Recent progress in 4D printing: materials, methods and applications

This review summarizes recent progress in 4D printing, explaining how additive manufacturing methods, stimulus-responsive materials, and design choices work together to produce structures whose shape and properties evolve over time. It highlights that material extrusion and vat photopolymerization are currently dominant because they provide a practical balance of process accessibility, compatible materials, and control over programmed shape change. Shape memory polymers are identified as the most widely used responsive materials, and hybrid/multi-material approaches are increasingly used to enable more localized and multifunctional actuation. The review emphasizes that 4D-printed behavior depends on the combined interaction between fabrication method, material response, activation mechanism, and structural design. It also points out major barriers to broader adoption: long-term reliability, manufacturing scalability, and design predictability.