Mechanically Robust and UV‐Curable Shape‐Memory Polymers for Digital Light Processing Based 4D Printing

Abstract

4D printing is an emerging fabrication technology that enables 3D printed structures to change configuration over “time” in response to an environmental stimulus. Compared with other soft active materials used for 4D printing, shape‐memory polymers (SMPs) have higher stiffness, and are compatible with various 3D printing technologies. Among them, ultraviolet (UV)‐curable SMPs are compatible with Digital Light Processing (DLP)‐based 3D printing to fabricate SMP‐based structures with complex geometry and high‐resolution. However, UV‐curable SMPs have limitations in terms of mechanical performance, which significantly constrains their application ranges. Here, a mechanically robust and UV‐curable SMP system is reported, which is highly deformable, fatigue resistant, and compatible with DLP‐based 3D printing, to fabricate high‐resolution (up to 2 µm), highly complex 3D structures that exhibit large shape change (up to 1240%) upon heating. More importantly, the developed SMP system exhibits excellent fatigue resistance and can be repeatedly loaded more than 10 000 times. The development of the mechanically robust and UV‐curable SMPs significantly improves the mechanical performance of the SMP‐based 4D printing structures, which allows them to be applied to engineering applications such as aerospace, smart furniture, and soft robots.

Smart Diffraction Gratings Based on the Shape Memory Effect

“…A 0.8 mL well-mixed precursor solution was dripped on the cleaned glass slide and then irradiated under UV light for 120 s. The energy of the laser was strong enough to ensure the complete polymerization of the precursor. [32] After UV exposure, the SMP films (≈0.5 mm in thickness) were peeled off from the glass slide. The SMP films were cut into squares substrate with a side length of 20 mm.…”

“…The high molecular weight of AUD cross-linkers and the presence of hydrogen bonds ensures the high stretchability of the polymer. Because the photopolymerized tBA long chain is bound by hydrogen bonds [32] and AUD chains, it presents a crimped state. The FTIR spectroscopy is sensitive to hydrogen bonding, [11,33] the formed hydrogen bonds between the N-H groups in SMP could be identified from their stretching vibrations near 3200-3400 cm -1 .…”

Rubber Seed Oil-Based UV-Curable Polyurethane Acrylate Resins for Digital Light Processing (DLP) 3D Printing

“…By measuring and plotting the cure depth of the resin as a function of the different exposure times, the data of Dp and t0 was obtained from the slope and the intercept of the fitted line, respectively [46]. As with previous reports, the viscosity of a polymer solution higher than 3 Pa•s was not suitable for DLP-based 3D printing [3]. Combined with the overall properties and viscosity of the RSO-PUA resin, the RSO-PUA/HEA40% was selected as the print model.…”

“…UV-curable materials have gained widespread attention for the advantages of high curing efficiency, low energy consumption, low solvent emission, low costs, and moderate curing condition. They are widely used in the fields of coatings, adhesives, and high value-added products [2,3]. However, most of the UV-curable raw materials were prepared from petrochemical products.…”

A brief review of mechanical designs for additive manufactured soft materials

“…4D printing is a novel concept where additive manufactured structures can change their shape or function upon external actuation [126] . Currently, most 4D printing research is based on soft materials, including polymers, hydrogels and biomaterials [127] , whose mechanical programming is the most crucial design step. In 4D printings based on active materials, mechanical design is required to predict the deformation pattern and actuation speed.…”