimal contact, they create a concentrated point for mechanical wear, heat generation, noise, vibration, and a potential risk for clinically significant blood damage [7]. Modern designs have employed contactless bearings using permanent or electromagnetics between the rotor and stator or hydrodynamic bearings as is the case of the HeartWare HVAD [8], which provide improved hemodynamics that show promise in helping to reduce the risk of blood damage [9]. A unique design used in the Thoratec HeartMate3 and Levitronix CentriMag systems is based on a “bearingless slice motor”, which combines the motor and bearing into a single component [10], [11]. Irrespective of their novel design and orientation, all rotary blood pump motors must be hemocompatible, generate sufficient torque to rotate the impeller/rotor, and provide translational forces to stabilize the rotation of the impeller/rotor. Motor designs may also be unique to each pump type, including different sized diameter impeller/rotors and operational ranges (pressures and flows) for the intended patient populations. This variance in geometries and operational parameters may directly impact the torques and forces the motor may be required to produce.

The proposed motor design for the Inspired Pediatric VAD is a MagLev system that completely levitates and rotates the pump impeller/rotor in a manner that eliminates physical contact between parts. The Inspired design includes a Voice Coil Actuator (VCA), to actively control the axial positioning of the impeller/rotor, and Passive Magnetic Bearings (PMB), to passively control the impeller/rotor radially. The impeller/rotor is levitated within the pump housing, providing a radial blood gap of 0.5 mm at the outer (between rotor and pump housing) and inner (between rotor and center post) gaps and an axial blood gap of 0.75 mm at the bottom of the rotor, with a total gap of approximately 2 mm between rotor and stator magnetic components (Figure 2B). With these dimensions defined, the performance of the pump impeller/rotor and surrounding fluid within the pump requires characterization over the anticipated operational range of the pump to define the design requirements for the MagLev motor. The motor performance characteristics include the required torque to rotate the impeller and propel the fluid (rotation about the Z-axis), the axial lift force (translation in the Z-axis) generated by the impeller acting on the fluid, and the hydrodynamic forces from the surrounding fluid acting on the impeller/rotor in the tangential, radial, and axial directions (X, Y, and Z-axis, respectively) (Figure 2A). In this article, we present in vitro testing of an Inspired Pediatric prototype VAD that was developed and tested to quantify and define several critical system design parameters.

Figure 2.

A) Exploded view of the Inspired Pediatric VAD concept detailing the impeller rotational direction (Z-axis) and impeller translational force directions (X, Y, Z-axis B) Cut-view of the Inspired Pediatric VAD concept detailing the blood/fluid gap between the impeller/rotor and pump housing (0.5 mm along sides, 0.75 mm along bottom) and the overall gap (3 mm) between rotor and stator magnetic components.

Methods

Prototype Construction

A prototype of the Inspired Pediatric VAD was constructed to quantify the required magnitude and range of impeller hydraulic torques and to benchmark hydrodynamic performance. This test device was assembled using a shaft to rotate the pump impeller via a permanent magnet DC (PMDC) motor in place of the future MagLev motor, and bench tested in a static flow loop (SFL, Figure 3A-C). This simplified shaft driven prototype allowed testing of critical parameters (pump performance, impeller torque) which will translate into engineering requirements to complete the MagLev motor design. The lower pump housing, impeller, and upper pump housing were fabricated using additive manufacturing techniques that meet design specifications in accordance with the defined geometries calculated using computational models, as previously described [2]. The components were printed using stereolithography with a high-resolution ABS-like clear material (Watershed XC). The impeller was fabricated without a center opening in the rotor body to allow permanent attachment of an 8 mm diameter stainless steel shaft. The pump housing was mounted on a custom fixture via two threaded posts which anchored its position with the PMDC motor at the base approximately 10 cm away (Figure 4A). The permanently attached impeller shaft was coupled to the permanent shaft of the PMDC motor using a radial clamping coupler with locking set screws (Figure 4A). The axial positioning of the impeller/rotor inside the mounted pump housing was set using a 0.75 mm plastic spacer placed in the axial blood gap area and by adjusting the height of the impeller shaft within the radial clamping coupler. A nitrile rubber double-lip seal was added to the lower pump housing as a leak-proof entry for the impeller shaft coupled to the PMDC motor shaft (Figure 4A). A laser-based tachometer (PLT200, Monarch Instrument, Amherst, NH) was used to measure the rotational speed of the shaft and impeller.

Figure 3.

