The stiffness of hydrogel-based bioink impacts mesenchymal stem cells differentiation toward sweat glands in 3D-bioprinted matrix.

Mechanical aspects of printable hydrogels can impact cell behavior in 3D-bioprinted constructs, and in this context the stiffness of hydrogel-based bioink can serve as an important physical cue in regulating cell differentiation. Here we bioprinted mesenchymal stem cells (MSCs) by the commonly used bioink alginate-gelatin (Alg-Gel) blends and investigated the influence of stiffness on MSC differentiation toward sweat glands. Mechanical properties were assessed through compression testing and it was found that higher compressive modulus was associated with the higher Alg-Gel concentrations. Using these Alg-Gel blends for bioprinting, we demonstrated that stiffness variance cannot cause differences in cell spreading, adhesion and viability. However, MSCs bioprinted by stiffer hydrogels were found to further upregulate the protein and gene expression of sweat gland cell phenotype, function and development of signaling pathways. Furthermore, we found that the increased Yes-associated protein (YAP) localization of nuclei in MSCs when bioprinted by stiffer hydrogels. These results illustrated that the stiffness of Alg-Gel blends is a potent regulator of MSC differentiation, which was possibly achieved through a YAP-dependent mechanotransduction mechanism.