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| 3. |
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| 4. |
- Fornell, Anna, et al.
(författare)
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A microfluidic platform for SAXS measurements of liquid samples
- 2022
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Konferensbidrag (refereegranskat)abstract
- Small-angle X-ray scattering (SAXS) is a technique that can measure the size and shape of small particles such as proteins and nanoparticles using X-rays. At MAX IV, we are developing a microfluidic sample delivery platform to measure liquid samples containing proteins under flow using SAXS. One of the main advantages of using microfluidics is that the sample is continuously flowing, thus minimizing the risk of radiation damage as the sample is continuously refreshed. Other advantages include low sample volume and the possibility to study dynamic processes, e.g. mixing. To obtain good SAXS signals, the X-ray properties of the chip material are essential. The microfluidic chip must have low attenuation of X-rays, low background scattering, and high resistance to X-ray-induced damage, and preferably be low cost and easy to fabricate. In this work, we have evaluated the performance of two different polymer microfluidic chips for SAXS measurements.
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| 5. |
- Fornell, Anna, et al.
(författare)
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A Microfluidic Platform for Synchrotron X-ray Studies of Proteins
- 2021
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Konferensbidrag (refereegranskat)abstract
- New tools are needed to allow for complex protein dynamics studies, especially to study proteins in their native states. In the AdaptoCell project a microfluidic platform for academic and industrial users at MAX IV Laboratory is being developed. MAX IV is a Swedish national laboratory providing brilliant synchrotron X-rays for research. Due to the high photon flux, sensitive samples such as proteins are prone to rapid radiation damage; thus, it is advantageous to have the liquid sample underflow to refresh the sample continuously. This, in combination with small volumes, makes microfluidics a highly suitable sample environment for protein studies at MAX IV. The AdaptoCell platform is being integrated at three beamlines:Balder (X-ray absorption/emission spectroscopy), CoSAXS (small angle x-ray scattering) and Micromax (serial synchrotron crystallography). Currently, the platform is fully available atBalder, under commissioning at CoSAXS and being developed for MicroMAX.
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| 6. |
- Fornell, Anna, et al.
(författare)
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Acoustic focusing of beads and cells in hydrogel droplets
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The generation of hydrogel droplets using droplet microfluidics has emerged as a powerful tool with many applications in biology and medicine. Here, a microfluidic system to control the position of particles (beads or astrocyte cells) in hydrogel droplets using bulk acoustic standing waves is presented. The chip consisted of a droplet generator and a 380 µm wide acoustic focusing channel. Droplets comprising hydrogel precursor solution (polyethylene glycol tetraacrylate or a combination of polyethylene glycol tetraacrylate and gelatine methacrylate), photoinitiator and particles were generated. The droplets passed along the acoustic focusing channel where a half wavelength acoustic standing wave field was generated, and the particles were focused to the centre line of the droplets (i.e. the pressure nodal line) by the acoustic force. The droplets were cross-linked by exposure to UV-light, freezing the particles in their positions. With the acoustics applied, 89 ± 19% of the particles (polystyrene beads, 10 µm diameter) were positioned in an area ± 10% from the centre line. As proof-of-principle for biological particles, astrocytes were focused in hydrogel droplets using the same principle. The viability of the astrocytes after 7 days in culture was 72 ± 22% when exposed to the acoustic focusing compared with 70 ± 19% for samples not exposed to the acoustic focusing. This technology provides a platform to control the spatial position of bioparticles in hydrogel droplets, and opens up for the generation of more complex biological hydrogel structures.
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| 7. |
- Fornell, Anna, et al.
(författare)
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Acoustic focusing of microparticles in two-phase systems - Towards cell enrichment or medium exchange in droplets
- 2015
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Ingår i: MicroTAS 2015 - 19th International Conference on Miniaturized Systems for Chemistry and Life Sciences. - : Chemical and Biological Microsystems Society. - 9780979806483 ; , s. 1026-1028
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Konferensbidrag (refereegranskat)abstract
- We present a method to first laterally position microparticles inside droplets by acoustic forces and then split the droplet into three daughter droplets to achieve a 2+fold enrichment of microparticles inside the center droplet. We show that acoustic forces can be applied to both manipulate polystyrene beads (5 μm) and red blood cells inside droplets. The presented technology opens up for development of droplet operations used for medium exchange and particle concentration in droplet-based cell assays.
