An efficient planar accordion-shaped micromixer: from biochemical mixing to biological application

Mixing Performance of a Planar Asymmetric Contraction-and-Expansion Micromixer

Micromixers are one of the critical components in microfluidic devices. They significantly affect the efficiency and sensitivity of microfluidics-based lab-on-a-chip systems. This study introduces an efficient micromixer with a simple geometrical feature that enables easy incorporation in a microchannel network without compromising the original design of microfluidic devices. The study proposes a newly designed planar passive micromixer, termed a planar asymmetric contraction-and-expansion (P-ACE) micromixer, with asymmetric vertical obstacle structures. Numerical simulation and experimental investigation revealed that the optimally designed P-ACE micromixer exhibited a high mixing efficiency of 80% or more within a microchannel length of 10 mm over a wide range of Reynolds numbers (0.13 ≤ Re ≤ 13), eventually attaining approximately 90% mixing efficiency within a 20 mm microchannel length. The highly asymmetric geometric features of the P-ACE micromixers enhance mixing because of their synergistic effects. The flow velocities and directions of the two fluids change differently while alternately crossing the longitudinal centerline of the microchannel, with the obstacle structures asymmetrically arranged on both sidewalls of the rectangular microchannel. This flow behavior increases the interfacial contact area between the two fluids, thus promoting effective mixing in the P-ACE micromixer. Further, the pressure drops in the P-ACE micromixers were experimentally investigated and compared with those in a serpentine micromixer with a perfectly symmetric mixing unit.

A review on acoustic field-driven micromixers

A review on acoustic field-driven micromixers is given. This is supplemented by the governing equations, governing non-dimensional parameters, numerical simulation approaches, and fabrication techniques. Acoustically induced vibration is a kind of external energy input employed in active micromixers to improve the mixing performance. An air bubble energized by an acoustic field acts as an external energy source and induces friction forces at the interface between an air bubble and liquid, leading to the formation of circulatory flows. The current review (with 200 references) evaluates different characteristics of microfluidic devices working based on acoustic field shaking.

A new two-layer passive micromixer design based on SAR-vortex principles

Micromixers are key components of microfluidic systems for sample analysis, bioreactors, drug delivery, and many other applications. To date, numerous passive micromixer designs have been proposed. Among those, several designs with complex design structures have been demonstrated to be efficient. In the present work, the authors try to propose a new efficient design with low complexity in terms of fabrication. The new design is two-layer and is based on the split and recombination (SAR) and vortex mixing principles. It is suggested to fabricate the new design in polydimethylsiloxane (PDMS) using the soft lithography technique. This new design is chosen among three new designs simulated using the computational fluid dynamics (CFD) software ANSYS Fluent 17.0. The three new designs are named ND1, ND2, and ND3 and their mixing performances are evaluated numerically using mixing index (MI) and mixer effectiveness (ME) quantities at four different Reynolds (Re) numbers in the range of 0.1–100. Calculated values are compared with those obtained for the classical Y-shaped (CY) micromixer. Flow and mixing patterns are computed by solving the continuity, Navier–Stokes, and the convection–diffusion equations. CFD results for the CY micromixer are compared with available experimental and numerical data and reasonable agreement is observed. According to the results, ND3 has the highest performance (ME up to 36.86 percent/mm) among the investigated micromixer designs in the entire range of Re numbers. The maximum pressure drop (35099.9 Pa at Re = 100 for ND3) is still in the range of acceptable pressure drops reported in the literature. ND3 can be used as an efficient substitute for CY. Although ND3 is highly efficient (MI up to 99.52%) at Re numbers lower than 0.3 or higher than 50, its performance at the intermediate Re numbers (0.3 < Re < 50) is poor and unacceptable (MI as low as 44%). This can be simply improved by adding extra mixing units to provide adequate mixing also at the intermediate Re numbers.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Ultrafast star-shaped acoustic micromixer for high throughput nanoparticle synthesis

We present an acoustically actuated microfluidic mixer, which can operate at flowrates reaching 8 ml min^-1, providing a 50-fold improvement in throughput compared to previously demonstrated acoustofluidic approaches. The device consists of a robust silicon based micro-mechanical oscillator, sandwiched between two polymeric channels which guide the fluids in and out of the system. The chip is actuated by application of an oscillatory electrical signal onto a piezoelectric disk coupled to the substrate by adhesive. At the optimal frequency, this acoustofluidic system can homogenise two fluids with a relative mixing efficiency of 91%, within 4.1 ms from first contact. The micromixer has been used to synthesize two different systems: Budesonide nanodrugs with an average diameter of 80 ± 22 nm, and DNA nanoparticles with an average diameter of 63.3 ± 24.7 nm.

Novel Variable Radius Spiral⁻Shaped Micromixer: From Numerical Analysis to Experimental Validation

A novel type of spiral micromixer with expansion and contraction parts is presented in order to enhance the mixing quality in the low Reynolds number regimes for point-of-care tests (POCT). Three classes of micromixers with different numbers of loops and modified geometries were studied. Numerical simulation was performed to study the flow behavior and mixing performance solving the steady-state Navier⁻Stokes and the convection-diffusion equations in the Reynolds range of 0.1⁻10.0. Comparisons between the mixers with and without expansion parts were made to illustrate the effect of disturbing the streamlines on the mixing performance. Image analysis of the mixing results from fabricated micromixers was used to verify the results of the simulations. Since the proposed mixer provides up to 92% of homogeneity at Re 1.0, generating 442 Pa of pressure drop, this mixer makes a suitable candidate for research in the POCT field.