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Tecnologia FCT/MCTES (PIDDAC) and Centro2020, Grant/Award Number: UIDB/04044/2020 and UIDP/04044/2020; Associate Laboratory ARISEand PAMI, Grant/Award Number: LA/P/0112/2020 and ROTEIRO/0328/2013; Research Unit INESC MN and FCT, Grant/Award Number: UID/05367/2020 and UIDB/50022/2020. Aim: This study aimed to experimentally validate a computational fluid dynamics (CFD) model, using micro-particle image velocimetry (micro-PIV) measurements of the irrigation flow velocity field developed in confluent canals during irrigation with a side-vented needle. Methodology: A microchip with confluent canals, manufactured in polydimethylsiloxane was used in a micro-PIV analysis of the irrigation flow using a side-vented needle placed 3 mm from the end of the confluence of the canals. Velocity fields and profiles were recorded for flow rates of 0.017 and 0.1 ml/s and compared with those predicted in CFD numerical simulations (using a finite volume commercial code –FLUENT) for both laminar and turbulent regimes. Results: The overall flow pattern, isovelocity and vector maps as well as velocity profiles showed a close agreement between the micro-PIV experimental and CFD predicted data. No relevant differences were observed between the results obtained with the laminar and turbulent flow models used. Conclusions: Results showed that the laminar CFD modelling is reliable to predict the flow in similar domains. info:eu-repo/semantics/publishedVersion

Cancer kills millions of individuals every year all over the world (Global Cancer Observatory). The physiological and biomechanical processes underlying the tumor are still poorly understood, hindering researchers from creating new, effective therapies. Inconsistent results of preclinical research, in vivo testing, and clinical trials decrease drug approval rates. Three-dimensional tumor-on-chip models integrate biomaterials, tissue engineering, fabrication of microarchitectures, and sensory and actuation systems in a single device, enabling reliable studies in fundamental oncology and pharmacology. This review includes a critical discussion about their ability to reproduce the tumor microenvironment, the advantages and drawbacks of existing tumor models and architectures, and major components and fabrication techniques. The focus is on current materials and micro/nanofabrication techniques used to manufacture reliable and reproducible microfluidic tumor-on-chip models for large-scale trial applications.

Overall Objective: Using input from A3.2.1-A3.2.4, INESC MN and IPQ and will write a design document for a new mechanically active on-chip flow pump that will be integrated in a microfluidic device for use as a transfer standard in drug discovery and in organ on-a-chip applications for flow rates lower than 100 nL/min.

Infusion therapy is the most common form of therapy used in health care. However, the existing infusion devices show higher flow discrepancies as flow rates decrease to a few nL min−1. As a result, dosing errors can contribute to the morbidity and mortality of patients. In the scope of project 18HLT08 MeDD II – Metrology for drug delivery, this investigation aims at the development of a silicon microchip flow pump capable of steadily and continuously dispense very low flow rates of a few nL min−1. The fabrication methodologies explored here use a combination of typical cleanroom micro/nanofabrication techniques and off-the-shelf equipment. Preliminary tests show flow rates as low as 45 nL min−1 can be obtained in this microfluidic electroosmotic pump. The experimental flow rates are in good agreement with results predicted by multiphysics simulation, with less than 8% deviation ratio. This cost effective electroosmotic micropump has the potential to act as a steady and continuous drug delivery system to neonatal patients as well as to organs on chip (OoC), determining the stability of the shear stress imposed on the cells or the right cell culture medium conditions.

Wettability of surfaces used in microdevices, either on the fabrication of fluidic passages or integration of sensing and actuating elements can impact the flow. The easiness of fabrication may dictate the materials and processes to use, that can subsequently have their surface wettability spatially controlled. The work reports surface wettability modification (SWM) by room temperature chemical vapor deposition (CVD) with HMDS (hexamethyldisilazane) and FDTS (perfluorodecyltrichlorosilane) on flat surfaces of silicon (Si), glass, SU-8 photoresist and PDMS (polydimethylsiloxane). The effect of SWM has been evaluated by the measurement of contact angles (CA) of 6 μL droplets of deionized water and phosphate-buffered saline buffer (PBS). Time of surface exposure and evolution of CA after modification have been investigated for each pair surface/fluid. The time of surface activation with HMDS or FDTS and the chemical affinity of these to the surface are seen to govern the efficiency of surface coverage and consequently the efficiency and stability of SWM. For both HMSD and FDTS SWM, hydrophilic surfaces (glass and Si) became more hydrophobic (CA rising from 20° up to ˜70°) while SU-8 hydrophobic surfaces became more hydrophilic (CA decreasing from 120° down to ˜100°) upon 30 min activation. PDMS surfaces shows no relevant SWM after activation with HMDS nor with FDTS. SWM of Si surfaces has remained irreversible following CVD exposure (HMDS and FDTS) for at least 65 h.

