Interconnected Microchannels Research Articles

Preparation and Characterization of Ni-Mn-Ga-Cu Shape Memory Alloy with Micron-Scale Pores

Porous Ni-Mn-Ga shape memory alloys (SMAs) were prepared by powder metallurgy using NaCl as a pore-forming agent with an average pore size of 20–30 μm. The microstructure, phase transformation, superelasticity, and elastocaloric properties of the porous alloys were investigated. The prepared porous alloy had a uniform pore distribution and interconnected microchannels were formed. Cu doping can effectively improve the toughness of a porous alloy, thus improving the superelasticity. It was found that porous Ni-Mn-Ga-Cu SMAs have a flat stress plateau, which exhibits a maximum elongation of 5% with partially recoverable strain and a critical stress for martensite transformation as low as about 160 MPa. In addition, an adiabatic temperature change of 0.6 K was obtained for the prepared porous alloy at a strain of 1.2% at about 150 MPa. This work confirms that the introduction of porous structures into polycrystalline Ni-Mn-Ga SMAs is an effective way to reduce costs and improve performance, and provides opportunities for engineering applications.

Three-dimensional numerical investigation on flow and heat transfer characteristics and multi-objective optimization of interconnected microchannels

The interconnected microchannel demonstrates excellent performance in enhancing flow heat transfer. However, the optimal width of the interconnecting slot has not been thoroughly investigated. To address this gap, this paper numerically simulates the three-dimensional flow and heat transfer of interconnected microchannels featuring varied slot widths and channel depths. The investigated slot widths range from 50 to 1000 μm and depths of 100, 200, and 300 μm. Evaluation of overall performance encompasses heat transfer and flow characteristics such as average wall temperature, heat transfer coefficient, thermal resistance as well as pressure drop. It is the interconnected slots that interrupt the velocity and thermal boundary layers, contributing to enhanced heat transfer. Furthermore, the back propagation neural network and non-dominated sorting genetic algorithm-II are utilized for multi-objective optimization of thermal resistance and pressure drop. The technique for order preference by similarity to an ideal solution (TOPSIS) method combined with the entropy weight method is employed to select the compromise optimal solution from the Pareto optimal solutions. The optimized slot widths are 369, 424, and 167 μm for channel depths of 100, 200, and 300 μm, respectively. This research provides data support for the optimization design and engineering manufacturing of interconnected microchannels.

Advanced fabrication of polymer waveguide interferometric sensor utilizing interconnected holey fibers

A universally applicable approach is proposed for the fabrication of fiber-optic polymer sensors. The hollow-core fibers (HCFs) with inner diameters of 30 µm, 50 µm, and 75 µm are spliced coaxially with dual-hole fiber (DHF) or photonic crystal fiber (PCF). Owing to the sized-matched air holes within HCF and DHF/PCF, an interconnected in-fiber microchannel is constructed, which facilitates rapid and complete filling of the HCF’s central hole with liquid glue. After the ultraviolet-induced polymerization, a polymer Fabry-Perot interferometer is achieved by cutting the HCF end with a desired cavity length. Besides, the interference visibility is significantly enhanced by adding a refractive-index-modulated polymer cap onto the cutting surface. Experimental results demonstrate the optimized interference spectra and the interconnection of the matched air-hole fibers. The polymer sensor exhibits a signal-to-noise ratio of 56.8 dB for detecting pulsed ultrasonic waves, which is more than twice that of a partially polymer-filled sensor. Due to the hermetically-sealed structure, the sensor probe presents constrained performance with a temperature sensitivity of 230.2 pm/°C and a humidity sensitivity of 93.7 pm/%RH, which can be further improved by releasing the polymer waveguide from fiber cladding. Based on interconnected holey fibers, the proposed approach has a uniform size-controlled polymer waveguide dimension with increased spectrum visibility, rendering it suitable for a diverse range of microstructure-matched optical fibers.

