Chondrogenic differentiation of human mesenchymal stem cells on photoreactive polymer-modified surfaces

Human mesenchymal stem cells (MSCs) were cultured on polystyrene surfaces modified with photoreactive azidophenyl-derivatives of three different chargeable polymers, poly(acrylic acid) (PAAc), polyallylamine (PAAm), and poly(ethylene glycol) (PEG). The MSCs adhered and spread both on a PAAm-modified surface and on PAAc-modified and polystyrene (control) surfaces. However, the cells adhered more easily to the PAAm-modified surface. The MSCs did not attach to the PEG-modified surface and aggregated to form pellets immediately after cell seeding. The cells proliferated on the PAAc-, PAAm-modified and control surfaces with culture time, formed a monolayer, and aggregated to form pellets. The cells in the pellets that formed on the PAAm- and PEG-modified surfaces after 2 weeks culture had a round morphology and the extracellular matrices were positively stained by safranin O and toluidine blue, while those that formed on the PAAc-modified and control surfaces had a spindle, fibroblast-like morphology and were not positively stained by safranin O and toluidine blue. The pellets that formed on the PAAm- and PEG-modified surfaces contained significantly higher levels of sulfated glycosaminoglycans than did those that formed on the PAAc-modified and control surfaces. Type II collagen and cartilage proteoglycan were immunohistologically detected in the pellets that formed on PAAm- and PEG-modified surfaces, but not those that formed on the PAAc-modified and control surfaces. The MSCs cultured on the PAAm- and PEG-modified surfaces expressed a high level of cartilaginous genes encoding type II collagen and aggrecan, while the MSCs cultured on the PAAc-modified and control surfaces did not express these genes. These results suggest that the PAAm-modified surface supported cell adhesion and proliferation and also promoted chondrogenic differentiation of the MSCs. The PAAc-modified and polystyrene surfaces supported cell adhesion and proliferation, but not chondrogenic differentiation. The PEG-modified surfaces did not support cell adhesion, but did promote chondrogenic differentiation. The adhesion, proliferation, and differentiation of the MSCs could be controlled by surface chemistry.