Supramolecular hydrogels for soft nanotechnology

In the last two and half decades, nanotechnology has grown explosively and evolved into a subfield of science. In the meantime, the nanoscale sizes and surface characters shared between physical science and biological science have led to the recognition that “future developments in nanoscience could provide the basis for artificial life”1 because living cells consist of arrays of dynamically self-assembled nanostructures (e.g., enzymes, receptors, microtubules, ribosomes, or molecular motors) for carrying out metabolic processes, proliferation, differentiation, and other biological functions. These conceptual advancements have resulted in the development of soft nanotechnology, a branch of nanotechnology that focuses on the synthesis, properties, and functions of organic nanostructures for mimicking and interacting with naturally existing nanostructures. Because supramolecular interaction is one of the fundamental driving forces for the formation of cellular nanostructures2 via selfassembly, it is reasonable to use it for generating organic nanostructures. Based on this simple logic, supramolecular hydrogels, consisting of water and molecular nano-fibers formed by self-assembly, should be an ideal candidate for the development of soft nanotechnology. Therefore, in this chapter, we describe several representative cases of supramolecular hydrogels, especially their applications, to illustrate their promises for developing soft nanotechnology.