Importance of Cell Alignment in Cardiac Tissue Engineering

Native myocardium is a structurally anisotropic and electromechanically integrated tissue in which cardiomyocytes, extracellular matrix fibers, vascular structures, and conduction pathways are organized across multiple length scales. A key feature of this architecture is not a simple stack of discrete layers with slight misalignment, but a continuous transmural variation in predominant myofiber angle from the endocardial to the epicardial surface. This organization supports anisotropic electrical propagation, regional deformation, ventricular torsion, wall thickening, and efficient blood ejection. Conventional two-dimensional culture systems often produce randomly oriented and immature cardiomyocytes, limiting their ability to reproduce native myocardial mechanics or disease-associated remodeling. This narrative review revises and expands the discussion of cardiomyocyte alignment in cardiac tissue engineering, with emphasis on nanofiber-based scaffolds, electrospinning, biomaterial selection, electrical stimulation, mechanical conditioning, bioprinting, and vascularization strategies. We compare spheroids, organoids, conventional scaffolds, aligned nanofibers, three-dimensional bioprinting, and biophysical stimulation approaches in terms of alignment mechanism, maturation readouts, advantages, limitations, and translational challenges. Particular attention is given to scaffold design parameters, including fiber diameter, degree of alignment, porosity, stiffness, degradation behavior, conductivity, surface functionalization, and extracellular matrix coating. We also discuss why alignment strategies should be adapted to the target ventricular region, because left and right ventricular myocardium differ in geometry, loading condition, fiber architecture, and contractile pattern. Finally, we highlight remaining barriers to clinical translation, including vascularization, oxygen and nutrient diffusion, host-tissue electrical integration, arrhythmia risk, scalability, reproducibility, and standardized functional assessment.