Artificial muscles enable the design of soft implantable devices which are poised to transform the way we mechanically support the heart today. Heart failure is a prevalent and deadly disease, which is treated with the implantation of rotary blood pumps as the only alternative to heart transplantation. The clinically used mechanical devices are associated with severe adverse events, which are reflected here in a comprehensive list of critical requirements for soft active devices of the future: low power, no blood contact, pulsatile support, physiological responsiveness, high cycle life, and less-invasive implantation. In this review, we investigate and critically evaluate prior art in artificial muscles for their applicability in the short and long term. We highlight the main challenges regarding the effectiveness, controllability, and implantability of recently proposed actuators and explore future perspectives for attachment, physiological responsiveness, durability, and biodegradability as well as equitable design considerations.

 Introduction: One way to improve exercise performance and protect heart health is the extended synchronization of the stepping with the diastolic phase of the cardiac cycle. Cardiac-locomotor coupling (CLC) happens when the step rate (SR) equals the heart rate (HR). The extent of CLC in daily life is unknown. This study aims to analyze spontaneous occurrences of CLC during daily activities.

Methods: A retrospective analysis of daily life recordings from a wrist-worn sensor was undertaken (PMData, N = 16, 5 months duration). The deviation between HR and SR was used to define CLC (deviation ≤ 1%) and weak CLC (1%< deviation ≤ 10%). The occurrence and the probability of CLC during everyday life were computed from the recordings. The CLC occurrences were stratified depending on the duration and intensity of the physical activity. Finally, a Monte Carlo simulation was run to evaluate the probability of random occurrences of CLC vs. the observed recordings.

Results: Participants couple for 5% and weakly couple for 35% of the observational period. The ratio of 1:1 between HR and SR is the dominating occurrence across the study population and this overrepresentation is significant. CLC occurs mostly for long activities. The extent of CLC for various intensities of activity is subject-dependent. The results suggest that CLC is feasible for most people.

Conclusions: CLC occurs spontaneously during unsupervised daily activity in everyone in our cohort, which suggests a mechanistic interaction between the cardiac and the locomotor systems. This interaction should be investigated for medical rehabilitation and sports applications in the future.

 One way to improve hemodynamic efficiency is the synchronization of the stepping with the diastolic phase of the cardiac cycle (diastolic stepping) minimizing peak pressures on the heart level. At head level, we expect maximized blood flow in diastolic stepping and minimized blood flow in systolic stepping. This study aims to verify suggested blood flow patterns via analysis of the pulse wave (PW) amplitudes in the ear during synchronized walking. Four participants (2 men, 2 women, 27 ± 3 years) walked on a treadmill at a comfortable speed, guided by auditory signals (Pulson, USA) to perform diastolic and systolic stepping. PW amplitudes were continuously measured in the ear using an optosensor (TCRT1000,Vishay, USA) and compared to heart rate (HR) from an ECG chest strap (Movesense, Finland). Results showed that the PW amplitude increased by 20 ± 16% across all subjects during diastolic stepping compared to systolic stepping, with lower HRs detected from the optosensor (0.73 ± 1.4 beats/min) than from the ECG. The findings suggest that synchronized walking modulates PW amplitude during diastolic stepping with different extent across subjects.

The field of durable mechanical circulatory support (MCS) has undergone an incredible evolution over the past few decades, resulting in significant improvements in longevity and quality of life for patients with advanced heart failure. Despite these successes, substantial opportunities for further improvements remain, including in pump design and ancillary technology, perioperative and postoperative management, and the overall patient experience. Ideally, durable MCS devices would be fully implantable, automatically controlled, and minimize the need for anticoagulation. Reliable and long-term total artificial hearts for biventricular support would be available; and surgical, perioperative, and postoperative management would be informed by the individual patient phenotype along with computational simulations. In this review, we summarize emerging technological innovations in these areas, focusing primarily on innovations in late preclinical or early clinical phases of study. We highlight important considerations that the MCS community of clinicians, engineers, industry partners, and venture capital investors should consider to sustain the evolution of the field.

This work presents a modular approach to the development of strain sensors for large deformations. The proposed method separates the extension and signal transduction mechanisms using a soft, elastomeric transmission and a high-sensitivity microelectromechanical system (MEMS) transducer. By separating the transmission and transduction, they can be optimized independently for application-specific mechanical and electrical performance. This work investigates the potential of this approach for human health monitoring as an implantable cardiac strain sensor for measuring global longitudinal strain (GLS). The durability of the sensor was evaluated by conducting cyclic loading tests over one million cycles, and the results showed negligible drift. To account for hysteresis and frequency-dependent effects, a lumped-parameter model was developed to represent the viscoelastic behavior of the sensor. Multiple model orders were considered and compared using validation and test data sets that mimic physiologically relevant dynamics. Results support the choice of a second-order model, which reduces error by 73% compared to a linear calibration. In addition, we evaluated the suitability of this sensor for the proposed application by demonstrating its ability to operate on compliant, curved surfaces. The effects of friction and boundary conditions are also empirically assessed and discussed.

