Cardiovascular devices: Soft hugs for healing hearts

Current status and future directions in pediatric ventricular assist device

A ventricular assist device (VAD) is a form of mechanical circulatory support that uses a mechanical pump to partially or fully take over the function of a failed heart. In recent decades, the VAD has become a crucial option in the treatment of end-stage heart failure in adult patients. However, due to the lack of suitable devices and more complicated patient profiles, this therapeutic approach is still not widely used for pediatric populations. This article reviews the clinically available devices, adverse events, and future directions of design and implementation in pediatric VADs.

Artificial Muscles and Soft Robotic Devices for Treatment of End-Stage Heart Failure

Medical soft robotics constitutes a rapidly developing field in the treatment of cardiovascular diseases, with a promising future for millions of patients suffering from heart failure worldwide. Herein, the present state and future direction of artificial muscle-based soft robotic biomedical devices in supporting the inotropic function of the heart are reviewed, focusing on the emerging electrothermally artificial heart muscles (AHMs). Artificial muscle powered soft robotic devices can mimic the action of complex biological systems such as heart compression and twisting. These artificial muscles possess the ability to undergo complex deformations, aiding cardiac function while maintaining a limited weight and use of space. Two very promising candidates for artificial muscles are electrothermally actuated AHMs and biohybrid actuators using living cells or tissue embedded with artificial structures. Electrothermally actuated AHMs have demonstrated superior force generation while creating the prospect for fully soft robotic actuated ventricular assist devices. This review will critically analyze the limitations of currently available devices and discuss opportunities and directions for future research. Last, the properties of the cardiac muscle are reviewed and compared with those of different materials suitable for mechanical cardiac compression.

Direct Cardiac Compression Devices to Augment Heart Biomechanics and Function

The treatment of end-stage heart failure has evolved substantially with advances in medical treatment, cardiac transplantation, and mechanical circulatory support (MCS) devices such as left ventricular assist devices and total artificial hearts. However, current MCS devices are inherently blood contacting and can lead to potential complications including pump thrombosis, hemorrhage, stroke, and hemolysis. Attempts to address these issues and avoid blood contact led to the concept of compressing the failing heart from the epicardial surface and the design of direct cardiac compression (DCC) devices. We review the fundamental concepts related to DCC, present the foundational devices and recent devices in the research and commercialization stages, and discuss the milestones required for clinical translation and adoption of this technology. Expected final online publication date for the Annual Review of Biomedical Engineering, Volume 24 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Computational methods for parametric evaluation of the biventricular mechanics of direct cardiac compression

Despite the increasing incidence of heart failure, advancements in mechanical circulatory support have become minimal. A new type of mechanical circulatory support, direct cardiac compression, is a novel support paradigm that involves a soft deformable cup around the ventricles, compressing it during systole. No group has yet investigated the biomechanical consequences of such an approach. This article uses a multiscale cardiac simulation software to create a patient-specific beating heart dilated cardiomyopathy model. Left and right ventricle (LV and RV) forces are applied parametrically, to a maximum of 2.9 and 0.46 kPa on each ventricle, respectively. Compression increased the ejection fraction in the left and right ventricles from 15.3% and 27.4% to 24.8% and 38.7%, respectively. During applied compression, the LV freewall thickening increased while the RV decreased; this was found to be due to a change in the balance of the preload and afterload in the freewalls. Principal strain renderings demonstrated strain concentrations on the anterior and posterior LV freewall. Strains in these regions were found to exponentially increase after 0.75 normalized LV force was applied. Component analysis of these strains illuminated a shift in the dominating strain from transmural to cross fiber once 0.75 normalized LV force is exceeded. An optimization plot was created by nondimensionalizing the stroke volume and maximum principal strain for each compression profile, selecting five potential compression schemes. This work demonstrates not only the importance of a computational approach to direct cardiac compression but a framework for tailoring compression profiles to patients.