Numerical Investigation of Flow Boiling in Interconnected Microchannels at Varying Mass Fluxes

Numerical Investigation of Flow Boiling in Interconnected Microchannels at Varying Mass Fluxes

A MEMS Electrochemical Angular Accelerometer with Silicon-Based Four-Electrode Structure.

This paper presents a MEMS electrochemical angular accelerometer with a silicon-based four-electrode structure, which was made of thousands of interconnected microchannels for electrolyte flow, anodes uniformly coated on structure surfaces and cathodes located on the sidewalls of flow holes. From the perspective of device fabrication, in this study, the previously reported multi-piece assembly was simplified into single-piece integrative manufacturing, effectively addressing the problems of complex assembly and manual alignment. From the perspective of the sensitive structure, in this study, the silicon-based four-electrode structure featuring with complete insulation layers between anodes and cathodes can enable fast electrochemical reactions with improved sensitivities. Numerical simulations were conducted to optimize the geometrical parameters of the silicon-based four-electrode structure, where increases in fluid resistance and cathode area were found to expand working bandwidths and improve device sensitivity, respectively. Then, the silicon-based four-electrode structure was fabricated by conventional MEMS processes, mainly composed of wafer-level bonding and wafer-level etching. As to device characterization, the MEMS electrochemical angular accelerometer with the silicon-based four-electrode structure exhibited a maximum sensitivity of 1458 V/(rad/s2) at 0.01 Hz and a minimum noise level of -164 dB at 1 Hz. Compared with previously reported electrochemical angular accelerometers, the angular accelerometer developed in this study offered higher sensitivities and lower noise levels, indicating strong potential for applications in the field of rotational seismology.

Improved Water Collection from Short-Term Fog on a Patterned Surface with Interconnected Microchannels.

Fog harvesting is considered a promising freshwater collection strategy for overcoming water scarcity, because of its environmental friendliness and strong sustainability. Typically, fogging occurs briefly at night and in the early morning in most arid and semiarid regions. However, studies on water collection from short-term fog are scarce. Herein, we developed a patterned surface with highly hydrophilic interconnected microchannels on a superhydrophobic surface to improve droplet convergence driven by the Young-Laplace pressure difference. With a rationally designed surface structure, the optimized water collection rate from mild fog could reach up to 67.31 g m-2 h-1 (6.731 mg cm-2 h-1) in 6 h; this value was over 130% higher than that observed on the pristine surface. The patterned surface with interconnected microchannels significantly shortened the startup time, which was counted from the fog contact to the first droplet falling from the fog-harvesting surface. The patterned surface was also facilely prepared via a controllable strategy combining laser ablation and chemical vapor deposition. The results obtained in outdoor environments indicate that the rationally designed surface has the potential for short-term fog harvesting. This work can be considered as a meaningful attempt to address the practical issues encountered in fog-harvesting research.

Improved flow boiling performance and temperature uniformity in counter-flow interconnected microchannel heat sink

