Hierarchical Microchannel Research Articles

Recyclable wood-structured bimetallic carbon aerogel for high-performance bulk catalytic antibiotic decomposition

Harnessing renewable low-cost, bulk wood-structured materials with highly porous, anisotropic and compressible properties that fulfills sustainable water purification is imperative yet still challenging to push forward a circular bioeconomy. In this work, a bimetallic Fe-Co implanted, N-doped wood carbon aerogel (Fe-Co/NWCA) is constructed to guarantee the facile regeneration in high-performance catalytic antibiotic decomposition via activating peroxymonosulfate (PMS). A rapid, reversible and excellent tetracycline (TC) elimination performance (∼90% in 12 min) within a wide pH range of 3–11 is achieved by Fe-Co/NWCA-mediated system. Importantly, the as-prepared hydrophilic Fe-Co/NWCA not only delivers a favorable robustness to interfering anions (e.g., Cl−, H2PO4− and HCO3−), but also presents a superior recyclability with over 90% retention after the fourth cycling operation via a convenient squeezing behavior. Integration of radical quenching experiments and electron paramagnetic resonance demonstrates the participation of reactive oxygen species (ROS) into catalytic TC oxidation, wherein the dominant contributor is 1O2 followed by O2•‾, SO4•‾ and •OH. As an important non-radical route, the directly interfacial electron transfer is confirmed by electrochemical measurements and density-functional-theory computations. In the context of activating PMS, the multi-valent Fe, Co-coordinated species function as the redox reactive site to trigger diversiform ROS with accelerated kinetics, while N, O-associated surface defects and unsaturated functional groups (e.g., −COOH and ketonic C=O) contribute to the 1O2 formation and electron shuttling. This universal approach paves a critical avenue to manufacture the reactive wood-based aerogels with hierarchical microchannels in the practical pollutant remediation, shedding the valuable insights on multifunctional biomass-water nexus.

Vascular tissue-derived hard carbon with ultra-high rate capability for sodium-ion storage

Vascular tissue helps quickly pass the nutrients and water through the plant. Inspiringly, the transport of electrolyte solutions within such biological tissue may also play an essential role in governing the high-current performance of sodium-ion storage. Herein, we report a facile and efficient approach to fabricate a vascular tissue-derived hard carbon (VHC) by an integrated procedure of leave stripping, carbonization and alkali/acid washing. By meticulously adjusting the pyrolysis temperatures, hierarchical microchannel carbon with abundant turbostratic nanodomains, suitable pore size and special surface functional groups can be obtained, enabling high specific capacity and excellent rate performances. It is believed that the vascular tissue-derived carbon can significantly shorten sodium ion transport paths and further enhance the storage performance on the surface and within the electrode materials, making it a promising candidate for sodium-ion batteries.

OpenFOAM-based Numerical Simulation on Capillary Flow in Closed Hierarchical Microchannels

OpenFOAM-based Numerical Simulation on Capillary Flow in Closed Hierarchical Microchannels

Spontaneous Separation of Immiscible Organic Droplets on Asymmetric Wedge Channels with Hierarchical Microchannels.

Spontaneous separation of immiscible organic droplets has substantial research implications for environmental protection and resource regeneration. Compared to the widely explored separation of oil-water mixtures, there are fewer reports on separating mixed organic droplets on open surfaces due to the low surface tension differences. Efficient separation of mixed organic liquids by exploiting the rapid spontaneous transport of droplets on open surfaces remains a challenge. Here, through the fusion of inspiration from the fast droplet transport capability of Sarracenia trichome and the asymmetric wedge channel structure of shorebird beaks, this work proposes a spine with hierarchical microchannels and wedge channels (SHMW). Due to the synergistic effect of capillary force and asymmetric Laplace force, the SHMW can rapidly separate mixed organic droplets into two pure phases without requiring additional energy. In particular, the self-spreading of the oil solution on the open channel surface is utilized to amplify the surface energy difference between two droplets, and SHMW achieves the pickup of oil droplets floating on the surface of the organic solution. The maximum separation efficiency on 3-SHMW can reach 99.63%, and it can also realize the antigravity separation of mixed organic droplets with a surface tension difference as low as 0.87 mN·m-1. Furthermore, SHMW performs controllable separation, oil droplet pickup, and continuous separation and collection of mixed organic droplets. It is expected that this cooperative structure composed of hierarchical microchannels and wedge channels will be realized in resource recovery or chemical reactions in industrial production processes.

