SPHERpower: MSC spheroid-based bioequivalent lead to the efficient restoration of the scarred vocal folds

This study evaluated a mesenchymal stromal cell spheroid-based PEG-fibrin bioequivalent for treatment of scarred vocal folds and compared it with PEG-fibrin alone, PEG-fibrin with MSC suspension, and untreated controls in a rabbit vocal fold scar model. Human gingival MSC spheroids were first characterized as compact, viable, vimentin-positive, actin-organized 3D microtissues with outer densely packed cells and an inner ECM-rich zone. In vitro, spheroid-loaded PEG-fibrin supported high cell viability, metabolic activity, and pronounced sprouting, suggesting that spheroids function as more effective cellular units in hydrogel than dispersed cells. In vivo, both MSC-containing bioequivalents improved regeneration after scar excision, but the spheroid-based formulation produced the best restoration. Three months after implantation, the MSC spheroid group showed mature stratified squamous epithelium without dystrophy, relatively loose longitudinally oriented collagen fibers, mild immune infiltration, and a lamina propria thickness of 116.42 ± 42.77 µm that did not differ from intact vocal folds. By contrast, untreated scars and PEG-fibrin alone remained thicker and more fibrotic, while the MSC suspension group improved healing but still had a thicker lamina propria than intact tissue. Mechanical testing further showed that the vocal folds treated with MSC spheroids had Young’s modulus values not significantly different from intact tissue, supporting the conclusion that MSC spheroids improved both tissue architectonics and biomechanical restoration more effectively than cell suspension.