Microchannel flow boiling is one of the most effective solutions to the problem of heat dissipation caused by high power electronic devices. However, inherent drawbacks such as low critical heat flux due to dry-out of the liquid film near the channel exit, relatively high two-phase flow pressure drop, severe temperature nonuniformity and boiling instability at high heat flux still prevent widespread commercial application. In this study, based on the idea of uniform vapor quality along the flow direction, a copper Counter-Flow Interconnected Microchannel (CFIM) was proposed to address the main issues currently faced by two-phase microchannel heat sink. A comprehensive comparative study of CFIM, Co-Current Microchannel (CCM) and Counter-Flow Microchannel (CFM) was carried out from the aspects of boiling stability, boiling heat transfer characteristics and temperature uniformity. Three slots of 0.2 mm, 0.5 mm and 0.8 mm in width, denoted as IM0.2, IM0.5 and IM0.8, respectively, are considered. Experiments are conducted at mass fluxes of 291–618 kg/m2·s, saturation temperature of 40 °C and effective heat fluxes of 3–293 W/cm2, using the dielectric fluid R1233zd(E) as the working fluid. The results show that the CHF and average two-phase heat transfer coefficient (HTC) of CFIM are increased by 40.6 ∼ 100.5 % and 70.4–83.6 %, respectively, while the two-phase pressure drop is decreased by 17–32.6 % compared to CCM. The design of the counter-flow interconnected structure can manipulate the void fraction and two-phase flow pattern, resulting in a near uniform void fraction and flow pattern. The structure of these connecting slots promotes nucleate boiling and fluid mixing of neighboring channels. More importantly, the flow boiling instability and temperature non-uniformity in CFIM are well suppressed. In addition, IM0.2 has higher heat dissipation than IM0.5 and IM0.8 due to enhanced bubble nucleation, reducing superheat requirements and periodic rewetting to the center of the channel. The results of this research reveal that utilizing a microchannel heat sink with a counter-flow interconnected configuration can effectively improve heat transfer performance during flow boiling. Furthermore, it helps to mitigate issues such as flow boiling instability and temperature non-uniformity.

Biomass derived evaporator with highly interconnected structure for eliminating salt accumulation in high-salinity brine

Solar-driven evaporator is regarded as an energy-saving and eco-friendly desalination technology. However, available unfriendly synthetic materials and salt crystallization problems limit the evaporator's performance and development, especially in high-salinity condition. Hence, inspired by the highly interconnected microchannels, a carbonized white gourd (CWG) derived self-desalting evaporator was developed to evaporate and desalinate seawater. To evaluate the efficacy of the porous features, the effect of different porosity configurations on water evaporation and anti-salt abilities of CWG was discussed. High and stable evaporation rates of 1.76 and 1.44 kg·m−2·h−1 were reached for 3.5 wt% and 20 wt% NaCl solutions, respectively, which were attributed to the highly efficient water transport and self-desalting capabilities, and it further increased to 2.19 kg·m−2·h−1 by adding an extra convective air (2 m/s) located at the evaporation interface. Moderate airflow effectively enhanced the evaporation efficiency and delayed re-crystallization of salt, promoting a long-term stable desalination process. Conversely, excessive convective flow (4 m/s) may directly impair evaporative stability and salt resistance. This research is expected to provide a new insight into the design of high performance, low cost, eco-friendly and salt-resistant evaporator applied to solar desalination.

Flexible and Stretchable Liquid‐Metal Microfluidic Electronics Using Directly Printed 3D Microchannel Networks

AbstractThis paper describes a method for fabricating microfluidic electronics with 3D interconnected networks by direct ink writing (DIW)‐based 3D printing. Existing 3D printing technologies have yet to simultaneously realize 1) direct printing of interconnected multilayered microchannels without supporting materials or post‐processing and 2) integration of electronic elements with microchannels during the process of printing. This research aims to develop a method to fabricate support‐free microchannels consisting of silicone sealant without the collapse of the extruded structure while integrating electronic elements during the fabrication by DIW. The injection of liquid metal into 3D‐printed microchannels allows the formation of electrical connections between 3D conductive networks and the embedded electronic elements, enabling the fabrication of flexible and stretchable liquid metal antenna coils. To demonstrate a practical application, 1) a skin‐attachable radio‐frequency identification (RFID) tag using a commercial skin‐adhesive plaster as a substrate and 2) free‐standing flexible wireless light‐emitting devices with a small footprint (21.4 mm × 15 mm) for potential implantable applications are produced. This technology will offer a new capability to realize the automated fabrication of stretchable printed circuits with 3D configuration of electrical circuits consisting of liquid metals.

