Browsing by Subject "Microfluidics"
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Item Open Access 3D modeling of on-chip acoustophoretic particle manipulation in a polymer microfluidic device(Chemical and Biological Microsystems Society, 2016) Çaǧatay, E.; Özer, M. B.; Çetin, BarbarosThis study focuses on understanding of the sensitivities of the acoustophoretic process on uncertainties/errors in the geometric properties of the chip material and the piezoelectric actuators. The sensitivity of the acoustophoretic process is investigated both numerically and experimentally. For the numerical simulations a three dimensional finite element model is used. In the experimental analysis, a microfluidic chip with two stations is used. The first station has the accurate geometric values of the design and the second station has the introduced error in a geometric parameter so that the effect of this error can be demonstrated on the same chip and the channel.Item Open Access 3D printed microfluidic reactor for high throuhput chitosan nanoparticle synthesis(Chemical and Biological Microsystems Society, 2016) Aşık, M. D.; Çetin, Barbaros; Kaplan, M.; Erdem, Yegan; Saǧlam, N.The major bottleneck for the commercialization of nanoparticle related technologies is the mass production of the nanoparticles. One approach to overcome this bottleneck is use of microfluidic devices. In this paper, a 3D printed, high throughput micro-reactor that is capable of synthesizing both chitosan and chitosan coated iron oxide nanoparticles is presented.Item Open Access Analysis of monodisperse microfluidic droplet generation and its biochemical applications(Bilkent University, 2020-11) Kalantarifard, AliDroplet fluidic systems have dramatically improved precision in many applications, such as polymerase chain reaction, biochemical analysis, and particle synthesis in which accurate control of sample volume plays a significant role. Despite the well-understood physics of squeezing regime droplet formation in two-phase flow systems, the long-sought-after goal of generating identical, equal size droplets is challenging. Although the individual parameters that affect the droplet size were identified as channel dimension, wettability, viscosity, and flow rate or pressure ratio of the two immiscible fluids, the governing mechanism of droplet size variation is not completely analyzed. More importantly, the limit of monodispersity for droplet generation systems is still unknown. This is due to the difficulty in analytical modeling of droplet formation that is usually compensated by experimental approaches, which fall short in leading to universal conclusions. In this thesis, depending on the flow source used for driving fluids we present an analytical approach that takes into account all the system dynamics and internal and external factors that disturb monodispersity. We use the analogy between fluidic and electrical circuits to analyze the factors that influence droplet monodispersity. Interestingly, we enable to model the dynamics of a segmented two-phase flow system using a single-phase flow analogy, electron flow, in electrical circuits. Doing so, we reveal the sources of disturbances that lead to variation in droplet volume. We offered a unique solution and designed guidelines to ensure ultramonodisperse droplet generation. Our analytical conclusions are experimentally verified using a T-junction and flow-focusing droplet generator design driven by a pressure supply. Equally importantly, we show the limiting experimental factors for reaching the theoretical maximum of monodispersity. For the displacement pump case, we propose a more effective and widely applicable solution to improve flow stability, by controlling off-chip compliances to minimize fluctuations due to the flow source. Eventually, we compare the performance of the two common drive units (pressure-driven and displacement pump) in terms of droplet monodispersity, while using our proposed methods and guidelines. Finally, we did study in reaction kinetics of poly dopamine and hydrogen peroxide and synthesize silica and polyethylene glycol (PEG) particles and supramolecular polymer capsules with high monodispersity using ultra-monodisperse droplets.Item Open Access Antibacterial properties and osteoblast interactions of microfluidically synthesized chitosan – SPION composite nanoparticles(Wiley Periodicals LLC, 2023-05-26) Kafali, M.; Şahinoğlu, O. Berkay; Tufan, Y.; Orsel, Z. C.; Aygun, Elif; Alyuz, Beril; Saritas, Emine Ulku; Erdem, E. Yegan; Ercan, B.In this research, a multi-step microfluidic reactor was used to fabricate chitosan – superparamagnetic iron oxide composite nanoparticles (Ch – SPIONs), where composite formation using chitosan was aimed to provide antibacterial property and nanoparticle stability for magnetic