Frequency- and Temperature-Dependent Rheological Properties of an Amphiphilic Block Co-polymer in Water and Including Cell-Culture Media

This paper examines the effects of cell-culture media on the rheological properties of Pluronic F127, an amphiphilic triblock co-polymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO). In an aqueous environment, F127 exhibits a reversible sol-gel transition upon an increase of temperature and has found wide applications as an injectable biomaterial. In contrast to most of the present polymer-physics studies of hydrogels in water, we examined its rheological properties in Dulbecco's Modified Eagle Medium (DMEM), DMEM with calf serum and phosphate-buffered saline (PBS) solution, compared with those in deionized water. The critical gelation temperatures (T(gel)) were found to be lowered as compared to that in pure water. The differences among the three experimental groups were relatively less significant. The zero viscosity eta(0) of sols and equilibrium modulus G(e) of gels were enhanced at a given temperature, but they kept universal values under a given temperature difference, T - T(gel). The basic frequency-related scaling characteristics of a typical percolated network, G' approximately omega(n) and G'' approximately omega(n), remained in Pluronic hydrogels at the gel points. Two power laws, eta(0) approximately ((T(gel) - T)/T(gel))(-s) and G(e) approximately ((T - T(gel))/T(gel))(m) described well the sols and gels near T(gel), respectively. All the four systems exhibited similar critical scaling exponents. As a result, our studies illustrate that the changes of transition points and rheological properties of Pluronic hydrogels in cell-culture media should be taken into consideration but are not awfully large.