Scope and Objectives

Following are the scope and objectives of the project- Design methodology for blood pump with the minimum possible volume and weight of the pump which will guarantee the least hemolysis and no thrombus formation ensuring the required flow rate and head. Fabrication of such a pump from the bio compatible material. Electrical drive and support system of the pump rotor to ensure the minimum friction, maximum reliability with a constraint of power consumption. A controller in compliance with the above goals. Rigorous tests in a mock circulation loop.

Deliverables

Main deliverables of the project are bulleted below- Deliverable will be the technology for developing a low cost left ventricular assist device with indigenous design. The product is targeted for people so that finally the beneficiary of the technology will be citizens of the country suffering from cardiac ailments. Additionally medical establishments and companies will be engaged for the proper execution of the project. Development of a Mock Circulation Loop to simulate human cardiovascular circulation considering heart with four chambers, lungs and body resistance with connected flow passages. The loop will simulate systolic and diastolic phases of the ventricles as realistically as possible. The loop will also have the provision to introduce faults for the simulation of diseased heart. Further, it will be possible to incorporate the developed LVAD in the system facilitating the study of improvement/modification in the circulation in presence of a LVAD. The loop is partially developed and further improvisations are being made. A fully numerical simulation is being done to simulate working of a heart for normal and diseased condition. Considering tissue structure of the heart and its systolic and diastolic movements, the simulation is done based on fluid structure interaction. A pump testing loop under construction. The loop will be fully instrumented and suitable for testing small pumps handling bio-fluids. A BLDC motor suitable for LVAD is under development. Testing facility for such small BLDC motor along with its control mechanism will be developed.

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Scientific Output

The summary of progress has been compartmentalized under following heads and discussed further. Pump Design, Simulation of the heart, Novel design of integrated LVAD-pump and motor, Motor Design, Mock Circulation Loop. Pump Design A comprehensive literature survey has been done to study the history of development of ventricular assist devices and the paradigm shift in the technology over the last few decades which is based on the analysis of patient outcomes and post-operative complications. The patient based feedback of outcomes has revealed merits and demerits in existing design of VADs and possible changes have been formulated to improve on the demerits. The new design is based on certain modifications to overcome challenges like thrombosis and hemolysis of existing devices. A pump design has been selected after rigorous CFD simulations of effect of various preliminary design parameters like - blade profile, number of blades, flow rate, rotational speed and blade wall roughness. Shear stress and pressure head are basis for selection of optimum design. Simulation of the heart Numerical study of hydrodynamics inside the human heart has been done. This simulation study also incorporates the effect of an LVAD on heart. Novel design of integrated LVAD pump and motor The size and compactness of LVAD are among the most important design parameters which are dictated by the space in chest cavity. The weight of the device is also very important parameter to be taken care while designing. Keeping in mind, these parameters, a very compact design has been conceived which will have drive and support systems (motor and bearing) along with impeller in the same housing (fig. 3). Lowest possible weight to volume ratio is proposed to be maintained in this design. Motor Design The motor is integrated with the pump. However, we have separately designed the motor in accordance with the requirements of the pump (fig. 4a, 4b). Some of the parameters involved in the design of pump are also important for the design of the motor. Rotational speed, moving torque, weight of the motor etc. are some important parameters to be considered for motor design. A controller is used to control the torque and speed of BLDC motor as per the requirement. A close loop control has to be implemented to achieve desired result for which a preliminary control configuration is decided. Mock Circulation Loop Mock circulation loops (MCL) are used as a mechanical representation of the human cardiovascular system (fig. 5) for in vitro testing of artificial heart valves, pulsatile and continuous flow ventricular assist devices, total artificial hearts, aortic balloon pumps, and almost any other cardiovascular device. Basic systems can consist of a pre-load chamber to deliver constant flow and a resistance valve to alter the pressure drop, however new systems have been developed including features such as physiologically accurate pulsatile flow, compliance, resistance, fluid inertia, atrial contraction, systemic and pulmonary circuits, cardiovascular device insertion, septal defects, valve regurgitation, and many more. We are developing a MCL to assess the performance of the developed LVAD.

