Use of Liquid Crystalline Elastomers as artificial muscles for assisting cardiac mechanical function

Heart failure (HF) and cerebral stroke associated to Atrial Fibrillation (AF) are some of the most dreadful and frequent diseases in high-developed countries. HF and AF are both associated with impairment of cardiac mechanical function. Despite advances in cardiovascular medicine, no treatments can restore contractility, highlighting the need for artificial muscles. Liquid crystalline elastomers (LCEs) are biocompatible polymers that change shape in response to stimuli, offering potential for cardiac support but still present some limitations, such as slow response times and modest tension modulation during activation. Overcoming these limitations could make LCEs a valuable tool for addressing the mechanical dysfunction seen in HF, AF, and other muscular diseases. The study examines an LCE mixture containing 0.1-1% Disperse Red 1 Acrylate to induce photo-responsiveness to low-intensity blue light (<5 mW/mm²). LCE contraction was modulated in terms of light intensity, temperature, film thickness, preload, stimulation frequency, and Ton/Toff ratio to adapt the contraction amplitude and timing to that of the human heart. Key findings of this study include: • Film thickness (tested range 10-40µm) had little impact on force production when short light pulses (e.g., 250 ms) were used, matching the timing of cardiac contraction. • Force decreased with a reduction in the dye percentage in the LCE mixture. • Force was higher at 37°C compared to 20°C, particularly with the application of a modest preload. • Using synchronized light and electrical stimuli, higher global force production occurred when the LCE film and intact cardiac muscle preparations contract simultaneously in parallel, while the series configuration caused a negligible force increase compared to the contraction of a single element. These studies concluded that to generate macroscopic forces, double-side illumination and multilayer assembly are necessary. Therefore, a biomimetic contractile unit (BCU), combining LCE films with micro-LED matrices, was designed, enabling precise control over force and shortening dynamics. The performance of the BCU, in terms of the extent and kinetics of contractile force, can be finely tuned by applying the specific conditions previously evaluated, allowing the reproduction of the mechanical dynamics of native muscles. In summary, the study suggests that development of devices like the BCU based on LCEs could represent a promising solution for treating mechanical dysfunctions in diseases such as HF and AF, bringing the realization of functional artificial muscles for biological applications closer to reality. This PhD study included two more projects related to model dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy (ACM). Due to the absence of a large animal model of DCM, in collaboration with School Sant’Anna of Pisa, a genetically modified minipig model of primitive DCM (c.43628insAT in TTN) was developed and characterized. These mutated minipigs showed increased cardiac mass, enlarged left ventricle chamber volume, and reduced left ventricle ejection fraction, with disease progression observed over 1-3 years. Ex vivo tests revealed reduced twitch amplitude and altered contraction dynamics in mutated pigs, suggesting worsened cardiac function compared to wild type controls, giving the rationale to use mutated minipigs as a valuable animal model for studying DCM. Instead, at Eurac Research Institute for Biomedicine, cardiac mesenchymal stromal cells (CStCs) were used as in vitro model of ACM in basal condition and under fibro-fatty stimuli. Specifically, the role of mitochondria in the pathophysiology of ACM and evaluation of the effect of mitochondria-related compounds to reduce fibro-adipose infiltration were evaluated. Finally, optimization of an in vitro cell culture system for disease modelling and drug testing, with the inclusion of hiPSC-derived cardiac fibroblasts and cardiomyocyte was performed in order to enhance the structural, electrical, mechanical and metabolic maturation of cardiomyocytes.