Shape memory photonic materials: fabrication and emerging applications

Shape memory photonic materials (SMPMs) are intelligent stimuli-responsive materials combining two different disciplines: shape memory polymers and photonic crystals. SMPMs can be programmed to one or more optically stable temporary configurations and recover to the initial configuration after being triggered by various external stimuli. In the shape memory cycle, the variation and fixation of structural colors are synchronized with the changes occurring in their micro/nanostructure of SMPMs. Because of the unique shape memory effect of micro/nanostructures, the variation of structural color can accurately convert the external stimuli into visualized optical signals in the shape memory cycles. Therefore, SMPMs have shown great potential in various applications, including actuators, visual sensors, anti-counterfeiting labels, and smart display units. This review summarizes shape memory mechanisms, micro/nanostructure design strategies, recent developments, and promising applications of SMPMs. Finally, the current challenges and future perspectives of SMPMs are discussed. This review aims to clarify the design principle for SMPMs and serve as a roadmap for exploring next-generation SMPMs.