Update: Design of Ven­tric­u­lar Assist Devices at the Penn State College of Medicine

Over the past few years, researchers at the Division of Applied Bio­med­ical Engi­neer­ing at the Penn State College of Medicine have been using CAESES in com­bi­na­tion with CONVERGE as a CFD Inte­grated Opti­miza­tion Platform for the devel­op­ment of safer and more effi­cient ven­tric­u­lar assist devices, see this first blog post from 2018 for a full background.

The over­ar­ch­ing goal of these studies is to reduce the size of the pump while reducing the risk of adverse events such as hemol­y­sis, degra­da­tion of von Wille­brand factor, and thrombus for­ma­tion. In order to effi­ciently create a wide range of design variants, the complete flow-path geometry of the pump was para­me­ter­ized in CAESES. The assess­ment of the design variants during the opti­miza­tion process is focused on esti­mat­ing the sus­cep­ti­bil­ity for adverse effects, ini­tially by looking at vol­u­met­ric averages of the tur­bu­lent energy dis­si­pa­tion (EPS), but has since been aug­mented by several addi­tional eval­u­a­tions from the CFD analysis:

• Pres­sures (across pump inflow/​outflow, radial and axial gaps).
• Plasma free hemo­glo­bin (PlHb) pro­duc­tion and con­cen­tra­tion using an in-house devel­oped EPS-based hemol­y­sis model.
• Strain-rate and an in-house devel­oped strain-rate based thrombus sus­cep­ti­bil­ity poten­tial (TSP) model.
• Wall shear stress.
• Vari­a­tion of both radial and axial forces and torques on the rotor (pressure and viscous).

Pump Geometry Parameterization

While the first opti­miza­tion studies were focused on the blades, more and more addi­tional geometry features have been added over time, leading to a complete para­me­ter­i­za­tion of the pump and a much-extended design space for inves­ti­ga­tion. This includes the toroidal rotor body onto which the blades are attached, which can now be con­trolled in height, width, and edge fillet radii, as well as the sur­round­ing fluid gaps in axial and radial direction.

The spiral scroll, or volute, is a crucial com­po­nent in deter­min­ing the per­for­mance of any cen­trifu­gal tur­bo­ma­chine. In this case, knowing that the flow leaving the pump is complex and has a tendency to form Dean vortices, various scroll geome­tries were analyzed to minimize said vortices. The spiral path was pre­scribed math­e­mat­i­cally by entering the (para­met­ric) spiral equa­tions in a generic curve. The cross-sections of the volute scroll were then swept along this guide, always starting with a circular profile – con­trolled by its radius – and ending with a variable cross-section that can take on a diamond, square, and circular shape – addi­tion­ally con­trolled by its width.

Finally, another key feature of the pump is the endcap that is located just opposite of the blades. The profile of the middle spike is of impor­tance, as it was intro­duced to help guide flow towards the volute. The spike design vari­ables dictate the overall height and base width.

H‑Q and T‑Q Mapping

Along­side the design vari­a­tion studies, auto­mated pump per­for­mance sim­u­la­tions for head/​torque vs. flow (H‑Q and T‑Q, respec­tively) mapping of the dif­fer­ent pump designs were per­formed. The CAESES Design Assem­bler was used to struc­ture the sim­u­la­tion queue while out­putting pressure, rotor torque mag­ni­tude, and the esti­mated effi­ciency (not con­sid­er­ing losses), as well as EPS or PlHb esti­mates in a targeted region in the outflow of the pump. Based on the col­lected results, 2D H‑Q and T‑Q per­for­mance curves can be plotted. By over­lay­ing results such as pump effi­ciency or PlHb as the z‑coordinate of each H‑Q point a 3D surface plot can be gen­er­ated that shows a more in-depth view of the pump performance.

The results from all these new numer­i­cal design studies and opti­miza­tions are cur­rently under­go­ing exten­sive in-vitro and in-vivo ver­i­fi­ca­tion and we will make sure to come back with a further update once the results have been peer-reviewed and published.

Learn More

See this overview for the pos­si­bil­i­ties and capa­bil­i­ties that CAESES offers for medical applications.

Ques­tions?

Please do not hesitate to get in touch with us if you have ques­tions in the context of your specific appli­ca­tion. We look forward to dis­cussing it together with you!