Rheological studies of PLLA-PEO-PLLA triblock copolymer hydrogels

We report detailed rheological data on aqueous gels formed from triblock copolymers of L-lactide and ethylene oxide including the dependence of the viscoelastic moduli on frequency and applied stress of these systems for the first time. We are able to create strong gels with elastic moduli greater than 10,000 Pa, which is an order of magnitude higher than previously achieved with related biocompatible physically associated gels of similar chemistry. Moreover, the value of the elastic modulus strongly depends on PLLA block length, offering a mechanism to control the mechanical properties as desired for particular applications. At the gel point, we observe scaling that is characteristic of a percolated network, G' approximately G" approximately omega(Delta), but with an exponent that is lower than predicted by percolation, Delta=0.36. Our results have implications for the design of new materials for soft tissue engineering, where native tissues have moduli in the kPa range.