Measuring the modulus and reverse percolation transition of a degrading hydrogel.

In light of the growing importance in understanding and controlling the physical cues presented to cells by artificial scaffolds, direct, temporally resolved measurements of the gel modulus are needed. We demonstrate that an interpolation of macro- and microrheology measurements provides a complete history of a hydrogel modulus during degradation through the reverse percolation transition. The latter is identified by microrheology, which captures the critical scaling behavior of reverse percolation, a transition of key importance in controlling cell migration, implant degradation, and tissue regeneration.