articles+ search results

Materials Chemistry, Polymers and Plastics, Organic Chemistry, General Chemical Engineering, Enginyeria mecànica [Àrees temàtiques de la UPC], Volatile organic compounds, Polymers, Gas sensors, Hybrid polymers, Selectivity, Solubility parameters, Volatile organic compounds (VOCs), Compostos orgànics volàtils, and Polímers

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.

Skin, Perspiration, Wearable technology, Electronic instruments, Skin models, Skin phantom, Artificial skin, Sweat, Wearables, In vitro testing, Pell, Perspiració, Electrònica -- Aparells i instruments, Dispositius microfluidics, Enginyeria mecànica [Àrees temàtiques de la UPC], Review, skin models, skin phantom, artificial skin, perspiration, sweat, wearables, in vitro testing, integumentary system, Filtration and Separation, Chemical Engineering (miscellaneous), Process Chemistry and Technology, Wearable computer, Additional research, medicine.symptom, medicine, business.industry, business, Sweat gland, medicine.anatomical_structure, Computer science, Microfluidics, Human–computer interaction, Sweat analysis, lcsh:Chemical technology, lcsh:TP1-1185, lcsh:Chemical engineering, and lcsh:TP155-156

Skin models offer an in vitro alternative to human trials without their high costs, variability, and ethical issues. Perspiration models, in particular, have gained relevance lately due to the rise of sweat analysis and wearable technology. The predominant approach to replicate the key features of perspiration (sweat gland dimensions, sweat rates, and skin surface characteristics) is to use lasermachined membranes. Although they work effectively, they present some limitations at the time of replicating sweat gland dimensions. Alternative strategies in terms of fabrication and materials have also showed similar challenges. Additional research is necessary to implement a standardized, simple, and accurate model representing sweating for wearable sensors testing This research was funded by the Agència de Gestió d’Ajuts Universitaris i Recerca (AGAUR), for the Industrial PhD grant number 2019 DI 18. This work was partially funded thanks to the Red Nacional de Microfluídica RED2018-102829-T and the Spanish Ministry of Economy and Competitivity, grant CTQ2017-84966-C2-1-R

Biomedical Engineering, Biomaterials, Search engine, Elution, Blood typing, Lab-on-a-chip, law.invention, law, Cellulose fiber, Cellulose, chemistry.chemical_compound, chemistry, Chromatography, Materials science, Enginyeria paperera::Primeres matèries papereres [Àrees temàtiques de la UPC], Wood-pulp, Papermaking, Plant fibers, Sisal (Fiber), Blood typing test, Eucalyptus paper, Paper-based microfluidics, Point-of-care testing, Sisal-based paper, Sisal paper, Pasta de paper, Pasta de paper -- Tractament, Cel·lulosa -- Investigació, and Fibres vegetals

This study presents an enhanced paper-based analytical device (PAD) for forward and reverse group blood typing. The proposed PAD uses a novel methodology, which provides highly reliable results on a fully cellulose based device. The PAD was printed on different cellulose substrates. These substrates were made of different cellulose fibers (sisal and eucalyptus), different grammages, refining steps, and wet additive content. Best parameters were chosen to achieve high reliability on both forward and reverse blood typing. The substrates were patterned with five hydrophilic channels and two hydrophobic areas. For reverse blood typing, the hemoagglutination reaction took place on the hydrophobic surface of the paper before being transferred to the paper web, where together with the forward blood typing tests were all washed with saline solution to read the results by elution. This device allows direct read-out of results; the stains show were agglutination happens. Different blood types were in full agreement between the reverse and forward method and in agreement with traditional methods. The time and simplicity of this methodology confirmed its utility.

Enginyeria mecànica [Àrees temàtiques de la UPC], Laser beams, Laser --Industrial applications, Microfabrication, Femtolaser, Biofabrication, Blood/plasma separation, Microfluidics, Femtosecond laser, Feixos de làser, Làsers -- Aplicacions industrials, Microfabricació, Biomedical Engineering, General Medicine, Biomaterials, Biochemistry, Bioengineering, Biotechnology, Materials science, Microelectromechanical systems, Optoelectronics, business.industry, business, Aspect ratio (image), Fabrication, Femtosecond, Stiction, Polydimethylsiloxane, chemistry.chemical_compound, and chemistry

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 devices

Article, organ-on-a-chip, vein-on-a-chip, impedance, microfluidics, hemostasis, Microfluidics, Hemostasis, Impedance plethysmography, Organ-on-a-chip, Vein-on-a-chip, Impedance, Microfluídica, Hemostàsia, Pletismografia d'impedància, Enginyeria mecànica [Àrees temàtiques de la UPC], Ciències de la salut::Medicina [Àrees temàtiques de la UPC], lcsh:Mechanical engineering and machinery, lcsh:TJ1-1570, Electrical and Electronic Engineering, Mechanical Engineering, Control and Systems Engineering, Coagulation, Biomedical engineering, Platelet, Apixaban, medicine.drug, medicine, Materials science, Population, education.field_of_study, education, and Dielectric spectroscopy

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-effective 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 µ
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 time.

