A self-strengthening epidermis-like smart coating enabled by dynamic iron sequestration

Abstract

Living organisms rely on materials sequestration from the environment to strengthen their bodies. Such constant activity provides necessary supplies for critical biological functions, which is difficult by man-made structures due to the lack of a dynamic sequestration mechanism. In this study, it is shown that an epidermis-like smart coating can respond to changes in salinity to allow a spontaneous and progressive strengthening when supported by steel as a sustained iron source. The self-strengthening is enabled by reaction-coupled diffusion, which makes possible the dynamic sequestration of iron from the in situ rusted steel, partially mimicking the iron accumulation process in a mussel. The emergence of iron-phenolic coordination bonds continuously improves modulus, hardness, and adhesion, achieving a strengthening efficiency comparable to mussel byssus. Interestingly, the bilayer design ensures long-term self-healing performance even during strengthening and a mechanically robust anticorrosion coating with an autonomic protection mechanism and gradually enhanced barrier properties during prolonged service. Our results provide a new venue for the design of stimuli-responsive smart materials characteristic of an open biological system and may serve as the basis for creating highly intelligent devices with sophisticated functionality.