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| 8. |
- Fornell, Anna
(författare)
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Acoustic manipulation of cells and microbeads in droplet microfluidics
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Droplet microfluidics has emerged as a promising platform for miniaturisation of biological assays on-chip. In droplet microfluidics small water droplets (nL-pL) surrounded by an immiscible carrier oil are generated at high throughput. In these droplets particles such as cells or microbeads can be encapsulated, and the idea is that each of these droplets can be used as small reaction chambers for biological analyses. However, one key bottleneck for the full implementation of droplet microfluidics in biology has been the lack of a method to position and enrich particles inside droplets. In this thesis I present for the first time a microfluidic system where cells and microbeads encapsulated inside droplets can be manipulated using acoustic standing waves (i.e. acoustophoresis). The developed microfluidic systems were fabricated in silicon and sealed with glass lids. In the experiments, water droplets containing particles were generated, and an acoustic standing wave-field was created between the channel walls by actuating a piezoelectric transducer attached to the chip. In the first study it was shown that at application of the ultrasound at the first harmonic (1.8 MHz), the encapsulated particles were focused to the centre of the droplets i.e. the pressure node. It was shown that both red blood cells and polystyrene microbeads could be aligned in the centre of the droplets. The usefulness of the technology was proved by combining acoustophoresis with a trident-shaped droplet split to allow for particle enrichment. At application of the ultrasound at the first harmonic close to 90% of the particles were positioned in the centre daughter droplets when approximately 2/3 of the original droplet volume was removed. To better understand the physics of the system, in the second study a theoretical model was developed where the acoustic field inside droplets was investigated. In the third study, switching of encapsulated particles between different microfluidic pathways was shown. At application of the ultrasound at the first harmonic the encapsulated particles were directed into pathway 1 (the centre daughter droplets) while at application of the ultrasound at the second harmonic the encapsulated particles were directed into pathway 2 (the side daughter droplets). In the fourth study, two-dimensional acoustophoresis was used to increase the detectability of particles encapsulated inside droplets by pre-aligning the particles before the droplet generation site. In the fifth and last study, it was demonstrated that acoustophoresis can be used to separate two different particle species originally encapsulated in the same droplet into different daughter droplets based on the acoustic properties of the particles.This thesis proves that acoustophoresis is a versatile technology that can find various applications in droplet microfluidics. The combination of droplet microfluidics and acoustophoresis opens up for new possibilities for miniaturisation of biological assays on-chip.
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| 11. |
- Fornell, Anna, et al.
(författare)
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Acoustophoretic particle manipulation in droplet microfluidics at higher resonance modes
- 2016
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Konferensbidrag (refereegranskat)abstract
- In this paper we investigate focusing of microparticles in the presence of multiple pressure nodes inside aqueous droplets by using bulk acoustic waves. The microfluidic chip s for droplet generation and particle encapsulation (within the droplets) were fabricated using anisotropic wet - etching of a silicon wafer. Subsequently, piezoelectric transducers featuring different thicknesses were glued on the chips to build the final devices. The transducer thicknesses were chosen as to match the acoustic resonances of the embedded micro channel at the fundamental frequency, the first and the second harmonics. The actuation of the devices at the first three resonance modes enabled the positioning of the microparticles in one, two or three bands, in accordance with the presence of pressure nodes within the droplet contained in the microchannel. This acoustic particle manipulation technique opens up for new possibilities to perform biological assays using droplet microfluidic platforms.
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| 12. |
- Fornell, Anna, et al.
(författare)
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AdaptoCell : Microfluidics at MAX IV Laboratory
- 2022
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Ingår i: 25th Swedish Conference on Macromolecular Structure and Function.
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Konferensbidrag (refereegranskat)abstract
- The AdaptoCell project at MAX IV has developed a microfluidic sample delivery platform for academic and industrial users to enable studies of protein samples in solution and in microcrystals underflow. The platform is compatible with various X-ray techniques and has so far been integrated onto two beamlines at MAX IV: the CoSAXS beamline for small angle X-ray scattering studies and the Balder beamline for X-ray absorption spectroscopy studies. Initial implementation of the platform for serial crystallography sample delivery is ongoing and will be integrated onto the BioMAX and MicroMAX beamlines once commissioned. With this platform, we aim to meet the demand from our user community for studying proteins at physiologically relevant temperatures and give the ability to follow dynamical processes in situ as well as decreasing sample volumes and radiation damage.To determine the optimized flow rates and components for mixing etc. using different microfluidic chips, a dedicated off(beam)line test station with a microscope has been established at the Biolab. The Biolab also provides a number of characterization techniques, such as Dynamic Light Scattering, UV-Vis spectrophotometry, for quality control of the samples; as well as an anaerobic chamber for preparation and characterization of metalloproteins. The microfluidic flows are controlled via syringe pumps or a pressure-driven system. Channel design varies, depending on the needs of the experiment, from straight channel, cross-junction to herringbone micromixers etc. On-chip mixing of buffers with different viscosity, pH, ion strength and protein concentrations has been demonstrated successful and will be presented.
