Compressive Behaviors of Micropillar Patterns Made of PDMS Material using the Finite Element Method

Hydrophobic surface is a surface having the ability of water repellent which is frequently coated on medical devices and marine structures. This hydrophobic surface can fabricate from micro-pattern sheets consisting of groups of micropillars arranged into unique micro-patterns which are normally made of low surface energy materials. Thai Microelectronics Center (TMEC) has fabricated micropillar sheets from PDMS for various micropillar array patterns from soft lithography techniques. However, these micropillar sheets were relatively weak under pushing forces. This research aimed to understand compressive behaviors of rectangular prism micropillars having different aspect ratios (ratio of width to length of a rectangular cross-section) and micro-patterns consisting of micropillars having rectangular cross-section and square cross-section by using ANSYS Mechanical APDL program. We found that the aspect ratio of prism micropillars had not influents on both elastic stiffness and compressive strength under compressive loading. The lateral collapse of micropillars were observed on all micro-patterns during compressive loading. Furthermore, the sharklet micro-pattern had the highest compressive strength with maximum compressive pressure of 9.87 kPa. Finally, as loading contact area of micro- patterns increases, the compressive strength increases while the water contact angle decreases

Compressive Behaviors of Micropillar Sheets Made of PDMS Material Using the Finite Element Method

Thai Microelectronics Center fabricates micropillar sheets from soft lithography techniques and roll-to-roll process which were used as superhydrophobic and superoleophobic surfaces coated on marine structures and medical devices. This research aimed to study appropriate constitutive models and mechanical behaviours of PDMS micropillar sheets with two substrate thicknesses of 1,910 µm and 150 µm under compressive loading using ANSYS Mechanical APDL program. The constitutive models consisted of Mooney-Rivlin (2, 3 and 5 parameters), Ogden (1st, 2nd and 3rd orders), Neo-Hookean, Polynomial (1st and 2nd orders), Arruda-Boyce, Gent and Yeoh (1st, 2nd and 3rd orders) models were curved fitting with experiment data from uniaxial compression test. We found that the most accurate constitutive model was Mooney-Rivlin 5 parameter model for the low strain range . The compressive strength and the lateral collapse of micropillars depended on substrate thickness were studied. The lateral collapse of micropillars was found when the substrate thicknesses were 150 µm and 1,910 µm. As the substrate thickness decreased, the compressive strength decreased while the elastic stiffness increased. The maximum compressive forces per one micropillar were 21.060 µN and 18.549 µN for the 1,910 µm and 150 µm thick substrates respectively

Mechanical Diaphragm Structure Design of a MEMS-Based Piezoresistive Pressure Sensor for Sensitivity and Linearity Enhancement

An improved design of the micro-electromechanical system (MEMS) piezoresistive pressure sensor with a combination of a petal edge, a beam, a peninsula, three cross beams and a center boss is proposed in this work for an operating range of low pressure in order to improve the sensor performance, i.e. the sensitivity and the linearity. The finite element method (FEM) is utilized to predict the stress and the deflection of the MEMS piezoresistive pressure sensor under the applied pressure of 1-5 kPa. The functional forms of the longitudinal stress, the transverse stress and the deflection are formulated by using the power law and then are used to optimize the geometry of the proposed design. The simulation results show that the proposed design is able to produce the high sensitivity up to 34 mV/kPa with the low nonlinearity of 0.11% full-scale span (FSS). The nonlinearity error is lowered by the proposed design of the peninsula, three cross beams and the center boss. The sensitivity is enhanced by increasing the petal edge width. The sensor performance of the proposed design is also compared to that of the previous design in the literature. The comparison reveals that the proposed design can perform better than the previous one

Mixing-Performance Evaluation of a Multiple Dilution Microfluidic Chip for a Human Serum Dilution Process

This paper is aimed to propose a numerically designed multiple dilution microfluidic chip that can simultaneously deliver several serum dilutions in parallel. The passive mixing scheme is selected for dilution and achieved by the serpentine mixing channel in which Dean vortices are induced to increase the contact area and time for better diffusion. The mixing performance at the exit of this dilution chip is numerically evaluated using five commonly-used mixing indices with the goal that the homogeneity of the mixture over the exit cross-sectional area of the mixing channel must be greater than 93.319% to fulfill the six-sigma quality control

CFD Investigation into Influences of a Transversely and Periodically Deforming Microchannel on Shear Stress Behavior in a Gut-on-a-chip Device

Organ-on-a-chip allows dynamic microenvironment of the actual organ to be simulated in vitro. In this study, the CFD simulation is used to investigate the behaviors of fluid flow and shear stress due to the effect of a transversely deforming membrane caused by the cyclic deformation of the microchannel sidewalls in a gut-on-a-chip device. The result reveals that the shear stress varies linearly along the length of the microchannel. The average shear stress per cycle is approximately three times greater than that of the stationary microchannel. The amplitude and frequency of the cyclic deformation also significantly affect the flow and shear stress behaviors. The highly dynamic shear stress in the gut-on-a-chip device could be one of the major factors that makes this kind of device more viable than the traditional static cell culture

