4D printing: reality or myth?

Purpose Additive manufacturing (AM) is one of the nine pillars of the design-fabrication cycle in Industry 4.0. However, although some limitations hinder its full implementation in our quotidian, a new concept is already emerging: 4D printing (4DP). Conceptually, 4D-printed parts are additive manufactured with stimuli-responsive materials, able to self-adapting or self-assembly when exposed to the correct stimuli. Although this concept is an establish reality, due to the lack of a normalized ASTM/ISO standard is published in confusing and, sometimes, opposite directions that almost present it as a myth. Design/methodology/approach This article reviews current 4DP applications, discusses their shortcomings in addressing the manufacturing approach and synthesizes their scientific contributions. Based on the synthesis, the paper theorizes the progress on this topic. Findings 4DP remains an emerging technological tool requiring further research to achieve widespread adoption. Although reversibility is implied in the definition of 4DP, only 119 out of 1,303 scientific papers in the Web of Science database (as of the review writing date) address the 4DP as a reversible shape transformation. Inquisitive debates must be conducted to establish consensual terminology, standardized production and regulatory investment in characterization methodologies. Originality/value From the research status, some questions arose whether the current reality of 4DP is sometimes considered a myth, as the concept is often misapplied. This paper provides an in-depth discussion of the conceptualization of 4DP, and the urgent need to establish regulatory standards for 4D-printed structures. The scalability of the stimuli-responsive structures in industrial applications and challenges to put 4DP products in the market are also explored.