Controlled molecular self-assembly of complex three-dimensional structures in soft materials

Significance We demonstrate a unique growth mode to form complex 3D shapes in hydrogels by invoking the bottom-up approach analogous to cell enlargement and proliferation found in living animal tissues and plants. For this purpose, we control the oxygen concentration to modulate polymerization of monomers in porous hydrogel, wherein postgelation networks continue to expand––a process similar to the growth of living tissues in nature. The applicability of this experimental technique to a variety of situations in biology is demonstrated with several examples of the formation of complex 3D architectures through successful biomimetics of tissue morphogenesis in both animals and plants. These results offer possibilities for a diverse set of applications in tissue engineering, soft robotics, and flexible electronics.