Design And Performance Study Of A Novel Passively Suspended Left Ventricular Assist Device

Heart failure is one of the leading causes of morbidity and mortality.Heart transplantation is still one of the most effective means of treating patients with end-stage heart failure.However,from a global perspective,the donor heart is seriously insufficient.Therefore,the development of alternatives to heart transplantation is desirable.The ventricular assist device can be partially replaced the function of natural heart to prolong the life of patient.It can be used as prolonged bridge to transplant or destination therapy.Currently,the rotary blood pumps with noncontact bearings,such as magnetic or hydrodynamic bearings,have been developed to improve the durability of the devices.In the blood pump with magnetic bearing,the impeller is levitated by the magnetic force generated by the controllable electromagnet.The blood pump requires active control and additional displacement-sensing which would result in additional power consumption and extra space in the casing for the control system.However,the impeller is levitated within the pump cavity at high bearing gap,which is contributed to the decrease of the shear stress.In the blood pump with hydrodynamic bearing,the impeller is levitated by the suspension force generated either by the grooves or the tapered blade surfaces.The hydrodynamic bearing does not require complex control circuits and the displacement-sensing modules,which offers high reliability and low energy consumption compared with a magnetic bearing.As the suspension of each direction requires extremely small gap(usually less than 0.1 mm),the casing and rotor should be manufactured and assembled very precisely with low tolerance,thus increasing the cost of the device.Furthermore,the hydrodynamic bearing has some disadvantages,such as the destruction of red blood cells and thrombus formation caused by high shear stress and flow stagnation in its small bearing gap.Therefore,based on the advantages and disadvantages of magnetic bearing and hydrodynamic bearing,this study is aimed to design a left ventricular assist device with a passively suspended bearing and a large bearing gap.The design does not require complex control circuits and reduce the hemolysis and the manufacturing cost.In this study,a passively suspended left ventricular assist device with a large bearing gap is taken as the research object.The key technologies of the design of passive suspension bearing and the performance of blood pump are studied.The research contents and conclusions are as follows:1.Design and optimization of conical hydrodynamic bearingFor the rotor of rotating component,the conical wedge bearing and conical step bearing was designed.The parameters of both bearings were designed based on the two-dimensional model.Taking radial bearing capacity of conical hydrodynamic bearing as target,the computational fluid dynamics software fluent was utilized to optimize the parameter of the conical bearing.Finally,the conical step bearing was chosen as our design scheme.2.Design and principle verification of the impeller with injection channelsBased on the traditional impeller of the blood pump,a novel design with six injection channels was designed.The basic motion equations of the flow in the channels and outflow of the injection channels are established to theoretically verify the effectiveness of the injection.In addition,the software Fluent was used to establish the flow field in the whole blood pump under steady-state condition.The localized pressure around the outlet of injection channels was observed.Experimental system was built to measure the suspension force generated by injection.Finally,the axial suspension gap of the rotating component within the inverted blood pump was measured to further verify the effectiveness of injection.3.Performance evaluation of blood pump with conical hydrodynamic bearing and impeller with injection channelsThe blood pump with conical hydrodynamic bearing and impeller with injection channels was regarded as the object of study.The experimental system was set up to measure radial and axial motion of the rotating component within the pump cavity.At the same time,the H-Q curves and power consumption were measured to evaluate the hydraulic performance of the developed blood pump.The computational fluid dynamics(CFD)software Fluent was applied to evaluate the hemolysis performance and in vitro hemolysis test was conducted to obtain the normalized index of hemolysis(NIH)value compared with commercial blood pump BPX-80.The temperature rise of blood pump was evaluated.In order to evaluate antithrombogenicity,an in vitro antithrombogenic test was conducted on the developed blood pumps using a mock circulation loop.In addition,the structure of the channels was optimized to further improve the hemolytic performance of the developed blood pump.4.Design and performance evaluation of blood pump with passively suspended rotating component with injection channelsIn order to further reduce the processing difficulty of the conical step bearing,the rotating component with twelve injection channels was designed,which produced axial and radial levitation force by the injection.Based on the developed blood pump,the axial and radial movement of the rotating component was obtained,which verified that the rotating component could be totally suspended within the pump cavity.At the same time,the hydraulic performance of the developed blood pump was measured.The CFD software Fluent was applied to evaluate the hemolysis performance and in vitro hemolysis test was conducted to obtain the NIH value.The temperature rise of blood pump was evaluated.In order to evaluate antithrombogenicity,an in vitro antithrombogenic test was conducted on the developed blood pumps using a mock circulation loop.In addition,the outflow angle of the injection channels was optimized to further improve the hemolytic performance of the developed blood pump.In summary,this study aims to design a passively suspended blood pump with a large bearing gap.The rotor with conical hydrodynamic bearing and the impeller with injection channels were designed to generate the axial and radial suspension force.One blood pump with conical hydrodynamic bearing and injection channels and the other blood pump with twelve injection channels were designed respectively.The motion of the rotating component within the pump cavity was quantitatively measured.The results showed that the rotating components can be suspended in a large gap,and the stability of the rotor with conical hydrodynamic bearing and injection channels was better than that of the rotor with twelve injection channels.At the same time,hemolysis of the both optimized blood pump could reach the requirements of long-term implantation of the human body.The blood pump with twelve injection channels was superior to the blood pump with conical hydrodynamic bearing and injection channels in reducing manufacturing cost,but the energy consumption is higher.