Bioprinting organoids for functional cardiac constructs: Progress and unmet challenges

Developing physiologically relevant cardiac engineered in vitro models has been a longstanding challenge in cardiac tissue engineering. Bioprinting technologies have been utilized to recreate the complex architecture of the human heart, via precise placement of cells and biomaterials. Concurrently, self-organizing cardiac organoids have emerged as powerful tools for developing cardiac tissues accurately mimicking the heart’s biological composition. This review explores the merging of these two rapidly evolving fields to produce functionally mature engineered cardiac tissues. Together, bioprinting can provide spatial control and mechanical support to guide cardiac self-organization, including strategies to directly print cardioids or incorporate them as modular units, while cardioid differentiation protocols promote multicellular complexity and developmental relevance to improve the functionality of engineered cardiac constructs. We discuss the key processing challenges and goals across the bioprinting workflow—spanning pre-processing, processing, and post-processing—and evaluate how they intersect with cell viability, structural integrity, and electromechanical function. We then explore the formation and functional features of self-organized cardioids, outlining major differentiation protocols, signaling cues, and functional outcomes. Finally, we propose a convergence between bioprinting and cardioid technologies to produce the next generation in vitro cardiac models.