Viscoelastic properties and gelation of an elastin-like polypeptide

Tropoelastin, the native monomeric form of elastin, and elastin-like polypeptides undergo a process of temperature-induced phase separation (coacervation) resulting in self-organization of a polymeric network that can subsequently be cross-linked into an elastomeric polymer. In this study, the rheological properties of a recombinantly produced polypeptide mimicking the sequences and domain arrangements of tropoelastin were investigated to understand post-coacervation changes in structure and assembly. This polypeptide, designated EP20-24-24, consisted of three hydrophobic domains of native human tropoelastin flanking two cross-linking domains. Temperature-induced formation of coacervate droplets resulted in a small increase in viscosity. A higher temperature produced a second temperature-dependent transition ( T v ) to a gel state characterized by a much higher viscosity, strong shear thinning, and a high ratio of storage to loss moduli. This gel state was fully reversible if the temperature was immediately lowered. However, incubation above T v for 60 min resulted in a further transformation of the network, limiting thermal reversibility of the gelation process. These results demonstrate that for elastin-like polypeptides mimicking the sequence and domain arrangements of tropoelastin, temperature-induced coacervation and transition of the coacervate to a gel-like state are distinguishable events with separate transition temperatures. Moreover, gels formed by these elastin-like polypeptides undergo a process of maturation, reducing the reversibility of the gel state.