Secondary vortex drag reduction and heat transfer enhancement of nanofluids in hierarchical microchannels applied to thermal management of electronic components

In order to improve the heat dissipation performance of electronic components, two hierarchical microchannel structures with curve and straight corners are proposed, and semi-circular and trapezoidal secondary flow structures are introduced into the structure with the best performance. The effects of coolant (Fe3O4-water nanofluid), layered structure and secondary flow structure on the comprehensive performance of MCHS were studied by numerical simulation. Results showed that deionized water is more suitable for the heat dissipation of microchannels at this scale. The hierarchical structure has the effect of enhancing heat transfer, and Nu can be increased by up to 67.32 %. The introduction of secondary flow structure has drag reduction effect in a certain Reynolds number range. The hierarchical MCHS with semi-circular secondary flow structure has drag reduction effect in the Reynolds number range of Re = 200–400, and the pressure drop can be reduced by up to 1.89 %. The hierarchical MCHS with trapezoidal secondary flow structure always has a drag reduction effect in the range of Reynolds number Re = 200–600, and the maximum pressure drop can be reduced by 2.46 %, showing excellent drag reduction ability. In addition, the introduction of trapezoidal secondary flow in MCHS increases the Nusselt number by 9.70 %, the comprehensive performance index reaches 1.10, and the cooling performance and comprehensive performance are optimal. The combination of hierarchical structure and secondary flow structure has excellent drag reduction and heat transfer enhancement effects, and has broad application prospects in the field of thermal management of electronic devices.

Thermal management of electronic components based on hierarchical microchannels and nanofluids

In order to enhance the heat dissipation of electronic components, hierarchical microchannels and nanofluids were applied into the thermal management of electronic components in this paper. Two kinds of hierarchical microchannels (rectangular microchannels and circular microchannels) were considered, and three different channel equivalent diameters (microchannel-a, microchannel-b, microchannel-c) of microchannel were analyzed. In addition to above factors, influence of nanoparticle concentration on the pressure drop, cooling uniformity, thermal resistance, and heat transfer coefficient was studied. For rectangular microchannel, microchannel-a has the lowest cooling uniformity and microchannel-b has the highest heat transfer coefficient, but for circular microchannel, microchannel-b has the lowest cooling uniformity and microchannel-a has the highest heat transfer coefficient. The comprehensive performance index of the microchannel was also studied. It can be concluded that the rectangular microchannel has a lower comprehensive evaluation coefficient than the circular microchannel. The maximum PEC of rectangular microchannel is 1.08, and the circular microchannel can reach 1.26. However, the heat transfer capacity of the rectangular microchannel is stronger, and the thermal resistance is about 0.00005 smaller than that of the circular microchannel.

Hierarchically patterned protein scaffolds with nano-fibrillar and micro-lamellar structures modulate neural stem cell homing and promote neuronal differentiation.

Biophysical factors are essential in cell survival and behaviors, but constructing a suitable 3D microenvironment for the recruitment of stem cells and exerting their physiological functions remain a daunting challenge. Here, we present a novel silk fibroin (SF)-based fabrication strategy to develop hierarchical microchannel scaffolds for biomimetic nerve microenvironments in vitro. We first modulated the formation of SF nanofibers (SFNFs) that mimic the nanostructures of the native extracellular matrix (ECM) by using graphene oxide (GO) nanosheets as templates. Then, SFNF-GO systems were shaped into 3D porous scaffolds with aligned micro-lamellar structures by freeze-casting. The interconnected microchannels successfully induced cell infiltration and migration to the SFNF-GO scaffolds' interior. Meanwhile, the nano-fibrillar structures and the GO component significantly induced neural stem cells (NSCs) to differentiate into neurons within a short timeframe of 14 d. Importantly, these 3D hierarchical scaffolds induced a mild inflammatory response, extensive cell recruitment, and effective stimulation of NSC neuronal differentiation when implanted in vivo. Therefore, these SFNF-GO lamellar scaffolds with distinctive nano-/micro-topographies hold promise in the fields of nerve injury repair and regenerative medicine.