Application of a novel rectangular filtering microfluidic device for microfilarial detection

The rectangular filtering microfluidic chip was invented using microfluidics device fabrication technology and can separate living microfilariae from blood samples without a syringe pump. The diagnostic results are highly effective. The device is based on the principle of separating millions of blood cells from microfilariae using a rectangular filter structure. It disperses fluid evenly into the flow-passage channel, and its rectangular filter structure is the key to success in reducing the pressure and separating blood cells from microfilariae effectively. The flow rate and blood cell concentration were optimized in our study. The chip is intended to be a point-of-care device that can reduce the use of superfluous instrumentation in the field. The technology is designed to be rapid, accurate, and easy-to-use for all users, especially those in remote areas

Modelling and simulation of SiGe n-channel HFETs for low power applications

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Study of optimization condition for spin coating of the photoresist film on rectangular substrate by Taguchi design of an experiment

There are four parameters concerning the spin coating of a positive photoresist film. This paper focuses on spin coating of the positive photoresist Clariantz AZ-P4620 on a 2x7 cm rectangular substrate. By ways of Taguchi L16 (44) method, the number of experiments can be reduced from 256 to 16. By analyzing the main impact plot of the signal to noise ratio, it is found that the most suitable values of the four parameters giving the desired thickness and uniformity is a photoresist dispense time of 13 seconds, then spin at a speed of 700 rpm for 5 seconds, and then accelerate at 2,000 rpm per seconds to 4,000 rpm. The speed is maintained at 4,000 rpm for 60 seconds with an exhaust pressure of 300 Pa. The substrate is later baked at 100 oCfor 90 seconds. The calculated thickness of the final film is 48,107.70±1,096 Angstroms. The analysis of the deviation showsthat no parameter has a significant on the thickness and uniformity of the final photoresist film with a confidence level of 95%. This DOE can be used in many applications in the micro and nano fabrication industry

Investigation of Leukocyte Viability and Damage in Spiral Microchannel and Contraction-Expansion Array

Inertial separation techniques in a microfluidic system have been widely employed in the field of medical diagnosis for a long time. Despite no requirement of external forces, it requires strong hydrodynamic forces that could potentially cause cell damage or loss during the separation process. This might lead to the wrong interpretation of laboratory results since the change of structures and functional characteristics of cells due to the hydrodynamic forces that occur are not taken into account. Therefore, it is important to investigate the cell viability and damage along with the separation efficacy of the device in the design process. In this study, two inertial separation techniques—spiral microchannel and contraction-expansion array (CEA)—were examined to evaluate cell viability, morphology and intracellular structures using a trypan blue assay (TB), Scanning Electron Microscopy (SEM) and Wright-Giemsa stain. We discovered that cell loss was not significantly found in a feeding system, i.e., syringe, needle and tube, but mostly occurred in the inertial separation devices while the change of cell morphology and intracellular structures were found in the feeding system and inertial separation devices. Furthermore, percentage of cell loss was not significant in both devices (7–10%). However, the change of cell morphology was considerably increased (30%) in spiral microchannel (shear stress dominated) rather than in CEA (12%). In contrast, the disruption of intracellular structures was increased (14%) in CEA (extensional and shear stress dominated equally) rather than spiral microchannel (2%). In these experiments, leukocytes of canine were used as samples because their sizes are varied in a range between 7–12 µm, and they are commonly used as a biomarker in many clinical and medical applications

Enhancing Performance of a MEMS-Based Piezoresistive Pressure Sensor by Groove: Investigation of Groove Design Using Finite Element Method

The optimal groove design of a MEMS piezoresistive pressure sensor for ultra-low pressure measurement is proposed in this work. Two designs of the local groove and one design of the annular groove are investigated. The sensitivity and linearity of the sensor are investigated due to the variations of two dimensionless geometric parameters of these grooves. The finite element method is used to determine the stress and deflection of the diaphragm in order to find the sensor performances. The sensor performances can be enhanced by creating the annular or local groove on the diaphragm with the optimal dimensionless groove depth and length. In contrast, the performances are diminished when the local groove is created on the beam at the piezoresistor. The sensitivity can be increased by increasing the dimensionless groove length and depth. However, to maintain low nonlinearity error, the annular and local grooves should be created on the top of the diaphragm. With the optimal designs of annular and local grooves, the net volume of the annular groove is four times greater than that of the local groove. Finally, the functional forms of the stress and deflection of the diaphragm are constructed for both annular and local groove cases