Integrated micro/nano-fluidic system for mixing and preconcentration of dissolved proteins

Microfluidic Bioreactor with Fibrous Micromixers for In Vitro mRNA Transcription

A new type of microfluidic bioreactor with fibrous micromixers for the ingredient mixing and a long macrochannel for the in vitro transcription reaction was fabricated for the continuous production of mRNA. The diameter of the fibrous microchannels in the micromixers was tuned by using an electrospun microfibrous disc with different microfiber diameters. The micromixer with a larger diameter of fibrous microchannels exhibited a better mixing performance than the others. The mixing efficiency was increased to 0.95 while the mixture was passed through the micromixers, suggesting complete mixing. To demonstrate the continuous production of mRNA, the ingredients for in vitro transcription were introduced into the perfluoropolyether microfluidic bioreactor. The mRNA synthesized by the microfluidic bioreactor had the same sequence and in vitro/in vivo performances as those prepared by the bulk reaction. The continuous reaction in the microfluidic bioreactor with efficient mixing performance can be used as a powerful platform for various microfluidic reactions.

Fabrication of Microfiber-Templated Microfluidic Chips with Microfibrous Channels for High Throughput and Continuous Production of Nanoscale Droplets

A polydimethylsiloxane (PDMS) microfluidic chip with well-interconnected microfibrous channels was fabricated by using an electrospun poly(ε-caprolactone) (PCL) microfibrous matrix and 3D-printed pattern as templates. The microfiber-templated microfluidic chip (MTMC) was used to produce nanoscale emulsions and spheres through multiple emulsification at many small micro-orifice junctions among microfibrous channels. The emulsion formation mechanisms in the MTMC were the cross-junction dripping or Y-junction splitting at the micro-orifice junctions. We demonstrated the high throughput and continuous production of water-in-oil emulsions and polyethylene glycol-diacrylate (PEG-DA) spheres with controlled size ranges from 2.84 μm to 83.6 nm and 1.03 μm to 45.7 nm, respectively. The average size of the water droplets was tuned by changing the micro-orifice diameter of the MTMC and the flow rate of the continuous phase. The MTMC theoretically produced 58 trillion PEG-DA nanospheres per hour without high shear force. In addition, we demonstrated the higher encapsulation efficiency of the PEG-DA microspheres in the MTMC than that of the microspheres fabricated by ultrasonication. The MTMC can be used as a powerful platform for the large-scale and continuous productions of emulsions and spheres.

A hybrid micromixer with planar mixing units

The application of microfluidic systems in chemical and biological assays has progressed dramatically in recent years. One of the fundamental operations that microfluidic devices must achieve is a high mixing index. Of particular importance is the role of planar mixing units with repetitive obstacles (MURO) in the formation of micromixers. To date, a myriad of planar passive micromixers has been proposed. However, a strategy for the combination of these units to find an efficient planar mixer has not been investigated. As such, five different MURO have been selected to form a “hybrid micromixer,” and their combination was evaluated via numerical and experimental methods. These mixing units include ellipse-like, Tesla, nozzle and pillar, teardrop, and obstruction in a curved mixing unit. Since these units have distinctive dimensions, dynamic and geometric similarities were used to scale and connect them. Afterwards, six slots were designated to house each mixing unit. Since the evaluation of all possible unit configurations is not feasible, the design of experiment method is applied to reduce the total number of experiments from 15 625 to 25. Following this procedure, the “hybrid” micromixer proposed here, comprising Tesla, nozzle and pillar, and obstruction units, shows improved performance for a wide range of Re (i.e., mixing index of >90% for Re 0.001–0.1, 22–45) over existing designs. The use of velocity profiles, concentration diagrams, vorticity and circulation plots assist in the analysis of each unit. Comparison of the proposed “hybrid” micromixer with other obstacle-based planar micromixers demonstrates improved performance, indicating the combination of planar mixing units is a useful strategy for building high-performance micromixers.

Taguchi-optimized “hybrid micromixer” has been proposed which can be utilized in a wide range of chemical and biological applications.

Microfluidic Mixing and Analog On-Chip Concentration Control Using Fluidic Dielectrophoresis

Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available active microscale mixing methods capable of dynamically controlling on-chip solute concentrations in real-time. Hence, multiple microfluidic fluid handling steps are often needed for applications that require buffers at varying on-chip concentrations. Here, we present a novel electrokinetic method for actively mixing laminar fluids and controlling on-chip concentrations in microfluidic channels using fluidic dielectrophoresis. Using a microfluidic channel junction, we co-flow three electrolyte streams side-by-side so that two outer conductive streams enclose a low conductive central stream. The tri-laminar flow is driven through an array of electrodes where the outer streams are electrokinetically deflected and forced to mix with the central flow field. This newly mixed central flow is then sent continuously downstream to serve as a concentration boundary condition for a microfluidic gradient chamber. We demonstrate that by actively mixing the upstream fluids, a variable concentration gradient can be formed dynamically downstream with single a fixed inlet concentration. This novel mixing approach offers a useful method for producing variable on-chip concentrations from a single inlet source.