High-Efficient Fog Harvest from a Synergistic Effect of Coupling Hierarchical Structures.

Fog harvesting is an important method to solve the water shortage in arid and semi-arid areas by collecting water from air. Improving fog harvesting efficiency is still a big challenge to be overcome. Herein, under the inspiration of natural creatures, a novel harvesting structure that couples a hierarchical microchannel (HMC) needle with the Janus membrane by taking a conical pore as their junction is proposed. Such an HMC-conical pore-Janus membrane system can improve the harvesting efficiency by regulation of liquid behavior in the whole fog harvesting process involving droplet capture from air, high speed transport on the microchannel, and droplet detachment from Janus. The synergistic effects of the hierarchical channel-conical pore-Janus structure are exploited in terms of capture, transport, and detachment capabilities, and their underlying mechanism to enhance fog harvesting efficiency is built. Compared with the traditional harvesting structure, the proposed hierarchical channel-conical-Janus coupling mode was demonstrated to improve fog harvesting efficiency by 90%. Such a coupled system has potential applications in efficient fog harvesting systems, microfluidic devices, and liquid manipulation.

3D bioprinting of osteon-mimetic scaffolds with hierarchical microchannels for vascularized bone tissue regeneration

The integration of three-dimensional (3D) bioprinted scaffold’s structure and function for critical-size bone defect repair is of immense significance. Inspired by the basic component of innate cortical bone tissue—osteons, many studies focus on biomimetic strategy. However, the complexity of hierarchical microchannels in the osteon, the requirement of mechanical strength of bone, and the biological function of angiogenesis and osteogenesis remain challenges in the fabrication of osteon-mimetic scaffolds. Therefore, we successfully built mimetic scaffolds with vertically central medullary canals, peripheral Haversian canals, and transverse Volkmann canals structures simultaneously by 3D bioprinting technology using polycaprolactone and bioink loading with bone marrow mesenchymal stem cells and bone morphogenetic protein-4. Subsequently, endothelial progenitor cells were seeded into the canals to enhance angiogenesis. The porosity and compressive properties of bioprinted scaffolds could be well controlled by altering the structure and canal numbers of the scaffolds. The osteon-mimetic scaffolds showed satisfactory biocompatibility and promotion of angiogenesis and osteogenesis in vitro and prompted the new blood vessels and new bone formation in vivo. In summary, this study proposes a biomimetic strategy for fabricating structured and functionalized 3D bioprinted scaffolds for vascularized bone tissue regeneration.

Highly Efficient Multiscale Fog Collector Inspired by Sarracenia Trichome Hierarchical Structure (Global Challenges 12/2021)

In article 2100087, Huawei Chen and co-workers design a bionic Sarracenia trichome with an on-demand regular hierarchical microchannel to achieve excellent fog harvesting and transport properties. With the combination of a Janus membrane, a highly efficient multiscale fog collector is developed, in which a gradient high-pressure field is purposely formed to improve, by threefold, fog harvesting performance compared with a single-scale structure.

Enhanced Fog Harvesting through Capillary-Assisted Rapid Transport of Droplet Confined in the Given Microchannel

A novel integrated bioinspired surface is fabricated by using an innovative capillarity-induced selective oxidation method, to achieve the combination of the fog-collecting characteristics of a variety of creatures, i.e., the micronanostructures of spider silk, the wettable patterns of desert beetle, the conical structure of cactus spine, and the hierarchical microchannel of Sarracenia trichome. The fog is captured effectively via multistructures on the cone tips, and captured droplet is collected and confined in the microchannel to realize rapid transport via the formation of wettable pattern on the surface and the introduction of wettable gradient in the microchannel. Consequently, the fog harvest efficiency reaches 2.48 g/h, increasing to nearly 320% compared to the normal surface. More interestingly, similar to Sarracenia trichome, the surface also presents two transport modes, namely, Mode I (water transport along dry microchannel) and Mode II (succeeding water slippage on the water film). In Mode II, the velocity of 34.10 mm/s is about three times faster than that on the Sarracenia trichome. Such a design of integrated bioinspired surface may present potential applications in high-efficiency water collection systems, microfluidic devices, and others.

