Inspired by biological examples of highly controlled nanofiber self-organization, such as the clustering of beetles’ tarsi, our group has pioneered the use of self-assembling synthetic nanofibers to generate previously unseen structures with unique helical patterns and hierarchical order. The structures are created using only a uniform periodic array of nanofibers and an evaporating liquid to provide a bending force; by varying the geometric, mechanical, and surface properties of the fibers, we have developed a model describing conditions that favor hierarchical self-assembly into bundles, and bundles of bundles, with helicity arising spontaneously as pillars and bundles twist around each other.
The chirality, shape, and size of the assembled structures are all highly sensitive to the delicate balance of elastic, capillary, and adhesive forces between adjacent fibers. In particular, we have discovered that surface adhesion after the system dries is a central player in several respects: chirality arises only if the adhesion is weak enough to allow touching fibers to slip relative to each other, and structures can undergo steps of hierarchical disassembly to arrive at sizes determined by the adhesion strength. We are exploring and modeling in detail how the dynamic interplay among all forces in the system gives rise to this fascinating assortment of structures, and how these forces can be harnessed to generate a variety of tunable chiral patterns at larger scales.