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| 13. |
- Fornell, Anna, et al.
(författare)
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AdaptoCell – Microfluidic Platforms at MAX IV Laboratory
- 2021
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Konferensbidrag (refereegranskat)abstract
- In the AdaptoCell project, we are developing microfluidic platforms for X-ray studies of liquid samples. Microfluidics is a suitable technology for samples that are prone to radiation damage, such as proteins. By having the sample underflow, the sample is continuously refreshed, and the risk of radiation damage is reduced. The technology is also suitable for investigating dynamic events such as in situ mixing. The microfluidic platforms are being integrated at three beamlines at MAX IV Laboratory: Balder (X-ray absorption/emission spectroscopy), CoSAXS (small angle x-ray scattering) and MicroMAX (serial synchrotron crystallography). Currently, the platforms are available for users at Balder and CoSAXS, which is under development at MicroMAX. In addition, we also provide a microfluidic offline test station where users can test their samples and optimise their devices before the beam time. The main components of the microfluidic setup are the pressure-driven flow controller and the microfluidic chip. We mainly use commercially available polymer microfluidic chips made of COC (cyclic olefin copolymer). COC is used as a chip material as it has high X-ray transmission and high resistance to radiation damage. There are several different chip designs available such as straight channel chips, droplet generator chips and mixing chips. We believe the AdaptoCell platforms will be useful and versatile sample environments for academic and industrial users at MAX IV Laboratory who want to perform experiments with liquid samples under flow.
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| 14. |
- Fornell, Anna, et al.
(författare)
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An acoustofluidic platform for non-contact trapping of cell-laden hydrogel droplets compatible with optical microscopy
- 2019
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Ingår i: Biomicrofluidics. - : AIP Publishing. - 1932-1058. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Production of cell-laden hydrogel droplets as miniaturized niches for 3D cell culture provides a new route for cell-based assays. Such production can be enabled by droplet microfluidics and here we present a droplet trapping system based on bulk acoustic waves for handling hydrogel droplets in a continuous flow format. The droplet trapping system consists of a glass capillary equipped with a small piezoelectric transducer. By applying ultrasound (4 MHz), a localized acoustic standing wave field is generated in the capillary, trapping the droplets in a well-defined cluster above the transducer area. The results show that the droplet cluster can be retained at flow rates of up to 76 mu l/min, corresponding to an average flow speed of 3.2 mm/s. The system allows for important operations such as continuous perfusion and/or addition of chemical reagents to the encapsulated cells with in situ optical access. This feature is demonstrated by performing on-chip staining of the cell nuclei. The key advantages of this trapping method are that it is label-free and gentle and thus well-suited for biological applications. Moreover, the droplets can easily be released on-demand, which facilitates downstream analysis. It is envisioned that the presented droplet trapping system will be a valuable tool for a wide range of multistep assays as well as long-term monitoring of cells encapsulated in gel-based droplets.
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| 15. |
- Fornell, Anna, et al.
(författare)
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An intra-droplet particle switch for droplet microfluidics using bulk acoustic waves
- 2017
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Ingår i: Biomicrofluidics. - : AIP Publishing. - 1932-1058. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- To transfer cell- and bead-assays into droplet-based platforms typically requires the use of complex microfluidic circuits, which calls for methods to switch the direction of the encapsulated particles. We present a microfluidic chip where the combination of acoustic manipulation at two different harmonics and a trident-shaped droplet-splitter enables direction-switching of microbeads and yeast cells in droplet microfluidic circuits. At the first harmonic, the encapsulated particles exit the splitter in the center daughter droplets, while at the second harmonic, the particles exit in the side daughter droplets. This method holds promises for droplet-based assays where particle-positioning needs to be selectively controlled.
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| 16. |
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| 17. |
- Fornell, Anna, et al.
