Critical Review on 4D Printing

Recently, one of the subjects that is receiving significant research attention has been the additive manufacturing (AM) of intelligent materials and structures. A smart material is one that can change its structure and properties in response to an external input, also known as stimuli-responsive materials (SRM). These advantages enable AM-fabricated components to adapt their structural properties in response to envi- ronmental factors or human input. In order to include the structural reconfiguration over time in AM processes, a new term, “4D printing,” is coined. While still in its infancy, this new subject has drawn a lot of interest since its inception in 2013. It may also produce items that can self-assemble and be repaired and have a variety of uses. In this study, it examines and categorizes prior studies on 4D printing in the aerospace industry in accordance with the triggers that are most likely to activate them. The advantages and applications of the materials used in 4D printing are also covered. A glimpse into 4D printing's future is shown