Homologous Sodium Alginate/Chitosan-Based Scaffolds, but Contrasting Effect on Stem Cell Shape and Osteogenesis

Stem cell shape appears to be involved in the regulation of osteogenesis, which has been confirmed in two-dimensional surfaces and three-dimensional hydrogels. The present study evaluated the effect of matrix-controlled cellular shape on osteogenesis in three-dimensional porous scaffolds based on sodium alginate (ALG) and chitosan (CS). Three ALG/CS scaffolds, especially including a stiff one, were fabricated from different precursor matrices. Soft scaffold A was fabricated from the ALG/CS polyelectrolyte and further cross-linked by Ca²⁺ and glutaraldehyde to achieve soft scaffold B with alternative hydrophilicity. Stiff scaffold C with "hard-to-deform" feature was fabricated from "ALG/CS preformed gel", which was an ALG gel network expanded by swelling force of the dissolving CS, and fixed using Ca²⁺ and glutaraldehyde. Scanning electron microscopy and F-actins staining showed rounded mesenchymal stem cells (MSCs) on the inner surfaces inside scaffold A with high swelling behavior, but spindlelike MSCs in scaffold B. Stiff scaffold C forced MSCs to adhere to polygonal shape. Fibronectin adsorption was found to be weakened in scaffold A. Integrin α5β1 expression, as well as osteogenesis-related genes (ALP, OCN) expression, was detected to be higher in the stiff scaffold C. Thus, the present study illustrated that the stiff scaffold C responded to cells with hard-to-deform information, leading to the amplification of focal adhesions and induction of high tension of cells, consequently enhancement of osteogenesis.