Beats Normally — And Still Fails: Soft Robotic Heart Model Created to Study HFpEF, the Most Insidious Form of Heart Failure

Engineers have built a soft robotic heart that can actively alter its stiffness while beating, enabling scientists to study heart failure with preserved ejection fraction (HFpEF) — one of the most common yet poorly understood cardiac conditions.

The new model reproduces the left side of the heart, including the left atrium and left ventricle. Its silicone chambers are surrounded by multiple layers of artificial muscle fibers composed of rubber tubes reinforced with spring-like coils. These fibers replicate the helical architecture of real cardiac muscle and respond to fluid pressure, relaxing during filling and contracting with controllable force.

HFpEF occurs when the heart ejects a normal fraction of blood with each beat, yet the ventricular wall has lost elasticity. Between contractions — during the diastolic phase — the stiff muscle fails to relax properly, so the chamber cannot fill with enough blood. As a result, the body receives insufficient cardiac output while pressures inside the heart and vessels rise.

Approximately half of all heart-failure patients suffer from HFpEF, with more than three million cases in the United States. Existing laboratory setups using rigid pumps and tubes cannot capture the dynamic interplay between wall stiffness and filling, while animal studies are expensive and do not fully mirror human disease progression.

The robotic platform overcomes these limitations through a closed-loop control system. Continuous pressure sensors feed data to a controller that instantly adjusts the resistance of the artificial fibers. Researchers can therefore increase or decrease ventricular compliance on demand, reproducing early-stage delayed relaxation as well as advanced, severely restricted filling.

This tunable stiffness allows scientists to observe how progressive loss of elasticity alters blood flow, chamber pressures, and overall hemodynamics — something impossible with static bench models. The device is expected to help engineers test cardiovascular implants and mechanical support systems under varying degrees of myocardial stiffness and to explore interventions that could restore elasticity before irreversible damage occurs.

Current clinical management of HFpEF focuses mainly on symptoms and comorbidities such as hypertension, obesity, and diabetes. While SGLT2 inhibitors have reduced hospitalizations for many patients, no approved drugs directly restore lost myocardial compliance. The robotic heart remains an experimental tool that will require faster actuators and further validation against patient data, but it is intended to complement — not replace — computational models, animal studies, and clinical trials.