| 1. |
- Lilliehorn, Tobias, et al.
(författare)
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Bioassays on ultrasonically trapped microbead clusters in microfluidic systems
- 2004
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Ingår i: Micro Total Analysis Systems 2004. - 0854048960 ; 2, s. 327-329
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Konferensbidrag (refereegranskat)abstract
- The handling of biochemically functionalised beads or particles is becoming increasingly important in µTAS. Bead-based analysis of e.g. proteins can be made sensitive due to the large active surface area and flexible by chemical design of the bead surface. We have developed a microfluidic device utilising an array of integrated and individually controlled ultrasonic microtransducers for particle trapping [1]. Particles inserted in the device are subjected to acoustic radiation forces [2] confining them at localised trapping sites. We would now, for the first time at an international conference, like to present a technique for performing bioassays on such ultrasonically trapped beads in microfluidic systems. The microfluidic device is shown in Fig. 1, where the piezoceramic ultrasonic transducers can be seen in the channel crossings in the insert. The device is designed as an acoustic resonator, to obtain localised standing acoustic waves at each transducer with essentially one pressure node in the middle of the 72 µm deep channel when operated near 10 MHz. This configuration is chosen to keep trapped particles away from the interior surfaces of the device, thus enabling fast switching of beads with a minimum in carry-over between assays. The fluidic chip, shown in Fig. 2, is designed to allow injection of microbeads, washing fluid and sample to the three trapping sites. It has been shown that the microbead clusters, as shown in Fig. 3, can be trapped at considerably high perfusion rates, up to 10 µl/min, Fig 4. As a model bioassay, 6.7 µm biotin-covered beads (PC-B-6.0, Gerlinde Kisker, Germany) were injected and transported to one tapping site using washing fluid (water). Activating the transducer trapped the beads. A solution of FITC-tagged avidin was perfused over the bead bed at 3 µl/min, using the corresponding orthogonal sample channel. After 100 s the sample flow was turned off and the bead trap was washed by perfusing water at 3 µl/min. The fluorescence response from the trapped bead clusters was monitored during the assay, and the result is shown in Fig. 5. After excess avidin was washed from the bead trap, a measured step response . indicated that avidin had bound to the beads. Finally the possibility of moving trapped microbeads between the individually controlled trapping sites in the device is shown in Fig. 6, where the transducers are activated sequentially while keeping the bead carrying washing fluid at 3 µl/min during the experiment. Work in the near future will be focused on optimising the device with respect to the bioassay performance, and in a longer perspective on expanding the concept to two dimensions to enable a new dynamic mode of generating bioanalytical arrays.
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| 2. |
- Evander, Mikael, et al.
(författare)
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Acoustic trapping of cells in a microfluidic format
- 2005
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Ingår i: Proceedings of µTAS 2005 Conference. ; 1, s. 515-517
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Konferensbidrag (refereegranskat)abstract
- This paper presents, for the first time, non-contact acoustic trapping of cells in a microfluidic format. The employed acoustic force maintains the cells in the center of a fluidic channel while allowing for perfusion of e.g. nutrients or drugs as well as optical monitoring of the cells. Neural stem cells have been acoustically trapped and tested for viability after 15 minutes of ultrasonic radiation. It is also shown that it is possible to grow yeast cells suspended in an acoustic standing wave while perfusing with cell media.
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| 3. |
- Evander, Mikael, et al.
(författare)
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Acoustic Trapping: System Design, Optimization and Applications
- 2006
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Ingår i: Proceedings of the sixth Micro Structure Workshop. ; 1, s. 33-33
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Konferensbidrag (refereegranskat)abstract
- Manipulation, separation and trapping of particles and cells are very important tools in today's bioanalytical and medical field. The acoustic no-contact trapping method presented at earlier MSW 2004 provides a flexible platform for performing cell and particle assays in a perfusion-based microsystem. To further develop the system microfabricated glass channels are now used, resulting in shorter fabrication times and a very inert channel material. The fluidic design has been revised to minimise the risks of leaking and hydrodynamic focusing has been incorporated to ensure a high trapping efficiency. A change of piezoelectric materials has resulted in less thermal losses in the material, higher reproducibility and shorter manufacturing time. The trapping force was estimated by calculating the fluid force exerted on a single particle levitated in the standing wave as a reference. The temperature increase due to the losses in the transducer was measured using a fluorescent dye, indicating a maximum temperature increase of 10 degrees Celsius. Live cells have been trapped and shown to be viable while still suspended in the standing wave, thus making it possible to do on-line studies on, for example, drug response of cell populations.
