The functionality of tunable liquid droplet adhesion is crucial for many applications such as self-cleaning surfaces and water collectors. However, it is still a challenge to achieve real-time and fast reversible switching between isotropic and anisotropic liquid droplet rolling states. Inspired by the surface topography on lotus leaves and rice leaves, herein we report a biomimetic hybrid surface with gradient magnetism-responsive micropillar/microplate arrays (GMRMA), featuring dynamic fast switching toward different droplet rolling states. The exceptional dynamic switching characteristics of GMRMA are visualized and attributed to the fast asymmetric deformation between the two different biomimetic microstructures under a magnetic field; they endow the rolling droplets with anisotropic interfacial resistance. Based on the exceptional morphology switching surface, we demonstrate the function of classification and screening of liquid droplets, and thus propose a new strategy for liquid mixing and potential microchemical reactions. It is expected that this intelligent GMRMA will be conducive to many engineering applications, such as microfluidic devices and microchemical reactors.
Smart surfaces with tunable wettability are promising due to their abilities to create diversified functionalities that the fixed surfaces cannot provide. However, limited by imprecise adjustment of structural geometry and almost conventional switching modes of wettability, it is still challenging to achieve the reversible switching between multiple wetting states. Herein, a novel tri-switchable wettability surface with an in situ switching ability is used for the manipulation of a given droplet, which consists of a stretchable substrate and a micron column array. The femtosecond laser direct writing technique is utilized to generate distinct wettability of the two components. Taking the advantage of good tensile properties, the surface morphology is adjusted in a rapid, reversible way to obtain diverse wetting performances from the lotus-like effect to rice-leaf-like anisotropy and then to the rose-petal-like effect. Based on the triplex wetting transition on the same surface, we further developed a multifunctional device to realize a range of in situ manipulations, including the surface self-cleaning, the directional transport of droplets, and the capture, the vertical transport, and release of droplets. This work paves the way for expanding the field of smart surfaces with tunable wettability beyond conventional dual-property wetting behavior and exhibits versatile manipulations of droplets for microfluidic applications.
Salvinia's long-term underwater air layer retention ability has inspired researchers to develop artificial microstructures. However, Salvinia has an exquisite combination of a complicated hollow structure and heterogeneous chemical properties, which makes artificial reproduction beyond the capabilities of traditional fabrication techniques. In addition, under extremely low underpressure conditions, the mechanism of retention and restoration of the underwater air layer of Salvinia remains unclear. Herein, by combining the shape memory polymer "top-constrained self-branching (TCSB)" and hydrophilic SiO2 microspheres trapping, four-branch hollow microstructures with heterogeneous chemical properties are fabricated. By applying underpressure, the crucial role of hydrophilic apexes is unveiled in air layer restoration. Through the calculation of the surface energy, the underlying mechanism is well interpreted. This study holds great promise for developing Salvinia-inspired artificial structures and reveals the underlying mechanism of the robust air retention and recovery capability of Salvinia leaves in extreme environments.
High-performance droplet transport is crucial for diverse applications including biomedical detection, chemical micro-reaction, and droplet microfluidics. Despite extensive progress, traditional passive and active strategies are restricted to limited liquid types, small droplet volume ranges, and poor biocompatibilities. Moreover, more challenges occur for biological fluids due to large viscosity and low surface tension. Here, a vibration-actuated omni-droplets rectifier (VAODR) consisting of slippery ratchet arrays fabricated by femtosecond laser and vibration platforms is reported. Through the relative competition between the asymmetric adhesive resistance originating from the lubricant meniscus on the VAODR and the periodic inertial driving force originating from isotropic vibration, the fast (up to ≈60 mm s-1 ), programmable, and robust transport of droplets is achieved for a large volume range (0.05-2000 µL, Vmax /Vmin ≈ 40â¯000) and in various transport modes including transport of liquid slugs in tubes, programmable and sequential transport, and bidirectional transport. This VAODR is general to a high diversity of biological and medical fluids, and thus can be used for biomedical detection including ABO blood-group tests and anticancer drugs screening. These strategies provide a complementary and promising platform for maneuvering omni-droplets that are fundamental to biomedical applications and other high-throughput omni-droplet operation fields.
