Polysaccharide nanofibers with variable compliance for directing cell fate.

Cells perceive their microenvironment through physical and mechanical cues, such as extracellular matrix topography or stiffness. In this study, we developed a polysaccharide scaffold that can provide combined substrate topography and matrix compliance signals to direct cell fate. Pullulan/dextran (P/D) nanofibers were fabricated with variable stiffness by in situ crosslinking during electrospinning. By varying the chemical crosslinking content between 10, 12, 14, and 16%, (denoted as STMP10, STMP12, STMP14, and STMP16 respectively), scaffold mechanical stiffness was altered. We characterized substrate stiffness by various methods. Under hydrated conditions, atomic force microscopy and tensile tests of bulk scaffolds were conducted. Under dry conditions, tensile tests of scaffolds and single nanofibers were examined. In addition, we evaluated the efficacy of the scaffolds in directing stem cell differentiation. Using human first trimester mesenchymal stem cells (fMSCs) cultured on STMP14 P/D scaffolds (Young's modulus: 7.84 kPa) in serum-free neuronal differentiation medium exhibited greatest extent of differentiation. Cells showed morphological changes and significantly higher expression of motor neuron markers. Further analyses by western blotting also revealed the enhanced expression of choline acetyltransferase on STMP14 (7.84 kPa) and STMP16 (11.08 kPa) samples as compared to STMP12 (7.19 kPa). Taken together, this study demonstrates that the stiffness of P/D nanofibers can be altered by differential in situ crosslinking during electrospinning and suggests the feasibility of using such polysaccharide nanofibers in supporting fMSC neuronal commitment.