A) Side and B) Top views of the prototype of the Inspired Pediatric VAD including SLA polymer impeller, lower pump housing, and 8mm metal shaft. C) VAD prototype attached to custom fixture with coupled PMDC motor and tachometer, which are connected to the D) static flow loop (SFL) for preliminary performance testing and evaluation.

Figure 4.

A) Pictures of the shaft-driven Inspired Pediatric VAD prototype highlighting key components of the pump, test fixture, shaft and coupler, and PMDC motor, B) Illustration of torque components; hydrodynamic impeller torque (τ_Hydro), torque due to friction and losses of the shaft and seal (τ_Friction), and torque of the DC motor (τ_DC), which all sum to form the measured total torque (τ_Total) of the Inspired Pediatric VAD running in the fluid filled SFL.

Determination of Impeller Hydraulic Torque

A brushed permanent magnet DC (PMDC) motor (12V/24V 3000/6000rpm, XD-3420, Guang Wan Motor Co, LTD.) powered by a variable DC power supply (PS280, Tektronix, Beaverton, OR) was used to rotate the VAD impeller. The motor current and supply voltage were measured with a pair of digital multimeters (Fluke 45, Fluke Corporation, Everett, WA). Additionally, this motor was used to determine the magnitude of hydraulic torque, τ_Hydro, (torque due to circulating fluid) acting on the impeller over a range of rotational speeds (500 - 6000 RPM) and pressures (ΔP 0 to ~420 mmHg) using the following protocol. First, an average implied motor torque constant (K_t) was determined for the motor to calculate the torque (τ) based on motor current (I), (Equation 1) [12].

$$\tau =K_t\times I$$ (1)

This measurement was obtained using another DC motor to back-drive the PMDC motor over a range of rotational speeds (400 to 7500 RPM). At each speed, the voltage generated by the motor was recorded (Supplement Table I), and an average back electromotive force (EMF) constant for the motor was determined (K_e, Equation 2). By converting the units, the average back EMF constant is equivalent to an implied motor torque constant K_t (Equations 3, 4) [12].

$$K_e={}^{Voltage(V)}∕_{RotationalSpeed(\omega )}$$ (2)

$$K_t={}^{MotorTorque({\tau }_{DC})}∕_{MotorCurrent(I)}$$ (3)

$$K_e=K_t$$ (4)

The calculated values were K_e = 3.311 V/kRPM and K_t= 31.57 N*mm/A. The PMDC motor was then operated using the variable power supply over the range of rotational speeds against no load. Motor voltage and current were recorded at each rotational speed in 500 RPM increments. The torque generated by the DC motor (τ_DC) alone was then calculated at each rotational speed (Supplement Table II) defined as the product of the motor current (I) and K_t. The calculated torque was plotted against rotational speed (Supplement Figure I), and a corresponding linear curve of best fit was obtained. The associated linear equation (Equation 5) (R²=0.9839) was used to generate a secondary equation to calculate the torque of the DC motor (τ_DC) at any rotational speed (n), including the motor viscous damping coefficient (B_m) and the kinetic friction of the motor (T_fm) [13]:

$$y=0.7948x+6.8301\to {\tau }_{DC}=(B_m\times n)+T_{fm}$$ (5)

The PMDC motor torque represents the base torque of the system, and any generated torque above PMDC motor torque would be due to friction losses from the shaft and pump housing seal and hydraulic forces acting against the impeller. The PMDC motor shaft was attached to the VAD impeller shaft with the clamping coupler and the axial blood gap within the pump housing was set. The Pediatric VAD was not filled with fluid. The dry VAD was operated over a range of rotational speeds (1000 RPM increments) and the torque representing frictional losses of the shaft and seal was calculated at each speed. These values (in the range of 7.83 to 9.16 mN-m) were averaged, resulting in mean frictional torque loss of 8.52 mN-m (τ_Friction).

The Pediatric VAD and SFL were then filled with the blood analogue solution and testing of the VAD prototype was conducted. The total torque (τ_Total) of the Inspired Pediatric VAD prototype at each speed and flow setting in the SFL was calculated using the measured motor current (I) and the derived torque constant (K_t) and torque of the PMDC motor (τ_DC) using Equation 5. The hydraulic torque (τ_Hydro) of the impeller was determined by subtracting the average frictional torque (τ_Friction) and the calculated PMDC motor torque (τ_DC) from the calculated total torque (τ_Total) of the VAD in the fluid filled SFL system, (Figure 4B) (Equation 6).

$${\tau }_{Hydro}={\tau }_{Total}-{\tau }_{DC}-{\tau }_{Friction}$$ (6)

