New Trends in 4D Printing: A Critical Review

Abstract

In a variety of industries, Additive Manufacturing has revolutionized the whole design–fabrication cycle. Traditional 3D printing is typically employed to produce static components, which are not able to fulfill dynamic structural requirements and are inappropriate for applications such as soft grippers, self-assembly systems, and smart actuators. To address this limitation, an innovative technology has emerged, known as “4D printing”. It processes smart materials by using 3D printing for fabricating smart structures that can be reconfigured by applying different inputs, such as heat, humidity, magnetism, electricity, light, etc. At present, 4D printing is still a growing technology, and it presents numerous challenges regarding materials, design, simulation, fabrication processes, applied strategies, and reversibility. In this work a critical review of 4D printing technologies, materials, and applications is provided.

4D food printing technology: Structural changes to culinary art and beyond

“…One important aspect that makes 4D printing more affordable than other methods is the decrease in material waste. During the shaping and cutting phases, conventional printing techniques like 3D printing could produce a significant amount of waste (Vatanparast et al, 2023). 4D printing reduces material waste by using smart materials that have shape-memory capabilities and react to outside stimuli.…”

Mechanistic prediction of folding angles in 4D printed shape memory polymers under varied loading conditions

“…The partition is performed vertically along the beam cross section as illustrated in figure 3. Let A i represent a segment of the beam cross section, R i denote the central plane location of area A i , and σ i represent the circumferential stress acting on area A i , as described in equation (2). The total cross-sectional area, denoted as A, is the sum of all individual segmental areas, expressed as A = ∑ A i , Consistent with the definitions provided by Cook and Yang [39] and Boresi and Schmidt [40], strain is nonlinearly distributed and is expressed in the following format,…”

“…Mathematically, this can be formulated as Min{σ = f i (ε) = Ga i + Gb i ε, i = −m to n}. Given a specific strain value ε, one can compare the stress values determined by each linear function within group equation (2). The linear equation that yields the minimum stress value best describes the stress-strain relationship at the current strain level.…”

“…These shape morphing structures are typically 3D-printed, then programmed into temporary geometries through external actions and subsequently recovered to their original shapes upon activation of external stimuli. Four-dimensional printing materials developed thus far since its advent respond to a variety of external stimuli, including but not limited to temperature, light, magnetics, and more [1,2]. Applications of 4D printing have been found in areas such as soft robots and actuators [3,4], biomedical engineering [5,6], electronic * Author to whom any correspondence should be addressed.…”

“…devices [7], textiles [8,9], metamaterials [10][11][12] and others. Detailed reviews on 4D printing can be found in [1,2,[13][14][15].…”