Equivalent pathways in melting and gelation of well-defined biopolymer networks

We use multiple particle tracking microrheology to study the melting and gelation behavior of well-defined collagen-inspired designer biopolymers expressed by the transgenic yeast P. Pastoris. The system consists of a hydrophilic random coil-like middle block and collagen-like end block. Upon cooling, the end blocks assemble into well-defined transient nodes with exclusively 3-fold functionality. We apply the method of time-cure superposition of the mean-square displacement of tracer beads embedded in the biopolymer matrix to study the kinetics and thermodynamics of approaching the gel point from both the liquid and the solid side. The melting point, gel point, and critical relaxation exponents are determined from the shift factors of the mean-square displacement and we discuss the use of dynamic scaling exponents to correctly determine the critical transition. Critical relaxation exponents obtained for different concentrations in both systems are compared with the currently existing dynamic models in literature. In our study, we find that, while the time scales of gelation and melting are different by orders of magnitude, and show inverse dependence on concentration, that the pathways followed are completely equivalent.