Overall hydraulic efficiency (η_H) of the shaft-driven prototype was calculated based on generated pressure (ΔP) in the SFL model and calculated hydraulic torque (τ_Hydro) of the impeller, (Equation 7).

$${\eta }_H=\frac{Q\times \Delta P}{{\tau }_{Hydro}\times n}$$ (7)

Static Flow Loop (SFL) Model Testing

A static flow loop (SFL) model consisting of a fluid reservoir (3 L), compliant tubing (Terumo 061070, Xcoating Tubing, 1/4” x 1/16” wall), and a screw-type clamp (to adjust flow resistance) was constructed (Figure 3D). The fluid reservoir was submerged in a heated water bath with a thermoregulator unit (Techne TE-10D, Cole-Parmer, Vernon Hills, IL) to maintain temperature at 37° C. The Inspired Pediatric VAD was inserted in-line with the SFL circulation. High-fidelity pressure transducers (MPR-500, Millar, Houston, TX) were placed at the pump inlet (P2) and outlet (P1), and a transit-time flow probe (6XL, Transonic, Ithaca, NY) at the pump outlet (VAD Flow). The SFL was filled with one liter of a blood analogue solution consisting of a saline-glycerol mixture with 3.6 cP viscosity (equivalent to the viscosity of 38% hematocrit blood [14], [15]). A 10 ml sample of the solution was tested using a calibrated Cannon-Fenske style viscometer submerged in a 37° C water bath to quantify the measured density of the sample (1.1096 g/ml with a viscosity of 3.66 cP).

The hydrodynamic performance of the Pediatric VAD was tested across the range of rotational speeds (500 – 6000 RPM) via the following protocol. The voltage of the DC power supply was adjusted to produce a VAD impeller rotational speed starting at 500 RPM, confirmed by the tachometer. With the resistance clamp completely open (no load), the pump inlet and outlet pressures, flow rate, and the motor voltage and current were measured at the set rotational speed. This condition provided the maximum flow rate of the pump against minimum resistance at the set rotational speed. The resistance clamp was then tightened to lower the pump flow rate at specified increments (0.15, 0.20, or 0.25 L/min, depending on rotational speed setting). At each incremental pump flow rate, all parameters were recorded. The resistance clamp was also tightened to fully occlude the system, resulting in a pump flow rate of 0 L/min and providing the maximum pressure of the pump at the set rotational speed. The system was reset with the resistance clamp completely opened, and this process was repeated for increasing rotational speeds (500 to 6000 RPM at 500 RPM increments). Experimental data for all test conditions were collected at a sampling rate of 400Hz using PowerLab 16/35 (ADInstruments, Sydney, Australia) and recorded by LabChart 8 (ADInstruments, Sydney, Australia) data acquisition system software.

Results

Pressure-Flow Curves

The full hydrodynamic performance of the Inspired Pediatric VAD was observed for the first time over the operational range (500 – 6000 RPM) of the pump. Flow rate (Q) and pressure (ΔP) results were plotted to form characteristic pressure-flow curves (HQ curves) for the pump (Figure 5A). The Inspired Pediatric VAD shaft-driven prototype was able to achieve flow rates as high as 4.27 L/min with pressures as high as 422 mmHg at 6000 RPM which exceeded the intended operating window for the device.

Figure 5.

A) Characteristic HQ curves (pressure versus flow rate) for the Inspired Pediatric VAD pump shaft-driven prototype for rotational speeds 500 to 6000 RPM, B) Hydraulic torque of the Inspired Pediatric VAD shaft-driven prototype impeller/rotor versus flow rate for rotational speeds 500 to 6000 RPM.

Torque Curves

The calculated hydraulic torques acting on the VAD impeller were plotted versus the pump flow rates producing characteristic torque curves for the pump (Figure 5B). Over the operational flow range of the pump (0.5 – 3.5 L/min), required torques to propel the fluid in the range of 0.97 to 15.56 mN-m were observed. Torques at the lower rotational range of the pump (500 – 2000 RPM) were low (<1 mN-m), with occasional negative values calculated due to the tare calculation (subtracting average friction and DC motor torque) to determine the hydraulic torque.

