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

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

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

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

Portable 3D-printed sensor to measure ionic strength and pH in buffered and non-buffered solutions

A miniaturized 3D-printed device has been designed, manufactured and validated to perform as a low-cost sensor for compositional analysis of buffered and non-buffered solutions in industrial or remote areas. The proposed sensor takes advantage of the transport phenomenon and colorimetric measurements. The novel design can simultaneously detect the ionic strength of the solution by measuring the diffusion width of the ions and the pH by image analysis of the pH indicator color change. The results showed that it can detect pH variations of 0.25 and ionic measure difference of 0.1 M in non-buffer solutions. In addition, the design showed its adaptability to be used as a self-referencing sensor. The 3D-printed sensor presented here is not only successful in the evaluation of some important chemical characteristics but also brings flexibility, cost-effectiveness, swiftness and user-friendliness.Peer ReviewedPostprint (author's final draft

A passive portable microfluidic blood-plasma separator for simultaneous determination of direct and indirect ABO/Rh blood typing

The blood typing test is mandatory in any transfusion, organ transplant, and pregnancy situation. There is a lack of point-of-care (POC) blood typing that could perform both direct and indirect methods using a single droplet of whole blood. This study presents a new methodology combining a passive microfluidic blood–plasma separator (BPS) and a blood typing detector for the very first time, leading to a stand-alone microchip which is capable of determining the blood group from both direct and indirect methods simultaneously. The proposed design separates blood cells from plasma by applying hydrodynamic forces imposed on them, which overcomes the clogging issue and consequently maximizes the volume of the extracted plasma. An axial migration effect across the main channel is responsible for collecting the plasma in plasma collector channels. The BPS novel design approached 12% yield of plasma with 100% purity in approximately 10 minutes. The portable BPS was designed and fabricated to perform ABO/Rh blood tests based on the detection of agglutination in both antigens of RBCs (direct) and antibodies of plasma (indirect). The differences between agglutinated and non-agglutinated samples were distinguishable by the naked eye and also validated by particle analysis of microscopic pictures. The results of this passive BPS in ABO/Rh blood grouping verified the quality and quantity of the extracted plasma in practical applicationsPostprint (author's final draft

Contaminant particle motion in lubricating grease flow: a computational fluid dynamics approach

In this paper, numerical simulations of particle migration in lubricating grease flow are presented. The rheology of three lithium greases with NLGI (National Lubricating Grease Institute) grades 00, 1 and 2 respectively are considered. The grease is modeled as a single-phase Herschel–Bulkley fluid, and the particle migration has been considered in two different grease pockets formed between two concentric cylinders where the inner cylinder is rotating and driving the flow. In the wide grease pocket, the width of the gap is much smaller compared to the axial length scale, enabling a one-dimensional flow. In the narrow pocket, the axial and radial length is of the same order, yielding a three-dimensional flow. It was found that the change in flow characteristics due to the influence of the pocket lateral boundaries when going from the wide to the narrow pocket leads to a significantly shorter migration time. Comparing the results with an existing migration model treating the radial component contribution, it was concluded that a solution to the flow in the whole domain is needed together with a higher order numerical scheme to obtain a full solution to the particle migration. This result is more pronounced in the narrow pocket due to gradients in the flow induced by the lateral boundaries.Peer ReviewedPostprint (published version

Hansen Solubility Parameters (HSPs): A Reliable Tool for Assessing the Selectivity of Pristine and Hybrid Polymer Nanocomposites in the Presence of Volatile Organic Compounds (VOCs) Mixtures

Polymeric materials are widely employed for monitoring volatile organic compounds (VOCs). Compared to other sensitive materials, polymers can provide a certain degree of selectivity, based on their chemical affinity with organic solvents. The addition of conductive nanoparticles within the polymer layer is a common practice in recent years to improve the sensitivity of these materials. However, it is still unclear the effect that the nanoparticles have on the selectivity of the polymer membrane and vice versa. The current work proposes a methodology based on the Hansen solubility parameters, for assessing the selectivity of both pristine and hybrid polymer nanocomposites. The impedance response of thin polydimethylsiloxane (PDMS) films is compared to the response of hybrid polymer films, based on the addition of multi-walled carbon nanotubes (MWCNTs). With the addition of just 1 wt.% of MWCNTs, fabricated sensors showcased a significant improvement in sensitivity, faster response times, as well as enhanced classification of non-polar analytes (>22% increase) compared to single PDMS layers. The methodology proposed in this work can be employed in the future to assess and predict the selectivity of polymers in single or array-based gas sensors, microfluidic channels, and other analytical devices for the purpose of VOCs discrimination.Peer ReviewedPostprint (published version

Hemostasis-on-a-chip: Impedance spectroscopy meets microfluidics for hemostasis evaluation

In the case of vascular injury, a complex process (of clotting) starts, involving mainly platelets and coagulation factors. This process in healthy humans is known as hemostasis, but when it is deregulated (thrombosis), it can be the cause of important cardiovascular diseases. Nowadays, the aging of the population and unhealthy lifestyles increase the impact of thrombosis, and therefore there is a need for tools to provide a better understanding of the hemostasis mechanisms, as well as more cost-e ective diagnosis and control devices. This study proposes a novel microflow chamber, with interchangeable biomimetic surfaces to evaluate global hemostasis, using reduced amounts of blood sample and reagents, and also a minimized time required to do the test. To validate the performance of this novel device, a study on the new oral anticoagulant Apixaban (APIX) has been performed and compared to previous conventional techniques. The test shows an excellent agreement, while the amount of the required sample has been reduced (only 100 L is used), and the amount of reagent as well. An imprinted electrode embedded in the chamber in order to measure the impedance during the coagulation process. This approach distinguishes the impedance behavior of plasma poor in platelets (PPP) and plasma rich in platelets (PRP) for the first timePostprint (published version