Functional groups of materials are known to affect cell behaviors, yet the corresponding effect on stem cell differentiation is always coupled with that of cell spreading; it is thus unclear whether the chemical groups influence cell differentiation directly or via cell spreading indirectly. Herein we used a unique surface patterning technique to decouple the corresponding effects. Mesenchymal stem cells (MSCs) derived from bone marrow were seeded on surfaces coated with alkanethiols with one of four functional end groups (-CH3, -OH, -COOH, and -NH2) and underwent 9 days of chondrogenic induction. The measurements of quartz crystal microbalance with dissipation confirmed less proteins adsorbed from the cell culture media on the neutral -CH3 and -OH surfaces than on the charged -COOH and -NH2 surfaces. The neutral surfaces exhibited less cell spreading and higher extents of chondrogenic differentiation than the charged surfaces, according to the characterizations of immunofluorescence staining and quantitative real-time polymerase chain reaction. We further used a transfer lithography technique to prepare patterned surfaces on nonfouling poly(ethylene glycol) hydrogels to localize single MSCs on microislands with self-assembly monolayers of different alkanethiols, under given microisland areas and thus well-defined spreading areas of cells. While small microislands were always beneficial for chondrogenic induction, we found that the type of functional groups had no significant effect on chondrogenic induction under the given cell spreading areas, implying that the chemical groups influence cell differentiation only indirectly. Our results hence illustrate that functional groups regulate stem cell differentiation via tuning protein adsorption and then nonspecific cell adhesion and thus cell spreading.
Keywords: chondrogenic differentiation; functional group; mesenchymal stem cell; poly(ethylene glycol) (PEG) hydrogel; self-assembly monolayer; surface patterning.