Efficiency

Hydraulic efficiency of the Inspired Pediatric VAD shaft-driven prototype was calculated over the range of tested rotational speeds based on achieved flow, pressure, and calculated impeller hydraulic torque. Efficiency curves for select rotational speeds are plotted against corresponding pressure-flow curves in Figure 6. Due to calculated negative torque values at lower rotational speeds (500 – 2000 RPM), efficiency curves could only be calculated for speeds above this range. Overall peak pump efficiency of 19% was achieved at 2.5 L/min and 300 mmHg at a speed of 6000 RPM. Peak efficiency at other rotational speeds occurred at 18.3% for 1.0 L/min, 66 mmHg, at 3000 RPM, 12.2% for 1.75 L/min, 105 mmHg, at 4000 RPM, and 15.7% for 2.25 L/min, 180 mmHg, at 5000 RPM.

Figure 6.

Characteristic HQ curves and calculated hydraulic efficiency curves for select rotational speeds 3000, 4000, 5000, and 6000 RPM for the Inspired Pediatric VAD shaft-driven prototype tested in the bench-top SFL model with best efficiency point (B.E.P.) highlighted for each curve.

Discussion

Inspired Pediatric VAD Performance

Hydrodynamic torque values for the impeller/rotor and the pump performance values (pressure and flow rate) for the Inspired Pediatric VAD were successfully quantified empirically using a prototype device in a SFL model. The shaft-driven prototype was able to achieve flows as high as 4.27 L/min against a pressure of 127 mmHg at 6000 RPM. At the VAD’s maximum intended design flow rate of 3.5 L/min, the pump was able to achieve pressures of 135 mmHg and 210 mmHg at 5500 and 6000 RPM, respectively. Importantly, the shaft-driven prototype was able to achieve the full pressure and flow range of the original design criteria (40 −150 mmHg, 0.5 – 3.5 L/min) within the envelope of rotational speeds tested (500 – 6000 RPM) as seen in Figure 5A

Calculated peak efficiencies for the shaft-driven prototype were all below 20%, while the overall best efficiency point (B.E.P.) was achieved at 6000 RPM at 2.5 L/min. Compared to other extracorporeal RBPs, such as the RotaFlow, Deltastream DP3 and Thoratec PediMag, the Inspired Pediatric VAD shaft-driven prototype achieved similar hydraulic efficiencies of 10-20% at lower flow rates (0.5 – 2.5 L/min) [5], [16], [17]. However, these devices achieved higher efficiencies of 20-30% at higher flow rates of 2.5 – 4 L/min while the Inspired Pediatric VAD remained in the ~20% range. Further work will be completed to help identify key areas of the Pediatric VAD design that may be altered to help improve overall pump hydraulic efficiency, including (1) entrance blade height to increase capacity, (2) modifications to the impeller blade shroud to reduce recirculation and fluid pre-rotation at the inlet, and (3) the addition of diffuser blades to reduce recirculation within the impeller blade gaps. Improving the pump hydraulic efficiency should reduce power consumption, enable reduction in size of the MagLev motor system, and reduce power losses in the pump that may lead to higher incidence of blood damage [18]

Indications for MagLev Motor Design

Empirical HQ and torque findings from this study provide insight into the design requirements for the development of the MagLev motor system. For the spinning motor component, the MagLev system will need to be able to rotate the impeller/rotor between 2000 and 5500 RPM and produce torques between 0.10 and 14 mN-m to achieve the desired pump operational range of 0.5 −3.5 L/min at 40 −150 mmHg. Translational force values were not able to be produced empirically in this study, but future work will focus on computational fluid dynamics (CFD) analysis of the Pediatric VAD impeller/rotor to help quantify force values in the x, y, and z-axis. Force values in the axial direction (z-axis) will be of particular interest for the design of the VCA, which will have to counteract lift forces generated by the rotating impeller. Tangential and radial forces (x and y-axis) will also be of interest in determining the required strength of the PMB to keep the impeller/rotor radially centered inside the pump housing.

Study Limitations

The objective of this study was to generate early performance data and calculate impeller hydraulic torque of the first Inspired Pediatric VAD prototype. Several design testing limitations were observed that may impact preliminary findings. First, there appears to be inconsistency in the generated torque curves in the 3000 - 4000 RPM range, which may be attributed to variances in voltage and current measurements associated with the tolerances of the PMDC motor. In future studies, multiple PMDC motors will be tested, and experiments conducted with randomized loop conditions with repeated measures to minimize experimental bias. Second, during this early stage of development, prototype impeller and pump parts were fabricated using 3D printing techniques that may exceed desired tolerances in relation to the small dimensions of the VAD design. Third, torque and force of the VAD impeller were not directly measured using a force transducer. Future studies will employ more robust measurement systems and techniques to ensure accurate, reliable measurements of these parameters. Fourth, testing a first-generation pump using a shaft and seal did not permit an evaluation of the potential for wobble of the impeller, which also needs to be assessed when the fully MagLev design is assembled and tested. Fifth, the shaft used to drive the impeller/rotor likely altered the hydrodynamics of the axial blood gap between the bottom of the rotor body and the lower pump housing by partially occluding the channel. Ideally, the axial blood gap should be completely open with a central opening in the center of the rotor body to allow for blood circulation. Subsequently, some stagnate flow around the perimeter of the shaft may have affected the flow around the radial blood gap, which may have adversely affected hydraulic torque measurements. Sixth, preliminary testing did not include measurements of thermal consequences that could potentially arise due to the power requirements to drive the system or directly assess power efficiencies that could impact battery time needed for transport. Therefore, thermal measurements will be incorporated into the next phase of our system development.

