4D Printing of Shape Memory Polymers: From Macro to Micro

Abstract

A novel and versatile shape memory ink system allowing 4D printing with light at the macroscale as well as the microscale is presented. Digital light processing (DLP) and direct laser writing (DLW) are selected as suitable 3D printing technologies to cover both regimes. First, a system based on monofunctional isobornyl acrylate and two crosslinkers consisting of a soft and a hard diacrylate is identified and proven to be compatible with both printing techniques. Employing DLP, a large variety of structures exhibiting distinct complexity is printed. These structures range from simple frames to more demanding 3D geometries such as double platform structures, infinity rings, or cubic grids. The shape memory effect is demonstrated for all the 3D geometries. Excellent shape fixity as well as recovery and repeatability is shown. Furthermore, the formulation is adapted for fast 4D printing at the microscale using DLW. Importantly, the 4D printed microstructures display remarkable shape memory properties. The possibility of trapping and releasing microobjects, such as microspheres, is ultimately demonstrated by designing, smart box-like 4D microstructures that can be thermally actuated-evidencing the versatility and potential of the reported system.

Reconfigurable 4D Printing of Reprocessable and Mechanically Strong Polythiourethane Covalent Adaptable Networks

“…Comparatively, shape memory polymers (SMPs) feature the advantages of large deformation, light weight, strong recovery stress, and fast response rates, and thus they play a principal role in 4D printing for various applications. [30][31][32][33][34] For instance, Zarek et al reported 4D printing of SMPs network and employed them for the construction of responsive flexible electronic devices. [35] A series of photo-curable SMPs were utilized to achieve multimaterial 4D printing, and the resulting geometries exhibited time-dependent sequential shape recovery dramatically.…”

“…Comparatively, shape memory polymers (SMPs) feature the advantages of large deformation, light weight, strong recovery stress, and fast response rates, and thus they play a principal role in 4D printing for various applications. [ 30–34 ] For instance, Zarek et al. reported 4D printing of SMPs network and employed them for the construction of responsive flexible electronic devices.…”

Novel, High‐Resolution, Subtractive Photoresist Formulations for 3D Direct Laser Writing Based on Cyclic Ketene Acetals

“…In addition, these technologies could work synergistically with other functional resists fabrication of functioning MEMS devices intrinsically capable of responding to external stimuli, [ 14,15 ] sensing, [ 16 ] show enhanced properties, [ 17–19 ] controlled actuation, [ 20,21 ] and shape recovery. [ 22 ]…”

“…In addition, these technologies could work synergistically with other functional resists fabrication of functioning MEMS devices intrinsically capable of responding to external stimuli, [14,15] sensing, [16] show enhanced properties, [17][18][19] controlled actuation, [20,21] and shape recovery. [22] Few solutions were proposed recently to bring subtractive manufacturing to DLW. Oxygen plasma, for example, can effectively remove thin structures, [13,23] but, by acting on the entirety of the structure, lacks sensitivity and thus requires optimization of the different printing parameters to obtain the desired design.…”

Charge Transfer Complexes (CTCs) with Pyridinium Salts: Toward Efficient Dual Photochemical/Thermal Initiators and 3D Printing Applications

“…[7][8][9][10][11][12] As a result, AM is making progress in various industrial and emerging applications, including biomedical, electrical energy storage, electronics, and so on. [13][14][15][16][17][18][19] Compared to conventional manufacturing techniques such as molding, vat (photo-curing) photopolymerization is one of the widely employed additive manufacturing process technologies due to its high precision, [20][21][22] low energy consumption, and nonpollution advantages, [16,[23][24][25] especially with the development of reversible deactivation radical polymerizations (RDRP). [26][27][28][29][30][31][32] Further developments in resin composition or formulation may lead to advances in potential 4D printing.…”