Right ventricular (RV) failure remains a significant clinical burden particularly during the perioperative period surrounding major cardiac surgeries, such as implantation of left ventricular assist devices (LVADs), bypass procedures or valvular surgeries. Device solutions designed to support the function of the RV do not keep up with the pace of development of left-sided solutions, leaving the RV vulnerable to acute failure in the challenging hemodynamic environments of the perioperative setting. This work describes the design of a biomimetic, soft, conformable sleeve that can be prophylactically implanted on the pulmonary artery to support RV ventricular function during major cardiac surgeries, through afterload reduction and augmentation of flow. Leveraging electrohydraulic principles, a technology is proposed that is non-blood contacting and obviates the necessity for drivelines by virtue of being electrically powered. In addition, the integration of an adjacent is demonstrate, continuous pressure sensing module to support physiologically adaptive control schemes based on a real-time biological signal. In vitro experiments conducted in a pulsatile flow-loop replicating physiological flow and pressure conditions show a reduction of mean pulmonary arterial pressure of 8 mmHg (25% reduction), a reduction in peak systolic arterial pressure of up to 10 mmHg (20% reduction), and a concomitant 19% increase in diastolic pulmonary flow. Computational simulations further predict substantial augmentation of cardiac output as a result of reduced RV ventricular stress and RV dilatation. 

The analysis of quantitative hemodynamics provides information for the diagnosis and treatment planning in patients with aortic coarctation (CoA). Patient-specific computational fluid dynamics (CFD) simulations reveal detailed hemodynamic information, but their agreement with the clinical standard 4D-Flow magnetic resonance imaging (MRI) needs to be characterized. This work directly compares in vivo CFD fluid-structure interaction (FSI) simulations against 4D-Flow MRI in patients with CoA (N = 5). 4D-Flow MRI-derived flow waveforms and cuff blood pressure measurements were used to tune the boundary conditions for the FSI simulations. Flow rates from 4D-Flow MRI and FSI were compared at cross-sections in the ascending aorta (AAo), CoA and descending aorta (DAo). Qualitative comparisons showed an overall agreement of flow patterns in the aorta between the two methods. The R 2 values for the flow waveforms in the AAo, CoA, and DAo were 0.97, 0.84 and 0.81 respectively, representing a strong correlation between 4D-Flow MRI measurements and FSI results. This work characterizes the use of patient-specific FSI simulations in quantifying and analyzing CoA hemodynamics to inform CoA treatment planning.

Human locomotion is typically studied independently ofthe cardiovascular system, although the two areintrinsically linked. An example of their interaction iscardiac-locomotor coupling (CLC), which refers to theentrainment of heart rate (HR) and step rate (SR) duringrhythmic exercise at a 1:1 ratio. Actively synchronizingthe stepping with each diastole of the cardiac cycle, hasbeen shown to provide improved cardiometabolicefficiency, demonstrated by a decrease in HR and inventilation [1]. Active CLC can therefore be one way toimprove hemodynamic efficiency, ensuring greaterendurance performances. Previous studies investigatedthe presence of CLC in laboratory settings whereasobservations during daily activities are still lacking. Wedo not know if and when CLC occurs physiologically.The aim of this study is to investigate the extent and theprobability of CLC during unsupervised daily activitiesin contrast to random chance.

Congenital heart diseases are the most frequently diagnosed birth defect of the cardiovascular system (CVS), occurring in 1% of live births globally. Mock circulatory loops (MCLs) replicate the physiological boundary conditions of the CVS, which allow for testing of cardiac assist devices (CADs), but also provide valuable in vitro data for optimizing imaging protocols as well as validating computational fluid dynamics simulations. However, innate limitations of traditional MCLs include the difficulty in tuning physical boundary conditions to match the dynamic patient’s physiology. To address these limitations, hybrid mock circulatory loops (HMCLs) incorporate elements of both in vitro and in silico modelling allowing for rapid changes in boundary conditions to be mimicked in closed-loop. In this study, a real-time HMCL testing platform was built, and its use exemplified in the study of aortic coarctation (AoC), a common congenital cardiovascular disorder caused by a narrowing of the descending aorta. Compliant 3D-printed stenosed tubes of varying severity were integrated into the HMCL to represent the AoC model. First their mechanical impedance was quantified using a chirp pressure signal. Second, the effect of the severity of coarctation on the simulated CVS variables (pressure difference, cardiac output) was assessed in dynamic interaction with the closed-loop CVS. This study lays the foundation for future studies into dynamic cardiovascular conditions, imaging improvements, and validation of fluid dynamics modelling.