Reconceptualizing Mesenchymal Stromal Cell Sheets: From Delivery Tool to Models of Morphogenesis

Over the past three decades, cell sheet technology has evolved from its original scaffold-free approach developed for epithelial cells into a versatile platform applicable to mesenchymal stromal cells (MSC). Despite numerous experimental achievements and convincing preclinical outcomes, MSC-based cell sheets have yet to reach the stage of a clinically reproducible product. This gap reflects not so much the technological limitations of the method as an incomplete understanding of its biological nature. MSC-based cell sheets represent more than a vehicle for cell delivery; they are self-organizing systems governed by intrinsic biophysical and morphogenetic principles. Their structural maturation involves (1) cellular condensation, (2) extracellular matrix deposition, and (3) contractile remodeling-processes that mirror the early phases of granulation tissue formation. Viewing the cell sheet as an in vitro model of connective tissue regeneration opens new research avenues extending beyond its therapeutic applications. This review summarizes the key milestones in the development of MSC-derived cell sheet technology, identifies major challenges and conceptual inconsistencies, and discusses the potential of studying these constructs as autonomous biological systems. The integration of mechanobiology, spatial omics technologies, and tissue engineering approaches may help reconceptualize MSC-based cell sheets both as tools for translational therapy and as a fundamental model for studying self-organizing regenerative processes.