Microphase Separation of Resilin-like and Elastin-like Diblock Copolypeptides in Concentrated Solutions

Diblock copolymers are valued for their ability to form thin films with nanoscale features that typically reflect those of their microphase-separated structures in concentrated solution. Here, we show that such self-assembled structures can be easily formed with diblock copolymers composed of thermally responsive polypeptides, such as resilin-like polypeptides (RLP) and elastin-like polypeptides (ELP), by exploiting the inverse temperature transition behavior of ELPs in aqueous media. Specifically, we examine the self-assembly of a series of RLP-b-ELP diblock copolypeptides in concentrated aqueous solution (30 and 50 wt %) by small-angle X-ray scattering (SAXS). By systematically varying RLP block length and temperature (10-45 °C), we observed microphase separation into hexagonally packed cylinders and lamellae. By analyzing the observed order-order transitions (OOT) and order-disorder transitions (ODT), we determined that self-assembly in this system is primarily driven by polymer-solvent interactions. While these thermally responsive polymers showed clear ODTs and OOTs at certain temperatures, temperature only had a weak effect on the spacing of the resulting nanostructures. In contrast, we found that nanostructure spacing was far more sensitive to RLP block length. Finally, we used atomic force microscopy (AFM) to demonstrate that spin casting RLP-b-ELP diblock copolypeptides also produce nanostructured thin films with spacings that correlate with those in concentrated solution.