A review on 4D printing of NiTi smart alloy: principle, manufacturing and their applications

Conventional static 3D printing possesses inherent limitations in achieving adaptive response and integrated functionality within dynamic systems. 4D printing integrates smart material with 3D printing technology to create structures that respond to external stimuli with programmed shape, property, or functional changes. The fundamental distinction between 4D printing and 3D printing lies in the transition from static fabrication to dynamic programmability. NiTi alloy is a typical smart material with shape memory and superelastic effects to form 4D-printed functional structure. Their excellent mechanical properties, wear resistance and biocompatibility effects underpin applications in fields such as aircraft morphing structures and biomedical implants. Consequently, 4D-printed NiTi alloy components possess sensing, control, and actuation capabilities, enabling self-adaptive adjustments through intelligent structural design. It shows promise in overcoming the limitations of conventional manufacturing and warrants further investigation. This review outlines the properties and phase transition mechanisms, additive manufacturing techniques, composite material design, structural optimization methods and potential applications of 4D-printed NiTi alloy.