Microfluidics and MEMS technology for membranes

Postprint (published version

The use of rapid prototyping techniques (RPT) to manufacture micro channels suitable for high operation pressures and uPIV

This paper aims to present a new methodology to manufacture micro-channels suitable for high operating pressures and micro particle image velocimetry (µPIV) measurements using a rapid-prototyping high-resolution 3D printer. This methodology can fabricate channels down to 250 µm and withstand pressures of up to 5 ± 0.2 MPa. The manufacturing times are much shorter than in soft lithography processes. The novel manufacturing method developed takes advantage of the recently improved resolution in 3D printers to manufacture an rapid prototyping technique part that contains the hose connections and a micro-channel useful for microfluidics. A method to assemble one wall of the micro-channel using UV curable glue with a glass slide is presented – an operation required to prepare the channel for µPIV measurements. Once built, the micro-channel has been evaluated when working under pressure and the grease flow behavior in it has been measured using µPIV. Furthermore, the minimum achievable channels have been defined using a confocal microscopy study. This technique is much faster than previous micro-manufacturing techniques where different steps were needed to obtain the micro-machined parts. However, due to current 3D printers ' resolutions (around 50 µm) and according to the experimental results, channels smaller than 250-µm2 cross-section should not be used to characterize fluid flow behaviors, as inaccuracies in the channel boundaries can deeply affect the fluid flow behavior. The present methodology is developed due to the need to validate micro-channels using µPIV to lubricate critical components (bearings and gears) in wind turbines. This novel micro-manufacturing technique overcomes current techniques, as it requires less manufacturing steps and therefore it is faster and with less associated costs to manufacture micro-channels down to 250-µm2 cross-section that can withstand pressures higher than 5 MPa that can be used to characterize microfluidic flow behavior using µPIV.Peer ReviewedPostprint (author's final draft

Enabling novel Lab-on-chip applications through optimization of integrated micropillar pumps

Prediction and reduction of pressure drop and resistance flow in micropillar arrays is important for the design of microfluidic circuits used in different lab-on-a-chip and biomedical applications. In this work, a diamond microchannel integrated micropillar pump (dMIMP) with a resistance flow 35.5% lower than circular based micropillar pump (cMIMP) has been developed via the optimization of the fluid-dynamic behavior of different post shapes in a low aspect ratio (H/D ranged from 0.06 to 0.2) integrated pillar micro-channel. Flow through the fabricated samples has been numerically solved and experimentally measured, with an agreement higher than 90%. The analysis of the results indicates that although porosity can be a determinant parameter to predict the resistance flow of MIMP, other geometrical parameters like, side distance between posts or post shape, play a major role in this scenarioPeer Reviewe

New method for lubricating wind turbine pitch gears using embedded micro-nozzles

This is a copy of the author 's final draft version of an article published in the journal Journal of mechanical science and technology. The final publication is available at Springer via http://dx.doi.org/10.1007/s12206-017-0131-3The increase of power generated by wind turbines has increased the stresses applied in all of its components, thereby causing premature failures. Particularly, pitch and yaw gears suffer from excessive wear mainly caused by inappropriate lubrication. This paper presents a novel method to automatically lubricate the wind turbine pitch gear during operation. A micro-nozzle to inject fresh grease continuously between the teeth in contact was designed, manufactured, and installed in a test bench of a 2 MW wind turbine pitch system. The test bench was used to characterize the fatigue behavior of the gear surface using conventional wind turbine greases under real cyclic loads. Measurements of wear evolution in a pitch gear with and without micro-nozzle show a decrease of 70 % of the wear coefficient after 2×104 cycles.Peer ReviewedPostprint (author's final draft

Advancements in microfabricated gas sensors and microanalytical tools for the sensitive and selective detection of odors

In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans’ olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoringPostprint (published version

EWOD-based sensor applied to immediate environmental impact Diagnosis through analyte-mediated surface tension change

Programa de doctorat: Doctorat en Enginyeria Tèxtil i Paperer

Cost-effective microfabrication of sub-micron-depth channels by femto-laser anti-stiction texturing

Micro Electro Mechanical Systems (MEMS) and microfluidic devices have found numerous applications in the industrial sector. However, they require a fast, cost-effective and reliable manufacturing process in order to compete with conventional methods. Particularly, at the sub-micron scale, the manufacturing of devices are limited by the dimensional complexity. A proper bonding and stiction prevention of these sub-micron channels are two of the main challenges faced during the fabrication process of low aspect ratio channels. Especially, in the case of using flexible materials such as polydimethylsiloxane (PDMS). This study presents a direct laser microfabrication method of sub-micron channels using an infrared (IR) ultrashort pulse (femtosecond), capable of manufacturing extremely low aspect ratio channels. These microchannels are manufactured and tested varying their depth from 0.5 µm to 2 µm and width of 15, 20, 25, and 30 µm. The roughness of each pattern was measured by an interferometric microscope. Additionally, the static contact angle of each depth was studied to evaluate the influence of femtosecond laser fabrication method on the wettability of the glass substrate. PDMS, which is a biocompatible polymer, was used to provide a watertight property to the sub-micron channels and also to assist the assembly of external microfluidic hose connections. A 750 nm depth watertight channel was built using this methodology and successfully used as a blood plasma separator (BPS). The device was able to achieve 100% pure plasma without stiction of the PDMS layer to the sub-micron channel within an adequate time. This method provides a novel manufacturing approach useful for various applications such as point-of-care devicesPeer ReviewedPostprint (author's final draft

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.Peer ReviewedPostprint (published version

Materials and manufacturing methods for EWOD devices: current status and sustainability challenges

Electrowetting-on-dielectric (EWOD) devices have proven to be effective tools for precise microfluidic manipulation or in liquid lenses that surpass conventional solid lenses in versatility. However, the fabrication of these devices presents many challenges, such as their scalability or the growing concern on their environmental impact due to materials used in their fabrication. This review provides a comprehensive analysis of the materials currently used in the fabrication of EWOD devices and the characteristics they must meet. In addition, a discussion of future challenges in the fabrication of EWOD devices is presented, in particular the environmental problems presented by some of the materials currently in use.The authors would like to acknowledge funding by Spain’s Ministry of Science and Innovation and Spain’s State Research Agency: PID2020-114070RB-I00 (CELLECOPROD).Peer ReviewedPostprint (published version

Microfluidic point-of-care blood panel based on a novel technique: Reversible electroosmotic flow

Copyright 2015 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.A wide range of diseases and conditions are monitored or diagnosed from blood plasma, but the ability to analyze a whole blood sample with the requirements for a point-of-care device, such as robustness, user-friendliness, and simple handling, remains unmet. Microfluidics technology offers the possibility not only to work fresh thumb-pricked whole blood but also to maximize the amount of the obtained plasma from the initial sample and therefore the possibility to implement multiple tests in a single cartridge. The microfluidic design presented in this paper is a combination of cross-flow filtration with a reversible electroosmotic flow that prevents clogging at the filter entrance and maximizes the amount of separated plasma. The main advantage of this design is its efficiency, since from a small amount of sample (a single droplet 10¿µl) almost 10% of this (approx 1¿µl) is extracted and collected with high purity (more than 99%) in a reasonable time (5–8 min). To validate the quality and quantity of the separated plasma and to show its potential as a clinical tool, the microfluidic chip has been combined with lateral flow immunochromatography technology to perform a qualitative detection of the thyroid-stimulating hormone and a blood panel for measuring cardiac Troponin and Creatine Kinase MB. The results from the microfluidic system are comparable to previous commercial lateral flow assays that required more sample for implementing fewer tests.Peer ReviewedPostprint (author's final draft