Development of a hierarchical microchannel heat sink with flow field reconstruction and low thermal resistance for high heat flux dissipation

With the development of microelectronics, power density continues to rise, which has put forward higher requirements for the thermal management. At present, the microchannel heat sinks have been investigated as an efficient way for heat dissipation for a long time. However, the optimization of microchannel heat sink is always concentrated on two-dimensional plane structure. In this paper, we proposed a hierarchical microchannel heat sink for heat transfer enhancement. Taking micro pin fin as an example, we designed three different hierarchical pin fins, and the model with the best performance is obtained through simulation under the Reynolds number from 1500 to 5500. The hierarchical heat sink shows better heat transfer performance than traditional heat sink, which is attributed to the flow field reconstruction with no significant increase in pressure drop. Typically, when the upper size (Wp1) of hierarchical pin fin increases to 375 μm, the maximum Nusselt number reaches 21 with the thermal performance factor up to 1.03 under the Reynolds number of 5500. Experimentally, three sizes of pin fins have been prepared and examined, and the results show that the heat loads exceeding 700 W/cm2 can be dissipated with the maximum temperature rise of 52 K, which is well matched with the simulation results. Anyway, the proposed in this work shows great potential in heat dissipation of electronics.

Highly Efficient Multiscale Fog Collector Inspired by Sarracenia Trichome Hierarchical Structure.

Fog harvesting through bionic strategies to solve water shortage has drawn considerable attention. Recently, an ultrafast fog harvesting and transport mode was identified in Sarracenia trichome, which is mainly attributed to its superslippery capillary force induced by its unique hierarchical microchannel. However, the underlying effect of hierarchical microchannel‐induced ultrafast transport on fog harvesting and the multiscale structural coupling effect on highly efficient fog harvesting are still great challenges. Herein, a bionic Sarracenia trichome (BST) with an on‐demand regular hierarchical microchannel is designed using a one‐step thermoplastic stretching approach on a glass fiber bundle. The BST is engineered to harbor major channels confined by an inner gear pattern along with junior microchannels that are automatically assembled by the glass fiber monofilaments. The BST shows enhanced capillary condensation and fog harvesting performance, in part due to its coupling effect with a Janus membrane (JM). Hence, a highly efficient multiscale fog collector is developed, in which a gradient high‐pressure field is purposely formed to improve by threefold fog harvesting performance compared with a single‐scale structure. This easy manufacturing and low‐cost fog collector may represent a useful tool for harvesting fog water for production and living and pave the way for further investigations.

A perfusable, multifunctional epicardial device improves cardiac function and tissue repair.

Despite advances in technologies for cardiac repair after myocardial infarction (MI), new integrated therapeutic approaches still need to be developed. In this study, we designed a perfusable, multifunctional epicardial device (PerMed) consisting of a biodegradable elastic patch (BEP), permeable hierarchical microchannel networks (PHMs) and a system to enable delivery of therapeutic agents from a subcutaneously implanted pump. After its implantation into the epicardium, the BEP is designed to provide mechanical cues for ventricular remodeling, and the PHMs are designed to facilitate angiogenesis and allow for infiltration of reparative cells. In a rat model of MI, implantation of the PerMed improved ventricular function. When connected to a pump, the PerMed enabled targeted, sustained and stable release of platelet-derived growth factor-BB, amplifying the efficacy of cardiac repair as compared to the device without a pump. We also demonstrated the feasibility of minimally invasive surgical PerMed implantation in pigs, demonstrating its promise for clinical translation to treat heart disease.

