Overall, the 2D IR dynamics showed changes in the local environment across all the secondary structures in the strongly bundled networks. The dynamics are relatively static in the picosecond time regime, as shown by the presence of an offset of up to 2 ps (Figure ), which indicates a small solvent exposure along the actin backbone. The fitting results are similar for filamentous and weakly bundled actin networks, but different for strongly bundled networks, irrespective of the backbone secondary structure. This finding is consistent with the changes in the 2D IR lineshapes, where a different lineshape is observed for the strongly bundled network. Under the depletion effects of PEG, actin undergoes morphological changes to form bundles, which affect the degree of solvent exposure around the amide I mode along the backbone when the space between neighboring filaments is depleted, causing different dynamics in strongly bundled networks. The changes in dynamics for a strongly bundled network could also be affected, albeit less substantially, by the coupling degree among the amide I modes along the actin backbone (supported by the cross peaks in Figure ). However, given the high similarities among the secondary structures of different morphologies, the coupling degree is probably kept constant, and thus an insubstantial factor for the changes in the dynamics of the strongly bundled network.