From responsiveness in biological matter to functional materials: analogies and inspiration towards the systematic design and synthesis of new smart materials and systems

Living organisms and, in general, bio-materials respond to external stimuli exhibiting specific functionalities (such as shape-morphing, color change, tissue growth and remodelling, programmed mechanical responses, adaptation of material properties, etc.) required for different needs (camouflage, locomotion, defense, food supply, biological processes, etc.). Functionalities in nature come from biochemo-physical-mechanical responsiveness of the complex architectures in which natural structures are organized across the nano-, micro- and meso-scales. Often inspired by natural structures and bio-functionalities, the development of synthetic responsive materials has attracted a huge interest in recent years, and increasingly still attracts the efforts of scientists to synthesize new smart materials and devices. The paper illustrates the most compelling morphing and functional responses observable in nature - displayed by biological matter, living individuals or by the collective behavior of large groups of organisms - developed for different functional purposes, and discusses the related underlying mechanisms. In parallel, the most relevant functional materials being developed in the last decades are presented with the related mathematical models, and their underlying driving mechanisms are compared with those observable in nature. The study is aimed at providing a broad overview and to explain the strategies used in nature to obtain functionalities; the analogies with those shown in artificial functional materials, with a particular emphasis on polymer-based or polymer-like materials, are investigated. Some multi-physics models, describing the response and enabling the systematic design, optimization and synthesis of functional materials suitable to the development of new advanced applications, are also illustrated. The knowledge of natural cunning can push forward the research in the field, offers new possibilities worth of investigation by materials scientists, physicists and engineers, and opens unexplored scenarios not yet fully considered in the existing literature.