Hierarchical Microchannel Carbons Derived from Biological Phloem Tissues as High-Performance Anode for Lithium-Ion Batteries

With the upgrading of consumption, the existing carbon-based anode materials are facing the major challenges of high preparation cost and low initial Coulomb efficiency. The fast-growing and developed sieve tube network is an inspiration to transform cattail phloem tissue (CPT) into a high-performance carbon-based anode for lithium-ion battery. In this study, porous carbon materials from CPT with abundant microchannel and nanochannel were prepared by a top-down strategy combined with an indispensable passivation process. The sidewall and end of the sieve tube are fully covered by a large number of pore structures and various supporting cells, thus ensuring the stiffness and tensile strength of phloem tissue. And benefiting from the neoteric hierarchical porous structure without Li⁺ trapping sites, the cells with CPT anode showed high electrochemical performance. For the passivated CPT electrode, the reversible capacity increased to 321.6 mAh/g, and the initial Coulomb efficiency was 1.47 times higher than that of the passivated CPT electrode. The CPT exhibits excellent rate performance under high current, which indicates that the abundant pore structure on the surface of the sieve tube is an effective measure to improve ion diffusion. Besides, the generation mechanism of high-performance CPT is analyzed through microstructure characterization. The improvement of electrochemical performance of CPT in this work has provided a clear strategy for the application of resource-rich natural biomass to electrochemical products.

Ultra-strong capillarity of bioinspired micro/nanotunnels in organic cathodes enabled high-performance all-organic sodium-ion full batteries

As one of the typical organic cathode materials for sodium ion batteries (SIBs), 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is formidably challenged in practical applications because of its low electrical conductivity, sluggish reaction kinetics, inferior rate capability and cycle life. Inspired by the ultra-strong capillarity of wood’s aligned hierarchical microchannels toward ions and water during metabolism, we have designed a novel composite nanofibrous organic cathode consisting of PTCDA/nitrogen-doped carbon/carbon nanotubes (PTCDA/NC/CNT) for SIBs. The PTCDA/NC/CNT cathode exhibits rapid ionic/electronic transport properties and ultrafast reaction kinetics owing to the synergistic effects of the interconnected conductive frameworks and ultra-strong capillarity deriving from the hierarchical micro/nanotunnels. As a result, a highly reversible capacity of 135.6 mA h g−1 at 50 mA g−1, excellent rate performance and ultra-long cyclic stability with over 95% capacity retention after 500 cycles at 1000 mA g−1 are achieved for the PTCDA/NC/CNT cathode in SIBs. Remarkably, an all-organic battery using the PTCDA/NC/CNT cathode and conjugated sodium carboxylate/CNT anode also delivers a high energy density of 85 W h kg−1 at a power density of 665 W kg−1. This bio-inspired design provides a promising strategy for the development of next-generation all-organic sodium-ion full batteries.

Modulated vibration texturing of hierarchical microchannels with controllable profiles and orientations

Hierarchical microchannels, which consist of the primary channel formation and superimposed secondary nanostructures, are attracting ever-increasing attention due to their unique capacity to enhance and modify the surface characteristics and functional performance. The mechanical machining methods for microchannel fabrication, such as micro-milling and diamond turning, can achieve high material removal rates without changing material properties. However, they have limited capacity to control the channel cross-section profiles and shapes due to the relative size between the channel dimension and tool geometry. This study proposes a new cutting-based approach for the fast and cost-effective fabrication of hierarchical microchannels with controllable profiles and orientations by utilizing modulated elliptical vibration texturing. The modulation motion is adopted to form the primary channel in an incremental approach, while the elliptical vibration texturing is utilized to create micro/nano-scale secondary textures. By controlling the tool modulation trajectory, hierarchical dimple arrays with controllable cross-section profiles are first demonstrated. Then, by programming the layout of dimples to adjust the overlapping ratio between each cut, channels can be formed with arbitrary cross-section profiles and orientations. The efficacy of the proposed process has been demonstrated through numerical simulation and experimental results. Hierarchical microchannels with straight and curving shapes, as well as different cross-section profiles (sinusoidal, triangular, trapezoidal), have been presented.

Laser Direct Structuring of Bioinspired Spine with Backward Microbarbs and Hierarchical Microchannels for Ultrafast Water Transport and Efficient Fog Harvesting.

