The field of implantable robotic devices is being transformed by a new wave of biomimetic robots constructed with materials with properties matching biological tissues and designed to mimic the motions of human tissues. The benefits of biologically inspired designs were first shown with extracorporeal robots. Now Frank Pigula and colleagues have developed a soft robotic sleeve that mimics the form and function of the heart. The researchers show that the soft robotic sleeve, which is implanted around the heart, can be selectively activated to compress and twist to provide ventricular assistance, and demonstrate the feasibility of the device to support cardiac function in a porcine model of heart failure.

The researchers used a novel form of pneumatic actuator, on the basis of the McKibben 'air muscle' concept, integrated into a soft robotic platform. “There are several advantages of our approach over previous efforts,” says Pigula. First, the sleeve was designed to mimic the orientation of the two outer layers of muscle in the heart: the individual contracting elements in the sleeve are oriented in two layers of helical and circumferential patterns, and the material's stiffness is similar to that of myocardial tissue.

Second, the force generated by the actuators is applied tangentially to the heart rather than perpendicularly. “This helps to reduce trauma and more closely approximates the natural contraction of the heart,” explains Pigula. Each actuator can act independently, and a control system allows programming and monitoring of the sleeve to synchronize it with the native heart motion. Furthermore, the sleeve can be controlled to act selectively on one ventricle more than the other.

Credit: V. Summersby/Macmillan Publishers Limited

Third, the actuators can elongate as well as contract. The twisting and untwisting actions have the potential to assist both relaxation and contraction of the heart. “This is the first device that shows promise in actually assisting the diastolic function of the heart as well as the systolic function,” remarks Pigula.

Finally, the device is not in contact with blood, thereby reducing the risk of thrombotic complications associated with current devices. “The field of mechanical circulatory support has focused on pump and valve technology, which requires open heart surgery and the exposure of the device to blood,” says Pigula, “and despite anticoagulation, blood clots, bleeding, and stroke remain common and devastating.” In the era of precision medicine, another important feature of the soft robotic sleeve is that it could be customized for each patient.

Although these findings demonstrate the feasibility and potential benefits of this soft robotic device, Pigula explains that much work remains before this technology can be brought to the clinic. Further refinements in the device, as well as long-term studies in animal models, are necessary before the soft robotic sleeve can be used in humans.