Optically detectable labels and probes are commonly used in bioapplications. Together with the miniaturization of analytical platforms based on microfluidic technology, with tuneable properties, they yield unparalleled opportunities towards faster, cheaper and more efficient biomolecule analysis. This work describes the preparation and testing of uniformly shaded polydimethylsiloxane (PDMS) membranes and microfluidic devices used to enhance or inhibit optical detection of fluorescent labels. The uniformly pigmented black-PDMS nanocomposite mixtures have been prepared by adding a known quantity of black pigment to PDMS, and its optical, spectroscopic and morphological properties have been characterized. The effect of pigment-to-DMS mixing ratio has been investigated by Ultra-Violet/Visible, near infrared and middle infrared spectroscopies; scanning electron microscopy and atomic force microscopy; and contact angle measurements. The results demonstrate that optical and spectroscopic properties of black-PDMS are strongly altered with the progressive inclusion of black pigment while wetting behaviour and morphology are maintained. Surface contact angle decreases more prominently with the decreasing ratio of DMS-to-curing agent than for the inclusion of pigment nanocomposite in the mixture. The ability to tune optical properties of PDMS has been experimentally demonstrated in a Black-PDMS nanocomposite microfluidic chip cast and bonded to glass. The results show double the signal-to-noise in fluorescence images as compared to pure PDMS devices, demonstrating a very promising integrated optical detection strategy for portable microfluidic systems.

The realization of microfluidic systems requires many technologies and protocols for microfabrication using materials and geometries compatible with fluidic phenomena. This chapter provides a summary of the strategies commonly used in microfluidic element fabrication. The technologies associated with microelectronic device production at large scales are the basis for the nano-micro feature definition in rigid substrates. However, competitive costs, material versatility, and 3D designs required for complex microfluidic systems have motivated many approaches different than those offered for microelectronics. These techniques are briefly described and supported by examples of fabricated polymeric microdevices.

Biomedical applications and point-of-use devices often rely on nanoparticle concentration strategies. In this paper, on-chip magnetic trapping and manipulation of 300–500 nm superparamagnetic nanoparticles are achieved using thin-film planar circular copper coils. The trap configuration combining a central coil surrounded by four other coils, all connected in series, successfully enables simultaneous attraction and repulsion, enhancing concentration of magnetic nanoparticle (MNP). The simultaneous attraction and repulsion has advantages over static permanent magnets, where unidirectional actuation allows either attraction or repulsion. Because the distance between traps and the MNP is large (hundred micrometer), large electric currents up to 500 mA are needed to achieve fields of the order of hundreds of microtesla, which requires thermal management. Joule heating is effectively tackled by resorting to a novel cooling scheme comprising triangular microchannels milled onto copper substrates. Experimental results combining thermal surface mapping, magnetic field mapping, and optical (fluorescence microscope) observations could validate the trapping efficacy of Estapor microspheres functionalized with BODIPY 515 fluorophores.

Integration of point-of-care assays can be facilitated with the use of actuated magnetic beads (MB) to perform testing in less expensive settings to enable the delivery of cost-effective care. In this paper we present six different designs of planar microelectromagnets traps (MEMT) with four external coils in series and one central coil connected for an opposite direction of manipulation of MB in microfluidic flows. The development of a simulation tool facilitated the rapid and efficient optimization of designs by presenting the influence of system variables on real time concentrations of MB. Real time experiments are in good agreement with the simulations and showed that the design enabled synchronous concentration and dispersion of MB on the same MEMT. The yield of local concentration is seen to be highly dependent on coil design. Additional coil turns between the central and external coils (inter-windings) doubled magnetic concentration and repulsion with no significant electrical resistance increase. The assemblage of a copper microchannel closed loop cooling system to the coils successfully eliminated the thermal drift promoted by joule heating generated by applied current.