Achieving effective dropwise capture and ultrafast water transport is essential for fog harvesting. In nature, cactus uses the conical spine with microbarbs to effectively capture fog, while Sarracenia utilizes the trichome with hierarchical microchannels to quickly transport water. Herein, we combined their advantages to present a novel configuration, a spine with barbs and hierarchical channels (SBHC), for simultaneous ultrafast water transport and high-efficient fog harvesting. This bioinspired SBHC exhibited the fastest water transport ability and the highest fog harvesting efficiency in comparison with the spine with hierarchical channels (SHCs), the spine with barbs and grooves (SBG), and the spine with barbs (SB). Based on the fundamental SBHC unit, we further designed and fabricated a two-dimensional (2D) spider-web-like fog collector and a three-dimensional (3D) cactus-like fog collector using direct laser structuring and origami techniques. The 2D spider-web and 3D cactus-like fog collectors showed high-efficient fog collection capacity. We envision that this fundamental understanding and rational design strategy can be applied in fog harvesting, heat transfer, liquid manipulation, and microfluidics.

Three-Dimensional Bioprinting of Perfusable Hierarchical Microchannels with Alginate and Silk Fibroin Double Cross-linked Network.

Vascularization is essential for the regeneration of three-dimensional (3D) bioprinting organs. As a general method to produce microfluidic channels in 3D printing constructs, coaxial extrusion has attracted great attention. However, the biocompatible bioinks are very limited for coaxial extrusion to fabricate microchannels with regular structure and enough mechanical properties. Herein, a hybrid bioink composed of alginate (Alg) and silk fibroin (SF) was proposed for 3D bioprinting of microchannel networks based on coaxial extrusion. The rheological properties of the bioink demonstrated that the hybrid Alg/SF bioink exhibited improved viscosity and shear thinning behavior compared with either pure Alg or SF bioink and had similar storage and loss modulus in a wide range of shear frequency, indicating a sound printability. Using a coaxial extrusion system with calcium ions and Pluronic F127 flowing through the core nozzle as cross-linkers, the Alg/SF bioink could be extruded and deposited to form a 3D scaffold with interconnected microchannels. The regular structure and smooth pore wall of microchannels inside the scaffold were demonstrated by optical coherence tomography. Micropores left by the rinse of F127 were observed by scanning electron microscope, constituting a hierarchical structure together with the microchannels and printed macropores. Fourier transform infrared spectroscopy analysis proved the complete rinse of F127 and the formation of β-sheet SF structure. Thus, Alg/SF could form a double cross-linked network, which was much stronger than the pure Alg network. Moreover, cells in the Alg/SF scaffold showed higher viability and proliferation rate than in the Alg scaffold. Therefore, Alg/SF is a promising bioink for coaxial extrusion-based 3D bioprinting, with the printed microchannel network beneficial for complex tissue and organ regeneration.

Hierarchical microchannel architecture in chitosan/bioactive glass scaffolds via electrophoretic deposition positive-replica.

One of the main challenges in the design of scaffolds for cortical bone regeneration is mimicking the highly oriented, hierarchical structure of the native tissue in an efficient, simple, and consistent way. As a possible solution to this challenge, positive replica based on electrophoretic deposition (EPD) was here evaluated as a technique to produce organic/inorganic scaffolds with oriented micro-porosities mimicking Haversian canals diameter and spacing. Two different sizes of 45S5 bioactive glass (BG) powders were chosen as inclusions and loaded in a chitosan matrix via EPD on micro-patterned cathodes. Self-standing chitosan scaffolds, with a homogeneous dispersion of BG particles and regularly-oriented micro-channels (ϕ = 380 ± 50 μm, inter-channel spacing = 600 ± 40 μm), were obtained. In vitro analysis in simulated body fluid (SBF) revealed the ability to induce a deposition of a homogenous layer of hydroxyapatite (HA), with Ca/P nucleation reactions appearing kinetically favored by smaller BG particles. Cell interaction with hybrid scaffolds was evaluated in vitro with bone osteosarcoma cells (SAOS-2). The osteoconductive potential of EPD structures was assessed by evaluating cells proliferation, viability and scaffold colonization. Results indicate that EPD is a simple yet extremely effective technique to prepare composite micro-patterned structures and can represent a platform for the development of a new generation of bone scaffolds. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.