Session: 04-13 SS: Active Hybrid Composites

Paper Number: 166070

166070 - Development of a Twisted and Coiled Artificial Muscle (Tcam)-Driven High-Fidelity Left Ventricle Simulator for Cardiac Research 

Congenital heart disease (CHD) is one of the most common birth defects, often requiring surgical intervention to replace the natural heart valves via prosthetic valve implantation. Despite significant advancements in heart assistive devices, the increase in morbidity and mortality still leaves a challenge due to the lack of an ideal in vitro testing method for prosthetic valves prior to implantation. Current heart simulators fail to fully replicate the biomechanical and hemodynamic properties of the human left ventricle, limiting their ability to provide physiologically useful data. To address this limitation, we aim to develop a high-fidelity benchtop left ventricle simulator that mimics the geometry, mechanics, and hydrodynamic behavior of the human heart. This system utilizes twisted and coiled artificial muscles (TCAMs), which offer high work capacity, large contractile stroke, lightweight properties, and durability. Additionally, TCAMs exhibit excellent flexibility, allowing compatible integration with soft materials, and their properties can be easily tuned by adjusting raw materials and geometric configurations. Due to these advantages, TCAMs have been applied in soft robotics and cardiac assistive devices, making them ideal for heart simulation. To achieve this goal, we propose a pressure–tissue–muscle (PTM) model, which incorporates TCAMs, passive elastic materials, and fluidic components to replicate the fundamental biomechanics of ventricular contraction. This research consists of three key phases: experimental evaluation of TCAMs, numerical simulations to optimize muscle volume fraction for realistic heart function, and development of high-frequency actuators.

First, we conducted isometric tests to assess TCAM performance. In these tests, actuators were fixed at a designated strain while measuring both passive force (intrinsic material resistance) and total force (sum of passive and active forces during actuation). By analyzing force–strain curves, we extracted passive and total stiffness values, which are essential for modeling heart muscle behavior. Inspired by the pressure–volume cyclic profile of the human heart, we introduced the isometric coefficient, allowing numerical approximation of the total force achievable when transitioning between isometric and isobaric conditions. This coefficient provides a predictive framework for TCAM force output under physiological conditions.

Second, we used the PTM model to simulate the relationship between muscle volume fraction, stroke, and pressure generation. Our simulations revealed a trade-off: increasing the muscle volume fraction enhances stroke, but peak pressure reaches an optimal value based on the relative magnitudes of passive and total stiffness that depend on the TCAMs. Beyond a threshold, additional muscle volume contributes less to pressure generation, suggesting the possibility of an optimized design. Furthermore, the pressure increase rate diminished as the muscle volume fraction grew, implying an optimal range for achieving both sufficient stroke and pressure. Also, we built a cyclic hydrodynamic system that mimics the circulatory system within the human body so that we can validate the efficacy of this model.

Lastly, we addressed the primary limitation of TCAMs—their slow cooling rate, which restricts actuation frequency. Since the physiological heart rate ranges from 60 to 100 beats per minute (bpm), achieving comparable TCAM contraction speeds is critical. We increased actuation frequency by reducing the raw nylon fiber diameter from 0.47 mm to 0.05 mm, significantly improving the working rate from 3 bpm to 60 bpm. Additionally, we integrated TCAMs with soft structures that mimic cardiac tissues, ensuring that the system replicates realistic ventricular motion.

In conclusion, we developed a TCAM-driven heart simulator that integrates soft structures to replicate the morphology and contraction mechanics of the human left ventricle. We introduced the PTM model as a computational tool for optimizing actuator configurations, ensuring physiologically relevant pressure and stroke profiles. Through experimental testing and numerical simulations, we demonstrated the feasibility of using TCAMs for cardiac simulation and prosthetic valve testing. Ultimately, we expect this benchtop beating heart to serve as a robust platform for mitral valve replacement studies and broader cardiovascular research.

Presenting Author: Jeongmin Kim University of Illinois Urbana-Champaign

Presenting Author Biography: Jeongmin Kim received the B.S. and M.S. degrees in mechanical engineering from Yonsei University in 2020 and 2021. She is currently pursuing a Ph.D. degree in mechanical engineering at University of Illinois – Urbana Champaign under the supervision of Prof. Sameh Tawfick. Her research interests include biomedical assistive devices, with a focus on artificial muscles and beating hearts.