resonance imaging (MRI). Monodispersed Ch – SPIONs had an average particle size of 8.8 ± 1.2 nm with a magnetization value of 32.0 emu/g. Ch – SPIONs could be used as an MRI contrast agent by shortening T2 relaxation parameter of the surrounding environment, as measured on a 3 T MRI scanner. In addition, Ch – SPIONs with concentrations less than 1 g/L promoted bone cell (osteoblast) viability up to 7 days of culture in vitro in the presence of 0.4 T external static magnetic field. These nanoparticles were also tested against Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), which are dangerous pathogens that cause infection in tissues and biomedical devices. Upon interaction of Ch – SPIONs with S. aureus and P. aeruginosa at 0.01 g/L concentration, nearly a 2-fold reduction in the number of colonies was observed for both bacteria strains at 48 h of culture. Results cumulatively showed that Ch – SPIONs were potential candidates as a cytocompatible and antibacterial agent that can be targeted to biofilm and imaged using an MRI.Item Open Access Boundary element method for optical force calibration in microfluidic dual-beam optical trap(SPIE, 2015) Solmaz, Mehmet E.; Çetin, Barbaros; Baranoglu, B.; Serhatloglu, Murat; Bıyıklı, NecmiThe potential use of optical forces in microfluidic environment enables highly selective bio-particle manipulation. Manipulation could be accomplished via trapping or pushing a particle due to optical field. Empirical determination of optical force is often needed to ensure efficient operation of manipulation. The external force applied to a trapped particle in a microfluidic channel is a combination of optical and drag forces. The optical force can be found by measuring the particle velocity for a certain laser power level and a multiplicative correction factor is applied for the proximity of the particle to the channel surface. This method is not accurate especially for small microfluidic geometries where the particle size is in Mie regime and is comparable to channel cross section. In this work, we propose to use Boundary Element Method (BEM) to simulate fluid flow within the micro-channel with the presence of the particle to predict drag force. Pushing experiments were performed in a dual-beam optical trap and particlea's position information was extracted. The drag force acting on the particle was then obtained using BEM and other analytical expressions, and was compared to the calculated optical force. BEM was able to predict the behavior of the optical force due to the inclusion of all the channel walls. © 2015 SPIE.Item Open Access Carbon-based nanomaterials and sensing tools for wearable health monitoring devices(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-10-05) Erdem, Özgecan; Derin, Esma; Shirejini, Saeedreza Zeibi; Sağdıç, Kutay; Yılmaz, Eylül Gülşen; Yıldız, Selvin; Akçeoğlu, Garbis Atam; İnci, FatihThe healthcare system has a drastic paradigm shift from centralized care to home-based and self-monitoring strategies; aiming to reach more individuals, minimize workload in hospitals, and reduce healthcare-associated expenses. Particularly, wearable technologies are garnering considerable interest by tracking physiological parameters through motion and activities, and monitoring biochemical markers from sweat, saliva, and tears. Through their integrations with sensors, microfluidics, and wireless communication systems, they allow physicians, family members, or individuals to monitor multiple parameters without any significant disruptions to daily routine. Integrating flexible and smart materials with wearable platforms have already enabled facile operations. Especially, carbon nanomaterials hold unique features, including low density, high strength, good conductivity, outstanding flexibility, versatile integration with materials and sensors. In this manuscript, carbon nanomaterials are comprehensively reviewed with their tremendous assets utilized in wearable technologies. Further, their integration with ultrasonic, acoustic and energy harvesting devices, optical and electrochemical platforms, microfluidics, and wireless communication technologies are presented.Item Open Access Chitosan coated iron-oxide nanoparticle synthesis using a droplet based microfluidic reactor(IEEE, 2019-06) Wahab, Malik Abdul; Erdem, E. YeganA microfluidic reactor for the synthesis of chitosan coated iron-oxide nanoparticles is described. Tapered double T-junction is used to generate droplets of reactants (iron chloride solution and chitosan solution) which were merged using a pillar array. Third reactant ammonia solution is introduced after the mixing of already merged droplets. Ammonia solution initiates the reaction and precipitates are collected at the outlet. Transmission electron microscope (TEM) imaging along with Fourier