Fabrication of Micro-Mixer for Life Sciences Applications (original) (raw)

Design of passive mixers utilizing microfluidic self-circulation in the mixing chamber

Lab on a Chip, 2004

This paper proposes the design of a passive micromixer that utilizes the self-circulation of the fluid in the mixing chamber for applications in the Micro Total Analysis Systems (mTAS). The micromixer with a total volume of about 20 mL and consisting of an inlet port, a circular mixing chamber and an outlet port was designed. The device was actuated by a pneumatic pump to induce self-circulation of the fluid. The self-circulation phenomenon in the micromixer was predicted by the computational simulation of the microfluidic dynamics. Flow visualization with fluorescence tracer was used to verify the numerical simulations and indicated that the simulated and the experimental results were in good agreement. Besides, an index for quantifying the mixing performance was employed to compare different situations and to demonstrate the advantages of the self-circulation mixer. The mixing efficiencies in the mixer under different Reynolds numbers (Re) were evaluated numerically. The numerical results revealed that the mixing efficiency of the mixer with self-circulation was 1.7 to 2 times higher than that of the straight channel without a mixing chamber at Re = 150. When Re was as low as 50, the mixing efficiency of the mixer with self-circulation in the mixing chamber was improved approximately 30% higher than that in the straight channel. The results indicated that the self-circulation in the mixer could enhance the mixing even at low Re. The features of simple mixing method and fabrication process make this micromixer ideally suitable for mTAS applications.

Reciprocating flow-based centrifugal microfluidics mixer

Review of Scientific Instruments, 2009

Proper mixing of reagents is of paramount importance for an efficient chemical reaction. While on a large scale there are many good solutions for quantitative mixing of reagents, as of today, efficient and inexpensive fluid mixing in the nanoliter and microliter volume range is still a challenge. Complete, i.e., quantitative mixing is of special importance in any small-scale analytical application because the scarcity of analytes and the low volume of the reagents demand efficient utilization of all available reaction components. In this paper we demonstrate the design and fabrication of a novel centrifugal force-based unit for fast mixing of fluids in the nanoliter to microliter volume range. The device consists of a number of chambers ͑including two loading chambers, one pressure chamber, and one mixing chamber͒ that are connected through a network of microchannels, and is made by bonding a slab of polydimethylsiloxane ͑PDMS͒ to a glass slide. The PDMS slab was cast using a SU-8 master mold fabricated by a two-level photolithography process. This microfluidic mixer exploits centrifugal force and pneumatic pressure to reciprocate the flow of fluid samples in order to minimize the amount of sample and the time of mixing. The process of mixing was monitored by utilizing the planar laser induced fluorescence ͑PLIF͒ technique. A time series of high resolution images of the mixing chamber were analyzed for the spatial distribution of light intensities as the two fluids ͑suspension of red fluorescent particles and water͒ mixed. Histograms of the fluorescent emissions within the mixing chamber during different stages of the mixing process were created to quantify the level of mixing of the mixing fluids. The results suggest that quantitative mixing was achieved in less than 3 min. This device can be employed as a stand alone mixing unit or may be integrated into a disk-based microfluidic system where, in addition to mixing, several other sample preparation steps may be included. Physics 80, 075102-1 075102-2 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-3 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-5 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-6 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-7 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒

SU-8 microfluidic mixer for use in lab-on-a-chip devices for biological fluids analyses

Proceedings of the IEEE International Conference on Industrial Technology, 2006

This paper describes an easy-to-fabricate and low-cost SU-8 microfluidic mixer suitable for enabling a mixing process based on diffusion. It is developed to be an integrated part of a labon-a-chip for measuring the concentration of four biomolecules in urine samples, by optical absorption. The design of the microfluidic system is based on computational fluid dynamics techniques. Mixing and reaction of the components of the process must be simulated by solving the flow and mass transport equation. A good design must guarantee the mixing of the reactants to assure an uniform mixture at the detection zone. The resulting design and the experimental results are supported by numerical simulations, which allow a reliable quantitative analysis of the concentrations after the mixing process. The reduced size, weight and the simultaneous measurement of more than one biomolecule concentration will improve the performance of biological fluids analyses in clinical laboratories and consequently the quality of the medical disgnostic.

