Capillary‐force‐driven self‐assembly is emerging as a significant approach for the massive manufacture of advanced materials with novel wetting, adhesion, optical, mechanical, or electrical properties. However, academic value and practical applications of the self‐assembly are greatly restricted because traditional micropillar self‐assembly is always unidirectional. In this work, two‐photon‐lithography‐based 4D microprinting is introduced to realize the reversible and bidirectional self‐assembly of microstructures. With asymmetric crosslinking densities, the printed vertical microstructures can switch to a curved state with controlled thickness, curvature, and smooth morphology that are impossible to replicate by traditional 3D‐printing technology. In different evaporating solvents, the 4D‐printed microstructures can experience three states: (I) coalesce into clusters from original vertical states via traditional self‐assembly, (II) remain curved, or (III) arbitrarily self‐assemble (4D self‐assembly) toward the curving directions. Compared to conventional approaches, this 4D self‐assembly is distance‐independent, which can generate varieties of assemblies with a yield as high as 100%. More importantly, the three states can be reversibly switched, allowing the development of many promising applications such as reversible micropatterns, switchable wetting, and dynamic actuation of microrobots, origami, and encapsulation.
In addition to superhydrophobicity/superoleophobicity, surfaces with switchable water/oil repellency have also aroused considerable attention because of their potential values in microreactors, sensors, and microfluidics. Nevertheless, almost all those as-prepared surfaces are only applicable for liquids with higher surface tension (> 25.0 mN m −1) in air. In this work, inspired by some natural models, such as lotus leaf, springtail skin, and filefish skin, switchable repellency for liquids (= 12.0-72.8 mN m −1) in both air and liquid is realized via employing 3D deformable multiply re-entrant microstructures. Herein, the microstructures are fabricated by a two-photon polymerization based 3D printing technique and the reversible deformation is elaborately tuned by evaporation-induced bending and immersion-induced fast recovery (within 30 s). Based on 3D controlled microstructural architectures, this work offers an insightful explanation of repellency/penetration behavior at any three-phase interface and starts some novel ideas for manipulating opposite repellency by designing/fabricating stimuli-responsive microstructures. Inspired by lotus leaves (Figure 1a(i)), springtail skin (Figure 1a(ii)), filefish skin (Figure 1a(iii)), and some other natural models, [1] scientists developed a variety of surfaces able to superrepel water in air, oil in air, water under oil, or oil under water, [2] which have found wide applications in antifouling, [3] generation of tiny liquid droplets, [4] oil-water separation, [5] and
Two‐photon lithography (TPL) is a powerful tool to construct small‐scale objects with complex and precise 3D architectures. While the limited selection of chemical functionalities on the printed structures has restricted the application of this method in fabricating functional objects and devices, this study presents a facile, efficient, and extensively applicable method to functionalize the surfaces of the objects printed by TPL. TPL‐printed objects, regardless of their compositions, can be efficiently functionalized by combining trichlorovinylsilane treatment and thiol–ene chemistry. Various functionalities can be introduced on the printed objects, without affecting their micro‐nano topographies. Hence, microstructures with diverse functions can be generated using non‐functional photoresists. Compared to existed strategies, this method is fast, highly efficient, and non photoresist‐dependent. In addition, this method can be applied to various materials, such as metals, metal oxides, and plastics that can be potentially utilized in TPL or other 3D printing technologies. The applications of this method on the biofunctionalization of microrobots and cell scaffolds are also demonstrated.
Biophysical restrictions regulate protein diffusion, nucleus deformation, and cell migration, which are all universal and important processes for cells to perform their biological functions. However, current technologies addressing these multiscale questions are extremely limited. Herein, through two-photon polymerization (TPP), we present the precise, low-cost, and multiscale microstructures (micro-fences) as a versatile investigating platform. With nanometer-scale printing resolution and multiscale scanning capacity, TPP is capable of generating micro-fences with sizes of 0.5–1000 μm. These micro-fences are utilized as biophysical restrictions to determine the fluidity of supported lipid bilayers (SLB), to investigate the restricted diffusion of Src family kinase protein Lck on SLB, and also to reveal the mechanical bending of cell nucleus and T cell climbing ability. Taken together, the proposed versatile and low-cost micro-fences have great potential in probing the restricted dynamics of molecules, organelles, and cells to understand the basics of physical biology. Graphic abstract
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