Cross-junction Microchannel Research Articles

Chitosan microfiber fabrication using a microfluidic chip and its application to cell cultures

In this study, a poly-methyl-methacrylate (PMMA) microfluidic chip with a 45° cross-junction microchannel is fabricated using a CO2 laser machine to generate chitosan microfibers. Chitosan solution and sodium tripolyphosphate (STPP) solution were injected into the cross-junction microchannel of the microfluidic chip. The laminar flow of the chitosan solution was generated by hydrodynamic focusing. The diameter of laminar flow, which ranged from 30 to 50 μm, was controlled by changing the ratio between chitosan solution and STPP solution flow rates in the PMMA microfluidic chip. The laminar flow of the chitosan solution was converted into chitosan microfibers with STPP solution via the cross-linking reaction; the diameter of chitosan microfibers was in the range of 50–200 μm. The chitosan microfibers were then coated with collagen for cell cultivation. The results show that the chitosan microfibers provide good growth conditions for cells. They could be used as a scaffold for cell cultures in tissue engineering applications. This novel method has advantages of ease of fabrication, simple and low-cost process.

Numerical simulation of droplet formation in a micro-channel using the lattice Boltzmann method

This study investigates droplet formation in a micro-channel using the lattice Boltzmann (LB) method. A cross-junction micro-channel and two immiscible, water and oil phase fluids, were used to form the micro-droplets. Droplets are formed by the hydrodynamic instability on the interface between two immiscible fluids when two immiscible fluids are imported simultaneously in a cross-junction micro-channel. The Shan & Chen model, which is a lattice Boltzmann model of two-phase flows, is used to treat the interaction between immiscible fluids. The detailed process of the droplet formation in the cross-junction micro-channel was illustrated. The results of the droplet formation by the LBM predicted well the experimental data by PIV (particle image velocimetry). The effect of the surface tension and the flow rate of water phase fluid on the droplet length and the interval between droplets was also investigated. As the surface tension increased, the droplet length and the interval between droplets were increased. On the other hand, when we increased the flow rate of the water phase fluid under the condition of the fixed oil-phase fluid flow rate, the droplet size was increased while the interval between droplets was decreased.

Three-dimensional lattice Boltzmann simulations of droplet formation in a cross-junction microchannel

An immiscible liquid–liquid multiphase flow in a cross-junction microchannel was numerically studied by the lattice Boltzmann method. An improved, immiscible lattice BGK model was proposed by introducing interfacial tension force based on the continuum surface force (CSF) method. The recoloring step was replaced by the anti-diffusion scheme in the mixed region to reduce the side-effect and control the thickness of the interface. The present method was tested by the simulations on a static bubble and the simulations of Taylor deformation. Laplace’s law, spurious velocities, the thickness of interface, the pressure distribution and the small deformation theory were examined. It proves that our model is more advantageous for the simulation of immiscible fluids over the original immiscible lattice BGK model. The simulations of droplet formation in a cross-junction microchannel were performed and compared with the experiments. The numerical results show good agreements with the experimental ones for the evolution of droplet and the droplet size at various inlet velocities. Besides, a dimensionless analysis was carried out. The resulting droplet sizes depend on the Capillary number to a great extent under current conditions.

Calcium alginate microcapsule generation on a microfluidic system fabricated using the optical disk process

This paper describes the generation of monodisperse calcium alginate (Ca-alginate) microcapsules on a microfluidic platform using the commercial optical disk process. Our strategy is based on combining the rapid injection molding process for a cross-junction microchannel with the sheath focusing effect to form uniform water-in-oil (w/o) emulsions. These emulsions, consisting of 1.5% (w/v) sodium alginate (Na-alginate), are then dripped into a solution containing 20% (w/v) calcium chloride (CaCl2) creating Ca-alginate microparticles in an efficient manner. This paper demonstrates that the size of Ca-alginate microparticles can be controlled from 20 µm to 50 µm in diameter with a variation of less than 10%, simply by altering the relative sheath/sample flow rate ratio. Experimental data show that for a given fixed dispersed phase flow (sample flow), the emulsion size decreases as the average flow rate of the continuous phase flow (sheath flow) increases. The proposed microfluidic platform is capable of generating relatively uniform emulsions and has the advantages of active control of the emulsion diameter, a simple and low cost process and a high throughput.

