Development of a novel shrouded impeller pediatric blood pump

Machine learning based on computational fluid dynamics enables geometric design optimisation of the NeoVAD blades

The NeoVAD is a proposed paediatric axial-flow Left Ventricular Assist Device (LVAD), small enough to be implanted in infants. The design of the impeller and diffuser blades is important for hydrodynamic performance and haemocompatibility of the pump. This study aimed to optimise the blades for pump efficiency using Computational Fluid Dynamics (CFD), machine learning and global optimisation. Meshing of each design typically included 6 million hexahedral elements and a Shear Stress Transport turbulence model was used to close the Reynolds Averaged Navier-Stokes equations. CFD models of 32 base geometries, operating at 8 flow rates between 0.5 and 4 L/min, were created to match experimental studies. These were validated by comparison of the pressure-flow and efficiency-flow curves with those experimentally measured for all base prototype pumps. A surrogate model was required to allow the optimisation routine to conduct an efficient search; a multi-linear regression, Gaussian Process Regression and a Bayesian Regularised Artificial Neural Network predicted the optimisation objective at design points not explicitly simulated. A Genetic Algorithm was used to search for an optimal design. The optimised design offered a 5.51% increase in efficiency at design point (a 20.9% performance increase) as compared to the best performing pump from the 32 base designs. An optimisation method for the blade design of LVADs has been shown to work for a single objective function and future work will consider multi-objective optimisation.

Structural improvement study of streamline design method, conical hub, and auxiliary blades for axial blood pump

The blood pump is a medical device used to assist or replace the diseased heart. Research on the structure of blood pumps has been committed to achieving better hemolysis and hydraulic performance. The purpose of this study was to find some effective ways to improve design methods and hydraulic structures. The research contents of improvement include: (1) improved blade streamline design method; (2) conical impeller hub; (3) additional auxiliary blades. Characteristic analysis and parameter design were carried out on the above three aspects. The methods used in this study included Dynamics (CFD) simulation, hydraulic experiments, and Particle Image Velocimetry (PIV) experiments. The results showed that this improved streamline design method could improve the distortion of blades and ensure a smaller impeller length. And, in the enhanced design of the hub, it is designed to be conical with inlet and outlet diameters of 7.5 and 12.8 mm, respectively. Furthermore, the auxiliary blades between the main blades are analyzed and designed. The results have the best performance optimization effect when the length of the auxiliary blades is 55% of the main blades. In general, the structural improvements in this study achieved the effect of improving hydraulic performance and avoiding increased hemolysis. These methods can be considered as an effective means of improving blood pump performance.

A Short-Term In Vivo Evaluation of the Istanbul Heart Left Ventricular Assist Device in a Pig Model

OBJECTIVES

A continuous-flow centrifugal blood pump system has been recently developed as an implantable left ventricular assist device for patients with endstage heart failure. The objective of this study was to evaluate the initial in vivo performance of a newly developed left ventricular assist device (iHeart or Istanbul heart; Manufacturing and Automation Research Center, Koc University, Istanbul, Turkey) in an acute setting using a pig model.

MATERIALS AND METHODS

Three pigs (77, 83, 92 kg) received implants via a median sternotomy, with animals supported for up to 6 hours. An outflow cannula was anastomosed to the ascending aorta. Anticoagulation was applied by intravenous heparin administration. During the support period, pump performance was evaluated under several flow and operating conditions. All pigs were humanely sacrificied after the experiments, and organs were examined macroscopically and histopathologically.

RESULTS

Flow rate ranged between 1.5 and 3.6 L/min with pump speeds of 1500 to 2800 revolutions/min and motor current of 0.6 to 1.3 A. Initial findings confirmed thatthe iHeart ventricular assist device had sufficient hydraulic performance to support the circulation. During the experimental period, plasma free hemoglobin levels were found to be within normalranges.Thrombus formation was not observed inside the pump in all experiments.

CONCLUSIONS

The iHeart ventricular assist device demonstrated encouraging hemodynamic performance and good biocompatibility in the pig model for use as an implantable left ventricular assist device. Further acute in vivo studies will evaluate the short-term pump performance prior to chronic studies for long-term evaluation.

EFFECT OF A HIGH-FREQUENCY VIBRATION BOUNDARY ON RBC

The vibrations in blood pumps were often caused by high speed, suspension structure, viscoelastic implantation environment and other factors in practical application. Red blood cell (RBC) was modeled using a nonlinear spring network model. The immersed boundary-lattice Boltzmann method (IB-LBM) was used to investigate the impact of high-frequency vibration boundary on RBC. To confirm the RBC model, the simulation results of RBC stretching were compared with experimental results. We examined the force acting on RBC membrane nodes; moreover, we determined whether RBC energy was affected by different frequencies, amplitudes, and vibration models of the boundary. Furthermore, we examined whether RBC energy was affected by the distance between the top and bottom boundaries. The energy of RBCs in shear flow disturbed by the vibration boundary was also investigated. The results indicate that larger amplitude (Am), frequency (Fr), and opposite vibration velocity of top and bottom boundary produced a larger force that acted on RBC membrane nodes and larger energy changes in RBCs. The vibration boundary may cause turbulence and alter RBC energy. When the blood pump was designed and optimized, the vibration frequency and amplitude of the blood pump body and impeller should be reduced, the phase of the blood pump body and impeller vibration velocity should be close. To alleviate the free energy of RBCs and to reduce RBC injury in the blood pump, the distance between RBCs and the boundary should not be less than 20[Formula: see text][Formula: see text]m.