transform infrared spectroscopy (FTIR) is used to characterize the nanoparticles. These nanoparticles have applications in nano-medicine where they can be used as drug carriers.Item Open Access CO2 laser polishing of microfluidic channels fabricated by femtosecond laser assisted carving(Institute of Physics Publishing, 2016-10) Serhatlioglu, M.; Ortaç, B.; Elbuken, C.; Bıyıklı, Necmi; Solmaz, M. E.In this study, we investigate the effects of CO2 laser polishing on microscopic structures fabricated by femtosecond laser assisted carving (FLAC). FLAC is the peripheral laser irradiation of 2.5D structures suitable for low repetition rate lasers and is first used to define the microwell structures in fused silica followed by chemical etching. Subsequently, the bottom surface of patterned microwells is irradiated with a pulsed CO2 laser. The surfaces were characterized using an atomic force microscope (AFM) and scanning electron microscope (SEM) in terms of roughness and high quality optical imaging before and after the CO2 laser treatment. The AFM measurements show that the surface roughness improves more than threefold after CO2 laser polishing, which promises good channel quality for applications that require optical imaging. In order to demonstrate the ability of this method to produce low surface roughness systems, we have fabricated a microfluidic channel. The channel is filled with polystyrene bead-laden fluid and imaged with transmission mode microscopy. The high quality optical images prove CO2 laser processing as a practical method to reduce the surface roughness of microfluidic channels fabricated by femtosecond laser irradiation. We further compared the traditional and laser-based glass micromachining approaches, which includes FLAC followed by the CO2 polishing technique.Item Open Access A confirmatory test for sperm in sexual assault samples using a microfluidic-integrated cell phone imaging system(Elsevier, 2020) Deshmukh, S.; İnci, Fatih; Karaaslan, M. G.; Öğüt, M. G.; Duncan, D.; Klevan, L.; Duncan, G.; Demirci, U.Rapid and efficient processing of sexual assault evidence to accelerate forensic investigation and decrease casework backlogs is urgently needed. Therefore, the standardized protocols currently used in forensic laboratories can benefit from continued innovation to handle the increasing number and complexity of samples being submitted to forensic labs. To our knowledge, there is currently no available rapid and portable forensic screening technology based on a confirmatory test for sperm identification in a sexual assault kit. Here, we present a novel forensic sample screening tool, i.e., a microchip integrated with a portable cell phone imaging platform that records and processes images for further investigation and storage. The platform (i) precisely and rapidly screens swab samples (<15 min after sample preparation on-chip); (ii) selectively captures sperm from mock sexual assault samples using a novel and previously published SLeX-based surface chemistry treatment (iii) separates non-sperm contents (epithelial cells and debris in this case) out of the channel by flow prior to imaging; (iv) captures cell phone images on a portable cellphone-integrated imaging platform, (v) quantitatively differentiates sperm cells from epithelial cells, using a morphology detection code that leverages Laplacian of Gaussian and Hough gradient transform methods; (vi) is sensitive within a forensic cut-off (>95% accuracy) compared to the manual counts; (vii) provides a cost-effective and timely solution to a problem which in the past has taken a great deal of time; and (viii) handles small volumes of sample (20 μL). This integration of the cellphone imaging platform and cell recognition algorithms with disposable microchips can be a new direction toward a direct visual test to screen and differentiate sperm from epithelial cell types in forensic samples for a crime laboratory scenario. With further development, this integrated platform could assist a sexual assault nurse examiner (SANE) in a hospital or sexual assault treatment center facility to flag sperm-containing samples prior to further downstream testing.Item Open Access Continuous triboelectric power harvesting and biochemical sensing inside poly(vinylidene fluoride) hollow fibers using microfluidic droplet generation(Wiley-Blackwell, 2016-11) Kanik, M.; Marcali, M.; Yunusa, M.; Elbuken, C.; Bayındır, MehmetTriboelectric power harvesting and biochemical sensing inside poly(vinylidene fluoride) hollow fibers. Fiber‐based microfluidic energy harvesting system, which is also utilized as self‐powered chemical and biosensor. In vitro device concept demonstrating that triboelectric effect can be used for cell detection.Item Open Access Damping hydrodynamic fluctuations in microfluidic systems(Elsevier, 