Microfluidics , Vibration , Lasers , Mechanical Phenomena , Surface Tension
We propose a new, to the best of our knowledge, technique to capture single particles in real-time in a microfluidic system with controlled flow using micro-pillar traps fabricated by one-step. The micro pillars are fabricated in parallel by femtosecond multi-foci laser beams, which are generated by multiplexing gratings. As the generation process does not need integration loops, the pattern and the intensity distribution of the foci array can be controlled in real-time by changing the parameters of gratings. The real-time control of the foci array enables rapidly fabricating microtraps in the microchannel with adjustment of the pillar spaces and patterns according to the sizes and shapes of target particles. This technology provides an important step towards using platforms based on single-particle analysis, and it paves the way for the development of innovative microfluidic devices for single-cell analysis.
Microrobots have attracted considerable attention due to their extensive applications in microobject manipulation and targeted drug delivery. To realize more complex micro-/nanocargo manipulation (e.g., encapsulation and release) in biological applications, it is highly desirable to endow microrobots with a shape-morphing adaptation to dynamic environments. Here, environmentally adaptive shape-morphing microrobots (SMMRs) have been developed by programmatically encoding different expansion rates in a pH-responsive hydrogel. Due to a combination with magnetic propulsion, a shape-morphing microcrab (SMMC) is able to perform targeted microparticle delivery, including gripping, transporting, and releasing by "opening-closing" of a claw. As a proof-of-concept demonstration, a shape-morphing microfish (SMMF) is designed to encapsulate a drug (doxorubicin (DOX)) by closing its mouth in phosphate-buffered saline (PBS, pH â¼ 7.4) and release the drug by opening its mouth in a slightly acidic solution (pH < 7). Furthermore, localized HeLa cell treatment in an artificial vascular network is realized by "opening-closing" of the SMMF mouth. With the continuous optimization of size, motion control, and imaging technology, these magnetic SMMRs will provide ideal platforms for complex microcargo operations and on-demand drug release.
Neoplasms , Robotics , Humans , HeLa Cells , Drug Delivery Systems/methods , Doxorubicin/pharmacology , Drug Liberation , Neoplasms/drug therapy
Soft pressure sensors based on liquid metals (LMs) may find broad applications, but it is challenging to fabricate such sensors that can achieve high stress resolution without additional parts. Herein, a method named laser-induced selective adhesion transfer (LISAT) is proposed. LISAT can pattern LM by selectively changing high adhesion of the poly(dimethylsiloxane) (PDMS) surface to LM into low adhesion with the aid of rough micro/nanostructures induced by a femtosecond laser. Based on this principle, LM microchannels with controllable shapes can be obtained by LM transfer and subsequent encapsulation. Since the smallest microchannel thickness is only â¼25 µm, sensor stress resolution can reach 0.0168 kPa without any additional parts to amplify the effect of pressure. As proof-of-concept demonstrations, the sensor is used for sensing the dynamic movement of a small sphere (â¼0.16 g) and even an ant (â¼0.025 g). LISAT provides a versatile platform for fabricating high-stress-resolution LM pressure sensors with controllable patterns and device structures to adapt to different application scenarios.
Dynamic self-assembly of micropillars has found wide applications in targeted trapping, micro-crystallization and plasmonic sensing. Yet the efficient fabrication of micropillars array with high flexibility still remains a grand challenge. In this Letter, holographic femtosecond laser multi-foci beams (fs-MFBs) based on a spatial light modulator (SLM) is adopted to efficiently create micropillars array with controllable geometry and spatial distribution by predesigning the computer-generated holograms (CGHs). Based on these micropillars array, diverse hierarchical assemblies are formed under the evaporation-induced capillary force. Moreover, taking advantage of the excellent flexibility and controllability of fs-MFBs, on-demand one-bead-to-one-trap of targeted microspheres at arbitrary position is demonstrated with unprecedentedly high capture efficiency, unfolding their potential applications in the fields of microfluidics and biomedical engineering.
