4D Printing at the Microscale

Abstract

Abstract3D printing of adaptive and dynamic structures, also known as 4D printing, is one of the key challenges in contemporary materials science. The additional dimension refers to the ability of 3D printed structures to change their properties—for example, shape—over time in a controlled fashion as the result of external stimulation. Within the last years, significant efforts have been undertaken in the development of new responsive materials for printing at the macroscale. However, 4D printing at the microscale is still in its early stages. Thus, this progress report will focus on emerging materials for 4D printing at the microscale as well as their challenges and potential applications. Hydrogels and liquid crystalline and composite materials have been identified as the main classes of materials representing the state of the art of the growing field. For each type of material, the challenges and critical barriers in the material design and their performance in 4D microprinting are discussed. Importantly, further necessary strategies are proposed to overcome the limitations of the current approaches and move toward their application in fields such as biomedicine, microrobotics, or optics.

In Situ Control of Reactive Mesogens Alignment During 3D Printing by Two‐Photon Lithography

“…[ 19 , 39 ] Consistent microstructures are fabricated by adjusting the slicing distance between layers and the hatching distance (H) between lines, according to the ribbons’ height and width, respectively. [ 16 , 17 , 19 ] All the structures in this study are printed in uniform planar NRMs films, sandwiched between two alignment substrates with parallel anchoring axes (see Figure 1 a and Experimental Section).…”

Closed‐Loop Recyclable Silica‐Based Nanocomposites with Multifunctional Properties and Versatile Processability

“…Moreover, 3D printing has become the gold standard in fabricating complex 3D architectures. [ 46 , 47 , 48 , 49 , 50 ] It is also particularly desirable in closed‐loop recycling where the high‐performance properties of the materials are fully retained. We show extrusion‐based 3D printing of the liquid prepolymer from the viscoelastic liquid state, its fluid‐like behavior allows the fabrication of a lattice structure with multiple layers (Figure 5k–m ).…”

Mechanical stimulation of single cells by reversible host-guest interactions in 3D microscaffolds

“…Thus, no additional covalent cross-linker is needed to form stable 3D microstructures. This aspect circumvents the typical challenge in printing stimuli-responsive 3D hydrogels, namely, that more cross-links are required to stabilize the network, which hinder its response at the same time ( 16 ). In our system, we were able to increase the number of cross-links and the functionality simultaneously.…”