2018) Kalantarifard, Ali; Haghighi, Elnaz Alizadeh; Elbüken, ÇağlarIn this article, we report a method to damp microfluidic hydrodynamic fluctuations caused by flow sources. We demonstrate that compliance of elastomeric off-chip tubings can be used to damp fluctuations and lead to steady flow rates. We analyze the whole microfluidic system using electrical circuit analogies, and demonstrate that off-chip compliances are significant, especially for displacement pump driven systems. We apply this hydrodynamic damping method to microfluidic droplet generation. Our results show that highly monodisperse microdroplets can be obtained by syringe pump driven systems utilizing this damping effect. We reached a coefficient of variation of 0.39% for the microdroplet area using a standard T-junction geometry. Additionally, we demonstrated that pressure pumps inherently use this effect, and have so far led the high performances reported in the literature in terms of droplet monodispersity. The presented off-chip hydrodynamic damping method is not only low-cost and practical, but can also be used in elastomeric and rigid microchannels without need to introduce additional components to the fluidic circuit.Item Open Access Design of a droplet based microfluidic reactor to synthesize chitosan coated iron oxide nanoparticles(Bilkent University, 2019-06) Wahab, Malik AbdulNanoparticles possess unique structural, mechanical, thermal, optical and chemical properties which are highly dependent on their size; therefore it is important to be able to synthesize them uniformly. In general they are synthesized using conventional batch-wise techniques; however microfluidic platforms are also used because they provide precise control over reaction conditions like mixing time, temperature, concentration and improved reaction kinetics. This work is the first study where coating of magnetic nanoparticles with chitosan is realized by utilizing a microfluidic platform. These particles have potential application in targeted drug delivery due to their magnetic behavior and the possibility of carrying drug in the chitosan layer. In the past, this synthesis reaction was performed by using batch wise techniques. In this work we demonstrate the synthesis of chitosan coated nanoparticles using a droplet based microfluidic platform. PDMS devices are fabricated using conventional soft lithography technique. Droplets from two different reagents are generated using double T junction with tapered geometry. The taper angle is optimized such that both reagents generate droplets alternatively with efficiency of more than 95%. Viscosity and surface tension of both droplet phase and continuous phase is taken into account to optimize the geometry. As both reagents need to be mixed in equal proportion, flow rates are adjusted to make the spacing and size of droplets identical. Later, two consecutive droplets are merged in a pillar structure by using the fact that increasing the width of channel will slow down the droplets. Dimensions of channels are optimized so that only two consecutive droplets are merging while pillars avoid accumulation of droplets at that location. Olive oil and silicon oil are used as the continuous phase while chitosan solution and iron chloride solution are used as dispersed phases to form alternating droplets. Then ammonia solution is added as dispersed phase and it forms another droplet at a T-junction and this droplet is merged with the upcoming droplet to initiate the reaction. Synthesized nanoparticles are characterized using transmission electron microscopy (TEM) and fourier-transform infrared spectroscopy (FTIR). As a side study, hydroxyapatite nanoparticles were also synthesized using this droplet-based microfluidic system at various concentration of reactants and results are analyzed using SEM imaging.Item Open Access Design of a droplet-based microfluidic system for hybrid polymer nanoparticle synthesis(Bilkent University, 2021-12) Şahinoğlu, Osman BerkayDroplet microfluidics is advantageous in synthesizing microparticles for both confining their size to the physical dimensions of the droplet and providing a monodisperse result due to rapid mixing inside the droplets. Thusly named microreactors became the focus of the microfluidics community in the recent decade due to their superior ability to control the reaction environment. In this study, for the application of microreactors, a hybrid organic-inorganic material that became prominent in last years named polyhedral oligomeric silsesquioxane (POSS) is chosen. POSS is a polymer that, beside its hybrid nature, shows heat resistance property which made its use in protective painting applications and high radical group affinity that can be utilized to further configure its material properties. This study proposes two microreaction