Self-assembly mechanisms of silk protein nanostructures on two-dimensional surfaces

Self-assembly processes are ubiquitous in natural systems, and their study can provide insight into the harnessing of unique properties for engineering of new materials from the bottom up. Models for diffusion-limited assembly behavior have shown that structures formed have a characteristic fractal dimensionality that is smaller than the embedding space or the lattice. Typically however, these processes have only been studied via theoretical and computational tools, with relatively few natural systems having been reported to approach the limiting conditions assumed. Sericin, a protein critical to silk macrostructure, displays the remarkable ability to self-assemble through different modes of classical and non-universal diffusion-limited aggregation to produce radially-branched dendritic architectures. We report on the characterization of these assemblies by pure proteins from different species of silkworms in the absence of any charge shielding or modulation by salts. It is shown how physical differences between colloidal systems can yield remarkable changes in branching architectures from proteins that are functionally similar. This represents a novel system for fundamental and applied studies of particle aggregation and the development of biomaterials based on self-similarity at multiple length scales.