Microfluidics, Clinical chemishy, Diagnosis, Laboratory, Blood--Examination, Microfluídica, Química clínica, Diagnòstic de laboratori, Sang -- Examen, Enginyeria mecànica::Mecànica de fluids::Reologia [Àrees temàtiques de la UPC], Biomedical Engineering, General Chemistry, Biochemistry, Bioengineering, Blood typing, ABO blood group system, Biomedical engineering, Hydrodynamic forces, Materials science, Separator (oil production), Blood plasma, Whole blood, and Blood grouping

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 applications.

point-of-care, passive mixer, micromixer, spiral micromixer, mixing, Enginyeria mecànica [Àrees temàtiques de la UPC], Mixing machinery, Numerical analysis, Point-of-care, Passive mixer, Micromixer, Spiral micromixer, Mixing, Batedores, Anàlisi numèrica, Physics::Fluid Dynamics, Computer Science::Other, lcsh:Mechanical engineering and machinery, lcsh:TJ1-1570, Article, Electrical and Electronic Engineering, Mechanical Engineering, Control and Systems Engineering, Mechanics, Reynolds number, symbols.namesake, symbols, Materials science, Streamlines, streaklines, and pathlines, Computer simulation, Experimental validation, and Pressure drop

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&ndash
Stokes and the convection-diffusion equations in the Reynolds range of 0.1&ndash
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.

lubricating grease flow, velocity profiles, rheology, lubrication, computational fluid dynamics (CFD), double restriction seal, contaminants, and particle migration

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.

Surfaces, Coatings and Films, Surfaces and Interfaces, Mechanical Engineering, Mechanics of Materials, Grease, Materials science, Geometry, Fluid mechanics, Newtonian fluid, Computational fluid dynamics, business.industry, business, Velocimetry, Lubrication, Composite material, Shear thinning, Rheology, Physics::Fluid Dynamics, Condensed Matter::Soft Condensed Matter, Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC], Lubrication and lubricants, Lubricating grease flow, Velocity profiles, Computational fluid dynamics (CFD), Double restriction seal, Contaminants, Dinàmica de fluids computacional, Reologia, and Lubrificació i lubrificants

In this paper, numerical simulations of lubricating grease flow in the grease pocket of a double restriction seal geometry using computational fluid dynamics are presented. The grease is treated as a single-phase Herschel–Bulkley fluid with different rheological properties corresponding to NLGI grade 00, 1 and 2. The numerical code and rheology model have been validated with a semi-analytical solution based on flow measurements using microparticle image velocimetry. The flow has been modelled for low and high rotational speeds driving the flow, and elevated temperatures. Also, the evolution of contaminant particles in the grease pocket is investigated. It was found that the flow and velocity distribution in the pocket—and consequently the contaminant particle concentration evolution, is characterized by the shear thinning rheology of the grease. With higher shear rates in the grease and higher temperatures, the grease approaches a more Newtonian type of behaviour leading to a reduced yield and shear thinning characteristics directly affecting the grease ability to transport contaminant particles.

Wind turbines, Gearing--Lubrication, Abrasive wear, Corrosive wear, Gears, Grease application, Lubricating greases, MEMS devices, Open gears, Oxidative wear, Power generation, Aerogeneradors, Engranatges, Lubrificació i lubrificants, Enginyeria mecànica [Àrees temàtiques de la UPC], Mechanical Engineering, Mechanics of Materials, Turbine, Lubrication, Mechanical engineering, Engineering, business.industry, business, Nozzle, Wear coefficient, Power (physics), Electricity generation, Test bench, and Wind power

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/s12206-017-0131-3
The 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.

Enginyeria mecànica [Àrees temàtiques de la UPC], Manufacturing processes, Microfabrication, New technology, Rapid manufacturing, Mechanical engineering, Fabrication, Particle image velocimetry, Fabricació, Microfabricació, Industrial and Manufacturing Engineering, Mechanical Engineering, Velocimetry, Rapid prototyping, Materials science, and Micro particles

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.