Current status and future outlook of 4D printing of polymers and composites - A prospective

Four-dimensional (4D) printing represents a transformative advancement in additive manufacturing, integrating time-responsive behavior into traditionally static three-dimensional (3D) printed structures. This emerging technology leverages stimuli-responsive materials such as shape memory polymers, hydrogels, liquid crystal elastomers, and smart composites that undergo controlled and reversible transformations when exposed to external triggers, including temperature, humidity, light, and magnetic or electric fields. Over the past decade, substantial research efforts have been directed toward refining material properties, optimizing printing parameters, and expanding the applicability of 4D printing across high-impact industries. This review provides a comprehensive analysis of the fundamental principles, material innovations, and emerging applications of 4D printing in sectors such as biomedical engineering, aerospace, automotive, and soft robotics. Particular emphasis is placed on programmable structures, morphing mechanisms, and self-actuating materials, which drives the next generation of dynamic manufacturing. Additionally, this study critically examines existing challenges, including material limitations, scalability issues, and computational complexities that hinder widespread industrial adoption. By identifying these constraints and proposing future research directions, this review aims to accelerate the transition of 4D printing from a novel laboratory innovation to a fully integrated, industrial-scale technology.