Abstract
De novo peptide surfactant (I3K) gels provide an ideal system to study the complex dynamics of lightly cross-linked semiflexible fibers because of their large contour lengths, simple chemistry, and slow dynamics. We used single-molecule fluorescence microscopy to record individual fibers and Fourier decomposition of the fiber dynamics to separate thermal contributions to the persistence length from compressive states of prestress (SPS). Our results show that SPS in the network depend strongly on peptide concentration, buffer, and pH and that the fibril energies in SPS follow a Lévy distribution. The presence of SPS in the network imply that collective states of self-stress are also present. Therefore, semiflexible polymer gels need to be considered as complex load-bearing structures and the mean field models for polymer gel elasticity and dynamics often applied to them will not be fully representative of the behavior at the nanoscale. We quantify the impact of cross-links on reptation tube dynamics, which provides a second population of tube fluctuations in addition to those expected for uncross-linked entangled solutions.
Highlights
The gel state of matter is ubiquitous in nature and in our foods, diapers, contact lenses, adhesives, soaps, drug delivery systems, and biomaterials
Good-quality images were obtained and the dynamic single-molecule fluorescence microscopy experiments were unaffected by the buffer, as they are less sensitive to dye labeling density than stochastic optical reconstruction microscopy (STORM)
We have demonstrated that the complex networks of semiflexible fibrils can mask the intrinsic properties of the fibrils that compose them
Summary
The gel state of matter is ubiquitous in nature and in our foods, diapers, contact lenses, adhesives, soaps, drug delivery systems, and biomaterials. It is found both intra- and extracellularly in a wide range of organisms, e.g., inside amoeba and outside bacteria in biofilms. Despite over 50 years of intensive research, we still lack robust quantitative theories that relate the structure and dynamics of gels on the molecular scale to their performance on the macroscale.[1,2] Without such an understanding, it is hard to create new high-performance materials following the fundamental bottom-up approach. We present single-molecule experiments on the dynamics of gels to help motivate new models to bridge this gap in our understanding. We find the previously undocumented phenomena of prestresses in single molecules inside gels and predict that it will impact on the majority of physical phenomena in the gels, e.g., their elastic modulus, relaxation times, adhesion, phase separation, wetting behavior, response to external actuation (e.g., electric/magnetic fields and change in temperature), etc
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