Coordinating Thermogel for Stem Cell Spheroids and Their Cyto-Effectiveness

A polymer (mP) with thermogelling and metal coordinating properties is prepared by pyridine-dicarboxylate (PDC) connected poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) triblock copolymers. Tonsil-derived mesenchymal stem cells (TMSCs) are incorporated in the mP hydrogel by increasing the temperature of the cell-suspended aqueous mP solution to 37 degrees C. The TMSCs are randomly embedded in the in situ formed hydrogel at first; however, they aggregated to form live cell spheroids on day 7. In contrast, the spheroid formation is blocked in the Fe3+-incorporating mP thermogel. Compared with the conventional 2D-cultured stem cells, the stem cell spheroid in the 3D mP culture system exhibits significantly enhanced stemness biomarkers, angiogenic biomarkers, and anti-inflammatory biomarkers in the growth medium. In addition, the stem cell spheroid exhibits significantly greater biomarker expression for osteogenic, chondrogenic, and adipogenic differentiations than the stem cells cultured in the 2D system in each induction medium. This study suggests that a simple injection of stem cells suspended in the current aqueous mP solution can lead to the spontaneous formation of stem cell spheroids with excellent multipotency and retention in the in situ formed thermogel, and thus opens a direct injectable method for the application of the stem cells at a target site.