Using a cross-flow microfluidic chip and external crosslinking reaction for monodisperse TPP-chitosan microparticles

The purpose of this study is to generate monodisperse TPP-chitosan microparticles using a cross-flow microfluidic chip coupled with external crosslinking reaction. We have demonstrated that one can control the size of TPP-chitosan emulsions from 180 to 680 μm in diameter (with a variation of less than 10%) by altering the relative sheath/sample flow rate ratio. Our strategy is based on the sheath effect (focusing) to form uniform self-assembling sphere structures, the so-called water-in-oil (w/o) emulsions, in the cross-junction microchannel. These fine emulsions, consisting of aqueous 1% (w/v) chitosan, are then dripped into a solution containing 10% (w/v) tripolyphosphate (TPP). They then undergo an ionic-crosslinking reaction and create water-insoluble TPP-chitosan microparticles in an efficient manner. In addition, the size distribution of the resulting TPP-chitosan microspheres is narrow (about polyindex = 1) which is suitable to provide the optimal release rate in the administration of controlled release drugs. The proposed microfluidic chip is capable of generating relatively uniform micro-droplets and has the advantages of actively controlling the droplet diameter, and having a simple and low cost process, with a high throughput.

Numerical simulation of the droplet formation in a cross-junction microchannel using the Lattice Boltzmann Method

This study describes the numerical simulation of two-dimensional droplet formation and the following motion by using the Lattice Boltzmann Method (LBM) with the phase field equation. The free energy model is used to treat the interfacial force and the deformation of a binary fluid system, drawn into a cross-junction microchannel. While one fluid is introduced through the central inlet channel, the other fluid is drawn into the main channel through the two vertical inlet channels. Due to the effect of surface tension on the interface between the two fluids, the droplets of the first fluid are formed near the cross-junction. The aim in this investigation is to examine the applicability of LBM to the numerical analysis of the droplet formation and its motion in the microchannel. It was found from comparison with the experimentally visualized patterns that LBM with the free energy model can reproduce the droplet formation successfully. However because of the stability problem which is intrinsic for high surface-tension cases, it requires a very long computational time. This issue is to be resolved in the future.

Using a microfluidic chip and internal gelation reaction for monodisperse calcium alginate microparticles generation

In this paper, the manipulation of monodisperse Ca-alginate microparticles using a microfluidic chip and a reaction of internal gelation is presented. Our strategy is based on the sheath focusing effect to form uniform water-in-oil (w/o) emulsions in the cross-junction microchannel. These fine emulsions, consisting of 1.5 % w/v Na-alginate and 1.0 % w/v calcium carbonate, are then dripped into an oil solution containing 20 % v/v glacial acetic acid and 1 % v/v Tween 80 to obtain Ca-alginate microspheres in an efficient manner. The mechanism is that acetic acid reacts with the calcium carbonate to release the calcium ions, and these calcium ions, through crosslinking reaction with the alginate, produce Ca-alginate microspheres. We have demonstrated that it is possible to control the size of Ca-alginatemicroparticles from 80 microm to 800 microm in diameter (with a variation of less than 10 %) by altering the relative sheath/sample flow rate ratio. Experimental data has shown that for a given 0.01 mL/min of the dispersed phase flow (sample flow), the emulsion size decreased as the average velocity of the continuous phase (oil flow) increased. The same tendency was observed in the 0.05 mL/min and 0.10 mL/min of dispersed phase flow. The microfluidic chip is capable of generating relatively uniform micro-droplets and has the advantages of active control of droplet diameter, simple and low cost process, and a high throughput.

Manufacturing monodisperse chitosan microparticles containing ampicillin using a microchannel chip

The purpose of this study was using a developed microfluidic chip to prepare size-controlled monodisperse chitosan microparticles encapsulating ampicillin. Our strategy is that a chitosan aqueous solution (the disperse phase) is fed into the microfluidic chip equipped with a cross-junction microchannel, and is sheared by the viscous oil flows (the continuous phase) to form monodisperse semi-product, chitosan emulsions. These fine emulsions are then gelled into stability upon gelation by injection of copper sulfate solution at the terminal microchannel of the microfluidic chip, and finally the uniform chitosan microparticles are formed in an efficient manner. The proposed chip is fabricated by a CO(2) laser machine on a conventional poly methyl methacrylate (PMMA) substrate. This microfluidic chip has four inlet ports, one cross-channel and one outlet port. We have demonstrated that one can control the size of chitosan microparticles from 100 to 800 microm in diameter (with a variation less than 5%) by altering the relative sheath/sample flow rate ratio. Experimental data showed that when given a steady continuous phase (oil flow), the emulsion size increases with the increase in average velocity of the dispersed phase flow (sample flow). In addition, the release of the model drug (ampicillin) from these microspheres is proved to be once-daily for clinical application. We also revealed that appropriate particle sizes for different release patterns are predictable, enabling better applications of chitosan as a drug carrier.

C141 マイクロチャネル内の界面動電現象による流動センシングとその制御

Quantitative measurements of electrokinetically driven flow and pressure driven flow were performed by micro-resolution particle image velocimetry (micro-PIV) in a cross-junction microchannel and a right-angle microchannel, for further development of Lab-on-a-chip and μ-TAS. The objective of the present study was to control electrokinetivcally driven flow which is frequently utilized to transport and separate a very small amount of fluid in microchannels. Velocity profiles of electrokinetically driven flow were affected by the configuration of micorchannel and can be controlled by the applied electric field.