Effects of micro-slots in fully interconnected microchannels on flow boiling heat transfer

This study introduced the experimental work to assess the effect of micro-slots on the flow boiling characteristics of HFE-7100 in a microchannel heat sink. In this work, fully interconnected microchannels with three different slot sizes of 10 μm, 20 μm and 40 μm, are designed as active nucleation sites to enhance flow boiling and thin film evaporation. The different slots sizes are defined the name as 135, 125 and 112 slots per inch (SPI), respectively. This new configuration is developed based on the experimental and theoretical study of half interconnected microchannel design. Results shows that compared to the plain wall microchannels, the heat transfer coefficient and critical heat flux of the fully interconnected microchannels with 135 SPI are significantly improved by up to 5.5 and 1.82 times, respectively. In addition, the transient study indicates that flow boiling in the present design is more stable than that in plain wall microchannels. Moreover, a visualization study was conducted to investigate the mechanism of high-frequency rewetting through micro slots. The study verified the importance of the micro-slots in microchannels with respect to the heat transfer rates and pressure drop.

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.

Paper-based microfluidics: What can we expect?

Paper-based microfluidics: What can we expect?

Fabrication and Testing of Multi-Hierarchical Porous Scaffolds Designed for Bone Regeneration via Additive Manufacturing Processes.

Bone implants or replacements are very scarce due to the low donor availability and the high rate of body rejection. For this reason, tissue engineering strategies have been developed as alternative solutions to this problem. This research sought to create a cellular scaffold with an intricate and complex network of interconnected pores and microchannels using salt leaching and additive manufacturing (3D printing) methods that mimic the hierarchical internal structure of the bone. A biocompatible hydrogel film (based on poly-ethylene glycol) was used to cover the surface of different polymeric scaffolds. This thin film was then exposed to various stimuli to spontaneously form wrinkled micropatterns, with the aim of increasing the contact area and the material’s biocompatibility. The main innovation of this study was to include these wrinkled micropatterns on the surface of the scaffold by taking advantage of thin polymer film surface instabilities. On the other hand, salt and nano-hydroxyapatite (nHA) particles were included in the polymeric matrix to create a modified filament for 3D printing. The printed part was leached to eliminate porogen particles, leaving homogenously distributed pores on the structure. The pores have a mean size of 26.4 ± 9.9 μm, resulting in a global scaffold porosity of ~42% (including pores and microchannels). The presence of nHA particles, which display a homogeneous distribution according to the FE-SEM and EDX results, have a slight influence on the mechanical resistance of the material, but incredibly, despite being a bioactive compound for bone cells, did not show a significant increase in cell viability on the scaffold surface. However, the synergistic effect between the presence of the hydrogel and the pores on the material does produce an increase in cell viability compared to the control sample and the bare PCL material.

3D printed hydrogel/wesselsite-PCL composite scaffold with structural change from core/shell fibers to microchannels for enhanced bone regeneration

Corresponding to the process of bone formation, three-dimensional (3D) scaffolds should provide adaptive structural cues and microenvironment for bone repair at different stages. Herein, we fabricate a core-shell fiber scaffold by coating a layer of polycaprolactone (PCL)/SrCuSi4O10 (wesselsite, CS) on 3D printed hydrogel scaffolds. The core/shell scaffold provided enhanced mechanical support for the defect at the initial stage. Then, the degradation of hydrogels resulted in the transformation of core/shell fiber structure (hydrogel/PCL + CS) to interconnected microchannels (PCL/CS hollow channel), which provided increasing space and clear architectural cues for promoting bone formation and vascularization. Simultaneously, the chemokine stromal cell-derived factor-1α (SDF-1α) loaded in hydrogels achieved sustained release in the initial two weeks to facilitate the recruitment of bone marrow stromal cells (BMSCs) to defect. Subsequently, the degradation of CS nanomaterials yielded the sustained release of bioactive ions (Si, Sr and Cu), promoting osteogenesis and angiogenesis. The in vivo data showed that the prepared scaffolds exhibited enhanced bone repair capacity with abundant new bone formation and blood vessels ingrowth in the defect. Thus, this designed system shows great potential for bone tissue engineering application.

