Design of metabolism-inspired hydrogels driven by emergence of function

In the 21st century, bioinspired hydrogels have been developed using stimuli-responsive polymer networks in aqueous environments. In this review, "metabolism-inspired hydrogels" are discussed, focusing on the symbolic functions of living organisms. Considering that cell activities in animals and plants are driven by cyclic chemical reactions such as TCA cycle or Calvin-Benson cycle, catalyzed by multiple enzymes, we discuss artificial hetero-systems, especially, self-oscillating gel and artificial photosynthetic gel designs. By providing the necessary materials or photoenergy to gels, they can be converted into useful substances or mechanical energy. These gels can be categorized as chemomechanical or energy-converting gels. Copolymer networks with a redox catalyst convert substances and energy by acting as an active network during the phase transition of the polymer. The polymer itself is not necessary for the chemical reactions, but it acts as a critical active mediator for the emergence of function. To construct polymer networks, functional molecules or catalytic nanoparticles can be integrated using simple methods. This review focuses on the methodology for network design and stepwise integration. In the future, synthetic technologies, such as precise polymerization, are expected to promote a range of self-organized morphologies and efficient energy conversion. We hope that the discussions in this review will help leverage the huge potential of polymer networks in the development of soft materials.