Kinetics of network formation by telechelic polypeptides with trimeric nodes

Abstract

We study the kinetics of transient network formation by monodisperse telechelic polypeptides with collagen-like end blocks and a random coil middle block. Upon cooling, the end blocks associate reversibly into triple helices, leading to gels with well-defined, trimeric crosslinks. Formation of triple helices occurs in two steps: nucleation and propagation. At low protein concentrations, when a simultaneous encounter of three end blocks is rather infrequent, the limiting step is nucleation. With increasing concentration, propagation of triple helix becomes rate-limiting. The rate of helix formation controls the gelation process and the development of mechanical (rheological) properties. Not all helices contribute junctions to the developing network: a certain fraction forms mechanically irrelevant loops, particularly at low concentrations. We show, however, that it is possible to predict the time dependent gel properties with the help of an analytical model which accounts for loops and dangling ends. A connection between helix content and storage modulus can be established. Using this model we can accurately account for the experimental data.