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| 4. |
- Evander, Mikael, et al.
(författare)
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Noninvasive acoustic cell trapping in a microfluidic perfusion system for online bioassays
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:7, s. 2984-2991
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Tidskriftsartikel (refereegranskat)abstract
- Techniques for manipulating, separating, and trapping particles and cells are highly desired in today's bioanalytical and biomedical field. The microfluidic chip-based acoustic noncontact trapping method earlier developed within the group now provides a flexible platform for performing cell- and particle-based assays in continuous flow microsystems. An acoustic standing wave is generated in etched glass channels (600x61 microm2) by miniature ultrasonic transducers (550x550x200 microm3). Particles or cells passing the transducer will be retained and levitated in the center of the channel without any contact with the channel walls. The maximum trapping force was calculated to be 430+/-135 pN by measuring the drag force exerted on a single particle levitated in the standing wave. The temperature increase in the channel was characterized by fluorescence measurements using rhodamine B, and levels of moderate temperature increase were noted. Neural stem cells were acoustically trapped and shown to be viable after 15 min. Further evidence of the mild cell handling conditions was demonstrated as yeast cells were successfully cultured for 6 h in the acoustic trap while being perfused by the cell medium at a flowrate of 1 microL/min. The acoustic microchip method facilitates trapping of single cells as well as larger cell clusters. The noncontact mode of cell handling is especially important when studies on nonadherent cells are performed, e.g., stem cells, yeast cells, or blood cells, as mechanical stress and surface interaction are minimized. The demonstrated acoustic trapping of cells and particles enables cell- or particle-based bioassays to be performed in a continuous flow format.
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| 5. |
- Evander, Mikael, et al.
(författare)
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Versatile microchip utilising ultrasonic standing waves
- 2005
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Ingår i: IFMBE Proceedings 2005. ; , s. 123-124
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Konferensbidrag (refereegranskat)abstract
- This paper presents the concept and initial work on a microfluidic platform for bead-based analysis of biological sample. The core technology in this project is ultrasonic manipulation and trapping of particle in array configurations by means of acoustic forces. The platform is ultimately aimed for parallel multistep bioassays performed on biochemically activated microbeads (or particles) using submicrolitre sample volumes. A first prototype with three individually controlled particle trapping sites has been developed and evaluated. Standing ultrasonic waves were generated across a microfluidic channel by integrated PZT ultrasonic microtransducers. Particles in a fluid passing a transducer were drawn to pressure minima in the acoustic field, thereby being trapped and confined laterally over the transducer. It is anticipated that acoustic trapping using integrated transducers can be exploited in miniaturised total chemical analysis systems (µTAS), where e.g. microbeads with immobilised antibodies can be trapped in arrays and subjected to minute amounts of sample followed by a reaction, detected using fluorescence. Preliminary results indicate that the platform is capable of handling live cells as well as microbeads. A first model bioassay with detection of fluorescein marked avidin binding to trapped biotin beads has been evaluated.
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| 6. |
- Fröbert, Ole, et al.
