Influence of viscosity on bone marrow-derived mesenchymal stem cells trilineage differentiation during 3D culture

Stem cells can respond to mechanical stimuli such as stiffness, viscoelasticity, fluid shear stress, micropatterned geometry and hydraulic pressure. However, viscosity as an important cue is often overlooked. Thus, in this study, the influence of viscosity on trilineage differentiation (adipogenesis, chondrogenesis and osteogenesis) of human bone marrow-derived mesenchymal stem cells (hMSCs) was disclosed by three-dimensionally (3D) culturing hMSCs in viscous media. The viscosity was modulated using bioinert polyethylene glycol (PEG) at a range of 88.8-645.5 cP. A cuboid agarose hydrogel container was used to encapsulate the cells and viscous media to prevent cell leakage and PEG diffusion during cell culture. Viscosity showed inhibitory effects on trilineage differentiation of hMSCs during 3D culture in viscous media containing PEG. The inhibitory effect on adipogenic and chondrogenic differentiation was stronger than that on osteogenic differentiation. Viscosity also affected cell proliferation. Viscosity strongly promoted cell proliferation during chondrogenesis, and weakly promoted cell proliferation during osteogenesis, while inhibited cell proliferation during adipogenesis. The influences of viscosity on proliferation and trilineage differentiation of hMSCs were related to the formation of cell aggregates and spheroids during 3D culture in the viscous media. The results revealed the importance of viscosity on stem cell differentiation and could provide some information for tissue engineering applications.