Despite these limitations, this feasibility study provided empirical data that suggests the Inspired Pediatric VAD will be able to generate the desired pressures and flow rates to provide adequate circulatory support for pediatric heart failure patients. The performance results compare favorably to other clinical blood pumps used in the pediatric population, including the BP-50, RotaFlow, Deltastream DP3, and Thoratec PediMag [4]-[6], [19]-[23]. Comparison of design specifications for the Inspired Pediatric VAD to these devices, including rotor diameter, priming volume, rotational speed ranges and flow ranges, are presented in Table 2. The BP-50 and PediMag are devices developed specifically for the pediatric population, but are limited to lower flows of up to 1.5 L/min. The DP3 and RotaFlow are adult devices that are often used in pediatric patients, providing higher flows, but require larger priming volume and size. These devices use physical bearings to rotate their impellers, which may lead to increased risk of blood damage and/or thrombus formation. The performance achieved by the Inspired Pediatric VAD prototype is encouraging when compared to these devices that are currently in clinical use. A comparison of the torque and force data generated by the Inspired Pediatric VAD to these devices is challenging since these values are directly determined by the pump’s impeller/rotor diameter and size as well as hydrodynamic conditions.

Table 2.

Comparison of dimensions, performance, and design components of the Inspired Pediatric VAD to other extracorporeal RBPs clinically in use in the pediatric population including the Medtronic BP-50, Maquet RotaFlow, Medos DP3, and Thoratec PediMag.

Device	Rotor/Impeller Diameter (mm)	Priming Volume (mL)	Rotational Speed (RPM)	Flow Rate (L/min)	Bearing Type (Radial/Axial)	Motor Drive
Medtronic Bio-Pump BP-50 [4], [21]	79	48	1,400 – 4,500	Up to 1.5	Mechanical Contacting Polycarbonate Journal Bearing	Magnetic Coupling
Maquet RotaFlow [5], [20]	49	35	0 – 5,000	0-10	Mechanical Contacting Stainless Steel/Sapphire Pivot Bearing	Magnetic Coupling
Medos Deltastream DP3 [6], [22], [23]	25	16	500 – 10,000	0.5 - 8	Mechanical Contacting Ceramic Bearing	Magnetic Coupling
Thoratec PediMag [4], [19], [20]	32.5	14	0 – 5,500	Up to 1.5	Magnetic Contactless Active/Active Magnetic Bearing	Integral
Inspired Pediatric VAD	27.4	9.5	2,000 – 6,000	0.5 – 3.5	Magnetic Contactless Passive/Active Magnetic Bearings	Integral

The development effort described in this report provides the design input requirements needed to advance the design of the pediatric pump module, MagLev motor and controller. Prototypes of the motor and controller have also been under development that are designed to fit within a small, compact enclosure the size of a 7.5-ounce container. The system will have no cables and a minimal number of connectors to allow attachment of a battery and to access logged data. The design objectives outlining the desired advantages of the Universal MCS System are presented in Table 1.

Conclusion

While our previously reported work focused on the initial design of the Inspired Pediatric VAD impeller with preliminary CFD model analysis, the objective of this article is to present experimental results used to inform the design of a novel MagLev motor for the Inspired Universal system. The data acquired in this investigation will be instrumental in advancing the design of the MagLev motor to ensure that it is able to produce adequate torque to drive the impeller/rotor. Future work will include development and validation of a CFD model for analysis of the impeller/rotor to help determine required MagLev system translational forces as well as the design, fabrication, and testing of the MagLev motor and controller. Inspired Therapeutics aims to develop the novel concept of the Inspired System as a universal platform for multiple pump modules with a fully magnetically levitated impeller/rotor design to provide pediatric and adult cardiac and respiratory support.