Nature-inspired magnetically responsive intelligent topography surfaces have attracted considerable attention owing to their controllable droplet manipulation abilities. However, it is still challenging for magnetically responsive surfaces to realize three-dimensional (3D) droplet/multidroplet transport in both horizontal and vertical directions. Additionally, the droplet horizontal propulsion speed needs to be improved. In this work, a 3D droplet/multidroplet transport strategy based on magnetically responsive microplates array (MMA) actuated by a spatially varying and periodic magnetic field is proposed. The modified superhydrophobic surface can transport droplets rapidly both in horizontal and vertical directions, and it can even realize against-gravity upslope propulsion. The rapid horizontal droplet propulsion (â¼58.6 mm/s) is ascribed to the abrupt inversion of the modified surface induced by the specific magnetic field. Furthermore, the nonmagnetically responsive microplates (NMMs)/MMA composite surface is constructed to realize 3D multidroplet manipulation. The implementations of MMA in manipulation of continuous fluids and liquid metal are further demonstrated, providing a valuable platform for microfluidic applications.
Natural evolution has endowed diverse species with distinct geometric micro/nanostructures exhibiting admirable functions. Examples include anisotropic microgrooves/microstripes on the rice leaf surface for passive liquid directional rolling, and motile microcilia widely existed in mammals' body for active matter transportation through in situ oscillation. Till now, bionic studies have been extensively performed by imitating a single specific biologic functional system. However, bionic fabrication of devices integrating multispecies architectures is rarely reported, which may sparkle more fascinating functionalities beyond natural findings. Here, a cross-species design strategy is adopted by combining the anisotropic wettability of the rice leaf surface and the directional transportation characteristics of motile cilia. High-aspect-ratio magnetically responsive microcolumn array (HAR-MRMA) is prepared for active droplet transportation. It is found that just like the motile microcilia, the unidirectional waves are formed by the real-time reconstruction of the microcolumn array under the moving magnetic field, enabling droplet (1-6 µL) to transport along the predetermined anisotropic orbit. Meanwhile, on-demand droplet horizontal transportation on the inclined plane can be realized by the rice leaf-like anisotropic surface, showcasing active nongravity-driven droplet transportation capability of the HAR-MRMA. The directional lossless transportation of droplet holds great potential in the fields of microfluidics, chemical microreaction, and intelligent droplet control system.
Cilia/chemistry , Oryza/chemistry , Plant Leaves/chemistry , Anisotropy , Particle Size , Surface Properties , Wettability
Efficient calculation of the light diffraction in free space is of great significance for tracing electromagnetic field propagation and predicting the performance of optical systems such as microscopy, photolithography, and manipulation. However, existing calculation methods suffer from low computational efficiency and poor flexibility. Here, we present a fast and flexible calculation method for computing scalar and vector diffraction in the corresponding optical regimes using the Bluestein method. The computation time can be substantially reduced to the sub-second level, which is 105 faster than that achieved by the direct integration approach (~hours level) and 102 faster than that achieved by the fast Fourier transform method (~minutes level). The high efficiency facilitates the ultrafast evaluation of light propagation in diverse optical systems. Furthermore, the region of interest and the sampling numbers can be arbitrarily chosen, endowing the proposed method with superior flexibility. Based on these results, full-path calculation of a complex optical system is readily demonstrated and verified by experimental results, laying a foundation for real-time light field analysis for realistic optical implementation such as imaging, laser processing, and optical manipulation.
Artificial microstructures composed of chiral building blocks are of great significance in the fields of optics and mechanics. Here, it is shown that highly ordered chiral structures can be spontaneously assembled by a meniscus-directed capillary force arising in an evaporating liquid. The chirality is facilitated by rationally breaking the intrinsic symmetry in the unit cells through cooperative control of the geometry and spatial topology of the micropillars. The interfacial dynamics of the assembly process are studied to show that the sequential self-organization of the micropillars is influenced by the geometries, stiffness, and spatial arrangements. A diversity of chiral assemblies with controlled handedness is yielded by varying the pillar number, height, cross-section, laser power, and spatial topology. Lastly, the differential reflectance of light carrying opposite orbital angular momentums on the assembled chiral architectures are investigated, showcasing their potential in the field of chiral photonics concerning enantioselective response and exceptional optical functions.
