Design and Fabrication of a Biomimetic Circulatory Simulator with Overlaid Flow and Respiration Mechanism for Single Ventricle Physiology

Fontan surgery is performed for a wide range of patients with congenital cardiac defects. This palliative treatment connects the systemic and pulmonary vasculature in series which results in severe pathophysiological consequences. Mock circulatory flow loops for the Fontan circulation aim to better understand the complex physiology and provide a benchtop platform for device testing. In this work we describe the design and fabrication of a biomechatronic Fontan mock circulatory loop, guided by anatomy. We recreate Fontan flow by mimicking both respiratory and flow biomechanics. First, we build a respiratory simulator comprised of a thorax, abdomen, and a soft robotic diaphragm. Next, we design an electromechanical control system to activate the diaphragm and recreate pressure changes mimicking regular breathing. Then we overlay the respiratory simulator with a lumped parameterfluid model. The fluid model includes constant pressure head reservoirs as flow sources, a blood analog, compliance vessels, resistance valves, and a total cavompulmonary connection that is 3D printed from patient data. We achieve physiologic fluid dynamics, ranging from 0-2.3 l/min and pressures of 14-26 mmHg. A rigid windkessel compliance vessel was used to represent the upper body vasculature. Pulmonaty and abdominal vasculatures are subject to changing breathing pressures, to recreate this vasculature we designed elastic compliance vessels made of silicone membranes. Effective vessel compliance was characterized to be 50 ml/mmHg. Upon overlaying breathing mechanics with the flow system, which in Fontan patients accounts for up to 30 % of venous return, we see an impact of breathing pressures on flow in the inferior vena cava, which is representative of a Fontan patient.