On 4D printing as a revolutionary fabrication technique for smart structures

Since the inception of additive manufacturing (AM) which is colloquially known as 3D printing, tremendous technological advancements have been achieved over the years thanks to the unwavering research efforts. Particularly, the progress in the 3D printable materials to include stimuli-responsive materials has been hailed as one of the most significant breakthroughs in AM. The combination of the smart materials and the AM's ability to fabricate intricate geometries has given rise to an emerging fabrication method which has been dubbed 4D printing due to its ability to imbue the printed structure with dynamic capabilities (4th dimension). 4D printing has received unprecedented research interest owing to its potential applications in a myriad of fields including medical, aerospace, soft electronics, morphing structures, and even fashion wear. In the spirit of furthering the concept of 4D printing; this review presents its general background, recent advancements, various methods of 4D printing, applications, current challenges, and future possibilities.