Muscle-powered Soft Robotic Ventricular Assist Devices
Creators: name: Jooli Han
Publisher: name: Carnegie Mellon University
Year: 2021
Subjects: subject: 90399 Biomedical Engineering not elsewhere classified
subject: FOS: Medical engineering
subject: FOS: Medical engineering

description: Congestive heart failure (CHF) remains one of the most costly diseases in the industrialized world, both in terms of healthcare dollars and the loss of human life. This epidemic is responsible for over $40 billion dollars per year in medical costs and lost productivity, and worse, 280,000 deaths each year in the U.S. alone. Despite great strides made in the treatment of CHF using mechanical ventricular assist devices, more than half of those who develop CHF die within 5 years of diagnosis. This is because conventional ventricular assist devices (VADs) continue to be extremely problematic with long term use due to infections caused by percutaneous drivelines and the persistent risk of clot formation associated with blood-contacting surfaces.To address both these longstanding problems, we have developed two types of completely implantable, non-blood-contacting circulatory support systems in this thesis work. An implantable muscle energy converter (MEC) was previously developed in this lab and operates by converting the contractile energy of the latissimus dorsi muscle (LDM) into hydraulic power that can be used to drive any pulsatile blood pump with power requirements consistent with steady-state MEC/LDM output capacity. The two main advantages of this implantable power source are that it significantly reduces infection risk by avoiding a constant skin wound created by percutaneous drivelines and improves patient quality-of-life by eliminating all external hardware components. In this thesis, we combined this unique biomechanical power source with 1) an extra-aortic balloon pump (EABP) to make a muscle-powered extra-aortic counterpulsation VAD (eVAD) and 2) a soft robotic direct cardiac compression sleeve (DCCS) to make a muscle-powered cardiac compression copulsation VAD (cVAD).The eVAD compresses the external surface of the ascending aorta during the diastolic phase of the cardiac cycle, offering increased cardiac output and improved coronary perfusion without touching the blood. The MEC-EABP interface was designed to: 1) amplify MEC volume displacement to achieve proper balloon inflation, 2) maintain a secure and comfortable anatomic fit, 3) optimize energy transfer efficiency, 4) meet muscle force and speed requirements, 5) balance work storage and delivery for rapid balloon inflation/deflation, 6) minimize tissue/device reactivity, and 7) maximize device durability. The eVAD was then prototyped and bench tested to assess its viability as a long-term cardiac assist device. Results showed that the manufactured MEC-EABP system meets all seven design criteria listed above, demonstrating the overall feasibility of this approach. The cVAD represents an alternate approach to delivering muscle power via the MEC to boost cardiac output. Like the eVAD, this device supports the heart without touching the blood and so avoids the serious thromboembolic complications commonly associated with long-term VAD use. Unlike the eVAD however, which unloads the left ventricle indirectly via aortic counterpulsation delivered during cardiac diastole, the cVAD is designed to compress the epicardial surface of both ventricles during the systolic portion of the cardiac cycle, thereby providing support to both sides of the heart. Sleeve design was optimized via finite element analysis (FEA) simulations while biventricular deformations were simulated under various intra-ventricular and epicardial pressures to quantify the compression pressures required to achieve clinically significant improvements in cardiac performance. The sleeve material and manufacturing method were selected after a series of rigorous material testing and iterative prototyping processes. Results showed that a soft robotic sleeve 3D printed with ChronoSil meets all material and performance criteria for this application.Ultimately, whether the chosen approach is counterpulsation EABP or copulsation DCCS, these muscle-powered systems serve to both reduce the risk of infection and enhance patient quality-of-life by eliminating the need for external hardware components. Moreover, and of equal importance, using muscle power to actuate these non-blood-contacting pumps avoids thromboembolic events and obviates the need for long-term antithrombotic therapies. Therefore, these devices would, in principle, be a more attractive option for destination therapy as they would be simpler to maintain and hence less expensive in aggregate than traditional blood pumps, thereby resulting in wider availability and reduced costs for healthcare providers.