systems for monomer POSS with ther-mal and photopolymerization methods that aim to increase monodispersity and solve the clogging problem encountered in previous studies by introducing the oil phase in the system. Feasibility of systems was investigated numerically using COMSOL Multiphysics and analyses showed adequate heating of and mixing in microreactors. A robust post-processing procedure is proposed to remove excess oil from the sample. Measurements showed microdroplet and sub-micron particle generation where the size distribution of these particles are quantified using MATLAB. Though the use of oil in the system proved to be another challange, hexane based substitute materials are proposed for future work.Item Open Access Design of a high-resolution microfluidic microwave MEMS phase shifter(Wiley, 2011) Ozbey, B.; Ozturk, S.; Aktas, O.In this article, a novel microwave microelectromechanical phase shifter based on a microfluidic design is proposed and demonstrated. The design principles, the fabrication process, and experimental results (S-parameters and phase shift plots) are presented. The proposed system has a high bandwidth, high-power handling capacity, and a high-resolution along with a small settling time.Item Open Access Dielectrophoresis in microfluidics technology(2011) Çetin B.; Li, D.Dielectrophoresis (DEP) is the movement of a particle in a non-uniform electric field due to the interaction of the particle's dipole and spatial gradient of the electric field. DEP is a subtle solution to manipulate particles and cells at microscale due to its favorable scaling for the reduced size of the system. DEP has been utilized for many applications in microfluidic systems. In this review, a detailed analysis of the modeling of DEP-based manipulation of the particles is provided, and the recent applications regarding the particle manipulation in microfluidic systems (mainly the published works between 2007 and 2010) are presented. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access The diffusion-driven microfluidic process to manufacture lipid-based nanotherapeutics with stealth properties for siRNA delivery(Elsevier, 2022-07) Eş, Ismail; Malfatti-Gasperini, A. A.; de la Torre, L. G.Our study investigated the manufacturing of lipid-based nanotherapeutics with stealth properties for siRNA delivery by employing a diffusion-driven microfluidic process in one or two-steps strategies to produce siRNA-loaded lipid nanocarriers and lipoplexes, respectively. In the one-step synthesis, siRNA in the aqueous phase is introduced from one inlet, while phospholipids dispersed in anhydrous ethanol are introduced from other inlets, generating the lipid nanocarriers. In the two-steps strategies, the pre-formed liposomes are complexed with siRNA. The process configuration with an aqueous diffusion barrier exerts a significant effect on the nanoaggregates synthesis. Dynamic light scattering data showed that lipid nanocarriers had a bigger particle diameter (298 ± 24 nm) and surface charge (43 ± 6 mV) compared to lipoplexes (194 ± 7 nm and 37.0 ± 0.4 mV). Moreover, DSPE-PEG(2000) was included in the formulation to synthesize lipid-based nanotherapeutics containing siRNA with stealth characteristics. The inclusion of PEG-lipid resulted in an increase in the surface charge of lipoplexes (from 33.7 ± 4.4–54.3 ± 1.6 mV), while a significant decrease was observed in the surface charge of lipid nanocarriers (30.3 ± 8.7 mV). The different structural assemblies were identified for lipoplex and lipid nanocarriers using Synchrotron SAXS. Lipid nanocarriers present a lower amount of multilayers than lipoplexes. Lipid-PEG insertion significantly influenced lipid nanocarriers’ characteristics, drastically decreasing the number of multilayers. This effect was not observed in lipoplexes. The association between process configuration, lipid composition, and its effect on the characteristics of lipid-based vector systems can generate fundamental insights, contributing to gene-based nanotherapeutics development.Item Open Access Digital microfluidics for reconfigurable antennas(IEEE, 2014) Damgaci, Y.; Çağatay, Engin; Bıyıklı, Necmi; Cetiner, B. A.Usage of fluids (microfluidic or otherwise) in antennas provides a conceptually easy reconfiguration mechanism in the aspect of physical alteration. However, a requirement of pumps, valves, etc. for liquid transportation makes the antenna implementations rather impractical for the real-life scenarios. This work reports on the theoretical calculations and experiments conducted to evaluate the electrowetting on dielectric (EWOD) driven digital microfluidics as a reconfiguration mechanism for antennas and RF circuits. © 2014 European Association on Antennas and Propagation.Item Open Access A droplet-based microfluidic reactor for silica nanoparticle