(författare)
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Thrombus Aspiration during ST-Segment Elevation Myocardial Infarction
- 2013
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Ingår i: New England Journal of Medicine. - : Massachusetts Medical Society. - 0028-4793 .- 1533-4406. ; 369:17, s. 1587-1597
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundThe clinical effect of routine intracoronary thrombus aspiration before primary percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is uncertain. We aimed to evaluate whether thrombus aspiration reduces mortality. MethodsWe conducted a multicenter, prospective, randomized, controlled, open-label clinical trial, with enrollment of patients from the national comprehensive Swedish Coronary Angiography and Angioplasty Registry (SCAAR) and end points evaluated through national registries. A total of 7244 patients with STEMI undergoing PCI were randomly assigned to manual thrombus aspiration followed by PCI or to PCI only. The primary end point was all-cause mortality at 30 days. ResultsNo patients were lost to follow-up. Death from any cause occurred in 2.8% of the patients in the thrombus-aspiration group (103 of 3621), as compared with 3.0% in the PCI-only group (110 of 3623) (hazard ratio, 0.94; 95% confidence interval [CI], 0.72 to 1.22; P=0.63). The rates of hospitalization for recurrent myocardial infarction at 30 days were 0.5% and 0.9% in the two groups, respectively (hazard ratio, 0.61; 95% CI, 0.34 to 1.07; P=0.09), and the rates of stent thrombosis were 0.2% and 0.5%, respectively (hazard ratio, 0.47; 95% CI, 0.20 to 1.02; P=0.06). There were no significant differences between the groups with respect to the rate of stroke or neurologic complications at the time of discharge (P=0.87). The results were consistent across all major prespecified subgroups, including subgroups defined according to thrombus burden and coronary flow before PCI. ConclusionsRoutine thrombus aspiration before PCI as compared with PCI alone did not reduce 30-day mortality among patients with STEMI. (Funded by the Swedish Research Council and others; ClinicalTrials.gov number, NCT01093404.)
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| 7. |
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| 8. |
- Johansson, Linda, et al.
(författare)
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Temperature and trapping characterization of an acoustic trap with miniaturized integrated transducers - towards in-trap temperature regulation
- 2013
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Ingår i: Ultrasonics. - : Elsevier BV. - 0041-624X .- 1874-9968. ; 53:5, s. 1020-1032
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Tidskriftsartikel (refereegranskat)abstract
- An acoustic trap with miniaturized integrated transducers (MITs) for applications in non-contact trapping of cells or particles in a microfluidic channel was characterized by measuring the temperature increase and trapping strength. The fluid temperature was measured by the fluorescent response of Rhodamine B in the microchannel. The trapping strength was measured by the area of a trapped particle cluster counter-balanced by the hydrodynamic force. One of the main objectives was to obtain quantitative values of the temperature in the fluidic channel to ensure safe handling of cells and proteins. Another objective was to evaluate the trapping-to-temperature efficiency for the trap as a function of drive frequency. Thirdly, trapping-to-temperature efficiency data enables identifying frequencies and voltage values to use for in-trap temperature regulation. It is envisioned that operation with only in-trap temperature regulation enables the realization of small, simple and fast temperature-controlled trap systems. The significance of potential gradients at the trap edges due to the finite size of the miniaturized transducers for the operation was emphasized and expressed analytically. The influence of the acoustic near field was evaluated in FEM-simulation and compared with a more ideal 1D standing wave. The working principle of the trap was examined by comparing measurements of impedance, temperature increase and trapping strength with impedance transfer calculations of fluid-reflector resonances and frequencies of high reflectance at the fluid-reflector boundary. The temperature increase was found to be moderate, 7 degrees C for a high trapping strength, at a fluid flow of 0.5 mm s(-1) for the optimal driving frequency. A fast temperature response with a fall time of 8 s and a rise time of 11 s was observed. The results emphasize the importance of selecting the proper drive frequency for long term handling of cells, as opposed to the more pragmatic way of selecting the frequency of the highest acoustic output. Trapping was demonstrated in a large interval between 9 and 11.5 MHz, while the main trapping peak displayed FWHM of 0.5 MHz. A large bandwidth enables a more robust manufacturing and operation while allowing the trapping platform to be used in applications where the fluid wavelength varies due to external variations in fluid temperature, density and pressure.
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| 9. |
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| 10. |
- Johansson, Linda, et al.
(författare)
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Temperature evaluation of soft and hard PZT transducers for ultrasonic
- 2005
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Ingår i: Proceedings of µTAS 2005 Conference. ; 2, s. 1428-1430
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Konferensbidrag (refereegranskat)abstract
- This paper reports a comparison of soft and hard piezoceramic transducer materials used for ultrasonic particle trapping in a microfluidic bioanalytical platform. The investigation is made with the objective to obtain high acoustic forces with a minimum of temperature increase. Themperature is a critical parameter for bioassays and most often need to be kept below a certain level to allow handling of e.g. temperature sensitive proteins. The main conclusion in this paper is that it is possible to get efficieint trapping with a temperature increase of only a few degrees using a hard type III transducer material.
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