Bioprinting‐Assisted Tissue Assembly to Investigate Endothelial Cell Contributions in Cardiac Fibrosis and Focal Fibrosis Modeling

Cardiac fibrosis is characterized by excessive extracellular matrix (ECM) deposition, driven by the activation of cardiac fibroblasts (cFBs) and endothelial‐to‐mesenchymal transition (EndMT). Endothelial cells (ECs) contribute to cardiac fibrosis through EndMT, transforming into myofibroblasts that promote fibrosis, while also playing a regulatory role through signaling pathways, such as PI3K‐Akt and Notch. In this article, engineered heart tissue models, composed of cardiomyocytes and cFBs (CMF) and vascularized model incorporating ECs (CMFE) tissues is created to investigate the role of ECs in transforming growth factor‐β (TGF‐β)‐induced cardiac fibrosis. Prior to fibrosis induction, CMFE exhibits enhanced activation of fibrosis‐related signaling, endothelial integrity pathways, and PI3K‐Akt and Notch signaling compared to CMF. Following TGF‐β treatment, CMF exhibits typical fibrotic features, including increased ECM deposition, tissue stiffening, and reduced contractility. In contrast, the CMFE demonstrates attenuated fibrotic responses, maintaining tissue mechanics and contractile function. Gene expression and histology reveals both fibrotic and protective processes in CMFE. Moreover, the bioprinting‐assisted tissue assembly (BATA) approach enable focal fibrosis modeling, revealing that fibrotic regions disrupted calcium propagation and induced electrophysiological abnormalities. These findings highlight BATA as a promising platform for studying cardiac fibrosis and developing targeted therapeutic strategies.