(författare)
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Binary acoustic trapping in a glass capillary
- 2021
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 54:35
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Tidskriftsartikel (refereegranskat)abstract
- Acoustic trapping is a useful method for handling biological samples in microfluidic systems. The aim of this work is twofold: first to investigate the physics behind acoustic trapping in a glass capillary and secondly to perform binary acoustic trapping. The latter is achieved by increasing the density of the fluid in the trapping channel. The trapping device consisted of a glass capillary with a rectangular inner cross-section (height 200 µm × width 2000 µm) equipped with a small piezoelectric transducer. The piezoelectric transducer was actuated at 4 MHz to generate a localised half-wavelength acoustic standing-wave-field in the capillary, comprising of a pressure field and a velocity field. Under acoustic actuation, only particles with higher density than the fluid, i.e. having a positive dipole scattering coefficient, were trapped in the flow direction. The numerical and analytical modelling of the system show that the trapping force which retains the particles against the flow depends only on the dipole scattering coefficient in the pressure nodal plane of the acoustic field. The analytical model also reveals that the retention force is proportional to the dipole scattering coefficient, which agrees with our experimental findings. Next, we showed that in a mixture of melamine particles and polystyrene particles in a high-density fluid it is possible to selectively trap melamine particles, since melamine particles have higher density than polystyrene particles.
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| 18. |
- Fornell, Anna, et al.
(författare)
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Binary particle separation in droplet microfluidics using acoustophoresis
- 2018
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 112:6
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Tidskriftsartikel (refereegranskat)abstract
- We show a method for separation of two particle species with different acoustic contrasts originally encapsulated in the same droplet in a continuous two-phase system. This was realized by using bulk acoustic standing waves in a 380 mu m wide silicon-glass microfluidic channel. Polystyrene particles (positive acoustic contrast particles) and in-house synthesized polydimethylsiloxane (PDMS) particles (negative acoustic contrast particles) were encapsulated inside water-in-oil droplets either individually or in a mixture. At acoustic actuation of the system at the fundamental resonance frequency, the polystyrene particles were moved to the center of the droplet (pressure node), while the PDMS particles were moved to the sides of the droplet (pressure anti-nodes). The acoustic particle manipulation step was combined in series with a trifurcation droplet splitter, and as the original droplet passed through the splitter and was divided into three daughter droplets, the polystyrene particles were directed into the center daughter droplet, while the PDMS particles were directed into the two side daughter droplets. The presented method expands the droplet microfluidics tool-box and offers new possibilities to perform binary particle separation in droplet microfluidic systems.
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| 19. |
- Fornell, Anna, et al.
(författare)
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Controlled Lateral Positioning of Microparticles Inside Droplets Using Acoustophoresis
- 2015
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 87:20, s. 10521-10526
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we utilize bulk acoustic waves to control the position of micropartides inside droplets in two-phase microfluidic systems and demonstrate a method to enrich the micropartides. In droplet microfluidics, different unit operations are combined and integrated on-chip to miniaturize complex biochemical assays. We present a droplet unit operation capable of controlling the position of micropartides during a trident shaped droplet split. An acoustic standing wave field is generated in the microchannel, and the acoustic forces direct the encapsulated micropartides to the center of the droplets. The method is generic, requires no labeling of the micropartides, and is operated in a noncontact fashion. It was possible to achieve 2+-fold enrichment of polystyrene beads (5 mu m in diameter) in the center daughter droplet with an average recovery of 89% of the beads. Red blood cells were also successfully manipulated inside droplets. These results show the possibility to use acoustophoresis in two-phase systems to enrich micropartides and open up the possibility for new droplet-based assays that are not performed today.
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| 20. |
- Fornell, Anna, et al.
(författare)
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Fabrication of Silicon Microfluidic Chips for Acoustic Particle Focusing Using Direct Laser Writing
- 2020
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Ingår i: Micromachines. - : MDPI AG. - 2072-666X. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a fast and simple method for fabricating microfluidic channels in silicon using direct laser writing. The laser microfabrication process was optimised to generate microfluidic channels with vertical walls suitable for acoustic particle focusing by bulk acoustic waves. The width of the acoustic resonance channel was designed to be 380 µm, branching into a trifurcation with 127 µm wide side outlet channels. The optimised settings used to make the microfluidic channels were 50% laser radiation power, 10 kHz pulse frequency and 35 passes. With these settings, six chips could be ablated in 5 h. The microfluidic channels were sealed with a glass wafer using adhesive bonding, diced into individual chips, and a piezoelectric transducer was glued to each chip. With acoustic actuation at 2.03 MHz a half wavelength resonance mode was generated in the microfluidic channel, and polystyrene microparticles (10 µm diameter) were focused along the centre-line of the channel. The presented fabrication process is especially interesting for research purposes as it opens up for rapid prototyping of silicon-glass microfluidic chips for acoustofluidic applications.