Atherothrombosis‐on‐Chip: A Site‐Specific Microfluidic Model for Thrombus Formation and Drug Discovery (Adv. Biology 7/2022)

Atherothrombosis-on-Chip In article 2101316, Ta and co-workers conducted a study to mimic the site-specific atherothrombosis formation on the chip and design a unique microfluidic device with two interconnected microchannels. The device allows the site-specific introduction of plaque components to develop localized thrombosis and provides a universal platform for studying the crosstalk between blood cells and plaque components. The device is expected to benefit drug testing and carrier designing.

Design and fused filament fabrication of multilayered microchannels for subwavelength and broadband sound absorption

A comprehensive procedure to design and manufacture multilayered microchannels presenting competitive mechanical properties, effective subwavelength and near perfect broadband sound absorption in targeted frequency ranges is presented. The acoustic properties of microchannels are predicted with the Johnson-Champoux-Allard-Lafarge (JCAL) model. The JCAL parameters are calculated with the Two-scale Asymptotic Method (TAM) and the sound absorption coefficient of multilayered microchannels is simulated with the transfer matrix method (TMM). The simplex Nelder-Mead optimization method is used to find the size of the channels and the stacking sequence leading to effective acoustic absorption for three different frequency ranges (500–2400 Hz, 2400–6500 Hz and 500–6500 Hz). 30 mm-thick samples with up to 30-layers of unobstructed and non interconnected channels and microchannels were successfully produced via fused filament fabrication (FFF). The minimum channel size is ~ 100 µm which is very appropriate to produce micro-perforated panels or acoustic liners with optimal absorption and different degrees of freedom. Multilayered microchannels with absorption average up to 0.87 and noise reduction coefficient (NRC) up to 0.49 were produced. The multilayered microchannels offer a good compromise between effective acoustic properties and useful mechanical properties compared to other 3D printed acoustic structures and can be considered as viable candidates for applications where structural resistance is required. • Multilayered microchannels with high broadband sound absorption at three frequency ranges are presented. • Innovative FFF manufacturing technique allows production of 100 μm perforations and structure with up to 30-layer. • 30mm-thick multilayered microchannels present sound absorption average up to 0.87. • PLA 3D printed multilayered microchannels exhibit up to 468MPa compressive modulus and 9MPa compressive yield strength.

A Print-and-Fuse Strategy for Sacrificial Filaments Enables Biomimetically Structured Perfusable Microvascular Networks with Functional Endothelium Inside 3D Hydrogels.

A facile and flexible approach for the integration of biomimetically branched microvasculature within bulk hydrogels is presented. For this, sacrificial scaffolds of thermoresponsive poly(2-cyclopropyl-2-oxazoline) (PcycloPrOx) are created using melt electrowriting (MEW) in an optimized and predictable way and subsequently placed into a customized bioreactor system, which is then filled with a hydrogel precursor solution. The aqueous environment above the lower critical solution temperature (LCST) of PcycloPrOx at 25°C swells the polymer without dissolving it, resulting in fusion of filaments that are deposited onto each other (print-and-fuse approach). Accordingly, an adequate printing pathway design results in generating physiological-like branchings and channel volumes that approximate Murray's law in the geometrical ratio between parent and daughter vessels. After gel formation, a temperature decrease below the LCST produces interconnected microchannels with distinct inlet and outlet regions. Initial placement of the sacrificial scaffolds in the bioreactors in a pre-defined manner directly yields perfusable structures via leakage-free fluid connections in a reproducible one-step procedure. Using this approach, rapid formation of a tight and biologically functional endothelial layer, as assessed not only through fluorescent dye diffusion, but also by tumor necrosis factor alpha (TNF-α) stimulation, is obtained within three days.

