New viscoelastic materials for more realistic cell biology*

Hydrogels are increasingly used in cell biologic studies in order to cultivate cells on soft surfaces that more closely mimic the physiological environment than rigid glass or plastic surfaces.  Such studies have revealed how changes in the elastic properties of substrates impact cell structure and function.  Real biological tissues are not only elastic, but they also have viscous properties that dissipate cell-generated forces.  Cellular responses to the viscous aspects of their substrates are much less well characterized, in part because of the lack materials with independently tunable elastic and viscous moduli.  We have developed a method to make viscoelastic gels with mechanical properties resembling soft biological tissues, and suitable for cell culture in vitro. These gels can be used for traction force microscopy experiments. Use of these new materials demonstrates that multiple cell types respond to the viscoelasticity of their substrate and that viscous dissipation has an influence on cell spreading, contractility and motility. Differences in the effect of viscous dissipation on normal and transformed cells might help define the abnormalities that occur in diseased tissues.