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| 21. |
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| 22. |
- Fornell, Anna, et al.
(författare)
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Improved acoustic particle enrichment in droplets by optimising the droplet split design
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Droplet microfluidics has emerged as a valuable platform for miniaturisation of biological experiments on-chip. In droplet microfluidic chips monodisperse droplets containing cells or other bioparticles can be generated at high throughput, and each droplet can be used as an isolated reaction chamber for individual measurements. A general trend in droplet microfluidics is reducing the size of the droplets, but the challenge is maintaining the particles in the droplets after splitting. We have previously reported on an acoustofluidic chip where bulk acoustic waves were used to control particle positioning in a trident-shaped droplet split. However, the reported particle enrichment was modest (3-fold), and the aim of this study is to increase the particle enrichment by optimising the droplet split design. With our new optimised droplet split we show up to 16.7-fold particle enrichment with high particle recovery.
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| 23. |
- Fornell, Anna, et al.
(författare)
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Intra-droplet acoustic particle focusing : simulations and experimental observations
- 2018
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Ingår i: Microfluidics and Nanofluidics. - : Springer Berlin/Heidelberg. - 1613-4982 .- 1613-4990. ; 22:75
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to study resonance conditions for acoustic particle focusing inside droplets in two-phase microfluidic systems. A bulk acoustic wave microfluidic chip was designed and fabricated for focusing microparticles inside aqueous droplets (plugs) surrounded by a continuous oil phase in a 380-μm-wide channel. The quality of the acoustic particle focusing was investigated by considering the influence of the acoustic properties of the continuous phase in relation to the dispersed phase. To simulate the system and study the acoustic radiation force on the particles inside droplets, a simplified 3D model was used. The resonance conditions and focusing quality were studied for two different cases: (1) the dispersed and continuous phases were acoustically mismatched (water droplets in fluorinated oil) and (2) the dispersed and continuous phases were acoustically matched (water droplets in olive oil). Experimentally, we observed poor acoustic particle focusing inside droplets surrounded by fluorinated oil while good focusing was observed in droplets surrounded by olive oil. The experimental results are supported qualitatively by our simulations. These show that the acoustic properties (density and compressibility) of the dispersed and continuous phases must be matched to generate a strong and homogeneous acoustic field inside the droplet that is suitable for high-quality intra-droplet acoustic particle focusing.
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| 24. |
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| 25. |
- Fornell, Anna, et al.
(författare)
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Optimisation of the droplet split design for high acoustic particle enrichment in droplet microfluidics
- 2020
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Ingår i: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 226
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Tidskriftsartikel (refereegranskat)abstract
- We have characterised three droplet split designs for acoustic particle enrichment in water-in-oil droplets. The microfluidic channel design included a droplet generation junction, acoustic focusing channel and a trident-shaped droplet split. The microfluidic channels were dry-etched in silicon and sealed with glass lids by anodic bonding. To each microfluidic chip a piezoelectric transducer was glued, and at actuation of the transducer at the fundamental resonance frequency of the acoustic focusing channel (1.91–1.93 MHz), a half wavelength standing wave field was created between the channel walls. The acoustic force focused the encapsulated particles (3.2 μm, 4.8 μm and 9.9 μm diameter polystyrene microbeads) to the centre-line of the droplets, and when the droplets reached the droplet split the particles were directed into the centre daughter droplets. The results show that the design of the droplet split and the flow ratio between the centre and side outlet channels are the main factors that affect the particle enrichment and particle recovery in the centre daughter droplets. The highest particle enrichment was achieved in the droplet split design having the smallest centre channel (38 μm wide). Using this microfluidic chip design, we demonstrate up to 16.7-fold enrichment of 9.9 μm diameter polystyrene microbeads in the centre daughter droplets. This is almost three times higher particle enrichment than what has previously been presented using other intra-droplet particle enrichment techniques. Moreover, the acoustic technique is label-free and biocompatible.
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