Sensitivity analysis and study of the mixing uniformity of a microfluidic mixer

We consider a microfluidic mixer based on hydrodynamic focusing, which is used to initiate the folding process of individual proteins. The folding process is initiated by quickly diluting a local denaturant concentration, and we define mixing time as the time advecting proteins experience a specified to achieve a local drop in denaturant concentration. In previous work, we presented a minimization of mixing time which considered optimal geometry and flow conditions, and achieved a design with a predicted mixing time of 0.10 µs. The aim of the current paper is twofold. First, we explore the sensitivity of mixing time to key geometric and flow parameters. In particular, we study the angle between inlets, the shape of the channel intersections, channel widths, mixer depth, mixer symmetry, inlet velocities, working fluid physical properties, and denaturant concentration thresholds. Second, we analyze the uniformity of mixing times as a function of inlet flow streamlines. We find the shape of the intersection, channel width, inlet velocity ratio, and asymmetries have strong effects on mixing time; while inlet angles, mixer depth, fluid properties, and concentration thresholds have weaker effects. Also, the uniformity of the mixing time is preserved for most of the inlet flow and distances of down to within about 0.4 µm of the mixer wall. We offer these analyses of sensitivities to imperfections in mixer geometry and flow conditions as a guide to experimental efforts which aim to fabricate and use these types of mixers. Our study also highlights key issues and provides a guide to the optimization and practical design of other microfluidic devices dependent on both geometry and flow conditions.

DESIGN AND SIMULATION OF MICROFLUIDIC PASSIVE MIXER WITH GEOMETRIC VARIATION

Microfluidic designs are advantageous and are extensively used in number of fields related to biomedical and biochemical engineering. The objective of this paper is to perform numerical simulations to optimize the design of microfluidic mixers in order to achieve optimum mixing. In the present study, fluid mixing in different type of micro channels has been investigated. Numerical simulations are performed in order to understand the effect of channel geometry parameters on mixing performance. A two dimensional " T shaped " passive microfluidic mixer is restructured by employing the rectangular shaped obstacles in the channel to improve the mixing performance. The impact of proper placement of obstacles in the channel is demonstrated by applying the leakage concept. It has been observed that, the channel design with non-leaky obstacles (i.e. without leaky barriers) has presented better mixing performance in contrast to channel design with leaky obstacles (i.e. leaky barriers) and channel design without obstacles. The mixing occurs by virtue of secondary flow and generation of vortices due to curling of fluids in the channel on account of the presence of obstacles. This passive mixer has achieved complete mixing of fluids in few seconds or some milliseconds, which is certainly acceptable to utilize in biological applications such as cell dynamics, drug screening, toxicological screening and others.

Rapid circular microfluidic mixer utilizing unbalanced driving force

This paper proposes a novel rapid circular mi-crofluidic mixer for micro-total-analysis-systems (µ-TAS) applications in which an unbalanced driving force is used to mix fluids in a circular chamber at low Reynolds numbers (Re). The microfluidic mixer has a three-layered structure and is fabricated on low-cost glass slides using a simple and reliable fabrication process. Using hydrodynamic pumps, fluids are driven from two inlet ports into a circular mixing chamber. Each inlet port separates into two separate channels, which are then attached to opposite sides of the 3-dimensional (3-D) circular mixing chamber. The unequal lengths of these inlet channels generate an unbalanced driving force, which enhances the mixing effect in the mixing chamber. Numerical simulations are performed to predict the fluid phenomena in the mixing chamber and to estimate the mixing performance under various Reynolds number conditions. The numerical results are verified by performing flow visualization experiments. A good agreement is found between the two sets of results. The numerical and experimental results reveal that the mixing performance can reach 91% within a mixing chamber of 1 mm diameter at a Reynolds number of Re = 3. Additionally, the results confirm that the unbalanced driving force produces a flow rotation in the circular mixer at low Reynolds numbers, which significantly enhances the mixing performance. The novel micromixing method presented in this study provides a simple solution for mixing problems in Lab-on-a-chip systems.

A Picoliter-Volume Mixer for Microfluidic Analytical Systems

Analytical Chemistry, 2001

Mixing confluent liquid streams is an important, but difficult operation in microfluidic systems. This paper reports the construction and characterization of a 100-pL mixer for liquids transported by electroosmotic flow. Mixing was achieved in a microfabricated device with multiple intersecting channels of varying lengths and a bimodal width distribution. All channels running parallel to the direction of flow were 5 µm in width whereas larger 27-µm-width channels ran back and forth through the parallel channel network at a 45°angle. The channel network composing the mixer was ∼10 µm deep. It was observed that little mixing of the confluent solvent streams occurred in the 100-µm-wide, 300-µm-long mixer inlet channel where mixing would be achieved almost exclusively by diffusion. In contrast, after passage through the channel network in the ∼200-µm-length static mixer bed, mixing was complete as determined by confocal microscopy and CCD detection. Theoretical simulations were also performed in an attempt to describe the extent of mixing in microfabricated systems.

A Novel Microfluidic Mixer Based on Successive Lamination

2003

The unique properties of flow in microfluidic channels make mixing a significant challenge[l] for which many ingenious solutions have been developed[2-121. We demonstrate the efficacy of a novel mixing channel based on the principle of flow lamination. A unique method for characterizing the extent of mixing is employed that allows characterization of the extent of mixing without a complete 3-dimensional resolution of the concentration field.