synthesis and post processing of quantum dots(Bilkent University, 2017-07) Nikdoost, ArsalanThe unique properties of nanoparticles mainly depend on their size and morphology; thus, it is of the utmost importance to synthesize them monodispersely to be useful in an application. Micro uidic reactors enable a monodisperse nanoparticle synthesis through a precise control over the reaction conditions such as temperature, residence time, and reactant concentrations. Droplet-based microreactors facilitate the rapid mixing of reactants with a reduced diffusion length, while maintaining a uniform residence time because of the circulating ow profile in contrast to the parabolic ow profile in continuous ow microreactors. In this thesis, a droplet-based silicon microreactor was fabricated and used for silica nanoparticle synthesis. Silica nanoparticles were obtained with a size range of 25:0 2:7 nm. Considering the shorter processing time and the decreased amount of materials used alongside the comparable size range and monodispersity, this method was later implemented to be used for silica coating of quantum dot semiconductors. Silica coating of quantum dots maintain their photostability and preserve their optical properties. This thesis is the first attempt to coat CdSe/CdS core/shell quantum dots with a silica layer inside a microreactor. The accurate control over the reaction could enable the adjustable size and size distribution of the synthesized nanoparticles. The initial results are presented as part of this thesis.Item Open Access Droplet-based microfluidic systems for silica coating and synthesis of conjugated polymer nanoparticles(Bilkent University, 2015-07) Özkan, AlicanNanoparticles have unique electronic, optic and magnetic properties due to their large area to volume ratio. In order for them to preserve their properties for longer times, some of them need to be coated with a protective layer such as silica (silicon dioxide) layer. This coating has to be made uniformly to obtain monodisperse size distributions, which is essential to obtain uniform properties for all nanoparticles. Obtaining monodisperse size distribution relies on the control over reaction conditions such as residence time, concentration and temperature. This thesis presents a microuidic reactor that can achieve strict control over reaction conditions by utilizing a meandering geometry of microchannels and droplet-based ow. Meandering channels reduce the time needed for mixing due to the reduced diffusion lengths; whereas droplet-based flow provides uniform residence time inside the reactor due to the circulating flow profile of droplets as opposed to parabolic ow profile in straight channels. Before fabricating the device, the mixing performance of droplets at different channel cross-sections and meandering geometries were simulated by using Comsol Multiphysicsr. As a result, it is concluded that the channel cross-section and meandering dimensions should be as small as possible for faster mixing. Based on these simulation results, the microuidic device was designed and later fabricated in polydimethyl siloxane (PDMS) by using the soft lithography technique. This system was used to understand the effect of solvent concentrations and residence time on silica formation in order to be able to control the coating thickness compared to batchwise methods. Initially silica nanoparticle formation inside droplets were tested; and 102 nm ± 4 nm diameter of silica nanoparticles were obtained; which is a significant improvement compared to the bath-wise synthesis methods. Additionally, experimental studies on the synthesis of green Conjugated Polymer Nanoparticles (CPN) was also conducted. By using three different methods, bulk solution, continuous ow and droplet-based ow, nanoparticles were synthesized. From the results, it was acquired that droplet-based ow provided higher quality of nanoparticles in terms of nanoparticle size, uniformity and monodispersity.Item Open Access Fabrication and characterization of liquid metal-based micro-electromechanical DC-contact switch for RF applications(CRC Press, 2012) Çağatay, Engin; Noyan, Mehmet Alican; Damgaci, Y.; Cetiner, B. A.; Bıyıklı, NecmiWe demonstrate that room-temperature liquid metal alloy droplets of Eutectic Gallium Indium (EGaIn) and Gallium Indium Tin alloy (Galinstan) can be actuated using electro-wetting-on-dielectric (EWOD) effect. With the application of 80-100V across the actuation electrode and ground electrode, the metallic liquid droplets were observed to be actuated. We have studied the actuation characteristics using different electrode architectures in open-air configuration as well as in encapsulated microfluidic channel test-beds. The resulting microfluidic DC actuation might potentially be used for RF switching applications.