Soil improvement using ureolytic bacteria or other biological agents is a promising technique currently under investigation. It is based on the precipitation of calcium carbonate (biocement) due to the enzymatic hydrolysis of urea. The biocement produced clogs the soil pores, consequently bonding the soil grains and increasing overall strength and stiffness while reducing permeability. This study focused mainly on pore clogging effects. The effect of the enzyme and feeding solution concentrations was studied in small test tubes to find the maximum amount of precipitate found when changing the concentrations of both. Based on it, selected concentrations of enzyme and feeding solution were tested in a microfluidic device conceived to mimic a two-dimensional uniform porous size medium. Qualitatively, the amount of precipitate was proportional to that of the concentrations used. The location of the precipitate was clearly related with the direction of fluid flow during inoculation. These preliminary results highlight the fact that the use of alternative testing devices such as the one developed is a potential tool for the study of clogging phenomena occurring during this treatment.

In this paper, MEMS fabrication techniques are used to assemble a micro device which integrates a simulated heat source, a multi-microchannel heat sink and flow sensors. The front side of the silicon chip comprises one 1000 nm-thick Aluminum heater and six 400 A-thick Ruthenium thermal sensors microfabricated to achieve precise and interface-free heat flux imposition and temperature measurements, respectively. The heat sink on the backside is made of 27 parallel rectangular channels with hydraulic diameter D h = 96 μm, length to diameter ratio L / D h = 104 and relative roughness of 2.4%. The channels are closed with glass to allow visualization of the flow, and sealed by anodic bonding, instead of using adhesives, thermal fusion or mechanical sealing, in order to guarantee resistant sealing over the entire range of operating pressures and temperatures while still preserving the depth of the microchannels. Primary fabrication tests are performed to evaluate the influence of geometrical parameters (thin film width and length) in thermal response and joule heating performance for surface temperatures in the range from 25 °C to 106 °C obtained with currents from 0 mA to 250 mA. The temperature coefficient of electrical resistivity, TCR, of the Ru thermal sensors is found to be (1.72 ± 0.45) × 10 −3 K −1 . The thermo-fluid-dynamic performance of the device is assessed with hydrofluoroether coolant (HFE-7000) with Reynolds numbers up to 640 (mass flux up to 2727 kg m −2 s −1 ) and constant wall heat fluxes q ″ up to 10.8 W cm −2 . Preliminary tests have shown that, without boiling, the temperature of the chip can be kept below 85 °C ( T w,avg = 65.4 °C) with a maximum heat flux of 10.8 W cm −2 and a flow rate of 3050 mL h −1 . Boiling of the coolant fluid allows to increase the heat flux up to 26.6 W cm −2 with a flow rate of 1300 mL h −1 (Re = 277) with perfect robustness and reliability of the system.

Microfluidic technology usually, but not exclusively, aims at the miniaturization of conventional laboratorial processes to handle fluids (liquids and/or gases) within submillimeter ranges.

The horizontally assembled circular microchannel (Dh= 543μm, LHT = 60mm) made of transparent borosilicate glass is kept under constant wall heat flux conditions by means of a transparent metallic thin film deposit at the channel external wall as in Silverio and Moreira [1]. Heat transfer and pressure drop measurements are achieved by measuring the temperature and pressure at the channel inlet and outlet. Temperature is also measured along the channel outer wall. Experiments are carried with two different fluids, ethanol and methanol. Inlet liquid subcooling is of 297K, mass fluxes, G, up to 689kg.m−2.s−1 and imposed heat fluxes, q"s, up to 12.5W.cm−2 at ΔTsub from 0.8 to 50K. Synchronized high-speed visualization and microscope optics are used to determine dominant two-phase flow patterns and characterize hydrodynamic instabilities. Vapor qualities, χ, of −0.1 (indicating a subcooled liquid state) to 0.5 are under investigation. Semi-periodic variation of the flow patterns is noticeable for different flow conditions.