Atherothrombosis-on-Chip: A Site-Specific Microfluidic Model for Thrombus Formation and Drug Discovery.

Atherothrombosis, an atherosclerotic plaque disruption condition with superimposed thrombosis, is the underlying cause of cardiovascular episodes. Herein, a unique design is presented to develop a microfluidic site-specific atherothrombosis-on-chip model, providing a universal platform for studying the crosstalk between blood cells and plaque components. The device consists of two interconnected microchannels, namely main and supporting channels: the former mimics the vessel geometry with different stenosis, and the latter introduces plaque components to the circulation simultaneously. The unique design allows the site-specific introduction of plaque components in stenosed channels ranging from 0% to above 50%, resulting in thrombosis, which has not been achieved previously. The device successfully explains the correlation between vessel geometry and thrombus formation phenomenon as well as the influence of shear rate on platelet aggregation, confirming the reliability and the effectiveness of the design. The device exhibits significant sensitivity to aspirin. In therapeutic doses (50 × 10-6 and 100× 10-6 m), aspirin delays and prevents platelet adhesion, thereby reducing the thrombus area in a dose-dependent manner. Finally, the device is effectively employed in testing the targeted binding of the RGD (arginyl-glycyl-aspartic acid) labeled polymeric nanoparticles on the thrombus, extending the use of the device to examine targeted drug carriers.

Thermoresponsive Hydrogels with Improved Actuation Function by Interconnected Microchannels

Stimuli−responsive hydrogels are important in soft actuators research, as they change volume in response to environmental factors. Thermoresponsive hydrogels, such as poly(N‐isopropylacrylamide) (pNIPAM), typically have slow response rates and exert comparably weak forces, which usually limit their use as artificial muscles. Herein, it is shown that the incorporation of interconnected microchannels into the pNIPAM hydrogel by a template‐assisted approach leads to a significant increase in both the response rate and the volume change. For a microchannel density of only 5 vol%, a volume reduction of 90% is achieved, compared with only 12% for the bulk material, while material stiffness of the swollen hydrogels remains unchanged. By tailoring the channel density and the stiffness of the material, it is further possible to adjust the response rate and the exerted stroke force in an actuation setting. It is shown in a demonstrator gripper setup driven by the pNIPAM‐based artificial muscle that the performance of the gripper is strongly improved by the microengineered material compared with conventional bulk pNIPAM. The strategy of incorporating microchannels into the pNIPAM hydrogel provides a practical approach for the future use of volume phase transition‐based responsive materials in soft robotic applications.

3D printed hydrogel scaffolds with macro pores and interconnected microchannel networks for tissue engineering vascularization

The macro pores and interconnected microchannels in three-dimensional (3D) scaffolds are important architecture cures to support new tissues growth and vascularization. To date, the fabrication of hydrogel scaffold possessing both designed macro pores and fully interconnected microchannel (FIM) networks is still a challenge. Herein, we reported a facile method to effectively fabricate hydrogel scaffold containing designed macro pores and FIM networks by 3D printing and surface crosslinking. The surface of the printed scaffold is crosslinked, while the inner parts of the filaments are still in uncrosslinked state, after soaking the scaffold in crosslinking solution for a certain time. Then, the FIM networks are generated by removing the uncrosslinked gels from the printed filaments. The created FIM scaffold shows improved mechanical properties and structural integrity after post treatment. The channel wall with barrier function endows the scaffold with the ability of fast perfusion of liquid in the microchannels. Human umbilical vein endothelial cells are well adhered on the inner surface of the microchannels with high cell viability. In vivo study shows the excellent performance to facilitate vessels formation not only in the interface zone between scaffolds and host tissue, but also in the center of the FIM scaffolds. It also demonstrate that FIM scaffolds hold the potential capability to promote wound healing. In conclusion, the present study proposes a facile method to fabricate hydrogel scaffolds with both macro pores and FIM networks, and demonstrates their strong potential for tissue engineering application.