Advances in shape memory polymers: Remote actuation, multi-stimuli control, 4D printing and prospective applications

Shape memory polymer (SMP) is an excellent smart material, which can sense and perform active shape change as preprogrammed. So far, there are a wide variety of stimulus-responsive SMPs being developed, including thermal-, electro-, magnetic-, photo-, microwave-, ultrasound-responsive SMPs and so on. Heating and electricity are traditional stimuli for contact actuating SMPs. In recent decades, the remote actuation of SMPs through light irradiation, magnetic field, microwave field and ultrasound field have received tremendous attentions, especially applied in biological environment, aqueous environment as well as aerospace environment. Besides, the multi-stimuli control and multi-stage deformation of SMP intelligent systems can be flexibly realized by combining various actuation methods. For rapid fabrication of personalized smart structures and architectures, 4D printing using SMPs have been proposed and underwent increasing growth to meet the practical demands. This review summarizes the progress in SMP research, with the focus on remote-actuation strategies, multi-stimuli-controlled structures, and the 4D printing of intelligent integrated systems. Besides, the comprehensive exploitation of their shape memory functions in biomedical engineering, soft robots, actuators, aerospace engineering and information storage are addressed effectively. At last, the application prospects, current problems and future challenges facing research are elaborated, so as to provide appropriate guidance for interdisciplinary study and further development.