Influence of molecular size on gel-forming properties of telechelic collagen-inspired polymers

We studied the influence of molecular size on the formation of transient networks by telechelic protein polymers with 2.3 kDa collagen-like triple helix-forming end-blocks and much longer random coil mid-blocks. We compared triblock copolymers with mid-blocks of 400 and 800 amino acids (37 and 73 kDa, respectively) and two different amino acid sequences, all of which were secreted to high concentration by recombinant yeast cells. At the same molar concentration of protein and crosslink-forming end-blocks, the storage modulus of the longer polymers was higher than that of the shorter polymers. Differences in storage modulus values were also observed for the polymers with mid-blocks of the same amino acid composition but different amino sequence, which correlated to differences in the measured hydrodynamic radius of the mid-blocks. The melting temperature of the triple helices was the same for both larger and smaller polymers; however, the elastic properties of the gels were lost at lower temperature for the smaller polymers than for the larger polymers. Using an analytical model based on classical gel theory and accounting for the well-defined multiplicity of the network, we could ascribe these differences to the lower probability of the longer chains to form intramolecular loops.