Enhancing Performance and Safety of Medical Implantable Devices with Multiphysics Simulation

• Analytics & Modeling - Digital Twin / Simulation
• Analytics & Modeling - Predictive Analytics
• Analytics & Modeling - Real Time Analytics

• Healthcare & Hospitals
• Life Sciences

• Product Research & Development
• Quality Assurance

• Predictive Maintenance
• Remote Patient Monitoring
• Digital Twin

• Software Design & Engineering Services
• System Integration

The development of a device meant to assist or completely replace the functioning of the heart is undeniably complex. This design process involves immense challenges, from supplying power to the device to ensuring it does not interfere with normal biological functioning. Researchers at St. Jude Medical use multiphysics simulation to engineer LVADs, Left Ventricular Assist Devices, in an ongoing effort to improve the outlook and quality of life of patients with heart failure. The condition typically begins with the left side of the heart, as the left ventricle is responsible for pumping oxygen-rich blood throughout the body, a greater distance than the right ventricle, which pumps blood through the lungs. Often, in patients with a poorly functioning left ventricle, an LVAD can provide mechanical circulatory support. The ventricle assist device is one of the most complex machines ever implanted in a human being. An LVAD must circulate the entire human blood stream and support life, as well as be compatible with the internal environment of the human body. Thoratec, now part of St. Jude Medical, brought LVADs to a wide market in 2010, after years of clinical trials.

St. Jude Medical is a leading medical device company focused on developing innovative solutions to improve the lives of patients with heart failure. The company specializes in creating ventricle assist devices (VADs) that provide mechanical circulatory support to patients with poorly functioning left ventricles. St. Jude Medical employs advanced numerical simulation techniques throughout the design process to address various aspects of device development, including thermal effects, fluid dynamics, and power transfer. The company's research and development efforts are centered on enhancing the biocompatibility, hemocompatibility, and immunocompatibility of their devices to ensure they do not elicit adverse immune responses or interfere with other bodily systems. With a commitment to improving patient outcomes and quality of life, St. Jude Medical continues to innovate and refine their LVAD technology.

The design of an LVAD must take many factors into consideration. The device must be small enough to connect to the heart and be made of compatible materials and geometry that permit the device to reside in the body without being rejected. Fluid dynamics, power supply, and thermal management must also be considered. As multiple interacting physical effects must be accounted for at each area of development, multiphysics simulation is vital to the design process. Freddy Hansen, Sr. R&D Engineer at St. Jude Medical, uses his expertise in physics and mathematical modeling to characterize complex implantable medical devices like LVADs before experimental studies. Hansen has been using COMSOL Multiphysics® software since 2011 and has since created upwards of 230 models that address a wide range of design challenges pertaining to the unique physics of artificial pumping devices. With each generation of LVADs introduced to the market, improvements are made that contribute to enhanced safety and quality of life for the patient. Research and development efforts at St. Jude Medical are centered on improving biocompatibility, hemocompatibility, and immunocompatibility, such that the device does not elicit an adverse immune response, nor interfere with other bodily systems. Geometry and size of the device play an important role in its overall effectiveness. To implant the LVAD, the surgeon connects one end of the LVAD to the left ventricle and the other end to the ascending aorta. If the device is smaller, it is less cumbersome, and less likely to interfere with neighboring organs or tissue. Simulation allows for the evaluation of changes in size or geometry of the LVAD design before implementation of a physical prototype.

• Many simulations were used in the development of the centrifugal pump of the LVAD. One challenge associated with engineering these devices is the prevention of blood clotting in any space in or around the pump. To address this, a magnetically levitated rotor was developed, which eliminated the need for ball bearings and other components with geometries that might promote clotting. Hansen used the Rotating Machinery modeling technology available in the software to model both the magnetically levitated rotor and turbulent fluid flow.
• A permanent magnet in the pump rotor is driven by coils in the stator, which exert a torque on the rotor and provide active control of the position of the rotor axis. The vertical position — or levitation — of the rotor is accomplished by magnetic field line tension and does not need active control. The rotor receives blood axially and redirects it radially, into the volute, or fluid collector. Some of the blood flows back around the outer edge of the rotor and into the rotor inlet, resulting in a constant washing of the blood, which serves to eliminate places where the blood can stagnate and clot.
• Another significant advance was the development of a pump system with pulsatile flow, rather than continuous flow, which more closely mimics a functioning heart. The pulsatile flow aids in the washing of the blood, preventing blood clots, and is also believed to have a positive physiological effect on blood vessels throughout the body.

• Hansen has created upwards of 230 models addressing a wide range of design challenges.
• Thoratec, now part of St. Jude Medical, brought LVADs to a wide market in 2010 after years of clinical trials.