In this Letter, we demonstrate a laser fabrication strategy that uses the long focal depth femtosecond axilens laser beam to manufacture the high-aspect-ratio (HAR) micropillars and atomic force microscopy (AFM) probes by one-step exposure. The long depth of focus is generated by modulating laser beam focused at different positions. By adjusting the exposure height, the morphology of HAR micropillars can be tuned flexibly, and the micropillar with an ultra-high aspect ratio (diameter of 1.5 µm, height of 102 µm, ${\rm AR}={70}$AR=70) can be fabricated within 10 ms which is a great challenge for other processing methods to obtain such a HAR microstructure in such a short time. In addition, the HAR micropillar is fabricated onto a cantilever to form the AFM probe. The homemade probe shows fine imaging quality. This method greatly improves the processing efficiency while ensuring the fabrication resolution which provides a powerful method for processing HAR microstructures.
Thermally responsive paraffin-infused slippery surfaces have demonstrated intriguing performance in manipulating the behaviors of versatile droplets. However, present methods have been limited to ex situ rigid heat sources with a high voltage of 220 V or certain specific photothermal materials, which greatly hinders its practical applications. To solve this problem, an intelligent droplet motion control actuator (DMCA) composed of paraffin wax, hydrophobic micropillar-arrayed ZnO film, and a flexible transparent silver nanowire heater (SNWH) is reported in this work. Due to the good portability of DMCA, in situ switchable wettability for several liquid droplets with different surface tensions can be achieved by simply loading and unloading Joule heat at an ultra-low voltage (12 V). The relationship among sliding velocity and droplet volume and inclined angles was quantitatively investigated. By virtue of the flexible and mechanical endurance, this smart DMCA is dramatically functional for droplet motion manipulation ( e.g., reversible control between sliding and pinning) on complex 3D surfaces. Significantly, an impressive self-healing ability within 22 s is also demonstrated through the in situ application of Joule heat on the scratched DMCA, which renders its practical usability in various harsh conditions. This work provides insights for designing intelligent, flexible, and portable actuators dealing with the challenges of smart temperature-responsive surfaces.
Structured laser beam based microfabrication technology provides a rapid and flexible way to create some special microstructures. As an important member in the propagation of invariant structured optical fields, Mathieu beams (MBs) exhibit regular intensity distribution and diverse controllable parameters, which makes it extremely suitable for flexible fabrication of functional microstructures. In this study, MBs are generated by a phase-only spatial light modulator (SLM) and used for femtosecond laser two-photon polymerization (TPP) fabrication. Based on structured beams, a dynamic holographic processing method for controllable three-dimensional (3D) microcage fabrication has been presented. MBs with diverse intensity distributions are generated by controlling the phase factors imprinted on MBs with a SLM, including feature parity, ellipticity parameter q, and integer m. The focusing properties of MBs in a high numerical aperture laser microfabrication system are theoretically and experimentally investigated. On this basis, complex two-dimensional microstructures and functional 3D microcages are rapidly and flexibly fabricated by the controllable patterned focus, which enhances the fabrication speed by 2 orders of magnitude compared with conventional single-point TPP. The fabricated microcages act as a nontrivial tool for trapping and sorting microparticles with different sizes. Finally, culturing of budding yeasts is investigated with these microcages, which demonstrates its application as 3D cell culture scaffolds.
Smart dynamic regulation structured surfaces, inspired by nature, which can dynamically change their surface topographies under external stimuli for convertible fluidic and optical properties, have recently motivated significant interest for scientific research and industrial applications. However, there is still high demand for the development of multifunctional dynamically transformable surfaces using facile preparation strategies. In this work, a type of Janus high-aspect-ratio magnetically responsive microplates array (HAR-MMA) is readily fabricated by integrating a flexible laser scanning strategy, smart shape-memory-polymer-based soft transfer, and a simple surface treatment. By applying external magnetic field, instantaneous and reversible deformation of Janus HAR-MMA can be actuated, so surface wettability can be reversibly switched between superhydrophobic (158°) and hydrophilic (40°) states, based on which a novel magnetically responsive water droplet switch can be realized. Moreover, inspired by the biological assimilatory coloration of chameleons, dynamically color conversion can be skillfully realized by applying different colors on each side of the Janus HAR-MMA. Finally, as a proof-of-concept demonstration in light manipulation, a HAR-MMA is applied as an optical shutter actuated by external magnetic field with eximious controllability and repeatability. The developed multifunctional HAR-MMA provides a versatile platform for microfluidic, biomedical, and optical applications.