Results and outcome till date

The outcomes of the project are given below - CFD simulation for pump design- The mechanical circulator or the pump is the heart of an LVAD. It has been decided to use a centrifugal pump. Such pumps are unique as they are small, with a limited number of vanes. Further, they should be able to supply the blood flow with low power consumption, high reliability. Weight, volume, and shear stress development should be within limit. CFD simulations have been used for the generation of velocity pressure and stress field inside the pump and the volute casing. Different characteristics curves have also been generated considering a large range of parametric variation. Pump with all the geometrical and performance parameters- Taking from the CFD simulation, optimal design parameters have been identified for the LVAD pump which will give the performance at a low shear stress maintaining the constraints of weight, volume and power. Finally, the design of the pump has been frozen. Preliminary fabrication of pump- To get idea of different components of the pump and their assembly initially a model pump of 2:1 scale has been fabricated by rapid prototyping. Next, a model of aluminum has been made using 5-axis milling machine for dimensional checking and laboratory testing. With some modification model made of stainless steel is ordered to professional manufacturer. Once the model could be successfully tested for performance in the laboratory, the final prototype will be made with bio-compatible material. Simulation for motor design- BLDC motor suitable for the LVAD and compatible with the pump design has been simulated. Preliminary design has been frozen. Its performance has also been simulated over an operating range. Preliminary fabrication of motor- Fabrication of the motor is undergoing, both in house and with some professional manufacturer. Simulation of heart and heart valves- As a parallel activity of the project, we have also taken up simulation of human heart both for normal and diseased condition. Based on MRI data a realistic three dimensional simulation of the heart has been made. The simulated heart contains different chambers, the valves and the venous and arterial inlets and outlets. Considering the cardiac cycle the dynamic operation of the heart has been simulated. The simulation incorporates the muscle action, operation of the valves and the fluid flow. A data bank is being created so that it can be used for input to the design and performance analysis of different subsystems of the LVAD. Mock Circulation Loop- A preliminary mock circulation loop has been developed to simulate the working of cardiovascular circulation system both under healthy and diseased condition. The system is being improved to incorporate the LVAD.

Societal benefit and impact anticipated

The growing prevalence of cardiovascular diseases (CVDs) like chronic heart failure (CHF) has become a global threat. According to World Health Organization (WHO), CVD is the number one cause for global deaths. More than 8 lakhs cases are reported every year and almost 30% of the global deaths are due to CVD. Out of these causalities almost 50% is due to CHF. For most of the cases of CHF causality can be avoided by heart replacement. Unfortunately, the availability of organ for heart transplant is only 3000 per year and shockingly this number is on the decline. For developing and under developed countries this devise is out of the reach of the most. In developing countries, due to the lack of awareness, heart donations are rare which worsens the problem even further. It is needless to say that the entire world is eagerly looking at the development of this very important device at an affordable cost. Low cost LVADs, no doubt will improve the lifespan and the lifestyle of millions.

Next steps

Following are the further steps to be carried out under the project- Simulation and manufacturing of the novel design of integrated LVAD-pump and motor. Design of a close loop control system for LVAD to achieve desired results. Design and fabrication of the test rig (which will be known as Mock Circulation Loop) for in vitro testing of LVAD. To design a MCL, following requirements have to be met- Design of ventricular and atrial simulators, Design of pulmonary and arterial compliances. Design of a pump testing loop which will be fully instrumented and suitable for testing small pumps handling bio-fluids. Design of a testing facility for such small BLDC motor along with its control mechanism.

Publications and reports

Conference Paper in FMFP 2018 titled: Conceptual Design of a complete Mock Circulation Loop.

Patents

None as of now.

Scholars and Project Staff

3 MS (Project) up to 2020 & 3 PhD (Institute).

Challenges faced

The hurdles experienced in this project are: Fabrication of Mock Circulation Loop to exactly mimic the human circulatory system. Producing accurate pulsatile flow and approximating the pressure volume relationship of fluids circulated in human circulatory system. Integration of motor and pump into a single unit. Pump should be such that it should cause minimal thrombosis and hemolysis. Although we have measured the wall shear stress from CFD simulations, certain design features and surface roughness promote formation of thrombosis & hemolysis. Bio-compatibility of pump is of paramount importance, although we are focusing on titanium, machining of titanium with high surface finish in-house is proving to be a challenge. Obtaining reliable data from medical domain for Indian patients is a challenge.