Capillary force is often regarded as detrimental because it may cause undesired distortion or even destruction to micro/nanostructures during a fabrication process, and thus many efforts have been made to eliminate its negative effects. From a different perspective, capillary force can be artfully used to construct specific complex architectures. Here, we propose a laser printing capillaryassisted self-assembly strategy for fabricating regular periodic structures. Microscale pillars are first produced by localized femtosecond laser polymerization and are subsequently assembled into periodic hierarchical architectures with the assistance of controlled capillary forces in an evaporating liquid. Spatial arrangements, pillar heights, and evaporation processes are readily tuned to achieve designable ordered assemblies with various geometries. Reversibility of the assembly is also revealed by breaking the balance between the intermolecular force and the elastic standing force. We further demonstrate the functionality of the hierarchical structures as a nontrivial tool for the selective trapping and releasing of microparticles, opening up a potential for the development of in situ transportation systems for microobjects.laser printing | capillary force | self-assembly | hierarchical structures | microobject trapping P eople learn from daily life experience that individual filaments can coalesce, as with wet hairs or paintbrushes pulling out of paint. Analogs of this elastocapillary coalescence exist and are often amplified in micro/nanoelectromechanical system manufacturing processes because the capillary force tends to dominate over the standing force that needs to be overcome for coalescence when the scale is reduced (1, 2). When one aims to create slender structures, the dominant capillary force drives them to collapse, cluster, or be completely destroyed. Some efforts such as adopting a supercritical-point dryer (3, 4) have been made to eliminate these unwanted behaviors when fabricating high-aspect-ratio structures. However, from another point of view, the capillary-driven bottom-up self-assembly can be exploited as a valuable tool to construct complex architectures. Compared with other driving forces for self-assembly such as magnetism (5), electrostatic force (6), and gravity (7), capillary force self-assembly features the advantage of simplicity, low cost, scalability, and tunability.The desire for scalable and cost-effective self-assembly schemes comes from observations of the natural world, where self-assembled filamentous structures with mechanical compliance at the microscopic and mesoscopic scale are ubiquitous and include, to name a few, actin bundles (8), gecko feet hairs (9), and Salvinia leaf (10). These structures give rise to diverse functions ranging from mechanical strengthening (11) and directional adhesion (12, 13) to superhydrophobicity (14) and structural colors (15), thus inspiring researchers to devote their efforts to mimic these multifunctional structures for decades. Many top-down fabricat...

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natural behavior, many works have been done to realize reconfigurable shape transformation with artificial soft materials in a controlled manner. [8][9][10][11] Heterogeneous structures composited of hydrogel constituents with different swelling/shrinkage ratio [12][13][14][15][16] or anisotropic swelling behavior [17,18] have been constructed to accomplish dynamic tunable morphologies. Large shape deformation is shown in photodeformable crosslinked liquid crystal polymer through the orientation change of liquid crystal molecules, [19][20][21][22] and thus light-driven movable microarchitecture can be obtained. Inflation of elastic polymers constrained by relative stiff materials are applied to realize reconfigurable shape transformation. [23][24][25] These aforementioned shape reconfigurable materials are highly desired for many applications in soft robotics, [23,24] smart textiles, [26] drug delivery, [27] self-shaping devices, [28] and actuators. [22,29] Although nature-inspired artificial dynamic architectures have been widely studied as referred above, so far most of the shape transformation are dependent on the whole material deformation due to the technical challenge to locally induce shape change in a bulk material. Efforts have been taken to achieve dynamic structural behavior such as self-folding through modification of the localized properties of active materials, but these can only be done in macroscale by embedding Architectures of natural organisms especially plants largely determine their response to varying external conditions. Nature-inspired shape transformation of artificial materials has motivated academic research for decades due to wide applications in smart textiles, actuators, soft robotics, and drug delivery. A "self-growth" method of controlling femtosecond laser scanning on the surface of a prestretched shape-memory polymer to realize microscale localized reconfigurable architectures transformation is introduced. It is discovered that microstructures can grow out of the original surface by intentional control of localized laser heating and ablation, and resultant structures can be further tuned by adopting an asymmetric laser scanning strategy. A distinguished paradigm of reconfigurable architectures is demonstrated by combining the flexible and programmable laser technique with a smart shape-memory polymer. Proof-of-concept experiments are performed respectively in information encryption/decryption, and microtarget capturing/ release. The findings reveal new capacities of architectures with smart surfaces in various interdisciplinary fields including anti-counterfeiting, microstructure printing, and ultrasensitive detection.

The capability to realize 2D-3D controllable metallic micro/nanostructures is of key importance for various fields such as plasmonics, electronics, bioscience, and chemistry due to unique properties such as electromagnetic field enhancement, catalysis, photoemission, and conductivity. However, most of the present techniques are limited to low-dimension (1D-2D), small area, or single function. Here we report the assembly of self-organized three-dimensional (3D) porous metal micro/nanocages arrays on nickel surface by ethanol-assisted femtosecond laser irradiation. The underlying formation mechanism was investigated by a series of femtosecond laser irradiation under exposure time from 5 to 30 ms. We also demonstrate the ability to control the size of micro/nanocage arrays from 0.8 to 2 μm by different laser pulse energy. This method features rapidness (∼10 min), simplicity (one-step process), and ease of large-area (4 cm(2) or more) fabrication. The 3D cagelike micro/nanostructures exhibit not only improved antireflection from 80% to 7% but also enhanced hydrophobicity from 98.5° to 142° without surface modification. This simple technique for 3D large-area controllable metal microstructures will find great potential applications in optoelectronics, physics, and chemistry.

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