Capillary-force-driven self-assembly (CFSA) has been combined with many top-down fabrication methods to be alternatives to conventional single micro/nano manufacturing techniques for constructing complicated micro/nanostructures. However, most CFSA structures are fabricated on a rigid substrate, and little attention is paid to the tuning of CFSA, which means that the pattern of structures cannot be regulated once they are manufactured. Here, by combining femtosecond laser direct writing with CFSA, a flexible method is proposed to fabricate self-assembled hierarchical structures on a soft substrate. Then, the tuning of the self-assembly process is realized with a mechanical-stretching strategy. With this method, different patterns of tunable self-assembled structures are obtained before tuning and after release, which is difficult to achieve with other techniques. In addition, as a proof-of-concept application, this mechanical tunable self-assembly of microstructures on a soft substrate is used for smart displays and versatile micro-object trapping.
Recently, interactions between one-dimensional structural stiffness of physical micro environments and cell biological process have been widely studied. However in previous studies, the influence of structural stiffness on biological process was coupled with the influence of micro fiber curvature. Therefore decoupling the influences of fiber curvature and structural stiffness on cell biological process is of prime importance. In this study, we proposed a novel cell culture substrate comprised of silicon nitride bridges whose structure stiffness can be regulated by altering the axial residual stress without changing material and geometry properties. Both theoretical calculations and finite element simulations were performed to study the influence of residual stress on structure stiffness of bridges. Then multi-positions AFM bending tests were implemented to measure local stiffness of a single micro bridge so as to verify our predictions. NIH/3T3 mouse fibroblast cells were cultured on our substrates to examine the feasibility of the substrate application for investigating cellular response to microenvironment with variable stiffness. The results showed that cells on the edge region near bridge ends were more spread, elongated and better aligned along the bridge axial direction than those on the bridge center region. The results suggest that cells can sense and respond to the differences of stiffness and stiffness gradient between the edge and the center region of the bridges, which makes this kind of substrates can be applied in some biomedical fields, such as cell migration and wound healing.
Cell Culture Techniques/methods , Fibroblasts/cytology , Silicon Compounds/chemistry , 3T3 Cells , Animals , Fibroblasts/metabolism , Mice
Although fundamental efforts have been made to engineer circular smooth muscle layers in vitro, engineering structured skeletal muscle tissue equivalents acting as sphincters remains to be investigated. Groove patterned substrates made of homogeneous materials usually lead to cell monolayers instead of patterned cell sheets while patterned matrices failed to generate circular myotubes because cell chirality blocks the end-to-end cellular sequence corresponding to pattern directions. In this paper, we proposed concentric circular and elliptical microgroove patterned substrates with glass substrates as grooves and polymers as ridges to direct ring-shaped myoblast patterns and maximize cell alignment with respect to constraint directions, which are essential for circular myotube generation towards sphincter tissue engineering. Our results showed that our substrates direct myoblasts to proliferate in and orient along the directions of glass grooves, leading to a higher cell alignment degree than homogeneous substrates can achieve. We also found that the cell alignment degree depends on dimensions and parallelism rather than the curvature of the constraint. On the basis of these findings, we proposed finite element models that quantitatively account for our experimental data and emphasized the role of intercellular forces in cell alignment modulation. These results suggest that narrow curved constraints with parallel boundaries can favourably maximize myoblast alignment and facilitate myogenic differentiation regardless of constraint curvature, which will underpin the design of substrates and scaffolds for urethral sphincter or other hollow tissue engineering applications.
