Nhut Tran-Minh

Design and optimization of non-clogging counter-flow microconcentrator for enriching epidermoid cervical carcinoma cells

Clogging failure is common for microfilters in living cells concentration; for instance, the CaSki Cell-lines (Epidermoid cervical carcinoma cells) utilizing the flat membrane structure. In order to avoid the clogging, counter-flow concentration units with turbine blade-like micropillar are proposed in microconcentrator design. Due to the unusual geometrical-profiles and extraordinary microfluidic performance, the cells blocking does not occur even at permeate entrances. A counter-flow microconcentrator was designed, with both processing layer and collecting layer arranged in terms of the fractal based honeycomb structure. The device was optimized by coupling Artificial Neuron Network (ANN) and Computational Fluid Dynamics (CFD). The excellent concentration ratio of a final microconcentrator was presented in numerical results.

An efficient passive planar micromixer with ellipse-like micropillars for continuous mixing of human blood

In this paper, a passive planar micromixer with ellipse-like micropillars is proposed to operate in the laminar flow regime for high mixing efficiency. With a splitting and recombination (SAR) concept, the diffusion distance of the fluids in a micromixer with ellipse-like micropillars was decreased. Thus, space usage for micromixer of an automatic sample collection system is also minimized. Numerical simulation was conducted to evaluate the performance of proposed micromixer by solving the governing Navier-Stokes equation and convection-diffusion equation. With software (COMSOL 4.3) for computational fluid dynamics (CFD) we simulated the mixing of fluids in a micromixer with ellipse-like micropillars and basic T-type mixer in a laminar flow regime. The efficiency of the proposed micromixer is shown in numerical results and is verified by measurement results.

A Simple and Low Cost Micromixer for Laminar Blood Mixing: Design, Optimization, and Analysis

The paper presents a design of micromixer for laminar blood mixing. In order to minimize the space usage for micromixer of an automatic sample collection system, a splitting and recombination (SAR) concept was employed to reduce the diffusion distance of the fluids. Moreover, ellipse-like micropillars were introduced to this concept to increase the mixing performance of micromixer. With software (COMSOL 4.3) for computational fluid dynamics (CFD) we simulated the mixing of fluids in a micromixer with ellipse-like micropillars and basic T-type mixer in a laminar flow regime. Numerical results illustrate that the micromixer with SAR concept achieves an outstanding mixing efficiency than the one without SAR concept. Numerical results also show that the SAR micromixer with ellipse-like micropillars is up to 99% efficient, and that efficiency reaches 90% in a short distance.

Pirani gauge based hermeticity monitoring for un-cooled micro bolometer array

This paper presents a novel method to analyze the thermal conductance under vacuum environment for MEMS devices. The Si/Ge-based Pirani gauge introduced is developed for monitoring the package hermeticity of MEMS Bolometer array, which has the total same structure as the single bolometer pixel for the characteristic of functional material. Meanwhile the ‘Extended Fouriers Law’ is verified by free molecular theory and is applied into the thermal analysis of the micro-structure under the pressure below 100Pa. Thermal interaction between Focus Plane Arrays (FPAs) and Pirani gauge is checked to guarantee the normal performance as the influence from each side are under 2×10−3K, which is acceptable for the products. This design can save the cost in fabrication significantly due to no extra process flow. The commercial value is affirmed by industry partner.

A novel design of hollow microneedle for blood sample collection

In this study, a novel design of microneedle is proposed based on structural and fluidic analysis. For blood collection applications, a hollow microneedle is designed with optimal features. The features and size of this microneedle provide improved structural strength for optimal skin penetration. Mechanical evaluations are studied with intensive calculations of maximum allowance axial and transverse forces, followed by numerical simulation of the insertion process. In addition, the fluid behavior is also investigated. The dual diameter design of the hollow part was shown to maximize the extraction efficiency and minimize the clogging problem for high-volume collection of blood. Our study proposes a design guideline on making a high-performance microneedle for blood collection.

Computational Fluid Dynamics Approach for Modeling a Non-Newtonian Blood Flow in a Split and Recombine Micromixer

In this work, the blood flow in a passive planar micromixer is analyzed in order to provide a case study for the use of different models of the blood dynamic viscosity in COMSOL Multiphysics. Regarding the Newtonian or non-Newtonian behavior, the blood is best approximated with a non-Newtonian model since its viscosity changes with dependence on the shear rate. The usual Newtonian model of blood viscosity, as well as two non-Newtonian models including Carreau model and the Power law model are used to study the wall shear stress. For the models study, a passive planar micromixer with ellipse-liked micropillars is proposed to operate in the laminar flow regime for high mixing efficiency.

Numerical and Experimental Mixing Studies in a Split and Recombine Micromixer with Ellipse-Like Micropillars

A passive planar micromixer with rapid mixing has been successfully demonstrated by simulations and experiments. The structure of this micromixer contains ellipse-like micropillars in the main channel. Adding micropillars to micromixer will reduce the diffusion distance of the fluids. So, this type of design can improve mixing efficiency.

A study on mechanical strength of pyramid-shaped microneedle

This paper introduces a novel design of hollow microneedle for efficient blood extraction. With special features such as square base and pyramid tip, our proposed microneedle may have better mechanical strength compared with that of previously proposed microneedles. We also provide mathematical frameworks for analyzing both mechanical strength and fluidic transport efficiency of microneedles. To evaluate the performance of our microneedle compared with that of previously proposed microneedles we conduct intensive calculations with various parameter settings. According to calculation results, our proposed microneedle may be optimal for blood collection. Moreover, our proposed microneedle provides continuous blood collection with higher volumes because of its optimal hollow width with recommended applied pressure.

A novel passive micromixer with trapezoidal blades for high mixing efficiency at low Reynolds number flow

In this paper, we propose a novel passive micromixer structure based on the effect of stretching-folding in both vertical and horizontal directions. The channel depth of the micromixer is tightened at two ends each mixing unit. The fluid flows are repeatedly twisted and bent from left to right and vice versa. With this special structure, our proposed micromixer can create vortices and transversal flow even at low Reynolds number. Therefore, it can efficiently mix low speed liquid flows, making it easy to be built into micro-devices. We conduct intensive simulation to evaluate the performance of our proposed mixer by using COMSOL Multiphysics package with Navier-Stokes, convection-diffusion equation and particle tracking method. The simulation results demonstrated that our micromixer may be the first device that is able to operate with high mixing efficiency independent of the Reynolds number in the range of 0.5 to 60. Especially, at very low Reynolds number the mixing efficiency of our proposed micromixer is 220-240% higher compared with those of rhombic mixer with branch channels and pure rhombic mixer.

Analytical and Numerical Approaches for Optimization Design of MEMS Based SU-8 Microneedles

This paper addresses the optimization design of the MEMS based SU-8 microneedles for blood extraction by studying the effects of axial and transverse force on SU-8 microneedles during skin insertion in both analytical and numerical points of view. The critical buckling load and maximum bending force that the needle can withstand are 4.486N and 0.123N for 1200μm length (300μm x 300μm) needle, respectively. As the results of numerical simulation, the maximum stress 1.0719MPa, which occurs at the tip, is smaller than 34MPa of yield strength of SU-8. The bending test is also proved by applying the force of 0.1N on the tip of needle, resulting 33.8MPa of maximum stress which is comparable to 34MPa of yield strength of SU-8. Based on these results, the numerical simulation also proves that the needle with our design is strong enough for inserting into human skin.