Self-assembly of genetically engineered spider silk block copolymers

The design, construction, and preliminary characterization of a novel family of spider silk-like block copolymers are described. The design was based on the assembly of individual spider silk modules, in particular, polyalanine (A) and glycine-rich (B) blocks, that display different phase behavior in aqueous solution. Spider silk was chosen as a model for these block copolymer studies based on its extraordinary material properties, such as toughness, biocompatibility, and biodegradability. Trends in spider silk-like block copolymer secondary structure and assembly behavior into specific material morphologies were determined as a function of the number of hydrophobic blocks, the presence of a hydrophilic purification tag and solvent effects. Structures and morphologies were assessed by Fourier transform infrared spectroscopy and scanning electron microscopy. In terms of structure, beta-sheet content increased with an increase in the number of polyalanine blocks, and the purification tag had significant impact on the secondary structure. In terms of morphology, spheres, rod-like structures, bowl-shaped micelles, and giant compound micelles were observed and the morphologies were linked with the size of the hydrophobic block, the presence of the purification tag, and the solvent environment. This study provides a basis for future designs of smart biomaterials based on spider silk chemistries, with controlled structure-architecture-function relationships.